Seafloor geomorphology of the SW Barents Sea and its glaci-dynamic implications

Abstract

Three-dimensional (3D) reflection seismic imaging techniques provide a unique means of identifying large-scale submarine geomorphic features produced by former ice sheets. We have used such techniques to image the geomorphology of the SW Barents Sea, but using a dense grid of 2D seismic, covering a 240 000 2 km large study area, supplemented with 3D seismic from selected areas. The study area is located at the convergence of ice flow from the former Fennoscandian, Barents Sea and Svalbard ice sheets. The morphology of the major cross-shelf troughs is characterized by elongated ridge-groove features, interpreted to be glacial bedforms produced by fast-flowing grounded glaciers. Mega-scale glacial lineations have been grouped into distinct flow sets related to three specific ice flow events. These events document the last glacial maximum (LGM) and two readvances during deglaciation. Of specific interest is a detailed and well-preserved set of seafloor imprints in the Bjørnøyrenna trough, which acted as the main pathway for ice streams draining the surrounding ice sheets. The geomorphic features indicate that Bjørnøyrenna hosted six separate ice stream lobes that diverged fan-like at their margins, but were not all active simultaneously. An end moraine zone 68 km wide, up to 85 m high and 300 km long filled the whole width of this major glacial trough as a result of high sediment flux within sub-ice stream deformable beds. The imprint of this ice stream system can be followed on our seabed images for 500 km; however, detailed geomorphologic elements demonstrate that these imprints reflect time-transgressive behaviour and do not indicate the length or width of single ice streams. The seismic-derived seafloor geomorphology demonstrates that the Barents Sea ice behaved in a much more dynamic way during the last glaciation than previously assumed, with major shifts between ice originating from the Fennoscandian, Spitsbergen and Barents Sea ice sheets.