ESS 53 Earth System Science Final Exam Review Sheet.

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ESS 53 Final Exam Review Sheet 2017 1.Ocean Circulation - esp. aspects that influence biology and carbon cycling: Location of upwelling zones and deep convective mixing, surface circulation patterns, subtropical gyres, deep water formation sites, thermohaline circulation & deep nutrient distributions.

Thermohaline circulation – from below the upper ocean currents to sea floor, water movements are driven by small differences in density.

At mid-latitudes surface convergence drives subtropical gyres, around a raised sea surface at the center.

Subtropical gyres have strong, narrow intensified western boundary currents, and broad, weaker eastern boundary currents, due to the center of the "hill" being offset towards the west. Found at mid-latitudes in all ocean basins.

At higher latitudes in the northern hemisphere surface divergence leads to subpolar gyres, around a depressed sea surface.

Winds blowing parallel to the California Coast towards the equator. These winds drive the coastal upwelling.

Main Zones： Antarctic Divergence - largely south of the ACC, divergence in surface waters due to eastward blowing winds to the north and westward blowing winds to the south.

Equatorial Upwelling - near the equator especially in the eastern Pacific, divergence in surface waters due to westward blowing winds north and south of the equator.

Coastal Upwelling - alongshore winds lead to offshore Ekman transport of surface waters. Occurs mainly in the Eastern Boundary Currents of the mid-ocean gyres, but also along the Somali coast and Arabian peninsula.

Upwelling brings nutrient and carbon rich waters to the surface. Low latitude waters upwell from ~200 meters depth. In the Southern Ocean deep ocean waters are brought to the surface at the Antarctic Divergence.

2. Carbon chemistry in seawater, linked DIC equations, controls on pCO​2​ values relative partitioning of the DIC pool between dCO​2​, bicarbonate, and carbonate ions, what factors can change this partitioning?

Chemical reaction of CO2 with H2O in seawater dCO2 + H2O -- H2CO3 -- H+ + HCO(3-) --2H+ +CO3(2-)

Most DIC is present as bicarbonate (HCO3), some is present as carbonate (CO3),

and a small fraction is present as dissolved CO2 gas and carbonic acid (H2CO3). Typical ocean values would have C partitioned as, ~1% dCO2 + ~88% HCO3- + ~11% CO32Decreasing temperature, lowers pCO2, increases solubility.

Decreasing DIC (TCO2), lowers pCO2, increases solubility.

Reducing alkalinity decreases solubility, increases pCO2.

Reducing salinity increases solubility, decreases pCO2.

3.Solubility Pump and impacts on atmospheric CO2 Solubility Pump Interaction of circulation and temperature effects on carbon chemistry that act to increase deep ocean DIC concentrations relative to surface waters.

Cold Water can hold more TCO2 (DIC) than Warm Water.

Temperature Effect on CO2 solubility and the pCO2 AS Temperature increases, pCO2 increases and solubility decreases, AS temperature decreases, pCO2 decreases and solubility increases As temperature goes up, the pCO2 increases, and the solubility decreases.

Solubility refers to the maximum amount of gas you could dissolve.

4.ocean uptake of anthropogenic CO​2​, key regions/processes, where is it currently stored in oceans?

Note differences in the vertical (depth) scales. Anthropogenic CO2 has penetrated to greater depth in the North Atlantic due to the formation of NADW. Over Next ~1000 Years Most of the anthropogenic CO2 added to the atmosphere will be absorbed by the oceans due to the solubility pump (~70-80%).

The anthropogenic CO2 will be carried throughout the deep ocean by the circulation, beginning to interact with the sediments.

Over Next ~10,000 Years As the anthropogenic CO2 is circulated throughout the deep ocean the decrease in pH will lead to dissolution of CaCO3 in the sediments. This dissolution will increase the alkalinity (and raise pH) allowing the water to absorb additional CO2 from the atmosphere when it is brought back to the surface (~10-15%).

