Adiabatic reduction of circulation‐related CO2 air‐sea flux biases in a North Atlantic carbon‐cycle model

Abstract

Physical transport processes of carbon, alkalinity, heat, and nutrients to a large extent control the partial pressure of CO2 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 CO2 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 CO2 uptake in the corrected regional model is larger by 25% compared to the uncorrected model.