Strong impact of sub-shelf melt parameterisation on ice-sheet retreat in idealised and realistic Antarctic topography

Future projections of sea-level rise under strong warming scenarios are dominated by mass loss in the marine-grounded sectors of West Antarctica, where thinning shelves as a result of warming oceans can lead to reduced buttressing. This consequently leads to accelerated flow from the upstream grounded ice. However, the relation between warming oceans and increased melt rates under the shelves is very uncertain, especially when interactions with the changing shelf geometry are considered. Here, we compare six widely used, highly parameterised formulations relating sub-shelf melt to thermal forcing. We implemented them in an ice-sheet model, and applied the resulting set-up to an idealised-geometry setting, as well as to the Antarctic ice sheet. In our simulations, the differences in modelled ice-sheet evolution resulting from the choice of parameterisation, as well as the choice of numerical scheme used to apply sub-shelf melt near the grounding line, generally are larger than differences from ice-dynamical processes such as basal sliding, as well as uncertainties from the forcing scenario of the model providing the ocean forcing. This holds for the idealised-geometry experiments as well as for the experiments using a realistic Antarctic topography.