Seasonal variability of the circulation system in a west Greenland tidewater outlet glacier fjord, Godthåbsfjord (64°N)

Abstract

Many tidewater outlet glacier fjords surround the coast of Greenland, and their dynamics and circulation are of great importance for understanding the heat transport toward glaciers from the ice sheet. Thus, fjord circulation is a critical aspect for assessing the threat of global sea level rise due to melting of the ice sheet. However, very few observational studies describe the seasonal dynamics of fjord circulation. Here we present the first continuous current measurements (April-November) from a deep mooring deployed in a west Greenland tidewater outlet glacier fjord. Four distinct circulation phases are identified during the period, and they are related to exchange processes with coastal waters, tidal mixing, and melt processes on the Greenland Ice Sheet. During early summer, warm intermediate water is transported toward the glacier at an average velocity of about 7 cm s-1. In late summer, the average velocity decreases to 3 cm s-1 during a period with significant subglacial freshwater discharges. During this period, a large variability in current velocities is also observed. The associated average heat transport in an intermediate-depth range corresponds to 568 GW in early summer and is reduced to 287 GW in late summer. These heat fluxes are at the higher end of previously reported fluxes. Our measurements show that the intermediate heat transport varies over time and during summer provides a major contribution to the heat budget and, thereby, potentially to glacial melt. We suggest that intermediate heat transport may play a similar important role in other fjords around Greenland