Essentials of Oceanography, 13th edition Alan P Trujillo Solution Manual

Type:

Solution Manual

Resource:

Essentials of Oceanography

Edition:

13th Edition

Author(s):

Alan P. Trujillo Harold Thurman

Chapter 1 Introduction to Planet “Earth” Overview Chapter 1 is an introduction to Earth and its oceans, including a discussion of the history of ocean exploration. The scientific method is presented in this chapter so that students will have a framework for understanding the nature of scientific inquiry. Theories that describe the origin of the solar system, Earth, the atmosphere, and the oceans are presented in addition to a discussion of the origin of life on Earth. The chapter is completed with a presentation of the geologic time scale and radiometric age dating.

Essential Concepts 1.1 Compare the characteristics of Earth’s oceans.

1.2 Discuss how early exploration of the oceans was achieved.

1.3 Explain why oceanography is considered an interdisciplinary science.

1.4 Describe the process of science and the nature of scientific inquiry.

1.5 Explain how Earth and the solar system formed.

1.6 Explain how Earth’s atmosphere and oceans formed.

1.7 Discuss why life is thought to have originated in the oceans.

1.8 Demonstrate an understanding of how old Earth is.

Chapter Outline 1.1 How Are Earth’s Oceans Unique?

1.1.1 Earth’s Amazing Oceans 1.1.2 How Many Oceans Exist on Earth?

1.1.3 The Four Principal Oceans, Plus One 1.1.3.1 Pacific Ocean 1.1.3.2 Atlantic Ocean 1.1.3.3 Indian Ocean SmartFigure 1.3: Earth’s oceans Web Animation: Earth’s Water and the Hydrologic Cycle 1.1.3.4 Arctic Ocean 1.1.3.5 Southern Ocean, or Antarctic Ocean 1.1.4 Oceans versus Seas 1.1.4.1 Comparing the Oceans to the Continents 1.2 How Was Early Exploration of the Oceans Achieved?

1.2.1 Early History 1.2.1.1 Pacific Navigators 1.2.1.2 European Navigators 1.2.2 The Middle Ages 1.2.3 The Age of Discovery in Europe

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1.2.4 The Beginning of Voyaging for Science 1.2.5 History of Oceanography . . . To Be Continued 1.3 What Fields of Science Does Oceanography Include?

1.4 What Is the Process of Science and the Nature of Scientific Inquiry?

SmartFigure 1.15 The process of science.

1.4.1 Observations 1.4.2 Hypothesis 1.4.3 Testing 1.4.4 Theory 1.4.5 Theories and the Truth 1.5 How Were Earth and the Solar System Formed?

1.5.1 The Nebular Hypothesis 1.5.2 Proto-Earth 1.5.3 Density and Density Stratification SmartFigure 1.18: The nebular hypothesis of solar system formation Web Animation: The Nebular Hypothesis of Solar System Formation 1.5.4 Earth’s Internal Structure 1.5.4.1 Chemical Composition versus Physical Properties SmartFigure 1.20: Comparison of Earth’s chemical composition and physical properties 1.5.4.2 Chemical Composition 1.5.4.3 Physical Properties Web Animation: How Seismic Waves Reveal Earth’s Internal Layers 1.5.4.4 Near the Surface 1.5.4.4.1 Lithosphere SmartTable 1.1 Comparing oceanic and continental crust 1.5.4.4.2 Oceanic versus Continental Crust 1.5.4.4.3 Asthenosphere 1.5.4.5 Isostatic Adjustment Web Animation: Isostatic Adjustment 1.6 How Were Earth’s Atmosphere and Oceans Formed?

1.6.1 Origin of Earth’s Atmosphere 1.6.2 Origin of Earth’s Oceans Web Animation: Formation of Earth’s Oceans 1.6.2.1 The Development of Ocean Salinity 1.7 Did Life Begin in the Oceans?

1.7.1 The Importance of Oxygen to Life 1.7.2 Stanley Miller’s Experiment SmartFigure 1.25 Creation of organic molecules.

Diving Deeper 1.1 Historical Feature The voyage of HMS Beagle: How it shaped Charles Darwin’s thinking about the theory of evolution 1.7.3 Evolution and Natural Selection 1.7.4 Plants and Animals Evolve 1.7.4.1 Photosynthesis and Respiration SmartFigure 1.26: Photosynthesis and respiration are cyclic and complimentary

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processes that are fundamental to life on Earth 1.7.4.2 The Great Oxidation Event/Oxygen Crisis 1.7.4.3 Changes to Earth’s Atmosphere 1.8 How Old Is Earth?

1.8.1 Radiometric Age Dating 1.8.2 The Geologic Time Scale Web Animation: Radioactive Decay Essential Concepts Review

Learning Outcomes Upon completion of this chapter, the student should be able to:

1.

Describe the principal oceans of Earth, including the following: a. location b. relative size c. land forms that border the ocean

2.

Name the deepest ocean trench and describe its exploration by humans.

3.

Discuss early ocean exploration and include the contributions of: a. early Pacific islanders (4000 B.C.–900 A.D.) b. the Kon Tiki voyage c. Phoenicians d. Greeks e. Romans

4.

Describe the contributions to oceanic exploration during the Middle Ages by the (a) Arabs and (b) Vikings.

5.

Elaborate on the contributions to oceanic exploration made by European explorers during the Renaissance (Age of Discovery), including: a. Prince Henry the Navigator b. Vasco da Gama c. Christopher Columbus d. John Cabot e. Vasco Nùñez de Balboa f. Ferdinand Magellan g. Juan Sebastian del Caño

6.

Discuss the contributions of James Cook to early ocean science.

7.

Explain why oceanography is considered an interdisciplinary science.

8.

Explain how scientists use the scientific process to investigate natural phenomena.

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9.

Distinguish between a hypothesis and a theory.

10.

Describe the formation of the solar system as outlined by the nebular hypothesis.

11.

Compare and contrast Proto-Earth and modern Earth.

12.

Describe density stratification in Earth and the resultant chemical structure, including the: a. crust b. mantle c. core

13.

Describe the physical structure of Earth, including the: a. inner core b. outer core c. mesosphere d. asthenosphere e. lithosphere

14.

Distinguish between continental crust and oceanic crust, including location, chemical, and physical properties of the crust.

15.

Differentiate between isostatic adjustment and isostatic rebound.

16.

Describe the formation of Earth’s initial atmosphere.

17.

Describe the formation of Earth’s oceans and discuss the origin of the salts in ocean water.

18.

Discuss the implications of Stanley Miller’s experiment involving the simulation of primitive Earth’s atmosphere on the origin of life on Earth.

19.

Explain how evolution and natural selection are related to one another.

20.

Define the following terms: a. autotroph b. heterotroph c. anaerobic d. chemosynthesis e. photosynthesis f. respiration

21.

Outline the effects of photosynthesis on primitive Earth’s atmosphere.

22.

Describe the process of radiometric dating and its implications estimating Earth’s age.

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Teaching Strategies Chapter 1 is a good starting point for any course. It is helpful to introduce students to all aspects of the oceans so that students understand how interdisciplinary the science of oceanography is.

This chapter contains many general broad ideas, some of which are revisited in more detail in future chapters of the book. It is a good idea to not focus too narrowly on topics in this chapter that you will be covering more thoroughly later in the course. It is important to stress that, although the topics in Chapter 1 might seem broadly diverse, they are all related to the study of oceanography as a whole.

Teacher’s Resources Films ▪ ▪ ▪ ▪ ▪

Challenge of the Oceans (McGraw-Hill), 29 minutes, DVD. Scripps Institute of Oceanography: Understanding and Protecting the Planet (University of California), 1 minute, www.youtube.com/watch?v=jN-231KVKNY&index=4&list= PLHy4NEP75tDnzONfhyLh9GLXI2li43OD7 Planet Earth: The Blue Planet (Program #2) (WQED, Pittsburgh, PBS), 58 minutes, http://learner.org/resources/series49.html Bridging World History: Unit 10—Connections Across Water (Oregon Public Broadcasting, 2004), 30 minutes. Discusses expansion of civilizations and trade using water routes. www.learner.org/resources/series197.html Life at Sea for NOAA Scientists and Crew (NOAA), 2 minutes, http://oceantoday.noaa.gov/lifeatsea/

Websites ● ● ●

www.noaa.gov —National Oceanic and Atmospheric Administration https://tos.org—The Oceanography Society http://education.nationalgeographic.org/encyclopedia/oceanography/—Oceanography from National Geographic

Concept Check (Questions and Answers) 1.1 How Are Earth’s Oceans Unique?

1. How did the view of the ocean by early Mediterranean cultures influence the naming of planet “Earth”?

Early Mediterranean cultures envisioned that marginal bodies of water, similar to the Mediterranean Sea, surrounded most of the continents. The name “Earth” describes the portion of the planet that is inhabited by man in spite of the fact that the majority of the planet’s surface is covered by water. Our planet was named before ocean exploration began.

2. Although the terms ocean and sea are sometimes used interchangeably, what is the technical difference between an ocean and a sea?

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In common use the terms sea and ocean are synonymous. Technically, seas are distinct from oceans in that: ● Seas are smaller in size and are relatively shallow. (The Arctic Ocean would be a “sea” using these criteria.) ● Seas are variably salty, although the Caspian Sea in Asia is basically a very large freshwater lake. ● Seas are usually enclosed by land, although strong ocean currents can define an area (e.g., Sargasso Sea in the Atlantic Ocean).

3. Where is the deepest part of the ocean? How deep is it, and how does it compare to the height of the tallest mountain on Earth?

The deepest part of the ocean is the Challenger Deep region of the Mariana Trench, near Guam in the Pacific Ocean. It is 11,022 meters (36,161 feet) below sea level. In comparison, Mount Everest is the tallest mountain on Earth at 8850 meters (29,035 feet), which is 2172 meters (7126 feet) shorter than the Mariana Trench is deep.

1.2 How Was Early Exploration of the Oceans Achieved?

1. While the Arabs dominated the Mediterranean region during the Middle Ages, what were the most significant ocean-related events taking place in northern Europe?

The Vikings roamed the North Atlantic from the 8th to the 13th centuries. Erik the Red sailed to establish colonies in Baffin Island in 891, and his son, Leif Eriksson, visited Vineland (now Newfoundland, Canada) in 995.

2. Describe the important events in oceanography that occurred during the Age of Discovery in Europe.

During the 30-year period from 1492 to 1522 (the Age of Discovery), the Western world came to realize the vastness of Earth’s oceans. Europeans explored the continents of North and South America. The circumnavigation of Earth was completed for the first time. Europeans discovered populations of indigenous peoples on other continents and islands. Bartholomeu Diaz, Vasco da Gama, Christopher Columbus, Vasco Nứñez de Balboa, and Ferdinand Magellan made important contributions to ocean exploration during the Age of Discovery.

3. List some of the major achievements of Captain James Cook.

During his three ocean voyages, Captain James Cook (1728–1779): ● Explored the southern oceans and charted the coasts of New Zealand and Australia. ● Was the first person to cross the Antarctic Circle in his search for a southern continent, Terra Australis. ● Discovered the Sandwich Islands and South George Island after failing to find the southern continent. ● Found a means of preventing scurvy, a disease resulting from vitamin C deficiency. ● Proved the value of John Harrison’s chronometer to determine longitude. ● Determined the outline of the Pacific Ocean. ● Led the way in sampling subsurface water temperatures, measuring winds and ocean currents, sounding to estimate depth, and data collection on coral reefs.

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Discovered the Hawaiian Islands and looked for the Northwest Passage around North America.

1.3 What Is Oceanography?

1. What was the impetus for studying ocean processes that led to the great expansion of the science of oceanography?

Humans have always used the oceans for a variety of purposes. However, as scientists began to study how ocean geology, chemistry, and physics work with biology to create good fishing grounds, we have come to realize how much of an impact humans have on the ocean. The result is an expansion of the science of oceanography.

2. What are the four main disciplines or subfields of study in oceanography? ● ● ● ●

Geological oceanography—studies sea floor structure, features, and change over time Chemical oceanography—studies chemical composition and properties of seawater; pollutants Physical oceanography—studies waves, tides, currents, ocean–atmosphere relationship, and transmission of light and sound in the oceans Biological oceanography—studies ocean life-forms

3. What does it mean when oceanography is called an interdisciplinary science?

Oceanography often examines in detail all the different disciplines of oceanography. It covers all disciplines of science as they pertain to the oceans.

1.4 What is the Process of Science and the Nature of Scientific Inquiry?

1. Describe the steps involved in the process of science, starting with an observation about the natural world.

Step 1: Observation: Ask Questions and Establish Scientific Facts Step 2: Hypothesis: Make Generalization Step 3: Test: Perform Experiment Step 4: Theory: Draw Conclusion 2. What is the difference between a hypothesis and a theory?

A hypothesis is a tentative, testable statement, or an initial idea about a concept. A theory is a well-substantiated explanation of some aspect of the natural world that can incorporate facts, laws, logical inferences, and tested hypotheses. A hypothesis has not been extensively tested or observed, whereas a theory has.

3. Briefly comment on the phrase “scientific certainty.” Is it an oxymoron (a combination of contradictory words), or are scientific theories considered to be the absolute truth?

Knowledge about the natural world is constantly changing because we are always adding new observations and data to our knowledge base. As new data become available (frequently due to new technologies giving more detailed and accurate data), hypotheses, theories, and scientific 7 .

facts are reexamined for consistency with the new information. As long as new data is being added, the nature of scientific truth will be subject to change. Thus, the phrase “scientific truth” is an oxymoron. Over time, scientific statements generally form a sequence of increasingly accurate statements, eventually coming to a point where they are no longer questioned. It is accurate to say that science arrives at that which is probably certain, based on available data.

4. Can a theory ever be so well established that it becomes a fact? Explain.

If an observation is repeatedly confirmed—that is, made so many times that it is assumed to be completely valid—then it can be called a scientific fact. As observations are made, humans attempt to sort out the observations to reveal underlying patterns. From these attempts to sort, humans develop hypotheses that predict certain occurrences that then lead to refinements of the hypotheses. If a hypothesis has been strengthened by additional observations and if it is successful in predicting additional phenomena, then it can be advanced to a theory.

1.5 How Were Earth and the Solar System Formed?

1. Discuss the origin of the solar system using the nebular hypothesis.

The nebular hypothesis suggests that bodies of the solar system formed from an enormous nebular cloud composed predominantly of hydrogen and helium with a small fraction of heavier elements. As the large dust cloud revolved around its rotational center, the Sun began to form due to the concentration of particles under gravitational forces. In the earliest stages, the volume of the Sun may have been equal to the diameter of our solar system today.

As the nebular matter that formed the Sun contracted, a small percentage of it was left behind in small eddies (similar to whirlpools in a stream). This material flattened itself into an increasingly compact disc. The disc became so compact that it became gravitationally unstable and broke apart into separate smaller clouds. These smaller clouds were the protoplanets and their orbiting satellites. These bodies became the modern-day planets and their moons.

2. How was proto-Earth different from Earth today?

Proto-Earth was a large mass with perhaps a 1000 times greater diameter than the present Earth, and Proto-Earth was 500 times more massive than Earth today. Proto-Earth was devoid of life or oceans. It is believed that Proto-Earth was a homogenous planet with uniform composition throughout the planet. Proto-Earth had an atmosphere that was largely hydrogen and helium.

3. What is density stratification, and how did it change Proto-Earth?

Density stratification is a result of gravitational forces and results in the layering of materials as a function of density. The denser (heavier) material is found beneath the lower density (lighter) material. This caused Proto-Earth (and other protoplanets) to undergo internal rearrangement as the heavier materials migrated to the center to form a heavy core. The result is a layered Earth with the lowest-density material on the surface and the greatest-density material in the core.

4. What are some differences between the lithosphere and the asthenosphere?

The lithosphere is a thin, relatively cool, rigid layer that includes all of the crust and the topmost portion of the mantle that acts as a single unit floating on the asthenosphere. It is about 100 kilometers, or about 62 miles, thick. In contrast, the asthenosphere is a relatively thick, hot,

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highly viscous, plastic region of Earth. The asthenosphere corresponds to the upper mantle, and it is about 700 kilometers, or about 430 miles, thick. When force is applied to the lithosphere, it will fracture. When a gradual force is applied to the asthenosphere, it will deform without fracturing.

1.6 How Were Earth’s Atmosphere and Oceans Formed?

1. Describe the origin of Earth’s oceans.

Evidence suggests that the oceans came from inside Earth by the process of outgassing. About four billion years ago, the surface of Earth cooled sufficiently to allow the water vapor being pumped into the atmosphere by volcanoes to condense and settle on Earth’s surface.

2. Describe the origin of Earth’s atmosphere. How is its origin related to the origin of Earth’s oceans?

Earth’s initial atmosphere was also outgassed from the interior along with the oceans, but its composition has changed through time.

3. Have the oceans always been salty? Why or why not?

Evidence suggests that the oceans have always been salty because many of the compounds eroded from surface rocks (where the ocean’s salinity originated) contain elements that comprise salt: chlorine, sodium, magnesium, and potassium.

1.7 Did Life Begin in the Oceans?

1. How does the presence of oxygen in our atmosphere help reduce the amount of ultraviolet radiation that reaches Earth’s surface?

Ultraviolet radiation is absorbed by oxygen in the form of ozone (O3) molecules in the upper atmosphere.

2. What was Stanley Miller’s experiment, and what did it help demonstrate?

Laboratory experiments by Stanley Miller in 1952 showed that exposing a mixture of compounds that were thought to exist in the early atmosphere (hydrogen, carbon dioxide, methane, ammonia, and water) to ultraviolet light plus an electrical spark (simulating the effect of lightning) will produce a large assortment of organic molecules that are the basis for life.

3. Earth has had three atmospheres (initial, early, and present). Describe the composition and origin of each one.

Earth’s initial atmosphere was composed of hydrogen and a small amount of helium. The atmosphere was outgassed from Earth’s interior, and it was replaced by the release of gases from the mantle by outgassing through volcanic activity to form an early atmosphere. These gases included water vapor, carbon dioxide, and smaller concentrations of other gases. The present atmosphere is composed mostly of nitrogen and oxygen gas. Atmospheric oxygen was produced by photosynthetic activity (or possibly outgassing from the mantle about 2.5 billion years ago).

Oxygen began to be a significant constituent of Earth’s atmosphere about two billion years ago.

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1.8 How Old Is Earth?

1. Describe how the half-life of radioactive materials can be used to determine the age of a rock through radiometric age dating.

Radioactive materials have a characteristic half-life, which is the time required for one-half of the atoms in a sample to decay to other atoms. The older the rock is, the more radioactive material will have been converted to decay product. Analytical instruments can accurately measure the amount of radioactive material and the amount of resulting decay product in rocks.

By comparing these two quantities, the age of the rock can thus be determined.

2. What is the age of Earth? Describe the major events that demark the boundaries between these time periods: (a) Precambrian/Proterozoic, (b) Paleozoic/Mesozoic, and (c) Mesozoic/Cenozoic.

Earth is 4.6 billion years old. (a) The boundary between the Precambrian and Proterozoic is marked by an explosion of life and the appearance of shelled organisms, particularly trilobites. (b) The Paleozoic/Mesozoic boundary saw one of the largest mass extinctions in Earth’s history, with 90% of marine species going extinct. (c) The Mesozoic/Cenozoic boundary is marked by the extinction of the dinosaurs and the subsequent rise of mammals.

Critical Thinking Questions (and Answers) 1.1 NASA has discovered a new planet that has an ocean. Using today’s technology, how would you propose studying that ocean, all that’s in it, and the sea floor beneath it?

Assume an unlimited budget.

Send autonomously operated vehicles containing onboard laboratory facilities, cameras, and other data collection devices to the new planet to make observations and return the data. This is assuming that the devices can reach the new planet in a reasonable period of time. Otherwise, using today’s technology the most we could hope to perform would be extreme distance observations using various forms of measurement of light waves and radio waves being transmitted from this newly discovered planet.

1.2 Discuss the technological advantages that allowed sea-faring Arabs during the Middle Ages to dominate the Mediterranean Sea and trade with East Africa, India, and southeast Asia.

The Arabs retained knowledge of the early Phoenicians, Greeks, and Romans after the destruction of the Library of Alexandria in 415 A.D. These technologies included the ability to determine latitude by measuring one’s angle to the North Star in the northern hemisphere and accurate estimations of distances based on calculations of Earth’s circumference. The Arabs also took advantage of their knowledge of monsoon winds to plot out trade routes that corresponded with the wind.

1.3 One of today’s most pressing problems is trash in the oceans. Describe how information from at least two different disciplines in oceanography contribute to understanding or potentially solving this problem.

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Answers will vary. One example could include a discussion of aspects of physics and chemistry.

Plastic in the ocean is moved around and concentrated into areas due to the behavior of ocean currents (physics). In the water, plastics can accumulate pollutants as certain chemicals adsorb to their surface (chemistry).

1.4 What is the difference between a fact and a theory? Can either (or both) be revised?

A scientific fact is an observation that has been repeatedly confirmed by independent testing (so many times that it is assumed to be valid). A theory is a well-substantiated explanation that incorporates facts, descriptive generalizations about the behavior of an aspect of the natural world (laws), logical inferences, and tested hypotheses. A theory is not an educated guess or a scientific hunch. A theory is an understanding that develops from extensive independent observation, experimentation, and data interpretation/reflection.

Facts and theories can be modified and/or revised as new data are collected and interpreted.

Scientific facts are more likely to change with time and new technology than scientific theories.

1.5 Describe how the chemical composition of Earth’s interior differs from its physical properties. Include specific examples.

If you consider the chemical composition of Earth, the interior can be divided into three layers: the crust, the mantle, and the core. The crust is the lowest-density layer composed mostly of silicate minerals. The mantle below the crust is the largest layer and is composed of denser iron and magnesium silicate rock. The high-density core is predominantly metal (mostly iron and nickel). In contrast, considering the physical characteristics of Earth and how the layers respond to temperature and pressure, Earth is composed of five layers: the lithosphere, the asthenosphere, the mesosphere, the outer core, and the inner core. The lithosphere is the outermost layer or brittle rock that fractures when pressure is applied. The asthenosphere is a plastic layer; it flows when a gradual force is applied. The mesosphere is below the asthenosphere (corresponds to the middle and lower mantle) and is rigid, due to the increased pressure at depth. The outer core below the mesosphere is liquid (capable of flow), and the inner core is rigid. Like the mesosphere, the pressure on the inner core produces a rigid layer incapable of flow when pressure is applied.

1.6 Compare the two ways in which Earth was supplied with enough water to have an ocean. Which is likely to have contributed most of the water on Earth?

Research suggests that not all water came from inside Earth. Comets, being about half water, could be a source of Earth’s oceans. However, because outgassing releases mostly water vapor, this is considered the primary source of water on Earth, including supplying the oceans with water.

1.7 How would you answer the accusation, made by some religious groups, that scientific theories such as Stanley Miller’s theory on the origin of life on Earth are inherently weak because it is a historic event that no one actually observed? Please explain your answer in detail.

Answers will vary. Good answers will make note of the fact that scientists often make use of proxy data to infer past conditions and events that were not witnessed or recorded in any way. Scientists also make use of all available data to generate testable hypotheses and subsequent theories that are well-substantiated explanations of the natural world. Theories are not guesses, but have been extensively tested or subjected to repeated observation.

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1.8 Explain how radiometric age dating works. Why does the parent material never totally disappear completely, even after many half-lives?

Radiometric age dating takes advantage of the fact that most rocks contain small amounts of radioactive isotopes of various elements. The half-life of these elements is the time it takes for half of the radioactive isotope to decay into other atoms. Older rocks will have more of the radioactive materials converted to the decay product. It is important to know the half-life of the isotope in the rock you are dating, and then compare the quantity of radioactive isotope to the quantity of resulting decay products in rocks. The parent material never disappears completely because the rate of decay is exponential. The rate of decay of radioactive parent will approach, but never reach, zero.

Active Learning Exercises 1.1 If all Earth’s glaciers melted, sea level would rise by about 70 meters (230 feet).

Since the average height of the continents is only 840 meters (2756 feet), a rise in sea level of this magnitude would seriously impact human activities, especially in low-lying areas. Based on your knowledge of worldwide geography, which areas of the globe would most likely be affected? Be sure to include major population centers that would be under water. Assess these impacts, and discuss as a group.

Southeast Asia would most notably be impacted, particularly islands in the Pacific Ocean; there are island nations that have already been abandoned due to sea-level rise. Low-lying countries such as Bangladesh have already experienced problems with just monsoonal flooding, so any sea-level rise could impact the livelihoods and homes of some of the world’s poorest people. Any coastal cities would be adversely impacted, especially those on low-lying continental shelves. Miami, New York, and Amsterdam would be cities that would notably be under water, their billions of residents displaced by rising tides.

1.2. Make a list of the 10 essential items you’d need to take with you on a month-long boat expedition to study the ocean (exclude clothes, personal items, and food). Compare and discuss your list with another student in class. How would your list of 10 essential items be different if you created it during the beginning of voyaging for science in the 1700s?

Items might include a cell phone, computer or tablet, books, mp3 players, headphones, magazines, radio communication, electronic navigational equipment, sunscreen, hats, sunglasses, wetsuits, swimsuits, SCUBA equipment, scientific equipment such as salinometers, and games. In the 1700s, modern technological equipment would not have been available, nor would most of the items on the list above. Early voyagers might have brought a compass, a sextant, and perhaps books, paper, and a pen and inkwell.

1.3. With another student in class, make a list of all the types of careers you would be qualified for with a degree in oceanography or marine science. As an example of someone who works in oceanography or marine science, consider your instructor.

College professor, marine biologist, physical oceanographer, geologist, marine chemist, military

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officer, environmental scientist, fishery biologist, and many others.

1.4. With another student in class, discuss if you believe nature is simple enough for humans to understand. Give reasons why or why not. If not, do you think it is still reasonable for scientists to make this assumption in applying the process of science in their work?

Viewpoints will vary. On the one hand, science assumes nature is consistent and predictable. In that sense, nature is simple and therefore should be easy enough for humans to understand. Conversely, there are aspects of the natural world that are inexplicable and complex, that require complicated mathematical functions to explain. Scientists take various paths to arrive at knowledge, and these paths may not necessarily be dependent upon following the scientific method in its raw form, but rather makes use of available information, observation, and experimentation.

1.5. The nebular hypothesis of solar system formation is a scientific hypothesis. Based on your understanding of the scientific method, describe to another student in class how sure of this hypothesis you think scientists really are. Why would scientists have this level of certainty?

Students should be able to distinguish between a hypothesis and a theory. A hypothesis is not a wellsubstantiated explanation, whereas a theory is and has been extensively tested and/or subject to repeated observations. Based on this, it would appear that scientists are not certain as to the nebular hypothesis. However, this is an area of scientific exploration that does not readily lend itself to testing or observation; therefore, despite the fact that this is a hypothesis, it is generally accepted by the scientific community.

1.6. With another student in class, describe in your own words how Earth’s oceans became salty.

Earth’s surface is made of minerals. These minerals, when dissolved and eroded into the oceans, will add elements to Earth’s oceans that will render them salty.

1.7. With another student in class, discuss which of these two statements has more validity: (a) the greatest environmental crisis of all time was the buildup of toxic oxygen in Earth’s atmosphere 2 billion years ago or (b) humans are causing the greatest environmental crisis of all time.

Answers will vary with student’s perspective. The buildup of oxygen altered the nature of the planet, but it was a very long time ago before the presence of life. A more human-centric approach will argue that humans are causing the greatest environmental crisis, since it is impacting life as we know it today. Interpretation of the term environmental can mean from a planetary point of view or from the perspective of how it impacts our current Earth.

1.8 Working as a team, construct a representation of the geologic time scale using an appropriate quantity of any substance (other than dollar bills or toilet paper, which are used as examples in Mastering Oceanography Web Diving Deeper 1.2). Be sure to indicate some of the major changes that have occurred on Earth since its origin, such as “Origin of Earth,” “Origin of oceans,” “Earliest known life forms,” “Oxygen-rich 13 .

atmosphere first occurs,” “First organisms with shells,” “Dinosaurs die out,” and “Age of humans.”

Student answers will vary, but it is important to stress accurate calculation of scale. The toilet paper model works because it makes it possible to see how events that are far apart are relative to each other. Although it does not make use of a substance, a depiction of the time scale using a sidewalk, measuring tape, and chalk will also give an accurate representation of how these major events relate to each other in both time and magnitude.

Additional Active Learning Exercises 1.2 Think of an industry that takes place in the ocean (e.g., oil and gas extraction). What disciplines are involved in the industry?

Answers will vary. Using the example above, for the oil and gas extraction industry, practitioners would need to use geology to locate the fossil fuels, physics to understand how the area of extraction is affected by currents and waves, and biology to ensure that local organisms are not disturbed during extraction.

1.8 With another student in the class, explain how radiometric dating is used to determine the age of rocks.

Most rocks contain radioactive material. Over time, the radioactive material decays into atoms of other elements at a known rate. By analyzing the amounts of the radioactive material and the decay products, scientists can determine how old a rock is.

Exploring Data Figure 1.4 1. Rank the four main world’s oceans from largest to smallest, and also from deepest to shallowest.

The largest ocean is the Pacific, followed by the Atlantic, Indian, and Arctic. The deepest ocean is the Pacific, followed by the Atlantic, Indian, and Arctic.

2. Using data, support the argument that the Arctic Ocean technically should be classified as a sea.

By definition, a sea is smaller and shallower than an ocean. This is why the Arctic Ocean might be more appropriately considered a sea.

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SmartFigure 1.20 1. Comparing the two halves of this figure, explain why the boundaries on the two sides don’t always align.

The left side of the diagram illustrates the Earth’s layers classified by chemical composition.

The right side of the diagram illustrates the Earth’s layers classified by physical properties.

The Earth can be broken into three layers, based on their chemical composition. The Earth can be subdivided into five layers, based on how the rock responds to heat and pressure at depth. Rocks with the same composition but at different depths will take on different physical characteristics as heat and pressure increase.

2. Other than the center of Earth and Earth’s surface, what is the one boundary that actually does match up?

The outer edge of the core matches up on both sides of the diagram.

SmartTable 1.1 Although the density difference between granite and basalt seems small, the units reported in Table 1.1 are for a very small volume, so let’s examine a larger volume.

Imagine a typical swimming pool, which has a volume of about 400 cubic meters. If that swimming pool was filled with liquid granite, how much would it weigh? Imagine a second identical pool that was filled with liquid basalt. How much would that pool weigh? And, what is the difference in weight (metric tons) between the two pools?

To solve this problem, we first need to convert 400 m3 to cm3.

1 m3 = 1 × 106 cm3 400 m3 = 4 × 108 cm3 Granite has a density of 2.7 g/cm3 Filled with granite, our pool would have a mass of 4 × 108 cm3 * 2.7 g/cm3 = 1.08 × 109 g Now, we need to convert from g to metric tons 1 metric ton = 1 × 106 g 1.08 × 109 g/ 1 × 106 metric tons/g = 1080 metric tons Basalt has a density of 3.0 g/cm3 Filled with basalt, our pool would have a mass of 4 × 108 cm3 * 3.0 g/cm3 = 1.2 × 109 g Now, we need to convert from g to metric tons 1 metric ton = 1 × 106 g 15 .

1.2 × 109 g/ 1 × 106 metric tons/g = 1200 metric tons The difference in mass between the two of them would be 1200 metric tons – 1080 metric tons = 120 metric tons Figure 1.28 1. Based on the graph, what is the average interval in millions of years between Earth’s major extinction events (labeled E)? Based on the last extinction event, is Earth overdue for one? Explain.

The first extinction event was at about 440 mya, the second was at about 360 mya, the third was at about 250 mya, the fourth was at about 200 mya, and the fifth was at about 65 mya.

On average, the interval between Earth’s major extinction events is about 94 million years.

Based on this average, the Earth is not overdue for another extinction event. However, there is quite a bit of variability in the data. For example, the interval between the third and fourth events was only 50 million years, but the interval between the fourth and fifth events was 135 million years. Consequently, we can’t conclusively say whether or not we are overdue for another extinction event. Furthermore, many ecologists believe that we are currently experiencing the beginning of a major extinction event (the sixth extinction). The major difference between this event and previous ones is that human actions are the cause of the current extinction event.

2. What is the relationship between atmospheric oxygen concentration and extinction events? Speculate about why this pattern occurs.

Mass extinction events are correlated with low atmospheric oxygen levels. Most organisms depend on oxygen for cellular respiration. As oxygen levels dropped, organisms could not survive.

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Chapter 2 Plate Tectonics and the Ocean Floor Overview Chapter 2 is a discussion of the nature of Earth’s crustal movements in the context of plate tectonic theory. This chapter presents a discussion of the historical development of our understanding of continental drift and how new discoveries shaped the development of current plate tectonic theory. The current knowledge of Earth’s internal structure is covered, and the implications of near-surface structures and plate movement are presented. Different types of plate boundaries and the types of crustal movements associated with each type of boundary are discussed. An emphasis on sea floor plate boundaries and plate movement is included in this chapter. The chapter concludes with some discussion of plate tectonic applications that include paleoceanography and predictions for future continental locations.

Essential Concepts 2.1 Evaluate the evidence that supports continental drift.

2.2 Summarize the evidence that supports plate tectonics.

2.3 Discuss the origin and characteristics of features that occur at plate boundaries.

2.4 Show how plate tectonics explains the origin of features not easily explained by other processes.

2.5 Describe how Earth has changed in the past and predict how it will look in the future.

Chapter Outline 2.1 What Evidence Supports Continental Drift?

2.1.1 Testing the Idea: Matching Sequences of Rocks and Mountain Chains 2.1.2 More Observations: Glacial Ages and Other Climate Evidence Web Animation: Breakup of Pangaea 2.1.3 Evidence from Fossils: Distribution of Organisms 2.1.4 Objections to the Continental Drift Model 2.2 What Additional Observations Led to the Theory of Plate Tectonics?

2.2.1 Earth’s Magnetic Field and Paleomagnetism 2.2.1.1 Rocks Affected by Earth’s Magnetic Field 2.2.1.2 Paleomagnetism SmartFigure 2.7: Earth’s magnetic field.

2.2.1.3 Magnetic Polarity Reversals Web Animation: Flipping of Earth’s Magnetic Field Diving Deeper 2.1 Research Methods in Oceanography Using moving continents to resolve an apparent dilemma: Did Earth ever have two wandering North magnetic poles?

2.2.1.4 True Polar Wandering 2.2.1.5 Paleomagnetism and the Ocean Floor 2.2.2 Sea Floor Spreading and Features of the Ocean Basins 17 .

Web Animation: Sea Floor Spreading and Plate Boundaries Web Animation: Convection in a Lava Lamp SmartFigure 2.10: Magnetic evidence of sea floor spreading.

Web Animation: Sea Floor Spreading and Rock Magnetism 2.2.3 Other Evidence from the Ocean Basins 2.2.3.1 Age of the Ocean Floor 2.2.3.2 Heat Flow 2.2.3.3 Worldwide Earthquakes 2.2.4 Detecting Plate Motion with Satellites 2.2.5 The Acceptance of a Theory Web Animation: Relationship between Plate Boundaries and Features SmartFigure 2.12: Earthquakes and tectonic plate boundaries.

2.3 What Features Occur at Plate Boundaries?

Web Animation: Motion at Plate Boundaries 2.3.1 Divergent Boundary Features SmartTable 2.1 Characteristics, tectonic process, features, and geographic examples of plate boundaries 2.3.1.1 Oceanic Rises versus Oceanic Ridges SmartFigure 2.17 Sequence of events in the formation of an ocean basin by sea floor spreading.

Web Animation: Formation of an Ocean Basin by Sea Floor Spreading 2.3.1.2 Earthquakes Associated with Divergent Boundaries Smart Figure 2.19: Comparing oceanic rises and ridges 2.3.2 Convergent Boundary Features 2.3.2.1 Oceanic–Continental Convergence Web Animation: Sea Floor Spreading, Subduction SmartFigure 2.20: The three subtypes of convergent plate boundaries and their associated features Web Animation: Collapse of Mount St. Helens 2.3.2.2 Oceanic–Oceanic Convergence 2.3.2.3 Continental–Continental Convergence 2.3.2.4 Earthquakes Associated with Convergent Boundaries 2.3.3 Transform Boundary Features Web Animation: Convergent Margins: India–Asia Collision Web Animation: Transform Faults 2.3.3.1 Oceanic versus Continental Transform Faults 2.3.3.2 Earthquakes Associated with Transform Boundaries 2.4 Testing the Model: Can Plate Tectonics Explain Other Features in the Ocean and on Land?

2.4.1 Hotspots and Mantle Plumes Web Animation: Tectonic Settings of Volcanic Activity SmartFigure 2.25: Origin and development of mantle plumes and hotspots SmartFigure 2.27 Hawaiian Islands–Emperor Seamount chain.

Web Animation: Hot Spot Volcano Tracks 2.4.2 Seamounts and Tablemounts Web Animation: Seamounts/Tablemounts and Coral Reef Stages 2.4.3 Coral Reef Development

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2.5 How Has Earth Changed in the Past and How Will It Look in the Future?

2.5.1 The Past: Paleogeography 2.5.2 The Future: Some Bold Predictions Web Animation: Terrane Formation Web Animation: Plate Motions through Time 2.5.3 A Predictive Model: The Wilson Cycle SmartFigure 2.32 The Wilson cycle of ocean basin evolution Essential Concepts Review

Learning Outcomes Upon completion of this chapter, the student should be able to: 1.

Restate the theory of plate tectonics.

2.

List the evidence used by Alfred Wegener to formulate his continental drift theory, including: a. continental fit, especially South America and Africa b. similarities in the rock sequences (age and structure) on opposite sides of ocean basins c. occurrence of past glacial activity in tropical areas d. similar fossil distributions in continents that were once connected

3.

Distinguish between Alfred Wegener’s continental drift theory and the modern theory of plate tectonics. Be certain that you outline the early ideas about continental drift that are extant in the modern theory.

4.

Describe the evidence that supports the current version of the theory of plate tectonics, including: a. orientation of magnetic particles in the Earth’s crust b. magnetic dip (function of the latitude at which the rock cooled) c. apparent polar wandering d. magnetic polarity reversals e. ocean floor magnetic anomalies f. sea floor spreading g. uneven heat flow in the Earth’s crust h. worldwide earthquake distribution i. use of satellite data to detect plate motion

5.

List the features found in the following types of plate boundaries: a. divergent plate boundary b. convergent plate boundary c. transform plate boundary

6.

Distinguish between mantle plumes and hotspots.

7.

Describe how the occurrence and distribution of mantle plumes and hotspots supports the current theory of plate tectonics.

8.

Illustrate the arrangement of the continents when the supercontinent Pangaea existed.

9.

Make predictions about continental position in the geologic future.

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Teaching Strategies Students benefit from interactive discussions, online activities, and films where they have to actively participate in finding information and respond. The online study tools come in very handy for students.

Once the chapter has been covered, it may be helpful to spend time recapping the key concepts and having the students do a comparison and contrast of each type of plate boundary with regard to the following: earthquakes (magnitude and depth), volcanic activity and volatility, and geologic features. Be sure to include the three types of convergent boundaries and examples.

Real-life examples that pertain to their everyday lives help students understand concepts. Using disasters in the recent news that are related to plate boundary issues may help make these connections.

Teacher’s Resources Films ▪ ▪ ▪ ▪ ▪ ▪ ▪

The Last Grand Challenge—Exploring the Sea Floor (NOAA), 2 minutes, http://oceantoday.noaa.gov/oceanexploration/ Plate Tectonics: The Changing Shape of the Earth (National Geographic), 6 minutes, http://education.nationalgeographic.org/media/plate-tectonics/ Mapping the Seafloor (NOAA), 2 minutes, http://oceanservice.noaa.gov/caribbeanmapping/mapping-video.html Continental Drift: Evidence (Encyclopedia Britannica), 2 minutes, 47 seconds, www.britannica.com/science/continental-drift-geology/images-videos Earth Revealed: The Restless Planet (Program #2) (The Annenberg/CPB Collection), 30 minutes, http://learner.org/resources/series78.html Earth Revealed: Plate Dynamics (Program #6) (The Annenberg/CPB Collection), 30 minutes, http://learner.org/resources/series78.html Scientists “See” Ocean Floor Using Sonar (National Geographic), 5 minutes, https://www.nationalgeographic.com.au/videos/drain-the-oceans/sonar-scanning-the-sea-floor5632.aspx

Websites ● ● ● ● ●

www.education.noaa.gov/Ocean_and_Coasts/Ocean_Floor_Features.html—Ocean Floor Features (NOAA). Website includes short flash videos of ocean floor features, interactive lessons, realworld data, fact sheets, and scientist career profiles, all related to the ocean floor. walrus.wr.usgs.gov/mapping/csmp/—California Seafloor Mapping Program (U.S. Geological Survey). Website includes short flash videos, seismic profiling data, news, photos, and mapping. www.learner.org/interactives/dynamicearth/drift3.html—Plate Tectonics Interactive (Annenberg Media). Put the continent arrangement maps in correct chronological order. www.learner.org/interactives/dynamicearth/plate2.html—Plates and Boundaries Challenge (Annenberg Media). Identify the major tectonic plates using a word bank and identify the types of boundaries. www.amnh.org/ology/features/plates/loader.swf—Plates on the Move Interactive (American Museum of Natural History). Zoom into various locations to see the type of tectonic activity.

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Concept Check (Questions and Answers) 2.1 What Evidence Supports Continental Drift?

1. When did the supercontinent of Pangaea exist? What was the ocean that surrounded the supercontinent called?

Pangaea existed about 200 million years ago. The single largest ocean surrounding Pangaea was Panthalassa.

2. Regarding glacial ages, why is it unlikely that the entire world was covered by ice 300 million years ago?

Coal deposits that are 300 million years old originated in large semitropical swamps.

3. Cite the lines of evidence Alfred Wegener used to support his idea of continental drift. Why did scientists of the time doubt that continents had drifted?

Alfred Wegener used the following evidence to support continental drift:

✓ ✓ ✓ ✓

The fit of the continental margins across ocean basins Matching rock sequences and mountain ranges on different continents Climate evidence such as glacial deposits in areas that are now close to the Equator The distribution of organisms across continents that are separated by oceans that these organisms could not have crossed

Although the evidence in support of continental drift seems compelling, scientists in Wegener’s time rejected the idea of continental drift because the mechanisms Wegener proposed as driving continental movement seemed too far-fetched to be plausible. Some scientists felt that Wegener’s proposal ran contrary to the understanding of the laws of physics in the early 20th century. When sea floor spreading data became available in the 1950s and 1960s, Wegener’s ideas about continental movement were combined with these data to provide a more current model that explained crustal movement.

2.2 What Additional Observations Led to the Theory of Plate Tectonics?

1. Describe what Earth’s magnetic field looks like and how it has changed through time.

Earth’s magnetic field resembles the magnetic field produced by a large bar magnet. Bar magnets have ends that are oppositely charged. The magnet ends are usually designated by “+” and “–” or “N” (for north) and “S” (for south). This opposite polarity causes magnetic objects to align parallel to the magnetic field produced by the bar magnet. Although Earth does not actually have a bar magnet inside, it behaves as if it did. Invisible lines of magnetic force originating from within Earth travel through the planet and out into space, Nature of Earth’s Magnetic Field).

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The strength of Earth’s magnetic field has changed through time (on the geologic time scale).

Additionally, Earth has experienced many dozens of magnetic field polarity reversals during the last 100 million years.

2. Describe sea floor spreading and why it was an important piece of evidence in support of plate tectonics.

The age relationships and pattern of symmetric stripes on the sea floor with respect to the axis of the mid-ocean ridge indicate that sea floor spreading occurs along the mid-ocean ridge. With sea floor spreading as a mechanism, many of the arguments against continental drift could no longer be supported, so it helped to advance the development of continental drift and the formation of plate tectonic theory.

3. Why does a map of worldwide earthquakes closely match the locations of worldwide plate boundaries?

Plate boundaries are locations where plates interact. Earthquakes frequently occur in areas where convergent or transform plate movements occur. There is a high correlation between worldwide earthquake location and plate boundaries.

2.3 What Features Occur at Plate Boundaries?

1. Most lithospheric plates contain both oceanic- and continental-type crust. Use plate boundaries to explain why this is true.

Plate boundaries rarely follow continental margins, so most large plates contain a continent (continental crust) as well as a large area of ocean floor (oceanic crust).

2. Describe the differences between oceanic ridges and oceanic rises. Include in your answer why these differences exist.

Spreading rates (the total widening rate of an ocean basin resulting from the motion of both plates away from the spreading center) vary along the mid-ocean ridge and profoundly affect the slope of the mountain range. The faster the spreading rate, the broader the mountain range associated with the spreading center. The rapidly spreading and gently sloping portions of the mid-ocean ridge are called oceanic rises. The slower and steeper-sloped areas of the mid-ocean ridge are called oceanic ridges. Oceanic ridges and oceanic rises are both part of the global midocean ridge system.

3. Using the profile view of the Mid-Atlantic Ridge in Figure 2.19a, calculate its total spreading rate over the past 50 million years (divide total distance by time). Then do a similar calculation for the East Pacific Rise (Figure 2.19b) and compare the two.

Mid-Atlantic Ridge: 280 miles/50 million years = 0.0000056 miles/year 0.0000056 miles × 5280 ft/mile × 12 in/1 ft = 0.35 inches/year East Pacific Rise: 230 miles/15 million years = 0.000015 miles/year = 0.97 inches/year

4. Convergent boundaries can be divided into three types, based on the type of crust contained on the two colliding plates. Compare and contrast the different types of convergent 22 .

boundaries that result from these collisions.

Oceanic–Continental: Denser oceanic plate subducts below the continental plate. Oceanic plate is heated as it subducts into the asthenosphere, releasing superheated gases that partially melt the overlying mantle, rising to the surface through the overriding continental plate. The rising basalt-rich magma mixes with the granite of the continental crust, producing lava in volcanic eruptions at the surface that is intermediate in composition between basalt and granite. The result of this volcanic activity on the continent above the subduction zone produces a type of volcanic arc called a continental arc.

Oceanic–Oceanic: Two oceanic plates converging, with the denser oceanic plate subducting.

Typically, the older oceanic plate is denser because it has had more time to cool and contract.

This type of convergence produces the deepest trenches. Similar to oceanic–continental convergence, the subducting oceanic plate becomes heated, releasing superheated gases and partially melting the overlying mantle. This buoyant molten material rises to the surface and fuels active volcanoes, which occur as an arc-shaped row of volcanic islands that is a type of volcanic arc called an island arc. The molten material is mostly basaltic because there is no mixing with granitic rocks from the continents, and the eruptions are not nearly as destructive.

Continental–Continental: Two continental plates converge because they are both too low in density to be pulled far down into the mantle; they are uplifted into tall mountain ranges. These mountains are composed of folded and deformed sedimentary rocks originally deposited on the sea floor that previously separated the two continental plates. The intervening oceanic crust between the two plates is subducted beneath such mountains as the plates collide.

5. Describe the difference in earthquake magnitudes that occur between the three types of plate boundaries, and include why these differences occur.

Divergent plate boundary: The magnitude of energy release along divergent plate boundaries is closely related to the spreading rate. Earthquakes in the rift valley of the slow-spreading MidAtlantic Ridge reach a maximum magnitude of about MW = 6.0, whereas those occurring along the axis of the fast-spreading East Pacific Rise seldom exceed MW = 4.5. These earthquakes are shallow, usually less than 10.0 kilometers (6 miles) in depth. Compared to the other types of plate boundaries, earthquakes along divergent plate boundaries are numerous, but relatively small because the sea floor is continually pulling apart, or rifting, here.

Convergent plate boundary: The forces involved in convergent plate boundary collisions are enormous and create infrequent but powerful earthquakes. Convergent plate boundaries are associated with some of the most powerful earthquakes in the world. Currently, the largest earthquake ever recorded was the Chilean earthquake of 1960 that occurred near the Peru-Chile Trench and had a magnitude of MW = 9.5. Earthquakes associated with convergent boundaries vary from shallow depths near the surface down to 6709 kilometers (415 miles deep); these are the deepest earthquakes in the world. These earthquakes are clustered in a band about 20 kilometers (12.5 miles) thick that closely corresponds to the location of the subduction zone.

Transform plate boundary: As one plate slowly moves past another, shallow but frequently strong earthquakes are produced. Magnitude MW = 7.0 have been recorded along some oceanic transform faults, and the San Andreas Fault (a continental transform fault) has experienced earthquakes up to MW = 8.5. These earthquakes are not as strong as those associated with convergent boundaries because the direction and type of plate movement is different.

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2.4 Testing the Model: Can Plate Tectonics Explain Other Features in the Ocean and on Land?

1. How is the age distribution pattern of the Hawaiian Islands–Emperor Seamount Chain explained by the position of the Hawaiian hotspot? What could have caused the curious bend in the chain?

From the island of Hawaii, the only active volcano in the chain, there extends a northwest trending line of islands and seamounts to about 188 degrees west longitude. At this point, the island chain makes a bend and turns sharply north as the Emperor Seamount Chain. The volcanoes in the island chain increase in age from Hawaii to about 40 million years (at the bend between the Hawaiian Islands and the Emperor Seamount) to about 81 million years at the north end of the Emperor Seamount Chain. The evidence indicates that all of the volcanoes that make up the chains formed when a portion of the ocean floor from which they extend passed over a stationary volcanic hotspot that now underlies the island of Hawaii and Loihi.

The bend probably indicates a change in the direction of the movement of the Pacific Plate.

During eruptions of the Emperor Seamounts, the plate was moving past the hotspot in a northerly direction. About 40 million years ago, Pacific Plate movement changed to a northwesterly direction, thus creating the bend between the two island chains.

2. What are the differences between a mid-ocean ridge and a hotspot?

A mid-ocean ridge is a divergent boundary where two plates are splitting apart. As the plates pull away from one another, there is an abundance of volcanic activity. Hotspots are areas of intense volcanic activity as well, but they are not necessarily associated with any particular type of plate boundary. The vast majority of hotspots do not coincide with plate boundaries; those that do not are concentrated along divergent boundaries where lithospheric plates are relatively thin.

3. How can plate tectonics be used to help explain the difference between a seamount and a tablemount?

Most oceanic islands form because of the volcanic activity at oceanic spreading centers. As the lithospheric plates move away from the oceanic ridge, ocean depth increases due to thermal contraction in the lithosphere. The islands will become inactive volcanoes within 30 million years because the plate will have moved and the volcanic islands will no longer be centered over the magma plume rising from the mantle that creates an active volcano. Inactive, they will be carried beneath the ocean’s surface. Those that have their surfaces flattened by wave erosion will become tablemounts.

4. Explain how plate movement has affected the age of Australia’s Great Barrier Reef.

The corals that built the Great Barrier Reef live in warm waters. As corals grow, they produce a hard skeleton of limestone. Each generation builds upward, on the skeletons of its predecessors.

The Indian-Australian Plate is moving northward, toward the equator. The thickest (and oldest) parts of the reef are found in the northern end of the reef, which was the first to reach water warm enough for corals to thrive.

2.5 How Has Earth Changed in the Past and How Will It Look in the Future?

1. Using the paleogeographic reconstructions shown in Figure 2.30, determine when the 24 .

following events first appear in the geologic record:

a. North America lies on the equator. 480 million years ago b. The continents come together as Pangaea. 240 million years ago c. The North Atlantic Ocean opens. 120 million years ago d. India separates from Antarctica. 60 million years ago

2. Determine the Wilson cycle stage for the following present-day locations, noting the features and processes that support your answers.

a. The Atlantic Ocean Mature. The Atlantic Ocean has opened up and continues to open. It started out as Pangaea split open with a small ocean basin. The Atlantic continues to widen at the Mid-Atlantic Ridge, in the center expanding on either side. This expansion will continue until the Pacific is closed off.

b. The Pacific Ocean Declining. Once a super ocean named Panthalassa, the Pacific Ocean continues to get smaller due to subduction at the trenches. Since the Earth remains with the same circumference, the amount of expansion along with the East Pacific Rise in the Atlantic Ocean has to be equaled out by the same amount of subduction occurring along the Pacific rim.

c. The Red Sea Juvenile. The Red Sea is a young seaway much like the Atlantic once was just after it opened up.

d. The Alps Suturing. The Alps are a collision boundary similar to the Himalayas. There was once an intervening ocean basin that was subducted until the continental crust collided. Neither plate containing continental crust is dense enough to subduct, creating a collision boundary uplifting the mountain ranges. e. The East Africa Rift Valleys Embryonic. It consists of rift valleys on the African continent. f.

Baja California Juvenile. It is a narrow sea along a faulting zone.

3. Examine Figures 2.30 and 2.32. In which ocean basin would you expect to find the oldest sea floor? Explain your reasoning.

The Pacific Ocean should have the oldest sea floor. Looking at the progression of continental movement, you can see that the Atlantic opened up much more recently, and when the continents were together as one landmass, what is today the Pacific Ocean surrounded that landmass.

Critical Thinking Questions (and Answers) 2.1 If you could travel back in time with three illustrations from this chapter to help Alfred Wegener convince the scientists of his day that continental drift does indeed exist, what would they be and why?

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Wegener was unable to describe the process that caused continental movement because there was an incomplete understanding of the structure of Earth in 1912. Figure 2.9, Process of Plate Tectonics, would provide Wegener with a modern understanding of Earth’s structure and the processes that drive plate movement. Two additional figures that provide supporting evidence for Wegener’s theory are Figures 2.12a and 2.12b, Earthquakes and Lithospheric Plates. Please note that student answers may vary.

2.2 If the sea floor didn’t exhibit any magnetic polarity reversals, what would that indicate about the history of Earth’s ocean basins?

The alternating (or striped pattern) reversals of Earth’s magnetic field recorded in sea floor rocks could be created when newly formed rocks at the mid-ocean ridges are magnetized and align with the direction of Earth’s magnetic field at the time of their formation. As these rocks move slowly away from the crest of the mid-ocean ridge, periodic magnetic pole reversals produce rocks with different magnetic orientation, recording polarity changes in sea floor rocks. This produces a pattern of magnetic polarity stripes in the sea floor that are symmetrical on either side of the mid-ocean ridge.

This pattern strongly supports the existence of sea floor spreading at mid-ocean ridges. If the sea flood did not exhibit any magnetic polarity reversals, it would indicate that the magnetic field did not change as the ocean basins formed. This would imply that the ocean basins formed quickly and are relatively young (geologically speaking).

2.3 Using Figure 2.12, analyze and describe the tectonic setting that contributed to these natural disasters: (a) the 1883 eruption of Krakatoa, Indonesia; (b) the 2010 Haitian earthquake; and (c) the 2011 earthquake and tsunami in northeastern Japan. (a) Krakatoa is located at the convergent boundary of oceanic plates. This type of boundary generates trenches due to subduction and volcanic islands adjacent. (b) Haiti is situated along a transform boundary between the Caribbean Plate and the North American Plate. Transform boundaries are prone to earthquakes. (c) Japan is located above a convergent boundary between the Pacific Plate and the Eurasian Plate.

This oceanic convergent boundary has the potential to generate underwater earthquakes; displacement of sea floor due to these earthquakes can cause a tsunami.

2.4 Describe the differences in origin between the Aleutian Islands and the Hawaiian Islands. Provide evidence to support your explanation.

The Aleutian Islands are created by the subduction of the Pacific Plate into the Aleutian Trench. As the subducted plate melts, the material mixes with other molten rocks and creates an andesitic volcanic island arc. Any volcanoes in the island arc could be active anytime due to continuing subduction.

The Hawaiian Islands were created by the Pacific Plate passing over the Hawaiian hotspot. The eruptions associated with the Hawaiian hotspot produce mostly basaltic lava. Only the volcanoes on the island (or two) directly over the hotspot are active, and each island further from the hotspot is progressively older.

2.5 Assume that you travel at the same rate as a fast-moving continent—at a rate of 10 centimeters (2.5 inches) per year. Calculate how long it would take you to travel from your present location to a nearby large city. Also, calculate how long it would take you 26 .

to travel across the United States from the East Coast to the West Coast.

The answer to this question will vary as a function of location. As an example, if the nearest large city is 100 kilometers (60 miles) away, then: 100 km × (1000 m/km) × (100 cm/m) × (1 year/10 cm) = 1,000,000 or 106 years. One million years is a surprisingly short length of geologic time for moving such a large distance.

The distance between Washington, D.C. (East Coast), and San Francisco, California (West Coast), is 4021 km (2498 miles), so: 4021 km × (1000 m/km) × (100 cm/m) × (1 year/10 cm) = 40,210,000 years or 40.21 × 106 years. Forty million years is a surprisingly short length of geologic time for moving such a large distance.

Active Learning Exercises 2.1. Create two teams to debate the evidence for and against continental drift. Use only knowledge of Earth processes that was available prior to the 1930s.

Evidence for continental drift: fossils matching on widely separated continents, discontinuous mountain belts that pick up again on another continent, similar species on different continents, evidence of glacier activity in currently tropical areas, glacier abrasion on differing continents, fit of the continents with each other.

Evidence against continental drift: no mechanism to move plates laterally, plate movement appears to defy laws of physics, continents cannot plow through ocean basins.

2.2. A recent discovery suggests that Jupiter’s moon Europa is composed of tin, brittle slabs of water ice that undergo plate tectonics, much like Earth’s lithospheric plates.

Research this discovery on the Internet and describe the evidence for the existence of plate tectonic processes on Europa.

Visual evidence of Europa’s icy crust expanding, cracks and ridges on Europa’s surface, evidence of subduction, evidence of Europa’s surface and surface features changing over time.

2.3. With another student in class, list and describe the three types of plate boundaries.

Include in your discussion any sea floor features that are related to these plate boundaries and include a real-world example of each. Construct a map view and cross section showing each of the three types of plate boundaries, including the direction of plate movement and associated features. ●

Convergent—two plates are moving toward each other and colliding. Sea floor features associated with these boundaries include trenches and volcanic mountain ranges/islands.

Examples include the Mariana Islands, Papua New Guinea, the Galapagos, and the Solomon Islands.

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● ●

Divergent—two plates are moving apart. You get mid-ocean ridges and rises in these places, such as the Mid-Atlantic Ridge. These ridges have underwater volcanic activity. Iceland is a place where the ridge is above the sea surface.

Transform—plates are sliding laterally past each other. These are generally transform faults such as the San Andreas fault, with a great deal of earthquake activity.

Maps will vary, but should resemble figures in section 2.3.

2.4. In pairs, investigate the idea that a mantle plume underlies Yellowstone National Park. Report to the class what evidence you have discovered. Using your understanding about plate tectonics, assess the implications for the future of this region.

The dynamics of this region cannot be currently explained by a simple mantle plume. However, the presence of such a feature would explain the hot geyser eruption for this region. The presence of a mantle plume could imply a future rift zone and opening of an ocean basin over time.

2.5. You and two of your fellow classmates are colonists on an Earth-sized planet orbiting within the habitable zone of a distant star. As a group, choose one of the following scenarios for your planet: (a) it has extremely active tectonics, (b) it exhibits Earth-like tectonic activity, or (c) it is tectonically dead. Then, based on your planet’s chosen level of tectonic activity, describe what your planet looks like, including details about various land-forms that would be visible.

Scenario (a): Students should note that high tectonic activity could lead to frequent earthquakes, high mountains as uplift outpaces erosion, a great deal of volcanic activity, and a rapidly changing landscape as plates are created and destroyed. Climate could be much warmer as greenhouse gases are emitted through tectonic activity. (b): Earth-like tectonics would have mountain ranges, volcanoes, earthquake activity, and plate motions similar to Earth. No major differences would be noted. (c): Tectonically dead would be a relatively featureless planet. There would be no mountains, trenches, or landscapes that evolve by means other than weathering and/or erosion. Earthquakes and volcanoes would not exist. Climate might be cooler since tectonic activity can release greenhouse gases.

Additional Active Learning Exercises 2.4 Draw a figure that illustrates the differences between a volcanic island, a seamount, and a tablemount. Be sure to show how each are formed.

This figure will look similar to Figure 2.28.

2.5 Using Figure 2.31, explain how the area in which you now live will differ 50 million years from now. For example, how will the climate change? Will the area be under water or near a coast?

Answers will vary, but for North America, the climate would likely cool since the continent is moving northward. Areas in the middle of the country may be covered by an inland sea and areas along the west coast will be separated from the rest of the continent.

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Exploring Data Figure 2.7 Using Figure 2.7b, describe the changes to a handheld magnetic dip needle if you carried one to the following locations: (1) the magnetic equator, (2) the magnetic North Pole, (3) halfway between the magnetic equator and the magnetic North Pole, and (4) the magnetic South Pole. Explain why the instrument would experience those changes.

The handheld magnetic dip needle aligns itself parallel to the lines of Earth’s magnetic force field. (1) At the magnetic equator, the dip needle would be aligned parallel to Earth’s surface. (2) At the magnetic North Pole, the dip needle would be pointed directly downward and would be perpendicular with Earth’s surface. (3) Halfway between the magnetic equator and the magnetic North Pole, the dip needle would be pointing diagonally downward toward Earth’s surface. (4) At the magnetic South Pole, the dip needle would be aligned perpendicular to Earth’s surface, but compared to the alignment at the magnetic North Pole, the opposite end of the magnet would be pointed toward Earth’s surface.

Figure 2.11 1. Where, in general, is the world’s youngest ocean crust? What sea floor feature is it associated with?

The youngest ocean crust is found on either side of a mid-ocean ridge.

2. Identify three locations where the world’s oldest ocean crust occurs. Explain why such old ocean crust exists here.

Answers will vary. In general, the oldest crust is found near the continental margins.

Continental margins surrounding ocean basins with slow spreading centers (such as the North Atlantic and the Indian Oceans) tend to have very old oceanic crust because the plates are moving very slowly. The North Pacific Ocean also has very old crust along the western border due to its distance from the spreading center.

Figure 2.19 1. Draw a profile view of an oceanic spreading center that has a spreading rate halfway between that of an oceanic ridge and an oceanic rise. Use the same scale as the profiles in Figure 2.19 and label the axes.

The profile will be somewhat steeper than Figure 2.19b, but not as steep as Figure 2.19a.

The x-axis will display 85 million years on either side of the spreading center.

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2. Next, draw a profile view of an ultra-slow oceanic spreading center. Use the same scale as the profiles in Figure 2.19 and label the axes.

The profile will be similar to figure 2.19a, except it will have a much larger rift valley in the middle of the spreading center and the x-axis will display a longer time period.

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Chapter 3 Marine Provinces Overview Chapter 3 presents a discussion of the major geomorphic oceanic provinces and ocean floor features, especially as they relate to plate tectonics. The theory of plate tectonics is covered in Chapter 2.

Bathymetry and bathymetric techniques are included in this chapter to help students understand how ocean scientists collect information about areas of the sea floor that have not been explored by humans.

Ocean floor features, including the mid-ocean ridges, are described in detail.

Essential Concepts 3.1 Discuss the techniques that are used to determine ocean bathymetry.

3.2 Describe the sea floor features that exist on continental margins.

3.3 Describe the sea floor features that exist in the deep-ocean basins.

3.4 Describe the sea floor features that exist along the mid-ocean ridge.

Chapter Outline 3.1 What Techniques Are Used to Determine Ocean Bathymetry?

3.1.1 Soundings Web Animation: Sonar and Echolocation 3.1.2 Echo Soundings SmartFigure 3.2: Multibeam sonar 3.1.3 Using Satellites to Map Ocean Properties from Space SmartFigure 3.6 Global sea surface elevation map from satellite data.

3.1.4 Seismic Reflection Profiles 3.2 What Features Exist on Continental Margins?

3.2.1 Passive versus Active Continental Margins SmartFigure 3.9 Diagrammatic view of passive and active continental margins.

3.2.2 Continental Shelf 3.2.3 Continental Slope 3.2.4 Submarine Canyons and Turbidity Currents SmartFigure 3.12: Submarine canyons and turbidity currents Web Animation: Turbidity Currents and the Formation of Graded Bedding 3.2.5 Continental Rise 3.3 What Features Exist in the Deep-Ocean Basins?

3.3.1 Abyssal Plains 3.3.2 Volcanic Peaks of the Abyssal Plains 3.3.3 Ocean Trenches and Volcanic Arcs 3.3.3.1 The Pacific Ring of Fire 3.4 What Features Exist Along the Mid-Ocean Ridge?

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3.4.1 Volcanic Features 3.4.2 Hydrothermal Vents DIVING DEEPER 3.1 Research Methods in Oceanography Earth’s Hypsographic Curve: Nearly everything you need to know about Earth’s oceans and landmasses in one graph SmartFigure 3A: Earth’s hypsographic curve.

PROCESS OF SCIENCE 3.1 Now You See It, Now You Don’t: The Unusual Case of the Missing Sea Floor Seismic Equipment 3.4.3 Fracture Zones and Transform Faults Web Video: Black Smoker Venting Fluid SmartFigure 3.23 The Eltanin Fracture Zone.

SmartFigure 3.24 Transform faults and fracture zones.

3.4.4 Oceanic Islands SmartTable 3.1: Comparison between transform faults and fracture zones Essential Concepts Review

Learning Outcomes The instructional objectives are performance-based and detail specific learning outcomes for Chapter 3.

The test items contained in the Test Bank are keyed to the learning objectives and Chapter in Review at the end of the chapter. The order of the objectives mirrors the content presentation in Chapter 3.

Upon completion of this chapter, the student should be able to: 1. Define bathymetry.

2. Describe the techniques used by early oceanic navigators to estimate the ocean depth.

3. Relate the fathom to vertical distance measured in meters and feet.

4. Distinguish among the following terms, and describe how each technology is used to make estimates of the ocean depth, including: a. echo sounding b. precision depth recording (PDR) c. SONAR (sound navigation and ranging) d. seismic reflection profiles 5. List the three major marine provinces and give the distinguishing features of each marine province.

6. Distinguish between passive continental margins and active continental margins, and describe the tectonic processes occurring at each continental margin.

7. Differentiate between convergent active continental margins and transform active continental margins. Provide a specific example of a location of each type of oceanic active margin.

8. Discriminate between the continental shelf and continental slope.

9. Give an example of a submarine canyon.

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10. Discuss the relationship between turbidity currents and the formation of submarine canyons.

11. Describe the topographic features of the continental rise, including: a. graded bedding b. turbidite deposits c. deep-sea fans (submarine fans) 12. Describe the characteristic features of the abyssal plain, including: a. seamounts b. abyssal hills (seaknolls) c. abyssal hill provinces 13. Discuss the relationship between the formation of an ocean trench and a volcanic island arc. Describe the tectonic processes that create these features.

14. Distinguish between a guyot and a tablemount.

15. Explain the relationship between the Pacific Ring of Fire and the location of plate margins in the Pacific Ocean. Include a discussion of the type of continental margins in these locations.

16. List the features that characterize the mid-ocean ridge.

17. Differentiate between a rift valley, an oceanic ridge, and an oceanic rise.

18. Distinguish among the following types of hydrothermal vents: warm-water vents, white smokers, and black smokers.

19. Compare and contrast transform faults and fracture zones found on the sea floor.

20. Describe a hypsographic curve and discuss the information that this graph illustrates.

Teaching Strategies Marine Provinces is one of the chapters that a lot of instructors without an Oceanography background are tempted to skip. However, it is the foundation for Chapter 4: Marine Sediments.

