The possibility that the CO₂ partial pressure of the surface waters of the ocean (and hence also of the atmosphere) is dependent on the rates of oceanic mixing is explored. The purpose of this exercise is to ascertain whether the abrupt rise in atmospheric CO₂ content at the end of the last glacial period could have been caused by a reorganization of deep-sea ventilation. We also have our eyes on the possibility that future warming of the planet induced by anthropogenic CO₂ will lead to a positive feedback (i.e. polar warming, reduced deep-sea ventilation rate, increase In the CO₂ partial pressure of surface ocean water). Our approach is to consider two end-member models for the distribution of CO₂ in the sea. One is thermodynamic, the other is biological. The surface-water CO₂ partial pressure difference between these end-member models is nearly a factor of two. We show that the situation for the real ocean probably lies roughly halfway between these extremes and explore how the ratio of deep-sea ventilation rate to air-sea CO₂-exchange rate might push the system closer to one extreme or the other. Our tentative conclusion is that decreases in the ventilation rate will push the ocean closer to the thermodynamic end member and hence raise the atmosphere’s CO₂ partial pressure. Such a decrease in ventilation rate may have occurred at the end of glacial time. A further decrease may be induced during the next hundred or so years by the build-up of CO₂ in the atmosphere.

This paper will be submitted in full to the Journal of Geophysical Research.