The ocean's forcing on the ice shelf of Petermann Gletscher, Greenland

Abstract

Petermann Gletscher is a large outlet glacier in northwest Greenland that transports 4% of the ice sheet into Petermann Fjord. At its marine terminus, Petermann Gletscher forms a 16-km-wide and 50-km-long floating ice shelf. Historically the ice shelf extended to 80 km, but large calving events in 2010 and 2012 reduced it to its current length. Hydrographic data collected adjacent to and underneath the Petermann Gletscher Ice Shelf between 2002 and 2017 expose a 0.26 +- 0.19°C warming of the surrounding deep ocean. Repeat summer hydrographic sections at the ice shelf terminus reveal a coincident increase in ocean heat flux towards the glacier and freshwater flux away from it, indicating stronger ocean-forced melt. Along with the large-scale impact of ocean warming on melt, local basal melt rate time series at a site on the ice shelf spanning 2015 to 2017 demonstrate a strong seasonal signal that relates to the air temperature. Mean basal melt rates increase from 2 m/yr during winter to 23 m/yr in summer when air temperatures eclipse freezing. Maximum melt rates of 80 m/yr also occur during this time. We attribute these high melt rates to increased discharge of subglacial runoff into the ocean at the grounding line, which strengthens under-ice currents and drives a greater ocean heat flux towards the ice base.