The total amount of inorganic carbon in the sea is about 35 000 PgC. This includes dissolved carbon dioxide, HCO^, and CO3 . The dissolved carbon dioxide forms only one per mille of the total. Most of carbon is stored in the form of HCO^. The share of CO2~ is less than 15% (about 13%).
The ocean storage is divided into surface water and deep sea. The surface water is in turn divided into cold surface water and warm surface water, both extending to 75 m depth - that is, the depth of seasonal thermocline. Warm surface water is a part of ocean between 40° N and 40° S where a well-defined permanent thermocline exists. Cold surface water is the rest of the ocean, which exchanges with deeper layers of the ocean by convection.
The surface water contains about 10% more carbon than the atmosphere that constitutes about 2% of the total carbon content in the ocean.
The concentration of dissolved carbon dioxide is proportional to its partial pressure above ocean surface (Pco2)- The coefficient of proportionality is called solubility coefficient. The solubility of CO2 varies with temperature suggesting a transfer of CO2 in the atmosphere from warm regions to polar regions where CO2 solubility is higher. This atmospheric transfer is balanced by the backward net oceanic transfer, the so-called 'conveyer belt'.
The dissolved carbon dioxide forms about 0.5% of the total dissolved inorganic carbon (DIC). The concentration of DIC also depends on Pco2, but in a more complicated way:
where £ is the buffer factor.
The surface water contains a significant amount of organic carbon: about 50 PgC of dissolved organic carbon (DOC), 30 PgC of particulate organic carbon (POC), and 3 PgC of plankton. The rate of photosynthesis varies from 0.06 gC m-2 d-1 in the desert regions which are characterized by downwelling and lack of nutrients to 0.6 gC m- d- in areas of intense upwelling. The total primary production amounts to 40PgCyr- . About 10% of the primary production reaches the deep water that contains about 900 PgC of DOC.
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