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

Abstract:

A long-standing hypothesis for near-synchronous interhemispheric ice cover changes on orbital timescales despite opposite insolation forcing invokes sea-level rise from increased loss of Northern Hemisphere ice sheets in response to insolation and greenhouse gas forcing causing grounding line retreat of marine-based sectors of the Antarctic Ice Sheet (AIS). Recent evidence indicates that the AIS also experienced substantial millennial-scale variability during and after the last deglaciation (e.g. Weber et al., 2014), further suggesting a possible sea-level forcing. Global sea-level change from ice-sheet mass loss is strongly nonuniform, however, suggesting that the response of AIS grounding lines to Northern Hemisphere sea-level forcing is likely more complicated than previously considered.

Here we show, using a coupled ice sheet - global sea-level model (Gomez et al., 2013), that Northern Hemisphere ice sheet retreat during deglaciation leads to a sea level forcing in Antarctica that reduces or exceeds the sea-level fall at Antarctic ice sheet 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 Northern Hemisphere glaciation, the associated sea-level fall acts to enhance grounding line advance in Antarctica. We find that including these effects causes Northern Hemisphere sea-level forcing to increase AIS volume during the Last Glacial Maximum and triggers an earlier retreat and millennial scale variability through the last deglaciation, consistent with geologic reconstructions of Last Glacial Maximum AIS extent and subsequent ice-sheet retreat and relative sea-level change in Antarctica.