The marine-based NW Fennoscandian ice sheet: glacial and deglacial dynamics as reconstructed from submarine landforms

The configuration of the marine-based NW Fennoscandian ice sheet during the Last Glacial Maximum (LGM) and deglaciation is reconstructed using detailed swath bathymetry and high-resolution seismic data. The investigated area covers about 10,000 km2 of the continental shelf off Troms, northern Norway. Large scale morphology is characterized by cross-shelf troughs, coast-parallel troughs and banks. Based on mega-scale glacial lineations (MSGL), lateral and shear zone moraines and grounding zone systems, the extent and dynamics of the ice sheet during the LGM are deduced. MSGL indicate fast-flowing ice streams in the cross-shelf troughs, while the glacial morphology on the banks indicates more sluggish ice here. The marine-based part of the Fennoscandian ice sheet was sourced from ice domes in the east via fjord and valley systems inshore. Using a balance flux approach, we estimate palaeo-ice stream velocities during the LGM to be approximately 350 m/year. Three deglaciation events have been reconstructed: i) During the Torsken-1 event the ice sheet halted or readvanced to form groundings zone wedges (GZW) and the Torsken moraine, ii) Several still-stands or readvances characterized the ice behaviour on the shallower banks during the Torsken-2 event, iii) During the Flesen event, prominent end moraines in the inner parts of the troughs and banks were deposited. The locations of the end moraines and GZW in the troughs indicate that the retreat of marine-based ice streams in areas of reverse bed slope was episodic, probably mainly due to the variation in widths of the cross-shelf troughs. ► High resolution data revealed excellent details of submarine glacial landforms. ► Estimated palaeo-ice stream velocities during LGM were about 350 m/year. ► A rapid early deglaciation in the troughs was followed by a stepwise recession. ► The deglaciation of the banks was characterized by minor halts and readvances. ► The trough widths probably exerted an important control on the deglacial dynamics.