Representing Grounding Line Dynamics in Numerical Ice Sheet Models: Recent Advances and Outlook
Recent satellite observations of the Antarctic and Greenland ice sheets show accelerated ice flow and associated ice sheet thinning along coastal outlet glaciers in contact with the ocean. Both processes are the result of grounding line retreat due to melting at the grounding line (the grounding line is the contact of the ice sheet with the ocean, where it starts afloat and forms an ice shelf or ice tongue). Such rapid ice loss is not yet included in large-scale ice sheet models used for IPCC projections, as most of the complex processes are poorly understood. Here we report on the state-of-the art of grounding line migration in marine ice sheets and address different ways in which grounding line migration can be attributed and represented in ice sheet models. Using two-dimensional ice flow models of the ice sheet - ice shelf system we carried out a number of sensitivity experiments with different spatial resolutions and stress approximations. These are verified with analytical steady state solutions. Results show that in largescale models, grounding line migration necessitates grid sizes well below 2.5 km in order to represent correctly grounding line migration.