Precise interpolar phasing of abrupt climate change during the last ice age

A new ice core from West Antarctica shows that, during the last ice age, abrupt Northern Hemisphere climate variations were followed two centuries later by a response in Antarctica, suggesting an oceanic propagation of the climate signal to the Southern Hemisphere high latitudes. Climate seesaw swings north to south The bipolar seesaw theory explains certain abrupt episodes of climate change as a consequence of an interhemispheric redistribution of heat; when one polar region is warming, the other cools. So far, it has been unclear if the Northern Hemisphere is forcing the Southern Hemisphere or vice versa, and whether the seesaw operates via oceanic or atmospheric mechanisms. This study, synthesizing data from several climate laboratories, uses high-resolution data from the recently drilled WAIS Divide Antarctic ice core, combined with data from Greenland, to show that during much of the past 65,000 years, the north has led the south for both cooling and warming events. Abrupt Northern Hemisphere climate variations were followed two centuries later by a response in Antarctica, suggesting an oceanic propagation of the climate signal to the Southern Hemisphere high latitudes. The last glacial period exhibited abrupt Dansgaard–Oeschger climatic oscillations, evidence of which is preserved in a variety of Northern Hemisphere palaeoclimate archives 1 . Ice cores show that Antarctica cooled during the warm phases of the Greenland Dansgaard–Oeschger cycle and vice versa 2 , 3 , suggesting an interhemispheric redistribution of heat through a mechanism called the bipolar seesaw 4 , 5 , 6 . Variations in the Atlantic meridional overturning circulation (AMOC) strength are thought to have been important, but much uncertainty remains regarding the dynamics and trigger of these abrupt events 7 , 8 , 9 . Key information is contained in the relative phasing of hemispheric climate variations, yet the large, poorly constrained difference between gas age and ice age and the relatively low resolution of methane records from Antarctic ice cores have so far precluded methane-based synchronization at the required sub-centennial precision 2 , 3 , 10 . Here we use a recently drilled high-accumulation Antarctic ice core to show that, on average, abrupt Greenland warming leads the corresponding Antarctic cooling onset by 218 ± 92 years (2 σ ) for Dansgaard–Oeschger events, including the Bølling event; Greenland cooling leads the corresponding onset of Antarctic warming by 208 ± 96