Considering ocean conditions within ice-shelf cavities moderately reduces projected mass loss from the Antarctic Ice Sheet

Abstract. Ocean-forced melt of ice shelves is a key determinant of the stability of the Antarctic Ice Sheet (AIS). Currently, most Earth-system models (ESMs) do not simulate ocean circulation in the cavities beneath ice shelves, and ice-sheet models must infer ice-shelf melt rates from ocean conditions external to the ice shelf. A recent configuration of the Energy Exascale Earth System Model, E3SMv2.1, resolves ocean conditions within ice-shelf cavities with an eddy-permitting mesh in the Southern Ocean. Using projected ocean temperatures from E3SMv2.1 that follow prescribed historical and SSP3-7.0 emission scenarios, we parameterize ice-shelf melt using 1) simulated thermal forcing (TF) within cavities and 2) extrapolated TF from the ice-shelf calving front, similar to the community-standard approach when ice-shelf cavities are absent. We then force the MPAS-Albany Land Ice (MALI) ice-sheet model with the parameterized melt from both methods and project AIS mass change to 2100. Results show that using simulated TF from ice-shelf cavities yields a smaller sea-level contribution (SLC) from the AIS through 2100, by ~4 mm (~13 %), compared to the experiment that uses extrapolated ocean conditions from the calving front. In the context of other ice-sheet model uncertainties, an SLC projection error of this size may be acceptable. If open ocean conditions become warmer than simulated cavity conditions beyond 2100, extrapolation risks overestimating the SLC by a larger margin. Our results demonstrate the value of using cavity-resolving ocean models for multi-century ice-sheet projections.