Southern Ocean Air-Sea Carbon Fluxes from Aircraft Observations: Modeling Datasets

The Southern Ocean plays an important role in determining atmospheric CO2, yet estimates of air-sea CO2 flux for the region diverge widely. We constrain Southern Ocean air-sea CO2 exchange by relating fluxes to horizontal and vertical CO2 gradients in atmospheric transport models and then apply atmospheric observations of these gradients to estimate fluxes. Aircraft-based measurements of the vertical atmospheric CO2 gradient provide robust flux constraints. We find an annual-mean flux of –0.55±0.23 Pg C yr–1 (net uptake) south of 45°S during 2009–2018. This is consistent with the mean of atmospheric-inversion estimates and surface-ocean pCO2-based products, but our data indicate stronger annual-mean uptake than suggested by recent interpretations of profiling-float observations.