Atmospheric carbon is sequestered into the ocean by three main pumps which have been known for 30 years: the solubility pump, the carbonate pump, and the biological carbon pump (BCP). The biological carbon pump is a vertical transmission pump driven mainly by the sinking of organic rich particles. Bacterial phytoplankton near the surface incorporate atmospheric CO2 and other nutrients into their biomass during photosynthesis. At the time of their death these phytoplankton, along with their incorporated carbon, sink to the bottom of the ocean where the carbon remains for thousands of years. The other biologically mediated sequestration of carbon in the ocean occurs through the microbial pump. The microbial pump is responsible for the production of old recalcitrant dissolved organic carbon (DOC) which is >100 years old. Plankton in the ocean are incapable of breaking down this recalcitrant DOC and thus it remains in the oceans for 1000s years without being respired. The two pumps work simultaneously, and the balance between them is believed to vary based on the availability of nutrients. Overall, the oceans act as a sink for atmospheric CO2 but also release some carbon back into the atmosphere. This occurs when bacterioplankton and other organisms in the ocean consume organic matter and respire CO2, and as a result of the solubility equilibrium between the ocean and the atmosphere.