Marine provinces and marine sediments are where most of oceanographic history comes from.

Spending time on this section will help lay the foundation for the next chapter, Marine Sediments, thereby further laying the foundation for nearly all things oceanographic.

Teacher’s Resources Films ▪ ▪ ▪

Earth Revealed: The Sea Floor (Program #4) (The Annenberg/CPB Collection), 30 minutes, http://learner.org/resources/series78.html Ocean Bathymetry and Water Properties (Yale Open Courses), 50 minutes, https://youtube.com/watch?v=EN8ynx-R0wY Hydrothermal Vents (National Geographic), 3 minutes, http://video.nationalgeographic.com/video/hydrothermal-vents

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▪

Ring of Fire PSURock Video—Dr. Richard Alley Sings about the Pacific Ring of Fire, 3 minutes, https://youtube.com/watch?v=fq22bVmxfuk

Websites ● ● ●

http://oceanexplorer.noaa.gov/gallery/maps/maps.html—NOAA Ocean Explorer, Video Animations of sea floor features. http://serc.carleton.edu/margins/collection/90777.html—Bathymetry of Rifted Margins: Interactive exercise. https://www.google.com/earth/—Google Earth illustrates global bathymetry

Concept Check (Questions and Answers) 3.1 What Techniques Are Used to Determine Ocean Bathymetry?

1. What is bathymetry?

Bathymetry is the measurement of ocean depths and the charting of ocean floor topography (shape and relief). Determining bathymetry involves measuring the vertical distance from the ocean surface down to the mountains, valleys, and plains on the sea floor.

2. Describe how an echo sounder works.

An echo sounder sends a sound signal (a ping) into the ocean. The sound signal bounces off any object that is a different density than seawater (such as live organisms or the ocean floor).

Analogous to the use of radar on land, the echosounder records the echoes that have bounced off the objects. The time that it takes for the echoes to return is used to determine ocean depth and the shape of the ocean floor.

3. Discuss the development of bathymetric techniques, including significant advances in technology.

Since early history, humans have determined water depth using depth soundings—made by attaching a heavy weight to a long line and lowering it over the side of a vessel—to determine water depth. The first systematic bathymetry of the oceans was made in 1872, when HMS Challenger began its historic three-and-one-half-year voyage. Throughout the voyage, the Challenger’s crew stopped to make depth soundings every few thousand kilometers. They also recorded various seawater properties at these locations.

In the 1920s, a new technology advanced ocean floor mapping: the invention of the echo sounder.

The precision depth recorder (PDR) was developed in the 1950s. With a more focused highfrequency sound beam (in comparison to the echosounder), it could provide depths to a resolution of about 1 meter (3.3 feet). Throughout the 1960s, PDRs were used extensively to provide a reasonably good representation of the ocean floor. Data collected by thousands of research vessel tracks produced the first reliable global sea floor bathymetric maps. These maps provided important evidence that supported plate tectonic theory and the idea of sea floor spreading.

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Today, multibeam echosounders and side-scan sonar give oceanographers a far more precise picture of the ocean floor. The first multibeam echosounder, Seabeam, made it possible for a survey ship to map the features of the ocean floor along a strip up to 60 kilometers (37 miles) wide. The system uses sound emitters directed away from both sides of the ship, with receivers permanently mounted on the ship’s hull. With these data, a map of the sea floor can be computergenerated. Sea MARC and GLORIA are the two types of side-scan sonar devices that are towed behind a survey ship.

To obtain a more detailed picture of the ocean floor, a side-scan sonar instrument must be towed behind a ship on a cable, so that it “flies” just above the ocean floor. The most recent technology in these deep-sea observational systems combines a side-scan sonar instrument with a subbottom imaging package. This allows a simultaneous view of the ocean floor surface and a cross section of the sediment below water depths of 6500 meters (21,325 feet).

The sea floor can also be mapped by using satellites that can detect slight irregularities in the height of the ocean surface caused by gravitational attraction of different sea floor features. The various satellite missions and their objectives are listed in Web Table 3.1.

3.2 What Features Exist on Continental Margins?

1. Describe the following major features of a passive continental margin: continental shelf, continental slope, continental rise, submarine canyon, and deep-sea fans.

The continental shelf extends seaward from the shoreline as a gently sloping surface with an average slope of about one-tenth of a degree. Its topography is usually similar to that of the coastal region of the continent. It is very narrow in some areas, such as off California, and reaches widths as great as 1300 kilometers (808 miles) off the Siberian coast; its average width is about 70 kilometers (43 miles). The average depth at which the shelf break that marks its seaward limit occurs is about 135 meters (443 feet), but the break is as deep as 350 meters (1148 feet) off Antarctica.

The continental slope, which extends from the continental shelf to the deep-ocean basins, has an average slope of four degrees. In the Pacific Oceans where mountainous coasts are common, the continental slope averages five degrees, in contrast to the Atlantic and Indian Oceans—where it averages three degrees. Submarine canyons resulting from turbidity currents cut the slopes and may even extend across the continental shelf in some cases.

The continental rise is a gently sloping surface that has about the same slope as the continental shelf. It extends from the base of the continental slope into the deep-ocean basins as a thinning wedge of sediment, most of which is probably deposited by turbidity currents when they reach the base of the continental slope and lose their energy. This sediment is greatly modified by deep boundary currents that erode it from some locations and deposit it as drifts as the currents slow, while turning at bends in the continental slope.

Submarine canyons are similar in size and design to river-cut canyons on land. They are found mostly on the continental slope, but some canyons extend landward across the continental shelf (such as the Hudson Canyon that extends toward the mouth of the Hudson River in New York).

Deep sea fans are formed when the turbidity currents reach the base of the continental slope and lose speed moving across the flatter deep-ocean floor. The sediment settles out of the slowmoving water to create deep-sea fans at the base of the slope. As the fans grow from deposits of 35 .

distributary channels flowing across their surface, they merge to produce the gently sloping continental rise at the base of the continental slope.

2. Explain how submarine canyons are created.

The most widely accepted phenomenon that has been used to explain the existence of submarine canyons is turbidity currents. Although no one has directly witnessed turbidity currents in action, there is good evidence to support their existence and erosive power. It is believed that the sediment on the continental slope may be dislodged by an event such as oversteepening of sediment, an earthquake, a hurricane, or another disturbance. The dislodged sediment mixes with water as it moves down the slope under the influence of gravity to produce a turbidity current.

This flow of dense fluid is erosive and cuts a gully in the slope. Subsequent turbidity currents deepen it to canyon proportions.

3. Explain what graded bedding is and how it forms.

Graded bedding is a type of sediment layering that becomes progressively finer within a sequence, and it is the result of deposition by turbidity currents. Material that was suspended in a turbidity current settles out in a distinct pattern: the larger pieces settle first, then progressively smaller pieces settle, and eventually even very fine pieces settle out. The settling process may take weeks or months. This creates a graded bedding sequence of coarser material at the bottom becoming progressively finer toward the top.

3.3 What Features Exist in the Deep-Ocean Basins?

1. Describe the process by which abyssal plains are created.

Abyssal plains are formed by fine particles of sediment slowly drifting down onto the crust of the deep-ocean floor, and over millions of years, producing thick sedimentary deposits analogous to marine dust. This process is called suspension settling because fine sediment is constantly settling out of suspension in the water column. With enough time, most irregularities of the deep ocean are covered by these deposits.

2. Discuss the origin of the various volcanic peaks of the abyssal plains: seamounts, tablemounts, and abyssal hills.

Seamounts are cone-shaped volcanic peaks that stand more than one kilometer above the sea floor. Tablemounts are seamounts that have had their tops flattened by wave energy. Most are now submerged beneath 1800 to 3000 meters (5900 to 9800 feet) of ocean water. Abyssal hills (seaknolls) are small, gently rounded volcanic hills that stand less than one kilometer above the ocean floor.

3. What is the difference between a submarine canyon and an ocean trench?

A submarine canyon is a deep gouge that exists on continental slopes/continental shelves and is thought to have been created by turbidity currents. An ocean trench is a much deeper and larger feature that is the physiographic representation of a subduction zone—where one tectonic plate plunges beneath another.

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3.4 What Features Exist Along the Mid-Ocean Ridge?

1. Describe characteristics and features of the mid-ocean ridge, including the difference between oceanic ridges and oceanic rises.

The global mid-ocean ridge is a continuous, fractured-looking submarine mountain range that extends through the middle of all the ocean basins for some 65,000 kilometers (40,400 miles). The width of the mid-ocean ridge varies along its length, but averages about 1000 kilometers (620 miles). The mid-ocean ridge is a topographically high feature, extending an average of 2.5 kilometers (1.5 miles) above the surrounding sea floor. The mid-ocean ridge: ● ● ● ● ● ● ●

is entirely volcanic in origin is composed of lavas with a basaltic composition has along its crest a central down-dropped rift valley created by sea floor spreading processes where two plates are diverging has an abundance of earthquake activity in the form of small, shallow quakes has a variety of volcanic features, including seamounts and recent underwater lava flows (pillow lava) is associated with hydrothermal vents where hot water seeps out of the sea floor and unusual life exists has deposits of metal sulfides that contain economic mineral deposits

Segments of the mid-ocean ridge are called oceanic ridges where they are mountainous with steep, irregular slopes and oceanic rises where the slopes are gentler. As explained in Chapter 2, the differences in overall shape between ridges and rises are due to spreading rate differences: Oceanic ridges have slower spreading rates than oceanic rises.

2. List and describe the different types of hydrothermal vents.

Hydrothermal vents are hot springs associated with mid-ocean ridge rift valleys that are caused by seawater seeping along fractures in the ocean crust. The water is heated when it comes in contact with underlying magma, and then rises upward and spews out of the sea floor. There are three types of hydrothermal vents: ● ● ●

Warm-water vents have water temperatures below 30°C (86°F).

White smokers have water that is white in color as a result of dissolved barium sulfate particles and a water temperature between 30°C and 350°C (662°F).

Black smokers have water that is black in color as a result of dissolved dark-colored metal sulfides and a water temperature above 350°C (662°F). Many of these black smokers spew water out of chimney-like structures composed of metal sulfide deposits up to 20 meters (66 feet) high.

3. What kinds of unusual life can be found associated with hydrothermal vents? How do these organisms survive?

Hydrothermal vent communities include large clams, mussels, vestiminiferan tubeworms, and other animals. The vents discharge hydrogen sulfide gas that is oxidized by bacteria and archaeons to provide the starting products to fix organic carbon in the absence of sunlight.

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4. Describe the origin of the three basic types of oceanic islands.

(1) Islands associated with volcanic activity along the mid-ocean ridge (such as Ascension Island along the Mid-Atlantic Ridge) (2) Islands associated with hotspots (such as the Hawaiian Islands in the Pacific Ocean) (3) Islands that are island arcs and associated with convergent plate boundaries (such as the Aleutian Islands in the Pacific Ocean).

Note that all three types are volcanic in origin.

5. Describe the differences between transform faults and fracture zones.

Transform faults are plate boundaries; fracture zones are intraplate. Transform faults have movement in opposite directions and fracture zones have movement in the same direction.

Transform faults are associated with many earthquakes and fracture zones rarely have earthquakes.

Critical Thinking Questions (and Answers) 3.1 Describe how satellite measurements of the ocean surface allow oceanographers to create a map of the sea floor.

Sea floor features directly influence Earth’s gravitational field. Deep areas such as trenches correspond to a lower gravitational attraction, and large undersea objects such as seamounts exert an extra gravitational pull. These differences affect sea level, causing the ocean surface to bulge outward and sink inward, mimicking the relief of the ocean floor. A 2000-meter (6500-foot)-high seamount, for example, exerts a small but measurable gravitational pull on the water around it, creating a bulge 2 meters (7 feet) high on the ocean surface. These irregularities are easily detectable by satellites, which use microwave beams to measure sea level to within 4 centimeters (1.5 inches) accuracy. After corrections are made for waves, tides, currents, and atmospheric effects, the resulting pattern of dips and bulges at the ocean surface can be used to indirectly reveal ocean floor bathymetry.

3.2 Draw and describe differences between passive and active continental margins from memory. Include a real-world example of each type, associated features, and how these features relate to plate tectonics.

Passive margins are found on the East Coast of the Americas and in the Indian Ocean, and turbidity currents travel directly down the continental margin and deposit sediment on the abyssal plains.

Active margins are characterized by a deep-ocean trench, earthquakes, and volcanoes. Examples of active margins are found along the Pacific Ring of Fire.

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3.3 In which ocean basin are most ocean trenches found? Use plate tectonic processes to help explain why.

Most ocean trenches are located in the Pacific Ocean because of the prevalence of convergent plate boundaries (with subduction zones) that ring the Pacific Ocean basin.

3.4 Using a labeled diagram, describe the differences between fracture zones and transform faults. Along which feature are earthquakes more likely to occur?

Transform faults occur between the ridge axis and denote a plate boundary. Fracture zones are found outside of the ridge axis and have a vertical scar with the younger portion at a higher elevation than the older portion of the same plate.

Transform Faults—more likely to have earthquakes

Occur between segments of the mid-ocean ridge Transform plate boundaries

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Movement in opposite directions

Occur beyond segments of the mid-ocean ridge Not plate boundaries Movement in the same direction

Fracture Zones

Active Learning Exercises 3.1. Use the Internet to research how a “fish finder” works on modern sport-fishing boats. How do these techniques compare to the sonar techniques described in this chapter?

A “fish finder” can only look in the region vertically under the boat. Sonar uses a wider scanning beam to search in all directions, including sideways.

3.2. Archeologists have discovered evidence of a submerged prehistoric human settlement including fire rings and pottery shards on a continental shelf that is now 50 kilometers (30 miles) offshore and in water that is 60 meters (200 feet) deep. With another student in class, discuss how this would be possible.

During Earth’s last Ice Age, which ended about 10,000 years ago, much water was locked up in ice, therefore lowering sea level and extending coastlines further out onto the continental shelf. As Earth warmed and this ice melted, sea level rose, flooding regions along coastlines that were formerly inhabited.

3.3. About170 kilometers (105 miles) offshore of Southern California is a famous big wave surf spot known as Cortez Bank. Working with another student in class, find Cortez Bank in Figure 3.11. Discuss whether or not Cortez Bank is part of the Southern California continental shelf.

Yes, this is part of the equivalent continental shelf because the continental slope is further seaward than Cortez Bank. Technically, this would be called a continental borderland because it is along a transform active margin, where the equivalent of a passive margin’s shelf is marked with a high degree of relief.

3.4. Working with another student, discuss how volcanoes on land are different from volcanoes at the mid-ocean ridge.

Mid-ocean ridge volcanoes are part of divergent plate boundaries, where lava is expelled as tectonic plates are pulled apart. Mid-ocean ridges are also marked by fracture zones and can be home to a variety of unusual life-forms. Mid-ocean ridge volcanoes tend to be basaltic and generate pillow basalts, and tend to form as a long line of volcanic activity.

Volcanoes on land are not often basaltic, but rather include lava that has continental rock features. They don’t typically form in long ridges as do the mid-ocean ridge volcanoes and are not home to specialized or unique life-forms.

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Additional Active Learning Exercises 3.1 Use Google Earth to compare the continental margins offshore of Los Angeles, California; Clearwater, Florida; and Tokyo, Japan.

The continental margin just offshore of Los Angeles is a continental borderland. It is dominated by a high degree of relief. There are islands, shallow banks, and deep basins.

The continental margin just offshore of Clearwater is a passive margin. It is characterized by a wide (~280 km), relatively flat continental shelf.

The continental margin just offshore of Tokyo is an active margin. The continental shelf is narrow (~60 km) and the continental slope drops down into the Japan Trench.

3.2 Your friend tells you that some islands are not volcanic in origin. Is your friend correct? Why or why not?

There are three basic types of oceanic islands: (1) islands associated with volcanic activity along the mid-ocean ridge; (2) islands associated with hotspots; and (3) islands that are associated with convergent plate boundaries. All three of these types of islands are volcanic in origin. There is a fourth type of island that exists: islands that are parts of continents.

These islands may be formed from nonvolcanic material; however, they are technically considered a part of a continent and not a true island.

Exploring Data Figure 3.1 1. Notice the strong sound reflection of the deep scattering layer (DSL) at a depth between 350 and 400 meters on the left side of the figure. Explain why a dense concentration of marine organisms would create such a feature on an echo sounding record.

An echo sounder sends a ping from the ship downward into the ocean. It produces an echo when it reflects off of anything denser than seawater, like an organism. Because the DSL is an area with a dense concentration of marine organisms, the echo sounder “sees” it as a solid layer.

2. Using the equation shown in Figure 3.7a, determine the time it takes sound to reach 350 meters depth and return to the surface. Use the average speed of sound in seawater of 1507 meters (4945 feet) per second.

Depth = speed of sound * travel time/ 2 350 m = 1507 m/s * travel time/ 2 0.464 s = travel time 41 .

Figure 3.7 Using the equation shown in Figure 3.7a, determine the time it takes sound to reach the deepest part of the ocean, the Challenger Deep in the Mariana Trench, which is 11,022 meters (36,161 feet) below sea level. Use the average speed of sound in seawater of 1507 meters (4945 feet) per second.

The equation in Figure 3.7a calculates depth based on the time for the sound to travel to the bottom and back: Depth = speed of sound * travel time/ 2 To calculate how long it takes for the sound to travel to the bottom, modify the equation: Depth = speed of sound * travel time 11,022 m = 1507 m/s * travel time 7.31 s = travel time

Figure 3.18 Calculate the average depth, width, and length of Pacific Ocean trenches. How do those values compare to the average dimensions of trenches in the Atlantic and Indian Oceans?

Pacific Ocean Average depth: 8.98 km Average width: 71.67 km Average length: 3341.67 km The average depth of trenches in the Pacific Ocean (8.98 km) is similar to the average depth of trenches in the Atlantic Ocean (8.4 km) and deeper than the depth of the Java Trench in the Indian Ocean (7.5 km).

The average width of trenches in the Pacific Ocean (71.67 km) is narrower than the average width of trenches in the Atlantic Ocean (105 km) and the width of the Java Trench in the Indian Ocean (80 km).

The average length of trenches in the Pacific Ocean (3341.67 km) is longer than the average length of trenches in the Atlantic Ocean (1500 km), but shorter than the length of the Java Trench in the Indian Ocean (4500 km).

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SmartFigure 3A Compare the average land elevation (height above sea level) versus the average ocean depth below sea level). Why are the values so dissimilar?

Oceanic crust is denser than continental crust. The more dense oceanic crust floats lower in the mantel than the less dense continental crust.

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Chapter 4 Marine Sediments Overview This chapter focuses on how deep-sea sediments are collected, the types of marine sediment, and what the analysis of deep-sea sediments reveals about Earth’s history. A classification scheme for marine sediments is presented. There are four main types of marine sediments: lithogenous, biogenous, hydrogenous, and cosmogenous. The origin, composition, and distribution of each of the four types of sediments are discussed, including a section on mixtures. A summary of neritic (continental margin) and pelagic (deep-ocean) sediment is presented, followed by information about ocean sediments as a resource.

Essential Concepts 4.1 Demonstrate an understanding of how marine sediments are collected and what historical events they reveal.

4.2 Describe the characteristics of lithogenous sediment.

4.3 Describe the characteristics of biogenous sediment.

4.4 Describe the characteristics of hydrogenous sediment.

4.5 Describe the characteristics of cosmogenous sediment.

4.6 Specify how the distribution of pelagic and neritic deposits is determined by proximity to sediment sources and agents of transport.

4.7 Identify the various resources that marine sediments provide.

Chapter Outline 4.1 How Are Marine Sediments Collected and What Historical Events Do They Reveal?

4.1.1 Collecting Marine Sediments 4.1.2 Environmental Conditions Revealed by Marine Sediments 4.1.3 Paleoceanography 4.2 What Are the Characteristics of Lithogenous Sediment?

4.2.1 Origin of Lithogenous Sediment 4.2.2 Composition of Lithogenous Sediment 4.2.3 Texture of Lithogenous Sediment 4.2.4 Distribution of Lithogenous Sediment 4.2.4.1 Neritic Deposits 4.2.4.1.1 Beach Deposits 4.2.4.1.2 Continental Shelf Deposits 4.2.4.1.3 Turbidite Deposits 4.2.4.1.4 Glacial Deposits 4.2.4.2 Pelagic Deposits 4.2.4.2.1 Abyssal Clay 4.3 What Are the Characteristics of Biogenous Sediment?

4.3.1 Origin of Biogenous Sediment 44 .

4.3.2 Composition of Biogenous Sediment 4.3.2.1 Silica

DIVING DEEPER 4.1 Oceans and People Diatoms: The Most Important Things You Have (Probably) Never Heard Of 4.3.2.2 Calcium Carbonate Squidtoons: How does the coccolithophore remove carbon from the water?

4.3.3 Distribution of Biogenous Sediment 4.3.3.1 Neritic Deposits 4.3.3.1.1 Carbonate Deposits 4.3.3.1.2 Stromatolites 4.3.3.2 Pelagic Deposits 4.3.3.2.1 Siliceous Ooze Web Animation: The Accumulation of Siliceous Ooze 4.3.3.2.2 Calcareous Ooze and the CCD SmartFigure 4.13: Accumulation of siliceous ooze.

SmartFigure 4.14 Characteristics of water above and below the calcite compensation depth (CCD).

SmartFigure 4.15: Sea floor spreading and sediment accumulation.

Web Animation: How Calcareous Ooze Can Be Found Beneath the CCD. SmartTable 4.3: Comparison of environments interpreted from deposits of siliceous and calcareous ooze in surface sediments.

4.4 What Are the Characteristics of Hydrogenous Sediment?

4.4.1 Origin of Hydrogenous Sediment 4.4.2 Composition and Distribution of Hydrogenous Sediment 4.4.2.1 Metal Sulfides 4.4.2.2 Manganese Nodules 4.4.2.3 Phosphates 4.4.2.4 Carbonates 4.4.2.5 Evaporites 4.5 What Are the Characteristics of Cosmogenous Sediment?

4.5.1 Origin, Composition, and Distribution of Cosmogenous Sediment 4.6 How Are Pelagic and Neritic Deposits Distributed?

4.6.1 Mixtures of Marine Sediment SmartFigure 4.20: Distribution of sediment across a passive continental margin.

SmartFigure 4.21: Distribution of neritic (nearshore) and pelagic (open ocean) sediments.

4.6.2 Neritic Deposits 4.6.3 Pelagic Deposits 4.6.4 4.6.5

Do Sea Floor Sediments Represent Surface Conditions?

Worldwide Thickness of Marine Sediments 4.7 What Resources Do Marine Sediments Provide?

4.7.1 Energy Resources 4.7.1.1 Petroleum 45 .

4.7.1.2 Gas Hydrates 4.7.2 Other Resources 4.7.2.1 Sand and Gravel 4.7.2.2 Evaporative Salts 4.7.2.3 Phosphorite (Phosphate Minerals) 4.7.2.4 Manganese Nodules and Crusts 4.7.2.5 Rare-Earth Elements

Essential Concepts Review

Learning Outcomes The instructional objectives are performance-based and detail specific learning outcomes for Chapter 4.

The test items contained in the Test Bank are keyed to the learning objectives and the Chapter in Review at the end of the chapter. The order of the objectives mirrors the content presentation in Chapter 4.

Upon completion of this chapter, the student should be able to: 1. Define lithogenous sediment and discuss the origin of this type of sediment.

2. Discuss the chemical (mineral) composition of lithogenous sediments.

3. Describe the Wentworth scale of grain size for sediments, including the sizes of: a. boulders b. cobbles c. pebbles d. granules e. sand f. siltn g. clay 4. Explain the impact of sediment sorting and maturity on sediment texture.

5. Differentiate between neritic and pelagic sediment deposits.

6. Distinguish between the various types of neritic sediment deposits, including: a. beach deposits b. continental shelf deposits c. turbidite deposits d. glacial deposits 7. Describe the mineral composition and texture of pelagic lithogenous sediments.

8. Define biogenous sediment and discuss the origin of this type of sediment.

9. Explain the difference between macroscopic and microscopic biogenous sediment and give an example of each.

10. Discuss the chemical (mineral) composition of biogenous sediments and list the organisms from which these sediments are derived.

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11. Define ooze. Distinguish between calcareous and siliceous oozes, and list the organisms responsible for the formation of the different oozes.

12. Discuss the distribution of biogenous sediments in neritic and pelagic environments, including: a. carbonate deposits including limestone and stromatolites b. siliceous ooze c. calcareous ooze 13. Outline the relationship between the calcite compensation depth (CCD) and the formation of calcareous oozes.

14. Define hydrogenous sediment and discuss the origin of this type of sediment.

15. Discuss the chemical (mineral) composition and the distribution of hydrogenous sediments, including: a. manganese nodules b. phosphates c. carbonates d. metal sulfides e. evaporites 16. Define cosmogenous sediment and discuss the origin of this type of sediment.

17. Describe the chemical (mineral) composition and distribution of cosmogenous sediments.

18. Explain how sea floor sediments mirror surface ocean conditions.

19. Summarize the relationship between sea floor sediments and Earth’s history.

20. List the commercially important resources provided by ocean sediments.

Teaching Strategies This is often one of the overlooked chapters in the text as there are not many people interested in “stinky mud.” However, as Dr. Wolfgang Berger so eloquently put it, “From the sediments the history of the ocean emerged with all its wonders….” (Ocean: Reflections on a Century of Exploration, 2009). This chapter shows how the secrets of the wonders are revealed. Instructors are encouraged to familiarize themselves with this chapter and to utilize the resources for educators found on the Ocean Drilling Program websites (listed below), as this chapter is a foundation subject for nearly everything oceanographic. The use of films and online resources can significantly aid students in grasping the many diverse concepts contained in this chapter, which are built upon those from Chapter 3. With these foundations fully grasped, the rest of oceanography is much easier to understand and much more interesting.

Teacher’s Resources Films ▪ ▪

A Planet in Motion (Ocean Drilling Program), 22 minutes Deep Sea Drilling Project (Association Sterling Films, 1974), 28 minutes, 47 .

▪ ▪ ▪ ▪

The Ring of Truth: Clues (Phillip Morrison/PBS), 60 minutes (examines evidence for the drying of the Mediterranean Sea) Windows to the Past: Discovering the Earth’s Future (Ocean Drilling Program), 13 minutes Stromatolites (NASA), 7 minutes, http://spacescience.arc.nasa.gov/microbes/movie/large-qt.html Tour the Chikyu—An Ocean Drilling Vessel (Smithsonian Institution), 2 minutes, 17 seconds, http://ocean.si.edu/ocean-videos/tour-chikyu

Websites ● ● ● ●

http://www-odp.tamu.edu—Ocean Drilling Program http://iodp.org—International Ocean Discovery Program http://sharkbay.org.au/nature-of-shark-bay-stromatolites.aspx—Stromatolites of Shark Bay, Australia http://geology.com/usgs/manganese/—What is manganese?

Concept Check (Questions and Answers) 4.1 How Are Marine Sediments Collected and What Historical Events Do They Reveal?

1. Using Table 4.1, list and describe the characteristics of the four main types of marine sediment.

Lithogenous: composed of fragments of preexisting rock material.

Biogenous: composed of the hard remains of dead marine organisms.

Hydrogenous: composed of material that is dissolved in water and precipitates to form deposits.

Cosmogenous: composed of material of extra-terrestrial origin.

2. Describe the process of how a drill ship like the JOIDES Resolution obtains core samples from the deep-ocean floor.

The drill ship JOIDES Resolution uses the rotary drilling method while holding its position at the surface constant with a dynamic positioning system to obtain deep-sea cores. JOIDES Resolution contains a tall metal drilling rig, which is used to lower sections of drill pipe in the middle of the ship. The pipe is in individual sections of 9.5 meters (31 feet), but can be screwed together to make a single string of pipe up to 9150 meters (30,000 feet). The pipe string has on its end a rotating drill bit as it is pressed against the bottom rock, allowing the ship to drill deeper and deeper into the ocean floor. Like a twirling soda straw drilling into a layer cake, the drilling operation crushes rock around the outside and retains a cylinder of rock (core sample) on the inside of the pipe. The drill crew lowers the core-recovering equipment through the string of drill pipe. Once the cores are retrieved from inside the pipe, they are collected and processed by scientists.

3. What types of past environmental conditions can be inferred by studying the cores of sediment?

By examining the sediment cores retrieved from ocean drilling and by interpreting them, oceanographers can ascertain environmental conditions and events such as: a. the timing of major extinctions b. global climate change 48 .

c. plate movements d. historical information about Earth’s geology and biology

4.2 What Are the Characteristics of Lithogenous Sediment?

1. Describe the origin, composition, texture, and distribution of lithogenous sediment.

Lithogenous sediment begins as rock material on continents or islands. Agents of weathering break the rock material into smaller pieces. Once the parent rock material is broken into fragments, smaller rocks can be easily eroded (picked up and transported) because the smaller pieces require less energy to move. The eroded material is the basic component from which all lithogenous sediment is composed.

Eroded material from the continents is carried into the oceans by a variety of transporting media including streams, wind, glaciers, and gravity. The sediment can be deposited in bays or lagoons near the ocean; it can be transported further by waves along the beach to produce beach deposits along the shoreline; or, it may be spread along the continental margin by currents. It can also be carried beyond the continental margin to the deep-ocean basin.

2. Why is most lithogenous sediment composed of quartz grains? What is the chemical composition of quartz?

Most lithogenous sediment is composed of quartz grains because quartz is one of the most abundant and chemically stable minerals in Earth’s crust (refer to Figure 4.5). Quartz is resistant to abrasion and, as a result, quartz can be transported large distances and deposited far from the source area. It should be no surprise that the majority of lithogenous sediment deposits are composed of quartz. Quartz is composed of silicon and oxygen (SiO2).

3. What is the difference between neritic and pelagic deposits? Give examples of lithogenous sediment found in each.

Lithogenous deposits are derived from rock or the lithosphere. Those sediments found nearshore, or neritic, vary in size and texture and are the main neritic deposits. Pelagic lithogenous sediments are usually very fine in size as they are small enough to travel the farthest from the source. One exception is the lithogenous sediments that are rafted by glaciers far from the source. These sediments can vary in size and are usually angular.

4.3 What Are the Characteristics of Biogenous Sediment?

1. Describe the origin, composition, and distribution of biogenous sediment.

Biogenous sediments are derived from biology. While most biology is found nearshore, most of the nearshore biogenous sediments are watered down with the vast amount of neritic sediments and are hard to find in abundance nearshore. However, very little lithogenous sediments travel out to the deep ocean, leaving the accumulation of biogenous sediments more available on the pelagic sea floor environment. However, the CCD plays an important role in the deposition of the calcareous sediments found in the pelagic environment as calcium carbonate sediments dissolve below the CCD, therefore calcium carbonate sediments found in the pelagic environment are found above the CCD in areas where the surface waters are warmer, while the siliceous sediments can be found anywhere there is a cold water environment at the surface.

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2. List the two major chemical compounds of which most biogenous sediment is composed and examples of the organisms that produce them. Sketch these organisms.

▪ ▪

Calcium carbonate (CaCO3): Foraminiferans and coccolithophorids; also pteropods and ostracods. Images of foraminiferans and coccolithophorids should resemble Figure 4.10 (a and c).

Silica (SiO2): Diatoms and radiolarians; also silicoflagellates. Images of diatoms and radiolarians should be similar to Figure 4.9 (a–c).

3. Technically, what must a biogenous ooze contain to be classified as ooze? What other component do all oozes contain?

It must contain at least 30% biogenous test material by weight. The other part is typically finegrained lithogenous clay that is deposited with biogenous tests in the deep ocean. Ooze consists of very fine-grained, mushy material.

4. If siliceous ooze is slowly but constantly dissolving in seawater, how can deposits of siliceous ooze accumulate on the ocean floor?

One way that siliceous oozes accumulate on the ocean floor is for the rate of deposition of siliceous tests to exceed the rate of dissolution for the tests. In this case siliceous tests will accumulate faster than they can be dissolved.

5. Explain the stages of progression that result in calcareous ooze existing below the CCD. Initially, calcareous ooze is deposited above the CCD (and there it will not dissolve) on a topographically high feature such as the mid-ocean ridge. Then, the calcareous ooze is covered by a deposit that is unaffected by the CCD, such as an abyssal clay or siliceous ooze, so that it is isolated from the environment. Finally, over millions of years, the ocean floor that was once at shallower depths is moved away from the mid-ocean ridge by the process of sea floor spreading, carrying with it the calcareous ooze covered by another sediment.

4.4 What Are the Characteristics of Hydrogenous Sediment?

1. Describe the origin, composition, and distribution of hydrogenous sediment.

Hydrogenous sediments are the sediments derived from water. These sediments either precipitate out of a solution or are formed when solids are left behind after the water evaporates. Evaporates occur when the water evaporates, leaving the dissolved salts behind. Precipitates occur when the salts or minerals precipitate directly from the seawater, such as at mid-ocean ridges or near the manganese nodule fields found in the sea floor.

2. Describe manganese nodules, including what is currently known about how they form.

Manganese nodules are rounded, hard lumps of manganese, iron, and other metals up to 30 centimeters (12 inches) long. When cut in half, the nodules often reveal that they have been formed by precipitating layers around a central nucleation object.

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The origin of manganese nodules continues to elude scientists. It is widely believed that the concentric layers of a manganese nodule form as a hydrogenous deposit around a central nucleation object. Scientists are still working on answering questions such as why manganese nodules have such high concentrations of manganese, and why they are not buried by ocean floor sediment. Recent research suggests that the formation of manganese nodules may be aided by asyet-unidentified marine organisms.

4.5 What Are the Characteristics of Cosmogenous Sediment?

1. Describe the origin, composition, and distribution of cosmogenous sediment.

Cosmogenous sediments are mostly made of space dust and partly made of meteorites and some asteroids. Cosmogenous sediments come from the cosmos. They are made up of small fragments of anything that was once in space and came to Earth, such as the dust from a comet’s tail or a meteor from the asteroid belt.

2. Describe the most common types of cosmogenous sediment and give the probable source of these particles.

Cosmogenous sediment consists of two main types: • Microscopic spherules that are microscopic globular masses composed of silicate rock material (called tektites) or composed mostly of iron and nickel. Although they were once thought to be the product of meteors, it is now believed they are produced by collisions between asteroids, which produce microscopic space dust particles that drift harmlessly through Earth’s atmosphere.

• Macroscopic meteor debris that forms near an impact site when meteors collide with Earth at great speeds.

4.6 How Are Pelagic and Neritic Deposits Distributed?

1. Why is it so rare to find a pure marine sediment type? Give some examples of mixtures of sediment.

The ocean is a messy place. Lithogenous and biogenous sediment rarely occur as absolutely pure deposits that do not contain other types of sediment. As a result, most marine sediments occur as mixtures.

2. Why is lithogenous sediment the most common neritic deposit? Why are biogenous oozes the most common pelagic deposits?

Lithogenous sediment is by far the most common type of neritic deposit because lithogenous material is derived in great quantity from the rocks on the nearby landmasses. The material is deposited rapidly near continental margins. It is such deposits that constitute the wedge of sediment underlying the continental shelf, slope, and rise.

One of the main reasons that biogenous oozes are the most common pelagic (deep-ocean) deposits is because there is so little lithogenous sediment deposited at great distance from the continents. Even though pelagic environments contain identifiable and even significant percentages of lithogenous and hydrogenous material, the deposition rates for sediments are low in the ocean basins that biogenous material dominates.

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3. How do fecal pellets help explain why the particles found in the ocean surface waters are closely reflected in the particle composition of the sediment directly beneath? Why is this unexpected?

The small particle common to pelagic sediment would require from 10 to 50 years to sink to the ocean floor, so the sediment on the ocean floor would not be expected to be similar to the makeup of the particle concentrations in the surface water immediately above. The slightest current would be expected to carry them from 3000 to 15,000 kilometers (1860 to 9320 miles) laterally before they could reach the bottom. The fecal pellets incorporate small particles into larger packages that can sink to the ocean floor in 10 to 15 days, allowing the composition of bottom sediment to resemble closely the composition of the particle content of the surface water immediately above.

4.7 What Resources Do Marine Sediments Provide?

1. Discuss the present importance and the future prospects for the production of petroleum; sand and gravel; phosphorite; and manganese nodules and crusts.

Petroleum production from marine deposits represents more than 95% of the value of nonliving resources exploited from oceans. Offshore petroleum will provide an increasing percentage of the oil and gas that provides most of our energy requirements in future years. Beyond the year 2020, the availability of conventionally produced petroleum will probably not be sufficient to meet the demand, and more exotic forms of petroleum recovery will be exploited.

Sand and gravel recovered from offshore is the next most valuable marine mineral resource after petroleum. It is used for beach fill, land fill, and concrete aggregate. Also, diamonds, tin, platinum, and gold have been recovered by offshore dredging. Nearshore mining operations may damage present beaches. If they are conducted too close to the beaches, they may cause beach sediment to move offshore.

Phosphorite is used as fertilizer but has not been mined commercially from the marine environment and probably will not be until well in the future.

Polymetallic crusts and nodules have created a lot of interest in the past three decades because of the abundance of manganese and other metals contained within them, but they will not be likely mined until later in the 21st century.

2.

What are gas hydrates, where are they found, and why are they important?

Gas hydrates (also known as clathrates) are a combination of two substances: water and natural gas, usually methane. They are found in deep-ocean sediments where pressures are high and temperatures are low. Generally, they are found at depths below 525 meters (1720 feet) and concentrated along continental margins, where high-productivity waters enrich ocean floor sediments below with organic matter. Here, natural gas is trapped inside a lattice-like cage of water molecules.

Gas hydrates have generated much scientific interest because their methane content may be potentially the world’s largest useable energy source today. Also, there is interest in knowing what role they play in sea floor instability and as contributors to global warming. Additionally, methane seeps support a rich community of organisms, many of which are species new to science.

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Critical Thinking Questions (and Answers) 4.1 A sediment core is retrieved from the middle of the North Pacific Ocean, about 1000 kilometers (620 miles) south of the Aleutian Islands (Alaska), and at a water depth of 5000 meters (16,400 feet). The core contains coral reef fossils, which are only found in shallow, tropical waters. Develop a hypothesis that could explain this occurrence. Also, develop a test for your hypothesis.

Tectonic plate movement over time could have relocated these former reefs to a colder, nontropical location. Subsidence of the place can account for the depth, as well as sea-level rise with warmer climates. Looking at patterns of islands formed by hotspots can give an indication of both the direction and rate of plate movement.

4.2 As part of a research operation you are reviewing a video of the sea floor near the coast of Greenland and see a large boulder lying on top of the sediment. Suggest a way that the boulder could have arrived there.

This boulder was most likely transported by a glacier through the process of ice rafting. The boulder was trapped in glacial ice that broke off and formed an iceberg. When the iceberg melted, the boulder was released.

4.3 How do oozes differ from abyssal clay? Discuss how productivity, destruction, and

dilution combine to determine whether an ooze or abyssal clay will form on the deepocean floor.

Oozes contain at least 30% biogenous particles (by weight); in contrast to abyssal clay that contains less than 30% biogenous material. The bulk of the remaining percentage (up to 70%) of abyssal clay deposits is comprised of lithogenous clays.

Whether or not an ooze forms depends on the relative rates of biogenous and lithogenous particle deposition in an area. The deposition rate of biogenous particles is a function of the rate at which they are produced (productivity) versus the dissolution rate (destruction) in ocean water. The seawater dissolution rate for silica is slow and steady at all ocean depths, but increases significantly with increasing water depth for calcium carbonate. Finally, if the deposition rate for lithogenous particles is greater than the deposition rate for biogenous particles, the lithogenous particles will dilute the concentration of biogenous particles and biogenous ooze will never form as a result of this dilution.

4.4 Construct a table that shows the various types of hydrogenous sediment and list both

their origin and how they are used by humans.

Silica

Cold

Diatoms (algae);

surfa

radiolarians

ce

(protozoans)

Siliceous (SiO2 ooze

⋅nH2

High-latitude regions; sea floor below CCD; upwelling areas where cold, deep water

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rises to the surface, especially

O)

water

that caused by surface current divergence near the equator

Manganese nodules

Abyssal plain

(manganese, iron, copper, nickel, cobalt) Hydr ogen ous

Phosphorite

Precipitation of dissolved

Continental shelf

(phosphorous)

materials directly from

Oolites (CaCO3)

seawater due to chemical

Shallow shelf in low-latitude

reactions

regions

Metal sulfides (iron,

Hydrothermal vents at mid-

nickel, copper, zinc,

ocean ridges

silver)

4.5 Using Mastering Oceanography Web Diving Deeper 4.2, describe what happened on

Earth at the Cretaceous–Tertiary (K–T) boundary. What evidence was used to confirm the event, and what environmental effects did it cause?

The K–T event is a major extinction on Earth that occurred about 65 million years ago between the Cretaceous and Tertiary Periods of geologic time. Evidence indicates that a 16-kilometer (10-mile)wide meteor collided with the Earth off the Yucatan coast in the Gulf of Mexico during this time, leading to the extinction of dinosaurs and two-thirds of all plant and animal species on Earth (including marine species). The meteorite caused a gigantic splash wave and left a 190-kilometer (120-mile)-wide and 30-kilometer (20-mile)-deep impact crater. It also ripped up large fragments from the sea floor and deposited iridium and shocked quartz around the globe, which have been recovered in core samples from the deep ocean. The impact could have kicked up so much dust that it blocked sunlight, chilled Earth’s surface, and brought about the extinction of dinosaurs and other species. Acid rains and global fires may have added to the environmental disaster. Additionally, such a large impact on Earth could easily have caused major volcanic activity to occur.

4.6 Using Figure 4.22, what is the dominant sediment type in the Pacific, Atlantic, and

Indian Oceans? Explain why the dominant sediment type differs from ocean to ocean.

Dominant sediment type Pacific - Abyssal clay Atlantic - Calcareous ooze Indian - Calcareous ooze Calcareous ooze is less common in the Pacific Ocean because much of the ocean basin is below the CCD.

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4.7 A company wants to mine sea floor minerals. What technological issues would there be

for developing a mining operation on the sea floor? Also, evaluate the environmental factors that should be considered before mining materials on the sea floor.

Technologically speaking, there are many issues with regard to mining at depth of mineral on the sea floor, including locating the resources and dealing with the extreme pressures. The costs of these technologies are typically greater than any profits that might be realized.

Environmentally speaking, there are issues regarding the extreme time required for these resources to be renewed, if they could be at all.

Active Learning Exercises 4.1 It has been said that in the early days of oceanography, collecting marine sediments using a dredge was akin to collecting land samples from a hot air balloon using a bucket—at a height above the ground of several kilometers (a few miles) and at night.

With another student in class, evaluate the effectiveness of this type of sample collection (e.g., is it representative of the environment being sampled?).

Collecting samples using a dredge only collects samples on the surface of the bottom of the ocean and mixes up these sediments and does not preserve stratigraphy or the layers beneath the surface.

Using a piston core preserves stratigraphy and allows scientists to go back in time by collecting deeper sediments and getting a more accurate snapshot in time.

4.2 With another student in class, discuss how a deposit with a coarse grain size indicates whether it was deposited by a high- or low-energy transporting mechanism.

Give several examples of various transporting mechanisms that would produce such a deposit.

A coarse grain size indicates a high-energy transporting mechanism. Higher-energy environments have deposition of larger, coarser particles. Rivers, wind, gravity-based depositions, and locations with wave activity are all transporting mechanisms that are associated with larger particle sizes.

4.3 Working with another student in class, sketch and label two examples of silicasecreting organisms that produce biogenous ooze and two examples of calcareoussecreting organisms that produce biogenous ooze.

Examples could look like those in Figure 4.9 for silica-secreting organisms, and those in Figure 4.10 for those that have calcareous tests.

4.4 Working with another student in class, design a hypothesis and an associated test to determine if manganese nodules form steadily over time or if they form episodically (in spurts).

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Radiometric dating of the centers and exteriors of many manganese nodules would give an idea of the time lapse between the generation of the initial nodule and how long it took to deposit subsequent layers, since manganese nodules grow in a layered fashion.

4.5 Working with another student in class, discuss why micrometeorites don’t form extensive sea floor deposits, even though they are constantly raining down through Earth’s atmosphere.

Many micrometeorites burn up upon entry into Earth’s atmosphere. Those that do not and land in Earth’s oceans tend to dissolve before they are able to become sea floor deposits.

Some micrometeorites do become sea floor deposits, but they are uncommon.

4.6 Working with another student in class, compare neritic and pelagic deposits (e.g., describe their location, composition, thickness, and distribution on the sea floor).

Neritic deposits are found in nearshore environments, close to land. They tend to be lithogenous in origin, coarse grained, constitute about 25% of the ocean floor, and are relatively thick in depth.

Pelagic deposits occur in the deep ocean, constitute about 75% of the ocean floor, are predominantly biogenous oozes and fine lithogenous clay, and are relatively thin deposits.

4.7 Working with another student in class, research the Internet to make a list of the everyday products that are made from these sea floor deposits: (1) the components found in manganese nodules and crusts and (2) the elements that comprise the rareearth elements.

Manganese nodules and crusts are used in the production of steel and can be used when making copper or aluminum alloys. Manganese nodules and crusts are mined by those who make battery cathodes, electronics, fertilizers, and animal feed. Manganese can be used to make water treatment chemicals, colorants for automobile undercoating, bricks, and glass.

Manganese violet is a color found in plastics, ceramic glazes, and cosmetic products.

Additional Active Learning Exercises 4.1 Imagine you and a partner are working on a paleoceanography investigation that is collecting ocean sediment cores to learn more about ancient climates. Where in the global ocean would you recommend the cores be collected from?

Answers will vary. However, since the ocean floor accumulates sediment as it moves away from the mid-ocean ridge, points near continental margins will have older sediment buried deep beneath the sea floor. These areas would provide information about the oldest climates.

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4.2 Imagine that you are starting a marine mining and drilling company. Create a job advertisement to recruit employees (your fellow classmates). As you are creating your advertisement, consider the following: What marine resource would you target in your operation? In what part of the world ocean would you find this resource? Is this resource easy to find and access? Would this operation be cost effective? Will your employees make a lot of money? How would you harvest the resource?

Answers vary. Refer to section 4.7 for more information about the resources.

Exploring Data Smart Figure 4.13 What would cause siliceous ooze to accumulate in one area of the sea floor but not in another? Assume the water depth is the same in both places.

The ocean is undersaturated with silica, which means that any solid particles made of silica tend to dissolve in seawater. However, in areas with high productivity of silica-secreting organisms, the tests will accumulate on the ocean floor faster than they can be dissolved.

Smart Figure 4.14 Assume a seamount in water 8 kilometers (5 miles) deep rises to within 3.5 kilometers (2.2 miles) of the ocean՚s surface. To what water depth will calcite accumulate on the seamount's flanks?

Calcite will accumulate on the seamount’s flanks from the top of the seamount to the calcite compensation depth (CCD). On average, the CCD is 4.5 km below sea level.

SmartFigure 4.15 Suggest a reason why the ocean surface water on one side of the mid-ocean ridge is more productive than surface water on the other side. (Hint: The process of upwelling occurs near continental margins.)

In areas of upwelling, cool, nutrient-rich water is transported to the surface, stimulating biological productivity.

Table 4.4 Using the depositional rates shown in Table 4.4, how long would it take to make a deposit 1 meter (3.3 feet) thick of biogenous ooze? A deposit 1 meter (3.3 feet) thick of abyssal clay?

Biogeneous ooze accumulates at a rate of 1 cm/1000 years.

1 m = 100 cm To accumulate 100 cm, it would take 1000 years * 100 = 100,000 years.

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Chapter 5 Water and Seawater Overview This chapter examines many aspects of water on Earth. It opens by looking at the chemical properties of water and how these properties affect the physical properties of water. A discussion of water’s thermal properties follows, in addition to information about the factors affecting the density of water. The focus of the chapter is the properties of seawater. Topics include various aspects of seawater salinity such as salinity variations, how dissolved components are added and/or removed from seawater, acidity and alkalinity of seawater, processes affecting salinity variation, and how salinity affects seawater density. In summary, the properties of pure water are contrasted with seawater. The chapter concludes with a discussion of desalination techniques.

Essential Concepts 5.1 Specify water’s unique chemical properties.

5.2 Discuss water’s important physical properties.

5.3 Demonstrate an understanding of what salinity is and how salinity is measured.

5.4 Explain why seawater salinity varies.

5.5 Specify how seawater salinity varies at the surface and with depth.

5.6 Specify how seawater density varies with depth.

5.7 Discuss the acid/base properties of seawater.

5.8 Describe factors that control the distribution of carbon and oxygen in the ocean.

Chapter Outline 5.1 Why Does Water Have Such Unusual Chemical Properties?

5.1.1 Atomic Structure 5.1.2 The Water Molecule 5.1.2.1 Geometry 5.1.2.2 Polarity 5.1.2.3 Interconnections of Molecules 5.1.2.4 Water: The Universal Solvent Web Animation: How Salt Dissolves in Water 5.2 What Important Physical Properties Does Water Possess?

5.2.1 Water’s Thermal Properties 5.2.1.1 Heat, Temperature, and Changes of State 5.2.1.1.1 Heat 5.2.1.1.2 Temperature 5.2.1.2 Water’s Freezing and Boiling Points Web Animation: Phase Changes of Water 5.2.1.3 Water’s Heat Capacity and Specific Heat 5.2.1.4 Water’s Latent Heats 58 .

5.2.1.4.1

Latent Heat of Melting SmartFigure 5.8: Latent heats and changes of state of water 5.2.1.4.2 Latent Heat of Vaporization SmartFigure 5.9: Hydrogen bonds in H2O and the three states of matter 5.2.1.4.3 Latent Heat of Evaporation 5.2.1.4.4 Latent Heat of Condensation 5.2.1.4.5 Latent Heat of Freezing 5.2.1.5 Global Thermostatic Effects 5.2.2 Water Density as a Result of Thermal Expansion and Contraction SmartFigure 5.12: Water density as a function of temperature and the formation of ice Web Animation: The Formation of Ice 5.3 Why Is Seawater Salty?

5.3.1 Salinity 5.3.2 Determining Salinity 5.3.3 Comparing Pure Water and Seawater SmartTable 5.2: Comparison of selected properties of pure water and seawater Diving Deeper 5.1 Oceans and People Forever Thirsty On A Water World 5.4 Why Does Seawater Salinity Vary?

5.4.1 Salinity Variations 5.4.2 Processes Affecting Seawater Salinity 5.4.2.1 Processes That Decrease Seawater Salinity SmartTable 5.3: Processes that affect seawater salinity 5.4.2.2 Processes That Increase Seawater Salinity 5.4.2.3 The Hydrologic Cycle 5.4.3 Dissolved Components Added to and Removed from Seawater Web Animation: Earth’s Water and the Hydrologic Cycle 5.5 How Does Seawater Salinity Vary at the Surface and with Depth?

5.5.1 Surface Salinity Variation 5.5.2 Salinity Variation with Depth 5.5.3 Halocline SmartFigure 5.23: Salinity variation with depth 5.6 How Does Seawater Density Vary with Depth?

5.6.1 Factors Affecting Seawater Density 5.6.2 Temperature and Density Variation with Depth SmartFigure 5.24: Comparing typical vertical profile curves for temperature and density in the low and high latitudes 5.6.3 Thermocline and Pycnocline 5.7 Is the Ocean Acidic or Basic?

5.7.1 The pH Scale SmartFigure 5.25: The pH scale, including pH values of common substances 5.7.2 The Carbonate Buffering System Web Animation: The Carbonate Buffering System SmartFigure 5.27 The carbonate buffering system.

5.8 What Factors Control the Distribution of Carbon and Oxygen in the Ocean?

Essential Concepts Review

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Learning Outcomes The instructional objectives are performance-based and detail specific learning outcomes for Chapter 5.

The test items contained in the Test Bank are keyed to the learning objectives and the Chapter in Review at the end of the chapter. The order of the objectives mirrors the content presentation in Chapter 5.

Upon completion of this chapter, the student should be able to: 1. Differentiate between an atom and a molecule.

2. Describe the structure of an atom, including the arrangement, relative size, and charge of the subatomic particles: proton, neutron, and electron.

3. Define ion and give an example.

4. Discuss the formation of covalent bonds between atoms.

5. Explain how the geometry of the water molecule contributes to its polarity.

6. Describe the formation of hydrogen bonds and discuss how hydrogen bonding between water molecules affects the physical and chemical properties of water.

7. List the reasons why water is considered a universal solvent.

8. Outline how hydrogen bonding affects the thermal properties of water.

9. Distinguish between heat and temperature and give the units of measurement for each.

10. Define: a. melting point b. freezing point c. boiling point d. condensation point 11. Compare and contrast heat capacity and latent heat.

12. Discuss how the physical properties of water affect global climate, including marine and continental effects.

13. Explain how the geometry of the water molecule affects the density of water as it changes states of matter.

14. Define salinity and discuss its origin and concentration in seawater.

15. Restate the principle of constant proportions.

16. Name the instrument used to accurately measure dissolved salts in seawater.

17. Compare and contrast pure water and seawater.

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18. Outline common methods for desalination and discuss their commercial viability.

19. Discuss the factors that affect the salinity of coastal and surface ocean waters.

20. List the processes that decrease seawater salinity.

21. List the processes that increase seawater salinity.

22. Draw and explain the hydrologic cycle.

23. Define residence time and discuss the implications of residence time for substances dissolved in seawater.

24. Outline how salinity varies with depth in the ocean.

25. Outline how density varies with ocean depth.

26. Differentiate between a halocline, a pycnocline, and a thermocline and discuss the location of each in the ocean.

27. Distinguish between an acid and an alkaline (base) and describe how the relative concentrations of ions are measured.

28. Discuss the forms of dissolved carbon dioxide that exist in the ocean and the relationship between water pH and the form of dissolved carbon dioxide that is present.

29. Discuss the solubility and distribution of oxygen in the ocean.

Teaching Strategies This chapter presents an overview of water. Important aspects of the chemical and physical properties are discussed. Many students will find that the background information on atomic structures is a review. Reviewing atomic structure is essential to understanding the basis for water’s unusual geometry, the polarity resulting from geometric spacing of oxygen and hydrogen atoms, and the ability of water to serve as a universal solvent. Usually students should read the chapters before coming to class. In this case it may be helpful to do a quick basic explanation of the contents in this chapter before the students attempt to read and understand it. Assessing whether the majority of the class has had any chemistry can help guide the amount of time needed to be spent on basic molecular structure. Since water is something with which everyone is familiar, capitalize on what people already know about water when introducing more complicated scientific ideas surrounding water.

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Teacher’s Resources Films ▪ ▪ ▪ ▪ ▪

Chemical Bond and Atomic Structure (University of Illinois), 16 minutes Chemical Changes All About Us (Coronet), 14 minutes Physics and Chemistry of Water (BFA Educational Media), 21 minutes The World of Chemistry: Water (Program #12) (The Annenberg/CPB Collection), 28 minutes, http://learner.org/resources/series61.html Taking the Ocean’s Temperature (Smithsonian Institution), 2.5 minutes

Websites ● www.nbclearn.com/portal/site/learn/freeresources/chemistry-now/chemistry-of-water— Chemistry of Water (NBC Learn), includes 5-minute video and illustration of the water cycle ● www.aoml.noaa.gov/ocd/ocdweb/index.html—NOAA Ocean Chemistry and Ecosystems Division

Concept Check (Questions and Answers) 5.1 Why Does Water Have Such Unusual Chemical Properties?

1. Sketch a model of an atom, showing the positions of the subatomic particles protons, neutrons, and electrons.

The sketch should look like Figure 5.1.

2. Describe what condition exists in water molecules to make them dipolar.

The unusual geometry of the water molecules is what causes them to be dipolar. Both hydrogen atoms are on the same side of the oxygen atom, separated by 105 degrees. This makes this side of the oxygen atom where they attach possess an excess of positive charge as the hydrogen nuclei are somewhat exposed. The electrons from the hydrogen atoms are spending most of their time on the side near the oxygen atom, which gives that side of the water molecules a net negative charge.

As a result, water molecules are dipolar (having separate charges).

3. Sketch several water molecules, showing all covalent and hydrogen bonds. Be sure to indicate the polarity of each water molecule.

The sketch should resemble Figure 5.3, with covalent bonds within the water molecule and hydrogen bonds between adjacent water molecules. The side of the water molecule that has two hydrogen atoms has a net positive charge.

4. How does hydrogen bonding produce the surface tension phenomenon of water?

Within a mass of water, hydrogen bonds can be oriented in all directions, but they must be oriented sideways or downward in the surface molecules. There is a greater amount of energy put into the lateral bonds at the water surface. This results in a strong skinlike surface layer of water molecules that creates the phenomenon known as surface tension.

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5. Discuss how the dipolar nature of the water molecule makes it such an effective solvent of ionic compounds.

Due to their dipolar nature, water molecules can weaken an electrical field to 1/80th of its normal intensity by aligning themselves in it. This reduces the strength of the electrical bond between ions in an ionic compound, and as the positive ends of the water molecules are attracted to the negative ends and vice versa, this further reduces the energy available for ion-to-ion bonds. Eventually each ion is hydrated, or surrounded, by water molecules and pulled out of the crystalline network.

5.2 What Important Physical Properties Does Water Possess?

1. Why are the freezing and boiling points of water higher than would be expected for a compound of its molecular makeup?

This is because not only van der Waals bonds (these must be overcome in changing the state of matter in all substances) but also hydrogen bonds (that are stronger than intermolecular bonds) must be overcome in the change of state for water. It takes more energy to overcome these bonds, resulting in much higher freezing and boiling points for water when compared to other similar chemical compounds.

2. How does the specific heat capacity of water compare with that of other substances?

Describe the effect this has on climate.

The heat capacity of water is higher than that of most commonly occurring substances. As a result, coastal climates are milder with a much narrower temperature range than inland regions.

This is because coastal water can gain or lose the same amount of heat as inland rocks and soil while undergoing only about half of the temperature change.

3. Why is the latent heat of vaporization so much greater than the latent heat of melting?

The latent heat of vaporization is much greater because to change water from a solid to a liquid, only a small percentage of the hydrogen bonds need to be broken. To convert liquid water to water vapor, every hydrogen bond must be broken.

4. Describe how excess heat energy absorbed by Earth’s low-latitude regions is transferred to heat-deficient higher latitudes through a process that uses water’s latent heat of evaporation.

To evaporate one gram of water from the ocean in the subtropics where the temperature of water is 20°C (68°F) requires 585 calories of heat energy. This energy is contained in the evaporated water molecules as they are transported to higher latitudes by the westerly wind belts. At about 60 degrees latitude, the air that is carrying the water rises and cools, and the water condenses as precipitation. For every gram of water that condenses, 585 calories of heat is released into the atmosphere at this latitude.

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5. As water cools, two distinct changes take place in the behavior of molecules: (1) Their slower movement causes water density to increase and (2) the formation of bulky ice crystals causes water density to decrease. Describe how the combination of these two factors causes pure water to experience its maximum density at 4°C (39.2°F).

In liquid water at all temperatures, there are molecules in two stages: ● Molecules bound to one another by hydrogen bonds ● Free unbound molecules As the molecules lose energy and the water cools, the unbound molecules occupy less space, making the water denser. At the same time, more and more of the low-energy molecules will form hydrogen bonds with their neighbors. As water cools above 4°C, its density increases because the dominant process is the clumping-together of unbound molecules. However, below a temperature of 4°C, the dominant process is the formation of clusters of molecules held together by hydrogen bonds. This process produces an increase in the volume of water with decreasing temperature because the crystalline lattice is an open structure that increases the distance between water molecules. Eventually almost all of the water molecules will be part of this crystalline structure held together by hydrogen bonds, and the liquid water will become ice.

6. Using everyday language, explain why ice is less dense than liquid water. From a chemical standpoint, why is this so unusual?

As water freezes, water molecules make a bulky, open structure on an atomic level. Chemically this is unusual because as most other substances freeze, their density increases because molecules slow down as they lose energy and subsequently take up less space. Frozen water has an expansive hexagonal structure.

5.3 How Salty Is Seawater?

1. What is the average salinity of seawater? What units are normally used, and why are those units useful?

Water is on average 35 parts per thousand (0/00). Converting to units we are used to seeing, water salinity is 3.5%.

2. What condition of salinity makes it possible to determine the total salinity of ocean water by measuring the concentration of only one constituent, the chloride ion?

The principle of constant proportions states that the major dissolved constituents that comprise the salinity of seawater occur nearly everywhere in the ocean in the exact same proportions, independent of salinity. Since the relative abundance of the major constituents of salinity is essentially constant, one can calculate the total salinity after determining the concentration of a single major constituent. The most abundant major constituent in seawater is the chloride ion (Cl−), which is most commonly used to determine salinity. Its concentration (called chlorinity) is also expressed in parts per thousand. The conversion formula is: Salinity (0/00) = Chlorinity (0/00) × 1.80655

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3. In what ways are seawater and pure water similar? How are the two different?

Both contain water and are liquids necessary for life. However, seawater contains nearly all the elements on the periodic table in some trace amounts. The dissolved ions change many of the properties. Pure water is a resistor, whereas seawater is a conductor. Pure water freezes at 4° C, whereas salts in seawater depress the freezing point. Seawater is denser than pure water, and space between the water molecules are filled with the salts, leaving more mass in the same volume of water.

5.4 Why Does Seawater Salinity Vary?

1. What physical conditions create brackish water in the Baltic Sea and hypersaline water in the Red Sea? The Baltic Sea is an enclosed sea that receives much fresh water input from streams that drain much of Europe, producing brackish water there. Conversely, the Red Sea is an enclosed sea that receives little fresh water input owing to the dry climate. It is characterized by a high evaporation rate that removes mostly fresh water and causes the Red Sea to have hypersaline conditions.

2. Describe the ways in which dissolved components are added and removed from seawater.

Dissolved components of seawater are primarily added by streams that dissolve the ions from continental rocks and carry them to the sea and by volcanic eruptions, both on land and on the sea floor. Other sources of dissolved components include the atmosphere (which contributes gases that are dissolved in seawater) and biological interactions.

Dissolved components of seawater are removed in many ways. Along mid-ocean ridges, the infiltration of seawater near hydrothermal vents causes magnesium and sulfate ions to become incorporated into sea-floor mineral deposits. These hydrothermal vents directly and actively influence the chemical composition of seawater. It has been estimated that the entire volume of ocean water is recycled through this hydrothermal circulation at the mid-ocean ridge every three million years. Therefore, the chemical exchange between ocean water and basaltic crust has a major influence on the nature of ocean water. Other methods of removal include the formation of salt spray by waves; the deposition in ocean sediments within the shells of dead microscopic organisms and animal feces; the drying of inland arms of the sea; and by the adsorption (physical attachment) to the surfaces of sinking clay and biological particles.

3. List the components (reservoirs) of the hydrologic cycle that hold water on Earth and the percentage of Earth’s water in each reservoir. Describe the processes by which water moves among these reservoirs.

Earth’s water reservoirs: ● Oceans = 97% ● Glaciers = 2% ● Groundwater = 0.6% ● Rivers and lakes = 0.02% ● Atmosphere = 0.001% Water evaporated from the surface of the oceans, rivers, and lakes is transported while stored as water vapor in the atmosphere and eventually returned to Earth’s surface as precipitation. The

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precipitation that falls on the continents is transported back into the oceans by flowing through lakes and rivers and as groundwater.

5.5 How Does Seawater Salinity Vary at the Surface and with Depth?

1. Why is there low surface salinity in the high latitudes, and why is there higher surface salinity in the low latitudes?

At high latitudes, abundant precipitation and runoff and the melting of freshwater icebergs all decrease salinity. In addition, cool temperatures limit the amount of evaporation that takes place (which would increase salinity). The formation and melting of sea ice balance out each other in the course of a year and are not a factor in changes in salinity. The pattern of Earth’s atmospheric circulation causes warm dry air to descend at lower latitudes near the Tropics of Cancer and Capricorn, so evaporation rates are high and salinity increases. In addition, little precipitation and runoff occur to decrease salinity. As a result, the regions near the Tropics of Cancer and Capricorn are the continental and maritime deserts of the world.

2. Explain the dip in surface salinity values near the equator, which is shown in Figure 5.21.

Daily rain showers are common along the equator, adding water to the ocean and lowering its salinity.

3. Describe the halocline, including where it occurs in the ocean.

Haloclines are separate layers of different salinity levels in the ocean. Haloclines tend to occur between the depths of about 300 meters (980 feet) and 1000 meters (3300 feet).

5.6 How Does Seawater Density Vary with Depth?

1. What are the three factors that affect seawater density? Describe how each factor influences seawater density, including which one is the most important.

• • •

As temperature increases (↑), seawater density decreases (↓) (due to thermal expansion).

As salinity increases (↑), seawater density increases (↑) (due to the addition of more dissolved material).

As pressure increases (↑), seawater density increases (↑) (due to the compressive effects of pressure).

2. Describe the thermocline, including where it occurs in the ocean.

A curved line that indicates a layer of rapidly changing temperature: in the low latitudes.

3. Describe the pycnocline, including where it occurs in the ocean.

A curved line that indicates a layer of rapidly changing density: in the low latitudes.

4. Why is there such a close association between (a) the curve showing seawater density variation with ocean depth and (b) the curve showing seawater temperature variation with ocean depth?

The similarity between the two curves is not surprising because the main factor affecting seawater density is temperature.

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5.7 Is the Ocean Acidic or Basic?

1. Explain the difference between an acidic substance and an alkaline (basic) substance.

An acid is a compound containing hydrogen that, when dissolved in water, releases hydrogen ions (H+), increasing the number of these ions per unit of water mass. A strong acid is one whose molecules readily release hydrogen ions when present in a dilute solution. The term alkali, or base, refers to compounds that, when dissolved in water, dissociate and increase the presence of hydroxyl ions (OH−). A strong base is a compound whose molecules readily release hydroxyl ions in dilute solutions.

2. How does the ocean’s buffering system work?

The carbonate buffering system serves to moderate changes in the pH of the ocean and has kept the ocean at a stable pH for long periods of time. If, for any reason, the pH of the ocean rises, chemical reactions occur to release H+ and lower the ocean’s pH. If the pH of the ocean decreases, chemical reactions raise the pH by removing H+. Buffering has been responsible for maintaining the ocean’s pH at an average of 8.1 with little variation through time.

5.8 What Factors Control the Distribution of Carbon and Oxygen in the Ocean?

1. Describe the relationship between solubility, temperature, pressure, and the

concentration of gases in seawater.

Solubility is the tendency of a substance to dissolve in a liquid. Carbon dioxide and oxygen become more soluble as the temperature of water decreases and pressure increases. Thus, cold water at high pressure tends to have high concentrations of oxygen and carbon dioxide.

2. Explain the difference between organic and inorganic carbon and describe a

reaction associated with each.

Organic carbon is found in the soft tissues of living organisms. Glucose (C6H12O6) is an example. Inorganic carbon is found in carbonate (CaCO3) containing shells of marine organisms.

3. Why would global warming cause the ocean to absorb less CO2? What about O2?

As the temperature of the ocean rises, the solubility of carbon dioxide will decrease.

