Abstract
Abstract. Accurate projections of the evolution of ice sheets in a changing climate require a fine mesh/grid resolution in ice sheet models to correctly capture fundamental physical processes, such as the evolution of the grounding line, the region where grounded ice starts to float. The evolution of the grounding line indeed plays a major role in ice sheet dynamics, as it is a fundamental control on marine ice sheet stability. Numerical modeling of a grounding line requires significant computational resources since the accuracy of its position depends on grid or mesh resolution. A technique that improves accuracy with reduced computational cost is the adaptive mesh refinement (AMR) approach. We present here the implementation of the AMR technique in the finite element Ice Sheet System Model (ISSM) to simulate grounding line dynamics under two different benchmarks: MISMIP3d and MISMIP+. We test different refinement criteria: (a) distance around the grounding line, (b) a posteriori error estimator, the Zienkiewicz–Zhu (ZZ) error estimator, and (c) different combinations of (a) and (b). In both benchmarks, the ZZ error estimator presents high values around the grounding line. In the MISMIP+ setup, this estimator also presents high values in the grounded part of the ice sheet, following the complex shape of the bedrock geometry. The ZZ estimator helps guide the refinement procedure such that AMR performance is improved. Our results show that computational time with AMR depends on the required accuracy, but in all cases, it is significantly shorter than for uniformly refined meshes. We conclude that AMR without an associated error estimator should be avoided, especially for real glaciers that have a complex bed geometry.
Highlights
The uncertainty in projections of ice sheet contribution to sea level rise in the century remains large, primarily due to the potential collapse of the West Antarctic Ice Sheet (WAIS; Church et al, 2013; Jevrejeva et al, 2014; Ritz et al, 2015; DeConto and Pollard, 2016)
We describe the implementation of an adaptive mesh refinement approach in the Ice Sheet System Model (ISSM v4.14) as well as the performance of our implementation in terms of accuracy of the simulated grounding line position and simulation time
Further analysis should be carried out to check the performance in real ice sheets and in higher computational scale, but the results presented in this study suggest that our adaptive mesh refinement (AMR) implementation strategy is adapted to the modeling questions being investigated
Summary
The uncertainty in projections of ice sheet contribution to sea level rise in the century remains large, primarily due to the potential collapse of the West Antarctic Ice Sheet (WAIS; Church et al, 2013; Jevrejeva et al, 2014; Ritz et al, 2015; DeConto and Pollard, 2016). Projections of the collapse of WAIS are based on the marine ice sheet instability (MISI) hypothesis (Weertman, 1974; Mercer, 1978; Thomas, 1979). This hypothesis refers to ice sheets grounded below sea level on retrograde bedrock slopes (as seen in Fig. 1), as is the case for many glaciers in WAIS (Fretwell et al, 2013). The GL retreat on retrograde bedrock slopes causes increased ice discharge, which in turn leads to further GL retreat, resulting in a non-linear positive feedback. A change in climate or ocean can potentially force a large-scale fast migration of the GL inland
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