The one-Layer Antarctic model for Dynamical Downscaling of Ice–ocean Exchanges (LADDIE) version 2.0

Abstract. Projections of Antarctic mass loss and its contribution to sea-level rise are highly sensitive to the applied ocean-driven melting. As fully coupled continental-scale ocean–ice sheet models are scarce, ice sheet models are typically run in standalone configurations, forced with parameterised sub-shelf melting. To provide a physically more detailed alternative to melt parameterisations, we here present version 2.0 of the one-Layer Antarctic model for Dynamical Downscaling of Ice–ocean Exchanges (LADDIE). LADDIE is a two-dimensional model of the upper mixed layer below ice shelves and can reproduce observed spatial patterns in sub-shelf melting. Version 2.0 has improved computational performance due to parallellisation, discretisation on an unstructured mesh, and a more stable time stepping scheme. The model is fully integrated with the UFEMISM ice sheet model, allowing for coupled simulations on the same mesh. We evaluate the model by comparing it to LADDIE 1.0, showing that the simulated melt patterns are consistent across both model versions, whilst the computation time can be reduced by one order of magnitude due to parallellisation. The model is evaluated against an ensemble of 3D ocean models in both idealised and realistic pan-Antarctic domains at 2 km resolution. In both cases, LADDIE melt rates, melt patterns, and melt sensitivities are close to the multi-model mean. An evaluation against four pan-Antarctic satellite estimates, shows an overall good agreement in integrated melt rates per ice shelf, without the need for regional tuning. At a resolution of 120 m, LADDIE is able to reproduce the fine-scaled network of basal channels, observed on Pine Island ice shelf. Finally, we compare an idealised coupled UFEMISM–LADDIE simulation to a simulation with a quadratic melt parameterisation. The coupled simulation produces a threefold increase in grounding line retreat and volume above floatation loss. Based on these results, we conclude that LADDIE 2.0 can be a useful tool to simulate ice–ocean interactions in a computationally efficient way.