Hydrostatic grounding line parameterization in ice sheet models

Abstract

Abstract. Modeling of grounding line migration is essential to accurately simulate the behavior of marine ice sheets and investigate their stability. Here, we assess the sensitivity of numerical models to the parameterization of the grounding line position. We run the MISMIP3D benchmark experiments using the Ice Sheet System Model (ISSM) and a two-dimensional shelfy-stream approximation (SSA) model with different mesh resolutions and different sub-element parameterizations of grounding line position. Results show that different grounding line parameterizations lead to different steady state grounding line positions as well as different retreat/advance rates. Our simulations explain why some vertically depth-averaged model simulations deviate significantly from the vast majority of simulations based on SSA in the MISMIP3D benchmark. The results reveal that differences between simulations performed with and without sub-element parameterization are as large as those performed with different approximations of the stress balance equations in this configuration. They also demonstrate that the reversibility test is passed at relatively coarse resolution while much finer resolutions are needed to accurately capture the steady-state grounding line position. We conclude that fixed grid SSA models that do not employ such a parameterization should be avoided, as they do not provide accurate estimates of grounding line dynamics, even at high spatial resolution. For models that include sub-element grounding line parameterization, in the MISMIP3D configuration, a mesh resolution finer than 2 km should be employed.

Projections of Future Sea Level Contributions from the Greenland and Antarctic Ice Sheets: Challenges Beyond Dynamical Ice Sheet Modeling

“…Most ISMs, however, determine grounding line positions directly, based on hydrostatic equilibrium. Refined grounding line position based on subgrid parameterizations (Pattyn et al, 2006;Seroussi et al, 2014) improved the ability of models to accurately simulate its position while limiting the need for high grid resolution. Models implementing the Stokes equations include a nonhydrostatic grounding line representation based on contact mechanics (Nowicki and Wingham, 2008;Durand et al, 2009).…”

Marine ice sheet model performance depends on basal sliding physics and sub-shelf melting

“…Studies in which simulations are carried out at multiple different mesh resolutions usually demonstrate convergent behaviour, but very fine resolution is often needed to approach a converged solution (Cornford et al, 2013;Gladstone et al, 2010a;Pattyn et al, 2012). Practical solutions have been suggested, such as parameterising the flux of ice across the grounding line as a function of ice thickness (Schoof, 2007;Pollard and DeConto, 2009), parameterising the grounding line position at sub-grid resolution (Gladstone et al, 2010b;Seroussi et al, 2014), or implementing adaptive mesh refinement to provide very high resolution at and near the grounding line (Cornford et al, 2013;Durand et al, 2009). These solutions all have limitations, and the computational cost of running a sufficiently high-resolution ISM to robustly represent grounding line motion remains high, even with adaptive refinement.…”

Progress in Numerical Modeling of Antarctic Ice-Sheet Dynamics

“…Therefore, a series of ice-sheet models have implemented a spatial grid refinement, mainly for the purpose of accurate data assimilation [28,50,83], but also for further transient simulations where the adaptive mesh approach enables the finest grid to follow the grounding-line migration [27,28]. However, MISMIP led to the development of subgrid interpolation schemes enabling grounding-line migration without necessarily decreasing the grid size drastically at the grounding line [29,45,114].…”