Critical Thinking Questions (and Answers) 5.1 Using chemical principles, explain why water is considered the universal solvent.

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Water is a polar molecule and can dissolve polar or ionic substances. However, water cannot dissolve a nonpolar substance such as grease or oil. Thus, oil and water do not mix. Water is known as the universal solvent because it can dissolve a lot of different substances. However, water cannot dissolve everything.

5.2 Explain the differences between the three states of matter, using the arrangement of water molecules and hydrogen bonds in your explanation.

Solids have definite shape and volume. Liquids have a definite volume but not shape. Gases do not have a definite shape or volume. Molecules in a solid are connected to each other. Molecules in a liquid can slip past one another breaking and remaking bonds such as the hydrogen bonds in water, thus no definite shape. A liquid takes on the shape of the container in which it rests. Gas atoms or molecules bounce off each other; their volume can expand and take on the shape of any container.

Gases may also dissipate into the environment.

5.3 Specify how the principle of constant proportions can be used to determine seawater salinity by measuring only one dissolved component.

The major dissolved constituents that comprise the salinity of seawater occur nearly everywhere in the ocean in the exact same proportions, independent of salinity. Since the relative abundance of the major constituents of salinity is essentially constant, one can calculate the total salinity after determining the concentration of a single major constituent.

5.4 What evidence is used to support the hypothesis that ocean salinity has remained constant through time?

The salts in the ocean are in steady state, which means the amount of salts entering the oceans are equal to the amount of salts leaving the oceans. The volume of salt relative to the volume of seawater on Earth has been thought to be constant through time. Early Earth had more erosion and more sinks. Both slowed down over time; however, relative to each other, the rate has remained constant.

5.5 Using the processes that affect seawater salinity, explain why there is such a large range of salinity variation at the surface but such a narrow range of salinity at depth.

All the processes that affect salinity occur at the surface, such as evaporation, precipitation, runoff, sea ice melting, or freezing.

5.6 Seawater density is inversely proportional to and largely controlled by its temperature.

In simple language, explain what this statement means.

As the seawater temperature increases, the molecules move faster, increasing the volume, not the mass. Density is mass/volume, so if the mass stays the same while the volume increases, the overall number decreases as volume is in the denominator.

5.7 What is the pH of surface waters? Is this value very acidic, slightly acidic, neutral, slightly alkaline, or very alkaline? Also, specify how pH changes with depth, and why those changes occur.

The pH of surface water is about 8.1, or slightly alkaline. The pH decreases with depth to a low of about 7.6 at the low-pH layer generated by marine animal respiration. pH increases very slightly

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with depth to between 7.7 and 7.8. Deep-ocean water is less alkaline than surface water because the colder temperatures of deeper water allow it to dissolve more carbon dioxide than surface water, thus lowering the pH.

5.8 Consider the two dissolved oxygen profiles in Figure 5.29. Think of two reasons that could explain why the concentration of oxygen in the surface water in part b of the figure is higher than it is in part a.

In surface waters, marine photosynthetic organisms are the major source of dissolved oxygen.

Upwelling, which brings nutrients to the surface, is common in high-latitude areas. Areas with upwelling tend to have high biomass. The photosynthetic organisms in this biomass would produce large amounts of oxygen. In addition, the concentration of oxygen in high-latitude surface waters is greater than that found in low latitudes due to the increased solubility of oxygen in colder water.

Active Learning Exercises 5.1 Water molecules exhibit polarity. Working with another student in class, discuss what polarity means and come up with a list of common household items that also exhibit polarity.

Polarity in a water molecule refers to the uneven distribution of electrical charges within the molecule; one end is slightly positively charged, whereas the other is slightly negatively charged.

Student interpretations of the general term “polarity” may vary and include references to physical shape or structure, water-based household substances, or objects with magnetic polarities.

5.2 Working with another student in class, explain the unusual fact that ice is less dense than liquid water. Be sure to use the terms thermal contraction, water molecules, and hydrogen bonds.

As the temperature of a substance decreases, its molecules have less energy and take up less space due to thermal contraction. Water also experiences thermal contraction until it cools to about 4°C. However, the hydrogen bonds between the water molecules allow these molecules to arrange themselves into an open, hexagonal, lattice-like structure. The open spacing of these molecules causes ice to be less dense than liquid water.

5.3 Working with another student in class, determine the amount of your state sales tax, in parts per thousand.

Answers will vary by state. Here at James Madison University in Virginia, state sales tax is 5.3%, or 53%.

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5.4 Divide the class into two groups. For each group, note that salinity levels in the ocean can vary. For the first group, work with a partner and give one example of how salinity levels might increase, including a location along North America where this might occur. For the second group, work with a partner and give one example of how salinity levels might decrease, including a location along North America where this might occur. Then, switch partners with the other side of the room and compare examples of how salinity in the ocean may be increased or decreased.

Processes that might increase salinity include formation of sea ice and evaporation of seawater; both of these processes remove freshwater while leaving dissolved components behind to increase the water salinity. Answers will vary for North American locations where these processes may happen, but might include formation of ice along higher-latitude coastlines such as the east coast of Canada or evaporation of water in warm places such as Florida or Mexico.

Processes that can decrease salinity include precipitation, runoff of freshwater into saline water, melting icebergs, and melting sea ice, all of which add fresh water into the oceans. Again, answers will vary for locations but could include places where major rivers run into a body of salt water, such as the Mississippi Delta, northern Canada where ice can melt seasonally, or the coast of Oregon, which receives a large amount of precipitation.

5.5 Working with another student in class, determine which processes increase seawater salinity and which processes decrease seawater salinity. For each process, describe how it works on a molecular scale.

Processes that increase seawater salinity are formation of sea ice and evaporation. Water is a polar substance that will readily dissolve ionic compounds. Major constituents of seawater include chloride, sodium, sulfate, magnesium, calcium, and potassium ions. When compounds containing these ions enter seawater, they are dissolved, increasing the number of dissolved solids in the water and increasing the salinity. When water freezes, hydrogen bonds between water molecules are necessary for creating the ice crystal structure. Thus, any dissolved compounds are excluded from this structure when water freezes and are left behind in the liquid water; this increases the water’s salinity. When water evaporates, it is only the water molecules that are capable of transitioning from liquid to gas form, thus any dissolved solids remain behind in the water.

Processes that decrease seawater salinity include precipitation, runoff of freshwater into saline water, melting icebergs, and melting sea ice. All of these processes add more H2O molecules into the system but not more ionic compounds that contribute to salinity. Therefore, the proportion of dissolved solids relative to water molecules has decreased.

5.6 Working with another student in class, discuss the following questions for both high-latitude and low-latitude regions: 1. Is there a pycnocline in this region? Why or why not?

2. Is there a thermocline in this region? Why or why not?

3. Is there a halocline in this region? Why or why not?

1. High latitudes will not have a pycnocline, and low latitudes will have a pycnocline. At high latitudes, surface water temperature is cold all year, thus there is little to no difference between surface and deep water. Since the pycnocline represents a measure of density and density varies

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with temperature, we see little to no density differences between surface and deep water at high latitudes. At low latitudes, surface water temperatures will be high, and deeper waters will be colder. Therefore, surface waters will be less dense than deeper waters.

2. High latitudes will have no thermocline, and low latitudes will have a thermocline. At high latitudes, surface water and deep water temperatures are similar all year since surface water temperatures are cold all year. At low latitudes, there is a pronounced difference in temperature between warmer surface waters and colder deep waters, which is reflected in the thermocline.

3. Both high and low latitudes have a halocline. At high latitudes, the halocline shows lower surface salinity, which increases with depth. This is because there is abundant precipitation, runoff, and melting of freshwater icebergs, all of which contribute to decreased surface salinity, as well as low rates of evaporation. At low latitudes, the halocline reflects high surface salinity. Warmer temperatures at low latitudes generate increased evaporation, which lowers surface salinity.

5.7 Using examples of common household items, work with another student in class to describe the pH scale.

Answers will vary by student, but SmartFigure 5.21 presents a good visual of common household items and their respective pH values.

5.8 Pair up with a classmate and take the position that oxygen is more important in the ocean than carbon, and have your classmate take the opposite position. Debate the issue by describing what happens to oxygen and carbon in seawater, and compare their roles in maintaining conditions necessary for life.

Answers will vary. Oxygen is critical to cellular respiration for nearly all organisms on Earth. On the other hand, carbon is the basis for all life on Earth. In the ocean, the carbonate buffering system maintains the ocean’s pH.

Additional Active Learning Questions Diving Deeper 5.1 One of the major concerns about seawater desalination is its high expense. Another concern is the disposal of leftover brine from the desalination process back into the ocean, which harms marine life. With another student in class, discuss whether these two concerns are enough to prohibit the widespread use of desalination as a source of drinking water.

Student opinions will vary. Issues in favor of using desalination as a source of drinking water might include concerns about drought and lack of fresh water for human needs in some parts of the world, population increases that outstrip the supply of regional fresh water, or pollution of local fresh water supplies, all of which are concerns that may outweigh expense and brine-disposal issues. Other students might argue that if anyone is willing to take on the expense of desalinization, they should not be prohibited from doing so.

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Arguments against desalinization might include using citizens’ tax money for more pressing issues, since desalinization only accounts for provision of less than 0.5% of human fresh-water needs. In addition, many species of marine life are already facing other environmental stressors, and it might be unethical to subject them to further harm.

5.2 San Diego, California and Phoenix, Arizona are located at nearly the same latitude and would be expected to have similar climates based on latitude alone. Make a graph using the data below to compare the mean average monthly temperatures in each city, according to the National Weather Service. Use the thermostatic effects of water to explain the differences.

Month 1 2 3 4 5 6 7 8 9 10 11 12

Phoenix Mean Average Temperature (°F) 56.4 59.7 65.2 72.7 82.1 90.8 94.8 93.6 88.4 76.7 64.1 55.4

San Diego Mean Average Temperature (°F) 57.1 57.9 59.4 61.7 64 66.4 70 71.6 70.6 66.7 61.3 56.5

Data retrieved from https://w2.weather.gov.

Water has a high heat capacity and is able to absorb and release large amounts of energy without changing temperature. Water’s heat capacity means that locations near a coastline tend to have similar temperatures year round. This is referred to as a marine effect. In contrast, areas farther inland tend to have a greater range of temperatures through the year. This phenomenon is known as the continental effect.

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Exploring Data SmartFigure 5.9 For the three states of matter, describe water as having either: (1) no hydrogen bonds, (2) some hydrogen bonds, or (3) all hydrogen bonds. In each case, where are the covalent bonds?

In the gas state, there are no hydrogen bonds. In the liquid state, there are some hydrogen bonds. In the solid state, there are the maximum number of hydrogen bonds. In all cases, the covalent bonds are within an individual water molecule, between the hydrogen and oxygen atoms.

SmartFigure 5.12 Describe the differences in the density curves between a typical liquid (green curve) and water (red curve) as temperature goes from 20°C to –2°C. Why does water exhibit such behavior?

With a typical liquid, density increases linearly as the temperature decreases. This happens because as the liquid cools, the molecules lose energy, slow down, and get closer together.

In water, density increases with a decrease in temperature above 4°C as the molecules lose energy, slow down, and get closer together. As the temperature drops below 4°C, the molecules begin to line up to form ice crystals. Ice crystals are bulky and the water molecules are widely spaced, which reduces the density.

SmartTable 5.2 In a sentence, describe the major differences in properties between pure water and seawater.

Pure water is odorless, tasteless, has a neutral pH, a freezing point of 0°C, a melting point of 100°C, and a density of 1 g/cm3; seawater has a marine odor, salty taste, alkaline pH, freezing point of –1.9°C, boiling point of 100.6°C, and a density of 1.028 g/cm3.

Figure 5.21 Is there relatively high or low seawater salinity in the high latitudes? Is there relatively high or low seawater salinity in the low latitudes? Explain.

Sea-surface salinity is lowest near the poles (high latitude), peaks near the Tropics of Cancer and Capricorn, and dips near the equator (low latitude). At high latitudes, runoff, precipitation, the melting of icebergs, and low rates of evaporation decrease sea-surface salinity. Near the Tropics of Cancer and Capricorn, high evaporation rates and little precipitation increase sea-

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surface salinity. Near the equator, evaporation rates are high, but increased precipitation and runoff offset the evaporation and reduce the sea-surface salinity.

SmartFigure 5.23 According to SmartFigure 5.23, there is a large amount of salinity variation at the ocean surface, yet only a small amount of salinity variation below 1000 meters (3300 feet). Explain why this is so.

The main processes that influence ocean salinity act near the surface.

SmartFigure 5.28 By examining the change in ∑CO2 with depth, identify the depth that corresponds to the bottom of the pycnocline. Hint: Recall that the pycnocline is a strong barrier to vertical water mixing in the ocean.

The bottom of the pycnocline is at a depth of 1000 m.

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Chapter 6 Air–Sea Interaction Overview One hallmark of the Earth system is that the oceans and atmosphere are inextricably linked. This chapter explores the coupling of the atmosphere and the ocean as a single system. The chapter opens with a discussion on the effects of uneven distribution of solar energy and the resultant uneven heating of Earth’s surface, which varies with latitude. It addresses why there are seasons on Earth. There is a section that introduces atmospheric composition and the global movement of air. The Coriolis effect is presented and examples of how the Coriolis effect operates are included. The background information at the beginning of the chapter is applied later in the chapter in a discussion about atmospheric circulation cells.

Atmospheric phenomena that are related to the oceans are presented, including wind patterns, storms, and tropical cyclones. A brief introduction of the global climate pattern of the oceans follows, as well as a section on how sea ice and icebergs form. The chapter concludes with a discussion about power from wind energy being harnessed as an energy source.

Essential Concepts 6.1 Explain variations in solar radiation on Earth, including the cause of Earth’s seasons.

6.2 Describe the physical properties of the atmosphere.

6.3 Demonstrate an understanding of the Coriolis effect.

6.4 Explain global atmospheric circulation patterns.

6.5 Describe how the ocean influences global weather phenomena and climate patterns.

6.6 Evaluate the advantages and disadvantages of harnessing winds as a source of energy.

Chapter Outline 6.1 What Causes Variations in Solar Radiation on Earth?

6.1.1 What Causes Earth’s Seasons?

Web Animation: Earth–Sun Relations SmartFigure 6.2: Perspective view of Earth’s orbit: Why Earth has seasons 6.1.2 How Latitude Affects the Distribution of Solar Radiation 6.1.3 Oceanic Heat Flow 6.2 What Physical Properties Does the Atmosphere Possess?

6.2.1 Composition of the Atmosphere 6.2.2 Temperature Variation in the Atmosphere 6.2.3 Density Variation in the Atmosphere 6.2.4 Atmospheric Water Vapor Content 6.2.5 Atmospheric Pressure 6.2.6 Movement of the Atmosphere 6.2.7 An Example: A Nonspinning Earth 6.3 How Does the Coriolis Effect Influence Moving Objects?

6.3.1 Example 1: Perspectives and Frames of Reference on a Merry-Go-Round 75 .

SmartFigure 6.10: A merry-go-round spinning counterclockwise as viewed from above illustrates some concepts about the Coriolis effect 6.3.2 Example 2: A Tale of Two Missiles Web Animation: Coriolis Effect 6.3.3 Changes in the Coriolis Effect with Latitude 6.4 What Global Atmospheric Circulation Patterns Exist?

6.4.1 Circulation Cells 6.4.2 Pressure 6.4.3 Wind Belts Web Animation: Global Wind Patterns 6.4.4 Boundaries SmartTable 6.2: Characteristics of wind belts and boundaries 6.4.5 Circulation Cells: Idealized or Real?

Web Animation: Seasonal Pressure and Precipitation Patterns.

Diving Deeper 6.1 Historical Feature Why Christopher Columbus Never Set Foot on North America 6.5 How Does the Ocean Influence Global Weather Phenomena and Climate Patterns?

6.5.1 Weather versus Climate Web Animation: Cyclones and Anticyclones 6.5.2 Winds SmartFigure 6.14: High- and low-pressure regions and resulting air flow in the Northern Hemisphere 6.5.2.1 Sea and Land Breezes 6.5.3 Storms and Fronts Web Animation: Cold Fronts and Warm Fronts 6.5.4 Tropical Cyclones (Hurricanes) 6.5.4.1 Origin SmartTable 6.3: The Saffir–Simpson scale of hurricane intensity 6.5.4.2 Movement SmartFigure 6.20: Typical North Atlantic hurricane storm track and detail of internal structure Web Animation: Hurricanes 6.5.4.3 Impact of Other Factors 6.5.4.4 Types of Destruction 6.5.4.5 Historic Destruction on the U.S. Mainland 6.5.4.6 The Record-Breaking 2005 Atlantic Hurricane Season: Hurricanes Katrina, Rita, and Wilma 6.5.4.7 The Historic 2017 Atlantic Hurricane Season: Hurricanes Harvey, Irma, and Maria 6.5.4.8 Historic Destruction in Other Regions 6.5.4.9 Future Threat to Life and Property 6.5.5 The Ocean’s Climate Patterns 6.6 Can Power from Wind Be Harnessed as a Source of Energy?

Essential Concepts Review

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Learning Outcomes The instructional objectives are performance-based and detail specific learning outcomes for Chapter 6.

The test items contained in the Test Bank are keyed to the learning objectives and the Chapter in Review at the end of the chapter. The order of the objectives mirrors the content presentation in Chapter 6.

Upon completion of this chapter, the student should be able to: 1. Define Earth’s ecliptic and describe its effect on Earth’s climate.

2. Describe Earth’s seasons, including the: a. vernal equinox b. summer solstice c. autumnal equinox d. winter solstice 3. Define declination as it relates to the Sun, Earth, and global climate variation.

4. Describe the location of the following: a. Tropic of Cancer b. Tropic of Capricorn c. Arctic Circle d. Antarctic Circle 5. Define albedo and the effect of differential albedo (ice/snow, land, and water) on climate.

6. Detail the following atmospheric properties: a. chemical composition b. temperature c. density d. water vapor content e. pressure f. movement 7. Explain the relationship between the solar heating of Earth and convection cells on a nonspinning Earth.

8. Discuss the effect of a rotating Earth on the direction of wind and water movement.

9. Draw and label the major global circulation patterns and the corresponding wind belts (remember that winds are named for the direction from which they blow), including Hadley cells, Ferrel cells, and polar cells, trade winds (northeast trades and southeast trades), westerlies, and polar easterlies.

10. Describe the location, direction of air movement, and corresponding air pressure for subtropical highs, polar highs, equatorial lows, and subpolar lows.

11. Distinguish between the doldrums, the horse latitudes, and the polar front, and give the location of each.

12. Define the Intertropical Convergence Zone (ITCZ).

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13. Differentiate between weather and climate.

14. Describe the relationship between air pressure and wind direction in cyclonic flow and anticyclonic flow.

15. List the factors in the development of land breezes and sea breezes.

16. Explain how storms form and the relationship between jet stream position and storm movement, and make the distinction between warm fronts and cold fronts.

17. Give the distinction between a hurricane, a typhoon, and a cyclone, and give the location where these weather phenomena occur.

18. Provide a brief explanation of the Saffir–Simpson Scale.

19. List the severe hurricanes, typhoons, and cyclones (and the location of landfall) that have damaged the coastal areas during the 20th century.

20. Draw Earth and label the following oceanic climate patterns on your sketch, including the equatorial region, the tropical regions, the subtropical regions, the temperate regions, the subpolar regions, and the polar regions.

21. Discuss how wind power can be used for energy and the advantages and disadvantages of it.

Teaching Strategies A common misconception is that seasons are caused by Earth’s varying proximity to the Sun. It is important to make sure students understand that it is Earth’s tilt on its axis that causes seasons.

Tie in the 23.5-degree tilt to the 23.5-degree latitudes of the Tropics of Cancer and Capricorn to help cement these facts. Some students have difficulty understanding the Coriolis effect. It may be helpful to point out that all locations on the globe make one rotation per 24 hours, but some places, for example the equator, need to cover more angular distance than locations with a higher latitude in the same amount of time. This surface speed discrepancy contributes to the Coriolis effect.

When presenting the three-cell model of Earth’s circulation, the two-dimensional drawing may be confusing to some students. Emphasize that the Hadley, Ferrell, and polar cells are vertical circulation cells and the surface horizontal components are the major wind belts.

This chapter also presents a good opportunity to stress the interconnectedness of different parts of the Earth system, with particular emphasis on the ocean–atmosphere coupling. For example, you can show how closely major ocean currents parallel atmospheric circulation patterns.

More detailed climate issues are covered in later chapters. It is good to lay the foundation for addressing those here but do not get into great detail with this chapter alone.

Some students who did not spend time on this material and who move on to chapters regarding ocean currents and climate issues find that they have to revisit Chapter 6 before they can fully understand the processes in future chapters.

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Teacher’s Resources Films ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪

Air–Sea Interaction (Encyclopedia Britannica), 15 minutes Atmospheric Science Series: Global Winds (Coronet), 12 minutes Danger’s Edge (The Weather Channel), 25 minutes (subject: hurricanes) Hurricane Force: A Coastal Perspective and Anatomy of a Hurricane (University of California), 34 minutes Nature of Sea Water (Local Naval District, Film MN-103-17), 29 minutes The Gulf Stream (Bullfrog Films), 28 minutes (emphasizes oceanic climate belts) Underwater Sound—Basic Principles (Local Naval District, Film MN-10287), 29 minutes The Weather (BBC), 240 minutes, but broken into much shorter topics that may stand alone A Private Universe (Harvard Smithsonian Center for Astrophysics), 20 minutes, http://learner.org/resources/series28.html# The Habitable Planet: A Systems Approach to Environmental Science, #2: Atmosphere (Harvard Smithsonian Center for Astrophysics), 30 minutes, http://learner.org/resources/series209.html

Websites ● www.weather.com—The Weather Channel ● www.nhc.noaa.gov/—National Hurricane Center ● www.ems.psu.edu/~fraser/Bad/BadCoriolis.html—Bad Coriolis, addressing Coriolis effect misconceptions ● http://environment.nationalgeographic.com/environment/natural-disasters/hurricane-profile/— Hurricanes, Engines of Destruction, from National Geographic ● http://video.nationalgeographic.com/search?q=hurricane—National Geographic, short hurricane videos

Concept Check (Questions and Answers) 6.1 What Causes Variations in Solar Radiation on Earth?

1. Sketch a labeled diagram to explain the cause of Earth’s seasons.

The sketch should look like SmartFigure 6.2.

2. Along the Arctic Circle, how would the Sun appear during the summer solstice? During the winter solstice?

At regions above the Arctic Circle (66.5 degree north latitude or higher) during the Northern Hemisphere summer solstice, there would be continual daylight (midnight sun). During the Northern Hemisphere winter solstice, there would be perpetual darkness (no sunrise). At regions above the Antarctic Circle (66.5 degree south latitude or higher), during the Northern Hemisphere summer solstice, there would be continual darkness (no sunrise), while during the Northern Hemisphere winter solstice, there would be perpetual daylight (midnight sun).

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3. If there is a net annual heat loss at high latitudes and a net annual heat gain at low latitudes, why does the temperature difference between these regions not increase?

Heat is transferred from the low latitudes to the high latitudes by atmospheric winds and ocean currents.

6.2 What Physical Properties Does the Atmosphere Possess?

1. Describe the physical properties of the atmosphere, including its composition, temperature, density, water vapor content, pressure, and movement.

The relationship between temperature, density, water vapor content, and pressure in the atmosphere is complex. The composition of the atmosphere (dry air) is: ● Nitrogen (N2) = 78.1% ● Oxygen (O2) = 20.9% ● Argon (Ar) = 0.9% ● Carbon dioxide (CO2) = 0.035% ● All others = trace Within the troposphere, the temperature of the atmosphere gets cooler with increasing distance from Earth’s surface. The atmosphere’s density is strongly related to temperature (among other properties) such that warm air is less dense (so it rises) and that cool air has a greater density (so it sinks). The water vapor content of the atmosphere changes with temperature: warm air can hold more water vapor and is typically moist, while cool air is typically dry. Atmospheric pressure is related to the weight of the air column above (static case), or for moving air (dynamic case), sinking air (movement toward the surface) causes high pressure at the surface and rising air (movement away from the surface) causes low pressure at the surface. In terms of movement, air always moves from high-pressure to low-pressure regions.

2. Explain how uneven heat distribution drives the movement of a convection cell.

Areas near Earth’s equator receive more solar radiation than areas near the poles. This solar radiation causes the surface air near Earth’s equator to be warmed more than the surface air near Earth’s poles. The warm air rises because it is less dense than the air around it. The warm air moves upward to the top of the troposphere where it begins to move toward the pole. Air is much cooler at high altitudes, so the air begins to cool and its density increases. Eventually, the cool, dense air sinks toward Earth’s surface. At the surface, the air moves toward the equator and warms. Eventually, it rises again to complete the convection cell. This specific convection cell is known as a Hadley cell (see Section 6.4).

6.3 How Does the Coriolis Effect Influence Moving Objects?

1. Describe the Coriolis effect in both the Northern and Southern Hemispheres.

The Coriolis effect causes objects in motion in the Northern Hemisphere to veer right of their intended course whereas it causes objects in motion in the Southern Hemisphere to tend to veer to the left.

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2. What is the underlying cause of the Coriolis effect?

The Coriolis effect is a result of the fact that points at different latitudes on Earth rotate at different velocities, ranging from 0 kilometers per hour at the poles to 1600 kilometers (1000 miles) per hour at the equator.

3. Explain how the strength of the Coriolis effect changes with latitude.

Since the rate of change of rotational velocity per degree of latitude is greater at higher latitudes, the effect is greater there. For instance, the change in the rate of Earth’s rotation is 200 kilometers (124 miles) per hour from the equator to 30 degrees latitude, while over the same number of degrees of latitude from 60 degrees latitude to the pole, the change is 800 kilometers (500 miles) per hour.

6.4 What Global Atmospheric Circulation Patterns Exist?

1. Sketch the pattern of surface wind belts on Earth, showing atmospheric circulation cells, zones of high and low pressure, the names of the wind belts, and the names of the boundaries between the wind belts.

The sketch should resemble Figure 6.12.

2. Why are there high-pressure caps at each pole and a low-pressure belt in the equatorial region?

The different pressures observed in these two regions result primarily from temperature differences in the columns of air overlying each of these regions. The air over the equator and at 60 degrees north or south latitude rises due to being heated, while cold air descends over the poles and at 30 degrees north or south latitude.

3. Discuss the patterns or trends that you notice about the global wind belts and boundaries as shown in Figure 6.12 and delineated in Table 6.2.

Patterns observed by the above-mentioned figure show a mirror image of north and south of the equator. The wind belts above and below the equator head in the same direction. Westerlies blow east, trade winds blow west, and polar easterlies blow west. They are named after the direction they are coming from, not going toward. Also this diagram is idealized as the Ferrel cells are not as stable or strong as the Hadley cells. Note that air moving from a latitude with a smaller circumference to a larger circumference will blow behind itself. The opposite is also true with blowing from a latitude with a larger circumference to a smaller circumference, which will blow ahead of itself in both hemispheres.

6.5 What Weather and Climate Patterns Occur in the Oceans?

1. Describe the difference between cyclonic and anticyclonic flow, and show how the Coriolis effect is important in producing both a clockwise and a counterclockwise flow pattern.

As air moves away from high-pressure cells and toward low-pressure cells, the Coriolis effect modifies the direction of air movement. In the Northern Hemisphere, this results in a counterclockwise flow of air around low-pressure cells (called cyclonic flow) and a clockwise flow of air around high-pressure cells (called anticyclonic flow). Note that in the Southern Hemisphere, the directions of air flow are reversed.

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2. How do sea breezes and land breezes form? During a hot summer day, which one would be most common and why?

Sea breezes and land breezes are caused by differential heating of land and ocean surfaces and are common in coastal areas. When an equal amount of solar energy is applied to both land and ocean, the land heats up about five times more due to its lower heat capacity. The land heats the air around it, and during the afternoon, the warm, low-density air over the land rises. This rising air creates a low-pressure region over the land and causes the cooler air over the ocean to be pulled toward the land, creating what is called a sea breeze. This condition is most pronounced on a hot summer day. At night, the land surface cools about five times more rapidly than the ocean and cools the air around it. This cool, high-density air sinks, creates a high-pressure region, and causes the wind to blow from the land. This is known as a land breeze, which is commonly well developed in the late-evening and early-morning hours.

3. Name the polar and tropical air masses that affect U.S. weather. Describe the pattern of movement across the continent and patterns of precipitation associated with warm and cold fronts.

The major polar air masses that affect weather across the United States are the polar maritime air masses of the North Pacific and North Atlantic oceans, as well as the polar continental air mass that originates over Canada. Tropical maritime air masses originate from the tropical Pacific and Atlantic oceans as well as the Caribbean Sea. A tropical continental air mass that originates over Mexico also affects U.S. weather.

Warm and cold fronts are influenced by the prevailing westerlies and generally move across the United States from west to east. In either case where a warm or a cold front is produced, the lessdense, warmer air always rises above the denser cold air. The rising air cools, and the water vapor in it condenses and falls as precipitation. A cold front is usually steeper, and the temperature difference across it is greater than a warm front. Therefore, rainfall along a cold front is usually heavier and briefer than rainfall along a warm front.

4. What are the conditions needed for the formation of a tropical cyclone? Why do most middle-latitude areas only rarely experience a hurricane? Why are there no hurricanes at the equator?

The conditions needed for the formation of a tropical cyclone are: ●

Warm ocean water greater than 25°C (77°F) that supplies the heat energy to the atmosphere by evaporation. ● Warm moist air that supplies additional heat as the water vapor in the air condenses. ● The Coriolis effect that causes the hurricane to spin (that’s why there are no hurricanes on the equator where the Coriolis effect is minimal). The air flowing toward the lowpressure center of a hurricane veers to its right in the Northern Hemisphere and to the left in the Southern Hemisphere, producing counterclockwise and clockwise rotation, respectively.

These conditions are found during the late summer and early fall, when the tropical and subtropical oceans are at their maximum temperature.

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The reason why most mid-latitude areas only rarely experience a hurricane is because ocean water temperature rarely gets warm enough to keep a hurricane going (however, there have been some notable exceptions to this when strong hurricanes reach the mid-latitudes). Once a hurricane travels over land or cool water, its energy source has been cut off, and it usually rapidly decreases in strength.

5. Describe the types of destruction caused by hurricanes. Of those, which one causes the majority of fatalities and destruction?

Destruction from hurricanes is caused by high wind speeds and floods due to intense rainfall. The majority of a hurricane’s fatalities and destruction is caused by a phenomenon called storm surge. A storm surge occurs when a hill of water that is created by winds moving toward the eye of the storm comes ashore. In severe hurricanes, storm surges can be up to 12 meters (40 feet) in height. Storm surge increases when storm landfall coincides with a spring tide (full moon or new moon) and occurs at high tide.

6.6 Can Power from Wind Be Harnessed as a Source of Energy?

1. Discuss the advantages and disadvantages of building an offshore wind farm.

Advantages: Wind energy is renewable and clean (does not produce greenhouse gases). Building a wind farm in the ocean has its own advantages. In particular, wind generally blows harder and more steadily offshore.

Disadvantages: Wind strength varies and sometimes it isn’t windy at all. Once the energy has been harnessed, it has to be transported to viable markets, which involves building new infrastructure (the power grid). Some people also don’t like the way wind turbines look (NIMBY).

2. Describe the location, timeframe, and power-generating capability of America’s first offshore wind farm.

Still in concept, there have been several political milestones. The location chosen is off of Cape Cod. Timeframe is still up in the air; as of 2012, there are big protests by the local residents not to build it near their beach. The consensus is that building and maintaining at sea will be very costly, and the original budget for this project is thought to be grossly underestimated. Wind farms may be more successful in remote locations on land before this is built.

Critical Thinking Questions (and Answers) 6.1 Earth’s axis of rotation is angled 23.5 degrees from perpendicular relative to the plane of its ecliptic. Specify how the tilt of Earth’s axis affects the change of seasons, the length of day, and the angle of sunlight over the time span of a year using as an example a location from both hemispheres.

Because the Earth is tilted 23.5 degrees from perpendicular relative to the ecliptic as it moves around the Sun, the Sun shines directly on the Southern Hemisphere between the latitudes of 0 and 23.5 degrees for half of a year, and on the Northern Hemisphere at the same latitude for the other half of a year. This produces Earth’s seasons. At the Northern Hemisphere summer and winter solstices, the Sun is at its most northerly and southerly positions relative to Earth’s surface (the Tropic of Cancer

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is 23.5 degree north and the Tropic of Capricorn is 23.5 degree south latitude, respectively). At these times, the portions of Earth’s surface below the Antarctic Circle (66.5 degree south) and above the Arctic Circle (66.5 degree north) receive no solar radiation from the Sun. It should be noted that when these areas are not receiving sunlight, the opposite pole is receiving continuous sunlight with no night.

6.2 In a nonspinning Earth, describe the basic atmospheric circulation pattern that would exist.

Wind at the surface would blow from regions of high pressure toward regions of low pressure with no deflection due to no Coriolis effect.

6.3 How does the Coriolis effect influence the direction of moving objects? How does it affect the speed of moving objects? Explain.

In the Northern Hemisphere, the Coriolis effect changes the path of a moving object to the right of the intended path. In the Southern Hemisphere, moving objects appear to deflect to the left of the intended path. The Coriolis effect does not change the speed of the moving object.

6.4 To help reinforce your knowledge of atmospheric circulation patterns, draw from memory the pattern of surface wind belts on Earth, showing atmospheric circulation cells in the upper/lower atmosphere, zones of high and low atmospheric pressure, the names of the wind belts, and the names of the boundaries between the wind belts.

This diagram should resemble Figure 6.12.

6.5 Specify differences between weather and climate. When it rains in a region that experiences an arid climate, does it mean the region’s climate has changed from dry to wet? Explain.

Weather describes the conditions of the atmosphere at a given time and place, whereas climate is the long-term average of weather. If it rains in a region that is arid, it does not mean that area has changed to a wet climate. It just happens to have rain in its weather that day. Changes need to be longer term to reclassify an area’s climate.

6.6 Specify some negative environmental factors that might inhibit the development of large offshore wind farms.

Cost of building, cost of maintenance, line loss, storm damage, damage from corrosion from salt in the air, and salt water. Close to shore they are visible, and they kill sea birds.

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Active Learning Exercises 6.1 With another student in class, make a list of changes that would occur if Earth’s axis of rotation was vertical (not tilted). For example, would seasons still exist?

Seasons would not exist on Earth. All latitudes would receive consistent amounts of sunlight all year, with the most intense heat focused on the equator and the poles receiving the least amount of sunlight. The poles would not have months of darkness. Length of day would be the same all year, as would times of sunrise and sunset. The Sun would always make the same overhead path every day.

The Tropics of Cancer and Capricorn would not have any significance and would just be ordinary latitudes.

6.2 With another student in class, use the Internet to research the ancient Greek story of Icarus. Based on the temperature profile of the atmosphere shown in Figure 6.6, is the tragedy that befalls Icarus based on physical fact? Explain.

The story of Icarus is about a man and his brother who construct wings using wax and feathers in an attempt to fly into the heavens. They succeed in taking flight, but their endeavor fails as they get higher into the sky, as the closer they get to the Sun, the hotter it becomes and it melts the wax holding their wings together. Ultimately Icarus and his brother fall to their deaths as their wings fall apart.

The story of Icarus is not based on physical fact. The temperature of the troposphere decreases with increasing altitude, so as Icarus and his brother gained altitude to a height of about 7 miles, they would have been getting colder. Assuming they could have even reached the top of Earth’s atmosphere, the temperature would not have increased beyond that, which was felt at Earth’s surface.

6.3 With another student in class, explain why the Coriolis effect is strongest at the poles. Then switch roles and explain why the Coriolis effect is nonexistent at the equator.

The Coriolis effect increases with increasing latitude and is thus strongest at the poles. The rotational velocity difference between two places at different latitudes close to the poles is going to be large.

The rate of change of rotational velocity increases the closer you get to the poles, which is going to cause more deflection of the path of a moving object.

The Coriolis effect is nonexistent at the equator because the rate of change of rotational velocity close to the equator is very small, thus causing no deflection to the path of a moving object.

6.4 With another student in class, discuss how the world’s idealized wind belts shown in Figure 6.12 are modified on the real Earth (Figure 6.12). Use specific examples including wind belts, boundaries, high and low atmospheric pressures, and differences between ocean and land. Report your findings to the class.

The idealized wind belts are modified by several factors. The tilt of Earth on its axis produces seasons and causes maximum solar radiation to vary by date for different locations. Seasonality shifts the three cells in the three-cell model of atmospheric circulation, and since the wind belts are the surface component of these cells, the wind belts also shift seasonally. Continents also affect wind belts. The 85 .

uneven heating of land versus water causes continental air to be colder in winter and warmer in summer, which shifts pressure differentials and gradients. The Northern Hemisphere also has more land than the Southern Hemisphere, which affects temperature gradients as well.

6.5 Pair up with another student in class. Using the Internet, have each student determine the latitude and today’s offshore surface-water temperature for one of the following two locations: San Diego, California and Charleston, South Carolina.

Working together, mark each location on the map shown in Figure 6.26. Using information from Figure 6.26, explain why the surface water temperature is so different at these two locations.

San Diego’s latitude = 32.7 degrees north Charleston’s latitude = 32.8 degrees north Water temperature in Charleston should generally be warmer than that in San Diego, despite their similar latitudes. Charleston, on the east coast of the United States, has water temperatures influenced by the warm current flows north from equatorial regions. San Diego, on the U.S. west coast, is situated next to a cold current flowing south along California’s coast from cold northern regions.

6.6 Working as a group and using Figure 6.27, identify a specific location on Earth that should allow wind turbines to work at maximum capacity year-round (not just during a particular season). Present your findings to the class, including the location and an explanation of your reasoning.

According to the map in Figure 6.78, there appear to be few locations that would allow year-round wind turbine optimization. Regions where this could be possible include a narrow region just north of Alaska, a band of ocean surrounding Antarctica, and a small patch of sea just east of Central America, bordering the top of the South American continent.

Additional Active Learning Exercises 6.1 With a partner, use two tennis balls (one for the Earth and one for the Sun) to demonstrate why the Earth has seasons.

As the students move the Earth around the Sun, they should demonstrate the following: (1) The Earth should be tilted 23.5 degrees and that angle should remain constant. (2) The North Pole should be pointed in the same direction at all times.

They should recognize that the tilt causes an area to be pointed more directly toward the Sun during the summer and away from the Sun during the winter.

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6.4 Use Figure 6.12 and what you know about high- and low-pressure zones to predict the latitudes that deserts are often found on land. After you make your predictions, use the Internet to determine where the major deserts are located.

Students should predict that the major deserts will be found at the same latitudes as the global highpressure areas (30 degrees and 90 degrees). Although the poles are not traditionally thought of as deserts, they have low precipitation and can be thought of in that way.

Exploring Data Figure 6.8 1. For cool, sinking air, what atmospheric pressure conditions are created at Earth’s surface?

Explain this in terms of molecular packing and the density of air.

When cool air sinks, it causes high pressure at Earth’s surface as the air molecules are packed tightly together.

2. For warm, rising air, what atmospheric pressure conditions are created at Earth’s surface?

Explain this in terms of molecular packing and the density of air.

When warm air rises, it causes low pressure at Earth’s surface as the air molecules are spread out.

Figure 6.11 Using Figure 6.11a, what is the approximate speed of Earth’s rotation at your present latitude?

Answers will vary depending on location. According to NASA.gov, this speed can be calculated in the following way. First, calculate the speed at the equator: the circumference of Earth is 40,070 kilometers, and the day is 24 hours long so the speed is 1670 kilometers/hour (1037 miles/hr). At other latitudes, the speed decreases by the cosine of the latitude, so, at a latitude of 45 degrees, cos(45) = .707 and the speed is .707 × 1670 = 1180 kilometers/hr.

Figure 6.12 Describe the patterns you notice in Figure 6.12 by examining, in order: (1) surface atmospheric pressure, (2) resulting typical weather, (3) major wind belts of the world, and (4) the boundaries between wind belts.

(1) Every 30 degrees in latitude, surface atmospheric pressure reverses. At 0 degrees, there is a lowpressure zone, at 30 degrees, there is a high-pressure zone, at 60 degrees, there is a low-pressure zone, and at 90 degrees, there is a high-pressure zone.

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(2) In areas of low pressure (0 degrees and 60 degrees), there is rising air, cloudy conditions, and lots of precipitation. In areas of high pressure (30 degrees and 90 degrees), there is descending air, clear conditions, and little precipitation.

(3) Major wind belts of the world are found between high- and low-pressure zones. The trade winds are found between 0 degrees (low pressure) and 30 degrees (high pressure). The prevailing westerlies are found between 30 degrees (high pressure) and 60 degrees (low pressure). The polar easterlies are found between 60 degrees (low pressure) and 90 degrees (high pressure).

Between each wind belt, there is an area with little wind since most of the air movement is either away from or toward Earth’s surface. The doldrums are found along the equator, at 0 degrees. The horse latitudes are found at 30 degrees. The polar front is found at 60 degrees.

Figure 6.14 Describe how this figure would be different if it showed conditions for the Southern Hemisphere.

The directions of the rotation would be reversed for the Southern Hemisphere because the Coriolis effect deflects wind in the opposite direction, compared to the Northern Hemisphere.

SmartTable 6.3 What is the Saffir-Simpson hurricane intensity and typical storm surge for the following situations?

(1) Some structural damage to buildings and foliage blown off trees The Saffir-Simpson hurricane intensity would be a category 3 and the typical storm surge would be 2.7–3.7m (9–12 feet).

(2) Entire building failures common; all shrubs, trees, and signs blown down; flooding of lower floors of coastal structures The Saffir-Simpson hurricane intensity would be a category 5 and the typical storm surge would be >5.8 m (>19 feet).

Figure 6.19 Describe the patterns you notice about historic tropical cyclone tracks over the past 150 years as shown in Figure 6.19.

Tropical cyclones originate in low latitudes and usually move from east to west as they are affected by the trade winds. In the Northern Hemisphere, they curve to the right and in the Southern Hemisphere, they curve to the left.

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Chapter 7 Ocean Circulation Overview This chapter explores ocean circulation; currents are presented as the horizontal or vertical movement of ocean water. The chapter begins with a section discussing the measurement of both surface and deepocean water. Surface currents are presented in detail, focusing on their wind-driven transport mechanism and the organization of surface currents into gyres. There are continuations of concepts from ocean– atmosphere interactions presented in Chapter 6. Important aspects of upwelling and downwelling are presented, including how these processes are accomplished by various methods. A description of surface current flow within each major basin and a tour of the ocean basins follow. A model of deep-ocean water circulation is presented as part of a discussion of deep-ocean currents, and the conveyer-belt circulation’s relationship to climate is addressed. The chapter ends by evaluating the potential of using ocean currents as an energy source and the advantages and pitfalls of doing so.

Essential Concepts 7.1 Demonstrate an understanding of how ocean currents are measured.

7.2 Explain the origin of ocean surface currents and how surface circulation patterns are organized globally.

7.3 Describe the conditions that produce upwelling.

7.4 Specify the main surface circulation patterns in each ocean basin.

7.5 Describe how sea ice and icebergs form.

7.6 Explain the origin and characteristics of deep-ocean currents.

7.7 Evaluate the advantages and disadvantages of harnessing currents as a source of energy.

Chapter Outline 7.1 How Are Ocean Currents Measured?

7.1.1 Surface Current Measurement 7.1.1.1 Direct Methods 7.1.1.2 Indirect Methods 7.1.2 Deep Current Measurement Diving Deeper 7.1 Oceans and People Running Shoes as Drift Meters: Just Do It 7.2 What Creates Ocean Surface Currents and How Are They Organized?

7.2.1 Origin of Surface Currents 7.2.2 Main Components of Ocean Surface Circulation 7.2.2.1 Subtropical Gyres Web Animation: Ocean Circulation 7.2.2.1.1 Equatorial Currents 7.2.2.1.2 Western Boundary Currents SmartTable 7.1: Subtropical gyres and surface currents 89 .

SmartFigure 7.5: Wind-driven surface currents 7.2.2.1.3 Northern or Southern Boundary Currents 7.2.2.1.4 Eastern Boundary Currents Web Video: Perpetual Ocean by NASA 7.2.2.2 Equatorial Countercurrents 7.2.2.3 Subpolar Gyres 7.2.3 Other Factors Affecting Ocean Surface Circulation 7.2.3.1 Ekman Spiral and Ekman Transport Web Animation: Ekman Spiral and Ekman Transport SmartFigure 7.7: The Ekman spiral produces Ekman transport 7.2.3.2 Geostrophic Currents 7.2.3.3 Western Intensification of Subtropical Gyres 7.2.4 Ocean Currents and Climate SmartTable 7.2: Characteristics of western and eastern boundary currents of subtropical gyres 7.3 What Causes Upwelling and Downwelling?

7.3.1 Diverging Surface Water 7.3.2 Converging Surface Water 7.3.3 Coastal Upwelling and Downwelling Web Animation: Ekman Spiral and Coastal Upwelling/Downwelling SmartFigure 7.12: Coastal upwelling and downwelling 7.3.4 Other Causes of Upwelling 7.4 What Are the Main Surface Circulation Patterns in Each Ocean Basin?

7.4.1 Antarctic Circulation 7.4.1.1 Antarctic Circumpolar Current 7.4.1.2 Antarctic Convergence and Divergence 7.4.2 Atlantic Ocean Circulation 7.4.2.1 The North and South Atlantic Subtropical Gyres 7.4.2.2 The Gulf Stream 7.4.2.2.1 The Sargasso Sea 7.4.2.2.2 Warm- and Cold-Core Rings 7.4.2.3 Other North Atlantic Currents 7.4.2.4 Climatic Effects of North Atlantic Currents 7.4.3 Indian Ocean Circulation 7.4.3.1 Monsoons Diving Deeper 7.2 Historical Feature. Benjamin Franklin: The World’s Most Famous Physical Oceanographer 7.4.3.2 Indian Ocean Subtropical Gyre 7.4.3.3 Leeuwin Current 7.4.4 Pacific Ocean Circulation 7.4.4.1 Normal Conditions 7.4.4.1.1 North Pacific Subtropical Gyre 7.4.4.1.2 South Pacific Subtropical Gyre 7.4.4.2 Fisheries and the Peru Current SmartFigure 7.22: Normal, El Niño, and La Niña conditions 7.4.4.3 Walker Circulation

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7.4.4.4 Pacific Warm Pool 7.4.4.5 El Niño–Southern Oscillation (ENSO) Conditions 7.4.4.5.1 ENSO Warm Phase (El Niño) 7.4.4.5.2 ENSO Cool Phase (La Niña) Web Video: Weekly Pacific Sea Surface Temperature Anomalies 7.4.4.5.3 How Often Do El Niño Events Occur?

7.4.4.5.4 Effects of El Niños and La Niñas 7.4.4.5.5 Examples from Recent El Niños 7.4.4.6 The 1982–1983 El Niño 7.4.4.7 The 1997–1998 El Niño 7.4.4.8 The 2015–2016 El Niño 7.4.4.8.1 Predicting El Niño Events 7.5 How Do Sea Ice and Icebergs Form?

7.5.1 Formation of Sea Ice 7.5.2 Formation of Icebergs 7.5.2.1 Shelf Ice 7.6 How Do Deep-Ocean Currents Form?

7.6.1 Origin of Thermohaline Circulation 7.6.2 Sources of Deep Water SmartFigure 7.30 Atlantic Ocean subsurface water masses.

7.6.3 Worldwide Deep-Water Circulation 7.6.3.1 Conveyer-Belt Circulation Web Animation: North Atlantic Deep-Water Circulation Web Animation: Deep-Ocean Conveyer-Belt Circulation 7.6.3.2 Dissolved Oxygen in Deep Water 7.6.3.3 Conveyer-Belt Circulation and Climate Change 7.7 Can Power from Currents Be Harnessed as a Source of Energy?

Essential Concepts Review

Learning Outcomes The instructional objectives are performance-based and detail specific learning outcomes for Chapter 7.

The test items contained in the Test Bank are keyed to the learning objectives and the Chapter in Review at the end of the chapter. The order of the objectives mirrors the content presentation in Chapter 7.

Upon completion of this chapter, the student should be able to: 1. Distinguish between wind-driven (or surface) and density-driven (or deep) ocean currents.

2. Describe methods used to measure the flow rate of surface currents, including: a. direct methods of flow measurement b. indirect methods such as internal density distribution/pressure gradient measurements, radar altimeter, and Doppler flow meter 3. Detail how deep current flow rates are estimated.

4. Define gyre and describe its formation.

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5. List the five subtropical gyres and describe their location.

6. Explain the formation of equatorial currents.

7. Discuss the relationship between the Coriolis effect and western boundary currents in gyres.

8. Give the physical characteristics of western boundary currents.

9. Give the physical characteristics of eastern boundary currents.

10. Differentiate between northern boundary currents and southern boundary currents, describing the location and direction of flow for each in both hemispheres.

11. Distinguish between equatorial currents and equatorial countercurrents.

12. Discuss the formation of the subpolar gyres and describe their location.

13. Describe the Ekman spiral and detail its implications for ocean water circulation.

14. Give the direction of Ekman transport in the Northern and Southern Hemispheres.

15. Define geostrophic current and give an example.

16. Discuss the factors that contribute to western intensification of subtropical gyres.

17. Differentiate between upwelling and downwelling and relate these phenomena to surface-water productivity in these areas.

18. Describe the causes of upwelling and list the places where upwelling would occur.

19. List, describe the location, and give the physical characteristics (temperature, size, etc.) of the major surface ocean currents, including: A. B. C. D. E. F. G. H. I. J. K. L.

Antarctic Circumpolar Current (West Wind Drift) East Wind Drift Atlantic Equatorial Countercurrent South Equatorial Current Brazil Current Benguela Current Gulf Stream North Equatorial Current Antilles Current Caribbean Current Florida Current Labrador Current

M. Irminger Current N. Norwegian Current O. North Atlantic Current P. Canary Current Q. Kurishio Current R. North Pacific Current S. California Current T. Alaskan Current U. East Australian Current V. Peru Current W. Agulhas Current X. West Australian Current Y. Leeuwin Current

20. Detail the relationship between global wind belts in tropical areas and seasonal variation in precipitation and temperature patterns (monsoons).

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21. Discuss the El Niño-Southern Oscillation (ENSO) in the Pacific Ocean, detailing the effects of ENSO on global weather patterns.

22. Describe the effects of El Niños and La Niñas on regional weather in the United States.

23. Differentiate between sea ice, shelf ice, and icebergs, and describe the formation of each.

24. Explain how water density drives thermohaline circulation.

25. List the source and location and describe the process of bottom-water (deep-water) formation.

26. Outline the conveyer-belt circulation model for ocean water.

27. Discuss how conveyer-belt circulation can affect climate, and how climate change can impact it.

Teaching Strategies Make sure students have a thorough understanding of wind belts and the Coriolis effect. Surface winds drive surface ocean currents and the Coriolis effect influences surface-water movement and Ekman transport.

If you want students to deeply understand the connection between the surface currents and the atmosphere, give them a blank map of the world and have them draw the major ocean surface currents and wind belts.

Some students have difficulty grasping the concept of the thermohaline conveyer-belt circulation. This is a case where it is useful to rely on an animation rather than a static drawing of this current.

Consider using real-time sea surface temperature (SST) data from NOAA when teaching about ENSO. Help students understand what an anomaly is and why they are important in scientific studies such as these. Have students decide for themselves, based on SST anomalies, whether there is an El Niño or La Niña event building or if there are normal conditions.

Teacher’s Resources Films ▪ ▪ ▪ ▪ ▪ ▪ ▪

The Gulf Stream (Bullfrog Films), 28 minutes The Ocean Currents (McGraw-Hill), 17 minutes The Upwelling Phenomenon (Counselor Films, Inc.), 15 minutes Vermilion Sea Expeditions: Hydrographic Work (University of California), 13 minutes Chasing El Niño (NOVA, PBS), 52 minutes The Weather (BBC), 240 minutes, but broken into much shorter topics that may stand alone, including a segment on the thermohaline conveyer The Habitable Planet #3: Oceans (Harvard Smithsonian Center for Astrophysics), 30 minutes, http://learner.org/resources/series209.html

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Websites ● ● ● ●

www.esrl.noaa.gov/psd/enso/—National Oceanic and Atmospheric Administration (NOAA) ENSO page www.climate.gov/enso—ENSO’s current status, NOAA www.learner.org/courses/envsci/unit/unit_vis.php?unit=3—The Habitable Planet: Oceans, Visuals; short animations and films illustrating ENSO https://www.ametsoc.org/index.cfm/ams/education-careers/education-program/k-12teachers/maury-project/—American Meteorological Society teacher outreach

Concept Check (Questions and Answers) 7.1 How Are Ocean Currents Measured?

1. Compare the forces that are directly responsible for creating horizontal and deep vertical circulation in the oceans. What is the ultimate source of energy that drives both circulation systems?

Horizontal ocean currents derive their energy directly from the wind. Vertical circulation is driven by density changes in surface water. This circulation is initiated by the creation of dense surface water in the high latitudes of the Atlantic Ocean where water temperatures are low, and salinity is increased during the winter months due to ice formation. The Sun is the ultimate source of energy for both circulation systems.

2. Describe the different ways in which currents are measured.

Surface currents can be measured either directly or indirectly: ●

●

Direct current measurement is accomplished by releasing a device that is transported by the current and is tracked through time, or by lowering into the water from a stationary position a current-measuring device capable of measuring flow rates (usually with a propeller).

Indirect current measurement is completed in one of three ways: by determining the internal distribution of density and the corresponding pressure gradient across an area of the ocean; by using radar altimeters mounted on satellites to determine the shape of the ocean surface (dynamic topography) from which current flow is inferred; or by using low-frequency sound signals sent through the ocean to determine differences in pressure, which indicate current movement.

Deep currents can be measured by using various drift devices, by detecting the presence of a telltale chemical tracer, or by measuring the distinctive temperature and salinity of a deep-water mass.

7.2 What Creates Ocean Surface Currents and How Are They Organized?

1. How many subtropical gyres exist worldwide? How many main currents exist within each subtropical gyre?

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There are five subtropical gyres: North Pacific, South Pacific, North Atlantic, South Atlantic, and the Indian Ocean below the equator. There is land above the equator at 30 degrees north, so no gyres form at this location; rather, this area experiences seasonal reversing monsoons. Each subtropical gyre has four currents: two that follow the wind belts traveling roughly east or west and two that are boundary currents that are deflected by land that travel either toward or away from the polar region. Of the latter two, one is western intensified or western boundary current and the other is eastern boundary current.

2. On a base map of the world, plot and label the major currents involved in the surface circulation gyres of the oceans. Use colors to represent warm versus cool currents and indicate which currents are western intensified. On an overlay, superimpose the major wind belts of the world on the gyres, and describe the relationship between wind belts and currents.

The map should resemble Figure 7.5, with the westerly boundary currents of all subtropical gyres marked as western intensified. The overlay should show that there is a correlation between ocean surface currents and the major wind belts of the world (refer to Figure 6.12); this makes sense because the surface currents are wind induced.

3. Explain why the subtropical gyres in the Northern Hemisphere move in a clockwise fashion while the subpolar gyres rotate in a counterclockwise pattern.

In the Northern Hemisphere, differences in pressure cause a clockwise flow of air around highpressure cells (anticyclonic flow; associated with subtropical gyres). Conversely, a counterclockwise flow of air occurs around low-pressure cells (cyclonic flow; associated with subpolar gyres). This movement of air drives the surface currents. As mentioned in Chapter 6, the screwdriver analogy applies here: to tighten a screw (equivalent to high pressure), the screwdriver is turned clockwise; to loosen a screw (equivalent to low pressure), the screwdriver is turned counterclockwise.

4. Diagram and discuss how Ekman transport produces the “hill” of water within subtropical gyres that causes geostrophic current flow. As a starting place on the diagram, use the wind belts (the trade winds and the prevailing westerlies). What causes the apex of the geostrophic “hills” to be offset to the west of the center of the ocean gyre systems?

In the Northern Hemisphere, the trade winds and the prevailing westerlies (dashed lines in the figure above) create a westerly and easterly current, respectively, flowing at 45 degrees to the 95 .

right of the winds. The Coriolis effect creates a clockwise flow as continents interrupt the currents. Ekman transport (solid lines with closed arrows in the figure above) shows a net transport of water at an angle of 45 degrees to the right of the surface current (in the Northern Hemisphere), pushing water toward the center of the rotating gyre.

The offset of the geostrophic “hills” to the west of center in ocean gyres is a result of an equilibrium reached among a number of forces, but the primary factor is the increasing strength of the Coriolis effect with latitude.

5. Describe western intensification, including the characteristics of western and eastern boundary currents of subtropical gyres.

The western intensification of the western boundary current is partly the result of the change in strength of the Coriolis effect with latitude and wind stress curl in combination with land blocking the equatorial current from just following the wind around the Earth. The Coriolis effect and Ekman transport deflect some of the water following the trade wind belt to flow slightly to the right in the Northern Hemisphere and slightly to the left in the Southern Hemisphere. This wind belt is close to the equator, and the Coriolis effect is very small here. On the other hand, the westerlies between 30 and 60 degrees drag surface waters along with it, and the Coriolis effect is stronger at this location, deflecting more water away from the intended path. Thus, in the Northern Hemisphere subtropical gyres, more water is deflected to the south from higher latitudes and less deflected to the north from lower latitudes. The result is that the rotational centers are shifted to the west along the 30-degree line.

7.3 What Causes Upwelling and Downwelling?

1. Draw and describe several different oceanographic conditions that produce upwelling. ● ● ● ● ● ●

Current divergence (equatorial upwelling) is caused when surface waters move away from an area on the ocean’s surface.

Ekman transport (coastal upwelling) occurs where surface water is moved away from shore.

Offshore winds move water away from shore.

Sea-floor obstructions restrict the flow of water and cause it to rise to the surface.

Coastline geometry produces upwelling where a sharp bend in the coastline causes deep water to surface.

High-latitude regions have upwelling because there is no pycnocline to present vertical water movement.

2. Explain why upwelling areas are associated with an abundance of marine life.

The areas of upwelling are rich in dissolved oxygen and nutrients that were hoisted up from the deeper ocean into the photic zone where primary producers and microorganisms, the base of the food web, can take advantage of all the necessities for life: light, nutrients, and water.

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7.4 What Are the Main Surface Circulation Patterns in Each Ocean Basin?

1. Explain why Gulf Stream eddies that develop northeast of the Gulf Stream rotate clockwise and have warm-water cores, whereas those that develop to the southwest rotate counterclockwise and have cold-water cores.

Since eddies are formed by the pinching-off of the meanders, the water is following a clockwise path in the meanders on the northwest side of the Gulf Stream and a counterclockwise path on the southeast side. This pattern of movement is maintained in the pinched-off meanders.

2. Describe changes in atmospheric pressure, precipitation, winds, and ocean surface currents during the two monsoon seasons of the Indian Ocean.

During the winter, the typical northeastern trade winds are called northeast monsoons. The rapid cooling of air over the Asian mainland during the winter strengthens them. This creates a highpressure cell that forces atmospheric masses off the continent and out over the ocean, where the air pressure is lower.

During the summer, the Asian mainland warms faster than the oceanic water. This results in a summer low-pressure cell developing over the continent, allowing high-pressure air to reverse direction and move from the Indian Ocean onto the Asian landmass. This produces the southeast monsoon that may be thought of as a continuation of the southeast trade winds across the equator. During this season, the North Equatorial Current disappears and is replaced by the Southeast Monsoon Current. It flows from west to east across the northern Indian Ocean. In September or October, the northeast trade winds are reestablished, and the North Equatorial Current reappears.

3. Describe changes in atmospheric and oceanographic phenomena that occur during El Niño/La Niña events, including changes in atmospheric pressure, winds, Walker Circulation, weather, equatorial surface currents, and coastal upwelling/downwelling, and the abundance of marine life, SST and the Pacific Warm Pool, sea-surface elevation, and position of the thermocline.

During El Niño events, the Walker Circulation between the southeastern Pacific high-pressure cell and the Indonesian low-pressure cell is weakened. Since this circulation reinforces the equatorial trade winds, they weaken and may even reverse themselves. With no trade winds pushing equatorial water into the dome of warm water (the Pacific Warm Pool) that forms near Indonesia, this water pushes east along the equator, aided by a strengthened equatorial countercurrent. The Pacific Warm Pool spreads along the equator and even as far as the coasts of North and South America. Its arrival manifests as high-SST anomalies in eastern Pacific waters. This wedge of warm water causes the thermocline to be abnormally deep and suppresses upwelling. In some cases, the sloshing of warm water against the western coast of South America causes downwelling. The lack of upwelling limits primary productivity in surface waters, causing marine life to be much less abundant.

In severe El Niños, worldwide weather patterns are disrupted that could cause local weather to be wetter, drier, hotter, or colder than normal, depending on the areas. Typically, severe El Niño events cause flooding, coastal erosion, and impacts on marine life along the eastern Pacific and droughts and wildfires on the western Pacific and Indian Oceans. Refer to Figures 7.22a and 7.22b for other global effects.

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4. How often do El Niño events occur? Using Figure 7.24, determine how many years since 1950 have been El Niño years. Has the pattern of El Niño events occurred at regular intervals?

El Niño events have occurred irregularly at intervals of 2–10 years. Since 1950, there have been 13 El Niño events of varying strength, the strongest of which occurred in 1982–1983. Figure 7.24 shows that the pattern of El Niño events does not occur at regular intervals.

5. How is La Niña different from El Niño? Describe the pattern of La Niña events in relation to El Niños since 1950 (see Figure 7.24).

La Niña is a cooling of surface ocean temperatures in the eastern Pacific, which commonly occurs following an El Niño. La Niña is characterized by trade winds that are very strong and surface waters in the equatorial South Pacific that are cooler than usual. Figure 7.24 shows that since 1950, conditions in the tropical Pacific have oscillated between La Niña and El Niño events, and that “normal conditions” have occurred rarely.

6. Describe the global effects of severe El Niños.

Severe El Niño events are associated with significant changes in global weather patterns (see Figure 7.25). Severe drought and brush fires in Australia, cold wet winters in the southeastern United States, drought in the intermountain western United States, and an active Pacific Ocean typhoon season are all effects of a strong El Niño event. Corals in the western portion of the South Pacific Ocean are stressed due to unusually high water temperatures, while primary productivity in the eastern Pacific Ocean significantly decreases, negatively impacting commercial fishing and marine wildlife.

7.5 How Do Sea Ice and Icebergs Form?

1. Why does the formation of sea ice tend to be a self-perpetuating process?

Sea ice forms over the surface, slowing down the swell/wave action. Slower water freezes easier than fast-moving water at the same temperature.

2. Describe differences between sea ice, icebergs, and shelf ice, including how each is formed.

Sea ice is ice that forms directly from freezing seawater on the ocean surface, in contrast to icebergs that are pieces of a land-based glacier that break away from the glacier and float out to sea. Shelf ice is thick, floating sheets of ice that are formed when the edges of glaciers break off into the ocean.

7.6 How Do Deep-Ocean Currents Form?

1. Discuss the origin of thermohaline vertical circulation. Why do deep currents form only in high-latitude regions?

In low-latitude regions, the temperature of the water is too high to become dense enough to sink, even when high salinity values develop, as they do in the subtropics. As a result, deep currents only form in high latitudes. Even in high-latitude regions where the surface-water temperatures are always low, sinking may only take place during the winter when sea-ice formation increases surface-water salinity.

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2. Using Figure 7.29, notice that AAIW and NACSW fall on the same density line. What single measurement would allow you to tell them apart? Explain.

AAIW is colder and less saline than NACSW, so you would be able to tell them apart by measuring either the salinity or temperature.

3. What are the two major deep-water masses? Where do they form at the ocean’s surface?

North Atlantic Deep Water forms in the Norwegian Sea and off the tip of Greenland in the North Atlantic Ocean. Antarctic Bottom Water forms primarily as a result of the mixing of water in the Weddell Sea with water from the West Wind Drift.

4. Explain why no matter where you are in the ocean, if you go deep enough, you will encounter Oceanic Common Water.

As you go deeper in the ocean below the surface currents, the deep currents dominate and move about the world’s oceans very slowly through the global conveyer system.

5. Describe how the distribution of life in the ocean would be different if there were very little dissolved oxygen in deep-water currents.

As the oxygen content in the deep ocean decreases, so does the life in the ocean. This has happened in Earth’s past during the carboniferous period. Warm anoxic oceans meant less life.

7.7 Can Power from Currents Be Harnessed as a Source of Energy?

1. Explain why ocean currents have the potential to generate even more power than wind farms, which are much more common today.

Ocean currents carry much more energy than wind because water has about 800 times the density of air.

2. Discuss the advantages and disadvantages of building an offshore current power system.

Advantages are the swell is always there to some degree or another and can be harnessed. The disadvantage of harnessing the wave energy on a large scale is that it changes the coastal environment. Also, biofouling is unavoidable, and the power system will have to be cleaned, much like keeping a boat hull clean of sea life.

Critical Thinking Questions (and Answers) 7.1 Compare and contrast the characteristics and origins of surface currents and deep currents.

The main differences are how they are generated and their speed. Surface currents are generated by surface wind belts and are much faster than deep currents. Surface currents are measured by drift meters, which measure the speed of the current they are drifting along with; stationary meters, which measure the flow of water past them; and satellite measurement. The angle of the surface measured by the satellite represents the speed of the current.

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Deep currents are measured by radioactive isotope and other tracers both man-made and natural.

These currents move extremely slowly.

7.2 From memory, construct a map showing the world’s five subtropical gyres, including nearby continents. For each gyre, name the main currents involved, including any that experience western intensification.

The diagram should resemble SmartFigure 7.5. Currents that experience western intensification are the Kuroshio Current, Gulf Stream, Agulhas Current, East Australian Current, and Brazil Current.

7.3 From a practical standpoint, give several reasons why upwelling is a much more intensely studied process than downwelling. For example, why are the world’s major fisheries associated with areas of upwelling?

Areas of upwelling are of more commercial value as well as a result of high-productivity regions of the oceans. Upwelling brings cooler waters and nutrients to the surface, and this attracts large numbers of fish.

7.4 Using Figure 7.22, specify the atmospheric and oceanic changes that occur between normal and El Niño conditions. Also, compare normal and La Niña conditions.

Under normal conditions, there is upwelling off the west coast of South America, equatorial currents blow east to west, low pressure exists near New Zealand and high pressure exists off the west coast of South America, and there is a prominent Walker circulation cell.

Under El Niño conditions, the Walker cell circulation is reversed, upwelling ceases, equatorial surface currents blow west to east, and there is high pressure near New Zealand and low pressure near South America’s west coast.

La Niña conditions resemble normal conditions, but they are intensified. Upwelling is stronger and more prominent, Walker circulation is stronger, the equatorial surface current flows more intensely from east to west, and the low pressure near New Zealand and the high pressure off the coast of South America are intensified.

7.5 Specify the places in the world where most icebergs form. What hazards do icebergs present?

Explain.

