Delayed Freshwater Export from a Greenland tidewater glacial fjord

Abstract Freshwater from the Greenland Ice Sheet is routed to the ocean through narrow fjords along the coastline where it impacts ecosystems both within the fjord and on the continental shelf, regional circulation, and potentially the global overturning circulation. However, the timing of freshwater export is sensitive to the residence time of waters within glacial fjords. Here, we present evidence of seasonal freshwater storage in a tidewater glacial fjord using hydrographic and velocity data collected over 10 days during the summers of 2012 and 2013 in Saqqarleq (SQ), a midsize fjord in West Greenland. The data revealed a rapid freshening trend of −0.05 ± 0.01 g/kg/day and −0.04 ± 0.01 g/kg/day, in 2012 and 2013, respectively, within the intermediate layer of the fjord (15–100 m) less than 2.5 km from the glacier terminus. The freshening trend is driven, in part, by the downward mixing of outflowing glacially−modified water near the surface and increasingly stratifies the fjord from the surface downwards over the summer melt season. We construct a box model which recreates the first−order dynamics of the fjord and describes freshwater storage as a balance between friction and density−driven exchange outside the fjord. The model can be used to diagnose the timescale for this balance to be reached, and for SQ we find a month lag between subglacial meltwater discharge and net freshwater export. These results indicate a fjord−induced delay in freshwater export to the ocean that should be represented in large−scale models seeking to understand the impact of Greenland freshwater on the regional climate system.