Ocean State Report 2 Summary - Copernicus Marine Service

Page 10

GREEN OCEAN CARBON CARBON CYCLE COMPONENTS

Phytoplankton is a single-celled algae found in both fresh and salty waters. It makes up the base of the marine food chain and plays an important role in the Earth’s carbon cycle. It grows through photosynthesis and requires nutrients.

Physical Carbon Pump

Organic Carbon Pump

Two mechanisms drive the physical carbon pump:

In order to grow, phytoplankton use sunlight, consume dissolved CO2 as well as nutrients, and release oxygen during photosynthesis. CO2, vital for the creation of life, is then transformed into organic carbon, building the phytoplankton cells. As this organic matter is processed by bacteria, zooplankton and their consumers, a fraction of it ends up as dead organic and fecal material that sinks into deeper ocean layers.

1) At high latitudes (e.g. subpolar ocean) ocean temperatures are cold. As a consequence, the solubility of CO2 is higher and ingassing of CO2 from the atmosphere into the ocean occurs. Carbon is then pulled into the deep ocean through convection and formation of deep water (see Blue Ocean) and is stored there and redistributed by ocean currents. 2) At low latitudes (e.g. tropics), ocean surface temperatures are high, and consequently the solubility of CO2 is lower. Additionally, winddriven ocean upwelling brings up stored carbon from the deep ocean layers to the surface, and outgassing occurs from the ocean into the atmosphere.

Bacteria decompose part of this sinking organic matter, using oxygen, and releasing CO2 and nutrients as part of a more general process called remineralization. The CO2 escapes back into the atmosphere (outgassing) or is reused or redistributed through ocean currents, along with the rereleased nutrients. Some of the dead organisms (organic carbon) sink into the deep ocean bottom layer, trapping carbon there for sometimes thousands of years.

Wind displaces surface waters allowing cold deep waters to upwell

Atmosphere CO₂

Ingassing

Atmosphere

CO₂

DEPTH

Carbon dissolved

Deep convection

Photosynthesis takes place at the ocean surface

Outgassing

Phytoplankton + consumers

Upwelling

CO₂

Outgassing

CO₂

+ nutrients

Remineralization

Carbon dissolved in deep waters

High lattitudes

CO₂

Ingassing

Sinking organic material

Low lattitudes

A fraction of the dead matter (organic carbon) can be trapped at ocean floor for thousands of years

Increase in temperature

THE OCEAN IS ABSORBING CO 2

CO2 Sea-to-Air Exchange

About 1/4 of human-induced CO2 in the atmosphere is stored in the ocean through carbon uptake. However, the price we pay for this buffering is the acidification of the ocean.

PgC.yr-1

Ocean State Report results show that during the 1990s there is a relatively stable carbon uptake in the global ocean and a sharp increase in the ocean’s uptake of carbon since the beginning of the 2000s. These results are consistent with previous findings.

This figure shows a negative CO2 Sea-to-Air Exchange over time, which means that the ocean is absorbing atmospheric CO2. The red line shows a CMEMS negative value of sea-to-air flux as expressed in petagrams of carbon per year (PgC.yr-1). The dashed lines show similar results from other scientific studies.

CO2 is leaving the atmosphere and going into the ocean.


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