Most icebergs form in the North Atlantic and near Antarctica. In the North Atlantic, they pose a danger to ship traffic. The Titanic was sunk because of an iceberg.

7.6 Antarctic Intermediate Water can be identified throughout much of the South Atlantic based on its temperature, salinity, and dissolved oxygen content. Why is it colder and less salty—and why does it contain more oxygen—than the surface-water mass above it and the North Atlantic Deep Water below it?

The Antarctic Intermediate Water forms at the surface and sinks at the Antarctic Convergence. Since it has recently left the surface of the ocean where the water is cold and has a relatively low salinity, it has a high capacity for holding atmospheric oxygen and a high level of diatom productivity around the Antarctic. Thus, it has a lower temperature and salinity and a higher dissolved oxygen concentration than the surface mass above it and the North Atlantic Deep Water mass beneath it.

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7.7 What are some environmental factors that could inhibit the development of offshore ocean current power systems?

Destruction of marine habitat in the coastal regions and cost to maintain such a power plant at sea.

Active Learning Exercises 7.1 Working with another student in class, compile a list of the ways in which both surface and deep currents are measured.

Surface currents: Floating drift meters, accidentally released items in currents, propeller flow meter, measuring pressure gradients in ocean’s surface, radar altimeters, and Doppler flow meters.

Deep currents: Argo profiling floats, measuring temperature and salinity characteristics of deepwater masses, and tracking telltale tracers.

7.2 With another student in class, describe what the pattern of ocean surface currents would look like if there were no continents on Earth.

Continents help to generate the oceanic gyres we see today. If continents did not exist, ocean currents would very closely mirror the winds in the major wind belts of Earth. Thus, in each hemisphere there would be a current between 0 and 30 degrees latitude associated with the trade winds; another current between 30 and 60 degrees latitude, which is generated by the westerlies; and a current between 60 degrees latitude and the pole, which is a result of the polar easterlies.

7.3 Working with another student in class, discuss this question: If Earth’s rotation on its axis were to suddenly stop, how would it affect the processes that cause both upwelling and downwelling?

If Earth were to stop spinning, atmospheric circulation as we know it would also cease. Equatorial upwelling is a direct result of the southeast trade winds causing surface waters to diverge, so that process would also stop. Coastal upwelling is produced by winds blowing parallel to the coastline.

Stopping Earth’s rotation would cause those winds to stop as well, and water would no longer diverge from the coastline, allowing for upwelling.

Downwelling can be caused by convergence surface currents, which are wind generated as well.

Coastal downwelling is also generated by winds blowing parallel to a coastline in the opposite direction of winds that cause upwelling. Stopping Earth’s rotation and stopping those winds would bring an end to downwelling.

7.4 During flood stage, the largest river in the world—the mighty Amazon River— dumps 200,000 cubic meters of water into the Atlantic Ocean each second. With another student in class, compare its flow rate with the volume of water transported by (1) the West Wind Drift and (2) the western-intensified Gulf Stream. How many times larger than the Amazon is each of these two ocean currents?

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The West Wind Drift transports more water than any other ocean surface current, and its flow amounts to 130,000,000 cubic meters per second. This is 129,800,000 more cubic meters per second more than the Amazon.

The western-intensified Gulf Stream transports 30,000,000 cubic meters per second, which is 29,800,000 more cubic meters per second than the Amazon.

The Amazon River’s flow rate at flood stage of 200,000 cubic meters of water per second equals 0.2 Sverdrups (remember that 1 Sverdrup=1 million cubic meters per second).

Flow Rate (Sverdrups) Magnitude (X larger than Amazon)

Amazon River 0.2

Gulf Stream West Wind Drift 90 190

______

450

950

7.5 Using the Internet and working with another student in class, find three instances within the past 10 years where icebergs have been involved in oceanic shipping or transportation accidents (or near accidents). Specify where the incidents took place.

Students may find various incidents. Their list might include: Explorer—2007, Antarctica Fram—2007, Antarctica Between 1980 and 2005, there were 57 documented ship–iceberg incidents in the Atlantic.

7.6 The density T–S graph shown as Figure 7.29 shows that the Antarctic Intermediate Water (AAIW) has about the same density as the North Atlantic Central Surface Water (NACSW). With another student in class, discuss how you can differentiate the two water masses based on physical properties (not just their locations). As a group, explain how it is possible that these two distinct water masses have nearly the same density.

The T–S diagram does not only reflect the densities of these masses of water. You could differentiate between the AAIW and the NACSW based on their salinities and/or their temperatures. The NACSW has both a higher salinity and a higher temperature than does the AAIW. Higher salinity causes the density of a mass of water to increase, but a higher temperature causes the density to decrease. Even though the AAIW is less saline than the NACSW, it is colder. The difference in temperature offsets the difference in salinity, allowing these two different water masses to have the same density.

7.7 With another student in class, discuss the advantages of current power devices that are attached to the sea floor and capable of operating in two or more directions.

Current power devices that are attached to the sea floor can be placed in water that has strong currents. Stronger currents are capable of generating a great deal of electricity relative to weaker currents. Devices that can swivel or operate in two or more directions can take advantage of any changes in current flows and continue to operate and provide energy.

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Additional Active Learning Exercises 7.4 ENSO events can impact weather conditions globally. Use the Internet to determine how ENSO warm and cold events affect weather in your area.

Answers will vary. For impacts in the United States, this website has good information: https://www.weather.gov/mhx/ensowhat.

7.7 If you were in charge of identifying a location for a new ocean current power system, where would you suggest the system be built? Explain using what you have learned about currents.

Answers will vary, but students should identify a western boundary current for maximum power generation. They should also take into account the distance between their station and a population center that could use the energy. Students may also consider the local weather and sea conditions. Ideally, the station should be located somewhere with little risk of damage from strong storms or waves.

Exploring Data SmartFigure 7.7 Describe how the Ekman spiral and Ekman transport are related to one another.

The Ekman spiral describes the direction and speed of water at various depths. The Coriolis effect deflects wind-driven surface water at a 45-degree angle to the right of the direction of the wind (Northern Hemisphere). The surface water sets layers below it in motion and when they begin to move, they are also deflected by the Coriolis effect 45 degrees to the right.

Ekman transport describes the average movement of the entire water column. Ekman transport moves water 90 degrees to the right of the wind direction (Northern Hemisphere).

Figure 7.9 Explain why ocean temperatures, which are represented by different colors in the figure, don’t follow lines of latitude that continue horizontally across the maps.

Ocean temperatures generally follow lines of latitude, but are modified by surface ocean currents.

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SmartFigure 7.12 Draw similar diagrams for the west coasts of the Southern Hemisphere, showing the same wind directions that parallel the coast, and describe differences in Ekman transport and upwelling/downwelling.

In the Southern Hemisphere, a wind blowing north to south along a west coast would produce downwelling because the Coriolis effect would deflect the water to the left and Ekman transport would move the water at a 90-degree angle to the left of the wind direction (onshore). A wind blowing from south to north would produce upwelling as the water would be moved offshore at a 90-degree angle to the direction of the wind.

Figure 7.16 1. According to the figure, what is the maximum flow rate in Sverdrups for the Gulf Stream? What is the flow rate in Sverdrups for the Canary Current? (Hint: Estimate!)

According to the figure, the maximum flow rate for the Gulf Stream is 100 Sverdrups and the maximum flow rate for the Canary Current is 4 Sverdrups.

2. According to the figure, what happens to surface waters once they reach the vicinity of Iceland? Using the physical properties of water, explain why the water does this.

According to the figure, surface waters sink when they near Iceland. As the water moves north, it gets colder and denser and eventually sinks.

Figure 7.19 Describe the differences in winds and surface currents between the Indian Ocean’s winter monsoon (part a) and its summer monsoon (part b).

In the winter, the air over the Asian mainland cools, creating a high-pressure zone. The wind blows from Southwest Asia off the continent and out over the ocean. In the summer, the continent warms, creating a low-pressure zone. The wind reverses, blowing from the ocean over the continent.

During the winter, offshore winds cause the North Equatorial Current to flow from east to west and the Somali Current flows south along the coast of Africa. An Equatorial Countercurrent is also established.

During the summer, the winds reverse, causing the North Equatorial Current to be replaced by the Southwest Monsoon Current, which flows in the opposite direction. The winds cause the Somali Current to reverse as well, and the North Equatorial Current reappears.

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SmartFigure 7.22 1. Carefully compare normal conditions (part a) with El Niño conditions (part b).

Describe at least eight separate items that are different between the two diagrams.

2. Carefully compare normal conditions (part a) with La Niña conditions (part c).

Describe at least eight separate items that are different between the two diagrams.

Figure 7.24 1. In this figure, “normal” conditions are represented by values that have an ENSO Index of positive or negative 0.5, with higher positive values representing El Niño conditions and lower negative values representing La Niña conditions. Knowing this, describe the conditions of the tropical Pacific since 1950.

El Niño conditions and La Niña conditions tend to alternate, but the overall pattern is highly irregular.

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2. On average, how long do El Niño conditions last? What about La Niña conditions?

El Niño and La Niña conditions occur for similar amounts of time. On average, they last for 12–18 months.

7.29 1. On an oceanographic research cruise, you take a sample of deep-ocean water that has a temperature of 4.5°C and a salinity of 34.1‰. Which water mass is it from, and what is its density?

The sample is from AAIW. The density is about 1.0270 g/cm3 2. On the same oceanographic research cruise, you take another sample of deep-ocean water that has a temperature of 4°C and a salinity of 35.0‰. Which water mass is it from, and what is its density? (Hint: Estimate!)

The sample is from NADW. The density is about 1.0278 g/cm3.

7.30 In almost all ocean basins, if you go deep enough, you will eventually encounter Antarctic Bottom Water. Explain why this is true.

Antarctic Bottom Water is the densest water in the open ocean, so it will almost always be found at the bottom of an ocean basin.

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Chapter 8 Waves and Water Dynamics Overview This chapter explores wave and water dynamics and begins with an introduction to waves and their movement by examining the forces that produce waves. Wave characteristics are presented, including aspects of circular orbital motion and the differences between deep-water and shallow-water waves. The chapter also includes a description of wind-generated ocean waves, where the terms “sea” and “swell” are defined. The unusual oceanographic conditions that generate rogue waves are also discussed. Once waves reach shallow water, they become breaking waves and may undergo physical changes that are described under the headings Surf, Wave Refraction, and Wave Reflection. Tsunami, a special type of longwavelength wave, can produce severe coastal damage. Descriptions of some historically important tsunami are included, as well as a discussion of the Pacific’s tsunami warning system. The chapter concludes with a consideration of power generated by wave energy.

Essential Concepts 8.1 Demonstrate an understanding of how waves are generated and how they move.

8.2 Describe the characteristics of waves.

8.3 Discuss how wind-generated waves develop.

8.4 Explain how waves change in the surf zone.

8.5 Specify the origin and characteristics of tsunami.

8.6 Evaluate the advantages and disadvantages of harnessing waves as a source of energy.

Chapter Outline 8.1 How Are Waves Generated, and How Do They Move?

8.1.1 Disturbances Generate Ocean Waves 8.1.2 Wave Movement 8.2 What Characteristics Do Waves Possess?

8.2.1 Wave Terminology 8.2.2 Circular Orbital Motion Web Animation: Wave Circular Orbital Motion SmartFigure 8.5: A floating rubber ducky shows circular orbital motion 8.2.3 Deep-Water Waves 8.2.4 Shallow-Water Waves 8.2.5 Transitional Waves 8.3 How Do Wind-Generated Waves Develop?

8.3.1 Wave Development 8.3.1.1 Capillary Waves, Gravity Waves, and the “Sea” 8.3.1.2 Factors Affecting Wave Energy SmartTable 8.1: Beaufort wind scale and the state of the sea 8.3.1.3 How High Can Waves Be? 107 .

8.3.1.4 Fully Developed Sea 8.3.1.5 Swell 8.3.2 Interference Patterns 8.3.2.1 Constructive Interference 8.3.2.2 Destructive Interference 8.3.2.3 Mixed Interference SmartFigure 8.15: Constructive, destructive, and mixed interference produce a variety of wave patterns 8.3.3 Rogue Waves Web Animation: Interference Patterns in Waves 8.4 How Do Waves Change in the Surf Zone?

8.4.1 Physical Changes as Waves Approach Shore Web Animation: Wave Motion and Wave Reflection 8.4.2 Breakers and Surfing 8.4.3 Wave Refraction Web Animation: Three Types of Breakers SmartFigure 8.21: Wave refraction Web Animation: Wave Motion and Wave Refraction SmartFigure 8.22: Wave reflection and constructive interference at The Wedge, Newport Harbor, California.

8.4.4 Wave Reflection 8.4.4.1 The Wedge: A Case Study of Wave Reflection and Constructive Interference 8.4.4.2 Standing Waves, Nodes, and Antinodes 8.5 How Are Tsunami Created?

SmartFigure 8.25: Tsunami generation, propagation, and destruction Web Animation: Tsunami 8.5.1 Coastal Effects 8.5.2 Some Examples of Historic and Recent Tsunami 8.5.2.1 The Cascadia Earthquake and Tsunami (1700) 8.5.2.2 The Eruption of Krakatau (1883) 8.5.2.3 Indian Ocean (2004) 8.5.2.4 Japan (2011) 8.5.2.5 Tsunami Warning System Diving Deeper 8.1 Oceans and People Waves of Destruction: The 2011 Japanese Tsunami 8.5.2.6 Tsunami Watches and Tsunami Warnings 8.5.2.7 Effectiveness of Tsunami Warnings 8.6 Can Power from Waves Be Harnessed as a Source of Energy?

8.6.1 Wave Power Plants and Wave Farms SmartFigure 8.32: How a wave power plant works 8.6.2 Global Coastal Wave Energy Resources Essential Concepts Review

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Learning Outcomes The instructional objectives are performance-based and detail specific learning outcomes for Chapter 8.

The test items contained in the Test Bank are keyed to the learning objectives and the Chapter in Review at the end of the chapter. The order of the objectives mirrors the content presentation in Chapter 8.

Upon completion of this chapter, the student should be able to: 1. List the factors that produce waves.

2. Differentiate between ocean waves, atmospheric waves, and internal waves.

3. Distinguish between splash waves, seismic sea waves (tsunami), and tides.

4. Describe the differences in the direction of water movement among longitudinal, transverse, and orbital waves.

5. Define the following wave characteristics and, where applicable, give the equation used to calculate the trait, including: a. crest b. trough c. wave height (H) d. wavelength (L) e. wave steepness f. wave period (T) g. frequency (f) 6. Explain the circular orbital motion of ocean water in relation to the movement of the waveform.

7. List the factors that affect the speed of deep-water waves.

8. Give the equation for calculating the wave speed (S) of deep-water waves.

9. List the factors that affect the speed of shallow-water waves.

10. Give the equation for calculating the wave speed (S) of shallow-water waves.

11. Discuss the development of wind-generated waves, including: a. capillary waves b. gravity waves c. “sea” d. swell 12. List the three factors that affect wave energy.

13. Describe the Beaufort Wind Scale and its relationship to the appearance of the ocean surface.

14. Differentiate between wave trains, wave dispersion, and decay distance in fully developed seas.

15. Distinguish between the effects of constructive interference, destructive interference, and mixed interference on waves.

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16. Define the surf zone.

17. Discuss the changes that waves undergo as they move from deep water to shallow water and move toward the shoreline.

18. Distinguish between a spilling breaker, a plunging breaker, and a surging breaker.

19. Describe the differences between wave refraction and wave reflection.

20. Define tsunami and describe the forces that produce these waves.

21. Discuss the effects of tsunami on coastal areas, and describe locations worldwide where tsunami occur.

22. List historical tsunami events and give their locations.

23. Discuss the Pacific Tsunami Warning Center (PTWC) and how tsunami watches and tsunami warnings are issued.

24. Understand the advantages and disadvantages of harnessing waves as an energy source.

25. Describe the LIMPET 500 and the potential for harnessing wave energy to generate electricity.

Teaching Strategies It may be helpful to give a little theory from the book and mix it in with some wave videos.

Surfers often know how a wave will behave without knowing why. After this chapter, they will know the “why” to their observations.

It is good to point out the different types of waves that exist, and note that there are many similarities in how they are described. Ask students what other types of waves with which they may be familiar, such as light waves and sound waves, and discuss how ocean waves are like these. Students who are not mathematically inclined may be put off by the equations in this chapter; use of visuals to illustrate the mathematical concepts here can be helpful in generating better understanding in the math phobic, as can showing both mathematically and nonmathematically how these principles work.

Point out that waves are a medium for the transport of energy and require a disturbance in order to occur. For the majority of waves, this disturbance comes from wind energy being transferred to wave energy. You might use the example of blowing on a cup of hot coffee: the surface is still until you blow across the top of it. Blowing generates capillary waves in the cup in much the same way as wind generates oceanic capillary waves on a much larger scale.

Having students understand the Beaufort wind scale can take advantage of common sense.

Rather than memorizing various wind speeds, have students make the connection between larger waves with more energy and stronger winds, as we see in SmartTable 8.1. You can connect these concepts to the length of time the wind blows coupled with wind energy as seen in Table 8.2 to tie these ideas together and have students really understand the wave energy.

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Many students struggle with understanding the wave interference patterns. Make use of SmartFigure 8.15 and the Web Animation on interference patterns in waves to help students visualize what these look like. Encourage them to use these resources on their own when studying if they still have difficulty understanding.

When discussing wave reflection, wave refraction, or even when deep-water waves become shallow-water waves, point out that at their most basic level, these are just instances of one mass colliding with another. Water, as a liquid, will bend or adjust to the shape of its container, and in this case it is a very large “container” to which water is adjusting.

Tsunami are a phenomenon all their own, and as the text points out, many people mistakenly call them “tidal waves.” In an oceanography course, it is important to point out how this is incorrect and make sure students use the correct terminology. Pointing out that tsunami are actually shallow-water waves that occur in the deep ocean may help students understand the volume of water that is involved and why these waves are so destructive. Use of SmartFigure 8.25 can help illustrate this concept. Ask the class if anyone has ever tried to move a small, 10-gallon fish tank.

Point out how difficult it was to move even this relatively small amount of water and then point how much more massive an amount of weight from a tsunami will be crashing upon the shore.

Discussion on the mass and the volume of water in tsunami is a great way to lead into discussing wave energy. You can talk about the sheer force generated by a volume of water and how this can be useful for harnessing waves as a source of energy.

Teacher’s Resources Films ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪

Oceanographic Studies off Georges Bank (NOAA, Film p-1056-25), 15 minutes Waves Across the Pacific (McGraw-Hill), 30 minutes Waves on Water (Revised Edition) (Encyclopedia Britannica), 16 minutes Earth Revealed #24: Waves, Beaches, and Coasts (Intelecom/Annenberg CPB), 30 minutes, http://learner.org/resources/series78.html Ocean Waves (NOAA Multimedia Discovery Missions), 10 minutes, http://oceanexplorer.noaa.gov/edu/learning/player/lesson09.html A Hypnotic Journey through Waves and Water (National Geographic), 4.5 minutes, http://video.nationalgeographic.com/video/short-film-showcase/a-hypnotic-journey-throughwaves-and-water Rare Video: Japan Tsunami 2011 (National Geographic), 3.5 minutes, http://video.nationalgeographic.com/video/news/japan-tsunami-2011vin?gc=%2Fvideo%2Fenvironment Tsunami 101 (National Geographic), 2.5 minutes, http://video.nationalgeographic.com/video/101videos/tsunami-101?gc=%2Fvideo%2Fenvironment

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Websites ● ● ● ● ●

http://noaacontent.nroc.org/lesson09/l9la1_a.html—Catch a Wave: Interactive computer activity allows students to see the effect of shore slope angle on breaking waves (NOAA) http://noaacontent.nroc.org/lesson09/l9la1_b.html—Measure a Wave: Interactive computer activity (NOAA) https://oceanexplorer.noaa.gov/edu/learning/player/lesson09/l9la2.htm—Tsunami Warning Systems: Interactive computer activity explores how animals sense tsunami versus human instrumentation sensing (NOAA) http://noaacontent.nroc.org/lesson09/l9ex1.htm—Explore the Indian Ocean 2004 Tsunami Computer Interactive (NOAA) www.npr.org/sections/13.7/2014/07/17/332211283/ocean-waves-as-you-have-never-seen-thembefore—Ocean waves as you have never seen them before (NPR), includes 3-minute video

Concept Check (Questions and Answers) 8.1 How Are Waves Generated and How Do They Move?

1. Discuss several different ways in which waves form. How are most ocean waves generated?

All waves begin as disturbances (releases of energy). This can be accomplished by a variety of mechanisms, including wind, the movement of fluids of different densities, mass movement into the ocean, underwater sea-floor movements, and the gravitational pull of the Moon and the Sun, and by human activities. Most ocean waves are generated by wind.

2. Why is the development of internal waves likely within the pycnocline?

Internal waves develop along density interfaces within the ocean. The greatest rate of density change in most parts of the ocean is found within the pycnocline, which is caused by a rapid change in temperature with depth (thermocline). Internal waves are often found within the thermocline (which is associated with the pycnocline).

3. Describe the three types of motion in which progressive waves move. Which type includes waves at the ocean surface?

Longitudinal waves: Particles move back and forth in the direction of energy transmission, and these waves can transmit matter through solids, liquids, or gases.

Transverse waves: Particles move back and forth in a direction at right angles to the direction of energy transmission, and these waves can transmit energy through solids.

Orbital waves: Particles move in circular orbits passing through the top half of the orbit in the direction of energy transmission. They develop when energy is being transmitted along a density interface between two fluids such as the low-density atmosphere and the denser ocean water.

Longitudinal and transverse waves are body waves.

Orbital waves are waves at the ocean surface.

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8.2 What Characteristics Do Waves Possess?

1. Can a wave with a wavelength of 14 meters ever be more than 2 meters high? Why or why not?

A wave with a wavelength of 14 meters (46 feet) could never be more than 2 meters high because its wave steepness would be too great and it would break. In fact, if any wave ever has a wave steepness that exceeds a 1:7 ratio, the wave would break.

2. What physical feature of a wave is related to the depth of the wave base? What is the difference between the wave base and the still-water level?

Wave base is at a depth equal to half the wavelength, measured from still-water level. Wave base is deeper than still-water level. Wave base is at a depth of half the wavelength, and still-water level (also known as zero energy level) is halfway between the crest and the trough.

3. Calculate the speed (S) in meters per second for deep-water waves with the following characteristics: a. L = 351 meter, T = 15 seconds b. T = 12 seconds c. F = 0.125 wave per second The following answers were determined using the most straightforward equations, but note that other equations may be used to determine deep-water wave speed, all of which will arrive at the correct answer. a. S = L/T = (351 meters)/(15 seconds) = 23.4 meters per second b. S = 1.56T = (1.56)(12 seconds) = 18.7 meters per second c. T = 1/f = 1/(0.125 seconds) = 8 seconds; S = 1.56T = (1.56)(8 seconds) = 12.5 meters per second 4. For each of the following statements about deep-water waves, determine if the statement is true or false, then explain why. a. The longer the wave, the deeper the wave base. b. The greater the wave height, the deeper the wave base. c. The longer the wave, the faster the wave travels. d. The greater the wave height, the faster the wave travels. e. The faster the wave, the greater the wave height.

Answers: a. True: Because wave base is half of wavelength measured from still-water level down.

Therefore, the longer the wavelength, the deeper the wave base. b. False: Wave base is independent of wave height. c. True: Wave speed = wavelength/period. d. False: Height and speed are independent. e. False: Speed and height are independent.

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8.3 How Do Wind-Generated Waves Develop?

1. Define swell. Does swell necessarily imply a particular wave size? Why or why not?

Swell describes uniform, symmetrical waves that have traveled out of the area of origination.

Although swell can often have a large wave height, swell does not necessarily imply a particular wave size. This is because swell describes any waves that have traveled out of their area of origination, independent of the factors that influence wave size (wind speed, duration, and fetch).

2. Waves from separate sea areas move away as swell and produce an interference pattern when they come together. If Sea A has a wave height of 1.5 meters (5 feet) and Sea B has a wave height of 3.5 meters (11.5 feet), what would be the height of waves resulting from constructive interference and destructive interference? Illustrate your answer (see Figure 8.15).

Constructive interference would produce waves 5 meters (16.4 feet) high (see the figure below, left) and destructive interference would produce waves 2 meters (6.6 feet) high (see figure below, right).

8.4 How Do Waves Change in the Surf Zone?

1. What is the 1:7 ratio? What happens to a wave when the 1:7 ratio is exceeded?

The 1:7 ratio is a ratio of a wave’s height to its wavelength, H/L, or steepness that, when reached or exceeded, causes a wave to break as surf.

2. Describe the physical changes that occur to a wave’s wave speed (S), wavelength (L), height (H), and wave steepness (H/L) as the wave moves across progressively shallower water to break on the shore.

As the orbiting articles begin to touch or feel the bottom when the water depth becomes less than ½ L, the waves will slow down and their S will be reduced. Since the leading wave will be in shallower water than the wave behind it, it will be slowed more and the trailing wave will decrease the distance between its crest and the crest of the wave ahead, reducing the L. Since there is the same volume of water in each waveform, it will have to increase its H as its length decreases. Since wave height has increased and wavelength has decreased, the H/L increases until it exceeds the 1:7 ratio and the wave breaks.

3. Describe the three different types of breakers and indicate the slope of the beach that produces each of the three types. How is the energy of the wave distributed differently within the surf zone by the three types of breakers?

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Spilling breakers result from a relatively gentle slope of the ocean bottom, which more gradually extracts energy from the wave, producing a turbulent mass of air and water that runs down the front slope of the wave. The wave energy in spilling breakers is spread over a large distance within the surf zone.

Plunging breakers have a curling crest that moves over an air pocket. This results because the curling particles literally outrun the wave, and there is nothing beneath them to support their motion. Plunging breakers form on moderately steep beach slopes and expend their energy over a shorter distance of the surf zone.

Surging breakers build up and break right at the shoreline in areas that have an abrupt beach slope. Consequently, the wave energy is compressed into an even shorter distance.

4. Using examples, explain how wave refraction is different from wave reflection.

Wave refraction is the bending of wave energy, such as how waves bend around an island or how waves bend as they approach the shore at an angle. Wave reflection is the bouncing back of wave energy once it hits any solid object such as a jetty, coastal cliff, or other solid structure.

5. Using orthogonal lines, illustrate how wave energy is distributed along a shoreline with headlands and bays. Identify areas of high- and low-energy release.

The illustration should resemble SmartFigure 8.21b.

8.5 How Are Tsunami Created?

1. Why is it more likely that a tsunami will be generated by the vertical movement of sea-floor faults rather than the horizontal movement of sea-floor faults?

When sea-floor faults move vertically, you are more likely to have vertical movement of water above the fault. This energy is transmitted throughout the water column and then moves away in circles, much like those created by throwing a pebble in a pond. Horizontal movement on a fault does not cause vertical movement in the water column or displacement of large volumes of water, and thus no tsunami is generated.

2. Describe the differences between wind-generated waves and tsunami. Which waves transmit more energy?

Wind-generated waves are generated by wind blowing over the surface of the ocean, while tsunami are caused by vertical fault movement on the sea floor. Wind-generated waves in the open ocean are deep-water waves that do not “feel” the sea floor, but tsunami, even in deep water, act as shallow-water waves that encompass the entire water column. Wind-generated waves typically do not cause as much damage as tsunami. Tsunami waves transmit more energy.

3. Explain what it would look like at the shoreline when the trough of a tsunami arrives there first. What is the impending danger?

If the trough of the tsunami arrives at a shore first, the water will suddenly withdraw and look as if an extreme low tide is occurring. The impending danger is that within the next few minutes, a strong surge of water will arrive at shore, followed by a series of withdrawals and surges many minutes apart.

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4. Explain how the tsunami warning system in the Pacific Ocean works. Why must the tsunami be verified at the closest tide recording station?

Since tsunami have small wave heights and are difficult to predict in the open ocean, the PTWC uses seismic waves to predict the occurrence of large waves. When a seismic disturbance occurs beneath the ocean surface that is large enough to be considered tsunamigenic, a tsunami watch is issued. At this point, a tsunami may or may not have occurred, but certainly the potential for one exists, so a station close to where the tsunami originated must verify the tsunami. Since the PTWC is linked to over 50 tide-measuring stations throughout the Pacific, the closest recording station to the earthquake is closely monitored for any indication of unusual wave activity. If unusual wave activity is verified, the tsunami watch is upgraded to a warning. Once a tsunami is detected, warnings are sent to all of the coastal regions that might encounter a destructive wave, along with an estimated time of arrival. This warning, usually just a few hours in advance of a tsunami, allows for the evacuation of people from low-lying areas and the removal of ships from harbors before the wave arrives. However, if the disturbance is nearby, there is not enough time for a warning to be issued because a tsunami travels so rapidly.

8.6 Can Power from Waves Be Harnessed as a Source of Energy?

1. Discuss some problems that might result from developing facilities for conversion of wave energy to electrical energy.

If a stretch of shore is deprived of wave energy that is needed to transport sediment along the shore, then the sediment will not be moved. As a result, a different portion of the shore will be deprived of its supply of sediment, which protects the shore from erosion. This portion of the shore, if exposed to wave energy, will begin to be eroded because the energy that was once used to transport sediment in the longshore current is now available to erode the exposed bedrock.

2. Describe the locations and the power-generating capability of existing offshore wave power plants and wave farms.

The LIMPET 500 is on Islay, a small island off the west coast of Scotland. Originally, it generated only 500 kilowatts of energy, but it has recently been upgraded and is continuously being improved.

Pelamis Wave Power has a wave farm off the coast of northern Portugal. It currently supplies up to 2.25 megawatts of power to Portugal’s electrical grid.

Generally, the larger swells occur in the southern ocean. However, taking into account proximity to the location where the energy will be used, the most efficient will be located near populated areas where the swell is large.

3. Worldwide, where are the best locations for new wave farms? Explain the oceanographic conditions that make these locations favorable.

Southern ocean has the largest swell year-round due to the water in the west wind drift not being impeded by land. Waves continue to grow in this region, with a larger area of wind that drives this current.

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Critical Thinking Questions (and Answers) 8.1 Compare and contrast the properties of the three types of progressive waves: longitudinal, transverse, and orbital waves.

Longitudinal waves: Particles move back and forth in the direction of energy transmission, and these waves can transmit matter through solids, liquids, or gases.

Transverse waves: Particles move back and forth in a direction at right angles to the direction of energy transmission, and these waves can transmit energy through solids.

Orbital waves: Particles move in circular orbits passing through the top half of the orbit in the direction of energy transmission. They develop when energy is being transmitted along a density interface between two fluids such as the low-density atmosphere and the denser ocean water.

8.2 To help reinforce your knowledge of wave terminology, draw a diagram of a simple progressive wave from memory. Include wave orbitals and label the crest, trough, wavelength, wave height, wave base, and still-water level.

The drawing should look like Figure 8.4a.

8.3 Using the information about the giant waves experienced by the USS Ramapo in 1933, determine the waves’ wavelength and speed.

The waves had a period (T) of 14.8 seconds; thus, the wave speed of these deep-water waves can be determined as follows: S =1.56T = (1.56) (14.8 seconds) = 23.1 meters per second.

Note that 23.1 meters per second = 83.1 kilometers (51.6 miles) per hour.

Now that wave speed is known, wavelength can be calculated: S = L/T, so L = S × T L = (23.1 meters per second) (14.8 seconds) = 342 meters (1121 feet).

8.4 As a wave comes into shallow water, it experiences five physical changes that cause the wave to break at the shore. Name each physical change and explain why each occurs.

Wave speed decreases—the shallower water depths interfere with orbital water movement, which slows down the wave.

Wavelength decreases—waveforms that follow slowing waves are still moving at their original speed, causing wave crests to pile up closer to each other.

Wave height increases—as the wave slows down, all the energy in that wave needs to go somewhere because energy cannot be created or destroyed.

Wave steepness increases—steepness = height/wavelength; as these two variables change as mentioned, this translates into an increase in wave steepness.

Waves break as surf—as wave steepness reaches the 1:7 ratio, they fall over and break.

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8.5 What ocean depth would be required for a tsunami with a wavelength of 220 kilometers (136 miles) to travel as a deep-water wave? Is it possible that such a wave could become a deepwater wave any place in the world ocean? Explain.

The ocean would have to be at least ½ L or 110 kilometers (68 miles deep). Since the deepest part of the ocean is just over 11 kilometers (about 7 miles deep), there is no place in the ocean where a tsunami of this wavelength would be considered a deep-water wave.

8.6 What are some negative environmental factors that could inhibit the development of ocean wave power systems? What are your ideas for how these issues could be overcome?

If a stretch of shore is deprived of wave energy that is needed to transport sediment along the shore, the sediment will not be moved. As a result, a different portion of the shore will be deprived of its supply of sediment, which protects the shore from erosion. This portion of the shore, if exposed to wave energy, will begin to be eroded because the energy that was once used to transport sediment in the longshore current is now available to erode the exposed bedrock. This issue could be overcome through the construction of jetties or groins perpendicular to the beach, to prevent the transport of this sediment.

Another environmental factor is that it could impact marine organisms that rely on wave energy for transporting food supplies, removing waste, or dispersal. In this case, humans would have to find ways to relocate these species, or feed them and artificially remove their wastes, as well as construct channels for these animals to use for dispersal.

Active Learning Exercises 8.1 Working in groups of three, have each student in class pick one of the following types of progressive waves: (1) longitudinal wave, (2) transverse wave, and (3) orbital wave. For each type of wave, use your own words to explain how the wave moves and whether the wave can transmit through the three states of matter: (a) solid, (b) liquid, and (c) gas. Then recombine as a group and have each student take turns explaining their wave type.

(1) Longitudinal wave—moves in a compressional motion, much like a coiled spring, where the coils are compressed and expand as energy travels through it. These waves can transmit through all the three states of matter.

(2) Transverse wave—moves side to side or up and down, with energy traveling perpendicular to the movement of the wave. These waves can only transmit energy through solids.

(3) Orbital wave—particles move in a circular path as energy moves forward along the wave. These waves transmit energy along the interface between two fluids of different densities, so they can transmit between two liquids, two gases, or a liquid and a gas.

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8.2 Working in pairs, have each student in class use Figure 8.8 to consider one of the following two deep-water waves: (1) a wave with a wavelength of 200 meters and (2) a wave with a wavelength of 400 meters. Determine the corresponding wave period and wave speed for each wave and compare your results. Then discuss how you determined your answers and what general relationships exist between wavelength, wave period, and wave speed.

(1) The wave speed for L = 200 meters is 17.5 meters/second, and the period is 11 seconds.

(2) The wave speed for L = 400 meters is 25.0 meters/second, and the period is 16 seconds.

The graph in Figure 8.8 defines the relationship between wavelength, speed, and period. If you know one of these variables, it is easy to read the chart to determine the others. The curve on the graph illustrates that there is not a linear relationship between these variables. However, in general, as the wavelength increases, wave speed and period also increase.

8.3 Working with another student in class, use Table 8.2 to determine the characteristics of the average height, wavelength, period, and highest 10% of waves created by the following two conditions: (1) a wind speed of 40 kilometers (25 miles) per hour and (2) a wind speed of 80 kilometers (50 miles) per hour. With a doubling of wind speed, are waves created that have double the properties? Explain.

The only property that doubles with a doubling of wind speed is the average wave period; we see this relationship defined in Figure 8.8. Speed is directly related to period by the equation below: Speed = wavelength/period As the speed of the wind increases, so does the speed of the wave and the average wavelength.

Wave height is related to how much energy is in a wave. As wind energy increases, so does wave energy. Other factors that affect how high a wave can become, and the highest 10% of waves, are the fetch, or the distance over which the wind has been blowing, and the length of time the wind has been blowing.

8.4 Working with another student in class and using the Internet, explain the basic physics of surfing. Your answer should include important properties of waves as well as important properties of surfboards.

Buoyancy of the water is what keeps the surfboard and surfer afloat. It is important for the surfboard to have waterproof characteristics in order to maintain its buoyancy; if water seeps in, it becomes less buoyant. This is why surfers wax their boards.

Gravity is an important part of surfing also. Gravity acts to pull the tops of waves, and any surfers on them, downward, at a constant acceleration. Surfers need to find their centers of gravity on their boards in order to not fall off or flip their boards as they ride a wave. Boards need to have their mass distributed fairly even along their lengths to make this easier for the surfer to find his or her center of gravity.

A surfer riding a wave will also have a net velocity. There are horizontal and vertical components to this velocity. The top of the wave will be moving vertically downward as it moves horizontally

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forward. A surfer on the top of this wave will have a net velocity defined by the horizontal and the vertical velocity vectors.

8.5 Working with another student in class, analyze this scenario: While shopping in a surf shop, you overhear some surfing enthusiasts mention that they would really like to ride the curling wave of a tidal wave at least once in their life because it is a single breaking wave of enormous height. What would you say to these surfers?

I would first clarify if they meant a tsunami. I would point out that tsunami do not generally manifest at the shoreline as a breaker that one might see with a wind-generated wave. A tsunami typically hits the shore as a giant wall of water, with the power of a very large column of water contained within. A surfer trying to ride this wave would probably be smashed against the shoreline, and find him- or herself in very deep flooding waters and possibly a great deal of debris.

8.6 Working as a group and using Figure 8.34, identify a specific location on Earth that has high wave power potential and is close to a major population center so that it is easy to distribute the generated electricity. Present your findings to the class, including the location and an explanation of your reasoning.

Answers will vary. Some locations with very high wave potential near population centers include the tip of Africa near Cape Town, off the west coast of Ireland by Cork, and the southern coast of Australia near Perth. Another location with high wave potential is near Lisbon, Portugal.

Additional Active Learning Exercises 8.3 With a partner, explain why the velocity of a wave train is half the velocity of an individual wave in the group.

As the train moves, energy in wave 1 is transferred into circular orbital motion. Wave 1 dies and is replaced by wave 2. At the same time, a new wave forms at the back of the train. As the train progresses, the first wave is constantly dying and a new wave is constantly forming at the back of the train. The total number of waves and the length of the train remains the same. See Figure 8.14.

8.4 Using what you know about the speeds of deep-water and shallow-water waves, explain why waves refract when they approach the shore.

Most waves are not parallel with the shore as they approach it. Instead, part of the wave will reach shallow water first and begin to “feel” the bottom. This part of the wave slows down while the part of the wave still in deep water continues to move more quickly. This causes the waves to refract (bend) as they approach the shore. See SmartFigure 8.21a.

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Exploring Data Figure 8.4 1. What happens to the wave base as a wave’s wave height is increased?

Wave base is controlled by wavelength, not wave height. So, if the wavelength doesn’t change, the wave base won’t change even if the wave height increases.

2. What happens to the wave base as a wave’s wavelength is increased?

When a wave’s wavelength increases, the wave base also increases.

Figure 8.8 1. For a deep-water wave that has a wavelength of 400 meters, what is its period and speed?

A deep-water wave that has a wavelength of 400 meters has a period of 16 seconds and a speed of 25 meters/second (82 feet/second).

2. For a deep-water wave that has a period of 5 seconds, what is its wavelength and speed?

A deep-water wave that has a period of 5 seconds has a wavelength of ~50 meters and a speed of ~ 7.5 meters/second (~24.6 feet/second).

SmartTable 8.1 1. What is the Beaufort wind scale number and descriptive term for a sea where small and medium-sized ships might for a time be lost from view behind waves?

The Beaufort wind scale number would be 11 and the descriptive term would be “violent storm.”

2. What is the Beaufort wind scale number and descriptive term for a sea that has dense streaks of foam?

The Beaufort wind scale number would be 9 and the descriptive term would be “strong gale.”

Figure 8.19 1. What happens to a wave when its steepness exceeds the critical 1/7 ratio?

When the wave steepness exceeds the critical 1/7 ratio, the wave pitches forward and breaks.

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2. Assume that there is a shallowly-submerged object that extends above the wave base on the left side of the figure. What will happen to waves there? Can a wave break twice?

If the object is shallow enough that the wave is pushed up and the wave steepness exceeds the critical 1/7 ratio, the wave will break. Waves can break more than once. The wave breaks any time the wave steepness exceeds the critical 1/7 ratio.

SmartFigure 8.21 Based on what you know about wave energy, what will eventually happen to the point of land and the lighthouse?

As waves approach the shore, wave refraction causes wave energy to be concentrated on headlands. Eventually, the point of land will be eroded away and the lighthouse will be destroyed.

SmartFigure 8.25 Will a tsunami likely be generated if the offshore fault has a horizontal (side-to-side) motion? Explain.

When sea-floor faults move vertically, you are more likely to have vertical movement of water above the fault. This energy is transmitted throughout the water column and then moves away in circles much like those created by throwing a pebble in a pond. Horizontal movement on a fault does not cause vertical movement in the water column or displacement of large volumes of water, and thus no tsunami is generated.

Figure 8.27 Using information on this figure, explain why the Atlantic Ocean experiences very few tsunami.

Tsunami are most often generated by earthquakes at convergent plate boundaries. The Atlantic Ocean only has two small convergent plate boundaries and so tsunami are rare in the Atlantic Ocean. In contrast, the Pacific Ocean is surrounded by convergent plate boundaries (the Pacific Ring of Fire) and tsunami commonly occur there.

Figure 8.34 Identify three specific locations that would make good wave energy generation sites.

Answers will vary. Students should recognize that wave energy is important, but so is location.

The wave energy generation site should be near a population center that can use the energy.

Some locations with very high wave potential near population centers include the tip of Africa near Cape Town, off the west coast of Ireland by Cork, and the southern coast of Australia near Perth. Another location with high wave potential is near Lisbon, Portugal.

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Chapter 9 Tides Overview This chapter examines tides and begins with an introduction to what causes tides in the oceans. The influence of Sun and Moon gravitational forces is examined, as are the resultant forces that affect tidal bulges. Tidal variations during monthly tidal cycles are explored and the relationship between tidal cycles and moon phases is introduced. The declination of both the Sun and the Moon affects the location of tidal bulges. Earth’s slightly elliptical orbit may combine with other factors to determine the tidal range of a particular location at a given time. These many factors allow scientists to generate idealized predictions of tides. Tidal waves rotate counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere around an amphidromic point, and the positions of the continents interrupt free movement of tidal bulges. Different tidal patterns exist globally depending on a number of factors. Tidal bores differ from tidal waves and are generated within rivers, and whirlpools may be generated where water bodies with different tidal cycles meet. Grunion are an interesting species that depend on tides to spawn.

Harnessing power from tides is being explored by many countries, with the United Kingdom leading the way. Several tidal power plants have been built to harness tidal energy.

Essential Concepts 9.1 Demonstrate an understanding of the forces that cause ocean tides.

9.2 Explain how tides vary during a monthly tidal cycle.

9.3 Specify what tides look like in the ocean.

9.4 Compare the characteristics and coastal locations of the three types of tidal patterns.

9.5 Describe tidal phenomena that occur in coastal regions.

9.6 Evaluate the advantages and disadvantages of harnessing tides as a source of energy.

Chapter Outline 9.1 What Causes the Tides?

9.1.1 Tide-Generating Forces 9.1.1.1 Gravitational and Centripetal Forces in the Earth–Moon System 9.1.1.2 Resultant Forces 9.1.1.3 Tide-Generating Forces SmartFigure 9.6: Resultant forces Web Animation: Tidal Forces 9.1.2 Tidal Bulges: The Moon’s 9.1.3 Tidal Bulges: The Sun’s Effect Web Animation: The Lunar Day SmartFigure 9.9: The lunar day 9.1.4 Earth’s Rotation and the Tides

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9.2 How Do Tides Vary during a Monthly Tidal Cycle?

9.2.1 The Monthly Tidal Cycle SmartFigure 9.11: Earth–Moon–Sun positions and the tides Web Animation: Monthly Tidal Cycle 9.2.2 Complicating Factors 9.2.2.1 Declination of the Moon and Sun 9.2.2.2 Effects of Elliptical Orbits Web Animation: Effects of Elliptical Orbits 9.2.3 Idealized Tide Prediction SmartFigure 9.16: Predicted idealized tides 9.3 What Do Tides Look Like in the Ocean?

9.3.1 Amphidromic Points and Cotidal Lines SmartFigure 9.17 Cotidal map of the world.

9.3.2 Effect of the Continents 9.3.3 Other Considerations 9.4 What Types of Tidal Patterns Exist?

9.4.1 Diurnal Tidal Pattern 9.4.2 Semidiurnal Tidal Pattern 9.4.3 Mixed Tidal Pattern Web Animation: Tidal Patterns 9.5 What Tidal Phenomena Occur in Coastal Regions?

9.5.1 An Example of Tidal Extremes: The Bay of Fundy 9.5.2 Coastal Tidal Currents Diving Deeper 9.1 Oceans and People Tidal Bores: Boring Waves These Are Not! 9.5.3 Whirlpools: Fact or Fiction?

9.5.4 Grunion: Doing What Comes Naturally on the Beach SmartFigure 9.21: Reversing tidal currents in a bay 9.6 Can Tidal Power Be Harnessed as a Source of Energy?

9.6.1 Tidal Power Plants Essential Concepts Review

Learning Objectives The instructional objectives are performance-based and detail specific learning outcomes for Chapter 9.

The test items contained in the Test Bank are keyed to the learning objectives and the Essential Concepts Review at the end of the chapter. The order of the objectives mirrors the content presentation in Chapter 9.

Upon completion of this chapter, the student should be able to: 1. Define tide.

2. Distinguish between gravitational force, centripetal force, resultant forces, and tide-generating forces in the context of the Earth–Moon–Sun system and tidal generation.

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3. Describe the barycenter in the Earth–Moon system.

4. Differentiate between the zenith and the nadir in terms of gravitational forces in the Earth–Moon system.

5. Distinguish between a lunar day and a solar day, and discuss the impact on timing of the tidal cycle.

6. Explain how lunar tidal bulges and solar tidal bulges are formed, and discuss their effect on the tidal cycle.

7. Diagram the monthly tidal cycle detailing the relative position of the Earth, the Moon, and the Sun to produce a new moon, a quarter moon, and a full moon. Include in your drawing the tidal range corresponding to each lunar phase (spring tide and neap tide).

8. Define syzygy and quadrature.

9. List and describe the phases of the moon in a lunar month, including: a. waxing crescent b. waxing gibbous c. full moon d. waning gibbous e. waning crescent f. new moon 10. Differentiate between the declination and the ecliptic with respect to the arrangement of the Earth, the Moon, and the Sun. 11. Illustrate the relative position of the Earth and the Sun at perihelion and aphelion.

12. Discuss the effect of perigee and apogee on tidal range, including the implications of proxigean tides for coastal areas.

13. Distinguish between an amphidromic point and a cotidal point in the tide.

14. Detail the effects of the continents on the movement of the tidal bulges around Earth.

15. Compare and contrast diurnal, semidiurnal, and mixed tidal patterns, and describe where you would be most likely to find each tidal pattern.

16. Explain the extreme tidal bore in the Bay of Fundy.

17. Discuss the formation, velocity, and direction of coastal tidal currents, including rotary currents and reversing currents.

18. Differentiate between a flood current and an ebb current and describe where these coastal currents form.

19. Explain the tidal forces that produce a whirlpool and give the locations of some infamous whirlpools.

20. List the advantages and disadvantages of using tidal power to generate electricity.

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Teaching Strategies Using three-dimensional models of the Sun–Earth–Moon system can help reinforce the relative positions of these bodies to each other. Most students are already familiar with the fact that the Moon influences tides. Many are surprised to learn that the Sun also has an effect. Emphasize that while the Sun is more massive and therefore exerts a greater gravitational pull, the Moon is much closer and therefore has a greater influence over the tides. Explaining the resultant and tide-generating forces in terms of relative roles of gravitational and centripetal forces may help students visually understand a physics concept they may find confusing.

Sometimes students have the misconception that Earth’s orbit is highly elliptical and that Earth is closer to the Sun during the summer months. This chapter presents the opportunity to correct these misconceptions. Be sure students understand that Earth has a slightly eccentric, or elliptical, orbit and that perihelion actually occurs in January. You can tie this into a discussion of how perihelion and aphelion affect tidal ranges.

Use of a globe or world map when explaining tidal patterns is useful for showing how different coastline configurations can influence the tides as well. This chapter presents the opportunity to explain what a tidal wave really is and why it should not be confused with tsunami, which were covered in the previous chapter.

Use of SmartFigure 9.16 can help students recognize the relationship between different tidal cycles and the predicted idealized tides. Consider presenting this in class and walking students through it, as well as having them consider it on their own.

Teacher’s Resources Films ▪ ▪ ▪ ▪

▪

Fish, Moon, and Tides: The Grunion Story (Academy Films), 14 minutes Ocean Tides: Bay of Fundy (Encyclopedia Britannica), 14 minutes Tides and Currents (NOAA, Film P-1056-24), 15 minutes Tides of the Ocean (Academy Films), 16 minutes Tides (NOAA), 10 minutes, http://oceanexplorer.noaa.gov/edu/learning/player/lesson10.html

Websites ● http://oceanexplorer.noaa.gov/edu/learning/player/lesson10/l10la1.html—Predicting the Tides, online interactive (NOAA) ● http://oceanexplorer.noaa.gov/edu/learning/player/lesson10/l10la2.html—Life in the Intertidal Zone, online interactive (NOAA) ● http://education.nationalgeographic.org/media/earths-tides/—Earth’s Tides interactive (National Geographic)

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Concept Check (Questions and Answers) 9.1 What Causes Ocean Tides?

1. Why are there tidal bulges on both sides of Earth (e.g., not just the side of Earth that faces the Moon or the Sun)?

There is an imbalance of forces when tidal bulges are created. In the tidal bulge facing the Moon, for example, the gravitational force of the Moon is greater than the needed centripetal force. On the opposite side of Earth from the Moon, the centripetal force exceeds the Moon’s gravitational pull.

2. Explain why the Sun’s influence on Earth’s tides is only 46% that of the Moon, even though the Sun is so much more massive than the Moon.

The Sun has a much greater mass than the Moon, so it generates a greater gravitational attraction (as mass increases, then gravity increases). Remember that the Sun is much farther away from Earth and that as distance increases, the gravitational force greatly decreases. Even though the Sun has a much greater mass, it is much farther away, so its influence on Earth tides is much less (about half of the Moon’s).

Approaching the question from a more mathematical perspective, the tide-generating influence of a body on Earth is proportional to its mass and inversely proportional to the cube of the distance from Earth. The Moon has a mass of 7.3 × 1019 tons, while the Sun’s mass is 2.0 × 1027 tons.

Taking a proportion gives: (2.0 × 1027)/(7.3 × 1019) = 2.74 × 107, which is 27.4 million Therefore, the Sun is over 27 million times as effective in generating Earth tides as the Moon based on mass.

The Moon is on average 390,500 kilometers from Earth while the Sun is 149,758,000 kilometers from Earth. Taking a proportion of these two values gives: (149,758,000)/(384,835) = 389.1 This shows that the Sun is 389.1 times farther from Earth than the Moon. The cube of 389.1 is 58,931,347, or almost 59 million. Comparing the two tide-producing factors gives: (27 million)/(59 million) = 0.46 × 100% = 46% Therefore, the Sun is only 46% as effective as the Moon in generating Earth tides.

3. Why is a lunar day 24 hours and 50 minutes long, while a solar day is 24 hours long?

The solar day is defined as the time that elapses between successive passages over a given meridian on Earth’s surface, which takes 24 hours. The lunar day is defined as the time that elapses between successive passages of the Moon over a given meridian on Earth’s surface, which is 24 hours and 50 minutes of solar time. The difference between the two involves the Moon’s movement relative to Earth. Since the Moon moves from west to east relative to Earth’s

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surface in its orbital path and requires 29.53 days to complete an orbit, the Moon moves through an angle of 12.2 degrees each solar day or 24 hours. Earth must rotate through 372.2 degrees (360 degrees +12.2 degrees) each lunar day. The time required for Earth to rotate the additional 12.2 degrees is 50 minutes.

4. If Earth did not have the Moon orbiting it, would there still be tides? Why or why not?

If Earth did not have the Moon orbiting it, there would still be tides on Earth caused by the Sun. However, the tides would be smaller than they are now and they would not alternate between spring- and neap-tide conditions.

9.2 How Do Tides Vary During a Monthly Tidal Cycle?

1. To help reinforce your knowledge of tides, draw the positions of the Earth–Moon–Sun system during a complete monthly tidal cycle from memory. Indicate the tide conditions experienced on Earth, the phases of the Moon, the time between those phases, and the syzygy and quadrature.

Drawings should resemble SmartFigure 9.11.

2. Explain why the maximum tidal range (spring tide) occurs during new moon and full moon phases and the minimum tidal range (neap tide) occurs at first-quarter and third-quarter moons.

During new and full moon phases, the Sun and the Moon are very nearly aligned with Earth, and the crests and troughs of the lunar and solar bulges overlap to produce constructive interference.

This results in a larger set of tidal bulges because the magnitude of the displacements of the crests above and the troughs below the still-water level are added together, thus creating a greater tidal range (spring tide conditions).

During quadratures (first- and third-quarter moon phases), the Sun and the Moon are at right angles to one another relative to Earth, resulting in destructive interference between the lunar and the solar tidal bulges because the magnitude of the lunar tidal crest and trough are reduced by an amount equal to the solar tide trough and crest, respectively (refer to Figure 9.10). This minimum tidal range is known as neap tide.

3. What is declination? Discuss the degree of declination of the Moon and the Sun relative to Earth’s equator. What are the effects of declination of the Moon and the Sun on the tides?

Declination is the angular distance of the Sun or the Moon above or below Earth’s equatorial plane. The Sun’s declination from the plane of Earth’s equator is equal to an angle of 23.5 degrees from perpendicular. The maximum declination of the Sun is always 23.5 degrees, and its period is one year.

The maximum declination of the Moon from Earth’s equatorial plane is 28.5 degrees from perpendicular. During the period of the Moon’s orbit (29.53 days), the declination of the Moon will move from its maximum value in one hemisphere across the equator to a maximum value in the other hemisphere and back. The period of the Moon’s declination is the same as that of its orbit.

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As Earth rotates through the tidal bulges with a declination relative to the equator, any location north or south of the equator will pass through one bulge nearer its center than when it passes through the other. Therefore, the two high tides and the two low tides experiences will not have the same tidal height. These differences are called diurnal inequalities.

4. Diagram the Earth–Moon system’s orbit about the Sun. Label the positions on the orbit at which the Moon and the Sun are closest to and farthest from Earth, stating the terms used to identify them. Discuss the effects of the Moon’s and Earth’s positions on Earth’s tides.

Refer to Figure 9.14. The Moon is closest to Earth during perigee (375,200 kilometers) and farther away at apogee (405,800 kilometers). Greater tidal ranges are experienced during perigean tides.

The Sun is closest to Earth during perihelion (148,500,000 kilometers) and farther away during aphelion (152,200,000 kilometers). Greater tidal ranges are experienced during perihelion tides.

The period of the Moon’s changing distance is 27.5 days while that of the Sun is one year, so perigean tides are experienced about once a month while perihelion tides occur only once a year.

9.3 What Do Tides Look Like in the Ocean?

1. Are tides considered deep-water waves anywhere in the ocean? Why or why not?

Nowhere in the ocean are tides considered deep-water waves because the ocean basins are so shallow relative to the long wavelength of the wave crests created by tidal phenomena.

2. What are amphidromic points and cotidal lines?

An amphidromic point is a location in the ocean where there is no tidal range, but the crests and troughs of tide waves rotate about this point. It is similar to the node of a sine wave. Cotidal lines radiate from amphidromic points and connect all nearby locations that high tide is occurring at that time.

3. Discuss reasons why the tides don’t follow a simple tidal bulge model.

The tidal bulge model is based on idealized tide prediction. In reality, the continents affect tides because they interrupt the free movement of the tidal bulges across the ocean. Ocean-bottom topography also influences motion of the tides; internal waves within the tides will break on shallower water, disrupting the smooth flow of the tide wave. There are other additional physiographic factors that affect the simple tidal bulge model, with almost 400 identified factors.

9.4 What Types of Tidal Patterns Exist?

1. What do the terms diurnal, semidiurnal, and mixed mean as related to tidal patterns?

Diurnal: Daily Semidiurnal: Twice daily Mixed: Twice daily, unequal high tides and low tides 2. Describe the number of high and low tides in a lunar day, the period, and any inequality of the following tidal patterns: diurnal, semidiurnal, and mixed.

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Diurnal tidal pattern—one high tide and one low tide per lunar day. Period: 24 hours and 50 minutes. There is no diurnal inequality because there is only one high tide and one low tide daily.

Semidiurnal tidal pattern—two high tides and two low tides per lunar day. Period: 12 hours and 25 minutes. There is no significant diurnal inequality.

Mixed tidal pattern—two high tides and two low tides per lunar day. Period: Throughout most of the month, the period will be 12 hours and 25 minutes, but there may be a few days when it is 24 hours and 50 minutes. The diurnal inequality is usually very significant, which causes the two high tides to be of different heights and the two low tides to be of differing heights as well.

3. Using the Internet, find a coastal tidal prediction for your birthday this year (or, if your birthday has already happened, find next year’s tide prediction). What tidal pattern is displayed?

Answers will vary. The website www.noaa.gov is a good resource for tide information.

4. Of the three tidal patterns, which one is most common along the U.S. East Coast? The U.S. West Coast? Worldwide?

East Coast: Semidiurnal West Coast: Mixed Worldwide: Mixed

9.5 What Tidal Phenomena Occur in Coastal Regions?

1. Discuss factors that help produce the world’s greatest tidal range in the Bay of Fundy.

Because the period of free oscillation in the Bay of Fundy is nearly the same as the tidal period resonance that is produced, a very large tidal range occurs at the northern end of Minas Basin due to constructive interference. The bay also narrows and becomes progressively shallower toward its northern end, which amplifies tidal effects. In addition, the Bay of Fundy is a rightcurving bay, so the Coriolis effect in the Northern Hemisphere adds to the tidal range.

2. Specify the difference between rotary and reversing tidal currents.

As the tidal current rotates through the open ocean, it follows a circular path as illustrated in Figure 9.17. This current is not very noticeable because there are no restrictions to its flow. Near the shore where the ocean floor shoals on approach to the continents, tidal current flow becomes a reversing current—flowing in and out (flood and ebb currents). These reversing currents can be very intense due to restrictions imposed on their flow by coastal topography.

3. Of flood current, ebb current, high slack water, and low slack water, when is the best time to enter a bay by boat? When is the best time to navigate in a shallow, rocky harbor?

Explain.

Generally, the best time to enter a bay by boat is during flood current because the boat will be carried into the bay by the incoming tidal current. The best time to navigate in a shallow, rocky harbor is during high slack water, when submerged obstacles are in the deepest water (refer to Figure 9.20).

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4. Describe the spawning cycle of grunion, indicating the relationship between tidal phenomena, where grunion lay their eggs, and the movement of sand on the beach.

The grunion spawning cycle is closely related to the rise and fall of the tides. Shortly after the maximum spring tide has occurred, these small silver fish come ashore to bury their fertilized eggs in the sand. During the summer months, the higher high tide occurs at night. As the high tides become higher each night while the maximum spring-tide range approaches, sand is eroded from the beach (refer to Figure 9b). After the maximum height of the spring tide has occurred, the higher high tide that occurs each night will be a little lower than the previous night. During the decreasing tidal heights produced as neap-tide conditions approach, sand is deposited on the beach. The grunion depend on this pattern of beach sand deposition and erosion for spawning success (refer to Box 9.2).

9.6 Can Tidal Power Be Harnessed as a Source of Energy?

1. Discuss at least two positive and two negative factors related to tidal power generation.

Responses to this question will vary. Positive factors include the fact that tidal power is a renewable energy resource, and there is a reduced pollution threat relative to other power sources. Negative factors include high initial costs; maximum generating potential does not always correspond to maximum power consumption; and the interference with maritime use in the area where the tidal power plant is located.

2. Explain how a tidal power plant works, using as an example an estuary that has a mixed tidal pattern. Why does the potential for usable tidal energy increase with an increase in tidal range?

A tidal power plant works by trapping seawater in an estuary during high tide and using that water to turn turbines and generate electricity as the water moves out to sea at low tide. A power plant situated at the entrance of an estuary would be able to allow water to enter the estuary during an incoming high tide (for a mixed tidal pattern, this occurs twice daily) and use the water for electricity generation as it flows out through the power plant. Factors that increase the usable tide-generating potential of an estuary include a large surface area of an estuary (more water), a large tidal range (higher potential energy), and a narrow mouth to the sea (greater ability to channel the water).

Critical Thinking Questions (and Answers) 9.1 Specify the forces involved in creating ocean tides.

Tide-generating forces are a combination of centripetal forces, gravitational attraction of the Moon, and the resultant forces from these acting together. The Sun also plays a role in tide generation, but because it is further from Earth than the Moon, its effects are less. The resultant tide-generating forces are small, but if there is a significant horizontal component, tidal bulges are produced. These forces generate two simultaneous tidal bulges, one on either side of Earth. Refer to Figure 9.5 for a detailed graphic of forces involved in tide generation.

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9.2 Specify differences between these two astronomical cycles that occur simultaneously: the 27½day perigee–apogee–perigee cycle and the 29½- day monthly tidal cycle.

The 27½-day perigee–apogee–perigee cycle occurs as the moon orbits Earth. The Moon’s orbit is slightly elliptical. It takes 27½ days for the Moon to travel from perigee (closest point to Earth) to apogee (most distant point from Earth) and back to perigee. This is a sidereal month.

The 29½- day monthly tidal cycle represents the time it takes for the Moon to move around Earth and return to the same position, relative to the Sun, as observed by someone on Earth. This cycle is longer because as the Moon is orbiting Earth, the Earth–Moon system is also orbiting around the Sun. This is the synodic or lunar month.

This video illustrates this concept well: http://www.sumanasinc.com/webcontent/animations/content/sidereal.html 9.3 Explain amphidromic points and cotidal lines. How do they influence tides in the open ocean?

Amphidromic points are locations where there is no tidal range. In the open ocean, cotidal lines radiate out from this point like branches. These cotidal lines connect points where the high tides will occur simultaneously. These cotidal lines extend out further where there are no significant landmasses to interrupt their trajectory. However, they may terminate where they intersect a continent or other large landmass. Occasionally, cotidal lines will terminate at amphidromic points at both ends of the lines; in these cases, maximum tidal range will be close to the midpoints of these lines. Refer to Figure 9.15 for a graphic.

9.4 Imagine that there are two moons in orbit around Earth that are on the same orbital plane but always on opposite sides of Earth, and that each moon is of the same size and mass of our Moon. How would this affect the tidal range during spring and neap conditions? Also, how would this affect the tidal pattern observed?

If there were two moons in orbit around Earth, the size of the lunar tidal bulges would be doubled.

Because the lunar bulges are already the primary factor that influences tides on Earth, the tidal range would be greater during both spring- and neap-tide conditions. Tidal patterns are affected by the depth, size, and shape of the ocean basins, so the patterns would not be affected by the two moons.

9.5 Examine a current monthly tide calendar for a coastal location. When is the best time for a field trip to the tide pools? If this were a grunion spawning month, when would the conditions be right for the next grunion spawning run?

Answers will vary depending on coastal location. The grunion spawning cycle is closely related to the rise and fall of the tides. Shortly after the maximum spring tide has occurred, these small silver fish come ashore to bury their fertilized eggs in the sand. During the summer months, the higher high tide occurs at night. As the high tides become higher each night while the maximum spring-tide range approaches, sand is eroded from the beach (refer to Figure 9b). After the maximum height of the spring tide has occurred, the higher high tide that occurs each night will be a little lower than the previous night. During the decreasing tidal heights produced as neap-tide conditions approach, sand is deposited on the beach.

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9.6 What are some negative environmental factors that could inhibit the development of ocean tidal power systems?

Answers may vary. Negative factors include high initial costs; maximum generating potential does not always correspond to maximum power consumption; and the interference with maritime use in the area where the tidal power plant is located.

Active Learning Exercises 9.1 Two students are talking about what causes the tides. Student A says that the tide comes in and goes out based on differences in the height of the sea level. Student B says that the changing tides are caused by Earth rotating into and out of the tidal bulges.

Working with another student in class, discuss the explanations of the tides by Student A and Student B. Which explanation is more technically correct? Explain your reasoning.

Student A is not correct as far as what causes the tides. Different coastal configurations can cause different water depths along the shoreline, and the effects of the tides may be more noticeable in those cases.

Student B is more technically correct. Alternating high and low tides are generated because Earth is continuously rotating inside tidal bulges that are created by the Moon and the Sun. Earth’s rotation carries different places on Earth in and out of these tidal bulges.

9.2 This is a take-home assignment. Observe the Moon from a reference location every night at about the same time for two weeks. Keep track of your observations about the shape (phase) of the Moon and its position in the sky. Then compare your observations to the reported tides in your area (or a coastal area you visit frequently) and report your findings to the class.

Answers will vary depending on when in the lunar cycle the assignment is started. For a two-week observation period, the diagram or observations should resemble about half of Figure 9.12. Over any two-week period, the student should have noticed one neap tide and one spring tide. The neap tides will have corresponded with a first-quarter or a third-quarter moon, and spring tides will correlate with a new moon or a full moon.

9.3 Assume that the tides are free waves and are therefore governed by the conditions and equations for ocean waves in Chapter 8. Consider the tidal bulges as wave crests with a wavelength of one-half Earth’s circumference—about 20,000 kilometers (12,420 miles)—and assume that the average height of the lunar bulges is 3 meters (10 feet).

Working with another student in class and using information from Chapter 8, determine if tides are deep-water or shallow-water waves. Note that the average depth of the oceans is 3.7 kilometers (2.3 miles), and the deepest ocean depth is 11 kilometers (6.8 miles).

Shallow-water waves occur in water that has a depth of less than 1/20 the wavelength.

D < 1/20 × L D = 1/20 × 20,000 km = 1000 km

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Water depth must be less than 1000 km for a tide to be a shallow-water wave. Therefore, tides are shallow-water waves since 3.7 km < 1000 km and 11 km < 1000 km.

9.4 Working with another student in class, draw a monthly tidal curve for a fictional location. On the horizontal axis, use time in hours to show the length of two days; on the vertical axis, use tidal height. Also label the high and low tides. Present it to the class and indicate if it represents diurnal, semidiurnal, or mixed tide conditions.

Student answers will vary. Figure 9.19 illustrates these different tidal patterns for comparison.

9.5 Working with another student in class and using the Internet, find a monthly tidal chart for the Bay of Fundy. Discuss the tidal information that is displayed, including spring and neap-tide conditions, the corresponding phases of the Moon, and the amount of tidal range.

The tidal range in the Bay of Fundy is as high as 16 meters during a spring-tide condition. Even at other times, this region has a large tidal range. The spring-tide conditions occur when the Moon is full or new, and the neap-tide conditions occur when the Moon is in its first or third quarter. Even during neap tides, the tidal range exceeds that of most other places in the world.

9.6 Split the class into groups of two. In each group, have each student pick one of the two methods in which tidal power is harnessed. Debate the relative advantages and disadvantages of each method. For example, which method has fewer negative environmental concerns?

