Strong Southern Ocean carbon uptake evident in airborne observations

The Southern Ocean plays an important role in determining atmospheric carbon dioxide (CO2), yet estimates of air-sea CO2 flux for the region diverge widely. In this study, we constrained Southern Ocean air-sea CO2 exchange by relating fluxes to horizontal and vertical CO2 gradients in atmospheric transport models and applying atmospheric observations of these gradients to estimate fluxes. Aircraft-based measurements of the vertical atmospheric CO2 gradient provide robust flux constraints. We found an annual mean flux of -0.53 +/- 0.23 petagrams of carbon per year (net uptake) south of 45 degrees S during the period 2009-2018. This is consistent with the mean of atmospheric inversion estimates and surface-ocean partial pressure of CO2 (P-CO2)-based products, but our data indicate stronger annual mean uptake than suggested by recent interpretations of profiling float observations.

Automated summary

The Southern Ocean plays a crucial role in determining atmospheric carbon dioxide levels. This study found that the annual mean carbon uptake south of 45 degrees S is -0.53 +/- 0.23 petagrams per year, which is higher than some recent interpretations of profiling float observations.