University of Tokyo, Japan

Compared to the rapid glacial terminations, the buildup of glacial ice sheets in the Northern Hemisphere took tens of thousands of years. During the buildup phase, the growing ice sheets were subject to major orbitally induced summer insolation changes, without experiencing complete disintegration. The reason for this behavior still remains elusive. Here we propose that between 110 and 60 kyr B.P., every approximately 20 kyr increased summer insolation in high northern latitudes triggered massive instabilities of the Northern Hemispheric ice sheets, leading to glacial meltwater pulses and subsequent disruptions of the Atlantic Meridional Overturning Circulation (AMOC). Associated severe cooling of the northern extratropics may have offset the warming trends driven by increased precessional summer insolation. This temperature response diminished the melting trend and stabilized the ice sheets. Our results suggest that the competition between the direct insolation changes and the indirect climate response to AMOC disturbances may be an important negative feedback that supports the buildup of glacial ice sheets.