Sensitivity of Future Projections of the Wilkes Subglacial Basin Ice Sheet to Grounding Line Melt Parameterizations

Abstract. Projections of Antarctic Ice Sheet mass loss and therefore global sea level rise are hugely uncertain, partly due to how mass loss of the ice sheet occurs at the grounding line. The Wilkes Subglacial Basin (WSB), a vast region of the East Antarctic ice sheet, is thought to be particularly vulnerable to deglaciation under future climate warming scenarios. However, future projections of ice loss, driven by grounding line migration, are known to be sensitive to the parameterisation of ocean-induced basal melt of the floating ice shelves, and specifically, adjacent to the grounding line – termed Grounding Line Melt Parameterizations (GLMPs). This study investigates future ice sheet dynamics in the WSB with respect to four GLMPs under both the upper and lower bounds of climate warming scenarios from the present to 2500, with different model resolutions and choices of sliding relationships. The variation in these GLMPs determines the distribution and the amount of melt applied in the finite element assembly procedure on partially grounded elements (i.e., elements containing the grounding line). Our findings indicate that the GLMPs significantly affect both the trigger-timings of tipping points and the overall magnitude of ice mass loss. We conclude that applying full melting to the partially grounded elements, which causes melting on the grounded side of the grounding line, should be avoided under all circumstances due to its poor numerical convergence and substantial overestimation of ice mass loss. We recommend preferring options that depend on the specific model context, either 1) not applying any melt immediately adjacent to the grounding line or 2) employing a sub-element parameterisation. Based on our best model results, a tipping point is projected to occur between 2200 and 2300, leading to massive and rapid retreat across the WSB and a significant increase in ice discharge from 200 to 500 Gt a^-1. In this context, our simulations suggest that the WSB ice sheet could contribute between 0.23 to 0.34 m to global sea level rise by 2500.