Southern Ocean carbon sink enhanced by sea-ice feedbacks at the Antarctic Cold Reversal

• Published in: Nature Geoscience
• Main Authors: Fogwill, CJ, Turney, CSM, Menviel, L, Baker, A, Weber, ME, Ellis, B, Thomas, ZA, Golledge, NR, Etheridge, D, Rubino, M, Thornton, DP, van Ommen, TD, Moy, AD, Curran, MAJ, Davies, S, Bird, MI, Munksgaard, NC, Rootes, CM, Millman, H, Vohra, J, Rivera, A, Macintosh, A, Pike, J, Hall, IR, Bagshaw, EA, Rainsley, E, Bronk-Ramsey, C, Montenari, M, Cage, AG, Harris, MRP, Jones, R, Power, A, Love, J, Young, J, Weyrich, LS, Cooper, A
• Format: Article in Journal/Newspaper
• Language: English
• Published: Nature Publishing Group 2020
• Subjects: Earth Sciences; Physical geography and environmental geoscience; Palaeoclimatology; Antarctic; Southern Ocean; The Antarctic; Antarc*; ice core; Sea ice
• Online Access: https://doi.org/10.1038/s41561-020-0587-0; http://ecite.utas.edu.au/139595

The Southern Ocean occupies 14% of the Earths 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 airsea carbon flux remains poorly understood. A key period in this regard is the Antarctic Cold Reversal (ACR, 14.612.7 kyr bp ), when mid- to high-latitude Southern Hemisphere cooling coincided with a sustained plateau in the global deglacial increase in atmospheric CO 2 . 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 CO 2 sequestration and created a substantial regional marine carbon sink, which contributed to the plateau in CO 2 during the ACR. Our results highlight the role Antarctic sea ice plays in controlling global CO 2 , and demonstrate the need to incorporate such feedbacks into climatecarbon models.