Morphology of Younger Dryas subglacial and ice‐proximal submarine landforms, inner Vestfjorden, northern Norway

The sea‐floor morphology of two pronounced across‐fjord bedrock thresholds located at the mouths of Ofotfjorden and Tysfjorden, northern Norway, has been analysed based on swath bathymetry and seismic data. The Younger Dryas ice front was located here during the recession of one of the large palaeo‐ice streams of the Fennoscandian Ice Sheet. The thresholds are several kilometres long and wide, rising to several hundred metres above the adjacent sea floor, and the slopes are steep, up to 25°. The Ofotfjorden threshold is draped by acoustically discontinuous to chaotic sediments partly infilling the bedrock relief. A pattern of well‐developed, subglacial bedforms (e.g. crag‐and‐tail formations, drumlins and glacial lineations) on top of both thresholds suggests fast‐flowing ice. A series of smaller transverse ridges is identified on both thresholds and probably records ice‐front oscillations during the final deglaciation. The distal parts of the sediments have been remobilized by slides that occurred after glacial retreat from the thresholds. Earthquake activity due to the isostatic rebound following ice retreat from this area was the most likely triggering mechanism for the slides. The location of the ice front on a prominent bedrock threshold indicates that the basin configuration was important in locating the maximum position of the climatically induced re‐advance, i.e. a topographic control on the maximum Younger Dryas position in the Ofotfjorden and Tysfjorden area is suggested.