Spatial distribution of air-sea CO2 fluxes and the interhemispheric transport of carbon by the oceans

The dominant processes controlling the magnitude and spatial distribution o f the preindustrial air-sea flux of CO2 are atmosphere-ocean heat exchange and the biological pump, coupled with the direct influence of ocean circula tion resulting from the slow time-scale of air-sea CO2 gas exchange equilib ration. The influence of the biological pump is greatest in surface outcrop s of deep water, where the excess deep ocean carbon resulting from net remi neralization can escape to the atmosphere. In a steady state other regions compensate for this loss by taking up CO2 to give a global net air-sea CO2 flux of zero. The predominant outcrop region is the Southern Ocean, where t he loss to the atmosphere of biological pump CO2 is large enough to cancel the gain of CO2 due to cooling. The influence of the biological pump on upt ake of anthropogenic CO2 is small: a model including biology takes up 4.9% less than a model without it. Our model does not predict the large southwar d interhemispheric transport of CO2 that has been suggested by atmospheric carbon transport constraints.