Method 1: Tidal water trapped behind coastal barriers. An advantage of using this method is that the trapped water can be released to generate electricity any time it is needed. These power-generated plants can be strategically placed to take advantage of large tidal ranges, and are capable of generating large amounts of electrical power. Disadvantages of this method can include high initial costs, disruption of ecosystems or marine communities that previously accessed the regions now blocked by barriers, and blockage of maritime waterways.

Method 2: Using tidal currents that pass through narrow channels to turn underwater turbines. An advantage of using this method is that as long as there is a powerful current flowing through the turbines, electricity can be generated. It does not produce carbon emissions and takes advantage of water flow that is naturally occurring anyway. A disadvantage is that if tidal flow slows or ceases, electricity is no longer being generated, there is a high initial cost, and it can be disruptive to underwater marine communities.

Additional Active Learning Questions 9.1 Most people would say that the Moon orbits Earth. Are these people correct?

To an observer on Earth, it appears that the Moon orbits Earth. However, the Moon and Earth actually rotate around a common center of mass called the barycenter, which is located about 1700 kilometers beneath Earth’s surface. See Figure 9.1.

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9.6 At this point in the book, students have learned about several types of renewable energy that can be generated from resources in the ocean. Energy can be harnessed using offshore windfarms (Chapter 6), currents (Chapter 7), wave energy (Chapter 8), and tides (Chapter 9).

Have the students imagine they are energy consultants for a coastal town that would like to increase its renewable energy generation. Break the class into four groups, with each group researching the pros and cons of one of the energy sources listed above. Then, hold a town hall meeting in which each group presents their energy type and, as a class, determine which type is best for your town.

Answers will vary, but students should consider cost, locational constraints (not all locations are equally suited for all types of renewable energy generation), environmental impacts, economic impacts, and support from the public.

Exploring Data SmartFigure 9.6 Describe two key differences between the centripetal forces (red arrows) and the gravitational forces (black arrows).

In the diagram, red arrows illustrate centripetal force and black arrows illustrate gravitational force. Each arrow points in the direction of the force and the length of the arrow indicates the magnitude of the force at that location. Centripetal force is the same magnitude and is oriented in the same direction at all locations on Earth. The magnitude of the gravitational force increases the closer the point is to the Moon. The direction of the gravitational force is different at each point because the force is oriented directly at the Moon’s center of mass.

Figure 9.8 Why does Earth have not just one tidal bulge on the side of Earth facing the Moon but two equal tidal bulges on both sides of Earth?

The tide-generating forces create two bulges, one on each side of Earth. On the side directly facing the Moon, the bulge is created because the provided gravitational force is greater than the required centripetal force. Conversely, on the side facing away from the Moon, the bulge is created because the required centripetal force is greater than the provided gravitational force.

SmartFigure 9.9 1) Describe the differences between a solar day and a lunar day.

The solar day is measured from the time the Sun is directly overhead of an observer to the next time the Sun is directly overhead. A solar day is 24 hours long.

The lunar day is measured from the time the Moon is directly overhead to the next time the Moon is directly overhead. The lunar day is 24 hours, 50 minutes long. The lunar day is 135 .

longer than the solar day because as Earth was rotating, the Moon continued moving 12.2 degrees along its orbit around Earth.

2) You are photographing a sunset at 6:00 P.M. and notice the full Moon rising in the east behind you. You decide to return the next evening to photograph the moonrise.

Based on your knowledge of the lunar day, what time would moonrise be?

The next moonrise will be at 6:50 P.M. SmartFigure 9.11 1) Explain why during some weeks tides are higher than during other weeks over the course of a month.

Spring tides have the greatest tidal range. They occur when the Sun, Earth, and Moon are aligned, which occurs twice during a lunar month: at new moon and full moon. One to two days leading up to and following a new moon or full moon will also have higher than average tides because the Sun, Earth, and Moon are nearly aligned at these times.

2) Explain why there is a pattern of two high tides and two low tides daily during a spring tide. Your answer must include the terms “tidal bulges” and “Earth’s rotation.”

Resultant forces create two tidal bulges, one on the side facing the Moon and one on the side facing away from the Moon. In the idealized tidal model, during a spring tide, Earth’s rotation moves every location on Earth through the two tidal bulges during the course of the day.

Figure 9.12 How many spring tides occur in the time it takes the Moon to make one complete orbit around Earth? Describe what the Moon looks like from Earth during each occurrence.

Two spring tides occur each time the Moon makes one complete orbit around Earth. These spring tides occur during a new moon and a full moon.

Figure 9.18 Describe the characteristics of the three main types of tidal patterns.

A diurnal tidal pattern shows one high and low tide each lunar day. A semidiurnal tidal pattern shows two highs and lows of approximately equal heights during each lunar day. A mixed tidal pattern shows two highs and lows of unequal heights during each lunar day.

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Figure 9.19 Based on the patterns shown in this figure, what is the approximate time interval between a spring tide and the next neap tide?

The time interval between a spring and neap tide is approximately 7 days.

SmartFigure 9.21 Based on the information in this figure, when would be the best time to navigate a ship into a small, rocky harbor? When would be the best time to set sail and leave the harbor?

Reversing currents can cause navigational hazards for ships. When sailing into the harbor, you would want to time your entrance to coincide with a period of time when the water was moving into the harbor at a lower velocity, such as just after 6, just before 12, just after 18 or just before 24. Likewise, when sailing out of the harbor, you would want to leave when the water was moving slowly out of the harbor, such as just after 0, just before 6, just after 12, or just before 18.

Figure 9.23 Describe the pattern of grunion spawning in relation to the tides.

Grunion deposit their eggs on sandy beaches for 3–4 days after the highest spring tides. The low tides during the neap conditions won’t wash the eggs from the sand until they are ready to hatch about 10 days later. As the next spring tide is approached, successively higher high tides wash the eggs free and allow them to hatch.

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Chapter 10 Beaches, Shoreline Processes, and the Coastal Ocean Overview This chapter examines the coast and discusses the terminology used to describe various coast, beach, and shore regions. Beach composition is mentioned. Sand movement on the beach is investigated, with an analysis of both lateral and horizontal sediment movement mechanisms. The differences between winter and summer beaches are related to the strength of wave activity, which is seasonally variable. This chapter looks at factors that affect the longshore current and longshore transport. One subsection presents the variety of features associated with both erosional and depositional shores and the appropriate terminology applying to these features. This chapter also features a discussion of well-known shoreline features such as barrier islands, spits, and deltas. As sea level changes, this impacts beaches and coasts, and features of both emerging and submerging shorelines are examined within the context of past sea-level changes. There is a comparison of the different types of coasts that exist within the United States. Engineering technologies and use of structures to stabilize the shorelines are featured, with a look at the pros and cons of these techniques. The chapter concludes by examining coastal wetlands and some of the environmental issues that affect them. It discusses different types of wetlands and why they are valuable.

Essential Concepts 10.1 Use appropriate beach terminology to specify how coastal regions are defined.

10.2 Explain how sand moves on the beach.

10.3 Describe the characteristic features of erosional and depositional shores.

10.4 Discuss how changes in sea level produce emerging and submerging shorelines.

10.5 Describe the types of hard stabilization and evaluate various alternatives.

10.6 Compare the various types of coastal waters.

10.7 Specify the issues that face coastal wetlands.

Chapter Outline 10.1 How Are Coastal Regions Defined?

10.1.1 Beach Terminology 10.1.2 Beach Composition 10.2 How Does Sand Move on the Beach?

10.2.1 Movement Perpendicular to Shoreline 10.2.1.1 Mechanism 10.2.1.2 Light versus Heavy Wave Activity 10.2.1.3 Summertime and Wintertime Beaches Web Animation: Summertime/Wintertime Beach Conditions 10.2.2 Movement Parallel to Shoreline 10.2.2.1 Mechanism 10.2.2.2 Longshore Current and Longshore Drift (Longshore Transport) 10.2.2.3 Longshore Drift 138 .

SmartFigure 10.4: Longshore current and longshore drift Web Animation: Longshore Current and Longshore (Beach) Drift 10.2.2.4 The Beach: A River of Sand 10.3 What Features Are Typical of Erosional and Depositional Shores?

10.3.1 Features of Erosional Shores 10.3.2 Features of Depositional Shores 10.3.2.1 Barrier Islands 10.3.2.1.1 Human Impact on Barrier Islands Diving Deeper 10.1: Oceans and People Warning: Rip Currents . . . Do You Know What to Do? Web Video Rip Current 10.3.2.1.2 Features of Barrier Islands 10.3.2.1.3 Barrier Island Migration 10.3.2.2 Deltas 10.3.2.3 Beach Compartments 10.3.2.3.1 Beach Starvation Web Animation: Movement of a Barrier Island in Response to Rising Sea Level SmartFigure 10.14: Physiographic features of barrier islands and migration of a barrier island in response to sea-level rise Web Animation: Movement of Sand in a Beach Compartment SmartFigure 10.16:Beach compartments 10.4 How Do Changes in Sea Level Produce Emerging and Submerging Shorelines?

10.4.1 Features of Emerging Shorelines 10.4.2 Features of Submerging Shorelines 10.4.3 Changes in Sea Level 10.4.3.1 Movement of Earth’s Crust 10.4.3.1.1 Tectonic Movements 10.4.3.1.2 Isostatic Adjustment 10.4.3.2 Worldwide (Eustatic) Changes in Sea Level 10.4.3.2.1 Changes to Sea Level during Ice Ages Web Animation: Glacial Isostasy 10.5 How Does Hard Stabilization Affect Coastlines?

10.5.1 Groins and Groin Fields SmartFigure 10.20: Interference of sand movement 10.5.2 Jetties 10.5.3 Breakwaters Web Animation: Coastal Stabilization Structures 10.5.4 Seawalls 10.5.5 Alternatives to Hard Stabilization 10.5.5.1 Construction Restrictions 10.5.5.2 Beach Replenishment 10.5.5.3 Relocation 10.6 What are the Characteristics and Types of Coastal Waters?

10.6.1 Characteristics of Coastal Waters SmartFigure 10.30: Salinity variation in the coastal ocean

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10.6.1.1 Salinity 10.6.1.2 Temperature 10.6.1.3 Coastal Geostrophic Currents 10.6.2 Estuaries 10.6.2.1 Origin of Estuaries 10.6.2.2 Water Mixing in Estuaries SmartFigure 10.34: Classifying estuaries by mixing 10.6.2.3 Estuaries and Human Activities 10.6.2.3.1 Columbia River Estuary 10.6.2.3.2 Chesapeake Bay Estuary 10.6.3 Lagoons 10.6.3.1 Laguna Madre 10.6.4 Marginal Seas 10.6.4.1 A Case Study: The Mediterranean Sea 10.6.4.1.1 Mediterranean Circulation 10.7 What Issues Face Coastal Wetlands?

10.7.1 Types of Coastal Wetlands 10.7.2 Characteristics of Coastal Wetlands 10.7.3 Serious Loss of Valuable Wetlands Essential Concepts Review

Learning Objectives The instructional objectives are performance-based and detail specific learning outcomes for Chapter 10.

The test items contained in the Test Bank are keyed to the learning objectives and the Key Questions at the beginning of the chapter. The order of the objectives mirrors the content presentation in Chapter 10.

Upon completion of this chapter, the student should be able to: 1. Distinguish between a coast and a coastline.

2. Draw and label the features on a beach profile, including: a. backshore b. foreshore c. shoreline d. nearshore e. offshore zone f. beach g. beach face h. longshore bars i. longshore trough 3. Describe beach composition, including the physical and geologic factors that produce beaches of differing composition.

4. Discuss the factors that move sand and sediment perpendicular to the shoreline.

5. Differentiate between swash and backwash.

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6. Compare and contrast the appearance and composition of summertime and wintertime beaches, including a discussion of the relative location and the seasonal movement of sediments.

7. Discuss the factors that move sand and sediment parallel to the shoreline.

8. Distinguish between longshore current and longshore drift and discuss the impact of these processes on a sandy beach shoreline.

9. Make a distinction between a rip current and undertow.

10. List and describe the formation of features that characterize an erosional shoreline, including: a. headlands b. wave-cut cliffs c. sea caves d. sea arches e. sea stacks f. marine terraces 11. List and describe the formation of features that characterize a depositional shoreline, including: a. spit b. bay-mouth bar (bay barrier) c. tombolo d. barrier island e. delta 12. Illustrate the physiographic features of a temperate barrier island, including the locations of: a. ocean beach b. dunes c. barrier flat d. low salt marsh e. high salt marsh 13. Explain the movement of sand or sediment in beach compartments.

14. Detail the relationship between beach starvation and human activity on a sandy or muddy coastline.

15. List and describe the features of emerging shorelines, including stranded beach deposits.

16. List and describe the features of submerging shorelines, including: a. drowned beach b. submerged dune topography c. drowned river valley 16. Describe mechanisms for sea-level changes in the past, present, and future.

17. Describe the structures erected by man to stabilize the coast, including: a. groin b. jetty c. breakwater d. seawall

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21. Discuss alternatives to hard stabilization and their potential impact on coastal erosion and sediment transport.

22. Describe characteristics of coastal waters, including salinity, temperature, and coastal geostrophic currents.

23. Define estuary.

24. Describe the origins of four types of estuaries, including: a. coastal plain estuary b. fjord c. bar-built estuary d. tectonic estuary 25. Describe four types of estuaries classified by their water mixing, including: a. vertically mixed estuary b. slightly stratified estuary c. highly stratified estuary d. salt wedge estuary 26. Identify and discuss the effects of human activities on estuaries.

27. Recognize and describe lagoons.

28. Understand what a marginal sea is and how the Mediterranean Sea fits this description.

29. Identify and describe the two most important types of coastal wetlands: salt marshes and mangrove swamps.

30. Understand the characteristics of coastal wetlands.

31. Recognize and describe human impacts on wetlands and why wetlands are important.

Teaching Strategies Many students, depending on where they live, have been to at least one beach in their lives. It is useful to draw upon students’ knowledge of the beach environment based on what they have experienced since the technical terms for different parts of the coast will have more context for them. If you are physically located near a beach, it may be helpful to include local pictures of familiar features to help further or to schedule a field trip. It is also useful to use SmartFigure 10.4 or the web animation when discussing longshore transport and longshore drift so that students can visualize and understand the actual motion along the beach.

To help students understand the different types of hard stabilization, consider having them work together to draw an imaginary coastline. They should draw and label each structure and make note of what each does.

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Many of the geographic features, such as depositional shoreline features, estuaries, and wetlands, are environmentally sensitive locations. This chapter presents a good opportunity to introduce the idea of natural and human-made hazards, more of which are addressed in later chapters. However, getting students to think about why these environments are important and ways in which they are stressed is a good way to have your class generate an appreciation of how easily some coastal locations can be damaged.

Many people do not realize that there are different types of estuaries and that there are different types of circulation within estuaries. To best understand the circulation patterns within estuaries, students need to have a firm grasp on how both temperature and salinity affect water. Use of SmartFigure 10.34 in class is a good way to reinforce these concepts in relation to the different flows of water in different estuary types. Students will easily grasp how Mediterranean circulation is anomalous if they have this foundation but may find the concept difficult if they do not.

Teacher’s Resources Films ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪

Galveston Island Barrier Sands (Modern Talking Picture Service), 28 minutes Marine Erosion Processes—Cliffed Coasts (A. F. Films), 11 minutes The Beach: A River of Sand (Encyclopedia Britannica), 20 minutes The Beaches Are Moving (Environmental Media/North Carolina Public TV), 60 minutes Will Venice Survive Its Rescue? (NOVA), 60 minutes Earth Revealed #24: Waves, Beaches, and Coasts (Intelecom/Annenberg), 30 minutes, http://learner.org/resources/series78.html What if Your Home Was Slipping into the Ocean? Building on Barrier Islands (National Geographic), 5 minutes, http://video.nationalgeographic.com/video/news/140725-outer-bankssea-level-rise-vin The Value of Wetlands (Texas Parks and Wildlife Dept.), 3 minutes, www.pbslearningmedia.org/asset/lsps07_vid_wetlands/ Hurricane Katrina Wetland Destruction (NOVA Science Now), 2 minutes, www.pbs.org/wgbh/nova/sciencenow/3214/06-wetl-video.html Everglades (National Geographic), 4 minutes, http://video.nationalgeographic.com/video/everglades?source=searchvideo

Websites ● http://serc.carleton.edu/NAGTWorkshops/geomorph/activities/23373.html—Morphological Classification of Shorelines based on Hydrographic Regime (SERC), activity ● http://naturalsciences.org/docs/exploring-nc/508_BarrierIslandMigration_Activity.pdf—Barrier Island Migration activity ● www.nwrc.usgs.gov/index2.html—National Wetlands Research Center, U.S. Geological Survey ● www.fws.gov/wetlands/index.html—National Wetlands Inventory, U.S. Fish and Wildlife Service ● http://oceanservice.noaa.gov/education/kits/estuaries/estuaries07_adaptations.html—Adaptations to Life in the Estuary ● http://oceanservice.noaa.gov/podcast/supp_apr09.html#estuaries—Podcasts about estuaries

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Concept Check (Questions and Answers) 10.1 How Are Coastal Regions Defined?

1. Explain the difference between the shore and the coast.

The shore is closer to the ocean. It starts at the lowest low-tide level and extends inland to the highest elevation storm waves affect. The coast is more inland and ranges from the shore until ocean-related features can no longer be found. Refer to Figure 10.1.

2. What specific features are included in a typical beach?

A typical beach has a foreshore and a backshore. The foreshore is covered with water during high tide. As a geologic deposit of a shore area, a beach has sediment that has been pounded and impacted by waves. Beaches typically have a wave-cut bench, along which sediment moves; a berm, which is dry and gently sloping; a beach face, which is wet and slopes to the shoreline; and a longshore bar, which is an underwater sand bar paralleling the coast.

3. How does the berm differ from the beach face?

The berm is dry sand found at the base of coastal cliffs or sand dunes, whichever is present at that beach. The beach face is more oceanward of the berm. It is wet and sloping and extends down to the water’s edge. The berm is not covered during high tide, but the beach face may be partially covered.

4. How do beaches reflect the composition of locally available materials? Include examples in your answer.

Often, beach sediment is eroded material from the local continent. In this case, the beach mineral particles will have a coarser texture, as with sandy quartz beaches of the U.S. East Coast. If rivers feed into the area, sediment will be finer and mud flats will develop. Volcanic islands are made of basalt, and these are often black sand beaches. Areas that have abundant biological communities offshore and low relief inland, such as Florida, may have beaches that are wave-worked shell fragments or coral pieces.

10.2 How Does Sand Move on the Beach?

1. Describe differences between summertime and wintertime beaches. Explain why these differences occur.

Summertime beaches experience light wave activity and have a wide sandy berm and generally a steep beach face. The longshore bar is small to nonexistent. A wintertime beach experiences heavier wave activity and hence has a more flattened beach face with a narrow rocky berm.

Longshore bars are prominent.

2. What variables affect the speed of longshore currents?

As beach slope increases, higher angle of breaking waves relative to the shore, wave height, and wave frequency will increase the speed of a longshore current.

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3. What is longshore drift, and how is it related to a longshore current?

Longshore drift is also called longshore transport. It is the movement down the beach of the sediment in a zigzag pattern. The longshore current is responsible for this transport. By breaking at an angle, waves move sand and water on the beach in a zigzag manner.

4. Why does the direction of longshore current sometimes reverse? What is the primary direction of longshore current along the Pacific coast? Along the Atlantic coast? (See Figure 10.5 on page 318.)

Longshore current direction can reverse seasonally since direction of approaching waves may also change. The longshore current generally moves southward along both the Pacific and Atlantic coasts.

10.3 What Features Exist Along Erosional and Depositional Shores?

1. Discuss the formation of such erosional features as wave-cut cliffs, sea caves, sea arches, sea stacks, and marine terraces.

If waves release their energy along the base of a coastal cliff, they erode the cliff by abrasion with the force of water aided by sediment carried within the water, creating a wave-cut cliff. Sea caves typically begin along a weakness in the cliff (such as a fracture) and are further enlarged by wave erosion. If a headland juts into the ocean, waves refract around it and concentrate their energy release there. Waves may erode completely through the headland to create an opening through the rock called a sea arch. Continued erosion of the sea arch will cause the sea arch roof to collapse, separating the seaward side of the arch from the headland and forming a column of rock called a sea stack.

2. Describe the origin of these depositional features: spit, bay barrier, tombolo, and barrier island. ● ● ● ●

A spit is a beach extension that protrudes into the open water of the bay. It will usually have a curved end due to the flow of tidal currents in and out of the bay, and it will often be elongated in the predominant direction of longshore drift.

A bay barrier (bay-mouth bar) is a depositional feature that extends completely across the bay mouth and usually results from the depositional extension of a spit.

A tombolo is a depositional feature that connects an island with another island or the mainland. It forms in the wave shadow of the island, and it is an extension of a beach deposit away from the landmass to which it is attached.

Barrier islands are depositional features separated from the mainland by a lagoon. They may only be a few hundred meters wide but tens of kilometers in length (see Figure 10.12).

3. Describe the response of a barrier island to a rise in sea level. Why do some barrier islands develop peat deposits running through them from the ocean beach to the salt marsh?

Barrier islands are often associated with subsiding shores, but they are thought to move similar to a tractor’s tread (rolling itself and moving toward the mainland) in response to a relative rise in sea level. Evidence for such migration can be seen in peat deposits, which are the remnants of old marshes that lie beneath the barrier islands. As barrier islands migrate toward the continents, islands override the marshes so that peat deposits are exposed on the ocean beach (see SmartFigure 10.14).

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4. Discuss why some rivers have deltas and others do not. What are the factors that determine whether a “bird’s-foot” delta (like the Mississippi Delta) or a smoothly curved delta (like the Nile Delta) will form?

Since the last rise in sea level from melting glaciers, the ocean has invaded many rivers to the extent that they now stop flowing with sufficient velocity to carry sediment from the estuary heads many miles inland from the open ocean. These rivers will not create deltas until they have filled their estuaries with sediment. Once the river’s estuaries are filled and they deposit sediment on the continental shelf, they only build deltas if the sediment deposition rate is greater than the rate at which the longshore current can redistribute river sediment. If the longshore drift can carry away only a portion of the sediment deposits, then a curved delta front, similar to the Nile River Delta, will form. If the sediment deposition rate greatly exceeds the rate of sediment redistribution by the longshore current, a “bird’s-foot” delta, similar to the Mississippi River Delta, will form.

5. Describe the three parts of a beach compartment. What happens when dams are built across all the rivers that supply sand to the beach?

Beach compartments have three components: (1) a series of rivers that supply sand to a beach; (2) the beach itself where sand is moving due to longshore transport; and (3) submarine canyons that lie offshore where sand is drained away from the beach.

When dams are built across all of the rivers that supply sediment to beach compartments, it deprives the beach of sand that it would normally receive. The longshore transport process continues to operate in the absence of river sediment input, resulting in narrower beaches as the sand is moved from the beach offshore to the submarine canyon. If all of the streams supplying sediment to longshore transport are dammed, the beaches will nearly disappear.

10.4 How Do Changes in Sea Level Produce Emerging and Submerging Shorelines?

1. Compare the causes and effects of tectonic versus eustatic changes in sea level.

Tectonic changes in sea level result from uplift or subsidence of a continent along a shoreline segment as a result of processes related to global plate tectonics. Tectonic uplift is occurring along the west coast of the United States as a result of the collision of the North American Plate with the Pacific, Juan de Fuca, and Gorda Plates. Along the east coast, tectonic events of a more passive nature are causing the shoreline to subside due to thermal contraction as the continent moves farther from the Mid-Atlantic Ridge. Contributing to this subsidence is the increasing sediment load deposited at continental margins.

Eustatic sea-level changes are a worldwide phenomenon resulting from changes in the holding capacity of the ocean basins or the amount of water in them. The most readily identifiable cause of eustatic sea-level changes is the formation and melting of continental glaciers. Other types of eustatic sea-level change include those due to thermal expansion or contraction of water due to global warming or cooling and from changes in the shape of the sea floor due to increased or decreased rates of sea-floor spreading.

No matter what produced the sea-level change, similar deposits are left as evidence. For relative rises in sea level, drowned river mouths, drowned beaches, and dune topography are left as evidence. For relative drops in sea level, marine terraces and stranded beach deposits are left as evidence.

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2. List the two basic processes by which coasts advance seaward, and list their counterparts that lead to coastal retreat.

Coasts may advance seaward as a result of uplift or deposition. Retreating coasts can result from subsidence or erosion.

3. Describe how an ice age affects sea level.

Ice ages produce eustatic sea-level changes. Weight of the ice causes lowering of landmasses, which then will slowly rebound after ice melts or retreats. As land eustatically rebounds, sea level will slowly appear to lower in response. In addition, formation of land glaciers locks water up, effectively lowering sea level. Also, as seawater cools, it contracts, lowering sea level further.

10.5 How Does Hard Stabilization Affect Coastlines?

1. List the types of hard stabilization and describe what each is intended to do. ●

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Groins are barriers to sediment flow built perpendicular to a coastline. They are constructed of many kinds of material, but they are usually made of large blocky material called riprap. Sometimes, groins are even constructed of sturdy wood pilings (similar to a fence built out into the ocean). A groin is constructed with the express purpose of trapping sand. A groin interrupts the flow of longshore drift and will cause sediment to be deposited in its upstream side as the current is slowed and experiences a decreased ability to carry sediment. Downstream from the groin, waves begin to erode sediment from the beach because the wave’s energy that was once used to transport sediment along the length of the shore is now available to pick up and transport other sediment. Until the sediment moves around the groin, erosion downstream of the groin will continue.

A jetty is similar to a groin in that it is a structure that is built perpendicular to the shore, and it is also usually constructed of riprap. Jetties are built to protect harbor entrances from wave action, and they secondarily trap sand. Jetties are often built in closely spaced pairs, and they are usually longer than groins. As a result, they usually cause more pronounced upstream sediment deposition and downstream sediment erosion.

Breakwaters are hard stabilization built parallel to the shoreline that often protects a harbor or creates boat anchorage. From the experience at Santa Barbara and Santa Monica, California, breakwaters cause a buildup of sand inshore of them and unwanted erosion downstream from them.

Seawalls are built parallel to the shore along a beach to protect the coastline from high water and wave energy. Once waves begin breaking against a seawall, the turbulence generated by the abrupt release of wave energy quickly erodes the sediment on its seaward side, causing it to collapse in the surf. Where they have been used to protect barrier island property, the seaward slope of the island beach has steepened, increasing the erosion rate.

Seawalls destroy recreational beaches.

2. Overall, does a groin add any additional sand to the beach? Explain.

Groins trap sand on the upcoast side, creating the illusion of adding sand to the beach on that side; however, on the downcoast of the groin, more erosion immediately occurs. Because of the downcoast erosion, more groins are needed to prevent excess sediment loss, and this is why groin fields are created.

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3. Why do groins often multiply to form a groin field?

On the downcoast of a groin, more erosion immediately occurs. Because of the downcoast erosion, more groins are needed to prevent excess sediment loss, and this is why groin fields are created.

4. When a breakwater was built in Santa Monica, what unexpected problem occurred? What was done to alleviate the problem (before the breakwater was destroyed by waves)?

A beach bulge was created because the natural transport of sand was disrupted; the breakwater blocked the waves responsible for sand movement. Sand was dredged and pumped downcoast to alleviate the problem.

5. Describe alternatives to hard stabilization, including potential drawbacks of each.

There are several alternatives to hard stabilization: restriction of building in flood-prone, erosional coastal areas; beach replacement (beach nourishment); and relocation. In some coastal areas, residents are prohibited from rebuilding following a natural disaster in the hope of reducing future losses (financial and environmental). Beach replenishment involves the replacement of lost sand to the beach, and this process can be expensive as it must be done on a continual basis. Offshore sand is either dredged and deposited on the beach or pumped into the longshore drift for deposition. The average cost of beach replenishment is around $5.00 to $10.00 per cubic yard of sand (0.76 cubic meters). In some cases, the relocation of a valuable structure to an area that is not subject to erosion is necessary. The most notable example of relocation was moving the Cape Hatteras Lighthouse 884 meters (2900 feet) in 1999 at a cost in excess of $12 million.

10.6 What are the Characteristics and Types of Coastal Waters?

1. For coastal oceans where deep mixing does not occur, describe the effect that offshore winds and freshwater runoff have on salinity distribution. How will the winter and summer seasons affect the temperature distribution in the water column?

Freshwater runoff causes lowered surface salinities at the coast. Offshore winds tend to be dry and cause a great deal of evaporation that would increase salinity. The combination of these two causes vertical mixing, moderate salinity, and a water column that is isohaline.

In low- and high-latitude coastal regions, water is isothermal year-round. In midlatitude areas, surface temperatures are coolest in winter and warmest in summer. This generates a strong thermocline. These thermocline profiles are reversed for summer and winter, with deeper temperatures cooler in summer and warmer in winter than their corresponding surface temperatures.

2. Describe how coastal runoff of low-salinity water produces a coastal geostrophic current and give a specific location where a coastal geostrophic current can be found.

When there is a high volume of freshwater runoff at the shore, it produces a wedge of lowsalinity water that slopes toward the open ocean (Figure 10.32). This low-salinity water then flows toward the ocean. Because of the Coriolis effect, this flow is deflected to the right in the

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Northern Hemisphere and to the left in the Southern Hemisphere. The combination of these factors generates the circular coastal geostrophic currents.

One specific coastal geostrophic current is the Davidson Current, along the coast of Washington and Oregon. It can become more pronounced with rainy weather as more fresh water runs off the land.

3. Describe the four main types of estuaries, based on geologic origin. ● ● ● ●

Coastal plain estuary—forms with rising sea level that floods existing river valleys. Also called drowned river valleys. One example is the Chesapeake Bay. Fjord—forms when sea level rises and floods an existing glaciated valley. These valleys typically are U-shaped and have steep walls with glacier debris near their ocean entrances.

Bar-built estuary—includes lagoons that separate barrier islands from the mainland. They are generated from sand bars that are deposited parallel to the coast by ocean wave processes.

Tectonic estuary—forms with faulting or folding of rocks that generate a geologically dropped location that the sea floods.

4. Describe the difference between vertically mixed and salt wedge estuaries in terms of salinity distribution, depth, and volume of river flow. Which displays the more classical estuarine circulation pattern?

Vertically mixed estuaries have uniform salinity vertically in the water column, but salinity increases from head to mouth, they are shallow, and they have low-volume flows. Salt wedge estuaries do not have a horizontal salinity gradient like vertically mixed estuaries; rather, they have a halocline with a noticeable vertical salinity gradient. These estuaries are deep with a high-volume river flow. Salt wedge estuaries display the more classical circulation pattern.

5. Discuss factors that cause the surface salinity of Chesapeake Bay to be greater along its east side. Also, why are periods of summer anoxia in Chesapeake Bay’s deep water becoming increasingly worse?

The Coriolis effect causes water entering the bay from the ocean to move toward the east side, causing increased salinity along that side. Summer anoxia periods are worsening because of increases in sewage and agricultural fertilizers being put in the bay. These provide nutrients that increase algal blooms that cause the subsequent development of anoxic conditions as the algae uses up an abundance of oxygen.

6. What factors lead to a wide seasonal range of salinity in Laguna Madre?

Laguna Madre, along the Texas coast, is hypersaline and shallow, causing large seasonal changes in temperature and salinity. When local storms add large volumes of fresh water during dry periods, salinity can drop to two parts per thousand. In the hot season, when high evaporation from the surface occurs, salinity can increase to as high as 50 parts per thousand.

7. Describe the circulation between the Atlantic Ocean and the Mediterranean Sea, and explain how and why it differs from typical estuarine circulation.

This circulation pattern is called Mediterranean circulation. There is dry, extreme heat in the eastern part of the Mediterranean Sea, causing large volumes of water to evaporate from these surface waters. There is a large inflow at the surface of Atlantic Ocean water through the Strait 149 .

of Gibraltar to replace this evaporated water. This surface flow comes in along the northern coast of Africa and spreads northward across the Mediterranean Sea. Atlantic Ocean water sinks during winter as it travels eastward, and then this water flows westward and returns to the Atlantic Ocean as subsurface flow through the Strait of Gibraltar. This circulation is the opposite of what typical estuarine circulation is.

10.7 What Issues Face Coastal Wetlands?

1. Name the two types of coastal wetland environments and the latitude ranges where each will likely develop.

The two types of coastal wetland environments are salt marshes and mangrove swamps. Salt marshes typically grow between 30 and 65 degrees latitude and mangrove swamps grow in the tropics at latitudes lower than 30 degrees.

2. How do wetlands contribute to the biology of the oceans and the cleansing of polluted river water?

Wetlands are often spawning grounds and nurseries for fish that live in the oceans. They also provide stopping grounds for many species of migrating birds and waterfowl. Wetlands are also very efficient at cleaning polluted water, and they serve to remove agricultural runoff, toxins, and other pollutants from water before it reaches the ocean. Wetland mud has the ability to trap pollutants in this sediment and the unique nature of soils, and bacteria found in wetlands can trap and decompose nitrogen pollutants from runoff.

3. From the information in Figure 10.42, determine how large an area of wetlands has been lost in the conterminous United States. What percentage of original wetlands still remains?

What efforts are being made in the United States to reverse this trend?

There were originally 87 million hectares, and there are now 43 million hectares of wetlands remaining, which is a 44-million-hectare loss. About 49.7% of the original wetlands remain.

The U.S. Environmental Protection Agency (EPA) has established an Office of Wetlands Protection (OWP) to help with efforts to reverse these losses. The OWP has been tasked with enforcing regulations against wetland pollution and identifying the most important wetlands to be protected or restored.

Critical Thinking Questions (and Answers) 10.1 To help reinforce your knowledge of beach terminology, construct and label your own diagram similar to Figure 10.1 from memory.

Refer to Figure 10.1.

10.2 Imagine you are floating at the beach within the surf zone. You notice that the longshore current and the resulting longshore transport change direction (e.g., from northward to southward) throughout the day. Based on your knowledge of shoreline processes, explain how this is possible.

The longshore current has its flow determined by the direction at which the waves approach the beach. Since most coastal waves are wind generated, any change in wind direction over the course 150 .

of the day can change the angle or the direction of approach of the waves, thus reversing the direction of the longshore current and the longshore transport.

10.3 Specify the characteristics and coastal features that differentiate erosional and depositional shores.

An erosional shore features wave-cut cliffs and may have sea caves below these cliffs. Heavy wave action may cause differential erosion, resulting in sea arches; further erosion may produce sea stacks. A marine terrace is a gently sloping feature found on erosional shores as well.

A depositional shore has large deposits of sand, often those that were moved by longshore drift and modified by other coastal processes. A spit, or long bar of sand connected to the mainland, is one such feature. Further extension of a spit may produce a bay barrier, or bay-mouth bar, protecting a bay from the ocean. Tombolos are sand ridges that connect islands to the mainland. Barrier islands run parallel to the coast and are not naturally connected to the mainland. Barrier islands may migrate inland in response to wave action and other coastal processes, including sea-level rise.

Barrier islands are also often home to marshes and large peat deposits.

Depositional shores may also have a delta, which supplies sediment by way of a river flowing to the sea.

10.4 Specify the characteristics and coastal features that differentiate emerging and submerging shorelines.

An emerging shoreline has a marine terrace, which is lacking on a submerging shoreline. An emerging shoreline may also feature stranded beach deposits many meters above the present-day shoreline, which indicates that the former shoreline is now above sea level. A submerging shoreline includes, in contrast, drowned beaches, where the former shoreline is now underwater. Submerged dune topography and drowned river valleys may also prevail.

10.5 Draw an aerial view of a shoreline to show the effect on erosion and deposition caused by constructing a groin, a jetty, a breakwater, and a seawall within the coastal environment.

Refer to Figure 10.22 for a view of jetties and groins, Figure 10.25 for a breakwater, and Figure 10.27 for a seawall.

10.6 Based on their geologic origin, draw and describe the four major types of estuaries, and give an example of where each one occurs.

Refer to Figure 10.33 for drawings of each of the four types of estuaries. ● Coastal plain estuary—forms with rising sea level that floods existing river valleys. It is also called drowned river valleys. One example is the Chesapeake Bay. ● Fjord—forms when sea level rises and floods an existing glaciated valley. These valleys typically are U-shaped and have steep walls with glacier debris near their ocean entrances. These often occur along the coasts of Alaska, Canada, New Zealand, Chile, and Norway. ● Bar-built estuary—includes lagoons that separate barrier islands from the mainland. They are generated from sand bars that are deposited parallel to the coast by ocean wave processes.

These are common along the U.S. East Coast, such as North Carolina, and the U.S. Gulf Coast, such as Texas. ● Tectonic estuary—forms with faulting or folding of rocks that generate a geologically dropped location that the sea floods. One example is the San Francisco Bay. 151 .

10.7 Specify the reasons wetlands are being destroyed worldwide in spite of their many benefits.

Many people want to live near the ocean, so wetlands are being filled in for housing. Often many people view wetlands as useless land that has the potential to harbor disease, so they fill it in, favoring the building of industry and agriculture on these lands.

Active Learning Exercises 10.1 Working with another student in class, determine the technical term for the beach area where people go to sunbathe or to have a barbecue. Also, what is the technical term for the area of the beach where most people run in the sand? Include characteristics of each area.

The berm is where people might sunbathe or barbecue. It is dry, gently sloping, and slightly elevated.

The beach face is where people typically run. It is wet and sloping between the berm and the shoreline. Wet, hard-packed sand makes it ideal for runners.

10.2 Working with another student in class, discuss how the flow of water in a stream is similar to that of a longshore current. In addition, discuss how the two are different.

Longshore current is similar to stream flow in that both move water and sediment from one region to another. These two things are different because a longshore current moves in a zigzag pattern and can change direction, whereas streams move more linearly and do not change direction.

10.3 Working with another student in class, make a list of at least four factors that influence the classification of a coast as either erosional or depositional. Compare your lists with another group and discuss.

Erosional coasts: have well-developed cliffs, are in regions of tectonic uplift of the coast, and feature headlands, wave-cut cliffs, sea arches, sea stacks, and marine terraces. They tend to occur along the west coast of the United States.

Depositional coasts: commonly have barrier islands and sand deposits and high rates of erosion.

Features include spits, bay barriers, barrier islands, and tombolos. They tend to be found along the east coast of the United States.

10.4 Working with another student in class, make a list of at least four factors that influence the classification of a shoreline as either emerging or submerging. Compare your lists with another group and discuss.

Emerging shoreline: have marine terraces, stranded beach deposits, sea cliffs, and wave-cut benches; dominated by erosion.

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Submerging shoreline: wave-cut benches below sea level that contain drowned beaches, submerged dune topography, drowned river valleys, tidal flats, and estuaries; dominated by deposition.

10.5 Working with another student in class, evaluate the alternatives to hard stabilization and select one method that your group thinks would work best. Be sure to include your rationale as you present your answer to the class.

Student opinions will vary. However, here are the alternatives to hard stabilization and some of the advantages that might be presented by students.

Construction restrictions: This is simple because it restricts construction in coastal erosion areas. It would be cost efficient because it takes little or no money to implement.

Beach replenishment: This is also called beach nourishment, where sand that is eroded is replaced by sand added to the beach. This method can keep the beach at the status quo, and people using or living near the beach would not have to adapt to changing beach sediment conditions.

Relocation: This involves moving existing structures in high-erosion zones to lower hazard sites and allowing nature to reclaim the beach. Advantages of this method include allowing humans to live with the natural processes that dominate the region while preserving as many structures as possible in a safer location.

10.6 With another student in class, describe the temperature variation of the coastal ocean in (1) the low latitudes, (2) the high latitudes, and (3) the middle latitudes. In each of the three locations, discuss if a thermocline exists (and explain why) or if the water column is isothermal (and explain why).

(1) Low-latitude oceans are uniformly heated by solar radiation. Therefore, coastal ocean temperatures tend to be consistent throughout the year. Because of this, there is no thermocline and the water is isothermal, or the same uniformly warm temperature throughout the water column.

(2) In the high latitudes, there is little solar radiation throughout the year. Coastal ocean temperatures remain uniformly cold, usually close to freezing, all year round. Due to this, there is no thermocline, and the water column is isothermal, with uniformly cold temperatures from surface to depth.

(3) The middle latitudes see the most annual temperature variation in the coastal ocean. In the summer months, the surface ocean heats up and is warmer than deeper water. We see a thermocline with temperatures of the water becoming increasingly cooler with depth. In the winter, we see the reverse. Coastal ocean surface temperatures become cold, and waters at depth are warmer. There is an opposite thermocline from what we see in the summer, with water temperatures increasing with depth in the coastal ocean.

10.7 Working with another student in class, discuss the steps you would recommend be taken to bring back lost coastal wetlands.

Student responses will vary. Responses could include increasing the number of laws regarding coastal wetland activity, strengthening laws requiring replacement of wetlands that have been

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destroyed by human activity, actively seeking out locations to create wetlands along the coast, destructing the structures that in the past destroyed wetlands, or finding ways to expand the existing coastal wetlands.

Additional Active Learning Questions 10.6 With a partner, use the Internet to learn more about the causes and consequences of the anoxic conditions in Chesapeake Bay Estuary. Then, develop a plan to improve the conditions in the estuary.

Answers will vary, but should include strategies to reduce the impact of fertilizers, sewage, and human development on the estuary.

This website has some great information: https://www.chesapeakebay.net/

10.7 With a partner, describe at least three benefits of coastal wetlands.

Answers will vary.

Benefits include: ● ● ● ●

Coastal wetlands serve as nurseries for more than half the species of commercially important fishes in the southeastern U.S. Wetlands remove nutrients, including nitrogen and phosphorus, that run off farmlands and down rivers. If nutrients are not removed, harmful algal blooms can form, resulting in eutrophication and anoxic conditions.

Wetlands trap carbon in their soils and prevent the carbon from entering the atmosphere.

Wetlands protect shorelines from erosion and serve as a first line of defense against hurricanes and tsunami by dissipating wave energy and absorbing excess water

Exploring Data Figure 10.1 Examine Figure 10.1 and compare it to the beaches in your local area. Identify differences and/or similarities.

Answers will vary.

SmartFigure 10.4 How would your position relative to the beach be affected if you weren’t paying much attention and playing around in the waves within the surf zone?

If you were floating in the water for some of the time you spent in the ocean, you would be carried downcoast by the longshore current.

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Figure 10.5 Explain how the dominant direction of longshore current/longshore transport can go in the opposite direction of the main ocean surface current offshore. Along which U.S. coast does this occur?

Longshore current is generated by refracting waves in the surf zone. The direction from which the waves approach the shore determines the direction that the longshore current will move. In both the North Atlantic and North Pacific Oceans, the major storm centers are located north of the continental United States. Waves are generated in these storm centers and move outward in all directions. When the waves hit the shores of the east and west coasts of the United States, they approach from a northerly direction.

Thus, along both coasts, the longshore current moves from north to south. Along the East coast of the United States, the longshore current moves in the opposite direction of the main surface ocean current (the Gulf Stream). Surface ocean currents are driven by global wind patterns.

SmartFigure 10.16 Explain why a beach compartment is narrow and rocky near its upstream end and is wide and sandy near its downstream end.

Each beach compartment consists of three components: (1) a series of rivers that supply sand to a beach; (2) the beach itself, where sand is moving due to longshore transport; and (3) offshore submarine canyons, where sand is drained away from the beach. Each beach compartment begins just downcoast of a submarine canyon, where the sand in the previous compartment was drained away. Sand is added to the compartment by rivers and the beach gets wider near the downstream end.

Figure 10.18 Identify at least two specific places in the world where would you expect to see evidence of isostatic adjustment.

Areas that were covered with ice during the last glacial maximum sank under the weight of the ice. Once the ice melted, the areas began to isostatically rebound. Hudson Bay and the Gulf of Bothnia (between Sweden and Finland) are currently experiencing isostatic adjustment.

Figure 10.21 Based on evidence in the photo, how can the primary direction of longshore current be determined?

In a groin field, sand collects on the upcoast side of the groin and sand is eroded from the downcoast side of a groin. In this photo, the sand is collecting on the left side of the groin and eroding from the right side of the groin, so the longshore current must be moving from the top left corner to the bottom right corner of the photo.

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Chapter 10 Beaches, Shoreline Processes, and the Coastal Ocean Overview This chapter examines the coast and discusses the terminology used to describe various coast, beach, and shore regions. Beach composition is mentioned. Sand movement on the beach is investigated, with an analysis of both lateral and horizontal sediment movement mechanisms. The differences between winter and summer beaches are related to the strength of wave activity, which is seasonally variable. This chapter looks at factors that affect the longshore current and longshore transport. One subsection presents the variety of features associated with both erosional and depositional shores and the appropriate terminology applying to these features. This chapter also features a discussion of well-known shoreline features such as barrier islands, spits, and deltas. As sea level changes, this impacts beaches and coasts, and features of both emerging and submerging shorelines are examined within the context of past sea-level changes. There is a comparison of the different types of coasts that exist within the United States. Engineering technologies and use of structures to stabilize the shorelines are featured, with a look at the pros and cons of these techniques. The chapter concludes by examining coastal wetlands and some of the environmental issues that affect them. It discusses different types of wetlands and why they are valuable.

Essential Concepts 10.1 Use appropriate beach terminology to specify how coastal regions are defined.

10.2 Explain how sand moves on the beach.

10.3 Describe the characteristic features of erosional and depositional shores.

10.4 Discuss how changes in sea level produce emerging and submerging shorelines.

10.5 Describe the types of hard stabilization and evaluate various alternatives.

10.6 Compare the various types of coastal waters.

10.7 Specify the issues that face coastal wetlands.

Chapter Outline 10.1 How Are Coastal Regions Defined?

10.1.1 Beach Terminology 10.1.2 Beach Composition 10.2 How Does Sand Move on the Beach?

10.2.1 Movement Perpendicular to Shoreline 10.2.1.1 Mechanism 10.2.1.2 Light versus Heavy Wave Activity 10.2.1.3 Summertime and Wintertime Beaches Web Animation: Summertime/Wintertime Beach Conditions 10.2.2 Movement Parallel to Shoreline 10.2.2.1 Mechanism 10.2.2.2 Longshore Current and Longshore Drift (Longshore Transport) 10.2.2.3 Longshore Drift 138 .

SmartFigure 10.4: Longshore current and longshore drift Web Animation: Longshore Current and Longshore (Beach) Drift 10.2.2.4 The Beach: A River of Sand 10.3 What Features Are Typical of Erosional and Depositional Shores?

10.3.1 Features of Erosional Shores 10.3.2 Features of Depositional Shores 10.3.2.1 Barrier Islands 10.3.2.1.1 Human Impact on Barrier Islands Diving Deeper 10.1: Oceans and People Warning: Rip Currents . . . Do You Know What to Do? Web Video Rip Current 10.3.2.1.2 Features of Barrier Islands 10.3.2.1.3 Barrier Island Migration 10.3.2.2 Deltas 10.3.2.3 Beach Compartments 10.3.2.3.1 Beach Starvation Web Animation: Movement of a Barrier Island in Response to Rising Sea Level SmartFigure 10.14: Physiographic features of barrier islands and migration of a barrier island in response to sea-level rise Web Animation: Movement of Sand in a Beach Compartment SmartFigure 10.16:Beach compartments 10.4 How Do Changes in Sea Level Produce Emerging and Submerging Shorelines?

10.4.1 Features of Emerging Shorelines 10.4.2 Features of Submerging Shorelines 10.4.3 Changes in Sea Level 10.4.3.1 Movement of Earth’s Crust 10.4.3.1.1 Tectonic Movements 10.4.3.1.2 Isostatic Adjustment 10.4.3.2 Worldwide (Eustatic) Changes in Sea Level 10.4.3.2.1 Changes to Sea Level during Ice Ages Web Animation: Glacial Isostasy 10.5 How Does Hard Stabilization Affect Coastlines?

10.5.1 Groins and Groin Fields SmartFigure 10.20: Interference of sand movement 10.5.2 Jetties 10.5.3 Breakwaters Web Animation: Coastal Stabilization Structures 10.5.4 Seawalls 10.5.5 Alternatives to Hard Stabilization 10.5.5.1 Construction Restrictions 10.5.5.2 Beach Replenishment 10.5.5.3 Relocation 10.6 What are the Characteristics and Types of Coastal Waters?

10.6.1 Characteristics of Coastal Waters SmartFigure 10.30: Salinity variation in the coastal ocean

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10.6.1.1 Salinity 10.6.1.2 Temperature 10.6.1.3 Coastal Geostrophic Currents 10.6.2 Estuaries 10.6.2.1 Origin of Estuaries 10.6.2.2 Water Mixing in Estuaries SmartFigure 10.34: Classifying estuaries by mixing 10.6.2.3 Estuaries and Human Activities 10.6.2.3.1 Columbia River Estuary 10.6.2.3.2 Chesapeake Bay Estuary 10.6.3 Lagoons 10.6.3.1 Laguna Madre 10.6.4 Marginal Seas 10.6.4.1 A Case Study: The Mediterranean Sea 10.6.4.1.1 Mediterranean Circulation 10.7 What Issues Face Coastal Wetlands?

10.7.1 Types of Coastal Wetlands 10.7.2 Characteristics of Coastal Wetlands 10.7.3 Serious Loss of Valuable Wetlands Essential Concepts Review

Learning Objectives The instructional objectives are performance-based and detail specific learning outcomes for Chapter 10.

The test items contained in the Test Bank are keyed to the learning objectives and the Key Questions at the beginning of the chapter. The order of the objectives mirrors the content presentation in Chapter 10.

Upon completion of this chapter, the student should be able to: 1. Distinguish between a coast and a coastline.

2. Draw and label the features on a beach profile, including: a. backshore b. foreshore c. shoreline d. nearshore e. offshore zone f. beach g. beach face h. longshore bars i. longshore trough 3. Describe beach composition, including the physical and geologic factors that produce beaches of differing composition.

4. Discuss the factors that move sand and sediment perpendicular to the shoreline.

5. Differentiate between swash and backwash.

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6. Compare and contrast the appearance and composition of summertime and wintertime beaches, including a discussion of the relative location and the seasonal movement of sediments.

7. Discuss the factors that move sand and sediment parallel to the shoreline.

8. Distinguish between longshore current and longshore drift and discuss the impact of these processes on a sandy beach shoreline.

9. Make a distinction between a rip current and undertow.

10. List and describe the formation of features that characterize an erosional shoreline, including: a. headlands b. wave-cut cliffs c. sea caves d. sea arches e. sea stacks f. marine terraces 11. List and describe the formation of features that characterize a depositional shoreline, including: a. spit b. bay-mouth bar (bay barrier) c. tombolo d. barrier island e. delta 12. Illustrate the physiographic features of a temperate barrier island, including the locations of: a. ocean beach b. dunes c. barrier flat d. low salt marsh e. high salt marsh 13. Explain the movement of sand or sediment in beach compartments.

14. Detail the relationship between beach starvation and human activity on a sandy or muddy coastline.

15. List and describe the features of emerging shorelines, including stranded beach deposits.

16. List and describe the features of submerging shorelines, including: a. drowned beach b. submerged dune topography c. drowned river valley 16. Describe mechanisms for sea-level changes in the past, present, and future.

17. Describe the structures erected by man to stabilize the coast, including: a. groin b. jetty c. breakwater d. seawall

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21. Discuss alternatives to hard stabilization and their potential impact on coastal erosion and sediment transport.

22. Describe characteristics of coastal waters, including salinity, temperature, and coastal geostrophic currents.

23. Define estuary.

24. Describe the origins of four types of estuaries, including: a. coastal plain estuary b. fjord c. bar-built estuary d. tectonic estuary 25. Describe four types of estuaries classified by their water mixing, including: a. vertically mixed estuary b. slightly stratified estuary c. highly stratified estuary d. salt wedge estuary 26. Identify and discuss the effects of human activities on estuaries.

27. Recognize and describe lagoons.

28. Understand what a marginal sea is and how the Mediterranean Sea fits this description.

29. Identify and describe the two most important types of coastal wetlands: salt marshes and mangrove swamps.

30. Understand the characteristics of coastal wetlands.

31. Recognize and describe human impacts on wetlands and why wetlands are important.

Teaching Strategies Many students, depending on where they live, have been to at least one beach in their lives. It is useful to draw upon students’ knowledge of the beach environment based on what they have experienced since the technical terms for different parts of the coast will have more context for them. If you are physically located near a beach, it may be helpful to include local pictures of familiar features to help further or to schedule a field trip. It is also useful to use SmartFigure 10.4 or the web animation when discussing longshore transport and longshore drift so that students can visualize and understand the actual motion along the beach.

To help students understand the different types of hard stabilization, consider having them work together to draw an imaginary coastline. They should draw and label each structure and make note of what each does.

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Many of the geographic features, such as depositional shoreline features, estuaries, and wetlands, are environmentally sensitive locations. This chapter presents a good opportunity to introduce the idea of natural and human-made hazards, more of which are addressed in later chapters. However, getting students to think about why these environments are important and ways in which they are stressed is a good way to have your class generate an appreciation of how easily some coastal locations can be damaged.

Many people do not realize that there are different types of estuaries and that there are different types of circulation within estuaries. To best understand the circulation patterns within estuaries, students need to have a firm grasp on how both temperature and salinity affect water. Use of SmartFigure 10.34 in class is a good way to reinforce these concepts in relation to the different flows of water in different estuary types. Students will easily grasp how Mediterranean circulation is anomalous if they have this foundation but may find the concept difficult if they do not.

Teacher’s Resources Films ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪

Galveston Island Barrier Sands (Modern Talking Picture Service), 28 minutes Marine Erosion Processes—Cliffed Coasts (A. F. Films), 11 minutes The Beach: A River of Sand (Encyclopedia Britannica), 20 minutes The Beaches Are Moving (Environmental Media/North Carolina Public TV), 60 minutes Will Venice Survive Its Rescue? (NOVA), 60 minutes Earth Revealed #24: Waves, Beaches, and Coasts (Intelecom/Annenberg), 30 minutes, http://learner.org/resources/series78.html What if Your Home Was Slipping into the Ocean? Building on Barrier Islands (National Geographic), 5 minutes, http://video.nationalgeographic.com/video/news/140725-outer-bankssea-level-rise-vin The Value of Wetlands (Texas Parks and Wildlife Dept.), 3 minutes, www.pbslearningmedia.org/asset/lsps07_vid_wetlands/ Hurricane Katrina Wetland Destruction (NOVA Science Now), 2 minutes, www.pbs.org/wgbh/nova/sciencenow/3214/06-wetl-video.html Everglades (National Geographic), 4 minutes, http://video.nationalgeographic.com/video/everglades?source=searchvideo

Websites ● http://serc.carleton.edu/NAGTWorkshops/geomorph/activities/23373.html—Morphological Classification of Shorelines based on Hydrographic Regime (SERC), activity ● http://naturalsciences.org/docs/exploring-nc/508_BarrierIslandMigration_Activity.pdf—Barrier Island Migration activity ● www.nwrc.usgs.gov/index2.html—National Wetlands Research Center, U.S. Geological Survey ● www.fws.gov/wetlands/index.html—National Wetlands Inventory, U.S. Fish and Wildlife Service ● http://oceanservice.noaa.gov/education/kits/estuaries/estuaries07_adaptations.html—Adaptations to Life in the Estuary ● http://oceanservice.noaa.gov/podcast/supp_apr09.html#estuaries—Podcasts about estuaries

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Concept Check (Questions and Answers) 10.1 How Are Coastal Regions Defined?

1. Explain the difference between the shore and the coast.

The shore is closer to the ocean. It starts at the lowest low-tide level and extends inland to the highest elevation storm waves affect. The coast is more inland and ranges from the shore until ocean-related features can no longer be found. Refer to Figure 10.1.

2. What specific features are included in a typical beach?

A typical beach has a foreshore and a backshore. The foreshore is covered with water during high tide. As a geologic deposit of a shore area, a beach has sediment that has been pounded and impacted by waves. Beaches typically have a wave-cut bench, along which sediment moves; a berm, which is dry and gently sloping; a beach face, which is wet and slopes to the shoreline; and a longshore bar, which is an underwater sand bar paralleling the coast.

3. How does the berm differ from the beach face?

The berm is dry sand found at the base of coastal cliffs or sand dunes, whichever is present at that beach. The beach face is more oceanward of the berm. It is wet and sloping and extends down to the water’s edge. The berm is not covered during high tide, but the beach face may be partially covered.

4. How do beaches reflect the composition of locally available materials? Include examples in your answer.

Often, beach sediment is eroded material from the local continent. In this case, the beach mineral particles will have a coarser texture, as with sandy quartz beaches of the U.S. East Coast. If rivers feed into the area, sediment will be finer and mud flats will develop. Volcanic islands are made of basalt, and these are often black sand beaches. Areas that have abundant biological communities offshore and low relief inland, such as Florida, may have beaches that are wave-worked shell fragments or coral pieces.

10.2 How Does Sand Move on the Beach?

1. Describe differences between summertime and wintertime beaches. Explain why these differences occur.

Summertime beaches experience light wave activity and have a wide sandy berm and generally a steep beach face. The longshore bar is small to nonexistent. A wintertime beach experiences heavier wave activity and hence has a more flattened beach face with a narrow rocky berm.

Longshore bars are prominent.

2. What variables affect the speed of longshore currents?

As beach slope increases, higher angle of breaking waves relative to the shore, wave height, and wave frequency will increase the speed of a longshore current.

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3. What is longshore drift, and how is it related to a longshore current?

Longshore drift is also called longshore transport. It is the movement down the beach of the sediment in a zigzag pattern. The longshore current is responsible for this transport. By breaking at an angle, waves move sand and water on the beach in a zigzag manner.

4. Why does the direction of longshore current sometimes reverse? What is the primary direction of longshore current along the Pacific coast? Along the Atlantic coast? (See Figure 10.5 on page 318.)

Longshore current direction can reverse seasonally since direction of approaching waves may also change. The longshore current generally moves southward along both the Pacific and Atlantic coasts.

10.3 What Features Exist Along Erosional and Depositional Shores?

1. Discuss the formation of such erosional features as wave-cut cliffs, sea caves, sea arches, sea stacks, and marine terraces.

If waves release their energy along the base of a coastal cliff, they erode the cliff by abrasion with the force of water aided by sediment carried within the water, creating a wave-cut cliff. Sea caves typically begin along a weakness in the cliff (such as a fracture) and are further enlarged by wave erosion. If a headland juts into the ocean, waves refract around it and concentrate their energy release there. Waves may erode completely through the headland to create an opening through the rock called a sea arch. Continued erosion of the sea arch will cause the sea arch roof to collapse, separating the seaward side of the arch from the headland and forming a column of rock called a sea stack.

2. Describe the origin of these depositional features: spit, bay barrier, tombolo, and barrier island. ● ● ● ●

A spit is a beach extension that protrudes into the open water of the bay. It will usually have a curved end due to the flow of tidal currents in and out of the bay, and it will often be elongated in the predominant direction of longshore drift.

A bay barrier (bay-mouth bar) is a depositional feature that extends completely across the bay mouth and usually results from the depositional extension of a spit.

A tombolo is a depositional feature that connects an island with another island or the mainland. It forms in the wave shadow of the island, and it is an extension of a beach deposit away from the landmass to which it is attached.

Barrier islands are depositional features separated from the mainland by a lagoon. They may only be a few hundred meters wide but tens of kilometers in length (see Figure 10.12).

3. Describe the response of a barrier island to a rise in sea level. Why do some barrier islands develop peat deposits running through them from the ocean beach to the salt marsh?

Barrier islands are often associated with subsiding shores, but they are thought to move similar to a tractor’s tread (rolling itself and moving toward the mainland) in response to a relative rise in sea level. Evidence for such migration can be seen in peat deposits, which are the remnants of old marshes that lie beneath the barrier islands. As barrier islands migrate toward the continents, islands override the marshes so that peat deposits are exposed on the ocean beach (see SmartFigure 10.14).

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4. Discuss why some rivers have deltas and others do not. What are the factors that determine whether a “bird’s-foot” delta (like the Mississippi Delta) or a smoothly curved delta (like the Nile Delta) will form?

Since the last rise in sea level from melting glaciers, the ocean has invaded many rivers to the extent that they now stop flowing with sufficient velocity to carry sediment from the estuary heads many miles inland from the open ocean. These rivers will not create deltas until they have filled their estuaries with sediment. Once the river’s estuaries are filled and they deposit sediment on the continental shelf, they only build deltas if the sediment deposition rate is greater than the rate at which the longshore current can redistribute river sediment. If the longshore drift can carry away only a portion of the sediment deposits, then a curved delta front, similar to the Nile River Delta, will form. If the sediment deposition rate greatly exceeds the rate of sediment redistribution by the longshore current, a “bird’s-foot” delta, similar to the Mississippi River Delta, will form.

5. Describe the three parts of a beach compartment. What happens when dams are built across all the rivers that supply sand to the beach?

Beach compartments have three components: (1) a series of rivers that supply sand to a beach; (2) the beach itself where sand is moving due to longshore transport; and (3) submarine canyons that lie offshore where sand is drained away from the beach.

When dams are built across all of the rivers that supply sediment to beach compartments, it deprives the beach of sand that it would normally receive. The longshore transport process continues to operate in the absence of river sediment input, resulting in narrower beaches as the sand is moved from the beach offshore to the submarine canyon. If all of the streams supplying sediment to longshore transport are dammed, the beaches will nearly disappear.

10.4 How Do Changes in Sea Level Produce Emerging and Submerging Shorelines?

1. Compare the causes and effects of tectonic versus eustatic changes in sea level.

Tectonic changes in sea level result from uplift or subsidence of a continent along a shoreline segment as a result of processes related to global plate tectonics. Tectonic uplift is occurring along the west coast of the United States as a result of the collision of the North American Plate with the Pacific, Juan de Fuca, and Gorda Plates. Along the east coast, tectonic events of a more passive nature are causing the shoreline to subside due to thermal contraction as the continent moves farther from the Mid-Atlantic Ridge. Contributing to this subsidence is the increasing sediment load deposited at continental margins.

Eustatic sea-level changes are a worldwide phenomenon resulting from changes in the holding capacity of the ocean basins or the amount of water in them. The most readily identifiable cause of eustatic sea-level changes is the formation and melting of continental glaciers. Other types of eustatic sea-level change include those due to thermal expansion or contraction of water due to global warming or cooling and from changes in the shape of the sea floor due to increased or decreased rates of sea-floor spreading.

No matter what produced the sea-level change, similar deposits are left as evidence. For relative rises in sea level, drowned river mouths, drowned beaches, and dune topography are left as evidence. For relative drops in sea level, marine terraces and stranded beach deposits are left as evidence.

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2. List the two basic processes by which coasts advance seaward, and list their counterparts that lead to coastal retreat.

Coasts may advance seaward as a result of uplift or deposition. Retreating coasts can result from subsidence or erosion.

3. Describe how an ice age affects sea level.

Ice ages produce eustatic sea-level changes. Weight of the ice causes lowering of landmasses, which then will slowly rebound after ice melts or retreats. As land eustatically rebounds, sea level will slowly appear to lower in response. In addition, formation of land glaciers locks water up, effectively lowering sea level. Also, as seawater cools, it contracts, lowering sea level further.

10.5 How Does Hard Stabilization Affect Coastlines?

1. List the types of hard stabilization and describe what each is intended to do. ●

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Groins are barriers to sediment flow built perpendicular to a coastline. They are constructed of many kinds of material, but they are usually made of large blocky material called riprap. Sometimes, groins are even constructed of sturdy wood pilings (similar to a fence built out into the ocean). A groin is constructed with the express purpose of trapping sand. A groin interrupts the flow of longshore drift and will cause sediment to be deposited in its upstream side as the current is slowed and experiences a decreased ability to carry sediment. Downstream from the groin, waves begin to erode sediment from the beach because the wave’s energy that was once used to transport sediment along the length of the shore is now available to pick up and transport other sediment. Until the sediment moves around the groin, erosion downstream of the groin will continue.

A jetty is similar to a groin in that it is a structure that is built perpendicular to the shore, and it is also usually constructed of riprap. Jetties are built to protect harbor entrances from wave action, and they secondarily trap sand. Jetties are often built in closely spaced pairs, and they are usually longer than groins. As a result, they usually cause more pronounced upstream sediment deposition and downstream sediment erosion.

Breakwaters are hard stabilization built parallel to the shoreline that often protects a harbor or creates boat anchorage. From the experience at Santa Barbara and Santa Monica, California, breakwaters cause a buildup of sand inshore of them and unwanted erosion downstream from them.

Seawalls are built parallel to the shore along a beach to protect the coastline from high water and wave energy. Once waves begin breaking against a seawall, the turbulence generated by the abrupt release of wave energy quickly erodes the sediment on its seaward side, causing it to collapse in the surf. Where they have been used to protect barrier island property, the seaward slope of the island beach has steepened, increasing the erosion rate.

Seawalls destroy recreational beaches.

2. Overall, does a groin add any additional sand to the beach? Explain.

Groins trap sand on the upcoast side, creating the illusion of adding sand to the beach on that side; however, on the downcoast of the groin, more erosion immediately occurs. Because of the downcoast erosion, more groins are needed to prevent excess sediment loss, and this is why groin fields are created.

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3. Why do groins often multiply to form a groin field?

On the downcoast of a groin, more erosion immediately occurs. Because of the downcoast erosion, more groins are needed to prevent excess sediment loss, and this is why groin fields are created.

4. When a breakwater was built in Santa Monica, what unexpected problem occurred? What was done to alleviate the problem (before the breakwater was destroyed by waves)?

A beach bulge was created because the natural transport of sand was disrupted; the breakwater blocked the waves responsible for sand movement. Sand was dredged and pumped downcoast to alleviate the problem.

5. Describe alternatives to hard stabilization, including potential drawbacks of each.

There are several alternatives to hard stabilization: restriction of building in flood-prone, erosional coastal areas; beach replacement (beach nourishment); and relocation. In some coastal areas, residents are prohibited from rebuilding following a natural disaster in the hope of reducing future losses (financial and environmental). Beach replenishment involves the replacement of lost sand to the beach, and this process can be expensive as it must be done on a continual basis. Offshore sand is either dredged and deposited on the beach or pumped into the longshore drift for deposition. The average cost of beach replenishment is around $5.00 to $10.00 per cubic yard of sand (0.76 cubic meters). In some cases, the relocation of a valuable structure to an area that is not subject to erosion is necessary. The most notable example of relocation was moving the Cape Hatteras Lighthouse 884 meters (2900 feet) in 1999 at a cost in excess of $12 million.

10.6 What are the Characteristics and Types of Coastal Waters?

1. For coastal oceans where deep mixing does not occur, describe the effect that offshore winds and freshwater runoff have on salinity distribution. How will the winter and summer seasons affect the temperature distribution in the water column?

Freshwater runoff causes lowered surface salinities at the coast. Offshore winds tend to be dry and cause a great deal of evaporation that would increase salinity. The combination of these two causes vertical mixing, moderate salinity, and a water column that is isohaline.

In low- and high-latitude coastal regions, water is isothermal year-round. In midlatitude areas, surface temperatures are coolest in winter and warmest in summer. This generates a strong thermocline. These thermocline profiles are reversed for summer and winter, with deeper temperatures cooler in summer and warmer in winter than their corresponding surface temperatures.

