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II RELATIONSHIP BETWEEN OCEAN AND ATMOSPHERE

5st PART

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OCEAN AND CARBON DIOXYDE

The CO2 (carbonic gas) gas present in the atmosphere is constantly exchanged with biomass (breathing and damage of plants) and the ocean (by solution of gas in water). LBiomass contains about 2 times more CO2 than the atmosphere and the ocean 50 times more ! Every 10 years the CO2 is renewed by exchange with the biomass and the ocean which would mean that this gas is controlled by the ocean.

But this control depends above all on the rate of water renewal that is in contact with the atmosphere as carbon transport is dissolved by oceanic currents that directs the oceanic carbon cycle. Thermohaline circulation is the main point driver of this renewal.

However, the ocean also contains a significant biomass: plankton. It is about 10 times lower than the continental biomass. Oceanic biomass is renewed 10 times faster than the continental biomass and the rate of organic carbon creation in the ocean is comparable to that of the continents.

Due to their low temperature, Antarctic waters absorb a lot of CO2. In fact, most oceanic mass is cold, more it absorbs carbon dioxide.

                               
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This animated map shows the seasonal exchange of CO2 between the atmosphere
and ocean (g months C/m2). Positive values correspond to the absorption
of CO2 and the negative values in the emission of CO2 by the ocean.

Some of the CO2 is reabsorbed by the ocean, by dissolution in water. Then by dissolved form this gas can be transported by oceanic currents. Seaweed and algae assimilate carbon dioxide that goes into the chain of life. Then by particular form it can either be deposited in the depths of the abyss or be rapidly remineralized by the action of bacteria on surface.


Click here to enlarge this diagram of the control of CO2 by the ocean


The Southern Ocean uptake 30 to 50% of the amount of carbon dioxide conveyed into Earth's atmosphere, while it represents only 10% of the oceanic surface. It is what scientists call a « carbon sinks » . In ten years, within the context of the Antares program they started in 1990 at the initiative of the Brest IUEM the researchers of oceanography discovered this particuliarity of the Antarctic Ocean. They are now able to quantify the amount of CO2 taken up each year by the oceans : 2 billions of tons !

They also discovered over 60 campaigns conducted in the Southern Ocean, of which some number fullfiled by the « Marion Dufresne », that this aspiration varies in intensity depending on the variation of temperature a more or less degree of the ocean. This temperature variation would be to link to the effect of El Nino that occurs regularly in the Pacific and causes considerable damages on both sides of the ocean.


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