The Winds of Change: The effects of katabatic winds on fjord circulation, sea-ice export and glacier stability at Sermilik Fjord and Helheim Glacier
Katabatic winds or downslope wind events, across the southeast of Greenland, can lead to large scale changes in fjord circulation, sea-ice export and glacier terminus stability, but despite this few studies have investigated their wider implications. In period of rapidly retreating tidewater glaciers, katabatic winds are known to aid retreat indirectly, through inducing warm Atlantic origin water influx into the fjord, and directly via the removal of the ice melange in front of the glacier terminus. Using ERA5 reanalysis data, verified by two local weather stations, katabatic winds across Sermilik Fjord are shown to occur predominately in non-summer months with no clear long-term trend. Hydrographic data, from 2009-2013, positioned across the fjord and adjacent shelf waters, showed the expected warm water influxes are lower in scale in comparison to intermediary circulation associated with barrier winds. However, submarine melt rates at the top of the fjord can increase during downslope wind events by up to 1000%. Melt rates vary according to katabatic wind strength. Thresholds of katabatic wind speeds for the removal of sea-ice from the shelf and the removal of the ice-melange of 12m/s and 20m/s, respectively, were observed. Rapid retreat of Helheim glacier occurred during strong downslope wind events which removed the ice melange, and 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. Although previous research has dismissed katabatic winds as relatively unimportant due to much greater heat influxes associated with barrier winds, direct influences on Helheim Glacier terminus stability show perhaps katabatic winds play a much large role in glacier retreat in southeast Greenland than previously appreciated.