Climate evolution at the last deglaciation: the role of the Southern Ocean

Abstract

Two sediment sequences recovered close to, and south of, the present Polar Front (50°, 53°S) in the Atlantic sector of the Southern Ocean were analysed in order to evaluate the environmental evolution of the Southern Ocean surface over the last deglaciation and the Holocene. Our reconstruction is based on radiocarbon-dated records of diatom-based sea surface temperature and sea-ice proxies and planktic foraminiferal stable isotopes. The onset of the deglacial warming and gradual southward retreat of the winter sea-ice field between 18 and 17 cal kyr BP, occurrence of a thermal reversal centered at ca. 13 cal kyr BP (Antarctic Cold Reversal, or ACR), and early Holocene occurrence of the “climatic optimum” well correlate with climatic reconstructions available from the Indian Southern Ocean and from Antarctic ice cores. Time correspondence of Southern Ocean warming and Heinrich event 1 in the North Atlantic is compatible with the transmission of the climate signal from the Northern to the Southern Hemisphere through the “bipolar seesaw.” Our data support modeling results suggesting that the Northern Hemisphere Bølling warming and turn-on of the North Atlantic Deep Water formation are triggered by gradual warming and sea-ice retreat in the Southern Ocean. Meltwater shedding into the Southern Ocean associated with the ACR may maintain Northern Hemisphere warming during the Allerød. The development of sea surface warming and sea-ice retreat is compatible with a Southern Ocean control on the atmospheric CO 2 increase during the deglaciation. During the early Holocene (9–7 cal kyr BP), our southern core records renewed surface ocean cooling and northward readvance of the winter sea-ice field. Such early Holocene cooling is common to cores from the high-latitude Atlantic sector, and might be brought about by expansion of the Weddell Gyre circulation at that time.