There is another important impact of biological processes to the uptake/release of carbon into/out of the ocean. This is the formation of calcium carbonate by little organisms such as coccolithophores, foraminifera and corals in the ocean surface waters. As it is visible in the chemical formula below, the biological formation of calcium carbonate (from left to right) also produces CO2 and therefore counteracts the uptake of CO2 from the atmosphere into the ocean.
Ca2+ + 2HCO3- ↔ CaCO3(s) + H2O + CO2
On the other hand, the dissolution of calcium carbonate (from right to left in the formula above) in the deeper ocean reduces the amount of dissolved CO2 and when this water wells up to the surface, more CO2 can be taken up.
Reference: Chester, R. and Jickells, T. (2012) Nutrients, Oxygen, Organic Carbon and the Carbon Cycle in Seawater, in Marine Geochemistry, John Wiley & Sons, Ltd, Chichester, UK. doi: 10.1002/9781118349083.ch9 — Laura Arnold 2014/04/16 08:05
