The Antarctic Ice Sheet response to glacial millennial-scale variability

Abstract

Abstract. The Antarctic Ice Sheet (AIS) is the largest ice sheet on Earth and hence a\nmajor potential contributor to future global sea-level rise. A wealth of\nstudies suggest that increasing oceanic temperatures could cause a collapse\nof its marine-based western sector, the West Antarctic Ice Sheet, through the\nmechanism of marine ice-sheet instability, leading to a sea-level increase of\n3–5\u2009 m . Thus, it is crucial to constrain the sensitivity of the AIS\nto rapid climate changes. The last glacial period is an ideal benchmark\nperiod for this purpose as it was punctuated by abrupt Dansgaard–Oeschger\nevents at millennial timescales. Because their center of action was in the\nNorth Atlantic, where their climate impacts were largest, modeling studies\nhave mainly focused on the millennial-scale evolution of Northern Hemisphere\n(NH) paleo ice sheets. Sea-level reconstructions attribute the origin of\nmillennial-scale sea-level variations mainly to NH paleo ice sheets, with a\nminor but not negligible role of the AIS. Here we investigate the AIS\nresponse to millennial-scale climate variability for the first time. To this\nend we use a three-dimensional, thermomechanical hybrid, ice sheet–shelf\nmodel. Different oceanic sensitivities are tested and the sea-level\nequivalent (SLE) contributions computed. We find that whereas atmospheric\nvariability has no appreciable effect on the AIS, changes in submarine\nmelting rates can have a strong impact on it. We show that in contrast to the\nwidespread assumption that the AIS is a slow reactive and static ice sheet\nthat responds at orbital timescales only, it can lead to ice discharges of\naround 6\u2009 m SLE, involving substantial grounding line migrations at\nmillennial timescales.