2. Describe how coastal runoff of low-salinity water produces a coastal geostrophic current and give a specific location where a coastal geostrophic current can be found.

When there is a high volume of freshwater runoff at the shore, it produces a wedge of lowsalinity water that slopes toward the open ocean (Figure 10.32). This low-salinity water then flows toward the ocean. Because of the Coriolis effect, this flow is deflected to the right in the

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Northern Hemisphere and to the left in the Southern Hemisphere. The combination of these factors generates the circular coastal geostrophic currents.

One specific coastal geostrophic current is the Davidson Current, along the coast of Washington and Oregon. It can become more pronounced with rainy weather as more fresh water runs off the land.

3. Describe the four main types of estuaries, based on geologic origin. ● ● ● ●

Coastal plain estuary—forms with rising sea level that floods existing river valleys. Also called drowned river valleys. One example is the Chesapeake Bay. Fjord—forms when sea level rises and floods an existing glaciated valley. These valleys typically are U-shaped and have steep walls with glacier debris near their ocean entrances.

Bar-built estuary—includes lagoons that separate barrier islands from the mainland. They are generated from sand bars that are deposited parallel to the coast by ocean wave processes.

Tectonic estuary—forms with faulting or folding of rocks that generate a geologically dropped location that the sea floods.

4. Describe the difference between vertically mixed and salt wedge estuaries in terms of salinity distribution, depth, and volume of river flow. Which displays the more classical estuarine circulation pattern?

Vertically mixed estuaries have uniform salinity vertically in the water column, but salinity increases from head to mouth, they are shallow, and they have low-volume flows. Salt wedge estuaries do not have a horizontal salinity gradient like vertically mixed estuaries; rather, they have a halocline with a noticeable vertical salinity gradient. These estuaries are deep with a high-volume river flow. Salt wedge estuaries display the more classical circulation pattern.

5. Discuss factors that cause the surface salinity of Chesapeake Bay to be greater along its east side. Also, why are periods of summer anoxia in Chesapeake Bay’s deep water becoming increasingly worse?

The Coriolis effect causes water entering the bay from the ocean to move toward the east side, causing increased salinity along that side. Summer anoxia periods are worsening because of increases in sewage and agricultural fertilizers being put in the bay. These provide nutrients that increase algal blooms that cause the subsequent development of anoxic conditions as the algae uses up an abundance of oxygen.

6. What factors lead to a wide seasonal range of salinity in Laguna Madre?

Laguna Madre, along the Texas coast, is hypersaline and shallow, causing large seasonal changes in temperature and salinity. When local storms add large volumes of fresh water during dry periods, salinity can drop to two parts per thousand. In the hot season, when high evaporation from the surface occurs, salinity can increase to as high as 50 parts per thousand.

7. Describe the circulation between the Atlantic Ocean and the Mediterranean Sea, and explain how and why it differs from typical estuarine circulation.

This circulation pattern is called Mediterranean circulation. There is dry, extreme heat in the eastern part of the Mediterranean Sea, causing large volumes of water to evaporate from these surface waters. There is a large inflow at the surface of Atlantic Ocean water through the Strait 149 .

of Gibraltar to replace this evaporated water. This surface flow comes in along the northern coast of Africa and spreads northward across the Mediterranean Sea. Atlantic Ocean water sinks during winter as it travels eastward, and then this water flows westward and returns to the Atlantic Ocean as subsurface flow through the Strait of Gibraltar. This circulation is the opposite of what typical estuarine circulation is.

10.7 What Issues Face Coastal Wetlands?

1. Name the two types of coastal wetland environments and the latitude ranges where each will likely develop.

The two types of coastal wetland environments are salt marshes and mangrove swamps. Salt marshes typically grow between 30 and 65 degrees latitude and mangrove swamps grow in the tropics at latitudes lower than 30 degrees.

2. How do wetlands contribute to the biology of the oceans and the cleansing of polluted river water?

Wetlands are often spawning grounds and nurseries for fish that live in the oceans. They also provide stopping grounds for many species of migrating birds and waterfowl. Wetlands are also very efficient at cleaning polluted water, and they serve to remove agricultural runoff, toxins, and other pollutants from water before it reaches the ocean. Wetland mud has the ability to trap pollutants in this sediment and the unique nature of soils, and bacteria found in wetlands can trap and decompose nitrogen pollutants from runoff.

3. From the information in Figure 10.42, determine how large an area of wetlands has been lost in the conterminous United States. What percentage of original wetlands still remains?

What efforts are being made in the United States to reverse this trend?

There were originally 87 million hectares, and there are now 43 million hectares of wetlands remaining, which is a 44-million-hectare loss. About 49.7% of the original wetlands remain.

The U.S. Environmental Protection Agency (EPA) has established an Office of Wetlands Protection (OWP) to help with efforts to reverse these losses. The OWP has been tasked with enforcing regulations against wetland pollution and identifying the most important wetlands to be protected or restored.

Critical Thinking Questions (and Answers) 10.1 To help reinforce your knowledge of beach terminology, construct and label your own diagram similar to Figure 10.1 from memory.

Refer to Figure 10.1.

10.2 Imagine you are floating at the beach within the surf zone. You notice that the longshore current and the resulting longshore transport change direction (e.g., from northward to southward) throughout the day. Based on your knowledge of shoreline processes, explain how this is possible.

The longshore current has its flow determined by the direction at which the waves approach the beach. Since most coastal waves are wind generated, any change in wind direction over the course 150 .

of the day can change the angle or the direction of approach of the waves, thus reversing the direction of the longshore current and the longshore transport.

10.3 Specify the characteristics and coastal features that differentiate erosional and depositional shores.

An erosional shore features wave-cut cliffs and may have sea caves below these cliffs. Heavy wave action may cause differential erosion, resulting in sea arches; further erosion may produce sea stacks. A marine terrace is a gently sloping feature found on erosional shores as well.

A depositional shore has large deposits of sand, often those that were moved by longshore drift and modified by other coastal processes. A spit, or long bar of sand connected to the mainland, is one such feature. Further extension of a spit may produce a bay barrier, or bay-mouth bar, protecting a bay from the ocean. Tombolos are sand ridges that connect islands to the mainland. Barrier islands run parallel to the coast and are not naturally connected to the mainland. Barrier islands may migrate inland in response to wave action and other coastal processes, including sea-level rise.

Barrier islands are also often home to marshes and large peat deposits.

Depositional shores may also have a delta, which supplies sediment by way of a river flowing to the sea.

10.4 Specify the characteristics and coastal features that differentiate emerging and submerging shorelines.

An emerging shoreline has a marine terrace, which is lacking on a submerging shoreline. An emerging shoreline may also feature stranded beach deposits many meters above the present-day shoreline, which indicates that the former shoreline is now above sea level. A submerging shoreline includes, in contrast, drowned beaches, where the former shoreline is now underwater. Submerged dune topography and drowned river valleys may also prevail.

10.5 Draw an aerial view of a shoreline to show the effect on erosion and deposition caused by constructing a groin, a jetty, a breakwater, and a seawall within the coastal environment.

Refer to Figure 10.22 for a view of jetties and groins, Figure 10.25 for a breakwater, and Figure 10.27 for a seawall.

10.6 Based on their geologic origin, draw and describe the four major types of estuaries, and give an example of where each one occurs.

Refer to Figure 10.33 for drawings of each of the four types of estuaries. ● Coastal plain estuary—forms with rising sea level that floods existing river valleys. It is also called drowned river valleys. One example is the Chesapeake Bay. ● Fjord—forms when sea level rises and floods an existing glaciated valley. These valleys typically are U-shaped and have steep walls with glacier debris near their ocean entrances. These often occur along the coasts of Alaska, Canada, New Zealand, Chile, and Norway. ● Bar-built estuary—includes lagoons that separate barrier islands from the mainland. They are generated from sand bars that are deposited parallel to the coast by ocean wave processes.

These are common along the U.S. East Coast, such as North Carolina, and the U.S. Gulf Coast, such as Texas. ● Tectonic estuary—forms with faulting or folding of rocks that generate a geologically dropped location that the sea floods. One example is the San Francisco Bay. 151 .

10.7 Specify the reasons wetlands are being destroyed worldwide in spite of their many benefits.

Many people want to live near the ocean, so wetlands are being filled in for housing. Often many people view wetlands as useless land that has the potential to harbor disease, so they fill it in, favoring the building of industry and agriculture on these lands.

Active Learning Exercises 10.1 Working with another student in class, determine the technical term for the beach area where people go to sunbathe or to have a barbecue. Also, what is the technical term for the area of the beach where most people run in the sand? Include characteristics of each area.

The berm is where people might sunbathe or barbecue. It is dry, gently sloping, and slightly elevated.

The beach face is where people typically run. It is wet and sloping between the berm and the shoreline. Wet, hard-packed sand makes it ideal for runners.

10.2 Working with another student in class, discuss how the flow of water in a stream is similar to that of a longshore current. In addition, discuss how the two are different.

Longshore current is similar to stream flow in that both move water and sediment from one region to another. These two things are different because a longshore current moves in a zigzag pattern and can change direction, whereas streams move more linearly and do not change direction.

10.3 Working with another student in class, make a list of at least four factors that influence the classification of a coast as either erosional or depositional. Compare your lists with another group and discuss.

Erosional coasts: have well-developed cliffs, are in regions of tectonic uplift of the coast, and feature headlands, wave-cut cliffs, sea arches, sea stacks, and marine terraces. They tend to occur along the west coast of the United States.

Depositional coasts: commonly have barrier islands and sand deposits and high rates of erosion.

Features include spits, bay barriers, barrier islands, and tombolos. They tend to be found along the east coast of the United States.

10.4 Working with another student in class, make a list of at least four factors that influence the classification of a shoreline as either emerging or submerging. Compare your lists with another group and discuss.

Emerging shoreline: have marine terraces, stranded beach deposits, sea cliffs, and wave-cut benches; dominated by erosion.

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Submerging shoreline: wave-cut benches below sea level that contain drowned beaches, submerged dune topography, drowned river valleys, tidal flats, and estuaries; dominated by deposition.

10.5 Working with another student in class, evaluate the alternatives to hard stabilization and select one method that your group thinks would work best. Be sure to include your rationale as you present your answer to the class.

Student opinions will vary. However, here are the alternatives to hard stabilization and some of the advantages that might be presented by students.

Construction restrictions: This is simple because it restricts construction in coastal erosion areas. It would be cost efficient because it takes little or no money to implement.

Beach replenishment: This is also called beach nourishment, where sand that is eroded is replaced by sand added to the beach. This method can keep the beach at the status quo, and people using or living near the beach would not have to adapt to changing beach sediment conditions.

Relocation: This involves moving existing structures in high-erosion zones to lower hazard sites and allowing nature to reclaim the beach. Advantages of this method include allowing humans to live with the natural processes that dominate the region while preserving as many structures as possible in a safer location.

10.6 With another student in class, describe the temperature variation of the coastal ocean in (1) the low latitudes, (2) the high latitudes, and (3) the middle latitudes. In each of the three locations, discuss if a thermocline exists (and explain why) or if the water column is isothermal (and explain why).

(1) Low-latitude oceans are uniformly heated by solar radiation. Therefore, coastal ocean temperatures tend to be consistent throughout the year. Because of this, there is no thermocline and the water is isothermal, or the same uniformly warm temperature throughout the water column.

(2) In the high latitudes, there is little solar radiation throughout the year. Coastal ocean temperatures remain uniformly cold, usually close to freezing, all year round. Due to this, there is no thermocline, and the water column is isothermal, with uniformly cold temperatures from surface to depth.

(3) The middle latitudes see the most annual temperature variation in the coastal ocean. In the summer months, the surface ocean heats up and is warmer than deeper water. We see a thermocline with temperatures of the water becoming increasingly cooler with depth. In the winter, we see the reverse. Coastal ocean surface temperatures become cold, and waters at depth are warmer. There is an opposite thermocline from what we see in the summer, with water temperatures increasing with depth in the coastal ocean.

10.7 Working with another student in class, discuss the steps you would recommend be taken to bring back lost coastal wetlands.

Student responses will vary. Responses could include increasing the number of laws regarding coastal wetland activity, strengthening laws requiring replacement of wetlands that have been

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destroyed by human activity, actively seeking out locations to create wetlands along the coast, destructing the structures that in the past destroyed wetlands, or finding ways to expand the existing coastal wetlands.

Additional Active Learning Questions 10.6 With a partner, use the Internet to learn more about the causes and consequences of the anoxic conditions in Chesapeake Bay Estuary. Then, develop a plan to improve the conditions in the estuary.

Answers will vary, but should include strategies to reduce the impact of fertilizers, sewage, and human development on the estuary.

This website has some great information: https://www.chesapeakebay.net/

10.7 With a partner, describe at least three benefits of coastal wetlands.

Answers will vary.

Benefits include: ● ● ● ●

Coastal wetlands serve as nurseries for more than half the species of commercially important fishes in the southeastern U.S. Wetlands remove nutrients, including nitrogen and phosphorus, that run off farmlands and down rivers. If nutrients are not removed, harmful algal blooms can form, resulting in eutrophication and anoxic conditions.

Wetlands trap carbon in their soils and prevent the carbon from entering the atmosphere.

Wetlands protect shorelines from erosion and serve as a first line of defense against hurricanes and tsunami by dissipating wave energy and absorbing excess water

Exploring Data Figure 10.1 Examine Figure 10.1 and compare it to the beaches in your local area. Identify differences and/or similarities.

Answers will vary.

SmartFigure 10.4 How would your position relative to the beach be affected if you weren’t paying much attention and playing around in the waves within the surf zone?

If you were floating in the water for some of the time you spent in the ocean, you would be carried downcoast by the longshore current.

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Figure 10.5 Explain how the dominant direction of longshore current/longshore transport can go in the opposite direction of the main ocean surface current offshore. Along which U.S. coast does this occur?

Longshore current is generated by refracting waves in the surf zone. The direction from which the waves approach the shore determines the direction that the longshore current will move. In both the North Atlantic and North Pacific Oceans, the major storm centers are located north of the continental United States. Waves are generated in these storm centers and move outward in all directions. When the waves hit the shores of the east and west coasts of the United States, they approach from a northerly direction.

Thus, along both coasts, the longshore current moves from north to south. Along the East coast of the United States, the longshore current moves in the opposite direction of the main surface ocean current (the Gulf Stream). Surface ocean currents are driven by global wind patterns.

SmartFigure 10.16 Explain why a beach compartment is narrow and rocky near its upstream end and is wide and sandy near its downstream end.

Each beach compartment consists of three components: (1) a series of rivers that supply sand to a beach; (2) the beach itself, where sand is moving due to longshore transport; and (3) offshore submarine canyons, where sand is drained away from the beach. Each beach compartment begins just downcoast of a submarine canyon, where the sand in the previous compartment was drained away. Sand is added to the compartment by rivers and the beach gets wider near the downstream end.

Figure 10.18 Identify at least two specific places in the world where would you expect to see evidence of isostatic adjustment.

Areas that were covered with ice during the last glacial maximum sank under the weight of the ice. Once the ice melted, the areas began to isostatically rebound. Hudson Bay and the Gulf of Bothnia (between Sweden and Finland) are currently experiencing isostatic adjustment.

Figure 10.21 Based on evidence in the photo, how can the primary direction of longshore current be determined?

In a groin field, sand collects on the upcoast side of the groin and sand is eroded from the downcoast side of a groin. In this photo, the sand is collecting on the left side of the groin and eroding from the right side of the groin, so the longshore current must be moving from the top left corner to the bottom right corner of the photo.

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Chapter 11 Marine Pollution Overview This chapter discusses pollution as it affects the ocean. It opens by defining what pollution is in general and what specifically constitutes marine pollution. It addresses the problem of humans disposing of waste in the oceans and the types of environmental problems that may arise. One section of the chapter is devoted to petroleum pollution and examines the impacts of oil spills as well as some notable oil spills that have been highly damaging. Prevention and cleaning of oil spills are discussed. Marine environmental problems that are impacted by other types of chemical pollution are explored, with some focus on sewage, pesticides, and mercury. This section of the chapter looks at bioaccumulation and biomagnification of pollution in marine organisms. The chapter also examines non-point source pollution and trash. It has a discussion of plastic trash as a particular problem and looks at ways to mitigate this issue. Part of this chapter looks specifically at biological pollution, such as the introduction of non-native species into ocean habitats.

Essential Concepts 11.1 Explain how pollution is defined.

11.2 Specify the marine environmental problems associated with petroleum pollution.

11.3 Specify the marine environmental problems associated with non-petroleum chemical pollution.

11.4 Specify the marine environmental problems associated with non-point source pollution, including trash.

11.5 Describe actions you can take to help prevent marine pollution.

11.6 Specify the environmental problems associated with biological pollution.

Chapter Outline 11.1

11.2

What Is Pollution?

11.1.1 Marine Pollution: A Definition 11.1.2 Environmental Bioassay 11.1.3 The Issue of Waste Disposal in the Ocean What Marine Environmental Problems Are Associated with Petroleum Pollution?

11.2.1 The 1989 Exxon Valdez Oil Spill SmartFigure 11.3: Comparison of selected oil spills 11.2.2 Other Oil Spills 11.2.2.1 How Damaging Is Oil Pollutant in the Ocean?

Diving Deeper 11.1 Focus on the Environment The 2010 Gulf of Mexico Deepwater Horizon Oil Spill 11.2.2.2 Other Concerns about Oil in the Ocean 11.2.2.3 Cleaning Oil Spills SmartFigure 11.10: Processes acting on oil spills 156 .

11.2.2.4 Preventing Oil Spills 11.3 What Marine Environmental Problems Are Associated with Non-Petroleum Chemical Pollution?

11.3.1 Sewage Sludge 11.3.1.1 New York’s Sewage Sludge Disposal at Sea 11.3.1.2 Boston Harbor Sewage Project 11.3.2 DDT and PCBs 11.3.2.1 DDT and Eggshells 11.3.2.2 DDT and PCBs Linger in the Environment 11.3.3 Mercury and Minamata Disease 11.3.3.1 Minamata Disease 11.3.3.2 Bioaccumulation and Biomagnification 11.3.3.3 How Much Mercury-Rich Seafood Is Safe to Eat? 11.3.4 Other Types of Chemical Pollutants SmartFigure 11.17: How biomagnification concentrates toxins in higherlevel organisms SmartFigure 11.18: Methylmercury concentration in fish, fish consumption rates for various populations, and the danger levels of mercury poisoning 11.4 What Marine Environmental Problems Are Associated with Non-Point Source Pollution, Including Trash?

11.4.1 Non-Point Source Pollution and Trash 11.4.2 Plastics as Marine Debris 11.4.2.1 A Brief History of Plastics SmartFigure 11.21: International laws regulate ocean dumping in U.S. waters.

11.4.2.2 Plastic Nurdles in the Marine Environment 11.4.2.3 Microplastics 11.4.2.4 The Issue of Plastics in the Ocean 11.4.2.5 Reducing the Amount of Plastics in the Ocean 11.5 What Can You Do to Help Prevent Marine Pollution?

Diving Deeper 11.2 Focus on the Environment Twelve simple things you can do to help prevent marine pollution 11.6 What Marine Environmental Problems Are Associated with Biological Pollution?

11.6.1 The Seaweed Caulerpa taxifolia 11.6.2 Zebra Mussels 11.6.3 Other Notable Examples of Marine Biological Pollution 11.7 What Laws Govern Ocean Ownership?

11.7.1 Mare Liberum and the Territorial Sea 11.7.2 Law of the Sea Essential Concepts Review

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Learning Objectives The instructional objectives are performance-based and detail specific learning outcomes for Chapter 11.

The test items contained in the Test Bank are keyed to the learning objectives and the Chapter in Review at the end of the chapter. The order of the objectives mirrors the content presentation in Chapter 11.

Upon completion of this chapter, the student should be able to: 1. Define pollution.

2. Define marine pollution and describe the World Health Organization’s definition of marine pollution.

3. Describe what an environmental bioassay does.

4. Discuss the issue of waste disposal in the ocean.

5. Identify the marine environmental problems that are associated with petroleum pollution.

6. Recognize major notable oil spills, including: A. Exxon Valdez B. Ixtoc #1 C. Deepwater Horizon D. Persian Gulf Spill 7. Describe how hydrocarbons and other toxic compounds from oil spills are damaging to marine life.

8. Describe how oil spills are cleaned, including the use of bioremediation.

9. Understand how oil spills may be prevented.

10. Describe non-petroleum chemical pollution, including: A. sewage sludge B. DDT C. PCBs D. mercury E. pharmaceuticals F. agricultural runoff G. caffeine 11. Understand how sewage sludge is handled, including primary treatment and secondary treatment.

12. Describe the New York and Boston Harbor sewage sludge disposal issues.

13. Recognize how DDT has damaged animal populations and how it has affected eggshells of nesting bird populations.

14. Describe the damaging effects of PCBs in marine organisms.

15. Understand how mercury causes damage to marine environments and how it is converted to methylmercury.

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16. Recognize the role of mercury in causing Minamata disease, as well as the symptoms of this disease.

17. Understand how biomagnification concentrates toxins in higher-level organisms and how bioaccumulation causes toxins to accumulate in living tissues.

18. Discuss whether mercury-containing seafood is safe to eat or not.

19. Define non-point source pollution.

20. Specify what international laws regulate ocean dumping in U.S. waters.

21. Discuss how plastic pollutes the marine environment and specific ocean pollution issues associated with plastic trash and debris.

22. Describe how nurdles form and how they are damaging to ocean environments.

23. Recognize the origins of microplastics and how they cause ocean pollution issues.

24. Understand what MARPOL is and describe how people are taking steps to reduce plastic pollution in oceans.

25. Specify what the Eastern Pacific Garbage Patch is, how large it is, and how it formed.

26. Define biological pollution and understand how non-native species can be considered biological pollution.

27. Recognize notable non-native species, including: A. Caulerpa taxifolia B. Zebra mussels

Teaching Strategies Most students will come to class having an idea of what pollution is, but taking a few minutes to have them define it can be useful for getting them to really think holistically about the concept.

You may find it helpful to ask them why they think the World Health Organization thinks marine pollution is important enough that they came up with their own definition of it. Since major oil spills have been recent news, these news stories are a good opening point for a discussion of marine pollution. Talk about oil spills and why they are important enough to be major news stories. SmartFigure 11.3 can be helpful for putting the scale of notable oil spills in perspective.

Have students think in terms of units they might understand; for example, the Exxon Valdez spilled 44 million liters, or 11.6 million gallons, of oil. How many bottles of soda or milk would this be? How many gas tank fill-ups for your car? Pictures of affected marine life can be disturbing but can often generate sympathy for just how damaging oil pollution can be.

When discussing sewage sludge, you might ask students what types of things they regularly flush or rinse down drains, or what they think others might dispose of via plumbing.

From there, you can talk about how these items ultimately make their way into the ocean and how they might impact the ocean. Although many countries have banned the use of DDT and PCBs, there are others who have not. You can use this point to stimulate a discussion of how the 159 .

continued use of these pollutants might impact global oceans and why some countries choose to keep using these harmful substances. A discussion of mercury and Minamata disease is a good way to introduce the concepts of bioaccumulation and biomagnification. SmartFigure 11.17 may be useful to present in class as an illustration of how higher-level organisms can concentrate pollutants, and you can specify how some organisms humans might eat can cause health issues in people.

Trash is a large problem in the oceans, and plastics are a special problem. Have students think about all the plastic products they might use in one day. Then ask them how many of those plastic items are disposable. You can then talk about how those items could one day end up in the ocean, and show them pictures of ocean trash and the Eastern Pacific Garbage Patch. Lead a discussion on making intelligent choices to minimize having an impact on the environment and how non-point source pollution is an issue that the general public is directly responsible for.

Often students are unfamiliar with the concept of biological pollution. Have them describe ways that invasive species can be damaging to the local population.

Teaching Resources Films ▪ The following short videos are available from NBC Learn at www.nbclearn.com/portal/site/learn/freeresources/chemistry-now/chemistry-of-dispersants o How to Wash an Ocean: Testing Chemical Dispersants on Oil Spill Clean-Up, 6 minutes o How to Clean Up Oil on Coast? Try Super-Vacs, Pom-Poms, 2:16 minutes o Blown Out Oil Well Faces Final Pressure Test, 2:27 minutes o The Gulf Oil Spill One Year Later, 4:32 minutes ▪ Why the Ocean Matters (National Geographic), 2:40 minutes, http://video.nationalgeographic.com/video/why-ocean-matters ▪ Ocean Pollution (NOAA), 7 minutes, www.montereyinstitute.org/noaa/lesson13.html ▪ Oil Spill: Exxon Valdez (PBS), 4:44 minutes, www.pbslearningmedia.org/resource/ess05.sci.ess.watcyc.exxon/oil-spill-emexxon-valdezem-1989/ ▪ Synthetic Sea—Plastic Pollution in the Ocean (Algalita Marine Research and Education), https://www.youtube.com/watch?v=pEKohTXF4Xw

Websites ● www.cbf.org/—Chesapeake Bay Foundation ● https://cfpub.epa.gov/watertrain/index.cfm—Watershed Academy, EPA ● http://education.nationalgeographic.org/oil-spills/—Oil Spills, National Geographic ● www.education.noaa.gov/Ocean_and_Coasts/Ocean_Pollution.html—Ocean Pollution, NOAA

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Concept Check (Questions and Answers) 11.1

What Is Pollution?

1. Examine the World Health Organization’s definition of pollution. Why does it need to be so specific?

Pollution has a very broad definition, and different pollutants may be harmful to different species. The World Health Organization has a specific interest in human health and therefore has a specific definition of pollution as it impacts humans in some way or form.

We have no baseline from which to determine how pollutants have altered the environment. The definition needs to be specific because it can be ambiguous just how much of a substance that causes pollution must be present to be characterized as a pollutant. Quantity is sometimes important in whether or not it will have deleterious effects.

2. What is an environmental bioassay? What are some drawbacks to using an environmental bioassay to determine whether or not a substance should be classified as a pollutant?

It is a widely used technique for determining the pollution concentration that affects marine organisms. A drawback is that it does not predict the long-term effect of pollutions on sea animals. Also, it does not take into account chemical reactions between pollutants, which may generate new, different substances. Environmental bioassays are time consuming and organism specific.

3. From memory, define pollution. Then consider these items and determine whether each one is a pollutant based on your definition (and refine your definition as necessary): a. dead seaweed on a beach b. natural oil seeps c. a small amount of sewage d. warm water from a power plant dumped into the ocean e. sound from boats in the ocean Student answers may vary. The following is a framework for potential answers.

Pollution is defined as any harmful substance. There is some variation for interpretation of the term “harmful,” as in harmful to whom or what? a. Dead seaweed occurs naturally in the environment. In and of itself, it is not harmful and therefore not a pollutant. However, if there are unusually large amounts of seaweed present, and it begins to have a detrimental impact on the immediate environment, it could be considered a pollutant. b. Natural oil seeps may occur naturally, but oil is a pollutant. It has been recognized as harmful to organisms. There are some microscopic organisms that eat oil, so small amounts of oil that are naturally seeped and destroyed by these oil-eating creatures would not harm the environment, but any excess amounts of oil would be a pollutant. c. Sewage is waste and generally harmful. Even if there is a small amount of sewage in one region, it is likely there are larger amounts elsewhere. Sewage does not naturally occur in the environment and is a pollutant. d. Warm water from a power plant will disrupt the natural temperature regime of the local environment, threatening the life and health of any organisms that rely on that local environment. Therefore, this warm water can be considered a pollutant for the area it immediately impacts.

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e. Sound from boats in the ocean would be considered noise pollution. Evidence has shown that in particular for marine organisms that rely on echolocation and long-distance sound waves in the ocean for communication, this noise can be disruptive to their life and mating cycles.

Therefore, even though it may not be tangible to humans, boat noise may be considered to be a pollutant.

11.2

What Marine Environmental Problems Are Associated with Petroleum Pollution?

1. Explain why many marine pollution experts consider oil among the least damaging pollutants in the ocean.

Many marine pollution experts consider oil to be among the least damaging marine pollution because oil—a hydrocarbon—is a naturally occurring source of energy that is biodegradable. In fact, natural undersea oil seeps have occurred for millions of years, and the ocean ecosystem seems to be unaffected (or even, since oil is a source of energy, enhanced) by their presence.

2. Discuss techniques used to clean oil spills. Why is it important to begin cleanup immediately?

Once an oil spill occurs in the ocean, lower-density oil initially floats on top of the higher-density water. Skimming the surface with specially designed skimmers can collect the floating oil, or it can be soaked into absorbent materials. However, the collected oil (or oiled materials) must still be disposed of elsewhere. Additionally, cleanup must begin immediately after the spill or the oil will begin to disperse and come ashore or form tar balls and sink. Because oil is a natural energy source, it is naturally biodegraded by microorganisms such as bacteria and fungi. The method of using these organisms to help clean spills is called bioremediation. Bioremediation has proven to be one of the most successful methods for coping with the deleterious effects of oil spills.

3. Describe the world’s largest accidental and intentionally released oil spills. How many times larger was each than the Exxon Valdez oil spill?

The largest oil spill on record occurred because of intentional dumping by the Iraqi army during their invasion of Kuwait during the 1991 Persian Gulf War. By the time the Iraqis were driven out of Kuwait and the leaking oil wells and sabotaged production facilities were brought under control, more than 908 million liters (240 million gallons) of oil had spilled into the Persian Gulf.

The amount of oil from this spill was over 20 times larger than the spill from the Exxon Valdez, one of the larger oil spills in history in U.S. waters. The Deepwater Horizon spill, which began in April 2010 and was capped 10 months later, released 780 million liters (206 million gallons) of oil into the Gulf of Mexico, making it the world’s largest accidental spill into the ocean, about 20 times larger than the Valdez disaster.

11.3

What Marine Environmental Problems Are Associated with Non-Petroleum Chemical Pollution?

1. How would dumping sewage in deep water off the East Coast help reduce the negative effects to the ocean floor?

If the sludge is dropped in deeper water with a layer of rapidly changing density (pycnocline) between the warmer surface water and the colder deep water, internal waves moving along the density gradient will keep the sludge in suspension until it is moved laterally up to 100 times its

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sinking rate. This will make the sludge available to detritus-feeding zooplankton and reduce the sludge concentration on the ocean bottom.

2. Discuss the animal populations that clearly suffered from the effects of DDT and the way in which this negative effect was manifested.

Birds are the animals that have clearly suffered the most from the effects of DDT in the environment. Most notably, ospreys of Long Island Sound, New York, and brown pelicans of Anacapa Island, California, produced thin eggshells after ingesting DDT. It resulted in most of their eggs being broken by the weight of the parents during incubation. Populations of these birds subsequently declined but have been in recovery since many countries banned the use of DDT. 3. What causes Minamata disease? What are the symptoms of the disease in humans?

Minamata disease is a form of mercury poisoning caused by contact with or ingestion of high levels of the metal mercury. Many people who have been affected by this disease acquired it by ingesting fish containing high levels of methylmercury. Fish can become high in mercury from living in waters with industrial methylmercury discharge. Symptoms include neurological disorders that affect the human nervous system. It causes sensory disturbances, including blindness, tremor, brain damage, birth defects, and death.

11.4

What Marine Environmental Problems Are Associated with Non-Point Source Pollution, Including Trash?

1. What is non-point source pollution and how does it get to the ocean? What other ways does trash get into the ocean?

Non-point source pollution is any type of pollution entering the ocean from sources other than underwater pipelines. Mostly, non-point source pollution arrives at the ocean via runoff from storm drains. Trash can enter the ocean from non-point source pollution or from either legal or illegal ocean dumping.

2. What properties contributed to plastics being considered a miracle substance? How do those same properties cause them to be unusually persistent and damaging in the marine environment?

The properties of plastics that contribute to them being considered a miracle substance are that plastic products are lightweight, strong, durable, and inexpensive. The same properties cause them to be unusually persistent and damaging in the marine environment: ● ● ● ●

Their lightweight property causes them to float and be concentrated at the surface.

Their high strength results in entanglement of marine organisms.

Their durability means that they don’t biodegrade easily, causing them to last almost indefinitely.

Their inexpensive cost allows them to be mass produced and used in almost everything.

11.5 What Can You Do to Help Prevent Marine Pollution?

1. List four main ways you can help the environment in general and the ocean in particular.

Answers will vary. In this section in the textbook, students will read about actions they can take, including reducing the amount of waste they generate, using nontoxic or less hazardous products 163 .

around the house, reusing items, recycling items, using alternate items that generate less waste, becoming politically aware and active, and learning more about science and the ocean.

2. List several specific actions you can take to help reduce marine pollution.

Answers will vary. See Diving Deeper 11.2 for a discussion of this topic.

11.6

What Marine Environmental Problems Are Associated with Biological Pollution?

1. What are non-native species? Why can they be so damaging to ecosystems?

Non-native species are species that are not indigenous to an area but are introduced by human activities (either accidentally or intentionally) to a new area. Because the introduced species are not native, they do not have natural predators or diseases to control their population size. Many non-native marine species are introduced through bilge water or released into a new area by home aquarium enthusiasts. Non-native species frequently displace native species in the ecosystem. Examples of problematic introduced marine species include Caulerpa taxifolia (green algae) and zebra mussels.

2. How did the invasive species Caulerpa taxifolia and zebra mussels get released into new environments?

Caulerpa taxifolia is grown for saltwater aquariums. It is likely that people dumped their aquariums into local seas and this species took hold in places such as the Mediterranean Sea. Zebra mussels appear to have entered North American waters from the ballast (stability) waters of a freight ship coming from Europe.

Critical Thinking Questions (and Answers) 11.1 Why do some experts believe that the ocean can be a repository for many of society’s wastes? If we do use the ocean as a disposal site, what conditions should be required?

Some experts believe that if we monitor the ocean properly, it can be a repository for society’s wastes. They believe that to a certain point, waste in the ocean will be diluted up to a certain finite holding capacity for these wastes. Disposal of waste in the ocean should be accompanied by rigorous monitoring to make sure the waste is not adversely affecting organisms or the environment.

Any waste that is put in the ocean should also not be something that has been shown to be harmful in small amounts or that has been proven to alter the reproduction or life cycles of any organisms it may come into contact with.

11.2 Specify the marine environmental problems associated with petroleum pollution.

Petroleum pollution kills sea animals, including mammals and birds. Birds whose feathers are coated with oil are not resistant to cold and rain. Petroleum contains toxic hydrocarbons, which can cause health issues in marine organisms; if humans eat affected marine organisms, it can harm human health as well. Animals in oil-polluted environments have had their gene expressions altered and lower reproductive success. It can take a long time for marine environments to recover from spilled petroleum.

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11.3 Specify the marine environmental problems associated with non-petroleum chemical pollution.

Sewage sludge can contain many toxic elements, including human waste, heavy metals, pesticides, and other chemicals. In addition to being harmful to the marine organisms in the environment, this waste washing up on beaches hurts tourism. DDT is a particularly bad pesticide that has been banned by many countries; one of its major problems is that when it gets into the bodies of birds, those birds lay eggs with such fragile shells they do not have reproductive success. PCBs are industrial chemicals that were used in insulation and coolants. They were later discovered to cause cancers and genetic mutations in many animal species, as well as reproductive issues. Mercury in the ocean is neurotoxic and has been responsible for Minamata disease, which is a degenerative neurological disorder that has affected humans. Hormones and pharmaceuticals that wash into the oceans can alter the biology of organisms in the environment and can also harm humans who might eat any sea creatures that have consumed these chemicals.

11.4 List and describe the three main problems that floating plastic trash presents to marine organisms. Of the three, which one is potentially the most serious threat? Explain.

1. Ingestion—marine birds and oceanic animals have died from ingesting plastic. It does not break down, and they die from starvation. Marine turtles have died from eating floating plastic bags, mistaking them for jellyfish.

2. Entanglement—animals get entangled in plastic waste and are strangled.

3. Affinity of plastics for toxins—this is potentially the most serious threat. Large amounts of DDT, PCBs, and other oil pollutants can accumulate on plastic trash pieces. If an organism ingests this trash, it suddenly has acquired huge amounts of toxic materials, in addition to plastic, in its body.

11.5 One of the best ways of preventing marine pollution is to keep it from getting into the marine environment in the first place. Considering all the different types of marine pollution, brainstorm ideas on how this could be best accomplished.

Answers will vary.

11.6 Specify the marine environmental problems associated with biological pollution.

Biological pollution is when non-native species are introduced into new environments where they did not naturally occur before. These species may lack natural predators or other natural controls, and therefore may proliferate and take over an ecosystem at the expense of organisms already living there. These species may also introduce new parasites or diseases. These species can completely destroy and transform ecosystems, causing both ecological and economical damages.

Active Learning Exercises 11.1 Working with another student in class, determine five common characteristics of pollution.

Then write down as many different types of marine pollution as you can in two minutes. Share your answers with the class.

Student answers may vary. Common characteristics of pollution include harmful to the environment, harmful to living organisms, waste material, present in large enough quantities to be a problem, causing changes to its surroundings, and other issues that students may determine.

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Student answers may vary. Marine pollution types include petroleum, pesticides (including DDT), fertilizer runoff, sewage sludge, industrial chemicals (e.g., PCBs), mercury, warm water from factories, invasive species, trash of all descriptions, medical waste, and plastics.

11.2 Working with another student in class and using the blue circles shown in Figure 11.3, calculate the total amount of oil that has been spilled into the oceans since the 1991 Persian Gulf War from “natural seeps and regular human activities such as transportation.” Using the circles in Figure 11.3 for scale, sketch circles that represent the amounts in both U.S. waters and globally. Compare these values to the other circles shown in Figure 11.3 and share your results with the class.

Oil input is 1.4 billion liters annually. In 2016, 25 years since the Persian Gulf War, this amounts to: 1.4 billion liters/year × 25 years = 35 billion liters. Any circle will then be about 10 times larger in area than the circles indicating the spillage during the Persian Gulf War. 11.3 Working with another student in class, discuss what we should do with sewage sludge if we can’t dump it into the ocean. What are the most feasible options?

Students may have their own interpretations of these issues. One of the most feasible options is burial of the sludge on land in landfills. Alternatives could involve engineering solutions, such as finding ways to mitigate the toxic compounds within the sludge. Burial of the sludge deep in the sea may also be presented as an option, though it would be a logistically difficult one.

11.4 Working with another student in class, describe the two main sources of microplastics, and discuss problems that microplastics create in the oceans.

One of the main sources of microplastics is cosmetics, cleaners, and scrubbing soaps, some of which contain microbeads to aid in scrubbing, in conjunction with industrial processes that use these microbeads for air blasting. The other main source is larger pieces of plastic that break down into much smaller pieces over time. These small plastics can be an issue as they are frequently ingested by marine organisms, including those low in the food web. Ingestion of these microplastics can be harmful to the creatures that swallow them. These microplastics have been found in Arctic sea ice, and they are being found in extremely large volumes in the oceans, with amounts continuing to increase. Microplastics are known transporters of pollutants as well.

11.5 With another student in class, review the 12 suggested actions to help prevent marine pollution in Diving Deeper 11.2. Of the 12 items listed, which ones are you already doing? Also, which ones could you easily adopt and get others to adopt? Have each group report their findings to the class.

Answers will vary.

11.6 Working with another student in class, search the Internet to find information about one of the invasive species listed in the section “Other Notable Examples of Marine Biological Pollution.” Determine how the species got to its new location, what damage it is currently doing, and what measures are being done to prevent its spread. Report your findings to the class.

Answers will vary, depending on the source of the information.

Atlantic comb jelly (Mnemiopsis leidyi) was transported in ballast water to the Black Sea from the American Atlantic coast. M. leidyi eat zooplankton that would be eaten by commercially important fish species. In addition, they eat the eggs and larva of these same commercial fish species. The invasion contributed to the near total collapse of the Black Sea fishery. In 1997, another invasive 166 .

species of comb jelly (Beroe ctenophore) was accidently introduced. B. ctenophore feeds on M. leidyi and has controlled its population size.

Atlantic cordgrass (Spartina alterniflora) has invaded soft-bottom coasts of California, Washington, and China. It was introduced unintentionally in various ways. For example, it is believed that S. alterniflora was introduced by accident into Willpa Bay in Washington State when seeds were transported in the same barrels that oysters were being shipped in. In addition, in some locations, S. alterniflora was introduced intentionally by landowners. S. alterniflora can alter nutrient cycling, hydrology, and sediment deposition patterns. As it alters the landscape, it can create conditions in which only it can survive. Open intertidal mudflats can be transformed into elevated meadows filled with nothing but S. alterniflora. Various methods have been used to try to control the spread of S. alterniflora, including hand pulling, mowing, herbicide application, and biological control.

Water hyacinth (Eichhornia crassipes) infests tropical estuaries and other water bodies. It was intentionally introduced as an ornamental plant in the United States in 1884. It grows rapidly and will cover entire lakes or rivers, leading to clogged waterways, altered water temperature and chemistry, and exclusion of native plants and animals. Various methods have been used to try to control E. crassipes, including herbicides, draining waterways, and removal using harvesting machines/choppers.

European green crab (Carcinus maenas) arrived on the east coast of North America in the early 1800s in the holds of wooden ships. It arrived on the west coast in 1989 via packing material. It is altering coastal food webs as it feeds on a variety of intertidal animals including oysters, mussels, clams, and juvenile crabs. Attempts to control C. maenas are generally carried out through trapping and removal.

Red lionfish (Pterois volitans) has proliferated out of control in southeast U.S. and Caribbean coastal waters. P. volitans are popular ornamental fish in the aquarium trade and it is possible that they were intentionally released into the western Atlantic. Alternatively, they may have arrived in the ballast water of ships. P. volitans feeds on small crustaceans and fish, including commercially important species. At this time, attempts to control P. volitans are focused on targeted removals by divers.

Additional Active Learning Questions 11.1 Identify a coastal city of interest to the class. Imagine the city council is interested in addressing marine pollution in their community. Break the class up into groups representing the different types of marine pollution discussed in this chapter. Have each group use the Internet to research the pollution type assigned to them as it relates to the identified city.

Students should consider the following in their research: Is this pollution type of particular concern in this area? How could the pollution be addressed? How much would it cost to clean up the pollution? Etc. Then, have each group present their findings to the class. As a class, discuss how the city should use its funds to address marine pollution.

Answers will vary.

11.2 Use the Internet to learn about some of the strategies people are using to remove plastic from the ocean. Describe the strategy. Is it successful? What are some of the challenges in removing plastic from the ocean?

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Answers will vary, but one of the most talked-about systems is detailed here: https://www.theoceancleanup.com.

Exploring Data Figure 11.7 For the four key organisms shown in the figure that were affected by the Exxon Valdez oil spill in Alaska, how did each respond in the years after the spill?

The bald eagle population decreased in the first year and then increased through 1996 to a level higher than its starting population size in 1989.

The cormorant population decreased in the first year, increased through 1993, and decreased through 1996. The final population size in 1996 was higher than the population before the spill.

The harbor seal population declined 6% annually from 1989 to 1997.

The pacific herring population decreased from 1989 through 1991. It then increased slightly through 1992. From 1992 to 1993, the population collapsed, but this collapse was unrelated to the spill.

Figure 11.9 Describe the activities that contribute to marine pollution in each of the three categories of human sources of oil to the ocean. Of the three, which is the greatest source of oil to the ocean?

Petroleum consumption results in small and frequent releases of oil, from cars, boats, and other watercraft. It also includes runoff from paved urban areas. Petroleum consumption represents the greatest source of oil to the ocean contributed by humans (72%).

Petroleum transportation includes refining and distribution activities and accounts for about 22% of the oil released by humans. Petroleum extraction is associated with oil and gas exploration and production and accounts for about 6% of the oil released by humans.

SmartFigure 11.17 How many times more concentrated is DDT at each step of the biomagnification chain?

DDT in zooplankton is 13,333 times more concentrated than DDT in water. (0.04 / 0.000003 = 13,333) DDT in small fish is 12.5 times more concentrated than DDT in zooplankton (0.5 / 0.04 = 12.5) DDT in large fish is four times more concentrated than DDT in small fish (2 / 0.5 = 4) DDT in osprey is 12.5 times more concentrated than DDT in large fish (25 / 2 = 12.5) SmartFigure 11.18 1. How many grams of tuna and/or swordfish would you have to consume every day in order to ingest possibly hazardous levels of mercury? Assume both fish meet the FDA standard of 1.0 ppm of mercury.

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You would need to consume about 37 grams of tuna and/or swordfish a day to ingest possibly hazardous levels of mercury.

2. Approximately how many typical servings of tuna and/or swordfish per day does your answer to Question 1 correspond to?

A typical serving of fish is about 170 grams, so the answer to question 1 (37 grams) corresponds to 22% of a typical serving (37 / 170*100 =22%).

SmartFigure 11.21 Outside of 25 miles from shore, what is the one item that cannot legally be dumped at sea? Why is there such tight regulation for this substance?

Outside of 25 miles from shore, the only item that cannot legally be dumped at sea is plastic. Plastic is of particular concern because it is persistent, it floats, it entangles marine organisms, it adsorbs toxins, and marine organisms ingest it.

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Chapter 12 Marine Life and the Marine Environment Overview This chapter addresses the topic of what characterizes life and how living organisms are classified. The biological hierarchy of classification is discussed. The chapter narrows its focus to specifically address the classification of marine organisms. The distinction between plankton, nekton, and benthos is highlighted early in the chapter. There is a discussion of the number of marine organisms that exist and a section on how various marine organisms are adapted to ocean life. Temperature, viscosity, salinity, dissolved gas content, and transparency of ocean water are all factors that marine life needs to be able to handle in some way. The marine environment is not uniform and has a number of divisions with their associated organisms.

Essential Concepts 12.1 12.2 12.3 12.4 12.5

Discuss the characteristics of life and how living things are classified.

Demonstrate an understanding of how marine organisms are classified.

Specify the number of marine species that exist.

Explain how marine organisms are adapted to the physical conditions of the ocean.

Compare the main divisions of the marine environment.

Chapter Outline 12.1

12.2

12.3

12.4

What Are Living Things, and How Are They Classified?

12.1.1 A Working Definition of Life 12.1.2 The Three Domains of Life SmartFigure 12.1: The three domains of life and the six kingdoms of organisms 12.1.3 The Six Kingdoms of Organisms 12.1.4 Linnaeus and Taxonomic Classification SmartTable 12.1: Taxonomic classification of selected organisms Web Animation: A Visualization of Taxonomic Classification How Are Marine Organisms Classified?

12.2.1 Plankton (Drifters) 12.2.1.1 Types of Plankton 12.2.2 Nekton (Swimmers) 12.2.3 Benthos (Bottom Dwellers) 12.2.3.1 Hydrothermal Vent Biocommunities How Many Marine Species Exist?

12.3.1 Why Are There So Few Marine Species?

12.3.2 Species in Pelagic and Benthic Environments How Are Marine Organisms Adapted to the Physical Conditions of the Ocean?

12.4.1 Need for Physical Support 12.4.2 Water’s Viscosity 170 .

12.4.2.1 The Importance of Organism Size SmartFigure 12.12: Surface area-to-volume ratio of cubes of different sizes

12.5

12.4.2.2 Viscosity and Streamlining 12.4.2.3 Reproduction 12.4.3 Temperature 12.4.3.1 Comparing Cold- and Warm-Water Species 12.4.4 Salinity 12.4.4.1 Extraction of Salinity Components 12.4.4.2 Diffusion 12.4.4.3 Osmosis Web Animation: Osmosis 12.4.4.4 An Example of Osmosis: Saltwater versus Freshwater Fish SmartFigure 12.18: Salinity adaptations of freshwater and saltwater fish 12.4.5 Dissolved Gases 12.4.6 Water’s High Transparency 12.4.6.1 Transparency 12.4.6.2 Camouflage and Countershading 12.4.6.3 Daily Vertical Migration: The Deep Scattering Layer (DSL) Web Animation: Daily Movement of the Deep Scattering Layer (DSL) 12.4.6.4 Disruptive Coloration 12.4.7 Pressure Diving Deeper 12.1 Historical Feature Diving into the Marine Environment What Are the Main Divisions of the Marine Environment?

12.5.1 Pelagic (Open Sea) Environment 12.5.1.1 Epipelagic Zone SmartFigure 12.26: Abundance of dissolved oxygen and nutrients with

depth 12.5.1.2 Mesopelagic Zone 12.5.1.3 Bathypelagic and Abyssopelagic Zones 12.5.2 Benthic (Sea Bottom) Environment 12.5.2.1 Subneritic Province 12.5.2.2 Suboceanic Province Essential Concepts Review

Learning Objectives The instructional objectives are performance-based and detail specific learning outcomes for Chapter 12.

The test items contained in the Test Bank are keyed to the learning objectives and the Chapter in Review at the end of the chapter. The order of the objectives mirrors the content presentation in Chapter 12.

Upon completion of this chapter, the student should be able to: 1. Describe the classification of living organisms, including the following taxonomic distinctions: A. domain (1) Archaea 171 .

(2) Bacteria (3) Eukarya B. kingdom (1) Monera (2) Protista (Protoctista) (3) Fungi (4) Plantae (5) Animalia C. phylum (= division for organisms with cell walls) D. class E. order F. family G. genus H. species 2. Describe the classification of marine organisms as a function of their habitat, including: A. plankton (1) classified according to nutrition and cell type (a) phytoplankton (b) zooplankton (c) bacterioplankton (2) classified according to size (a) macroplankton (b) picoplankton (c) holoplankton (d) meroplankton B. nekton C. benthos 3. Compare species diversity in the marine and terrestrial environment A. Discuss difficulties in describing the extent of marine life B. Discuss the influence of marine environmental stability on species diversity C. Compare species diversity in pelagic and benthic marine environments 4. Discuss the distribution of marine life in the zonation of the oceanic water column, including: i. pelagic environment ii. benthic environment 5. Outline the physical and physiologic adaptations of organisms to life in the marine environment, including: A. strategies for body support B. strategies to prevent sinking (1) surface area-to-volume ratio (2) increasing surface area by adding appendages, spines, projections, etc.

C. streamlined body shape 6. Compare and contrast thermal tolerance in marine organisms including stenothermal and eurythermal organisms.

7. Compare and contrast euryhaline and stenohaline organisms. Give an example of a euryhaline and stenohaline marine/estuarine organism, and describe the environment in which it would live.

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8. Distinguish between diffusion and osmosis. How do the type of environment (living versus nonliving) and the state of matter affect these processes?

9. Distinguish between hypertonic, hypotonic, and isotonic solutions in terms of net water movement.

What are the implications for living cells placed in each of these environments?

10. Discuss the strategies employed by marine and freshwater fish to maintain salt and water balance.

11. Detail the strategies employed by marine organisms to accomplish gas exchange.

12. Explain the relationship between the transparency of water and the kinds of color patterns exhibited by open-ocean organisms. How do the strategies of countershading, disruptive coloration, and transparency affect predation?

13. Describe the deep scattering layer and vertical migration.

14. Describe the relationship between depth and atmospheric pressure in the ocean.

15. The ocean environment is divided into two distinct zones: open water (pelagic) and bottom (benthic).

16. The pelagic environment is divided into two provinces: the neritic (coastal) province and the oceanic province. The oceanic province is further subdivided as follows as a function of depth: A. epipelagic zone B. mesopelagic zone C. bathypelagic zone D. abyssopelagic zone 17. Distinguish among the following oceanic zones as a function of light availability: A. euphotic (photic) zone B. disphotic zone C. aphotic zone

Teaching Strategies This chapter introduces many terms with which students may not be familiar. It may be useful to begin teaching this chapter by defining the terms students will encounter. Specifically, introducing students to the terms for types of marine organisms (e.g., plankton, nekton, and benthos) and the environments in which they are found (e.g., pelagic and benthic) can make these terms seem less formidable when used in context. After introducing students to the taxonomic classification scheme and moving on to classification of marine organisms, frequently refer back to the taxonomic classification when introducing new types of animals and show students where in the hierarchy they fall. For example, if you are talking about dolphins and whales, stress that taken together, these two species are members of the same order. Use of SmartTable 12.1 in class as a demonstration tool and subsequently encouraging students to use this will help students understand these taxonomic classifications.

As you move forward and discuss environmental adaptations, stress the differences between marine and land environments and remind students of how much more of Earth’s surface is covered by ocean. As you discuss different adaptations to the ocean, it may be helpful to find an analogous equivalent

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on the land and determine if the same adaptations are necessary and why or why not. Finish by talking about the different environments within the ocean. Students may find it difficult to envision the sea floor with its darkness, so visuals of animals that inhabit this region and their adaptations may help stress these points.

You may find it helpful to point out that marine organisms do not necessarily have the ability to live anywhere in the water column, anywhere in the world. Hence, this necessitates the division of the ocean into different zones. Just as animals on land occupy various ecological niches, so do ocean species.

This chapter contains a lot of information, much of it highly detailed. It is important to pace yourself, and have students pace themselves, so that it does not seem too overwhelming.

Teacher’s Resources Films ▪ ▪ ▪ ▪ ▪ ▪

Mysteries of the Deep (Walt Disney Productions), 24 minutes Survival in the Sea: Where Land and Water Meet (Indiana University), 30 minutes Into the Deep (IMAX), 35 minutes Oceans (Disney), 84 minutes Ocean Odyssey (PBS), 60 minutes From Drifter to Dynamo: The Story of Plankton (PBS), 3 minutes, www.pbs.org/video/2365586775/

Websites ● ● ● ● ● ● ●

The Deep Sea Ocean Portal (Smithsonian Institution), http://ocean.si.edu/deep-sea Ocean Animal Encyclopedia (Oceana), http://oceana.org/marine-life Marine Life (Marine Bio), http://marinebio.org/oceans/creatures/ Ocean Life (National Geographic), http://ocean.nationalgeographic.com/ocean/ocean-life/ Phytoplankton Identification (University of California, Santa Cruz), http://oceandatacenter.ucsc.edu/PhytoGallery/phytolist.html Plankton Species List (Pacific Marine Science Organization), www.pices.int/projects/cpr/species/ Census of Marine Life, www.coml.org

Concept Check (Questions and Answers) 12.1

What Are Living Things, and How Are They Classified?

1. What characteristics should be included in a good working definition of life?

Life consumes energy from its environment and needs water or some other solvent to survive.

There should exist a membrane to distinguish a living thing from its environment. It should be adaptable to its environment, able to evolve, and able to reproduce.

2. List the three major domains of life and the six kingdoms of organisms. Describe the fundamental criteria used in assigning organisms to these divisions.

All living organisms can be divided into one of the three major domains (branches) of life: Archaea, Bacteria, and Eukarya.

A. Archaea is a group of simple microscopic bacterialike organisms that are believed to be the

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closest ancestors of primitive cells. They are often found living in extreme environmental conditions (temperature, pressure, salinity, etc.) that may be similar to the conditions of the primitive Earth. This group includes the methane producers and sulfur-oxidizing organisms found in hydrothermal vents.

B. Bacteria includes simple single-celled organisms that have cell walls and lack a defined nucleus. Members of this group include cyanobacteria (blue-green algae), purple bacteria, green non-sulfur bacteria, and many of the disease-causing bacteria.

C. Eukarya contains all organisms containing cells with membrane-bound organelles and a nucleus defined by a membrane. Protists, fungi, plants, and animals are all members of this domain.

Within the three domains of living organisms, six distinct kingdoms of life are recognized. These kingdoms are separated using the level of cellular complexity and cellular structures shared by the members of the kingdoms.

A. Kingdom Eubacteria includes all of the simple, single-celled microscopic organisms. These organisms lack discrete nuclei and the internal organelles present in all other organisms.

B. Kingdom Archaebacteria includes simple, microscopic bacterialike organisms. This group includes methane producers and sulfur oxidizers and are likely some of the oldest organisms on Earth.

C. Kingdom Protista includes all of the simple unicellular organisms with membrane-bound nuclei and organelles and many multicellular, photosynthetic organisms that have an independent unicellular phase in the life cycle, such as algae.

D. Kingdom Fungi includes complex multicellular heterotrophic organisms that have cell walls, including fungi and molds.

E. Kingdom Plantae includes complex multicellular photosynthetic organisms that have cells with cell walls; plants.

F. Kingdom Animalia includes complex multicellular heterotrophic organisms that lack cell walls (plasma membranes only); animals.

3. What are thought to be the ancestors of the three domains of life?

All organisms are thought to share one common ancestor. This idea is called universal common ancestry. These ancestors are thought to have been a community of early primitive cells, some of which engulfed neighbors, acquiring new genetic coding.

12.2

How Are Marine Organisms Classified?

1. Describe the lifestyles of plankton, nekton, and benthos. Why does plankton account for a much larger percentage of the ocean’s biomass than benthos and nekton combined? ● ● ●

Plankton are organisms that cannot swim against a current and drift in the ocean. Wind and water currents determine their movement.

Nekton are organisms that are active swimmers such as fish and marine mammals. They can determine their position in the water column and on the ocean’s surface because of their larger size and increased mobility (efficient locomotion).

Benthos are organisms that live on the ocean’s bottom.

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Since larger animals eat smaller animals and only a small percentage of the energy (10%) obtained by one population is passed on to the population that feeds on it, the percentage of ocean biomass represented by populations of large animals is necessarily less than that represented by smaller organisms. Because phytoplankton either directly or indirectly provide essentially all of the energy for all the oceans’ populations, they therefore must also represent by far the largest part of the biomass in the ocean.

2. List the subdivisions of plankton and benthos and the criteria used for assigning individual species to each.

Plankton ● Phytoplankton—photosynthetic, plantlike plankton ● Zooplankton—heterotrophic, animal-like plankton ● Bacterioplankton—unicellular, bacteria-like plankton ● Macroplankton—large plankton such as jellyfish ● Microplankton—small plankton that can be caught in a fine-meshed silk net ● Picoplankton—plankton that are smaller than 2 μm in diameter ● Holoplankton—organisms that spend their entire life cycle as plankton ● Meroplankton—organisms that spend only the larval stage as plankton and then become either nekton or benthos Benthos ● Infauna—sediment-dwelling benthos ● Epifauna—bottom-dwelling benthos ● Nektobenthos—animals that live on the bottom but are capable of swimming in the water above the bottom.

3. For the following marine organisms, determine if they are plankton, nekton, or benthos: (a) sharks, (b) octopi, (c) clams, (d) diatoms, (e) corals, (f) crabs, (g) giant kelps, (h) jellies, and (i) dolphins.

A. Sharks—nekton B. Octopi—nekton C. Clams—benthos D. Diatoms—plankton E. Corals—benthos F. Crabs—benthos G. Giant kelps—plankton H. Jellies—plankton I. Dolphins—nekton

12.3 How Many Marine Species Exist?

1. How many total species have been cataloged on Earth? How many marine species exist (both number and percentage of total)? Of marine species, how many are benthic versus pelagic?

Of the more than 1.8 million known species of organisms that live on Earth, only about 14% (250,000) inhabit the oceans. Of the marine species, 98% are benthic and only about 2% (about 5000 species) are pelagic.

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2. Why do scientists think that there are many more undiscovered species on Earth?

Much of the deep sea has not been explored due to difficulty and expense. In addition, as many as 2000 new species are discovered annually on land and in the oceans combined.

3. What factors account for the fact that most marine species inhabit the benthic environment?

There are great numbers of benthic environments that create assorted habitats for different organisms to inhabit. The pelagic environment is far more uniform.

12.4

How Are Marine Organisms Adapted to the Physical Conditions of the Ocean?

1. Discuss some adaptations other than size that organisms use to increase their resistance to sinking.

Organisms use several strategies to prevent sinking that are not related to size. Organisms can increase their drag in the water using adaptive body shapes that increase frictional resistance.

Organisms can also decrease their density relative to seawater. This is accomplished in several ways. The Portuguese Man-O-War has a gas bladder that it uses as a flotation device. Other organisms have evolved “sail-like” structures such as appendages that are perpendicular to the water surface. Pelagic large macroalgae have gas-filled bladders (pneumocysts) that keep these organisms near the surface where light is available for photosynthesis. The majority of bony fishes have internal gas bladders that they use to adjust water column position. Other organisms increase fat and/or oil concentrations in their bodies to decrease their density. Sharks have large fatty livers that increase their buoyancy. Some organisms—squid and dinoflagellates, for example—exchange heavier ions (such as sodium, molecular weight 23) for lighter ions (ammonium, molecular weight 18). The exchanged ions have the same electrical charge so that salt and water balance is not affected.

2. List differences between cold- and warm-water species in the marine environment. ● ● ● ●

In warmer waters, floating organisms are physically smaller than organisms in colder waters. This is probably related to the lower viscosity and density of seawater in low-latitude waters. Smaller tropical species can expose more surface area per unit of body mass.

Warm-water species are characterized by ornate appendages/plumage to increase surface area. The extra ornamentation is notably absent in cold-water species (refer to Figures 12.7 and 12.8).

Warmer temperatures increase biological activity rates that more than double with an increase of 10°C (18°F). Tropical organisms apparently grow faster, have a shorter life expectancy, and reproduce earlier and more frequently than their cold-water counterparts.

Tropical populations have increased species diversity in comparison to cooler-water marine populations. However, total planktonic biomass in colder, higher-latitude environments is much greater than at tropical latitudes.

3. Describe the process of osmosis. How is it different from diffusion? What three things can occur simultaneously across the cell membrane during osmosis?

Osmosis is the movement of a substance in solution from an area of higher concentration to an area of lower concentration across a selectively permeable membrane. Diffusion is the

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spontaneous movement of a substance from an area of higher concentration to an area of lower concentration. Osmosis occurs only in the liquid state of matter, and usually occurs only in living cells. In contrast, diffusion occurs in all three states of matter (solid, liquid, and gaseous) and occurs in both living and nonliving matter. The three simultaneous processes that occur across the cell membrane during osmosis are as follows: (1) Water molecules move through the semipermeable membrane toward an area of lower concentration.

(2) Water-soluble nutrient molecules or ions move from where they are more concentrated into the cell where they are used to maintain cell function.

(3) Water-soluble waste molecules move from the cell into the surrounding seawater.

4. What is the problem requiring osmotic regulation faced by hypotonic fish in the ocean?

What adaptation do these animals have to overcome this problem?

Hypotonic fish living in the ocean have body fluids with lower salinity and osmotic pressure than the salinity and osmotic pressure of the ocean water. As a result, their body fluids have a higher concentration of water than the surrounding ocean water, and they tend to lose water from their bodies by osmosis. To replace the lost water, they drink large quantities of ocean water, remove the salt through special cells, and thereby create a supply of replacement water. To conserve their body water, they excrete small volumes of very concentrated urine.

5. How does water temperature affect the water’s ability to hold gases? How do marine organisms extract the dissolved oxygen from seawater?

Reducing the temperature of seawater increases its capacity to hold gases in solution (cold water holds more dissolved gas in solution). To extract dissolved oxygen from seawater, most marine animals have specially designed fibrous respiratory organs called gills that serve to exchange oxygen and carbon dioxide directly with seawater.

6. What is the deep scattering layer (DSL), and why does it migrate vertically during the day?

The DSL is a sonar-reflecting surface that undergoes a daily vertical migration in response to light intensity between the depths of 100 and 200 meters (330 and 660 feet) about midnight, and 900 meters (2950 feet) at noon. The DSL is made of up organisms that migrate to deep waters during the day to hide from predators and they migrate to surface waters at night to feed.

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12.5 What Are the Main Divisions of the Marine Environment?

1. Construct a table listing the subdivisions of the pelagic and benthic environments and the physical factors used in assigning their boundaries.

2. Describe the three zones based on the availability of sunlight. Which one is where most marine life exists? ● ● ●

Euphotic zone—extends from surface to depth where photosynthesis can still happen, rarely deeper than 100 meters (330 feet).

Disphotic zone—is below the euphotic zone, has small but detectable amounts of light, and extends to about 1000 meters (3300 feet).

Aphotic zone—has no light and is generally found deeper than 1000 meters (3300 feet).

Most marine life exists in the euphotic zone.

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Critical Thinking Questions (and Answers) 12.1 Discuss why it is often difficult to differentiate between living and nonliving things.

Living things encompass a broad variety of organisms, some of which do not at all resemble each other. In addition, one general definition of life is that it takes energy from the environment.

However, some things, like a car, can also take energy from their environment but not be a living thing. Some organisms are complex and multicellular, whereas others are very simple, even consisting of cells that lack nuclei.

12.2 Explain why most of the ocean’s biomass is planktonic.

The term “plankton” is broad and describes a large variety of species. Some plankton are animals and others are plants. Plankton can also include bacteria and viruses. In addition, the reproductive stage of other organisms may be planktonic. Plankton generally form the base of any oceanic food chain or food web. By definition, the base of these food chains and webs is usually the most abundant organism.

12.3 Explain how environmental variability affects the number of species present.

On land, there are many different habitats, or ecological niches, for species to inhabit. Each species may uniquely adapt itself for a particular environment. More habitats, or niches, mean more species may be present. In the ocean, the benthic environment has many habitats, or niches, for organisms.

Therefore, the benthic environment can support more species due to more niches, or specialized habitats, for a wider variety of organisms than the fairly uniform open waters of the pelagic environment.

12.4 Determine the surface-to-volume ratio of an organism whose linear dimensions are (a) 1 centimeter (0.4 inch), (b) 3 centimeters (1.1 inches), and (c) 5 centimeters (2 inches). Which one is better able to resist sinking, and why?

One of the strategies used by pelagic marine organisms is frictional resistance. The greater surface area-to-volume ratio an organism possesses, the greater the amount of frictional resistance to sinking it will have per unit of body mass, and the slower it will sink.

The surface area of an object increases as the square of its linear dimension, and the volume (which is proportional to mass) increases with the cube of the linear dimension. As illustrated in the following table, an organism with an average linear dimension of 1 centimeter (0.4 inch) will have a surface-to-volume ratio three times that of an organism with an average linear dimension of 5 centimeters (2 inches; refer to Figure 12.12). As a result, the smaller the organism is, the higher its surface area-to-volume ratio. This increased ratio means that organism resists sinking better than larger organisms.

12.5 To help reinforce your knowledge of oceanic biozones, construct and label your own diagram similar to Figure 12.25 from memory.

Refer to Figure 12.25.

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Active Learning Exercises 12.1 With another student in class, construct a nested box diagram similar to Figure 12.3 showing the taxonomic classification of humans. Use the information from Table 12.1 to construct your diagram. Also, use the Internet to find taxonomic information about a marine invertebrate (which lacks a backbone) not listed in Table 12.1 and construct a nested box diagram for it.

The box should have at its center Homo sapiens as genus and species. Subsequent boxes in order of distance from the center are Family Hominidae, Order Primates, Class Mammalia, Subphylum Vertebrata, Phylum Chordata, and Kingdom Animalia.

Answers will vary widely for marine invertebrates. However, all nested box diagrams should have the genus and species at the center, with the kingdom as the outermost box.

12.2 Working with another student in class and the Internet, come up with a list of eight different marine organisms in each of the three main categories of marine life: plankton, nekton, and benthos. Do not duplicate any examples of organisms found in the text. Share your list with the class.

Answers will vary widely.

