Decadal grounding line migration and ice shelf melt regime of Petermann Glacier, North-West Greenland, from high-resolution InSAR data.

Petermann Glacier (80.75N, 60.75W) terminates in one of the most extensive remaining ice tongues of the Greenland Ice Sheet. The glacier is grounded 600 meters below sea level on a downsloping bed and could significantly contribute to sea level rise during the 21st century. Recent observations showed an ongoing acceleration in ice flow and kilometric-scale grounding line retreat after decades of stable dynamic conditions. Warming of the ocean waters surrounding Greenland has been indicated as the main driver of this process. However, the melting regime of the glacier at the interface between ocean waters and grounded ice is not well known and needs to be investigated.

In this study, we achieve this goal by employing a time series of satellite radar interferometry data available between 2011 and 2022. We document grounding line migration using high-frequency observations from the Italian COSMO-Skymed constellation and the Finnish ICEYE constellation. Furthermore, we use time-tagged digital elevation models from the German TanDEM-X mission to assess the ice shelf basal melt regime in a Lagrangian framework.

InSAR observations reveal kilometer-size grounding line migrations - (2-6 km) grounding zones - during tidal cycles, with preferential seawater intrusions of 6 km along pre-existing subglacial channels. In addition, results from the Lagrangian approach indicate that the highest ice shelf melt rates occur at these locations, with values reaching peaks ranging from 60 to 80 meters per year.

Such high melt rates concentrated in kilometer-wide grounding zones contrast with the traditional plume model adopted by physical models with zero melt at a fixed grounding line. Their inclusion in physical models will increase the glacier's sensitivity to ocean warming and double the projections of sea level rise from the glacier.

This work was supported by a grant from NASA.