Abstract

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... Show moreThe 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. Show less