The Southern Ocean occupies 14% of the Earth’s surface and plays a fundamental role in the global carbon cycle and climate. It provides a direct connection to the deep ocean carbon reservoir through biogeochemical processes that include surface primary productivity, remineralization at depth and the upwelling of carbon-rich water masses. However, the role of these different processes in modulating past and future air–sea carbon flux remains poorly understood. A key period in this regard is the Antarctic Cold Reversal (ACR, 14.6–12.7 kyr bp), when mid- to high-latitude Southern Hemisphere cooling coincided with a sustained plateau in the global deglacial increase in atmospheric CO2. Here we reconstruct high-latitude Southern Ocean surface productivity from marine-derived aerosols captured in a highly resolved horizontal ice core. Our multiproxy reconstruction reveals a sustained signal of enhanced marine productivity across the ACR. Transient climate modelling indicates this period coincided with maximum seasonal variability in sea-ice extent, implying that sea-ice biological feedbacks enhanced CO2 sequestration and created a substantial regional marine carbon sink, which contributed to the plateau in CO2 during the ACR. Our results highlight the role Antarctic sea ice plays in controlling global CO2, and demonstrate the need to incorporate such feedbacks into climate–carbon models.
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The data supporting this study is available at National Oceanic and Atmospheric Administration Paleoclimatology Database (https://www.ncdc.noaa.gov/paleo/study/29415). The data from core MD07-3134 are available on the PANGEA Database at https://doi.pangaea.de/10.1594/PANGAEA.819646 and https://doi.pangaea.de/10.1594/PANGAEA.789348. Source data for Figs. 1, 4 and 5 and Extended Data Fig. 1 are available with the paper.
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C.J.F., C.S.M.T., L.M., N.R.G., L.S.W. and A.C. are supported by their respective Australian Research Council (ARC) and Royal Society of NZ fellowships, and C.J.F. and A.G.C. thank Keele University for a Research Development Award that underpinned this research at Keele University IceLab and Exeter University. Fieldwork was undertaken under ARC Linkage Project (LP120200724), supported by Linkage Partner Antarctic Logistics and Expeditions, whose enduring support we acknowledge. CSIRO’s contribution was supported in part by the Australian Climate Change Science Program (ACCSP), an Australian Government Initiative. S.D. acknowledges financial support from Coleg Cymraeg Cenedlaethol and the European Research Council (ERC grant agreement no. 25923). M.E.W. acknowledges support from the Deutsche Forschungsgemeinschaft (grant no. We2039/8-1). Finally, we thank H. Glanville for comments on the final draft of the manuscript, and A. Jeffery for advice on SEM analysis.
The authors declare no competing interests.
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Reproducibility of fOM signal. 5 m resolved fOM concentration (Component 1; TRYLIS in red), plotted against data from a second parallel transect from the Patriot Hills transect (~3 m resolved black dashed line). The dashed lines represent replicate samples from the same transect which were taken in 2014/15 and measured in 2015 at UNSW Icelab (black dots), and subsequently reanalysed in 2019 at Keele Icelab (red triangles). The records are synchronised from water stable isotopes, site survey data and DGPS, and taken within 4 m of one another from a parallel transect (inset).
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Fogwill, C.J., Turney, C.S.M., Menviel, L. et al. Southern Ocean carbon sink enhanced by sea-ice feedbacks at the Antarctic Cold Reversal. Nat. Geosci. 13, 489–497 (2020). https://doi.org/10.1038/s41561-020-0587-0