Rapid circulation of warm subtropical waters in a major glacial fjord in East Greenland

The recent rapid increase in mass loss from the Greenland ice sheet(1,2) is primarily attributed to an acceleration of outlet glaciers(3-5). One possible cause of this acceleration is increased melting at the ice-ocean interface(6,7), driven by the synchronous warming(8-10) of subtropical waters offshore of Greenland. However, because of the lack of observations from Greenland's glacial fjords and our limited understanding of their dynamics, this hypothesis is largely untested. Here we present oceanographic data collected in Sermilik Fjord, East Greenland, by ship in summer 2008 and from moorings. Our data reveal the presence of subtropical waters throughout the fjord. These waters are continuously replenished through a wind-driven exchange with the shelf, where they are present all year. The temperature and renewal of these waters indicate that they currently cause enhanced submarine melting at the glacier terminus. Key controls on the melting rate are the volume and properties of the subtropical waters on the shelf, and the patterns of along-shore winds, suggesting that the glaciers' acceleration has been triggered by a combination of atmospheric and oceanic changes. Our measurements provide evidence for a rapid advective pathway for the transmission of oceanic variability to the ice-sheet margins.