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 of the prein dustrial air-sea flux of CO₂ are atmosphere-ocean heat exchange and the biological pump, coupled with the direct influence of ocean circulation resulting from the slow time-scale of air-sea CO₂ gas exchange equilibration. The influence of the biological pump is greatest in surface outcrops of deep water, where the excess deep ocean carbon resulting from net remineralization 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 the 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 uptake 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 southward interhemispheric transport of CO₂ that has been suggested by atmospheric carbon transport constraints.