A long-standing hypothesis for synchronous global ice-sheet evolution on orbital timescales invokes an interhemispheric sea level forcing, whereby sea-level rise due to ice loss in the Northern Hemisphere (NH) in response to insolation and greenhouse gas forcing causes grounding line retreat of marine-based sectors of the Antarctic Ice Sheet (AIS) 1-3. Recent evidence indicates that the AIS experienced substantial millennial-scale variability during and after the last deglaciation4-7, 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 considered1,2,6. Here we show, using a coupled ice sheet - global sea-level model, that a large or rapid NH sea-level forcing during 2 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.
|Publication status||Accepted/In press - 16 Sep 2020|