Improvements in one-dimensional grounding-line parameterizations in an ice-sheet model with lateral variations (PSUICE3D v2.1)

The use of a boundary-layer parameterization of buttressing and ice flux across grounding lines in a twodimensional ice-sheet model is improved by allowing general orientations of the grounding line. This and another modification to the model's grounding-line parameterization are assessed in three settings: rectangular fjord-like domains the third Marine Ice Sheet Model Intercomparison Project (MISMIPC) and Marine Ice Sheet Model Intercomparison Project for plan view models (MISMIP3d) and future simulations of West Antarctic ice retreat under Representative Concentration Pathway (RCP)8.5-based climates. The new modifications are found to have significant effects on the fjord-like results, which are now within the envelopes of other models in the MISMIPC and MISMIP3d intercomparisons. In contrast, the modifications have little effect on West Antarctic retreat, presumably because dynamics in the wider major Antarctic basins are adequately represented by the model's previous simpler one-dimensional formulation. As future grounding lines retreat across very deep bedrock topography in the West Antarctic simulations, buttressing is weak and deviatoric stress measures exceed the ice yield stress, implying that structural failure at these grounding lines would occur. We suggest that these grounding-line quantities should be examined in similar projections by other ice models to better assess the potential for future structural failure.