Abstract
Abstract. Ice sheet models differ in their numerical treatment of dynamical processes. Simulations of marine-based ice are sensitive to the choice of Stokes flow approximation and basal friction law and to the treatment of stresses and melt rates near the grounding line. We study the effects of these numerical choices on marine ice sheet dynamics in the Community Ice Sheet Model (CISM). In the framework of the Marine Ice Sheet Model Intercomparison Project 3d (MISMIP3d), we show that a depth-integrated, higher-order solver gives results similar to a 3D (Blatter–Pattyn) solver. We confirm that using a grounding line parameterization to approximate stresses in the grounding zone leads to accurate representation of ice sheet flow with a resolution of ∼2 km, as opposed to ∼0.5 km without the parameterization. In the MISMIP+ experimental framework, we compare different treatments of sub-shelf melting near the grounding line. In contrast to recent studies arguing that melting should not be applied in partly grounded cells, it is usually beneficial in CISM simulations to apply some melting in these cells. This suggests that the optimal treatment of melting near the grounding line can depend on ice sheet geometry, forcing, or model numerics. In both experimental frameworks, ice flow is sensitive to the choice of basal friction law. To study this sensitivity, we evaluate friction laws that vary the connectivity between the basal hydrological system and the ocean near the grounding line. CISM yields accurate results in steady-state and perturbation experiments at a resolution of ∼2 km (arguably 4 km) when the connectivity is low or moderate and ∼1 km (arguably 2 km) when the connectivity is strong.
Highlights
The Antarctic Ice Sheet is losing mass (Shepherd et al, 2018; Rignot et al, 2019), primarily from marine-based parts of the West Antarctic Ice Sheet (WAIS)
The p value has more impact on grounding line position than does resolution for shallow-shelf approximation (SSA) and BP. These results suggest that for problems similar to MISMIP3d, the uncertainties associated with basal friction near the grounding line are likely to be much greater than those associated with the grid resolution and stress approximation
We have studied the effects of different ice-flow approximations, basal-friction and basal-melting parameterizations, and grid resolution in marine ice sheet simulations with the Community Ice Sheet Model
Summary
The Antarctic Ice Sheet is losing mass (Shepherd et al, 2018; Rignot et al, 2019), primarily from marine-based parts of the West Antarctic Ice Sheet (WAIS). Antarctic applications have motivated us to test the accuracy and robustness of model numerics related to grounding line dynamics To this end, we will use the MISMIP3d (Pattyn et al, 2013) and MISMIP+ (Asay-Davis et al, 2016; Cornford et al, 2020) experiments as a framework to show that the conclusions of Leguy et al (2014) remain valid: grid resolution of ∼ 1 km (and, in some circumstances, coarser) is sufficient to accurately capture grounding line migration when using a GLP, when the ice sheet is hydrologically connected to the ocean, or both.
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