PICE Talk by Peisong Zheng

Title: An Early Warming Over the Southern Ocean During the Last Deglaciation

The last deglaciation, spanning approximately 18 to 10 thousand years before present (kiloyear before present; ky BP), represents the most recent period in which Earth’s climate underwent large-scale reorganizations comparable, albeit not strictly analogous, to those projected under future climate changes. However, the timing and spatial manifestation of the initial warming preceding these changes remain uncertain. Here we present a new method using Gaussian Mixture Model clustering to objectively decompose a model and proxy-based climate reconstruction into four distinct patterns of temperature change across the last deglaciation. Our analysis reveals that the high latitudes of the Southern Hemisphere exhibited the earliest signs of warming onsetting around 21 ka BP, coincident with an early retreat of sea ice across the Southern Ocean. Although contribution from a weakening in the Atlantic Meridional Overturning Circulation to this early warming cannot be excluded, our analysis using a process-based coupled sea ice—energy balance model shows that the early sea ice retreat and warming were likely linked to an initial increase in high-latitude summertime energy, dominated by enhanced obliquity-driven forcing. Our findings collectively suggest that insolation dynamics in the Southern Hemisphere were a critical trigger of the Last Deglacial onset and, further, may represent one of the key prerequisites for glacial terminations during the late Pleistocene. 

Peisong Zheng
PhD student in the AI4ER project, affiliated with the British Antarctic Survey and the Department of Geography, University of Cambridge.