Adiabatic reduction of circulation‐related CO 2 air‐sea flux biases in a North Atlantic carbon‐cycle model

Physical transport processes of carbon, alkalinity, heat, and nutrients to a large extent control the partial pressure of CO 2 at the sea surface and hence the oceanic carbon uptake. Using a state‐of‐the‐art biogeochemical model of the North Atlantic at eddy‐permitting resolution we show that biases in the simulated circulation generate errors in air‐sea fluxes of CO 2 which are still larger than those associated with the considerable uncertainties in parameterizations of the air‐sea gas exchange. A semiprognostic correction method that adiabatically corrects the momentum equations while conserving water mass properties and tracers is shown to yield a more realistic description of the carbon fluxes into the North Atlantic at little additional computational cost. Owing to upper ocean flow patterns in better agreement with observations, simulated CO 2 uptake in the corrected regional model is larger by 25% compared to the uncorrected model.