Keele Research Repository

The Southern Ocean occupies some 14% of the planet’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, remineralisation 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 rise 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 significant regional marine carbon sink, which contributed to the plateau in CO2 at the ACR. Our results highlight the role Antarctic sea ice plays in controlling global CO2, and demonstrates the need to incorporate such feedbacks into climate-carbon models.