Abstract

The Greenland Ice Sheet is losing mass at an accelerating pace. This decline in mass is a result of increased runoff during longer and warmer summers as well as the interaction of the ice sheet with the surrounding seas. Whereas the effect of atmospheric warming is relatively well established, little is known about the latter effect since ice-ocean interactions in glaciated fjords are poorly documented. Here, we use hydrographic data acquired in Kangerdlugssuaq Fjord and adjacent seas in 1993 and 2004, together with reanalysis from the Nucleus for European Modelling of the Ocean (NEMO), to establish the connection between water mass change in the fjord and offshore air-sea interactions. The hydrographic data show that the fjord contains warm subtropical waters and that fjord waters in 2004 were considerably warmer than in 1993. The ocean reanalysis shows that the warm properties of fjord waters in 2004 are related to a major peak in oceanic shoreward heat flux into a cross-shelf trough on the outer continental shelf. The heat flux into this trough varies according to seasonal exchanges with the atmosphere as well as from deep seasonal intrusions of subtropical waters. Both mechanisms contribute to high (low) shoreward heat flux when winds from the northeast are weak (strong). The combined effect of surface heating and inflow of subtropical waters is seen in the hydrographic data, which were collected after periods when along-shore coastal winds from the north were strong (1993) and weak (2004). The latter data were furthermore acquired during the early phase of a prolonged retreat of Kangerdlugssuaq Glacier. We show that coastal winds vary according to a large scale pressure gradient defined by a semi-permanent atmospheric high-pressure system over Greenland and a persistent atmospheric low situated near Iceland, i.e. the Icelandic Low, which defines the northern state of the North Atlantic Oscillation. The magnitude of this pressure gradient is controlled by longitudinal variability in the position of the Icelandic Low.