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Late Quaternary contourites and glaciomarine sedimentation in the Fram Strait

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Abstract

Two sites in the eastern Fram Strait, the Vestnesa Ridge and the Yermak Plateau, have been surveyed and sampled providing a depositional record over the last glacial-interglacial cycle. The Fram Strait is the only deep-water connection from the Arctic Ocean to the North Atlantic and contains a marine sediment record of both high latitude thermohaline flow and ice sheet interaction. On the Vestnesa Ridge, the western Svalbard margin, a sediment drift was identified in 1226 m of water. Gravity and multicores from the crest of the drift recovered turbidites and contourites. 14C dating indicates an age range of 8287 to 26 900 years BP (Early Holocene to Late Weichselian). The Yermak Plateau is characterized by slope sediments in 961 m of water. Gravity and multicores recovered contourites and hemipelagites. 14C ages were between 8615 and 46 437 years BP (Early Holocene to mid-Weichselian). Downcore dinoflagellate cyst analyses from both sites provide a record of changing surface water conditions since the mid-Weichselian, suggesting variable sea ice extent, productivity and polynyas present even during the Last Glacial Maximum. Four layers of ice-rafted debris were also identified and correlated within the cores. These events occurred ca at 9, 24 to 25, 26 to 27 and 43 ka, asynchronous with Heinrich layers in the wider north-east Atlantic and here interpreted as reflecting instability in the Svalbard/Barents Ice sheet and the northward advection of warm Atlantic water during the Late Weichselian. The activity of the ancestral West Spitsbergen Current is interpreted using mean sortable silt records from the cores. On the Vestnesa Ridge drift the modern mass accumulation rate, calculated using excess 210Pb, is 0·076 g cm−2 year−1. On the Yermak Plateau slope the modern mass accumulation rate is 0·053 g cm−2 year−1.

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