Supraglacial Lakes on George VI Ice Shelf from a multi-decadal perspective

In 2020, 11.8% of northern George VI ice shelf was covered by supraglacial lakes, and it has been speculated that this was a record high lake density. Supraglacial lakes are associated with ice shelf instability, and were implicated in the collapse of Larsen B in 2002, where ~10% lake density was recorded. Here we use optical satellite imagery from Sentinel-2 and Landsat-1-8 in combination with recorded and modelled climate data from Fossil Bluff AWS, the MAR climate model, and the community firn model to study lakes on George VI ice shelf between 1973 and 2020. We find that the high density of lakes in 2020 was not unique, with similar events occurring five times in the study period, including a record value of 12.1% density in 1989. Furthermore, we find lake density to be controlled by a combination of high firn air content, high air temperature and a neutral southern annular mode, thus a strong melt year alone is insufficient for producing high lake densities. 2020 had record-high melt and temperature values, which suggests that this should also be a record year for lake coverage. A thicker than usual snow/firn pack in the winter prior to the 2020 melt season however, had a dampening effect on lake formation and thus lakes were less abundant than in 1989. As temperatures at this location are projected to increase in coming decades, but snowfall is expected to stay the same, future high melt years are very likely to lead to new record high lake coverage. Since supraglacial lakes are an indicator of ice shelf stability, this suggests that George VI may be rendered unstable within our lifetime.