Examples of plankton may include those found here http://oceandatacenter.ucsc.edu/PhytoGallery/phytolist.html or here www.pices.int/projects/cpr/species/ Examples of nekton may include those found here http://web.vims.edu/bio/shallowwater/benthic_community/nekton.html or here http://montereybay.noaa.gov/sitechar/pelagic5.html Examples of benthos may include those found here www.buzzle.com/articles/list-of-plants-andanimals-of-the-benthic-zone.html or here www.chesapeakebay.net/discover/bayecosystem/bottom 12.3 Working with another student in class and the Internet, go to the Census of Marine Life Website at www.coml.org. Explore the site and make a list of five new species that were discovered during the census. Report your findings to the class.

During the decade the census took place, more than 1200 new species were discovered. Eight of them are summarized and pictured here: www.coml.org/discoveries/discoveries/new_species/newspecies.htm 12.4 Working with another student in class, describe how the depth of the DSL varies over the course of a day. Be sure to include reasons why it does this and which organisms comprise the DSL. Report your findings to the class.

The DSL is at its deepest during the day. It migrates to the surface at night. Organisms in the DSL move to deep waters in daytime to hide from predators, and then rise to surface waters at night to feed. Organisms that comprise the DSL include copepods, krill, and lantern fish.

12.5 Working with another student in class, explain why the two curves in Figure 12.26 have the shape that they do (e.g., why the oxygen-minimum layer exists and why it coincides with the nutrient maximum). Share your analysis with the class.

The oxygen-minimum layer exists at a depth of about 700 to 1000 meters (2300 to 3280 feet). At the surface, oxygen is abundant because these surface ocean layers mix with the atmosphere and there is 181 .

a great deal of phytoplankton photosynthesis. Nutrient content at the surface is low because it is quickly taken in by organisms who require the conditions present in surface waters. At the oxygenminimum layer, oxygen cannot be produced due to a lack of sunlight, and what oxygen is present is quickly depleted by the few organisms there. Because animal life also decreases below the photic zone, there is a decreased uptake of nutrients and therefore a nutrient maximum occurs in conjunction with the oxygen-minimum layer.

Additional Active Learning Exercises 12.1 Animals that can tolerate a wide range of salinities are known as euryhaline. Some animals can even move between freshwater and saltwater during their lives. Common examples include salmon, smelt, shad, striped bass, and sturgeon, North American eels, European eels, and bull sharks. Use the Internet to learn more about one such animal. Why does the animal move between freshwater and saltwater? What adaptations allow them to survive in both environments?

Answers will vary depending on the animal.

12.2 Human activities can reduce dissolved oxygen in the ocean so greatly that dead zones are created. Use the Internet to learn more about how these dead zones are created, where they are found, how they affect marine organisms, and how we can manage them.

Answers will vary, but students should learn that dead zones are created through eutrophication.

Nutrients, generally in the form of fertilizers, manure, or sewage, stimulate algal growth. The algae then sink and decompose in the water. Decomposition consumes oxygen and depletes the supply available to other organisms. Most organisms must move out of these areas or they will die. Dead zones occur along the coast and are often associated with the mouth of a large river. The second largest dead zone in the world is found in the Gulf of Mexico, at the mouth of the Mississippi River.

Dead zones are difficult to manage, but the best option is to limit the nutrients going into the ocean by improving water treatment facilities, reducing fertilizer use, and managing manure from large animal operations.

Exploring Data Figure 12.7 From memory, and without looking at the caption, identify the 16 benthos organisms shown in this figure.

See caption for Figure 12.7.

Figure 12.9 Explain why there are so many more marine benthic species as compared to marine pelagic species.

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The benthic environment has many different habitats (such as rocky, sandy, muddy, flat, sloped, irregular, mixed). Diverse habitats provide many niches and allow speciation to occur. In contrast, the pelagic environment is very uniform.

SmartFigure 12.12 What is the surface-to-volume ratio for an even larger organism that has a side = 8? How effective would that organism be at diffusing oxygen across its skin?

For an organism with a side = 8, Surface = 82 x 6 = 384 Volume = 83 = 512 Surface / volume = 384 / 512 = 0.75 Because the surface-to-volume ratio is so small, this organism could not rely on diffusion for its oxygen supply.

SmartFigure 12.18 What are the osmotic adaptation differences between hypertonic and hypotonic fish?

Hypertonic fish experience high osmotic pressure as water is absorbed through the skin. These fish do not drink, produce large amounts of urine, and their cells have the capacity to absorb salt.

Hypotonic fish experience low osmotic pressure as water is lost through the skin. These fish drink large amounts of water, produce a small amount of concentrated urine, and excrete salts through chloride-releasing cells in their gills.

Figure 12.22 Create a depth versus time chart showing the daily migration of organisms that inhabit the DSL.

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SmartFigure 12.26 There is a relationship between the two curves on this figure. Explain what that relationship is and why these two curves look the way that they do.

Near the surface, there is abundant oxygen due to mixing with the atmosphere and photosynthesis.

The photosynthetic algae in this layer uses the nutrients and so the nutrient concentration is low.

Through the mesopelagic zone, oxygen decreases because there is no mixing with the atmosphere, photosynthetic algae do not live below about 150 meters, and dead organic tissue is being decomposed by bacterial oxidation, which uses oxygen. Decomposition releases nutrients into the water and the concentration of nutrients increases through the mesopelagic zone because of this.

Below the mesopelagic zone, nutrient levels remain high and oxygen increases as it is replenished with high-oxygen cold water from the poles.

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Chapter 13 Biological Productivity and Energy Transfer Overview This chapter investigates the relationships between different types of productivity and food webs in the ocean environment. Primary productivity as the base of the food web is introduced as well as the organisms responsible for this type of productivity and ways to measure it. Nutrient availability is discussed, and it is assessed in relation to the availability of solar radiation at various depths in the ocean.

To this end, a discussion of the electromagnetic spectrum and color with respect to the ocean is presented.

Upwelling and nutrient availability are mentioned. A subsection of the chapter is devoted to exploring the types of photosynthetic marine organisms that exist, including plants and animals. A discussion of eutrophication and dead zones follows within this subsection. Primary productivity is not uniform throughout the oceans, and the relationship between productivities at different latitudes is compared. The chapter further diagrams the complexities of food chains and food webs that exist in the oceans and how energy flows between different trophic levels. Marine fisheries, and especially the topic of overfishing, affect humans, and another subsection of this chapter addresses the complexity of problems facing these issues.

Essential Concepts 13.1 13.2 13.3 13.4 13.5

Demonstrate an understanding of the mechanisms that control marine primary productivity.

Describe various kinds of photosynthetic marine organisms.

Explain variations in regional oceanic primary productivity.

Discuss how energy and nutrients are passed along in marine ecosystems.

Evaluate several issues that affect marine fisheries.

Chapter Outline 13.1 What Is Primary Productivity?

SmartFigure 13.1: Photosynthesis and respiration are cyclic and complementary processes that are fundamental to life on Earth 13.1.1 Measurement of Primary Productivity 13.1.2 Factors Affecting Primary Productivity 13.1.2.1 Availability of Nutrients 13.1.2.2 Availability of Solar Radiation 13.1.3 Light Transmission in Ocean Water 13.1.3.1 The Electromagnetic Spectrum SmartFigure 13.3: The electromagnetic spectrum and transmission of visible light in seawater 13.1.3.2 The Color of Objects 13.1.3.3 Water Color and Life in the Oceans 13.1.4 Why Are the Margins of the Oceans So Rich in Life?

13.1.4.1 Upwelling and Nutrient Supply Web Animation: Ekman Spiral and Coastal Upwelling/Downwelling 185 .

SmartFigure 13.6: Coastal Upwelling 13.2 What Kinds of Photosynthetic Marine Organisms Exist?

13.2.1 Seed-Bearing Plants (Anthophyta) 13.2.2 Macroscopic (Large) Algae 13.2.2.1 Green Algae 13.2.2.2 Red Algae 13.2.2.3 Brown Algae 13.2.3 Microscopic (Small) Algae 13.2.3.1 Golden Algae 13.2.3.1.1 Diatoms 13.2.3.1.2 Coccolithophores 13.2.3.1.3 Dinoflagellates 13.2.3.1.4 Red Tides 13.2.3.1.5 Dinoflagellate Toxins 13.2.4 Ocean Eutrophication and Dead Zones SmartFigure 13.14: How dead zones form 13.2.5 Photosynthetic Bacteria 13.3 How Does Regional Primary Productivity Vary?

SmartTable 13.1: Values of net primary productivity for various ecosystems 13.3.1 Productivity in Polar (High-Latitude) Oceans: 60 to 90 degrees north and south latitude 13.3.2 Productivity in Tropical (Low-Latitude) Oceans: 0 to 30 degrees north and south latitude 13.3.3 Productivity in Middle-Latitude (Temperate) Oceans: 30 to 60 degrees north and south latitude 13.3.3.1 Winter 13.3.3.2 Spring 13.3.3.3 Summer 13.3.3.4 Fall Web Animation: Oceanic Midlatitude Productivity 13.3.4 Comparing Regional Productivity 13.4 How Are Energy and Nutrients Passed Along in Marine Ecosystems?

13.4.1 Flow of Energy in Marine Ecosystems 13.4.1.1 Producers, Consumers, and Decomposers 13.4.2 Flow of Nutrients in Marine Ecosystems 13.4.2.1 Biogeochemical Cycling 13.4.3 Ocean Feeding Relationships 13.4.3.1 Feeding Strategies 13.4.3.2 Trophic Levels 13.4.3.3 Transfer Efficiency 13.4.3.4 Food Chains, Food Webs, and the Biomass Pyramid 13.4.3.4.1 Food Chains SmartFigure 13.28: Ecosystem energy flow and efficiency 13.4.3.4.2 Food Webs 13.4.3.4.3 Biomass Pyramid SmartFigure 13.30: Oceanic biomass pyramid 13.5 What Issues Affect Marine Fisheries?

13.5.1 Marine Ecosystems and Fisheries 13.5.2 Overfishing 13.5.2.1 Ecosystem Effects of Overfishing Large Predators 13.5.2.2 The End of Fish?

13.5.2.3 Recreational Fishing 13.5.2.4 World Fish Production 186 .

Diving Deeper 13.1 Focus on the Environment Fishing Down the Food Web: Seeing Is Believing 13.5.3 Incidental Catch 13.5.3.1 Tuna and Dolphins 13.5.3.2 Driftnets 13.5.3.3 Ghost Fishing SmartFigure 13.36: Methods and gear used in commercial fishing 13.5.4 Fisheries Management 13.5.4.1 Regulation of Fishing Vessels 13.5.4.2 A Case Study: Fisheries in the Northwest Atlantic 13.5.4.3 Deep-Water Fisheries 13.5.4.4 Ecosystem-Based Fishery Management 13.5.4.5 Effectiveness of Fishery Management 13.5.5 Effect of Global Climate Change on Marine Fisheries Diving Deeper 13.2 Focus on the Environment Protecting Our Oceans: What are Marine Protected Areas (MPAs) 13.5.6 Seafood Choices Essential Concepts Review

Learning Objectives The instructional objectives are performance-based and detail specific learning outcomes for Chapter 13.

The test items contained in the Test Bank are keyed to the learning objectives and the Chapter in Review at the end of the chapter. The order of the objectives mirrors the content presentation in Chapter 13.

Upon completion of this chapter, the student should be able to: 1.

Define biomass in the context of the marine environment.

2.

Define primary productivity and distinguish between photosynthesis and chemosynthesis with respect to primary productivity. Name locations in the ocean in which you would expect to find photosynthetic and chemosynthetic organisms.

3.

Outline the methods used to estimate primary productivity in marine environments, including: a. plankton nets b. SeaWiFS (Sea-viewing Wide Field-of-view Sensor) c. MODIS

5.

Name the nutrients that limit primary productivity in marine environments.

6.

Describe the sources of nutrient input into ocean systems, including: a. coastal runoff b. river input c. upwelling

7.

Define the compensation depth for photosynthesis and describe how it is measured.

8.

Explain the relationship between the compensation depth, the euphotic zone, and the depth to which solar radiation penetrates the ocean. How do these relationships change in coastal waters as opposed to waters of the epipelagic open ocean?

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9.

Provide an explanation as to why marine life is more abundant in coastal waters as compared to the open ocean. List all factors (biological, chemical, geologic, and physical) that affect species diversity, biomass, and the distribution of life in the ocean.

10.

Detail the electromagnetic spectrum for visible light, and explain the relationship between wavelength and energy. Discuss the implications of this relationship for light penetration in marine environments.

11.

Describe the measurement of water clarity in aquatic systems. What is the relationship between clarity and turbidity? How are these concepts related to primary productivity?

12.

Discuss the relationship between the color of ocean water and the productivity level of that area.

13.

Define eutrophic. How is eutrophication related to nutrient input? To primary productivity?

14.

Identify the different types of upwelling and where they are found globally.

15.

List the photosynthetic organisms commonly found in marine environments, their taxonomic classification, and their preferred habitat, including: a. sea grasses (Kingdom Plantae, Phylum Anthophyta) b. cord grass, Spartina alterniflora (Kingdom Plantae, Phylum Anthophyta]) c. mangroves, Rhizophora and Avicennia (Kingdom Plantae, Phylum Anthophyta]) d. brown algae (Kingdom Protista, Phylum Phaeophyta) e. green algae (Kingdom Protista, Phylum Chlorophyta) f. red algae (Kingdom Protista, Phylum Rhodophyta) g. golden algae (Kingdom Protista, Phylum Chrysophyta) h. diatoms (Kingdom Protista, Phylum Bacillariophyta) i. coccolithophorids (Kingdom Protista, Phylum Haptophyta) j. dinoflagellates (Kingdom Protista, Phylum Pyrrophyta) k. photosynthetic bacteria (Domain Bacteria)

16.

Describe the formation of a harmful algal bloom (HAB). List the causative organisms and the environmental factors that contribute to the development of HABs.

17.

Describe the causes and effects of cultural eutrophication and dead zones.

18.

Compare and contrast the productivity of polar, temperate, and tropical oceans. Describe the physical, chemical, and geologic factors that contribute to productivity differences as a function of latitude. Apply what you have learned in previous chapters.

19.

Distinguish between a community and an ecosystem. Give an example of each that you would find in a marine environment.

20.

Define entropy as it applies to marine systems.

21.

Differentiate between autotrophic and heterotrophic modes of nutrition. Give an example of a marine organism that would employ each nutritional strategy.

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22.

Define each of the following terms that describe the position of an organism in the food chain (trophic level) and an example of a marine organism that fits the category, including: a. producer b. consumer c. decomposer

23.

Distinguish among the following types of consumers in terms of the food they eat and their position on the food chain, and give an example of a marine organism that would fit into each category, including: a. herbivore b. carnivore c. omnivore d. bacteriovore

24.

Define detritus and describe how detritus fits into the energy flow in a marine ecosystem.

25.

Define biogeochemical cycling .

26.

Describe the various feeding strategies employed by marine organisms, including: a. suspension (filter) feeding b. deposit feeding c. carnivorous feeding

27.

Know the relationship between trophic level (caloric content) and the trophic transfer efficiency (gross ecological efficiency). What are the biological implications of a 90% energy loss between adjacent trophic levels?

28.

Distinguish between a food chain, a food web, and a biomass pyramid.

29.

Describe the role of microorganisms in the marine environment.

30.

Define fisheries.

31.

Define maximum sustainable yield (MSY). Discuss how MSY is determined and the implications of yield exceeding MSY, overfishing.

32.

Define bycatch and describe how the amount of bycatch relates to the type of fishing gear used and the area fished.

Discuss the impact of an addendum to the Marine Mammals Act in 1992 on dolphin populations and tuna fishing. How has “dolphin-safe” tuna labeling impacted accidental dolphin mortality rates in the tuna industry?

33.

34.

Distinguish between purse seines and drift nets (gill nets). Discuss the amount of bycatch resulting from the use of these nets.

35.

Define ghost fishing. Explain how ghost fishing affects marine organisms.

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36.

Detail the regulation and management of commercial fish species, including: a. problems facing fisheries management b. regulation of fishing vessels c. deep-water fisheries d. ecosystem-based fisheries management

36.

Discuss how global climate change is affecting marine fisheries.

37.

Outline how consumer choices affect commercial fisheries. Make recommendations regarding how consumer choice can impact fisheries management and harvest of target species.

Teaching Strategies The use of a globe or map of the world is useful for helping students to visualize where low- and highlatitude productivities are in relation to geographic features they may already know. A quick review of the difference between latitude and longitude may also be helpful before discussing high- and low-latitude regions. Also, having students draw their own thermoclines and explain what is going on in their diagrams and how they think it will relate to concepts such as productivity and upwelling may be helpful.

In addition, a scale diagram of ocean depth depicting compensation depths and euphotic zones relative to the volume of the ocean will help students grasp how limited this region is. Using a seafood menu in class, downloaded or brought in, the instructor may highlight different available choices and initiate a discussion of seafood choices and their impacts on ocean fisheries in a concrete way.

There is a lot of varied information in this chapter and being sure to break it down and not cover all of it too quickly will be vital for student retention of the information. A good strategy is to start with a discussion of the difference between food chains and food webs. Then introduce the concept of the primary producers and their role in these. Discuss how species in food chains and food webs are reliant upon each other, and then bring in the biomass pyramid to show how individual organisms differ as you move up through the trophic levels.

Next address the physical parameters involved, including the electromagnetic spectrum, ocean color, and penetration depth of the solar radiation. Upwelling will naturally follow as an additional physical parameter to consider.

Finish with addressing marine fisheries. Many students are aware of dolphin-safe tuna, so asking them what they think this means and why it is important is a good topic opener. It is easy from here to broach the topic of how difficult it is to enforce international regulations and how consumer choices affect the oceans. There is a subsection that addresses how global climate change will affect marine fisheries.

Later in the book, there is more detailed information addressing climate change, but this is a good place to introduce the topic and get students thinking about it early.

Teacher’s Resources Films ▪ Sargasso Sea: Ocean Desert (Films for the Humanities and Sciences), 9 minutes ▪ Seasons in the Sea (National Geographic), 55 minutes (subject: the kelp forest) ▪ Where the Bay Becomes the Sea (Bullfrog Films), 30 minutes, available for purchase and on YouTube, www.youtube.com/watch?v=YhUSCDeWcLA ▪ Essential Science for Teachers: Life Science. Session 7. Energy Flow in Communities (Annenberg Media) 60 minutes, https://www.learner.org/courses/essential/life/session7/

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Websites ● The Plankton Chronicles (Plankton Chronicles)—short, 1- to 3-minute videos about different types of plankton and accompanying text, http://planktonchronicles.org/en/episodes/ ● NOAA Fisheries (NOAA), www.nmfs.noaa.gov ● Mapping Blue Whale Migration (National Geographic), http://education.nationalgeographic.org/activity/mapping-blue-whale-migration/

Concept Check (Questions and Answers) 13.1

What Is Primary Productivity?

1. Discuss chemosynthesis as a method of primary productivity. How does it differ from photosynthesis?

Chemosynthesis differs from photosynthesis in that the energy that goes into the product of the reaction comes from the release of energy from chemical bonds rather than solar radiation.

Chemosynthesis can occur in the absence of sunlight such as in communities associated with hydrothermal vents along the mid-ocean ridge. Here the energy of hydrogen sulfide bonds (H2S) is released through oxidation to free (S) or sulfate (SO4). The bacteria that serve as food for filter-feeding benthos, and the chemosynthetic worms associated with these vents, produce their own food through chemosynthesis.

2. An important variable in determining the distribution of life in the oceans is the availability of nutrients. How are the following variables related: proximity to the continents, availability of nutrients, and the concentration of life in the oceans?

Continents are a source of nutrients due to runoff from the land, specifically nitrates and phosphates, which are essential for phytoplankton. The greatest concentrations of marine organisms are proximal to the continents because the continents are a major source of nutrients.

Phytoplankton use the nutrients to produce carbohydrates, fats, and proteins that make up the base of the food web.

3. Another important determinant of productivity is the availability of solar radiation. Why is biological productivity relatively low in the tropical open ocean, where the penetration of sunlight is greatest?

Even though there is a thicker column of sunlit water in the open ocean far from the continents than in the turbid water near their shores, photosynthesis is greatly restricted in the clear openocean water by the lack of nutrients in surface waters.

4. Discuss the general characteristics of the coastal ocean where unusually high concentrations of marine life are found.

Conditions that result in unusually high concentrations of marine life in some coastal regions are the result of coastal upwelling. Particularly where the surface water is moved offshore by Ekman transport, water from beneath the photosynthetic zone will rise to replace it. Since there is no plant or algal life growing in these deeper waters, they are rich in plant and algal nutrients and serve to continuously supply nutrients to the sunlit surface waters.

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5. Explain why everything in the deep ocean below the shallowest surface water appears bluegreen in color.

The blue-green appearance of objects below the ocean surface is caused by the fact that red wavelengths of light are selectively absorbed within the upper 10 meters (33 feet) of the water.

Unless divers bring their own light source, everything has a blue-green tint below this depth.

13.2 What Kinds of Photosynthetic Marine Organisms Exist?

1. Compare and contrast green, red, and brown algae in terms of composition, color, depth in which they grow, and size.

Brown algae: The dominant color is brown to black. They may grow attached to ocean bottoms at depths of 30 meters (100 feet) or more. The brown algae range in size from the small genus Ralfsia that is a common encrusting form on intertidal rocks to the 30-meter (100-foot) long Pelagophycus (bull kelp). In the Sargasso Sea, a free-floating brown alga gives the area its name, Sargassum.

Green algae: The dominant color is green, and green algae are found in the shallow intertidal zone only. The majority of species are less than 30 centimeters (12 inches) in maximum dimension. Ulva, sea lettuce, is common in tidal pools in colder waters while Codium, sponge weed, is widely distributed in warm water coastal areas.

Red algae: The dominant color is pink to dark red. These algae can use short blue and green wavelengths of light for photosynthesis; they are the group of algae found growing attached to the ocean floor at the lower portion of the photic zone. They have been found at depths up to 268 meters (880 feet), and Corallina is common in rocky intertidal areas. Red algae range in size from barely visible to 3 meters (10 feet) long.

2. The golden algae include two classes of important phytoplankton—diatoms and coccolithophores. Compare and contrast the composition and structure of their tests, and explain their importance in the geologic fossil record.

Diatoms secrete a siliceous cell wall composed of two halves (valves) that are an important constituent of siliceous sediment called diatomaceous earth that is used in filtering devices, industrial abrasives, polishing agents, and numerous other applications. Diatomaceous earth accumulates on the sea floor beneath surface waters that are relatively low in temperature such as in high-latitude regions where equatorial upwelling occurs.

Coccolithophorids are covered with tiny calcareous plates (coccoliths) that are abundant in calcareous oozes found on the sea floor beneath warm surface waters (not too deep because the calcium carbonate goes into solution below the calcite compensation depth [CCD]).

Both of these store food as carbohydrates and oils and both are microscopic algae. They are geologically important because they are preserved as sea-floor deposits, in which other larger organisms may be preserved as fossils.

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3. What is a red tide? What conditions cause red tides?

A red tide is a bloom of certain dinoflagellates. Sometimes the natural environment in the ocean will provide conditions to stimulate the productivity of these dinoflagellates, which proliferate.

Because of their great abundance and their color, this dinoflagellate bloom can make the surface waters appear red.

4. How does paralytic shellfish poisoning differ from amnesic shellfish poisoning? What types of microorganisms create each?

Paralytic shellfish poisoning (PSP) is caused by the dinoflagellate Gonyaulax, which is not poisonous to shellfish, but is concentrated in their tissues and is poisonous to humans who eat the shellfish, even after the shellfish is cooked. PSP affects the human nervous system and symptoms include incoherent speech, uncoordinated movement, dizziness, nausea, and even death.

Amnesic shellfish poisoning is caused by a diatom that produces domoic acid that accumulates in the tissues of unaffected organisms such as mussels and anchovies, but it can be poisonous to other organisms throughout the food web. Symptoms of amnesic shellfish poisoning in humans include permanent memory loss and, in severe cases, death.

5. What conditions create ocean eutrophication (dead zones)? What can be done to limit their spread?

Increased inorganic nutrient input, primarily nitrogen and phosphorus, from terrestrial sources (agriculture, urban runoff) stimulates coastal algal blooms. Eutrophication is caused by excess nutrient input into marine systems. Excessive algal growth pulls oxygen out of the water, producing low dissolved oxygen levels (less than 2.0 g/ml, hypoxia). When oxygen levels drop to 0 g/ml, a dead zone is created. Limiting nutrient input sources would reduce the frequency and severity of marine dead zones.

13.3 How Does Regional Primary Productivity Vary?

1. In your own words, describe how a biological pump works. What percentage of organic material from the euphotic zone accumulates on the sea floor?

The process of removing organic matter from the euphotic zone and concentrating this material on the sea floor is called a biological pump because it removes (“pumps”) carbon dioxide and nutrients from the upper ocean and concentrates them in deep-sea waters and sea floor sediments. Since the vast majority of organic matter is decomposed before it reaches the ocean floor, only about 1% of material from the euphotic zone accumulates on the deep-ocean floor.

2. Describe the yearly productivity pattern in polar oceans, including the main factor that limits productivity in polar oceans.

Many parts of the polar ocean experience darkness, and hence no photosynthetic phytoplankton, for about three months of the year. When sunlight is able to penetrate the ocean deep enough, plankton will start to develop and other organisms will feed on them. The Antarctic has somewhat greater productivity than the Arctic because North Atlantic Deep Water upwells near Antarctica with its high nutrient concentration. The main limiting productivity factor in polar oceans is the availability of solar energy.

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3. Why is the productivity in tropical oceans uniformly low year-round? What are the three environments that are exceptions to this, and what factors contribute to their higher productivity?

Productivity in tropical oceans is uniformly low year-round because uniform heating of the water all year generates a permanent thermocline. This effectively prevents surface water from mixing with the nutrient-rich layers deeper in the ocean. Therefore, the supply of nutrients from deeper waters is eliminated. Exceptions to this are in the following three environments that have these features: Equatorial upwelling: Where the trade winds drive westerly equatorial currents on either side of the equator, surface water diverges as a result of Ekman transport. The surface water that moves toward higher latitudes is replaced by nutrient-rich water that surfaces from depths of 200 meters (660 feet). Equatorial upwelling is best developed in the eastern Pacific Ocean.

Coastal upwelling: Where the prevailing winds blow toward the equator and along the western continental margins, surface waters are driven away from the coast. The displaced water is replaced by nutrient-rich water surfacing from depths of 200 to 900 meters (660 to 2950 feet).

This nutrient-rich upwelling promotes high primary productivity in these areas and, in turn, it supports large fisheries. In the Pacific, such conditions exist along the southern coast of California and the southwestern coast of Peru; in the Atlantic, they exist along the northwestern coast of Morocco and the southwestern coast of Africa.

Coral reefs: Organisms that comprise and live among coral reefs are superbly adapted to lownutrient conditions, in a similar manner to how some terrestrial organisms are adapted to a desert existence. Symbiotic algae living within the tissues of coral and other species allow coral reefs to be highly productive ecosystems. Additionally, coral reefs tend to hold and concentrate the low levels of nutrients in the ecosystem.

4. Describe the yearly productivity pattern in middle-latitude oceans. Describe the limiting factor(s) for both the spring and fall phytoplankton blooms.

There are pronounced seasonal variations at temperate latitudes, and this variation produces a more complex pattern of productivity than in either polar or tropical regions. During the winter, thermal stratification may be minimal, and the surface waters are rich in nutrients as a result of mixing between the deep- and surface-water layers. Productivity is low, however, due to the low angle at which the Sun’s rays strike the ocean surface. Very little solar radiation penetrates the water column, producing a low photosynthetic rate. As the Sun rises higher in the sky during the spring, sufficient sunlight penetrates the water column, producing a spring phytoplankton bloom.

The increased availability of solar radiation also results in the development of a thermocline that prevents the continued supply of nutrients from deep water, and productivity decreases until fall cooling begins to weaken the thermocline. Mixing again occurs, and a smaller fall phytoplankton bloom occurs. It is soon limited by decreased amounts of solar radiation because the Sun is lower in the sky and the day length decreases. To summarize, there is a high level of spring productivity that is limited by a reduced supply of nutrients and a fall increase in productivity that comes to an end because of the lack of solar radiation.

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13.4 How Are Energy and Nutrients Passed Along in Marine Ecosystems?

1. Describe the flow of energy through the biotic community and include forms into which solar radiation is converted. How does this flow differ from the manner in which mass is moved through the ecosystem?

Most energy enters the biotic community as radiant energy supplied by the Sun. Plants convert the solar energy to chemical energy. The chemical energy is stored in the bonds of the organic molecules created during photosynthesis. Chemical energy is released through respiration to be converted into kinetic energy and heat energy until it becomes biologically useless in a state of entropy. This unidirectional flow prevents the recycling of energy within the system once it has been released from its chemical state. Mass moved through the ecosystem is different because the energy represented by the mass of organic matter that is decomposed to inorganic forms is recyclable through the biological uptake of photosynthesis and chemosynthesis.

2. Describe the three types of feeding strategies utilized by marine organisms.

Filter feeding, also called suspension feeding, is when organisms filter plankton in seawater using specially designed anatomical structures.

Deposit feeding is where marine organisms feed on food that has been deposited on the sea floor; these deposits can include detritus and sea-floor sediment.

Carnivorous feeding is where organisms catch and eat other animals.

3. Describe the advantage a top carnivore gains by eating from a food web as compared to a single food chain.

A top carnivore is more likely to survive eating from a food web because it has alternative foods to eat if its preferred food diminishes or disappears.

4. Describe trends that occur in number of individuals, total biomass, and organism size at successive trophic levels going up a biomass pyramid. What conditions produce an inverted biomass pyramid?

The number of individuals is greatest at the bottom of a biomass pyramid. Total biomass decreases the higher up they are found in the pyramid but organism size increases. An inverted pyramid can occur when a small population has a high turnover rate but is the basis of food for a larger population at a higher trophic level.

13.5 What Issues Affect Marine Fisheries?

1. Define overfishing. When a species is overfished, what changes are there in the standing stock, the size of individuals in the remaining fish population, and the maximum sustainable yield?

Overfishing happens when fish are removed from the population so quickly that the remaining population is not yet sexually mature enough to reproduce, resulting in a decline in the fish population and the general size of the fish in that population. The MSY will be significantly reduced as well.

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2. What impact do lost or abandoned traps, nets, and fishing gear have on the environment?

A problem known as ghost fishing can occur, and this is a concern for fisheries. Lost and abandoned traps can continue to catch fish, marine mammals, and other organisms. Animals caught in this gear will die and this is wasteful and therefore harmful to the environment.

3. Describe three examples of unintended consequences that have occurred in marine ecosystems when top predators are removed.

Top predators keep smaller, lower trophic-level fish populations from overrunning ocean ecosystems to the point of destruction. Top predators also keep marine ecosystems healthy because they will prey first on the sick, lame, and old members of lower trophic levels. A coral reef ecosystem may be affected if top carnivores are removed because smaller fish may proliferate and allow for an increase in algae on the corals, which in turn suppresses coral growth.

4. As an environmentally conscious consumer, what factors should you take into consideration before purchasing seafood at a restaurant or grocery store?

Choosing only seafood that has a “sustainable” label means selecting seafood that has been certified by the Marine Stewardship Council and/or Friend of the Sea. This certification means fisheries that are sustainable and not exploited by overfishing are being supported. Referring to Figure 13.40 can give a good idea of best choices, good alternatives, and seafood to avoid for environmental reasons.

Critical Thinking Questions (and Answers) 13.1 As you take a day boat trip in the ocean, you notice the color of the water near the dock is green while the color of the water in deeper waters is blue. What inference can you make about life in the ocean from the water color difference between shallow and deep water?

Coastal waters tend to be yellow-green in color because of the presence of turbidity from continental runoff and because of the microscopic organisms that thrive in this high-nutrient environment. Even though photosynthetic marine algae are extremely small, their abundance can make the shallow waters in which they live appear to be green. Open-ocean water lacks this turbidity and concentrated abundance of nutrients and photosynthetic organisms and tends to be indigo blue. In addition, a physical property of deep water is that it scatters incoming solar radiation preferentially in the blue portion of the electromagnetic spectrum, making the water appear blue.

13.2 Compare and contrast the following: red tides, harmful algal blooms, ocean eutrophication, and dead zones.

A red tide is a proliferation of dinoflagellates to such an extent that they color the surface waters red. Because these dinoflagellates secrete potent biotoxins, these red tides are more correctly called harmful algal blooms (HABs). Ocean eutrophication can contribute to algal blooms by providing an overabundance of the nutrients these algae communities need to thrive. Too much algae will choke the region by depleting the available oxygen, which subsequently leads to the generation of an oxygen-lacking area called a dead zone. While red tides are specific to certain species of dinoflagellates, eutrophication and dead zone creation can be caused by any number of algae species. In addition, not all algae will cause a HAB because not all algae secrete potent biotoxins.

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13.3 Compare the biological productivity of polar, middle-latitude, and tropical oceans. Consider all factors such as seasonal changes in solar radiation, the development of a thermocline, and the availability of nutrients.

Polar regions: There is little seasonal variation in water temperature, which is always at or slightly above the freezing point. Since the surface water is so cold, there is little or no thermal stratification (no thermocline), and nutrient-rich water can readily move to the sunlit surface during the summer months to produce a sustained high level of biological productivity. Plant nutrients are usually available, and productivity is limited only by the availability of solar input. During the winter months, productivity ceases due to little or no solar radiation at high latitudes.

Tropical regions: There is very little seasonal variation in water temperature at low latitudes where the surface water temperatures are always high. The thermocline is permanent, and it prevents nutrient-rich colder water from moving to the surface, restricting primary productivity. At low latitudes solar input never restricts primary production, and primary production is limited by nutrient availability. Primary productivity in the open ocean at tropical latitudes is very low, except in coastal and upwelling areas with nutrient input.

Temperate regions: There are pronounced seasonal variations at temperate latitudes, and this variation produces a more complex pattern of productivity than in either polar or tropical regions.

During the winter, thermal stratification may be minimal, and the surface waters are rich in nutrients as a result of mixing between the deep- and surface-water layers. Productivity is low, however, due to the low angle at which the Sun’s rays strike the ocean surface. Very little solar radiation penetrates the water column, producing a low photosynthetic rate. As the Sun rises higher in the sky during the spring, sufficient sunlight penetrates the water column, producing a spring phytoplankton bloom. The increased availability of solar radiation also results in the development of a thermocline that prevents the continued supply of nutrients from deep water, and productivity decreases until fall cooling begins to weaken the thermocline. Mixing again occurs, and a smaller fall phytoplankton bloom occurs. It is soon limited by decreased amounts of solar radiation because the Sun is lower in the sky and the day length decreases. To summarize, there is a high level of spring productivity that is limited by a reduced supply of nutrients and a fall increase in productivity that comes to an end because of the lack of solar radiation.

13.4 The average efficiency of energy transfer between trophic levels is 10%. Use this efficiency to determine how much phytoplankton mass is required to add just 1 gram (0.04 ounce) of new mass to a killer whale, which is a third-level or top carnivore. Create a diagram that summarizes the different trophic levels and the relative size and abundance of organisms at each level. How would your answer change if the efficiency were half the average rate? Twice the average rate?

If the efficiency of energy transfer between trophic levels averages 10% (0.10), to add 1 gram of new mass to a killer whale at the fourth trophic level requires: 1 ÷ 0.10 ÷ 0.10 ÷ 0.10 ÷ 0.10 = 10,000 grams of phytoplankton mass Diagrams of trophic levels will vary but should contain the elements illustrated in Figure 13.19.

If the transfer efficiency were half the average rate of 10% (5% or 0.05), 1 gram of new mass on a killer whale would require: 1 ÷ 0.05 ÷ 0.05 ÷ 0.05 ÷ 0.05 = 160,000 grams of phytoplankton mass

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If the transfer efficiency were twice the average rate of 10% (20% or 0.20), 1 gram of new killer whale mass would require: 1 ÷ 0.20 ÷ 0.20 ÷ 0.20 ÷ 0.20 = 625 grams of phytoplankton mass Student diagrams will vary, but can resemble something similar to SmartFigure 13.28.

13.5 List several significant problems with current fisheries management practices. How can fisheries management be improved to increase the sustainability of the standing stocks? What changes can be made to fishing gear to reduce the damage to the ecosystem and unwanted bycatch?

Although fisheries management practices have been widely accepted worldwide, they have been largely ineffective. Fishers currently compete with each other for stock; removal of this competition would encourage all fishers to work to sustain the entire fishery in order for everyone’s catch to increase. Fishery management also currently focuses on individual species that are in trouble. If there were a shift to focusing on ecosystem-based management, the entire ecosystem would be healthier and generate a more natural sustainable environment for fish species. The deep sea is lightly regulated, with heavy impacts on the fish stocks. Claims to coastal waters have little efficacy, and it has been difficult to enforce imposed fishing regulations, especially since it is an international community of fishers. Large driftnets have been greatly responsible for ecosystem damage and unwanted bycatch. Changing these nets to make them smaller has helped with this issue, as have regulations limiting their usage and import of bycatch.

Active Learning Exercises 13.1 With another student in class, analyze how a marine organism’s ability to use color to “disappear” in the water column is affected by depth.

Most light we see is reflected from other objects, and all objects absorb and reflect different wavelengths of light. True colors of marine organisms can only be observed in natural light, which is found at surface layers of the ocean, but not at depth. Only the shorter-wave portion of the visible spectrum, with colors such as blue and violet, can be transmitted to deeper layers. Therefore, blue marine organisms will have a greater ability to “disappear” in the water column at deeper depths.

13.2 With another student in class, compile a list of ways to reduce harmful algae blooms in coastal areas.

Student answers may vary, but some ways to do this include reducing fertilizer-rich runoff into coastal waters, closely monitoring coastal industries to make sure they are not polluting waters with phosphorous or nitrogen, preventing nutrient-rich storm drain flow from entering coastal waters, aerating and promoting mixing in coastal waters to prevent accumulations of excess nutrients, and keeping sewage from entering coastal waters.

13.3 With another student in class, discuss how the distribution of nutrients in the ocean and the timing of peak productivity affects the migration of marine mammals such as blue whales from their breeding grounds in Baja California to their feeding grounds in the North Pacific.

Blue whales have a diet that consists mostly of zooplankton. They time their migrations to coincide with peak zooplankton productivities in the middle-latitude and high-latitude oceans. Zooplankton biomass in high-latitude oceans peaks starting in June. Blue whales travel to give birth in these high-

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latitude oceans, and timing their migration to coincide with the peak zooplankton abundances allows them to develop and support their large calves.

13.4 With another student in class, evaluate the fate of top carnivores (e.g., sharks and killer whales) as the catch of secondary consumers, such as tuna, increases.

As top carnivores, these animals rely on the continuous flow of energy through all trophic levels.

Depletion of a large part of one trophic level would have the potential to reduce the number of top carnivores as well, as their food sources become more scarce.

13.5 With another student in class, describe three things that can be done to facilitate the recovery, diversity, and abundance of large marine fish in the world ocean.

Answers may vary, but the list may include tighter regulation of marine fisheries, mitigation of the impacts of climate change, monitoring species in middle trophic levels to ensure there is an abundant supply of food for larger fish, and banning the use of ecosystem-damaging fishing techniques, for example, driftnets.

Additional Active Learning Exercises 13.5 According to the book, fisheries in danger of collapse can be brought back if the following three key items are implemented immediately: (1) set scientifically established quotas or limits on the amount of fish caught and enforce those limits, (2) reduce wasteful and unwanted bycatch, and (3) protect vital habitats that fish use as spawning and nursery areas. Use the Internet to learn more about how the fisheries in the Northwest Atlantic are being managed.

Are the fisheries healthy today? Have managers implemented the three key items listed above?

What challenges have managers encountered in this fishery? If you were managing the fisheries, what initiatives would you suggest be implemented?

Answer will vary.

The following websites are useful: Northwest Atlantic Fisheries Organization https://www.nafo.int NOAA Fisheries, Greater Atlantic Region: https://www.greateratlantic.fisheries.noaa.gov/educational_resources/seafood/fish/

Diving Deeper 13.2 Break the class into two groups: one side representing the benefits of marine protected areas (MPAs) and the other side representing the drawbacks. Give each group time to research MPAs using the textbook and the Internet. Then, bring the class together for a debate.

Answers will vary. However, MPAs with limits to harvest generally benefit organisms that live within the area by allowing populations to grow. The main criticism of MPAs is that they limit fishing grounds.

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Exploring Data Figure 13.21 1. Describe the factors that limit the spring bloom of phytoplankton.

The spring bloom of phytoplankton is limited by the amount of sunlight.

2. Describe the factors that limit the fall bloom of phytoplankton.

The fall bloom of phytoplankton is limited by the availability of nutrients.

Figure 13.22 As compared to the polar and middle latitudes, why do the tropical oceans have a steady, low rate of productivity year-round?

Productivity in tropical oceans is uniformly low year-round because uniform heating of the water all year generates a permanent thermocline. This effectively prevents surface water from mixing with the nutrient-rich layers deeper in the ocean. Therefore, the supply of nutrients from deeper waters is eliminated.

SmartFigure 13.28 For a 10-kilogram (22-pound) salmon at trophic level 4, how many kilograms of phytoplankton at trophic level 1 are needed to support it? Assume the relative efficiencies at each step as shown in the figure.

If the efficiency of energy transfer between trophic levels averages 10% (0.10), to add 10 kilograms of new mass to a salmon at the fourth trophic level requires: 10 ÷ 0.10 ÷ 0.10 ÷ 0.10 = 10,000 kilograms of phytoplankton mass

Figure 13.33 Explain why there is such a large discrepancy between the two curves on this graph.

The reported catch is lower than the estimated actual catch because some fish that were caught were not reported. The estimated actual catch was calculated using an analytical model.

Figure 13.38 According to the map, where specifically are some of the best fisheries management programs located? Where are some of the worst examples?

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Green areas indicate effective fisheries management programs. There are a few of these areas in the Pacific Ocean, far from the continents. Red areas indicate ineffective fisheries management programs. These areas are very common and are found along the coasts of many countries.

Figure 13.40 In examining the list of “avoid” (red) choices, list three items that you or someone you know has consumed.

Answers will vary.

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Chapter 14 Animals of the Pelagic Environment Overview This chapter provides a more detailed look at the animals that live in open water situations.

These animals are varied and have different adaptations to their environments. One way in which these organisms must adapt is in their ability to avoid sinking, which different types of animals accomplish in different ways. Since many of these animals are higher up in the food chain, they prey upon other organisms in the pelagic environment. Different strategies and adaptations of these various animals for catching prey are addressed, with a special look at sharks and the myths surrounding them. The other part of the predator–prey relationship is the animals that may be prey themselves. There is an examination of how different types of animals avoid being prey, either through behavior or evolutionary adaptations. Marine mammals are a category unto themselves and an entire section of the chapter is devoted to marine mammals and their characteristics. There is a look at their taxonomic relationships to other marine organisms and includes both mammals that live in the sea and others, such as polar bears, that live on the land.

There is an extended discussion of Order Cetacea, which includes intelligent marine mammals such as whales and dolphins. Lastly, migration of marine mammals is addressed, with a specific focus on gray whales and their migration patterns and problems with whaling.

Essential Concepts 14.1 Compare the various methods by which marine organisms are able to avoid sinking through the water column.

14.2 Specify adaptations that pelagic organisms possess for seeking prey.

14.3 Specify adaptations that pelagic organisms possess to avoid becoming prey.

14.4 Differentiate between the main groups of marine mammals based on their physical characteristics.

Chapter Outline 14.1

How Are Marine Organisms Able to Stay above the Ocean Floor?

14.1.1 Use of Gas Containers 14.1.1.1 Rigid Gas Containers SmartFigure 14.2: Swim bladder 14.1.2 Ability to Float 14.1.3 Ability to Swim 14.1.4 The Diversity of Planktonic Animals 14.1.4.1 Examples of Microscopic Zooplankton 14.1.4.2 Examples of Macroscopic Zooplankton

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14.2

14.3

14.4

14.1.4.3 Examples of Swimming Organisms SmartFigure 14.9: General features and fins of a fish 14.1.4.4 Types of Fins and Their Usage in Fish What Adaptations Do Pelagic Organisms Possess for Seeking Prey?

14.2.1 Mobility: Lungers versus Cruisers 14.2.2 Swimming Speed 14.2.2.1 Swimming Speed in Cold-Blooded versus Warm-Blooded Fish Diving Deeper 14.1 Oceans and People Some Myths (and Facts) about Sharks 14.2.3 Adaptations of Deep-Water Nekton What Adaptations Do Pelagic Organisms Possess to Avoid Becoming Prey?

14.3.1 Schooling 14.3.2 Symbiosis 14.3.3 Other Adaptations What Characteristics Do Marine Mammals Possess?

14.4.1 Mammalian Characteristics SmartFigure 14.18: Major groups of marine mammals 14.4.2 Order Carnivora SmartFigure 14.20: Skeletal and morphological differences between seals and sea lions 14.4.3 Order Sirenia 14.4.4 Order Cetacea 14.4.4.1 Modifications to Increase Swimming Speed 14.4.4.2 Modifications to Allow Deep Diving 14.4.4.2.1 Oxygen Usage 14.4.4.2.2 Muscular Adaptations 14.4.4.2.3 Do Cetaceans Suffer from the Effects of Deep Diving?

14.4.4.3 Suborder Odontoceti 14.4.4.3.1 Characteristics of Toothed Whales 14.4.4.3.2 Differences Between Dolphins and Porpoises 14.4.4.3.3 Echolocation and Hearing in Toothed Whales 14.4.4.3.4 How Intelligent Are Toothed Whales?

SmartFigure 14.26: Cutaway views comparing the echolocation system of a sperm whale and a dolphin 14.4.4.4 Suborder Mysticeti Web Animation: Feeding in Baleen Whales 14.4.4.4.1 Use of Baleen 14.4.4.4.2 Baleen Whales and Sounds Diving Deeper 14.2 Oceans and People Are Whales Still Hunted?

14.4.4.4.3 Baleen Whale Families Essential Concepts Review

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Learning Objectives The instructional objectives are performance-based and detail specific learning outcomes for Chapter 14. The test items contained in the Test Bank are keyed to the learning objectives and the Chapter in Review at the end of the chapter. The order of the objectives mirrors the content presentation in Chapter 14.

Upon completion of this chapter, the student should be able to: 1. Define the term biomass in the context of the marine environment.

2. Discuss the strategies employed by pelagic animals that prevent sinking in the water column, including: a. air chambers: gas bladder and swim bladder b. increased surface area: additional appendages, spines, and ornamentation c. fatty organs or fat deposits underneath the skin d. structural modifications for living at depth 3. Describe the zooplankton commonly found in the pelagic zone and discuss their role in pelagic food webs, including: a. radiolarian (Kingdom Protista, Phylum Polycystina) b. foraminferans (Kingdom Protista, Phylum Foraminifera) c. copepods (Kingdom Animalia, Phylum Arthropoda, Class Crustacea) 4. Describe the macroscopic planktonic animals commonly found in the pelagic zone and discuss their role in pelagic food webs, including: a. krill (Kingdom Animalia, Phylum Arthropoda, Class Crustacea) b. cnidarians—hydrozoans (Kingdom Animalia, Phylum Cnidaria, Class Hydrozoa), for example: Portuguese man-of-war (Physalia) and by-the-wind sailor (Velella) c. cnidarians—jellyfish (Kingdom Animalia, Phylum Cnidaria, Class Scyphozoa) d. tunicates—salps (Kingdom Animalia, Phylum Chordata, Subphylum Urochordata) e. ctenophores—comb jellies (Kingdom Animalia, Phylum Ctenophora), for example: sea gooseberry (Pleurobrachia) f. chaetognaths—arrowworms (Kingdom Animalia) 5. Describe the role of squid (Kingdom Animalia, Phylum Mollusca, Class Cephalopoda) in the pelagic ocean and give examples of specific pelagic genera.

6. List and describe the usual arrangement of fins in fishes, including: a. dorsal fins b. caudal fins c. pelvic fins d. pectoral fins e. anal fins

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7. Describe specialized pectoral fin modifications in fish, and provide specific examples of fish with highly modified pectoral fins.

8. Differentiate between the musculature of fish that wait for their prey (lungers) as compared to fish that swim at a constant speed (cruisers).

9. Relate the body size of a fish to its potential swimming speed.

10. Compare and contrast poikilothermic (cold-blooded) versus homeothermic (warm-blooded) temperature patterns in fish. Give examples of poikilothermic fish and of fish that approximate homeothermic regulation.

11. Discuss the available food sources for deep-water nekton. How does the body size and population density of deep-water nekton differ from that of coastal species?

12. Explain the function(s) of bioluminescence in deep-water nekton.

13. Suggest reasons why schooling behavior in fish is highly adaptive.

14. Differentiate among the following types of symbiotic relationships and give an example of each, including: a. commensalism b. mutualism c. parasitism 15. List the physiological and physical characteristics shared by all marine mammals.

16. Describe the characteristics shared by the members of the Class Mammalia, Order Carnivora (Kingdom Animalia, Phylum Chordata), including sea otters and polar bears. Describe the geographic distribution of the Carnivora and their food preferences.

17. Describe the characteristics shared by the members of the Class Mammalia, Order Pinnipedia (Kingdom Animalia, Phylum Chordata), including sea lions, walruses, and true seals.

Describe the geographic distribution of the Carnivora and their food preferences.

18. Describe the characteristics shared by the members of the Class Mammalia, Order Sirenia (Kingdom Animalia, Phylum Chordata), including manatees and dugongs. Describe the geographic distribution and food preference, and postulate as to why the number of these animals is declining.

19. Describe the characteristics common to members of the Class Mammalia, Order Cetacea (Kingdom Animalia, Phylum Chordata).

20. Discuss physiologic and anatomical modifications observed in Cetaceans for swimming and diving.

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21. Distinguish between the Cetacean Suborder Odontoceti and Suborder Mysticeti. Provide examples of marine mammals that belong to each taxon.

22. Define the term echolocation. Discuss the melon (spermaceti organ) in toothed whales and describe its function.

23. Describe feeding styles among baleen whales.

24. Differentiate among the three major groups of baleen whales, including: a. gray whales b. rorqual whales c. right whales 25. Describe the seasonal migration of the gray whale. How does latitude relate to the gray whale’s activities (feeding vs. reproduction)?

Teaching Strategies If you have not recently covered the pelagic environment elsewhere, it is important to redefine this term and stress that it covers the open water and you will not be talking about creatures that live on the sea floor or the beach. Students generally have a concept of ocean creatures as being swimmers, and this is a good starting point to ask if there could possibly be other ways besides swimming to keep pelagic animals afloat. Use of SmartFigure 14.2 in class can help illustrate the swim bladder for swimmers. From here, you can ask students what other adaptations marine organisms might use to prevent sinking. Although microscopic organisms have been presented earlier in the book, it is good to remind students that microscopic zooplankton are also marine creatures with their own adaptations to the marine environment. This is also a good opportunity to point out that not all planktonic animals are microscopic; for example, jellyfish are planktonic cnidarians. With the variety of different fin shapes and types, it is important to have a visual depiction of each as you introduce them.

As a transition from discussing adaptations to living in the ocean, consider asking students to discuss other ways animals survive in the marine environment, such as how they avoid being eaten. Some explanations of how organisms avoid becoming prey are self-evident, but having students work together to make a list of ways they think animals evade being eaten before introducing these ways can help students with retention of these ideas. Conversely, you might have students make a list of what they think would make a successful marine predator before introducing marine predators. Sharks hold a particular fascination for people, and you might mention or use clips from Discovery Channel’s Shark Week.

When discussing cold-blooded and warm-blooded fish, have students think of why there are these two different metabolisms and what purpose each would serve. From there, the idea of cruisers and lungers may make more logical sense as a larger concept.

A film with which many students will be familiar is Finding Nemo, and the clownfish/anemone home relationship is a good example of mutualism. Mentioning this movie or even showing a very brief clip will help reinforce this concept for students. There is also a short song sung by Nemo’s teacher about the different classes of animals in the ocean, which might help students remember those.

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Since people are mammals, highlighting what makes a mammal a mammal will help students understand marine mammals. For example, although a seal may not seem to have fur, by definition all mammals must have hair or fur. Students often wonder about the difference between dolphins and porpoises, so this is a good opportunity to discuss that and then discuss the wider variety of marine mammals.

When finishing with a discussion on migration, it may be helpful to begin with a discussion on whaling and why some countries still participate in it. Follow with maps of gray whale migration routes and migration timing, and discuss how whaling may have come about long ago and why it is still culturally significant to some people.

Teacher’s Resources Films ▪ Oceans (Disney), 84 minutes ▪ Gray Whale Migration (NOAA), 2:14 minutes, http://oceantoday.noaa.gov/graywhalemigration/ ▪ Whales 101 (NOAA), 3 minutes, http://oceantoday.noaa.gov/whales101/welcome.html ▪ Best Disguised Predator Fish? (National Geographic)—about the stonefish, 1:19 minutes, http://video.nationalgeographic.com/video/stonefish-predation?source=relatedvideo ▪ NG Live!: Demon Fish (National Geographic)—about sharks, 19 minutes, http://video.nationalgeographic.com/video/ng-live/eilperin-lecture-nglive?source=relatedvideo

Websites ● Jellyfish Facts, www.jellyfishfacts.net ● The Marine Mammal Center, www.marinemammalcenter.org ● Whale World, www.whale-world.com

Concept Check (Questions and Answers) 14.1

How Are Marine Organisms Able to Stay above the Ocean Floor?

1. Discuss why the rigid gas chamber in cephalopods limits the depth to which they can descend. Why do fish with a swim bladder not have this limitation?

The cephalopods Nautilus, Sepia, and Spirula all have rigid-chambered shells that contain gas at a pressure of 1 atmosphere (14.7 pounds per square inch). The maximum depth to which they can descend depends on the strength of the chambered shell. The shells of these cephalopods will collapse when the external pressure exceeds the strength of their shell. For example, the Nautilus will implode at a depth of about 500 meters (1640 feet). Animals with flexible air bladders, such as certain fish, do not suffer the threat of the swim bladder structurally collapsing because the bladder is flexible in contrast to the rigid cephalopod shell. These fish can also regulate the air pressure inside their air bladder.

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2. Explain why hydrozoans and scyphozoans (jellies) are classified as macroscopic forms of zooplankton. Why are they not considered nekton?

Hydrozoans and scyphozoans do not swim well. They propel themselves by way of muscular contraction or by floating on the sea and allowing the wind to push them across the ocean surface. In contrast, nekton can swim well continuously. As macroscopic zooplankton, these animals are large enough to see without a microscope but share the same methods of propulsion with microscopic zooplankton.

3. From memory, name and describe the different types of fins that fish exhibit. What are the five basic shapes of caudal fins, and what are their uses?

Most active swimming fish have two sets of paired fins used in maneuvers such as turning, braking, and balancing. These are the pelvic fins and pectoral fins. When not in use, these fins can be folded against the body. Vertical fins, both dorsal and anal, serve primarily as stabilizers.

The fin that provides most of the thrust for forward motion in high-speed fish is the caudal fin (tail fin). There are five basic shapes of caudal fins, as illustrated in Figure 14.11. a. The rounded fin is flexible and useful in accelerating and maneuvering at slow speeds. b. The truncate fin is somewhat flexible for better propulsion, but is also used for maneuvering. c. The forked fin is also used for better propulsion, is somewhat flexible, and can be used for maneuvering. d. The lunate fin is found on the fast-cruising fish such as tuna, marlin, and swordfish; it is very rigid and useless for maneuvering, but very efficient at propelling the fish. e. The heterocercal fin is asymmetrical, with most of its mass and surface in the upper lobe.

The heterocercal fin produces a significant lift as it is moved from side to side and is common in fish with no swim bladder, such as sharks.

14.2

What Adaptations Do Pelagic Organisms Possess for Seeking Prey?

1. Are most fast-swimming fish cold-blooded or warm-blooded? What advantage does this provide?

Most fast-swimming fish, such as mackerel, sharks, and tuna, are warm-blooded (homeothermic).

The higher body temperature of homeothermic cruisers increases the power output of their muscle tissue. Therefore, they can move faster more immediately than cold-blooded fish. These homeothermic fish conserve the heat needed to maintain body temperature by a modification of their circulatory system; they have cutaneous veins and arteries running along the sides of their body.

2. What are the two food sources of deep-water nekton? List several adaptations of deepwater nekton that allow them to survive in their environment.

The food source for deep-water nekton comes from one of two places: (1) detritus, dead and decaying organic matter and waste products that slowly settle through the water column from the highly productive surface waters, or (2) each other. There are a number of predatory species of nekton.

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Deep-water nekton have many special adaptations to allow them to be efficient at finding and collecting food. These include the following: ● Good sensory devices such as long antennae or sensitive lateral lines that are used to detect the movement of other organisms within the water column. ● Many species have large and sensitive eyes that enable them to see potential prey. To avoid becoming prey, most species are dark colored so that they blend in with the environment. ● Other species are blind and rely on their other senses to obtain food. For instance, the sense of smell is well developed in some species, and it allows certain fish to track down prey items by following a scent trail. ● Well over half of deep-sea fish have bioluminescence capabilities (the ability to biochemically produce light) by using specially designed structures or cells called photophores. ● Large sharp teeth. ● Expandable bodies. ● Hinged jaws that can disarticulate. ● Huge mouths in proportion to their body size.

3. Describe the mechanism by which bioluminescence is accomplished in deep-sea organisms.

What is bioluminescence useful for in the marine environment?

About 80% of bioluminescent organisms have light-producing organs called photophores. Light may be produced from substances that form during digestion, from specialized cells, or from symbiotic bacteria. A biological pigment called luciferin emits photons, which are packets of light, when oxygen is present or produced. Bioluminescence is useful for finding food or attracting prey, marking territory, communication, confusing predators, avoiding predators with distraction, or camouflage by using belly lights to simulate sunlight from above.

14.3

What Adaptations Do Pelagic Organisms Possess to Avoid Being Prey?

1. What are several benefits of schooling?

Although schooling is advantageous during spawning, as it ensures that males and females are in close proximity, most fish appear to school for the protection it provides from predators. ● If members of a species form schools, they reduce the percentage of ocean volume in which a cruising predator might find one of their species. ● Should a predator encounter a large school, it is less likely to consume the entire unit than if it encounters a small school or an individual. ● The school may appear as a single large and dangerous opponent to the potential predator and prevent some attacks. ● Predators may find the continually changing position and direction of the movement of fish within the school confusing, making attack particularly difficult for predators that can only attack one fish at a time.

2. What are the three types of symbiosis, and how do they differ?

Commensalism occurs when a smaller or less-dominant participant benefits without harming the host species that provides the commensal with food or protection. Mutualism occurs when both species benefit. Parasitism occurs when one organism (parasite) benefits at the expense of the host organism.

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3. Besides schooling and symbiosis, what other adaptations do pelagic animals possess to avoid being prey?

These adaptations include using speed, secreting poisons, and mimicking other poisonous or distasteful species. Some species use transparency, camouflage, or countershading.

14.4

What Characteristics Do Marine Mammals Possess?

1. What common characteristics do all organisms in Class Mammalia share?

All organisms in the Class Mammalia (including marine mammals) share the following common characteristics: 1. They are warm-blooded.

2. They breathe air.

3. They have hair (or fur) in at least some stage of their development.

4. They bear live young (except for the few egg-laying Australian mammals from the Subclass Prototheria, which includes the duck-billed platypus and the spiny anteater).

5. The females of each species have mammary glands, structures that give the class its name, that are used to produce milk for their young.

2. Describe marine mammals within the order Carnivora, including their adaptations for living in the marine environment.

Marine mammals within the Order Carnivora include sea otters, polar bears, and the pinnipeds (walruses, seals, sea lions, and fur seals), all of which have prominent canine teeth. Sea otters have dense fur that insulates them from the cold water in which they live. Polar bears have fur with hollow hair shafts for insulation and webbed feet for swimming. Pinnipeds have sensitive whiskers and prominent skin-covered flippers that are used to propel them through the water.

3. How can true seals be differentiated from the eared seals (sea lions and fur seals)?

Seals, also called earless seals or true seals, differ from sea lions and fur seals, also called eared seals, by the following distinguishing characteristics: ● Seals lack the prominent earflap that is specific to sea lions and fur seals. ● Seals have smaller and less-prominent front flippers (called fore flippers) than sea lions and fur seals. ● Seals have prominent claws that extend from their flippers that sea lions and fur seals lack. ● Seals have a different hip structure than sea lions and fur seals. Seals cannot move their rear flippers underneath their bodies as sea lions and fur seals can. ● Seals do not walk on land very well and can only slither along on their bellies (like a caterpillar); sea lions and fur seals use their rear flippers under their bodies and their large front flippers to walk easily on land; they can even ascend steep slopes, climb stairs, and do other acrobatic tricks. ● Seals propel themselves through the water by a back-and-forth motion of the rear flippers (similar to a wagging tail), in contrast to sea lions and fur seals that swim by flapping their large front flippers.

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4. Describe the marine mammals within the order Sirenia, including their distinguishing characteristics.

Marine representatives of the Order Sirenia include the manatees and dugongs, which are collectively referred to as “sea cows.” The manatees are concentrated in coastal areas of the tropical Atlantic Ocean, while dugongs populate the tropical regions of the Indian and Western Pacific Oceans. Both of these animals have a paddle-like tail and rounded front flippers. The land-dwelling ancestors of the sirenians were elephant-like, and extant sirenians today retain some of these unique characteristics, such as a large body size and the presence of toenails in manatees. The sirenians have sparse hairs covering their body but concentrated around the mouth.

5. How can dolphins be differentiated from porpoises?

Porpoises are generally smaller than dolphins, and they have a more “stout” (bulky and robust) body shape compared to the elongated and streamlined dolphin body. Generally, porpoises have a blunt snout (called a rostrum) in contrast to dolphins, which have a longer rostrum. Porpoises have a smaller and more triangular (or, on one species, no) dorsal fin, whereas the dolphin’s dorsal fin is sickle-shaped or falcate. The best way to tell the two apart is by their teeth. Dolphin teeth end in points, in contrast to porpoise teeth that are blunt or flat (shovel-shaped) and resemble human incisors.

6. Describe the differences between cetaceans of the suborder Odontoceti (toothed whales) from those of the suborder Mysticeti (baleen whales). Be sure to include examples from each suborder.

Suborder Odontoceti (toothed whales) has prominent teeth and includes killer whales, sperm whales, porpoises, and dolphins. Suborder Mysticeti (baleen whales) includes the great whales (the largest whales), such as the blue whale, the finback whale, the humpback whale, and the gray whale. The baleen whales have no teeth. Instead, they have baleen, plates of fibrous material that hang from the whale’s upper jaw on the inside of their mouths. Toothed whales have one external nasal opening (blowhole), in contrast to the baleen whales that have two external openings.

7. Compare echolocation systems in sperm whales and dolphins. Evaluate the differences and similarities between the two systems.

In the sperm whale’s large head, air is forced from the trachea through the nasal passages and past the lips of the “monkey’s muzzle.” Contractions of muscles in these structures produce sound that travels toward the head and reflects off the front of the skull, which is bowl-shaped and resembles a radar dish. The sound passes through an organ called the spermaceti organ, in which sound is concentrated by forming various shapes and sizes of lenses. In essence, the organ acts as an acoustical lens that focuses the sound.

Dolphins emit sound from phonic lips near the blowhole. A wide variety of complex sounds, such as clicks, buzzes, and whistles, can be produced from contraction of muscles in the blowhole area. These sounds pass through an organ called the melon, which sits on the skull. The sounds are concentrated as they pass through the melon and can be manipulated by the dolphin.

Both sperm whales and dolphins have the ability to concentrate sound before it leaves their bodies, and both produce sound through contraction of muscles. However, the dolphin uses the 211 .

melon to concentrate these sounds, whereas the sperm whale concentrates sound by passing sounds through a very different-shaped structure, the spermaceti.

8. Describe the mechanism by which baleen whales feed.

The main obstacle that baleen whales face in obtaining food is how to concentrate their small prey items and how to separate these items from seawater. To accomplish these tasks, baleen whales use their rows of fibrous baleen in their mouths that hang from their upper jaw and act as an ideal strainer. To feed, baleen whales fill their mouths with water that includes their prey, allowing their pleated lower jaw to balloon in size. The whales force the water out between the baleen slats, trapping small fish, krill, and other plankton on the inside of their mouths. Mostly, baleen whales feed at or near the surface, sometimes working cooperatively in large groups.

However, the gray whale has short baleen slats and feeds by filtering sediment from the shallow bottom of its North Pacific and Arctic feeding grounds, straining out a diet of benthic organisms.

Critical Thinking Questions (and Answers) 14.1 Explain how a swim bladder works.

A swim bladder is filled with gas that provides some slower-moving fish with buoyancy. The fish may add or remove gas from the bladder in order to maintain a constant gas volume. Some fish can add or release gas through a duct that connects to the esophagus. Other fish accomplish gas-volume change via diffusion through the blood, a much slower process.

14.2 What are the major structural and physiological differences between fast-swimming cruisers and lungers that patiently lie in wait for their prey?

Lungers (such as grouper) have a truncate caudal fin with an aspect ratio of 3 and white muscle tissue that can sustain only the short swimming bursts required to capture passing prey.

Cruisers (such as tuna) have a lunate caudal fin with an aspect ratio of 10 and a large percentage of muscle tissue that is composed of red fiber. The red fiber with its high concentration of myoglobin can reach metabolic rates six times greater than white muscle fiber. Therefore, red muscle fiber does not fatigue as fast as white muscle fiber.

14.3 Evaluate the advantages and disadvantages for a brightly colored yellow fish schooling within a large group of gray-colored fish.

Schooling provides many marine species protection from predators. In a school, there is less overall ocean volume in which one of the school’s species may be found. In addition, the sheer size of a school makes it appear large and potentially dangerous to a predator, which, if it attacks, is unlikely to consume the fittest members of the group. A school is advantageous for reproductive purposes as well since males and females are in close proximity. Bright yellow fish specifically may find an advantage by schooling in a large group of gray fish because the gray fish will blend in more with the ocean environment, especially out of surface waters. This way, the yellow fish may find they are somewhat camouflaged by the gray fish.

A disadvantage of yellow fish schooling within the gray fish is that humans have developed nets that can encircle entire schools of fish. If people are fishing for the gray fish, the yellow fish may find

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themselves entrapped as well. Also, if the gray fish are the preferred food of certain ocean predators, the yellow fish may also be inadvertently eaten as the gray fish are pursued.

14.4 List the modifications that are thought to give some cetaceans the ability to (a) increase their swimming speed, (b) dive to great depths without suffering the bends, and (c) stay submerged for long periods. a. Modifications that allow cetaceans to increase their swimming speed include the following: 1) Few hairs 2) Streamlining 3) A specialized skin structure that modifies the flow of water around their bodies and produces uniform flow conditions that reduce drag and turbulence b. Modifications that allow cetaceans to dive to great depths without suffering the bends include the following: 1) A collapsible rib cage that collapses by the time cetaceans reach a depth of 70 meters (230 feet). There is no air in the lungs to be absorbed under high pressure and the bends, decompression sickness, can be avoided.

2) Lungs within the rib cage also collapse, which removes all air from the alveoli where most gas absorption into the blood occurs.

