Can katabatic winds directly force retreat of Greenland outlet glaciers? Hypothesis test on Helheim Glacier in Sermilik Fjord

Abstract. Katabatic winds drive sea ice export from glaciated fjords across Greenland and other high latitude environments, but few studies have investigated the extent to which they also drive inflow of warm water and whether they have a direct impact on glaciers stability. Using ERA5 reanalysis data, verified by two local weather stations, we create a timeseries of katabatic winds across Sermilik Fjord in southeast Greenland. Using this along with hydrographic data, from 2009–2013, positioned across the fjord, we analyse changes in fjord circulation during individual katabatic flows. Changes in melange presence are analysed too, via the use of MODIS and Landsat-7 satellite imagery. We show that warm water influxes are associated with katabatic winds, and that the potential submarine melt rates vary up to four-fold, dependant on katabatic wind strength. Rapid retreat of Helheim Glacier occurred during strong downslope wind events which removed the ice melange, and so the well documented retreat of Helheim between 2001–2005 is predicted to be in part because of strong katabatic winds. Removal of the ice-melange led to a series of calving events, driven by a lack of buttressing and weakness propagation up the glacier causing a retreat of up to 1.5 km. In contrast to previous research in which katabatic winds were seen as having an indirect influence on glaciers, we report direct forcing on Helheim Glacier through episodes of retreat occurring in response to inflow of warm water masses and removal of proglacial ice melange after downslope wind events.