A Model for Antarctic Ice Shelf Hydrology and Stability (MONARCHS v1.0)

Abstract. Antarctica's floating ice shelves experience considerable surface melting, leading to the formation of supraglacial melt lakes. The presence of surface meltwater and the formation of these lakes leaves ice shelves vulnerable to meltwater-induced damage. This can lead to the loss of the buttressing effect provided by ice shelves on the grounded ice sheet, thus increasing Antarctica's potential sea level contribution. Understanding the surface hydrology of ice shelves in the present and the future is thus an essential first step to reliably project future vulnerability of Antarctic ice shelves to meltwater-driven hydrofracture and possible collapse events. Therefore, we have developed the first comprehensive 3-D Model for Antarctic Ice Shelf Hydrology and Stability, called MONARCHS.

MONARCHS calculates the surface energy balance of the ice shelf, heat transfer through the ice shelf and the volume of any subsequent meltwater that is produced when the surface energy balance is positive. The model simulates both vertical and lateral movement of this meltwater through the firn, calculating refreezing and saturation of firn air space as well the related changes in temperature and density. When firn is saturated and surface melt lakes can form, the model simulates the full lake lifecycle, including lake depth increases and full refreezing.

We present a case study focused on the George VI Ice Shelf on the Antarctic Peninsula where significant melt lake formation has been observed in recent years. The model shows reasonable agreement in lake extent and depth with observations. Furthermore, we demonstrate that the speed of lateral meltwater percolation through firn, a key uncertainty in firn modelling, has significant consequences for lake extent and depth, suggesting future research should focus on reducing this uncertainty. This community-driven, open-access model has been developed with input from observations, and will allows us to provide new insights into the surface meltwater distribution on Antarctica’s ice shelves.