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Understanding conditions at the grounding-line of marine-based ice sheets is essential for understanding ice sheet evolution. Offshore northwest Greenland, knowledge of the Last Glacial Maximum (LGM) ice sheet extent in Melville Bugt was previously based on sparse geological evidence. This study uses multibeam bathymetry, combined with 2-D and 3-D seismic reflection data, to present a detailed landform record from Melville Bugt. Seabed landforms include mega-scale glacial lineations, grounding-zone wedges, iceberg scours, and a lateral shear margin moraine, formed during the last glacial cycle. The geomorphology indicates that the LGM ice sheet reached the shelf edge before undergoing flow reorganization. After retreat of similar to 80 km across the outer shelf, the margin stabilized in a mid-shelf position, possibly during the Younger Dryas (12.9-11.7 ka). The ice sheet then decoupled from the seafloor and retreated to a coast-proximal position. This landform record provides an important constraint on deglaciation history offshore northwest Greenland.

Plain Language Summary Reconstructing the extent and dynamics of the Greenland Ice Sheet during the last ice age are important for helping us to predict how it may change in the future. This study uses the topography of the seafloor to investigate for evidence of landforms left behind by the Greenland Ice Sheet during the last ice age. These landforms indicate that the ice sheet extended to the continental shelf edge when it was at its largest extent. The ice sheet then retreated 80 km to the middle shelf, likely during a period of climate cooling called the Younger Dryas. The ice sheet margin remained stable here until it retreated a further 100 km toward the coastline during the final deglaciation. During this second stage of deglaciation the ice sheet appears to have retreated faster than during the first stage. This possible dramatic collapse has possible implications for our understanding of the future evolution of the Greenland Ice Sheet.