The threat of rapid climate change due to greenhouse gas build-up in the atmosphere is the result of the sources of greenhouse gas to the atmosphere exceeding the sinks. The transformation of CO2 in the atmosphere is very slow. In the previous chapter we considered how to change the radiative balance by adjusting the energy flux provided by the sun. We should now turn to examining the issues in using the ocean as a sink of carbon. Already the total mobile carbon in the oceanic waters is of the order of 40000GtC, much greater than the 2200GtC on the land. The carbon in the ocean is stored mostly as bicarbonate, and the total dissolved inorganic carbon has a concentration of order 2000μmol kg−1.

Carbon is cycled by the marine planktonic ecosystem. Houghton et al. (1996), in the second assessment report of the Intergovernmental Panel on Climate Change, concluded that if there were changes in the oceanic plankton, there is a large potential for the biological pump to influence CO2 concentrations in the atmosphere.

Carbon is also cycling in and out of the ocean as a result of the vertical circulation in the large ocean basins bringing water to the surface with a different partial pressure to that of the atmosphere above.