Past pinning points of Pine Island Glacier and the Brunt Ice Shelf mapped by swath bathymetry

Swath bathymetric surveys in formerly ice shelf covered areas can reveal high-resolution images of former ice shelf pinning points. We present swath bathymetry from two formerly ice shelf covered areas of Antarctica and investigate their implications for ice-shelf processes. Pine Island Glacier currently experiences the largest negative mass balance in comparison to other outlet glaciers in Antarctica. Here, we were able to access an area with pinning points that were still in contact with the ice shelf less than two years before data acquisition. The bathymetric data revealed three bathymetric highs. These data were used in combination with satellite data from the last decades to investigate the correlation of the bathymetric highs to recent calving dynamics of Pine Island Glacier. In the southeastern Weddell Sea, swath bathymetry acquired offshore Brunt Ice Shelf revealed numerous ramp-shaped seafloor bedforms. The Brunt Ice Shelf is currently intensively monitored due to imminent risk of large-scale calving or even disintegration, which is threatening the British polar research station Halley VI. We interpret that these ramps on the seafloor indicate past ice-shelf grounding events that occurred sometime less than 19000 years ago at a time when the ice shelf was more extensive than today. Most likely, keels of thick glacial ice slaps enclosed within the ice shelf by perennial sea-ice mélange created these bedforms. An analogue pattern of such ice slaps is observed in the modern-day ice shelf. The presence of these bedforms indicate that the ice shelf experienced several phases of ice shelf pinning and unpinning in the last few thousand years