Despite unequivocal global warming, Southern Ocean surface waters have largely cooled over the past ~40 years and Antarctic sea ice has expanded, in stark contrast to almost all historical climate model simulations. The Southern Ocean surface cooling is nearly circumpolar, except notably in the Amundsen-Bellingshausen Sea, where rapid warming and sea-ice retreat has been observed. In contrast to the overall surface cooling around Antarctica, subsurface ocean warming has been observed, both over the Antarctic shelf and in the abyssal ocean layers ventilated by Antarctic Bottom Water. The shelf water warming threatens to drive catastrophic retreat of Antarctica’s marine-terminating ice sheets, resulting in accelerated global sea-level rise. The bottom water warming likely indicates a slowdown of the overturning of dense water around Antarctica, with implications for the global cycling of heat and nutrients by the oceans. This talk will present an overview of the processes that have led to these oceanic temperature trends around Antarctica, and give an outlook of expected changes over the coming decades.
Deputy Director, UNSW Climate Change Research Centre