Over next ~100,000+ Years

The remaining anthropogenic CO2 in the atmosphere (~10%) will removed due to rock weathering on the continents.

slowly be

5.general global chlorophyll distribution patterns

6.Photosynthesis-Respiration equation Photosynthesis - plants combine carbon dioxide, water, and light energy to form plant biomass.

Respiration - Oxygen is used to break down biomass to produce carbon dioxide, water and energy.

Remineralization - The breakdown of organic matter into elemental and nutrient constituents.

Gross Primary Production - total carbon "fixation", conversion from CO2 to C-biomass by plants.

Net Primary Production - total carbon fixation by plants minus their respiration costs.

7.Light in the oceans - wavelength dependence, absorption by water, chlorophyll

compensation depth, critical depth,

Note that chlorophyll a absorbs strongly at wavelengths of 443nm and 680nm Sverdrup's Critical Depth Concept The critical depth is depth of mixing where integrated community photosynthesis is equal to integrated respiration. The spring bloom is initiated when the mixed layer depth becomes shallower than the critical depth, P > R, and there can be net accumulation of organic C. 8.Sverdrup’s spring bloom concept The Spring Bloom - A seasonal increase in phytoplankton biomass that occurs after deep winter mixing replenishes nutrient concentrations in surface waters.

The bloom begins in spring when mixed layer depths become shallow enough for net phytoplankton growth.

During and just after the spring bloom is often a time of maximum carbon/biomass export to the deep ocean.

The bloom ends when one of the essential nutrient concentrations is depleted.

9.Photoadaptation, accessory pigments

Photoadaptation - Phytoplankton can increase (decrease) their chl. and accessory pigment content in response to low (high) light levels.

Photoinhibition - Vary high irradiance levels (especially UV) can depress photosynthesis as cells are damaged.

The initial slope of the P vs. I curve is termed alpha (α), here shown as ΔP/ ΔI can vary somewhat as phytoplankton photoadapt.

Accessory pigments are light-absorbing compounds, found in photosynthetic organisms, that work in conjunction with chlorophyll a

10.Cell size and phytoplankton competition (3 factors) Cell size has three important implications: 1) Nutrient uptake efficiency 2) Grazing Losses 3) Sinking Losses Smaller cells are more efficient at nutrient uptake when nutrient concentrations are low (lower Ks values). This is due to their higher surface/volume ratios.

Smaller cells experience strong grazing pressure from the microzooplankton. These small zooplankton can reproduce at rates similar to the phytoplankton. Thus, smaller cells can never outstrip their grazer control and bloom.

Only large cells can directly sink out of surface waters, smaller cells have a negligible sinking rate unless aggregated into larger particles.

11.phytoplankton functional groups (key characteristics)

Diatoms (20-500+ μm) silicon requirement, important in in blooms and sinking carbon flux.

Coccolithophores - (10 - 30 μm) CaCO3 platelets, important in blooms and sinking carbon flux.

Dinoflagellates (20-500+ μm) some motility, blooms in coastal waters, main cause of red tides/toxic blooms.

Phaeocystis (3-9 μm, colonies to cm) important in blooms in polar waters, elevated C/N and C/P ratios.

Diazotrophs (cells ~ 1 μm, colonies mm) capable of utilizing N2, found in tropical and subtropical regions.

Picophytoplankton (< 2 μm) & the smaller nanophytoplankton (2-5 μm) efficient at nutrient uptake, experience strong grazing pressure.

The first four groups dominate phytoplankton blooms, strong grazing pressure keeps last two from blooming 12.Redfield ratio Redfield Ratio - refers to the relatively constant C/N/P ratios found in phytoplankton and in subsurface nutrient pools.

Ratios are molar. Relatively constant ratios...

The "classic" Redfield et al. (1963) 106/16/1 Anderson and Sarmiento (1994) 117/16/1based on an analysis of apparent remineralization at depths > 400m.

