Reversibility of the Marine Ice Sheet Instability

The potential loss of the West Antarctic ice sheet is the major uncertainty in projections of future sea-level rise. The ice sheet is thought to be susceptible to the Marine Ice-Sheet Instability. The extent to which it is genuinely unstable, in the sense that a collapse, once triggered, becomes irreversible and independent of changes in forcing has yet to be determined. Here we use the adaptive-mesh BISICLES model in an ensemble of experiments to investigate the potential for quasi-stable states and regrowth of the ice sheet. We find that the loss of the major ice shelves triggers a virtually complete collapse of the ice sheet over the course of several millennia. This collapse can, however, be reversed if ice shelves are allowed to regrow. The stabilizing mechanism appears to be related to increased flow of ice across the grounding line which promotes thickening, grounding and buttressing. Initial work suggests that well-defined multiple equilibria do not exist and regrowth is possible even after large-scale collapse. The work has implications for both committed future sea level rise under various emission scenarios, as well as understanding the contribution of the ice sheet to higher sea levels during the Last Interglacial.