Ice-sheet modelling at different spatial resolutions: focus on the grounding zone

A high-resolution time-dependent two-dimensional flowline model was developed, which takes into account all relevant stresses (i.e. both shear and longitudinal stresses), and which is solved on a fixed finite-difference grid. Special attention was paid to the computational efficiency. A comparison is made with a similar model that solves the velocity field according to the shallow-ice approximation. Both models were applied to an East Antarctic flowline for which the data on surface and bedrock elevation were sampled at different spatial resolutions. The numerical analysis deals with the importance of longitudinal stresses at the ice-sheet/ice-shelf interface at different grid sizes, and the importance of basal drag vs driving stress in basal sliding laws. At a grid resolution of 5-10 km the force balance indicates that all stress components are of equal importance in an area that is larger than the nominal grid size. When sliding becomes dominant, this transition zone considerably widens. Furthermore, the longitudinal stress deviator is found to var) considerably with depth due to the thermomechanical coupling.