Sarmiento and Gruber (2005) suggest an optimum ratio: 106 CO2 + 16 HNO3 + H3PO4 + 78 H2O <-> C106H175O42N16P + 150 O2 Exceptions: areas with denitrification (NO3 -> N2), sediments, Arabian Sea and eastern tropical Pacific.

Smaller cells are more efficient at nutrient uptake This is due to their higher surface/volume ratios 13.Eutrophication, what is it? Impacts on coastal oxygen?

Anthropogenic emissions of nitrogen from fossil fuel burning and agriculture have increased greatly in recent decades.

Phosphorus loading in terrestrial systems has also increased dramatically coming from fertilizer/agriculture and sewage systems.

The result is a doubling of the river transport of N and P to the oceans since the preindustrial era.

This causes large phytoplankton blooms and oxygen depletion in coastal regions (eutrophication).

14.microzooplankton vs. macrozooplankton Zooplankton - account for most grazing of phytoplankton, typically divided into two broad size classes:

micro-zooplankton - small diverse group of grazers, some single celled protists, fast reproduction macro-zooplankton - larger zooplankton, slow reproduction 15.key macrozooplankton groups, impacts on biogeochemical cycles Euphausiids: another group of crustacean, small shrimp-like grazers, includes Antarctic Krill important grazer in Southern Ocean.

Foraminifera (Forams) – amoebae that have a calcareous (CaCO3) shell (or test), key player in the carbonate pump, shells accumulate in sediments and are often used in paleoceanographic studies (i.e. sea surface and subsurface temperatures).

Pteropods – planktonic snail with a calcareous (CaCO3) shell, a secondary player in the carbonate pump, less abundant than Forams, but shells do accumulate in some ocean sediments.

Radiolarians – spherical, amoeboid protozoans with a “skeleton” made of biogenic Si, secondary player in the ocean Si cycle after the diatoms (a favorite food). Silica components accumulate in ocean sediments.

Salps: gelatinous filter feeders, that can form large swarms, and also make fast-sinking fecal-pellets.

Larvae: fish larvae and larval forms of many benthic species like clams, snails, barnacles, etc. spend the early part of their lives as pelagic macrozooplankton.

16.copepod influences on the biological pump Copepods: most common large zooplankton, type of crustacean, range in size from a few mm to several cm, important players in the biological pump: 1) formation of large fast sinking fecal pellets that export organic matter to deep ocean, and 2) some species vertically migrate over diel cycles, typically feeding near surface at night and moving to deeper waters during the day.

Calanoid copepods often comprise more than 70% of the large zooplankton biomass caught by nets.

Typically 70-80% of large zooplankton biomass, krill often 10%, other zooplankton make up rest.

17. zooplankton diel vertical migration, and seasonal vertical migrations at high latitudes a. Daily(diel) vertical migration at low to mid latitudes to avoid predators b. Seasonal vertical migration at high latitudes to survive the long, dark winter.

18.Dissolved organic Carbon (DOC), role in the biological pump and in microbial loop Dissolved Organic Matter (DOM): Dissolved organic material released to the marine environment mainly from phytoplankton through excretion, and as a byproduct of grazing or viral lysis.

Dissolved Organic Carbon (DOC): carbon portion of Dissolved Organic Matter, dissolved organic nitrogen (DON), DOP, etc.

DOM is remineralized by heterotrophic bacteria into inorganic carbon and nutrients.

DOM producers:

AUTOTROPHS + heterotrophs DOM consumers: HETEROTROPHS + autotrophs 19.microbial loop vs. the classic ocean food chain, trophic transfer efficiency The Microbial Loop – refers to the cycling (and recycling) of elements between inorganic nutrient pools, phytoplankton, dissolved organic pools, bacteria, and the microzooplankton.

The trophic transfer efficiency from phytoplankton to zooplankton is ~25-30%, at higher trophic levels this decreases to ~10%.

