Speaker: Dr. Anne Willem Omta, Postdoctoral Associate, MIT EAPS. Abstract: In view of the ongoing anthropogenic emissions of carbon, it is of crucial importance to understand which portion of future emissions will stay in the atmosphere and how large a portion will be taken up by the oceans. To get a deeper insight into this issue, we formulate an analytical theory for the ocean-atmosphere partitioning of carbon based on simple carbonate chemistry; a newly defined 'buffer factor' (O), analogous to the well-known Revelle buffer factor, turns out to be crucial for the theory development. We apply this framework to derive the dependence of the carbon partitioning on the average ocean temperature and alkalinity and we predict how the partitioning changes with increasing emissions. The most important effect impacting the carbon partitioning turns out to be neutralisation of carbonate ions at the ocean surface which decreases the carbon uptake capacity of the oceans. The predictions are found to be consistent with recent modeling studies and it is thus illustrated that the theory can provide a mechanistic explanation for oceanic carbon cycle simulation results. When applied to the next centuries, the theory and simulations suggest that the neutralisation of carbonate at the ocean surface will lead to a strong decrease of the portion of carbon emissions that are taken up by the ocean.