The potential of Marine Ice Cliff Instability for Amundsen Sea glaciers revisited

Marine ice cliff instability (MICI) is the hypothesis that selfsustained retreat of ice sheets can be initiated when sufficiently tall ice cliffs are exposed. Projections including MICI suggest substantial risk of large sealevel rise in coming centuries. However, to date, the number of modelling studies exploring this possibility is limited. Here we investigate the role of calving in ice loss and frontal retreat of the Amundsen Sea Glaciers, West Antarctica, using a high-resolution ice-flow model. This study employs a cliffheight-dependent calving parameterization from DeConto and Pollard (2016). Numerical convergence tests reveal that mesh resolutions finer than 2 km are essential for robust simulation of grounding line migration and frontal dynamics. Simulations assuming initial loss of ice shelves show spatially varied glacier response. For tall marine-terminating fronts, initial retreat driven by exposed cliffs is rapidly reversed as ice deformation lowers cliff height. In contrast, the same parameterization produces frontal retreat in slow-flowing grounded regions where cliff heights presently exceed 80 m. In those regions, however, no such retreat is currently observed. These findings suggest that direct application of this calving scheme both contradicts existing observational evidence, and is unlikely to drive sustained frontal retreat in fast-flowing marine-terminating glaciers under current conditions.