Ocean circulation and properties in Petermann Fjord, Greenland

Abstract

The floating ice shelf of Petermann glacier interacts directly with the ocean and isthought to lose at least 80% of its mass through basal melting. Based on three opportunisticocean surveys in Petermann Fjord we describe the basic oceanography: the circulationat the fjord mouth, the hydrographic structure beneath the ice shelf, the oceanic heatdelivered to the under‐ice cavity, and the fate of the resulting melt water. The 1100 m deepfjord is separated from neighboring Hall Basin by a sill between 350 and 450 m deep.Fjord bottom waters are renewed by episodic spillover at the sill of Atlantic water from theArctic. Glacial melt water appears on the northeast side of the fjord at depths between200 m and that of the glacier’s grounding line (about 500 m). The fjord circulation isfundamentally three‐dimensional; satellite imagery and geostrophic calculations suggest acyclonic gyre within the fjord mouth, with outflow on the northeast side. Tidal flowsare similar in magnitude to the geostrophic flow. The oceanic heat flux into the fjordappears more than sufficient to account for the observed rate of basal melting. Cold,low‐salinity water originating in the surface layer of Nares Strait in winter intrudes farunder the ice. This may limit basal melting to the inland half of the shelf. The melt rate andlong‐term stability of Petermann ice shelf may depend on regional sea ice cover andfjord geometry, in addition to the supply of oceanic heat entering the fjord.