Results of the Marine Ice Sheet Model Intercomparison Project, MISMIP

Abstract

Predictions of marine ice-sheet behaviour require models that are able to robustly simulate grounding line migration. We present results of an intercomparison exercise for marine ice-sheet models. Verification is effected by comparison with approximate analytical solutions for flux across the grounding line using simplified geometrical configurations (no lateral variations, no effects of lateral buttressing). Unique steady state grounding line positions exist for ice sheets on a downward sloping bed, while hysteresis occurs across an overdeepened bed, and stable steady state grounding line positions only occur on the downward-sloping sections. Models based on the shallow ice approximation, which does not resolve extensional stresses, do not reproduce the approximate analytical results unless appropriate parameterizations for ice flux are imposed at the grounding line. For extensional-stress resolving "shelfy stream" models, differences between model results were mainly due to the choice of spatial discretization. Moving grid methods were found to be the most accurate at capturing grounding line evolution, since they track the grounding line explicitly. Adaptive mesh refinement can further improve accuracy, including fixed grid models that generally perform poorly at coarse resolution. Fixed grid models, with nested grid representations of the grounding line, are able to generate accurate steady state positions, but can be inaccurate over transients. Only one full-Stokes model was included in the intercomparison, and consequently the accuracy of shelfy stream models as approximations of full-Stokes models remains to be determined in detail, especially during transients

Future sea-level rise from Greenland’s main outlet glaciers in a warming climate

“…processes of calving, grounding line retreat and submarine melting), it has a robust treatment of grounding line migration 28 and calving 29 , and reproduces the current observed dynamical behaviour of several narrow marine outlet glaciers well 13,14,21 .…”

Reducing uncertainties in projections of Antarctic ice mass loss

“…Such collapses have probably been driven by an unstable retreat of the marine-based regions (i.e., underlying bedrock below sea level), characterized by a retrograde bed slope. The underlying process, marine ice sheet instability (MISI), is supported by theoretical (Weertman, 1974;Schoof, 2007a) and numerical results (Durand et al, 2009;Pattyn et al, 2012). After MISI has been initiated, it could lead to a collapse of the contemporary west Antarctic ice sheet and have the potential to cause sea level to rise by ≈ 3.3 m (Bamber et al, 2009), leading to a drastic impact on human societies (Nicholls and Cazenave, 2010).…”

Hydrostatic grounding line parameterization in ice sheet models

“…They compare the sensitivity of modeled grounding line migration to numerical implementation (Pattyn et al, 2012(Pattyn et al, , 2013Pattyn and Durand, 2013). Results indicate that plan-view models need to include at least membrane stress components to be able to capture the grounding line position and that this position depends on the degree of sophistication of the model.…”

“…These methods overcome the difficulties associated to grounding line discretization but lead to more complicated frameworks and remain difficult to implement in parallelized architectures. Due to the high computational time associated with fine resolution meshes or grids, most studies investigating the impact of grounding line parameterization, mesh resolution or stress balance approximation are performed on onedimensional (1-D) flow line or two-dimensional (2-D) flowband models (e.g., Vieli and Payne, 2005;Pattyn et al, 2006;Schoof, 2007a, b;Katz and Worster, 2010;Gladstone et al, 2010a;Pattyn et al, 2012). They show the strong dependency of model results on mesh resolution in the grounding line transition zone.…”