Unique In-situ Measurements from Greenland Fjord Show Winter Freshening by Subglacial Melt

The interaction between glacier fronts and ocean waters is one of the key uncertainties for projecting future ice mass loss. Direct observations at glacier fronts are sparse but studies indicate that the magnitude and timing of freshwater fluxes are crucial in determining fjord circulation, ice frontal melt and ecosystem habitability. Particularly wintertime dynamics are severely understudied due to inaccessible conditions leading to a bias towards summer observations. In this study, we present novel in-situ observations of temperature and salinity acquired at the front of a marine-terminating glacier and in surrounding fjords in late winter in Greenland. The observations indicate the existence of an anomalously fresh pool of water by the glacier front. To our knowledge, our study is the first to document the existence of subglacially discharged freshwater outside the summer season, suggesting that meltwater generated at the bed of the glacier discharges into the fjord during winter. Our results have implications for the heat exchange between glacier fronts and ocean waters, glacier frontal melt rates, ocean mixing and currents, and biological production.