Sub-shelf melt patterns… does detail matter?

Observations show that some of the ice shelves surrounding Antarctica are thinning, driven by warming of the underlying ocean. These ice shelves play an important role in moderating the rate of mass loss from the ice sheet by buttressing the ice flow from the grounded parts of the ice sheet. The increased ocean-induced sub-shelf melt is therefore an important process for the stability of the ice sheet and representing it in ice sheet models is essential to study the evolution of the Antarctic Ice Sheet. Here, we present a coupled ice-ocean setup, applied to an idealised ice shelf.

The sub-shelf melting occurs in highly heterogeneous patterns, typically exhibiting higher melt rates near the grounding line. Currently, most ice sheet models rely on parameterisations which derive sub-shelf melt rates from far-field ocean hydrography. Despite their computational advantage and ease in handling grounding line migration, these parameterisations fall short of accurately representing the right details in the melt patterns. To capture more physically consistent melt patterns, we implemented an online coupling between the ice sheet model IMAU-ICE and the sub-shelf melt model LADDIE. The latter resolves the necessary physics governing the melt, including the Coriolis deflection and topographic steering of meltwater, and provides sub-shelf melt fields at sub-kilometre spatial resolution.

We will show the impact of detailed sub-shelf melt fields in an idealised set-up. We compare IMAU-ICE simulations using existing sub-shelf melt parameterisations with simulations in the coupled set-up with IMAU-ICE and LADDIE. Three parameterisations are considered for this comparison: the quadratic scaling with temperature, the box model PICO, and the plume model. All simulations are performed in the idealised MISMIP+ domain. We consider a range of oceanic temperature forcings similar to present-day temperatures in warmer and colder basins surrounding Antarctica. We present and discuss the results, primarily focusing on the evolution of three key indicators for ice sheet stability: grounding line position, ice shelf extent, and grounding zone shape. These results demonstrate the importance of accounting for realistic melt patterns in ice sheet models.