Identifying potential seasonal and historical drivers of marine-terminating glacier retreat in Disko and Uummannaq Bays, West Greenland

Abstract:

The variability in outlet glacier termini positions is an important indicator of overall glacier health and the net effects of ice-ocean-atmosphere interactions. Glacier margins fluctuate on both seasonal and interannual time scales and satellite imagery provides a critical spatially- and temporally-extensive resource for monitoring glacier behavior. Outlet glaciers have generally been retreating globally over recent decades, but the magnitude of seasonal variation, overall retreat, and foremost drivers have proven unique to each glacier. The outlet glaciers in central West Greenland are generally experiencing the same regional atmospheric forcing, yet previous studies have shown varying magnitudes of retreat over the last forty years. In this study, we utilize Landsat imagery between the years 1985 and 2014 to digitize a time series of glacier front positions of 18 marine-terminating outlet glaciers in the Disko and Uummannaq Bay regions of West Greenland. We examine potential drivers of trends in outlet glacier retreat through satellite observations of adjacent sea ice concentrations and sea surface temperatures. Additionally, reanalysis data and long-term automatic weather station measurements are investigated to contextualize the role of atmospheric drivers at both a regional and local scale. Results indicate retreat of all glaciers in the region over the study period and no indication of a south to north trend in magnitude of retreat on either a seasonal or long-term scale. The 11 glaciers in Uummannaq Bay retreated between 25 m and 3.5 km, an average of 1.22 ± 1.20 km over the entire study period. The retreat of 7 glaciers in Disko Bay ranged from 181 m to 2.3 km, an average of 1.0 ± 0.78 km over the period. Although the mean terminus retreat rate between the two bays is comparable, there remains a wide range of total retreat amounts among the glaciers. We investigate the degree of seasonal variation in terminus position as an indicator of longer-term trends in glacier behavior. Furthermore, a longer duration of sea ice presence within individual fjords may delay the initiation of terminus retreat in the spring. These findings underscore the importance of individual fjord geometries, as well as local-scale atmospheric and oceanographic forcings in modulating glacier retreat patterns across West Greenland.