Abrupt ice-age shifts in southern westerly winds and Antarctic climate forced from the north

The mid-latitude westerly winds of the Southern Hemisphere play a central role in the global climate system via Southern Ocean upwelling 1 , carbon exchange with the deep ocean 2 , Agulhas leakage (transport of Indian Ocean waters into the Atlantic) 3 and possibly Antarctic ice-sheet stability 4 . Meridional shifts of the Southern Hemisphere westerly winds have been hypothesized to occur 5 , 6 in parallel with the well-documented shifts of the intertropical convergence zone 7 in response to Dansgaard–Oeschger (DO) events— abrupt North Atlantic climate change events of the last ice age. Shifting moisture pathways to West Antarctica 8 are consistent with this view but may represent a Pacific teleconnection pattern forced from the tropics 9 . The full response of the Southern Hemisphere atmospheric circulation to the DO cycle and its impact on Antarctic temperature remain unclear 10 . Here we use five ice cores synchronized via volcanic markers to show that the Antarctic temperature response to the DO cycle can be understood as the superposition of two modes: a spatially homogeneous oceanic ‘bipolar seesaw’ mode that lags behind Northern Hemisphere climate by about 200 years, and a spatially heterogeneous atmospheric mode that is synchronous with abrupt events in the Northern Hemisphere. Temperature anomalies of the atmospheric mode are similar to those associated with present-day Southern Annular Mode variability, rather than the Pacific–South American pattern. Moreover, deuterium-excess records suggest a zonally coherent migration of the Southern Hemisphere westerly winds over all ocean basins in phase with Northern Hemisphere climate. Our work provides a simple conceptual framework for understanding circum-Antarctic temperature variations forced by abrupt Northern Hemisphere climate change. We provide observational evidence of abrupt shifts in the Southern Hemisphere westerly winds, which have previously documented 1 – 3 ramifications for global ocean circulation and atmospheric carbon dioxide. These coupled changes highlight the necessity of a global, rather than a purely North Atlantic, perspective on the DO cycle. The position of the Southern Hemisphere westerly winds responds immediately to abrupt North Atlantic climate events of the last ice age, with a spatially heterogeneous impact on Antarctic climate.