Simulating Marine Ice Sheets with the Community Ice Sheet Model

Abstract:

Simulating marine ice sheets remains challenging for large-scale numerical models, in part because of the high resolution needed to accurately track grounding-line motion. Here we show results from marine-ice simulations using version 2 of the Community Ice Sheet Model (CISM). CISM is a parallel, higher-order model that can solve several sets of flow equations, including the shallow-shelf approximation (SSA), a depth-integrated higher-order approximation, and the Blatter-Pattyn approximation. Using a new subgrid grounding-line parameterization (GLP) at moderate (~1 km) grid resolution, we have successfully run benchmark experiments for the Marine Ice Sheet Model Intercomparison Project (MISMIP and MISMIP3d). For a standard MISMIP experiment on a downward-sloping bed, CISM’s SSA results are in good agreement with the analytic boundary-layer solution, and higher-order results are similar to those from a Stokes model. For MISMIP3d experiments with basal-sliding perturbations, CISM simulates reversible migration of curved grounding lines. Without a GLP, much finer resolution (or alternatively, a basal-friction parameterization that smooths the transition between grounded and floating ice) is needed for similar accuracy. We are now using CISM to simulate the entire Antarctic Ice Sheet. We show early results and discuss the remaining work needed to simulate whole marine ice sheets at ~1 km resolution.