Abstract
Abstract. The use of a boundary-layer parameterization of buttressing and ice flux across grounding lines in a two-dimensional 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 (MISMIP+) 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 MISMIP+ 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.
Highlights
Accurate modeling of long-term Antarctic ice sheet variations requires simulation of ice dynamics in the zone between grounded ice and floating ice shelves, and grounding-line retreat and advance over century and millennial timescales
The model ice dynamics uses a hybrid combination of vertically integrated shallow ice and shallow shelf approximations (SIA, SSA), with the seaward ice flux at grounding lines imposed as a boundary condition according to an analytical expression relating ice flux to ice thickness (Schoof, 2007): qg =
To MISMIP+, our previous model produced larger and more rapid grounding-line advances than most other higher-order and/or higher-resolution models in the intercomparison (Pattyn et al, 2013), and the changes in total volume over flotation and cavity volume differed from most models (Pattyn and Durand, 2013)
Summary
Accurate modeling of long-term Antarctic ice sheet variations requires simulation of ice dynamics in the zone between grounded ice and floating ice shelves, and grounding-line retreat and advance over century and millennial timescales. The ice flux across grounding lines can be parameterized using an analytic boundary-layer treatment (Schoof, 2007) and embedded in an ice-sheet model (Pollard and DeConto, 2012), making long-term large-scale simulations feasible. This approach performs reasonably well in some idealized model intercomparisons (Docquier et al, 2011; Pattyn et al, 2012; c.f., Gudmundsson, 2013) but less well in others with smaller-scale transient experiments (Pattyn et al, 2013; Pattyn and Durand, 2013; Drouet et al, 2013; Cornford et al, 2020). We describe new modifications to the parameterized grounding-line flux approach and show that they significantly improve model performance in some intercomparisons
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