Early warming over the Southern Ocean during the last deglaciation

The last deglaciation, ca. 17,000-11,000 years before present (yr BP), marks the most recent period of large-scale climate reorganization on Earth. However, the timing and spatial patterns of the initial warming preceding these changes remain uncertain. Here, we develop a new method using Gaussian Mixture Model clustering to objectively segregate a reanalysis and climate model simulations, respectively, into four distinct patterns of temperature change throughout the last deglaciation. Our findings indicate that the earliest warming signs appeared around 21,000 yr BP in the Southern Hemisphere high latitudes. This early warming was accompanied by a cooling in the Northern Hemisphere high latitudes, resulting in a hemispherically asymmetric temperature pattern. Further analysis using single-forcing climate simulations suggests that the early warming and sea-ice retreat were likely driven by a weakening in the Atlantic Meridional Overturning Circulation, linked to orbital forcing.