20.new production vs. regenerated production a. New Production – Fraction of primary production that is fueled by new nutrients i.e., nitrate C and N are linked thru the biological pump at the Redfield ratio. Thus, estimates of new production can tell ys about export production over large enough spatial scales and temporal scales. b. Regenerated Production – Fraction of primary production that is fueled by regenerated nutrients (i.e. ammonium) f-ratio = new production/(new+regenerated production) High productive marine ecosystmes have high f-ratios – high export ratios and efficient export.

Low Prod(oligotropic) – have low f-ratios – low export ratios and inefficient export

21.export ratio, Ez-Ratio, twilight zone and remineralization Remineralization - The breakdown of organic matter into elemental and nutrient constituents.

22.mineral ballast hypothesis, three types of ballast Mineral ballast refers to the mineral components often present in the sinking flux in the oceans.

Mineral components have a density much greater than typical soft tissue organic matter or seawater.

The more mineral ballast present, the faster the sinking rate and deeper remineralization of the associated organic matter.

Thus, the mineral ballast components lead to more efficient downward transfer by the biological pump (Armstrong et al. 1999).

Mineral components include: dust particles - from the atmosphere biogenic silica – from mostly diatoms, w/ some radiolarians calcium carbonate (CaCO3) – from coccolithophores and some zooplankton (Pteropods and Foraminifera) This is another way plankton community composition can modify the biological pump efficiency.

23.impacts of new nutrient input levels on plankton community composition and the efficiency of the biological pump a. Efficiency of biological pump out of surface waters is a function of the biological community b. Community w/ large phytoplankton species and abundant copepod grazers will export organic matter out of the euphotic zone efficiently – most carbon into classic food chain c. Community dominated by picoplankton and nanoplankton w/ microzooplankton doing most of the grazing will not export organic material efficiently – most matter will be recycled I the euphotic zone – most carbon into the microbial loop.

25.Biological Pump, key organisms, role of communities, aggregation, mineral ballast Biological Pump (aka Organic Carbon Pump) When biological organisms take up dCO2 during photosynthesis, TCO2 (or total DIC) is reduced, therefore the pCO2 decreases. Some organic carbon sinks to deeper ocean (as POC) and is remineralized.

Over seasonal timescales the biological pump and the solubility pump often work in opposite directions.

26.Carbonate Pump, (organisms, influence on deep ocean DIC, surface pCO​2​) Carbonate Pump (aka CaCO3 Pump) When some biological organisms to form particulate CaCO3, some of which sinks and dissolves in the deep ocean.

Carbonate pump increases surface ocean pCO2 due to the influence of alkalinity change on the DIC partitioning.

When coccolithophores (or foraminifera or pteropods) take up bicarbonate ions (HCO3-) to form their CaCO3 shells/platelets, they decrease the TCO2 (DIC) by one unit but decrease alkalinity by two units. Has the net effect of increasing surface ocean pCO2 concentrations. calcification equation:

2 HCO3- + Ca2+ -> CaCO3 + CO2 + H2O Dissolution: CaCO3 + H+ -> Ca2+ + HCO3Thus, dissolution is favored as acidity increases.

Acidity increases with increasing DIC concentration (so with increasing depth in the oceans).

27.Key Planktonic Calcifiers: coccolithophores, pteropods and foraminifera a. CaCO​3​ comes in two forms, calcite and aragonite. b. Aragonite is less stable and dissolves more easily. Pteropods form aragonite shells, c. while coccolithophores, foraminifera, and coral form the calcite form of CaCO​3​. d. Coccolithophores, pteropods, and foraminifera export sinking CaCO​3​, the carbonate pump.

28.calcification equation, CaCO​3​ dissolution equation, rain ratio Rain Ratio = sinking flux of CaCO3 / sinking flux of POC Describes the relative magnitudes of the carbonate and biological pumps, typical value for sinking flux out of the euphotic zone ~ 0.07 (C/C). In the deep ocean (>2000m) ~ 1.0.

Changes in the rain ratio will alter surface ocean pCO2 values.