3) Insensitivity to nitrogen gas that causes the bends. c. Modifications that allow cetaceans to dive and stay submerged for long periods of time include the following: 1) An ability to alternate between periods of normal breathing and cessation of breathing.

2) At the surface, cetaceans take only one to three breaths per minute, which results in inhaled breath remaining in the alveoli longer.

3) The alveolar membrane, with its dense capillary beds, can extract up to 90% of the oxygen in the air.

4) Some cetaceans have twice as many red blood cells and nine times as much myoglobin in their muscle tissue as do terrestrial animals. Large supplies of O2 can be stored in the blood’s hemoglobin and myoglobin of muscle tissue.

5) Muscles can continue to function using anaerobic glycolysis when the oxygen is used up.

6) Additional oxygen conservation may be achieved by closing off the blood flow to most of the body’s organs except the heart and brain (the mammalian diving reflex). This can reduce the heart rate by 50%.

Active Learning Exercises 14.1 Pair up with another student in class. For each pair, have each person decide on which swim bladder adaptation they would like to describe: (1) adaptations that allow for rapid buoyancy changes or (2) adaptations that allow for slow buoyancy changes. Be sure to include how the buoyancy changes are achieved and determine which method is more advantageous.

Share your analysis with each other and then report out to the class.

(1) Fish that can rapidly change buoyancy often have a pneumatic duct that connects the swim bladder to the esophagus. These fish can rapidly add or remove gases from the swim bladder, and thus rapidly change their buoyancy. Addition of gas will make the fish more buoyant and removal of gas will allow the fish to descend lower into the water column.

(2) Fish that have slow changes in buoyancy have swim bladders that add or remove gases by way of interchange with their blood. These fish cannot change depth rapidly.

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Rapid buoyancy changes are more advantageous to the fish because it will aid in finding food and avoiding predators. Fish that need to wait a long time before they are able to change their depth may have a more difficult time preying on food (if they are predators) or avoiding becoming prey for other species.

14.2 Working with another student in class, list the advantages that marine fish have by being warm-blooded as compared to cold-blooded fish. Then compare your list with the list from another group of students in class.

Advantages of warm-blooded marine fish include the following: ● Higher metabolic rates, which translate into increased power output and more effective ability to seek and capture prey. ● Faster physiological processes within the body, which lead to faster-contracting muscles, faster neurological transmissions, and subsequent faster swimming speeds, better vision, and enhanced response times. ● Warm-blooded marine fish have an advantage as predators because of the aforementioned features.

14.3 Working with another student in class, list the advantages of schooling. Then compare your list with the list from another group of students in class.

Advantages of schooling include the following: ● Schooling reduces percentage of ocean volume where a predator might find one of the prey species’ type. ● If a predator does encounter a school of fish, the chances of survival for individual fish are greater. ● A school may look like a large, dangerous opponent to some predators. ● Schools rapidly change position and motion, making it potentially difficult for predators to attack. ● Fish in schools can swim greater distances because of the vortex created by fish swimming in the front of the school. ● There will likely always be males to fertilize eggs released by females, thus increasing reproductive success. ● Schools of small fish can invade the territory of larger fish because of the number of fish in the school.

14.4 Pair up with another student in class. For each pair, have each person decide on which table they would like to construct: (1) a table on the physical characteristics that differentiate true seals from eared seals (sea lions and fur seals) or (2) a table on the physical characteristics that differentiate dolphins from porpoises. Be sure to include the names of representative organisms. Share your table with each other and then compare with other students’ tables that were created in class.

(1) True Seals Lack prominent ear flaps

Eared Seals Have prominent ear flaps, as with sea lions and fur seals Larger, more-prominent front flippers No claws on fore flippers

Smaller, less-prominent front flippers Prominent claws on fore flippers

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Hip structure prohibits moving rear flippers under their bodies, such as with harbor seals Can only slither along on land, such as a crabeater seal Propel themselves through water with backand-forth motion of rear flippers

Hip structure allows rear flippers to be situated under their bodies, such as with sea lions Can use front and rear flippers to walk easily on land Propel themselves through water using large front flippers

(2) Dolphins Elongated, streamlined snout, for example, bottlenose dolphin Falcate or sickle-shaped dorsal fin Pointy teeth, for example, killer whales’ teeth More elongated, streamlined body shape

Porpoises Blunt snout Triangular dorsal fin Blunt or flat teeth Smaller, more stout body shape

Additional Active Learning Exercises Diving Deeper 14.1 With a partner, use the Internet to research the life history of one species of shark. Where do they live? How do they fit into the food web in their ecosystem? How long do they live? Do they migrate?

Where do they breed or give birth? Etc. Then, share your information with the class.

Answers will vary. Instructor may want to assign each pair a specific shark to prevent duplication within the class.

Diving Deeper 14.2 Currently, there is an international agreement, established by the International Whaling Commission (IWC), that bans commercial whaling. Recently, some countries have started pushing to have the ban lifted and establish annual whale fishing quotas. Break the class into two groups that will debate for or against such a measure. Each group should support their argument with scientific/ historical data on fisheries management and whaling.

Answers will vary.

Exploring Data SmartFigure 14.20 Describe the skeletal and morphological differences between seals and sea lions.

Seals Lack prominent ear flaps

Sea Lions Have prominent ear flaps, as with sea lions and fur seals Larger, more-prominent front flippers No claws on fore flippers

Smaller, less-prominent front flippers Prominent claws on fore flippers

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Hip structure prohibits moving rear flippers under their bodies, such as with harbor seals Can only slither along on land, such as a crabeater seal Propel themselves through water with backand-forth motion of rear flippers

Hip structure allows rear flippers to be situated under their bodies, such as with sea lions Can use front and rear flippers to walk easily on land Propel themselves through water using large front flippers

SmartFigure 14.26 Describe the differences in echolocation systems between sperm whales and dolphins.

In sperm whales, air passes through the tightly clinched “monkey’s muzzle,” causing it to snap shut and produce a loud click. The whale then focuses and magnifies the sound by lenses as it passes through the spermaceti organ and junk compartments. Sound is then reflected off the bowl-shaped skull and travels away from the animal. The sound strikes targets in the environment and is reflected. Reflected sound is received by the lower jaw and is transmitted to the ear via fatty and bony tissues.

Dolphins push air through phonic lips near the blowhole, generating a variety of sounds that are transmitted through a fatty tissue called the melon. Dolphins can change the shape of their melon, which focuses sounds forward. Sound reflects off targets in the environment and returns to the dolphin.

Reflected sound is received by the lower jaw and is transmitted to the ear via fatty and bony tissues.

Figure 14.27 Describe how baleen whales use their baleen to feed.

A baleen whale opens its mouth and allows krill and other small prey in. The animal then closes its mouth to force the water through its baleen, capturing its prey.

Process of Science 14.1 Using a calendar and tying your answer to productivity considerations, explain the seasonal cycle of migration for gray whales.

In the Northern Hemisphere, long summer days generate a bloom of phytoplankton at high latitudes, in the Arctic, during the mid to late summer. Gray whales take advantage of this increase in primary productivity to feed abundantly to fatten up for their migration south to warmer waters. The migration begins in September, just after the peak in productivity and after the whales have had enough time to feed and generate enough fat stores to migrate and, in the case of pregnant females, birth in the warmer waters. Gray whales then return to their Arctic grounds starting in late winter to early spring, arriving at the very start of the phytoplankton bloom of summer in early to late June.

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Chapter 15 Animals of the Benthic Environment Overview This chapter discusses animals that live in or on the ocean floor. Not all benthic animals live in the deepest parts of the ocean, although these communities are addressed. This chapter gives overviews of the physical environments that exist in various benthic communities and the adaptations of the organisms that live in these communities. Animals that live on rocky shores are introduced first, and these organisms are examined in the context of intertidal zonation on these rocky shores. Adaptations that animals have to various harsh environments are discussed.

This chapter also looks at the types of communities that inhabit sediment-covered shores and the adaptations various animals have to different zones within these shorelines. The communities that exist on shallow offshore ocean floors are introduced. Special attention is given to coral reefs, the animals that coexist with corals on these reefs, and the adaptations of organisms that live within reefs. The symbiosis and importance of algae with corals is addressed, as is the impact of predators on this system. Deep-ocean floor communities are examined, with attention given to the different types of deep-sea hydrothermal vent biocommunities and their discovery.

The differences between animals in these deep-sea biocommunities, which use chemosynthesis to survive, and photosynthesis-dependent organisms are investigated. Hydrothermal vents are also considered in relation to the origins of life on Earth. Abundant pictures throughout this chapter give a visual of some unusual-looking organisms.

Essential Concepts 15.1 Specify characteristics of the communities that exist along rocky shores.

15.2 Specify characteristics of the communities that exist along sediment-covered shores.

15.3 Specify characteristics of the communities that exist on the shallow offshore ocean floor.

15.4 Specify characteristics of the communities that exist on the deep-ocean floor.

Chapter Outline 15.1

What Communities Exist along Rocky Shores?

SmartFigure 15.1: Worldwide distribution of oceanic benthic biomass reflects overlying primary productivity 15.1.1 Intertidal Zonation SmartTable 15.1: Adverse conditions of rocky intertidal zones and organism adaptations SmartFigure 15.2: Rocky shore intertidal zones and common organisms 15.1.2 The Spray (Supratidal) Zone: Organisms and Their Adaptations 15.1.3 The High Tide Zone: Organisms and Their Adaptations 15.1.4 The Middle Tide Zone: Organisms and Their Adaptations 15.1.5 The Low Tide Zone: Organisms and Their Adaptations 217 .

15.2

15.3

15.4

What Communities Exist along Sediment-Covered Shores?

15.2.1 Physical Environment of the Sediment 15.2.2 Intertidal Zonation 15.2.3 Sandy Beaches: Organisms and Their Adaptations 15.2.3.1 Bivalve Mollusks 15.2.3.2 Annelid Worms 15.2.3.3 Crustaceans 15.2.3.4 Echinoderms 15.2.3.5 Meiofauna 15.2.4 Mud Flats: Organisms and Their Adaptations What Communities Exist on the Shallow Offshore Ocean Floor?

15.3.1 Rocky Bottoms (Subtidal): Organisms and Their Adaptations 15.3.1.1 Kelp and Kelp Forests Web Animation: Underwater Kelp Forests NOAA 15.3.1.2 Lobsters 15.3.1.3 Oysters 15.3.2 Coral Reefs: Organisms and Their Adaptations 15.3.2.1 Conditions Necessary for Coral Reef Development 15.3.2.2 Symbiosis of Coral and Algae 15.3.3 Coral Reef Development 15.3.3.1 Coral Reef Zonation 15.3.3.2 The Importance of Coral Reefs SmartFigure 15.20: Coral reef structure and zonation 15.3.3.3 Coral Reefs and Nutrient Levels 15.3.3.4 The Crown-of-Thorns Phenomenon 15.3.3.5 Coral Bleaching and Other Diseases 15.3.3.6 Coral Reefs in Decline What Communities Exist on the Deep-Ocean Floor?

15.4.1 The Physical Environment 15.4.2 Food Sources and Species Diversity 15.4.3 Deep-Sea Hydrothermal Vent Biocommunities: Organisms and Their Adaptations Diving Deeper 15.1 Research Methods in Oceanography How Long Would Your Remains Remain on the Sea Floor?

15.4.3.1 Discovery of Hydrothermal Vent Biocommunities 15.4.3.2 Chemosynthesis SmartFigure 15.28: Comparing chemosynthesis (top panel) and photosynthesis (bottom panel) 15.4.3.3 Discovery of Other Hydrothermal Vent Fields 15.4.3.4 Life Span of Hydrothermal Vents 15.4.3.5 Hydrothermal Vents and the Origin of Life 15.4.4 Low-Temperature Seep Biocommunities: Organisms and Their Adaptations 15.4.4.1 Hypersaline Seeps 15.4.4.2 Hydrocarbon Seeps 15.4.4.3 Subduction Zone Seeps 15.4.5 The Deep Biosphere: A New Frontier Essential Concepts Review

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Learning Objectives The instructional objectives are performance-based and detail specific learning outcomes for Chapter 15.

The test items contained in the Test Bank are keyed to the learning objectives and the Chapter in Review at the end of the chapter. The order of the objectives mirrors the content presentation in Chapter 15.

Upon completion of this chapter, the student should be able to: 1. Discuss the relationship between benthic biomass and depth of the ocean bottom and the productivity of the euphotic zone above.

2. Define epifauna in benthic marine environments and provide an example of organisms that are part of the marine epifauna.

3. Apply the terminology and concepts mastered in previous chapters to describe the morphology of a rocky shore, including the: a. spray (supralittoral) zone b. intertidal (littoral) zone c. high-water intertidal zone d. middle-water intertidal zone e. low-water intertidal zone 4. Describe the distribution of organisms within the intertidal zone. List the organisms commonly encountered in the spray zone and at differing heights in the intertidal zone. Discuss the physical and chemical factors that affect species distribution on the rocky shore.

5. Define the term sessile and give an example of a marine organism that exhibits this growth pattern.

6. Distinguish between a cnidoblast and a nematocyst. Give the function of these structures and name the phylum characterized by the presence of cnidocytes.

7. Explain the relationship between particle size, water velocity, and wave energy. Where do you find rocky shores, sandy beaches, and mud flats with respect to coastal morphology and wave energy?

8. Describe survival strategies employed by organisms that live in sandy or muddy areas. Include a discussion of the feeding styles of sediment dwellers, including suspension (filter) feeding, deposit feeding, and predation.

9. List and describe the lifestyle of animals found in the sediment-covered intertidal and subtidal zones, including the following: a. Phylum Mollusca, Class Bivalvia—clams, oysters, and scallops—animals with a soft body and a mantle that secretes a shell b. Phylum Annelida, Class Polychaeta—fan worms, feather duster worms, and lugworm— segmented bodies with paddle-like structures and bristles used for burrowing c. Phylum Arthropoda, Class Crustacea—external skeleton, segmented bodies, and jointed appendages; for example, lobsters, crabs, shrimp, and barnacles d. Phylum Echinodermata—spines cover the body, water vascular system with external tube feet, and adults are radially symmetrical; for example, sea urchins, brittle stars, and starfish

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10. Define meiofauna, describe where meiofauna are found in the sediments, and give examples of organisms that comprise the meiofauna.

11. Describe fiddler crab (Uca) claw-waving behavior and the preferred habitat where fiddler crabs are found.

12. Discuss the distribution of organisms found in temperate subtidal (sublittoral) zones with rocky bottoms. Describe the kelp forest in the Pacific Northwest and the adaptations of kelp to life in a rocky area with high wave energy.

13. Explain the structure of a coral polyp (Phylum Cnidaria, Class Anthozoa), and describe the colonial nature of a coral reef structure.

14. Discuss the worldwide distribution of corals. Why are corals more common on the western side of an ocean basin? List the physical and chemical parameters required for coral growth.

15. Describe the endosymbiotic relationship between coral polyps and zooxanthellae. What happens to the coral if the zooxanthellae die?

16. Define mixotroph and apply the term in the context of a coral reef.

17. Explain the three stages of coral reef development including fringing reefs, barrier reef, and atoll.

18. Explain the vertical and horizontal zonation of a coral reef from the windward side (high wave velocity area) to the reef crest to the reef flat in the lagoon. Describe the shape of corals that predominate in each zone and the other organisms that live in each zone.

19. List the biological functions that coral reefs serve in tropical marine environments. Why are they economically important?

20. Discuss anthropogenic impact on corals. How do coastal development, fishing, tourism, and farming/aquaculture affect coral reef health?

21. Detail the effect of Acanthaster planci, the crown-of-thorns sea star, on Pacific coral reefs. Is this a recent phenomenon?

22. Describe the process and causes of coral bleaching.

23. Describe the mechanisms by which coral reefs repair damaged areas.

24. Describe the physical and chemical environment of the deep ocean, including the salinity, temperature, currents, sediment load, and pressure.

25. List the factors that limit benthic biomass in abyssal regions.

26. Relate oceanic plate movement to the distribution of hydrothermal vent communities in the deep ocean. When, where, and by whom were these communities first discovered?

27. Describe a black smoker. Relate the chemical concentration of the vent water to the color of the chimney “smoke.”

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28. Relate the presence of Archaea in hydrothermal vent communities to the food web. How is carbon fixed in the absence of sunlight?

29. Compare and contrast the geographic distribution and biological diversity of hydrothermal vent communities and low-temperature seep communities.

30. List and describe the following low-temperature seep communities, including the following: a. hypersaline seep community b. hydrocarbon seep community c. subduction zone seep community 31. Define and describe the deep biosphere. What kinds of organisms inhabit this unique habitat?

Teaching Strategies The benthic environment may be thought of by many students as only being the deep ocean.

Stress early on that it can include locations students themselves may have experienced, such as shallow sandy beach oceans or rocky shores. Rather than asking students to memorize the names of all species found in different zones, encourage them to approach the topic more holistically and think of different adaptations that might be necessary for these sometimes very harsh environments. If they have seen any of these communities in person from visiting the shore, they can relate what they already know to the topic at hand. When discussing coral reefs, tie this in to changing ocean conditions with global warming, and emphasize the interconnectedness of the oceans to Earth as a system. The hydrothermal vents of the deep-ocean floor are a good example of how scientists, and oceanographers in particular, are always making new discoveries.

Sometimes students feel that we know all of what we need to know on Earth, and hydrothermal vents provide a good example of the fact that we do not.

Make extensive use of pictures of various organisms; the book has many good photographs of organisms that inhabit the communities addressed in the chapter. Have students figure out what types of adaptations the animals might have based on what they look like; sometimes students will intuitively know more than they realize. SmartFigure 15.2 can be very useful for delineating the various zones on a rocky shore. Be sure students understand that within the various benthic communities, there are subzones, and animals within different subzones will have their own specific adaptations.

Teacher’s Resources Films ▪ The World Between the Tides: A Guide to Pacific Rocky Shores (Earthwise Media LLC), 22 minutes ▪ Savage World of the Coral Jungle (The Undersea World of Jacques Cousteau), 48 minutes ▪ Jewels of the Caribbean (National Geographic), 50 minutes (subject: coral reefs) ▪ NOVA: City of Coral (WGBH/Peace River Films), 60 minutes ▪ The Intertidal Zone (Bullfrog Films), 17 minutes ▪ Ocean Odyssey: Secrets of the Deep (BBC), 120 minutes ▪ Earth Revealed: Episode 4, the Sea Floor (Annenberg Media), 30 minutes, http://learner.org/resources/series78.html ▪ Deep Sea (IMAX), 41 minutes 221 .

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Adventure Coral Reef 3-D: Under the Sea of Egypt (3-D Media.tv), 52 minutes Hydrothermal Vent Creatures (Smithsonian Institution), 3:26 minutes, http://ocean.si.edu/oceanvideos/hydrothermal-vent-creatures Deep Sea Hydrothermal Vents (National Geographic), 6:21 minutes, http://education.nationalgeographic.org/media/deep-sea-hydrothermal-vents/

Websites ● The Deep Sea (Smithsonian Institution), https://ocean.si.edu/ecosystems/deep-sea/deep-sea ● Deep Sea Benthos (NOAA), https://oceanexplorer.noaa.gov/explorations/02arctic/background/benthos/benthos.html ● Deep Sea (MarineBio Conservation Society), https://marinebio.org/oceans/deep-sea/ ● The Great Barrier Reef, www.greatbarrierreef.org/ ● Coral Tutorial (NOAA), http://oceanservice.noaa.gov/education/tutorial_corals/welcome.html ● Rocky Shores (Oregon Coast Aquarium), https://aquarium.org/exhibits/rocky-shores/

Concept Check (Questions and Answers) 15.1 What Communities Exist along Rocky Shores?

1. What are some of the adverse conditions of rocky intertidal zones? What are some organisms’ adaptations to those adverse conditions? Which conditions seem to be most important in controlling the distribution of life?

See SmartTable 15.1 for a list of adverse conditions in the intertidal zone and some adaptations of organisms that live there.

An organism’s success is closely tied to its ability to cope with the physical water conditions, the ocean floor, and other members of the biological community. One of the most prominent variables affecting species diversification of benthic organisms may be temperature. As well, the distribution of benthic biomass closely mirrors the distribution of photosynthetic productivity in the surface waters. This suggests that life on the ocean floor is very much dependent upon the primary photosynthetic productivity within the ocean’s surface waters.

2. One of the most noticeable features of the middle tide zone along rocky coasts is a mussel bed. Describe general characteristics of mussels and include a discussion of other organisms that are associated with mussels.

Mussel beds of the genera Mytilis and Modiolus attach to the middle tide zone rocks by secreting hairlike byssal threads. The base of the mussel bed is often very abrupt. A common and visible member of the mussel bed is the gooseneck barnacle, Pollicipes. The mussels are preyed upon by the sea stars, Pisaster and Asterias. Less visible algae, snails, hydroids, worms, clams, and crustaceans are also found in the mussel beds.

3. In which intertidal zone of a rocky shore would you typically find each of the following organisms: sea anemones, sea lettuce, rock louse, abalones, brittle stars, and buckshot barnacles?

Sea anemones: Middle Tide Zone Sea lettuce: Middle Tide Zone 222 .

Rock louse: Spray Zone Abalones: Middle Tide Zone Brittle Stars: Low Tide Zone Buckshot barnacles: High Tide Zone

15.2 What Communities Exist along Sediment-Covered Shores?

1. Describe how sandy and muddy shores differ in terms of energy level, particle size, sediment stability, and oxygen content.

This information is summarized in the following table:

Energy level Particle size Sediment stability Oxygen content

Sandy Shores High Medium- to coarse-grained Low High

Muddy Shores Low Fine-grained High Low

Sediment salinity increases and permeability (the ability of a substance to pass fluid) decreases with decreased particle size. The higher sediment stability of mud flats results from the high cohesive attraction between clay particles and the lower energy longshore current in mud flat regions. The fact that sand-sized particles are rounder and clay-sized particles are flat results in the higher permeability of muddy sediment. Large amounts of organic material must be anaerobically decomposed in these deposits. This often results in sediment from mud flats having a black color and a strong hydrogen sulfide odor.

2. How does the diversity of species on sediment-covered shores compare with that of the rocky shore? Suggest at least one reason why this occurs.

There are more species living on rocky shores than sediment-covered shores. A possible reason for this is that there are more environmental niches on rocky shores than on sediment-covered shores. An environment that has many niches creates conditions that produce high species diversity.

3. In which intertidal zone of a steeply sloping, coarse-sand beach would you typically find each of the following organisms: clams, beach hoppers, ghost shrimp, sand crabs, and heart urchins?

Clams: Low through middle tide zones Beach hoppers: Supratidal zone Ghost shrimp: Middle and high tide zones Sand crabs: Low and middle tide zones Heart urchins: Low tide zone

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15.3 What Communities Exist on the Shallow Offshore Ocean Floor?

1. Discuss the dominant species of kelp, their epifauna, and animals that feed on kelp in Pacific coast kelp forests.

The dominant species of kelp found in Pacific coast kelp forests are Macrocystis (giant brown bladder kelp) and Nereocystis. Smaller varieties of red and brown algae grow on the larger varieties along with hydroids and bryozoans. Nudibranchs feed on hydroids and bryozoans. Very few animals feed directly on living kelp plants. The sea hare, Aplaysia, and sea urchins do feed on living kelp.

2. Describe the environmental conditions required for development of coral reefs.

An environment suitable for coral reef growth must have a minimum average monthly temperature that exceeds 18°C (64°F) throughout the year. Reef-building corals rely on photosynthetic endosymbiotic dinoflagellates (zooxanthellae) that live within their tissues. As a result of this relationship, corals survive only in sunlit waters. Strong water circulation assures an adequate supply of food and oxygen. The water must also have normal salinity and have relatively low turbidity (low amount of suspended sediment) because suspended clay, silt, and detritus particles block light and can smother the coral. Additionally, corals need a hard substrate for attachment.

3. Draw and describe each of the three stages of coral reef development. How does this sequence tie into plate tectonics?

Refer to Figure 15.19, Stages of Development in Coral Reefs.

The fringing reef stage is where the buildup of reef materials is attached to the island; the reef materials exist along the fringe of the island, thus the name fringing reef. As the plate sinks, the reef material builds up vertically as sea level rises. This leaves less of the island exposed and an area between the island and the reef. This is the barrier reef stage.

As sea floor continues to sink lower, the sea level slowly rises. The coral growth keeps up with the rising sea level even when the island is totally submerged under water, leaving an atoll.

4. Describe the zones of the reef slope, the characteristic coral types, and the physical factors related to its zonation.

Physical factors related to the zonation of coral reefs usually include wave energy, salinity, water depth, and temperature. Coral is usually massive in high-energy, near-surface portions of the reef. With increasing depth, wave energy and light energy decrease, producing corals that are more delicate. Corals will not survive at all below about 150 meters (492 feet).

From the surface to a depth of 20 meters (66 feet), there is high-energy wave action and more than 60% of the surface light available. Massive branching corals and algae are found in this “buttress zone.” Between the depths of 20 meters (66 feet) and 50 meters (164 feet), the light level drops to 20% of the surface light, and wave energy decreases. Massive head corals are common in this zone. Light levels drop to about 4% of surface light at 150 meters (492 feet).

Wave energy is also minimal at this depth, and delicate plate corals are common in this zone.

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5. What is coral bleaching? How does it occur? What other diseases affect corals?

Coral bleaching is the loss of color in coral reef organisms that causes them to turn white. The cause of coral bleaching is due to the removal or expulsion of the coral’s symbiotic partner, the zooxanthellae (endosymbiotic dinoflagellates), due to elevated seawater temperature or other environmental stresses. Other diseases that affect corals include white plague, black band disease, white band disease, white pox, yellow band disease (yellow-blotch disease), patchy necrosis, and rapid wasting disease.

15.4 What Communities Exist on the Deep-Ocean Floor?

1. Where does the food come from to supply organisms living on the deep-ocean floor? How does this affect benthic biomass?

With the exception of chemosynthetic productivity that occurs around hydrothermal vents, all deep-ocean floor organisms receive their food from the surface waters above. Low food availability, not low temperature, low oxygen concentration, or high pressure, limits deep-sea benthic biomass.

2. Describe the characteristics of hydrothermal vents. What evidence suggests that hydrothermal vents have short life spans?

Hydrothermal vents occur along the crest of the mid-ocean ridge where the lithosphere is thin and volcanic activity is common. They exist in complete darkness at water depths ranging from 1525 meters (5000 feet) to 3600 meters (11,800 feet). Hydrothermal vents emit hot water up to 350°C (662°F) that is so rich in metal sulfides that it colors the water black, giving these features the name “black smokers.” The chimneys associated with these vents were first observed in 1979 and are composed primarily of copper sulfides, zinc sulfides, and silver sulfides. Hydrothermal vents are often colonized by unusual life-forms that comprise the hydrothermal vent biocommunities.

Evidence that suggests that hydrothermal vents have short life spans (a few years to a few decades) includes direct visitation to the sites that have been active only a few years ago but are no longer active. Other sites that have been visited at frequent intervals indicate an increase in volcanic activity.

3. What is the “dead whale hypothesis”? What other ideas have been suggested to explain how organisms from hydrothermal vent biocommunities populate new vent sites?

The “dead whale hypothesis” suggests that when large animals such as whales die and sink to the deep-ocean floor, they may provide a temporary stepping stone for organisms that inhabit the hydrothermal vent fields separated by large distances. Decomposition of a whale carcass provides an energy source for these organisms that breed and release their larvae, some of which make it to the next hydrothermal vent site.

Other researchers believe that deep-ocean currents are strong enough to transport drifting larvae to new sites. Still others have suggested that the rift valleys of mid-ocean ridges may have acted as passageways along which drifting larvae of hydrothermal vent organisms have traversed to inhabit new vent fields. By whatever means these organisms travel, evidence indicates that they are able to colonize new hydrothermal vents soon after the vents are created.

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4. What are the major differences between the conditions and biocommunities of the hydrothermal vents and the cold seeps? How are they similar?

In hydrothermal vent fields, water temperatures range as high as 12°C (54°F), while the temperatures at the cold water seeps are near ambient values of local water conditions (usually just a few degrees above freezing). Hydrothermal vents are found only in association with springs at the base of the Florida Escarpment, at hydrocarbon seeps, and at subduction zones where trench sediments have been folded. Additionally, the producers at hydrothermal vents are exclusively sulfur-oxidizing bacteria, while at the cold seeps, sulfur- and methane-oxidizing bacteria are important.

The overriding similarity of the communities found at the hydrothermal vents and cold water seeps is that the organisms are much larger than typical deep-sea species because of the large food supply that is locally available by chemosynthetic bacteria.

5. Discuss changes in the physical environment that occur as one moves from the shoreline to the deep-ocean floor.

Moving from the shore along the ocean floor to the deep-ocean basins, the physical environment changes significantly (available light, water temperature, pressure, salinity, etc.). The energy level decreases below wave base (variable, but generally shallow), light decreases gradually and is absent below 1000 meters (3300 feet), and the temperature drops to a fairly uniform 3°C (37.4°F). Pressure increases by 1 atmosphere (14.7 pounds per square inch) with each increase in depth of 10 meters (33 feet). Fine oozes and clays in the deep-ocean basins replace coarse sediment near shore.

Critical Thinking Questions (and Answers) 15.1 From memory, construct a diagram that shows a rocky-shore intertidal region. Name each zone and include characteristic organisms that are typically found there.

Student drawings will vary but should resemble SmartFigure 15.2.

15.2 From memory, construct a diagram that shows a sand-covered intertidal region. Name each zone and include characteristic organisms that are typically found there.

Student drawings will vary but should resemble Figure 15.8.

15.3 Discuss the relationship between corals and algae, and explain how corals benefit from having internal algae.

Corals and algae have a symbiotic relationship, meaning they are interdependent upon one another for survival. The algae are what give corals their varied colors as well. Corals benefit from these algae because corals generally live in nutrient-poor waters. The algae (zooxanthallae) provide the corals with a continual supply of food that they generate photosynthetically.

15.4 Using Figure 15.28, discuss the major differences between chemosynthesis and photosynthesis from a chemical standpoint.

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Chemosynthesis requires the presence of hydrogen sulfide and oxygen in order for the reaction to proceed. Conversely, photosynthesis requires sunlight and generates oxygen as its reaction happens.

Both chemosynthesis and photosynthesis result in the production of sugar, but chemosynthesis also generates sulfuric acid, whereas photosynthesis generates oxygen. Chemosynthesis does not require sunlight or light energy.

Active Learning Exercises 15.1 Divide the class into groups of four students each. Within each group, have each person select one of the four main intertidal zones along rocky shores: (1) the spray zone, (2) the high tide zone, (3) the middle tide zone, and (4) the low tide zone. Have each person select two different organisms that inhabit the intertidal zone and write down adaptations of each organism that allow it to survive there. Then compare your answers with your group and with the class.

Student answers will vary widely. SmartTable 15.1 provides a list of organisms that inhabit rocky intertidal zones and the adaptations they have in response to this environment.

15.2 Divide the class into groups of five students each. Within each group, have each person select one of the five main intertidal zones along sediment-covered shores. (1) The supratidal (backshore) zone, (2) the high tide zone, (3) the middle tide zone, (4) the low tide zone, and (5) the subtidal zone. Have each person select one organism that inhabits that intertidal zone and write down its adaptations that allow it to survive there. Then compare your answers with your group and with the class.

Student answers will vary widely. Refer to Figure 15.8 for details. Examples may include the following: (1) Beach hopper (Orchestoidea) and ghost crab (Ocypode) are crustaceans with hard exoskeletons that bury their bodies in the sand.

(2) Ghost shrimp (Calianassa) burrow in sand for protection.

(3) Bristle worms (Polychaeta) burrow in sediment for protection.

(4) Clams and sand crab (Emerita) burrow in sand; lugworm (Anenicola) have the ability to regrow parts if they are eaten; sand star (Astropecteri) can flatten body and use arms for movement in low tide zone and can regrow lost body parts; ice cream cone worm (Pectinaria) is designed for moving through sediment.

(5) Sand dollar (Echinarachnius) has flat edges that can burrow in sand, and their flat shape allows them to withstand rough waters; heart urchin (Echinocardium) shape allows them to burrow in sand, and they have breathing tubes to extend out of the sand; sea cucumber (Stichopus) can shed its internal organs to escape predators; horseshoe crab (Limulus) has hard shells and primitive immune response to bacteria.

15.3 Working with another student in class, answer this question: What in particular about the environment where corals are found makes the symbiotic relationship between corals and algae indispensable to both? Then share your answer with the class.

Corals are restricted to warm tropical waters, which tend to be nutrient-poor. The corals provide the algae with nutrients and the photosynthetic algae provide the corals with food. The symbiosis between these organisms allows both the corals and the algae to survive.

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15.4 Working with another student in class, create a table that compares the temperature of fluids emitted, characteristic features, and example locations of the following types of hydrothermal vents: (1) black smokers and (2) areas like Lost City in the Atlantic Ocean.

Which one is more likely to have created an environment for the development of early life on Earth?

Black Smokers Emitted fluid temperatures more than 350oC (662oF) pH between 3 and 4, releases metal sulfides, vent activity driven by magma-heated water

Lost City Types of Areas Emitted fluid temperatures around 90oC (194oF) pH between 9 and 11, releases methane and hydrogen, vent activity driven by serpentinization Nine miles west of mid-Atlantic ridge

Along mid-ocean ridge systems

Regions similar to the Lost City in the Atlantic are more likely to have created an environment for the development of early life on Earth.

Additional Active Learning Exercises 15.3 Worldwide, coral reefs are in rapid decline. Choose one human factor that is causing the decline and, with a partner, develop a management strategy to reverse this trend.

Answers will vary.

15.4 Use the Internet to learn more about one benthic organism that lives in the deep ocean, away from hydrothermal vents or cold-water seeps. Where does it live? What does it eat? Is it sessile or mobile? How long does it live? Etc. Answers will vary.

The following websites contain relevant information: ● The Deep Sea (Smithsonian Institution), https://ocean.si.edu/ecosystems/deep-sea/deep-sea ● NOAA Deep Sea Benthos, https://oceanexplorer.noaa.gov/explorations/02arctic/background/benthos/benthos.html ● MarineBio Conservation Society, https://marinebio.org/oceans/deep-sea/

Exploring Data SmartFigure 15.2 Describe the environmental hardships of organisms that inhabit each rocky shore intertidal zone, give an example of one, and discuss that organism's adaptations that allow it to survive in its particular zone.

Answers will vary. See SmartTable 15.1 for a complete discussion of hardships in the intertidal zone.

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In the high tide zone, the greatest environmental hardship is desiccation (drying out). Organisms like the periwinkle (Littorina) have hard shells to minimize water loss.

In the middle tide zone, the greatest environmental hardship is competition for rock space, especially among sessile organisms. Mussels (Mytilus and Modiolus) group together to form mussel beds.

In the low tide zone, organisms must deal with high wave energy. Organisms like the sea star (Asterias-Pisaster) have hundreds of tube feet that allow them to attach themselves firmly to the bottom.

Figure 15.19 Besides a volcano sinking, what other process might occur in the ocean that would cause a coral reef to build up to be thousands of meters thick, with coral material that is millions of years old at the bottom?

Glacial cycles cause sea level to fluctuate. During glacial periods (ice ages), sea level is lower and reefs are exposed to air, resulting in dissolution. During interglacial periods, sea level is higher, coral reefs are submerged, and deposition occurs. The alternating glacial and interglacial periods could cause a coral reef to develop.

Figure 15.20 How would the coral reef structure change if sea level suddenly rose by 20 meters (66 feet)?

What if sea level dropped by 20 meters (66 feet)?

Coral reefs grow very slowly (3–10 meters/1000 years). Any sudden change in sea level would be very stressful for the coral. In particular, a change in sea level would alter light levels, which would affect the coral growing there.

If the sea level suddenly rose by 20 meters, each zone would, in theory, shift 20 meters upward.

However, many of the organisms are sessile and would be unable to move and many would die. In addition, organisms living in the former surface zone would be unable to shift upward and many would likely die.

If the sea level suddenly dropped by 20 meters, the zones would, in theory, shift downward 20 meters.

However, many of the organisms are sessile and would be unable to move and many would die. In addition, the former surface zone would be exposed to the atmosphere and the organisms there would die if they were unable to move.

SmartFigure 15.28 By examining this figure, describe the chemical differences and similarities between photosynthesis and chemosynthesis.

The processes of photosynthesis and chemosynthesis include water and carbon dioxide as reactants and sugar as a product. The process of chemosynthesis also includes hydrogen sulfide and oxygen as reactants and sulfuric acid as a product. The process of photosynthesis also depends on light energy and includes oxygen as a product.

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Chapter 16 The Oceans and Climate Change Overview This chapter provides an in-depth look at how Earth’s climate system works. It also addresses human versus natural causes of climate variations and illustrates how the greenhouse effect works. One section of this chapter shows the ways in which people are altering the climate of Earth. There is a section that discusses the greenhouse effect not just as a global warming phenomenon but as an essential component of the Earth system that allows life to exist on the planet. The greenhouse effect is a result of gases in the atmosphere, and these gases help regulate Earth’s heat budget. The difference between longer-wave and shorter-wave radiation are introduced, and there is a discussion of how these different wavelengths affect Earth’s heat budget. Changes in the ocean are discussed. Increasing ocean temperatures is one obvious effect of global warming, but this chapter also addresses other effects such as changes in storm activity, ocean circulation alterations, pH changes within the ocean, and melting of polar ice into ocean waters. These ocean changes are also examined in light of how they affect various marine organisms. Measures taken by people to mitigate the effects of climate change are addressed, including the Kyoto protocol. This chapter ends by listing some of the ways we can reduce anthropogenic greenhouse gases and the ocean’s role in global warming.

Essential Concepts 16.1 Specify the components of Earth’s climate system, and the role of the carbon cycle.

16.2 Examine the evidence that shows how Earth’s recent climate change is caused by human activities, not a natural cycle.

16.3 Demonstrate an understanding of how the atmosphere’s greenhouse effect works.

16.4 Specify the changes that are occurring in the oceans as a result of global warming.

16.5 Evaluate options for what can be done to reduce greenhouse gases.

Chapter Outline 16.1

16.2

16.3

What Comprises Earth’s Climate System?

SmartFigure 16.1: Major components of Earth’s climate system SmartFigure 16.2: Examples of climate feedback loops The Carbon Cycle SmartFigure 16.3: The carbon cycle 16.2.1 The Ocean’s Biological Pump Earth’s Recent Climate Change: Is It Natural or Caused by Human Activities?

SmartFigure 16.8: Variations in Earth’s orbit 16.3.1 Is There Scientific Consensus about Human-Caused Climate Change?

16.3.2 The IPCC: Documenting Human-Caused Climate Change 16.3.3.1 The IPCC Assessment Reports 230 .

16.4

16.5

16.6

16.3.3.2 Other Scientific Reports Confirm IPCC Findings What Causes the Atmosphere’s Greenhouse Effect?

Web Animation: Global Warming 16.4.1 Earth’s Heat Budget and Changes in Wavelength 16.4.2 Which Gases Contribute to the Greenhouse Effect?

SmartTable 16.1: Human-generated greenhouse gases and their contribution to increasing the greenhouse effects Web Animation: Atmospheric Energy Balance 16.4.2.1 Carbon Dioxide 16.4.2.2 Methane Diving Deeper 16.1: Research Methods in Oceanography The Iconic Keeling Curve of Atmospheric Carbon Dioxide and the Father–Son Team Who Created It. SmartFigure 16a: The Keeling curve 16.4.2.3 Other Greenhouse Gases 16.4.2.4 Greenhouse Gases: Past and Future SmartFigure 16.20: Ice core data of atmospheric composition and global temperature SmartFigure 16.21: Scenarios for future atmospheric carbon dioxide levels and corresponding global temperature increase 16.4.3 Other Considerations: Aerosols 16.4.4 What Documented Changes Are Occurring Because of Global Warming?

What Changes Are Occurring in the Oceans as a Result of Global Warming?

16.5.1 Increasing Ocean Temperatures Web Video: Global Temperatures 1880–2010 16.5.1.1 Have Increased Ocean Temperatures Caused Increased Hurricane Activity?

Web Animation: North Atlantic Deep-Water Circulation 16.5.2 Changes in Deep-Water Circulation 16.5.3 Melting of Polar Ice Web Animation: Arctic Sea Ice Decline Web Video: Loss of Arctic Sea Ice 16.5.4 Ocean Acidification SmartFigure 16.29: Examples of marine organisms that are affected by increased ocean acidity 16.5.5 Rising Sea Level 16.5.6 Other Predicted and Observed Changes 16.5.6.1 Dissolved Oxygen in Seawater 16.5.6.2 Wind Speeds and Wave Heights 16.5.6.3 Migration of Mangroves 16.5.6.4 Oceanic Productivity 16.5.6.5 Effect on Marine Organisms What Can Be Done to Reduce Greenhouse Gases?

16.6.1 Approach #1: Renewable Clean Energy 16.6.2 Approach #2: Solutions for Reducing Greenhouse Gases—Changing Behavior 16.6.3 Approach #3: Global Engineering Solutions for Reducing Greenhouse Gases

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16.6.3.1 The Iron Hypothesis SmartFigure 16.35: The iron hypothesis 16.6.4 Marine Permaculture 16.6.5 Sequestering Excess Carbon Dioxide in the Oceans 16.6.6 Thinking Like a Scientist: What’s Next?

Essential Concepts Review

Learning Objectives The instructional objectives are performance-based and detail specific learning outcomes for Chapter 16.

The test items contained in the Test Bank are keyed to the learning objectives and the Chapter in Review at the end of the chapter. The order of the objectives mirrors the content presentation in Chapter 16.

Upon completion of this chapter, the student should be able to: 1. List and describe the five components of Earth’s climate system, including the atmosphere, hydrosphere, geosphere, biosphere, and cryosphere.

2. Describe the differences between a positive-feedback loop and a negative-feedback loop.

3. Describe Earth’s carbon cycle, including major reservoirs and fluxes.

4. Explain how the ocean functions as a biological pump.

5. Define paleoclimatology.

6. Discuss how proxy data are used to reconstruct models of Earth’s past climate.

7. Describe possible explanations for changes in Earth’s climate due to natural phenomena, including a. sunspots b. variations in Earth’s orbit c. volcanic eruptions d. movement of Earth’s tectonic plates 8. Recognize that there is a scientific consensus that current climate change is caused by human activities.

9. Describe the International Panel on Climate Change (IPCC) and detail its primary functions with respect to climate change research.

10. Recognize other scientific reports that confirm IPCC findings.

11. Discuss the greenhouse effect including a list of the gases that contribute to increased atmospheric temperature, including a. carbon dioxide b. methane c. nitrous oxide d. ozone e. chlorofluorocarbons

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12. Diagram and understand Earth’s heat budget.

13. Discuss and describe the Keeling curve.

14. Describe Earth’s climate under different emissions scenarios 15. Define aerosols and discuss their contributions to climate change.

16. Identify documented changes on Earth that are occurring because of global warming.

17. Describe the kinds of atmospheric/climate changes that are predicted in the near future by current climate models.

18. Detail the changes observed in the world’s oceans as a result of global warming.

19. Discuss increased hurricane activity as a potential effect of warmer oceans.

20. Describe changes in deep-water circulation as a result of climate change.

21. Identify causes of Arctic sea ice decline, and detail the loss of sea ice over the last four decades.

22. Describe how carbon dioxide increases the oceans’ acidity.

23. Discuss how marine organisms are affected by increased ocean acidity.

24. Describe how the ocean functions to absorb excess atmospheric heat.

25. Address causes behind rising sea level and some of the concerns that accompany rising sea levels.

26. Describe and evaluate predicted and observed changes in the oceans as a result of global warming, including: a. changes in dissolved oxygen in seawater b. increases in wind speeds and wave heights c. migration of mangroves d. changes in oceanic productivity e. direct effects on marine organisms 27. Discuss the impact of the Paris Climate agreement, the Kyoto Protocol, and other international climate agreements, including the role of the United States in the agreements.

28. Describe how renewable clean energy can reduce carbon emissions.

29. Explain how people can reduce their carbon footprint by changing their behaviors.

30. Discuss engineering solutions for reducing greenhouse gases, including: a. the iron hypothesis b. marine permaculture c. sequestering carbon in the oceans

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Teaching Strategies Open with asking students what the greenhouse effect is. Many people think the greenhouse effect is a bad thing, synonymous with climate change, and addressing this misconception from the start will lay the foundation for this chapter. Then initiate a lesson on what the different components of Earth’s climate system are and how the greenhouse effect is an intrinsic part of this. From here you can discuss how changes in the atmosphere affect the climate system and the evidence from the past that things are changing. It is important to show the natural causes of variation in the climate system and how these things can change the climate, but follow up and stress that humans are impacting the system more drastically and differently than Earth has ever experienced before. Channel this into a discussion of how global change affects the oceans and the life dependent upon them. The issue may have more meaning for students if the effects of ocean changes on human populations are also brought into the discussion. Finish by talking about how we can reduce greenhouse gas emissions and why this has been so difficult to implement. Have students brainstorm these ideas themselves before telling them some of the proposed solutions.

Some students may have difficulty understanding positive and negative feedback loops. Use of many examples can be helpful, as can the use of SmartFigure 16.2 in class. Have students review this figure on their own as well. Graphs in general are useful for highlighting the role humans have had on global warming. The Keeling curve is one example of data that illustrate changes in atmospheric composition. The Web Video that shows global temperatures between 1880 and 2010 is an excellent resource for showing quite vividly how temperatures have changed all over the globe since shortly after the Industrial Revolution. Stress that although climate has changed a great deal on Earth in the past, scientists have not found changes this dramatic in this short of a timeframe in the paleoclimatic record.

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Teacher’s Resources Films ▪ An Inconvenient Truth (Paramount), 96 minutes ▪ An Inconvenient Sequel (Paramount), 97 minutes ▪ Six Degrees Could Change the World (National Geographic), 96 minutes ▪ Energy Crossroads: A Burning Need to Change Course (Tiroir A Films), 55 minutes ▪ The 11th Hour: Turn Mankind’s Darkest Hour into Its Finest (Warner Brothers), 124 minutes Websites ● EPA website on climate change, https://www.epa.gov/climate-indicators ● Pew Center on Global Climate Change, https://www.c2es.org ● NASA Global Climate Change: Vital Signs of the Planet, includes short videos, https://climate.nasa.gov/ ● Climate Central, www.climatecentral.org ● NOAA Climate, www.noaa.gov/climate ● Sea Level Rise Viewer (NOAA digitalcoast website), https://coast.noaa.gov/digitalcoast/tools/slr.html

Concept Check (Questions and Answers) 16.1

What Comprises Earth’s Climate System?

1. List the five parts of Earth’s climate system.

The five components of Earth’s climate system are the atmosphere, the biosphere, the cryosphere, the hydrosphere, and the lithosphere. The atmosphere includes the gases and water vapor that form a thin insulating blanket over Earth’s surface. The biosphere is the living portion of Earth’s surface that includes all living organisms. The cryosphere includes all of the frozen water on Earth’s surface such as ice sheets, glaciers, and floating sea ice. The hydrosphere is the portion of Earth’s surface covered by water, and the lithosphere is the portion of Earth’s surface covered by rock.

2. What are the two types of climate feedback loops? Give an example of each type.

Climate feedback loops are climate processes that modify the end result of the process. There are two types of feedback loops: positive-feedback loops and negative-feedback loops. Positivefeedback loops reinforce the initial climate change. One example of a positive-feedback loop is the evaporation of water from Earth’s surface producing clouds as the water vapor rises, cools, and condenses. The water vapor absorbs atmospheric heat, preventing it from being lost to space.

Negative-feedback loops counteract the initial change; the formation of cloud cover is an example of a negative-feedback loop. Water vapor evaporates, condenses, and forms clouds that reflect solar energy and lower atmospheric temperatures.

3. An example of a feedback loop occurs when melting snow exposes more dark ground, which in turn absorbs additional heat and causes more snow to melt. Is this a positive-feedback loop or a negative-feedback loop? Explain your reasoning.

This is a positive-feedback loop because it enhances the original disturbance. Exposition of dark ground causes more melting of snow, which was the original alteration in the system.

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4. Describe how carbon enters and leaves the five “spheres” of Earth’s climate system by drawing a schematic diagram that lists the carbon inputs and outputs in each sphere.

Drawing should be similar to SmartFigure 16.3.

5. Methane, a greenhouse gas, exists in a solid form as frozen methane hydrates at the nearfreezing temperatures found deep in the ocean. If global warming causes deep water to heat up, thus causing methane hydrates to melt and release methane gas that would bubble up into the atmosphere, would that create a positive- or negative-feedback loop? Explain.

If global warming causes deep water to heat up, thus causing methane hydrates to melt and release methane gas, this would create a positive-feedback loop. The additional methane in the atmosphere would further increase Earth’s temperature, which would warm the ocean more, which would melt more methane hydrates.

16.2

Earth’s Recent Climate Change: Is It Natural or Caused by Human Influence?

1. What are proxy data? List several examples. Why are such data necessary for paleoclimatology studies?

Proxy data are data about Earth’s past climate events that are stored in natural processes such as tree growth rings, glacial ice alternating dark and light layers, fossilized pollen, coral reefs, cave deposits, historical documents, and marine sediments. By analyzing proxy data, paleoclimatologists are able to reconstruct past climate records with accuracy. Proxy data serve as substitutes for actual measurements of climate variables such as temperature or precipitation.

Actual recordings of these data go back only a few hundred years at most, and proxy data extend our climate record by using natural recorders of climate events.

2. List several examples of natural climate change. Do natural climate change mechanisms account for the recent climate changes that Earth is experiencing? Explain.

There are several natural mechanisms for climate change, including changes in solar energy input due to sunspot activity, variations in Earth’s orbit that change the distances between Earth and the Sun, volcanic eruptions add ash to the atmosphere blocking incoming solar radiation, and the movement of Earth’s tectonic plates. While these natural processes can cause changes in Earth’s atmospheric temperature, these processes would not explain recent changes. Current atmospheric carbon dioxide levels, which are causing Earth to warm, cannot be explained by any of these natural processes.

3. Is there scientific consensus about human-caused climate change? Explain.

There is a clear scientific consensus regarding human-caused climate change. Scientists who actively research climate change issues and publish their findings are nearly unanimous in their assertion that Earth’s warming trends cannot be explained without factoring in human-caused emissions.

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4. What is IPCC? What role does it have in documenting human-caused climate change?

IPCC stands for Intergovernmental Panel on Climate Change. It is an international panel of scientists that objectively researches climate and climate-change issues and provides reports on their findings. It has no political agenda, and its series of four reports spanning 20 years have shown the global scientific consensus that humans are affecting climate change.

5. What other recent reports have been published supporting human-caused climate change?

Many recent reports have been published supporting human-caused climate change, including: ● ● ●

Global Climate Change Impacts in the United States (U.S. Global Change Research Program, 2009) America’s Climate Choices (U.S. National Research Council, 2011) Climate Science Special Report: Fourth National Climate Assessment (published at the behest of the U.S. Congress, 2017)

16.3 What Causes the Atmosphere’s Greenhouse Effect?

1. Describe the fundamental difference between solar radiation absorbed at Earth’s surface and the radiation that is primarily responsible for heating Earth’s atmosphere.

The majority of the sunlight energy that strikes Earth’s surface is short wavelength, higher energy portions of the visible spectrum. Some of the radiation is absorbed. Earth, being cooler than the Sun, emits most of its radiation at longer wavelengths. In this way, it is re-radiating absorbed solar radiation. It is this long-wave radiation that is trapped by Earth’s atmosphere, specifically the greenhouse gases in the atmosphere, causing it to warm.

2. Discuss the greenhouse gases in terms of their relative concentrations in the atmosphere and their relative contributions to global warming.

See SmartTable 16.1 3. Why has the carbon dioxide level of the atmosphere been rising for more than 150 years?

Since the dawn of the Industrial Revolution in 1750, human activities that release carbon dioxide into the atmosphere have increased exponentially with the size of the human population.

Deforestation, burning of fossil fuels, and increasing human populations contribute an additional 2 parts per million (ppm) to atmospheric CO2 levels. Current atmospheric CO2 levels are at 387 ppm.

4. Explain what a commitment to warming means. What commitment to warming will Earth experience in the future?

Even if greenhouse gas emissions stopped today with no increase, Earth would continue to warm over the next century because it would need that time to stabilize the system. This future warming is often referred to as Earth’s commitment to warming. Earth will experience melting polar ice, shorter winters, species distribution changes, and steady rises in atmospheric and ocean temperatures.

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5. Describe how atmospheric temperatures and other factors are likely to change as carbon dioxide levels continue to increase.

Earth will experience higher atmospheric temperatures. Associated with this will be earlier summer seasons, longer and more intense heat waves, drought in some areas with increased flooding in others, retreat of ice fields and mountain glaciers, water contamination that can increase water-borne infections in humans, and changes in the distributions of plant and animal communities or outright extinction events.

16.4 What Changes Are Occurring in the Oceans as a Result of Global Warming?

1. Describe several changes that are already occurring in the oceans because of global warming.

The following changes are being observed in Earth’s oceans: a) Increasing ocean temperatures on average (0.6°C[1°F]) b) Increasing hurricane frequency and intensity c) Changes in deep-water circulation d) Melting polar ice e) Sea-level rise f) Increasing ocean acidity 2. Why is the Arctic one of the locations where the effects of global warming are being most keenly felt? Why are polar bears threatened by global warming?

The effects of global warming are most keenly felt in the Arctic because much of the Arctic ice is sea ice. Ice has a high reflectivity, meaning much of the solar radiation gets reflected off it. If the ice melts, it gives way to much darker oceans, which will absorb more solar radiation and amplify the warming. Polar bears require floating sea ice platforms to capture prey. As this floating sea ice disappears, polar bears are having more difficulty finding food and making dens in which to breed. As the Arctic warms, polar bears could lose almost half of their summer sea ice by the middle of the 21st century, which would reduce the polar bear population by twothirds.

3. Explain how excess carbon dioxide in the atmosphere affects the pH of seawater. Why is increasing ocean acidity such a problem in the ocean?

Some atmospheric carbon dioxide ends up dissolving in the ocean, where it becomes carbonic acid. This lowers the pH of seawater, increasing its acidity. Changing ocean acidity can make it hard for some marine animals such as corals or animals with shells to build and maintain hard parts made out of calcium carbonate. Increased acidity can disrupt biological functions in other marine organisms as well. Geological records show that past ocean pH changes have caused extinctions, and this could be a consequence of further ocean acidification today.

4. What factors contribute to worldwide sea-level rise? Based on tide measurements, how much sea-level rise has occurred in the past 150 years?

The main factors that contribute to sea-level rise are melting of glaciers and small ice caps, melting of the Antarctic and Greenland Ice Sheets, deep-ocean thermal expansion, and surface water thermal expansion. Based on tide measurements, sea level has risen as much as 40 centimeters (16 inches) over the last 150 years.

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16.5 What Should Be Done to Reduce Greenhouse Gases?

1. Starting with the Kyoto Protocol, name the international agreements that have attempted to bring nations together to curb greenhouse emissions and the years they were signed. ● ● ● ●

Kyoto Protocol (1997) Copenhagen Accord (2009) Durban Platform (2011) Paris Climate Agreement (2015)

2. What are the most important sources of renewable energy in the United States today?

In the United States, wind and solar are the most important sources of renewable energy today.

3. It has been said that Earth is better off if you eat fruits and vegetables from Argentina than beef from your local farmer. Considering each one’s carbon footprint, why would this be so?

Livestock releases between 15 and 50% of all greenhouse gas emissions. Cows produce large amounts of methane as they digest their feed and manure releases nitrous oxide. Both methane and nitrous oxide are potent greenhouse gases. Compared to carbon dioxide, a molecule of methane absorbs 28 times more infrared radiation and nitrous oxide absorbs 265 times more.

4. The input of human-generated greenhouse gases into the atmosphere over the last 150 years is an example of unintentional global engineering of the planet. Describe the concerns regarding the deliberate use of global engineering to counteract the effects of those emissions.

Rank all the proposals listed in this chapter in terms of their relative risk and benefit.

Using global engineering is controversial for a variety of reasons. Intentionally altering any of Earth’s systems on a global scale may have unintended side effects. In addition, some of the proposals would require constant maintenance and would be expensive. Finally, global engineering is unlikely to alleviate all of the impacts of climate change.

The text discusses three proposals: the iron hypothesis, marine permaculture, and sequestering excess carbon dioxide in the oceans. Each proposal has its risks and benefits. The iron hypothesis and sequestering excess carbon dioxide in the oceans would both likely increase ocean acidification. In addition, it is likely that the iron hypothesis would also reduce dissolved oxygen in fertilized areas. However, both proposals have the potential to remove large amounts of carbon from the atmosphere. Marine permaculture seems to present few risks, but implementing it on a scale to combat climate change would require massive infrastructure and considerable investment.

The iron hypothesis seems to have the most risks, followed by sequestering excess carbon dioxide in the oceans. Marine permaculture seems to have the fewest risks.

The iron hypothesis and sequestering excess carbon dioxide in the oceans seem to have a greater potential to combat climate change, as compared to marine permaculture.

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Critical Thinking Questions (and Answers) 16.1 To help reinforce your knowledge of Earth’s climate system, construct and label your own diagram similar to Figure 16.1 from memory.

Student drawings will vary but should resemble Figure 16.1.

16.2 Some friends tell you that they’ve heard that the recent climate change Earth is experiencing is just part of a natural cycle. What would you explain to them—including using any figures from this chapter—to help convince them otherwise?

Student explanations will vary. Figure 16.6 shows there is no correlation between Earth's temperature and natural solar activity. Figure 16.10 shows that the scientific consensus is that humans are causing climate change, and it is not part of a natural cycle. Archival ice core data (SmartFigure 16.17) clearly shows that atmospheric CO2 levels have not risen above 300 ppm until the 20th century, and the Keeling curve (SmartFigure 16a) shows the longest continuous record of atmospheric carbon dioxide direct measurements. Figure 16.19 clearly illustrates the instrumental record of temperature since 1865, just after the start of the Industrial Revolution. The rate of increase in atmospheric CO2 concentrations since the dawn of the Industrial Revolution clearly illustrates the impact of human activity.

16.3 Sketch a diagram that shows how Earth’s greenhouse effect works.

Student drawings will vary. At their simplest, they should resemble Figure 16.16. A more complex diagram will resemble Figure 16.17, which depicts Earth’s heat budget.

16.4 Of the changes that are occurring in the oceans as a result of global climate change, which ones are the most serious threats to the marine ecosystem?

Student responses will vary. Some serious threats to the marine ecosystem include changes in deepwater circulation that will affect species dependent upon ocean circulation; melting of polar ice, which will affect polar bears; increased sea levels, which can make some water too deep for corals and other sessile animals to live; changes in ocean acidity, which can affect shelled or calcareous organisms; increased hurricane activity, which can cause mass destruction of shallow water habitats, and increased water temperatures, to which many species may not be able to adapt.

16.5 Describe the iron hypothesis, and discuss the relative merits and dangers of undertaking such a global engineering project that could cause dramatic changes in the environment worldwide.

The iron hypothesis is an experimental technique for increasing primary productivity (thereby reducing the atmospheric carbon dioxide concentration) by fertilizing the ocean with finely ground iron. Preliminary results indicate that the iron hypothesis has promise; it could be attempted on a larger scale than in the trials. However, it should be noted that global engineering could produce more harm than benefit. It is unknown at this time what other kind of effects are likely in the ocean and the atmosphere if fertilizing the oceans with iron is done on a large scale.

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Active Learning Exercises 16.1 With another student in class, determine one positive-feedback loop and one negativefeedback loop that involves Earth’s ocean and/or atmosphere. Note that you cannot use any example already used in this textbook. Present your results to the class.

Answers will vary. Some positive-feedback loops include: ● As Earth warms, ice can melt, leaving behind darker surfaces that absorb more solar radiation, which will in turn cause more melting of ice. ● Changing climate can cause darker vegetation to colonize previously bare or light-colored areas; the darker vegetation will absorb and re-radiate more solar radiation, causing Earth to warm further. ● Methane release from thawing permafrost will cause warmer atmospheric temperatures, which will cause more thawing, which will trigger more methane releases. ● Any answer where the mechanism causes the cycle to perpetuate.

Some negative-feedback loops might include: ● As Earth warms, dark vegetation in some regions might die, leaving behind lighter soil, which will then reflect more radiation back into space. ● Surface temperature of Earth increases, evaporation from oceans increases, leading to more low clouds, which increase Earth’s reflectivity, causing surface temperature to decrease. ● Any answer where the mechanism reduces the initial change.

16.2 With another student in class, discuss differences between being a skeptic versus a denier of human-caused climate change. Make a list to compare the two. What is your own personal view on human-caused climate change? Then present your findings to the class.

Student answers will vary widely. However, a skeptic is someone who questions and looks for more evidence and answers to determine if there are data to support the position that human-caused climate change is not real. A denier generally insists that climate change is not caused by humans and is not seeking any evidence to support that position.

16.3 With another student in class, use the Internet to make a list of the characteristics of Venus’s atmosphere as compared to the atmosphere on Earth. Describe what happens when a planet has a “runaway” greenhouse effect (e.g., when there is too much carbon dioxide in the atmosphere). Also, find out what Earth would be like if the greenhouse effect did not exist.

Then present your findings to the class.

Venus’s atmosphere is 96% carbon dioxide, with small amounts of nitrogen and sulfuric acid. Earth’s atmosphere, in contrast, is 78% nitrogen, 21% oxygen, 1–4% water vapor, and less than 1% of argon, carbon dioxide, and other trace gases. When a planet has a runaway greenhouse effect, it tends to become very hot, as is the case with Venus. Even though Venus is further from the Sun than Mercury, the carbon dioxide atmosphere of Venus makes it hotter than Mercury. Carbon dioxide is a very potent greenhouse gas; even at less than 1% of Earth’s atmosphere, it still contributes significantly to keeping the planet habitable.

If Earth had no greenhouse effect, it would not sustain life since it would be too cold. Earth’s temperature would be about –18°C (0°F), instead of its current 15°C (59°F) average temperature.

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16.4 With another student in class and using the Internet, research the idea that global warming will result in an increase in hurricane activity. Make a list of the lines of evidence in support of the idea and lines of evidence that are contrary to the idea. Use only well-established scientific studies and ignore articles that voice only opinions. Then present your findings to the class.

Evidence supporting an increase in hurricane activity includes increased sea surface temperatures (SSTs), since deep warm water is necessary for hurricane formation. In addition, a wider band of SSTs that are warm enough for hurricane formation may form as oceans warm and tropical temperatures expand poleward. In addition, models predict that warm conditions needed for hurricane formation may exist for longer periods of the time during the year, effectively expanding hurricane season, which currently is from June 1 to November 30.

Some studies suggest a decrease in hurricanes due to projected stronger upper-level winds associated with global warming. Hurricanes need light winds in the ambient environment as they are forming, and these increased winds aloft will destroy any hurricane before it forms. Some models have shown that changes in surface winds will not necessarily decrease the number of hurricanes that form, but it is possible that Atlantic hurricanes will be steered such that fewer make landfall on North America.

16.5 With another student in class, discuss the personal choices you are willing to make to reduce your carbon dioxide “footprint” (e.g., the amount of carbon dioxide your actions release into the atmosphere each year).

Student answers will vary widely. Some possible answers could include driving less, maintaining a vehicle at optimum performance, turning down the thermostat in winter, using Energy Star appliances, turning off lights when leaving the room, printing only what is necessary, stopping junk mail, recycling, and eating less/no meat.

Additional Active Learning Exercises 16.4 Use the Sea Level Rise Viewer on the NOAA digitalcoast website (https://coast.noaa.gov/digitalcoast/tools/slr.html) to learn more about sea-level rise in the United States. Choose a coastal city on the East, West, and Gulf coasts of the United States and adjust the sea-level rise slider to see how the city will be affected by different sea-level rises. Which city will be the most affected? Which coast will be most affected? Why are some cities more vulnerable to sea-level rise?

Answers will vary.

The East and Gulf coasts will be most affected. Cities such as Miami or New Orleans that have low elevations are most vulnerable to sea-level rise.

16.5 If you were in charge of climate policy in the United States, which of the strategies for combating climate change that are presented in this chapter would you recommend be implemented? Discuss your answer with another student in the class.

Answers will vary, but students should consider feasibility, cost, and possible unintended consequences of the proposed solution.

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Exploring Data SmartFigure 16.3 Consider the annual fluxes of carbon between reservoirs. How much carbon would go into the atmosphere each year if the ocean could only absorb half the amount of CO2 it absorbs now?

Assume everything else stays the same.

Currently, 4 gigatons of carbon are added to the atmosphere and the ocean absorbs 2 gigatons of carbon every year. If the ocean absorbed half the carbon dioxide it currently does, 5 gigatons of carbon would be added to the atmosphere annually.

Figure 16.7 What does this graph tell you about the correlation between average solar irradiance and average temperatures on Earth between 1880 and 2020?

The graph shows a lack of correlation between average solar irradiance and average temperatures on Earth.

Figure 16.12 What is the main take-home message this graph is telling you?

The graph shows that there is a consensus among scientists that current climate change is caused by human activities. Furthermore, climatologists who are active publishers on climate change overwhelmingly agree that current climate change is caused by human activity.

SmartFigure 16.20 State the relationship between the three curves in the graph in part (a). Why do you think the Medieval Warm Period and Little Ice Age in part (b) have to be shown in an enlargement?

The graph shows that atmospheric carbon dioxide concentration, atmospheric methane concentration, and global temperatures are correlated. When global temperatures are high, atmospheric carbon dioxide and methane concentrations are high. When global temperatures are low, atmospheric carbon dioxide and methane concentrations are low.

The Medieval Warm Period and Little Ice Age have to be shown in an enlargement because the scale on the x-axis on the graph in part (a) would not allow you to see the necessary detail.

SmartFigure 16.21 What is this graph telling you?

This graph shows the predicted atmospheric carbon dioxide levels and global temperatures for various emissions scenarios. It shows that even a slow increase in carbon emissions will result in a 2.5-degree increase in global temperatures by the end of the century.

Figure 16.22 What is the trend or pattern that this graph shows?

The graph shows a general increase in global temperature since 1865.

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Figure 16.25 Near South America, the illustration shows surface currents diverging, flowing both north and south. Using what you know about ocean circulation, oceanic gyres, and global wind patterns, explain why this is so.

The current flowing north is part of the North Pacific Subtropical Gyre, which is driven by the northeast trade winds and the prevailing westerlies. The current flowing south is part of the South Pacific Subtropical Gyre, which is driven by the southeast trade winds and the prevailing westerlies.

Figure 16.28 Compare the relative proportions of land and water in East and West Antarctica. Using what you know about the continental effect on temperature, explain why West Antarctica is warming up faster than East Antarctica.

West Antarctica has a much higher proportion of water compared to East Antarctica. The warming ocean water in West Antarctica is causing the dramatic warming in that area.

Figure 16.33 Suppose all the ice on Earth were to melt. If temperatures continued to increase, would sea level continue to rise? Why or why not?

Water expands as it warms, so if the temperature continued to increase, the sea level would continue to rise.

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