2.3.2 The oceanic carbon cycle

A flux of CO₂ between the ocean and the atmosphere occurs when the CO₂ content of the ocean surface is not in equilibrium with the atmospheric concentration. The flux $\Phi$^CO₂ from the ocean to the atmosphere is proportional to this imbalance and can be computed as a function of the difference in partial pressure p^CO₂ between the two media:

where the subscripts A and W refer to air and water, respectively. k^CO₂ is a transfer coefficient which is strongly dependent of the wind velocity. At equilibrium, $p_W^{C{O}_2}$ is obviously equal to $p_A^{C{O}_2}$.

As the surface CO₂ concentration in the atmosphere is nearly homogenous, the repartition of the flux mainly depends on the oceanic p^CO₂. Supersaturated zones, where the partial pressure of CO₂ in sea water is higher than in the air, have a positive flux from the ocean to the atmosphere. In present-day conditions, this occurs in tropical regions, particularly in the eastern equatorial Pacific (Fig. 2.25). On the other hand, undersaturated areas, such as the mid to high latitudes around 40^o -60^o in both hemispheres (except the Northern Pacific), display CO₂ fluxes from the atmosphere to the ocean, i.e. an uptake of CO₂ from the atmosphere.

• 2.3.2.1 Inorganic carbon cycle
• 2.3.2.2 Biological pumps