Uncertain ground: impact of bed topography on Antarctic Ice Sheet projections.

Despite decades of effort to map bed elevation under the Antarctic Ice Sheet, significant gaps remain in this geometric boundary, controlling ice sheet flow and grounding line dynamics. The impact of such uncertainties on ice flow simulations of the Antarctic evolution, however, has received little attention. Here, we investigate their impact on the Antarctic evolution at the continental scale as well as the regional scale for the Bellingshausen and Aurora basins and compare them to the impact of climate forcing scenarios. Using error estimates reported in BedMachine Antarctica, our simulations show that bed topography affects the Antarctic contribution to sea level by more than 40 cm in 2150 and 1 m by 2300, comparable to changes caused by different emission scenarios. Variations in grounding line retreat and mass loss are especially important in the Amundsen Sea, Ross and Filchner-Ronne basins. The impact of bedrock uncertainties is even larger on regional- and glacier-scale simulations with a higher spatial resolution, resulting in more variations in grounding line positions and mass change. Overall, these results suggest that errors in bedrock elevation under the Antarctic Ice Sheet are a critical but underexplored source of uncertainty. Additional observations in critical regions are needed to help reduce these systemic uncertainties. This article is part of the Theo Murphy meeting issue 'Next generation ice-sheet bed measurements'.