29.lysocline, CCD, ocean sediment types and general distributions a. The ​lysocline​ is the depth where dissolution becomes strongly chemically favored. b. The ​CCD​ (Carbonate Compensation Depth) is the depth below which no accumulation of CaCO​3​ occurs in the sediments c. Oozes:​ sediments containing at least 30% biogenic silica or calcium carbonate.

Siliceous oozes and calcareous oozes accumulate at rates of 1-6 cm/kyr. d. Siliceous oozes:​ biogenic Si is coming from sinking diatoms and radiolarians.The dissolution of biogenic silica is chemically favored everywhere in the oceans.

Preservation in the sediments is largely a function of rain rate. In high flux areas > 30% of bSi can be buried, elsewhere < 3%. e. Calcareous oozes:​ CaCO​3​ is coming from sinking coccolithophores, foraminifera, and pteropods. f. Clays:​ small, fine terrigenous particles from atmospheric dust deposition to the oceans, accumulate at 0.2 cm/kyr. Clay dominated sediments are found beneath open ocean regions where there is little biological export.

g. Terrigenous:​ sediments derived from terrestrial sources, includes small clay particles from the atmosphere (dust, also inputs from rivers and ice-rafted debris). h. Turbidites:​ Formed by underwater avalanches of sediments down continental slopes. Unlike most sediments turbidite sediments are not layered neatly with age increasing steadily with depth. Instead they mix sediments from hundreds or thousands of years together and then redeposit on sea floor.

30.what controls the distribution of calcium carbonate in sediments? a. Sediment distributions in relation to ocean depth. b. Calcium carbonate (CaCO​3​) dominates in shallower regions along mid-ocean ridges. Some rains down from surface waters everywhere, but in deeper ocean areas this flux remineralizes, and thus is not preserved in the sediments.

31.calcium carbonate sediments – influence on ocean pH and anthropogenic CO​2​ uptake Ocean acidification will lead to dissolution of some sedimentary CaCO​3​, increasing alkalinity and decreasing surface ocean pCO​2​ values over ocean overturning circulation timescales

32.ocean acidification, what is it, what organisms most threatened and why, what organism might benefit?

The addition of anthropogenic CO2 to the oceans is slowly lowering the pH over time (ocean acidification).

Increasing CO2 would have negative impacts on the organisms that form CaCO3.

(Calcification, Reproduction) (Tropical corals, Molluscs) have positive impact (photosynthesis, Nitrogen Fixation)(Coccolithophores) 33.N cycle transformations - denitrification, nitrification, nitrogen fixation, (what are they ​ ​ where do they happen in the oceans, what are the beginning and end products of each) Denitrification​:​ ​When nitrate is used to breakdown organic matter, the resulting products are mostly N​2​ and a small amount of N​2​O. Denitrification takes place in ocean sediments and also in the Oxygen Minimum Zones (OMZs) at intermediate depths.

Nitrification​:​ is the conversion of ammonium (NH​4​+​) to NO​3​-​ by bacteria that happens everywhere in the oceans. Also produces small amounts of N​2​O.

Nitrogen Fixation:​ ​is the conversion of N​2​ into more bioavailable forms of nitrogen by the diazotrophs, happens in the euphotic zone.

34.Nitrous Oxide (N​2​O) - marine sources? these emissions arise from bacterial and fungal denitrification and nitrification processes 35.Oxygen Minimum Zones (OMZ) – where are they located, how/why do they form?

The main oxygen minimum zones are in the eastern tropical Pacific north and south of the equator and in the northern Indian Ocean.

These O​2​ minimum zones occur at mid-depths (~200-700m) where remineralization of lots of sinking organic material and a generally sluggish circulation leads to very low oxygen levels.

