TEAM GE-C
THE ROLE OF OCEAN IN CARBON-CYCLE WITH ATMOSPHERE
Carbon dioxide is weak acid, and minerals and organisms dissolved in the ocean are slightly weak alkalinity. So ocean can absorb carbon dioxide from atmosphere. Once carbon dioxide dissolved in ocean, it becomes DIC (dissolved inorganic carbon). If you look at the distribution of DIC in the global ocean, you can find two major characteristics.
Inorganic carbon and pH vary as a function of depth and latitude. (a) Vertical profiles typical of the mid-North Pacific showing variations of several seawater chemical parameters with depth. Adapted from Morel and Hering (1993) with calculations using constants from Dickson et al. (2007) and Lueker et al. (2000).
Distribution of dissolved inorganic carbon in seawater. (Illustration: GEOMAR)
http://www.eskp.de/en/a-consistent-data-base-for-ocean-carbon/
First, concentration of DIC becomes higher in the deep sea than surface. Second, the water formed newly from North Atlantic has lower amount of DIC than the old water from North Pacific. The air-sea exchange of carbon dioxide is determined largely by the gradient of partial pressure of carbon dioxide (pCO2) between atmosphere and ocean. This gas exchange rates increase with wind speed and depend on other factors such as precipitation, heat flux, sea ice and surfactants.
12 August 2006 (UTC), Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany
Especially three main ocean carbon pumps regulate the natural atmospheric changes by the ocean. This carbon pump carries carbon in the surface to deep sea. And it makes vertical carbon concentration gradient. This process linked together with whole cycle of earth’s ocean, makes the difference in inorganic carbon concentration between the large ocean.
First, ‘solution pump’ is adsorption or release carbon dioxide due to changes in solubility of gaseous carbon dioxide. Gases such as carbon dioxide can dissolve in ocean with lower temperature than higher temperature. Additionally, the average temperature is lower in high latitude than low latitude.
And there are two biological pump that one is ‘organic carbon pump’ and the other is ‘CaCO3 counter pump’. Organic carbon pump is changing in carbon fixation to POC in surface waters by photosynthesis and export of this carbon through sinking of organic particles out of the surface layer. So this pump usually lower the partial pressure of carbon dioxide in the atmosphere. Otherwise, CaCO3 counter pump lower the alkalinity of the ocean surface, so it lowers the carbon capacity of the ocean.
The organisms related to CaCO3 counter pump make their shells or bodies using dissolved carbonate(CO32-) to calcium carbonate(CaCO3). This process decrease the concentration of carbonate dissolved in ocean, and it breaks the balance of carbon species in ocean surface. Finally, this increase the partial pressure of carbon pressure in the ocean surface, and then gaseous carbon dioxide release to the atmosphere. In the mean time, sinking calcium carbonate is dissolved into calcium and carbonate in the deep sea. In result, this mechanism increase the alkalinity in the deep sea, but lower that in the surface of the sea.
Through these mechanisms, even though the emission of carbon dioxide gets slightly increased, atmosphere can maintain their concentration of carbon dioxide constant.