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Atle Nygård, University of Bergen (Norway)
Hans Petter Sejrup, University of Bergen (Norway)
Haflidi Haflidason, University of Bergen (Norway)
Ivar Mardal, University of Bergen (Norway)
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The relatively small size of the last British Ice Sheet together with its maritime position in close proximity to the oceanic convection centres in the North Atlantic makes it attractive for studying high-frequency climate variability and land-sea interactions through the last deglaciation. However, previous paleoglaciological reconstructions of the North Sea sector of the last British Ice Sheet have suffered from lack of chronology and proven ice front positions. Based on new sub-bottom profiler data and cores collected in 2005 and 2006 we present seismostratigraphical and chronological evidence showing that after the last glacial maximum, the British Ice Sheet reached its most expanded position in the North Sea basin in a two-phased advance at around 17.5-17 and 16-15.5 cal. ka BP (Fladen 1 and 2 events). This has been achieved by mapping out laterally extensive ice-marginal deposits, mainly grounding-zone wedges, interstratified with a well-dated, continuous marine section in the Witch Ground basin in the central part of the northern North Sea. Combining our observations with previously published data indicating a late deglaciation of the east Shetland shelf, we suggest a northeastern branch of the Brititsh Ice sheet encompassing Shetland at this time. The Fladen events correlate in time with the Clogher Head and Killard Point readvances previously documented from Ireland, showing that the British Ice Sheet had its main axis parallel to the continental margin from Shetland to Ireland, with extensive calving fronts. This new geometry adds plausibility to previously hypothesized impact potential of the ice sheet on Atlantic meridional overturning circulation and climate through release of ice bergs and meltwater.
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