36. Factors driving potential expansion with climate change, biogeochemical implications 37.4 key nutrients that limit phytoplankton growth - main ocean sources/ sinks for each General global spatial patterns of nutrient limitation for key functional groups The most common limiting nutrients in the oceans are nitrogen, phosphorus, iron, and silicon. These nutrients are present in the ocean mainly as N - nitrate, NO​3​-​ and ammonium NH​4​+ P - phosphate, PO​4​Si - silicate, SiO​2​Fe - most dissolved inorganic iron is bound to organic ligands (>99%), tiny amount as free Fe ions. Iron is very particle reactive and rapidly removed from the oceans by scavenging, residence time < 200 years.

38.What regions are iron-limited? Nitrogen-limited? Etc.. a. Iron is the limiting nutrient (in blue) in the three High Nutrient, Low Chlorophyll (HNLC) regions in the subarctic North Pacific, the equatorial Pacific, and the Southern Ocean. b. The subtropical gyres tend to be N (maroon) or P limited (green). There is good evidence for P limitation of growth in the North Atlantic subtropical gyre.

39.HNLC regions - what are they, where are they, why are they there?

High Nutrient, Low Chlorophyll (HNLC) regions in the subarctic North Pacific, the equatorial Pacific, and the Southern Ocean.

40. JGOFS program, what was it? goals?

Joint Global Ocean Flux Study 1) To determine and understand on a global scale the processes controlling the time varying fluxes of carbon and associated biogenic elements in the ocean, and to evaluate the related exchanges with the atmosphere, sea floor and continental boundaries.

2) To develop a capability to predict on a global scale the response of oceanic biogeochemical processes to anthropogenic perturbations, in particular those related to climate change.

41.marine iron cycle, iron sources to oceans, particle scavenging, residence time, a. Key sources​ of dissolved iron (dFe) to the oceans: Atmospheric Deposition (Fe from mineral dust, combustion) Marine Sediments (Fe flux proportional to POM loading) Hydrothermal Vents (key source in deep ocean) Riverine Inputs (smaller than other sources) b. ​Particle Scavenging

Iron is very particle reactive (tendency to stick to sinking particles) leading to very short ocean residence time (< 100yrs).

Other key nutrients (N, P, Si) have longer residence times (thousands of years).

The loss to particle scavenging means subsurface waters are typically deficient in iron, compared with other nutrients. c. ​Sparse Observations

Millions of measurements of N, P, and Si in the oceans, for dissolved Fe < 30,000 measurments..

42.Martin’s glacial hypothesis for the lowering of atmospheric CO​2 “Martin Hypothesis” for glacial-interglacial cycles. Namely that higher dust/iron inputs to the oceans during ice ages increased the efficiency of the biological pump, thus lowering atmospheric CO2 concentrations.

43.Iron fertilization experiments, what were they? What did they prove?

The Fe fertilization experiments have vindicated Martin and coworkers who argued that iron-limitation was key to the HNLC regions, and also support the hypothesis by Price et al., (1994) that the HNLC zones are actually "grazer-limited populations within Fe-limited ecosystems 44.typical ecosystem response to response to iron additions in HNLC regions?

- nutrients, phytoplankton groups, zooplankton communities, DIC, ocean pCO​2 a. Unlike most ocean regions where nitrate, phosphate, and silicate are seasonally depleted to very low concentrations, in the HNLC regions surface concentrations of these nutrients are perpetually at relatively high concentrations. b. iron-limitation was responsible for the HNLC conditions. c. Initially the small phytoplankton present increase their growth rates and biomass increases modestly over several days. d. Microzooplankton grazers respond by increasing their biomass, the increased grazing pressure prevents a small phyto bloom e. Over 1-2 weeks diatom populations increase dramatically, leading to large increases in chlorophyll, POC, and primary production. pCO2 , nitrate, phosphate, and silicate in surface waters decrease.

- effects of mixed layer depth and bloom self-shading a. Mixed layer depths strongly influence the development of blooms in the Iron fertilization exp. b. The largest blooms were observed where mixed layers were relatively shallow c. In the experiments with deeper mixed layers – the blooms likely became light-limiting due to SELF-SHADING d. Self Shading – refers to the decrease in avg. mixed layer light level as chlorophyll conc. Increase. e. As wind speed increases, the surface mixed layer deepens – leading to increasing light limitation.

