Strong Year-Round Variation in Circulation and Heat Transport in a Proglacial Southwest Greenland Fjord

Greenland's glacial fjords serve as pathways for the transport of heat and freshwater between the continental shelf and the outlet glaciers of the Greenland Ice Sheet. Despite increasing attention from the research community, seasonal studies in Greenland fjords remain scarce. This is especially true for near-surface measurements. Here, we present year-round, near-full water column velocity observations and water mass data in Nuup Kangerlua, a glacial fjord in southwest Greenland. In July, a strong exchange flow is present in the upper 200 m, coinciding with the presence of subglacial discharge waters in the upper 10–50 m. Fjord circulation remains active throughout the year. Net heat transport toward the glaciers is most pronounced in the glacial melt domain (upper 150 m) in summer, while the heat transport occurs mostly in deeper layers in the winter months. Episodic dense coastal inflows renew the deep water in the fjord and can profoundly increase or decrease fjord water temperatures depending on the timing and depth of the inflow. We estimate vertical diffusivity in deeper layers to be around (Formula presented.) (Formula presented.) during stagnant periods (i.e., when no inflows occur). This study underlines the importance of seasonal variations and episodic events in fjord current dynamics and associated heat transport as a potentially important control for the submarine melting of marine-terminating glaciers.