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Karin Andreassen, University of Tromso (Norway)
Monica Winsborrow, University of Tromso (Norway)
Jan Sverre Laberg, University of Tromso (Norway)
Tore O Vorren , University of Tromso (Norway)
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Imprints left behind by the former Bjørnøyrenna mega ice-stream are imaged and interpreted using extensive regional sets of 2D and 3D seismic and high-resolution bathymetric data from the SW Barents Sea and the western continental margin. This ice stream developed in an area of strongly confluent flow from the Svalbard, Barents Sea and Fennoscandian ice sheets. It was the largest outlet from the Eurasian Arctic Ice Sheet and delivered during glacial maxima sediments to The Bjørnøya Trough Mouth Fan, the largest of the North Atlantic glacial fans.
A semi-regional 3D seismic data set at the SW Barents Sea margin, where a 2-3 km record of former ice stream activity is preserved due to subsidence, reveal evidence of former ice stream activity during peak glaciations. Such activity is inferred from mega-scale glacial lineations on buried horizons, long chains of megablocks and rafts buried in thick till units between glacially eroded horizons, buried till deltas at shelf break and mass movement deposits on the slope. A continuous image of the seafloor geomorphology reveal the large-scale landforms of the glaciated Barents Sea and allows to place observations from smaller areas within a broad glacial context. The sea floor imprints document the last glacial maximum and two readvances during deglaciation. A well-preserved set of geomorphic features reveal that the Bjørnøyrenna mega-ice stream left behind imprints from six ice stream lobes that diverged fan-like at their margins during an early stage of deglaciation. These ice lobes were not all active simultaneously. A grounding zone wedge, up to 85 m high, 300 km wide and extending 70 km upstream, fills the whole width of this major glacial trough as a result of high sediment flux within the sub-ice stream deformable beds. The imprints of this mega-ice stream, that can be followed on the seabed image for over 500 km upstream, reflect time-transgressive behaviour and indicate that this mega-ice stream was grounded intermittently during the deglaciation.
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