Strong Southern Ocean carbon uptake evident in airborne observations

• Published in: Science (American Association for the Advancement of Science) Vol. 374; no. 6572; pp. 1275 - 1280
• Main Authors: Long, Matthew C., Stephens, Britton B., McKain, Kathryn, Sweeney, Colm, Keeling, Ralph F., Kort, Eric A., Morgan, Eric J., Bent, Jonathan D., Chandra, Naveen, Chevallier, Frederic, Commane, Róisín, Daube, Bruce C., Krummel, Paul B., Loh, Zoë, Luijkx, Ingrid T., Munro, David, Patra, Prabir, Peters, Wouter, Ramonet, Michel, Rödenbeck, Christian, Stavert, Ann, Tans, Pieter, Wofsy, Steven C.
• Format: Journal Article
• Language: English
• Published: Washington The American Association for the Advancement of Science 03.12.2021; American Association for the Advancement of Science (AAAS)
• Subjects: Aircraft; Atmospheric models; Carbon dioxide; Constraints; Continental interfaces, environment; Estimates; Fluctuations; Fluxes; Ocean, Atmosphere; Outgassing; Partial pressure; Sciences of the Universe; Transport processes; Southern Ocean
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.abi4355

Up in the air Understanding ocean-atmospheric carbon dioxide (CO 2 ) fluxes in the Southern Ocean is necessary for quantifying the global CO 2 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 CO 2 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 Aircraft observations show that the Southern Ocean region is a strong carbon sink. The Southern Ocean plays an important role in determining atmospheric carbon dioxide (CO 2 ), yet estimates of air-sea CO 2 flux for the region diverge widely. In this study, we constrained Southern Ocean air-sea CO 2 exchange by relating fluxes to horizontal and vertical CO 2 gradients in atmospheric transport models and applying atmospheric observations of these gradients to estimate fluxes. Aircraft-based measurements of the vertical atmospheric CO 2 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 CO 2 ( P co 2 )–based products, but our data indicate stronger annual mean uptake than suggested by recent interpretations of profiling float observations.