Interhemispheric Sea-Level Forcing of the Antarctic Ice Sheet During the Last Ice Age

Abstract

A long-standing hypothesis for global ice-sheet synchronization on orbital timescales invokes sea-level rise from increased loss of Northern Hemisphere (NH) ice sheets in response to insolation and greenhouse gas forcing causing grounding line retreat of marine-based sectors of the Antarctic Ice Sheet (AIS)(1-3). Recent evidence indicates that the AIS also experienced substantial millennial-scale variability during and after the last deglaciation(4-7), further suggesting a possible sea-level forcing. Global sea-level change from ice-sheet mass loss is strongly nonuniform8, however, suggesting that the response of AIS grounding lines to NH sea-level forcing is likely more complicated than previously considered(1,2,6). Here we show, using a coupled ice sheet - global sea-level model, that a large or rapid NH sea-level forcing during deglaciation reduces or exceeds the sea-level fall at AIS grounding lines driven by the gravitational and deformational effects of AIS mass loss, enhancing grounding line retreat and associated AIS mass loss. In contrast, during NH glaciation, the sea level forcing acts to enhance grounding line advance. We find that including these effects causes NH sea-level forcing to increase AIS volume during the Last Glacial Maximum (LGM, ~26-20 ka) and triggers an earlier retreat and millennial scale variability through the last deglaciation, consistent with geologic reconstructions of LGM AIS extent and subsequent ice-sheet retreat and relative sea-level change in Antarctica(3-7,9).