Abstract
We compare air-sea CO2 exchange in an ensemble of global
ocean hindcast models to a suite of observation-based products for
1990-2018. Individual products agree closely for regional fluxes, but
individual models vary widely in their regional estimates. Despite their
regional divergence, individual models estimate similar global mean
fluxes, indicating that significant regional compensation occurs to
balance in the global integral. Models diverge most strongly from the
observed mean flux in the northern and southern subtropics, despite
strong agreement in seasonality. In the Southern Ocean, models estimate
a wide range of both mean and seasonality. The ensemble of
observation-based products can be used to select the models that best
represent the regionally-resolved mean state of air-sea
CO2 exchange. Three models are within 3σ of the observed
estimates in all regions. With this selected model ensemble, the global
mean flux is slightly reduced and its uncertainty is reduced by 35%.