45.Annual map of air-sea CO​2​ flux, describe the influences of temperature, physics, chemistry, and biology in generating the regions of strong uptake and strong outgassing of CO​2​ to the atmosphere a. The net flux of gas (X) across the air-sea interface is Flux X = K (pXair pXseaw) b. As atmospheric pCO2 rises, ocean CO2 uptake increases. c. CO2 is diffusing into and out of the oceans everywhere, but the net flux is from the higher pCO2 pool (atmosphere or ocean) to the lower pCO2 pool. d. The strongest ocean uptake from the atmosphere is where poleward transport leads to cooling of surface waters AND there is strong biological drawdown of CO2

46.Ultimate fate of the CO​2​ we are currently adding to the atmosphere over longer timescales of 1000, 10,000, and 100,000 years a. Over Next 1000 Years Most of the anthropogenic CO​2​ added to the atmosphere will be absorbed by the oceans due to the solubility pump (~70-80%). The anthropogenic CO​2​ will be carried throughout the deep ocean by the circulation, beginning to interact with the sediments. b. ​Over Next 10,000 Years As the anthropogenic CO​2​ is circulated throughout the deep ocean the decrease in pH will lead to dissolution of some CaCO​3​ in sediments. This dissolution will increase the alkalinity (and raise pH) allowing the water to absorb additional CO​2​ from the atmosphere when it is brought back to the surface (~10-15%). c. ​Over next 100,000+ Years The remaining anthropogenic CO​2​ in the atmosphere (~10%) will slowly be removed due to rock weathering on the continents.

47.Sedimentary biogeochemical transformations 47.Atmospheric Nutrient deposition – importance for different nutrients, regions Nitrogen deposition to the oceans is increasing through time from anthropogenic influences, mainly agriculture and fossil fuels.

The largest increases since preindustrial times are downwind of the industrialized countries. In these regions, atmospheric N deposition can support > 20% of export production Humans have been adding increasing amounts of reactive N and P to the Earth System, perturbing the natural cycles of both elements High ​nitrogen fixation ​rates in low latitudes where surface nitrogen concentrations are low. N fixation is suppressed at high latitudes, and where Fe and P strongly limit diazotroph growth rates (eastern tropical Pacific, subtropical N. Atlantic).

48.What ocean changes are we observing today? (mostly Lecture 8) The number of ocean temperature and salinity observations have increased dramatically in recent decades.

Surface water DIC concentrations are increasing, following the atmospheric rise in CO​2 (absorbing anthropogenic CO​2​).

Rising DIC concentrations lead to higher pCO​2​ in surface waters and lower pH (ocean acidification).

Sea levels are also rising due to melting ice on land and warming of ocean waters Decreasing primary production and export production 49.Representative Concentration Pathways (RCPs) Representative Concentration Pathway were developed for the 5th IPCC Assessment Report. They represent assumptions about future human development and energy sources.

Four RCPs were defined by total radiative forcing RCP represent a broad range of climate outcomes and are neither forecasts nor policy recommendations.

50.RCP 4.5 vs. RCP 8.5 climate trajectories RCP 8.5 – Continued reliance on increasing fossil fuel use, rapidly warming climate.

RCP 4.5 – Dramatic shift away from fossil fuels by mid-century, stabilizing climate.

51.Earth System Model predictions for climate change impacts on: ocean temperature and salinity distributions, stratification and nutrient entrainment to surface waters, (​increasing stratification weakens the nutrient flux) net primary production, export production, and nutrient distributions (​Net primary production and Carbon Export in CMIP5 models decline, as sea surface temperatures warm and stratification increases​) 52.How and why might climate change impacts over multicentury timescales differ from the trends over the next decades to a century?

CO2 concentration pathway: the historical record to 2005, then RCP 8.5 to 2100, then ECP 8.5 to 2300