Strong Southern Ocean carbon uptake evident in airborne observations

Up in the air

Understanding ocean-atmospheric carbon dioxide (CO2) fluxes in the Southern Ocean is necessary for quantifying the global CO2 budget, but measurements in the harsh conditions there make collecting good data difficult, so a quantitative picture still is out of reach. Long et al. present measurements of atmospheric CO2 concentrations made by aircraft and show that the annual net flux of carbon into the ocean south of 45°S is large, with stronger summertime uptake and less wintertime outgassing than other recent observations have indicated. —HJS


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°S during the period 2009–2018. This is consistent with the mean of atmospheric inversion estimates and surface-ocean partial pressure of CO2 (PCO2)–based products, but our data indicate stronger annual mean uptake than suggested by recent interpretations of profiling float observations.

Long M. C., Stephens B. B., McKain K., Sweeney C., Keeling R. F., Kort E. A., Morgan E. J., Bent J. D., Chandra N., Chevallier F., Commane R., Daube B. C., Krummel P. B., Loh Z., Luijkx I. T., Munro D., Patra P., Peters W., Ramonet M., Rödenbeck C., Stavert A., Tans P. & Wofsy S. C., 2021. Strong Southern Ocean carbon uptake evident in airborne observations. Science 374: 1275-1280. Article (subscription required).

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