Evolution of the 79N ice shelf

The North-East Greenland Ice Stream is the largest ice stream of the Greenland Ice Sheet and drains an area of some 200,000 km², which equates to ~12% of the ice sheet, and the entire catchment holds sufficient water to impact eustatic sea level (~1.1 m). It appeared relatively resilient to atmospheric warming until the mid-2000s, since when two of the outlets, 79N and Zachariæ Isstrøm, have started to thin and accelerate. Zachariæ Isstrøm experience rapid retreat followed by loss of the ice shelf by 2010. This work focuses on the ~80 km long ice shelf fronting 79N, which has previously been shown to have thinned significantly since 1994. The main structural components of the ice shelf are identified and mapped, at approximately 5 yearly intervals, from Landsat imagery, spanning 1985 to 2024. Retreat of the grounding line is approximated by the migration of supraglacial meltwater ponds which migrate upflow over the timeseries. The location of lateral grounding lines are tracked using their topographic expression (Midgardsormen), along the margins of the ice shelf. Taking the surface elevation of the ice shelf from the Arctic DEM and the bed topography/bathymetry from BedMachine and assuming the floating part of the ice shelf is in hydrostatic equilibrium, a time series of ice shelf reconstructions are generated by tracking the migration of the Midgardsormen towards the fjord margins. Evolution of the grounding lines and the structure of the 79N ice shelf are assessed in relation to air and ocean temperature records across the timeseries.