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Marine geophysical evidence for former expansion and flow of the Greenland Ice Sheet across the north-east Greenland continental shelf
journal contributionposted on 06.09.2013, 08:04 by Jeffrey Evans, Colm O Cofaigh, Julian A. Dowdeswell, Peter Wadhams
High-resolution swath bathymetry and TOPAS sub-bottom profiler acoustic data from the inner and middle continental shelf of north-east Greenland record the presence of streamlined mega-scale glacial lineations and other subglacial landforms that are formed in the surface of a continuous soft sediment layer. The best-developed lineations are found in Westwind Trough, a bathymetric trough connecting Nioghalvfjerdsfjorden Gletscher and Zachariae Isstrøm to the continental shelf edge. The geomorphological and stratigraphical data indicate that the Greenland Ice Sheet covered the inner-middle shelf in north-east Greenland during the most recent ice advance of the Late Weichselian glaciation. Earlier sedimentological and chronological studies indicated that the last major delivery of glacigenic sediment to the shelf and Fram Strait was prior to the Holocene during Marine Isotope Stage 2, supporting our assertion that the subglacial landforms and ice sheet expansion in north-east Greenland occurred during the Late Weichselian. Glacimarine sediment gravity flow deposits found on the north-east Greenland continental slope imply that the ice sheet extended beyond the middle continental shelf, and supplied subglacial sediment direct to the shelf edge with subsequent remobilisation downslope. These marine geophysical data indicate that the flow of the Late Weichselian Greenland Ice Sheet through Westwind Trough was in the form of a fast-flowing palaeo-ice stream, and that it provides the first direct geomorphological evidence for the former presence of ice streams on the Greenland continental shelf. The presence of streamlined subglacially derived landforms and till layers on the shallow AWI Bank and Northwind Shoal indicates that ice sheet flow was not only channelled through the cross-shelf bathymetric troughs but also occurred across the shallow intra-trough regions of north-east Greenland. Collectively these data record for the first time that ice streams were an important glacio-dynamic feature that drained interior basins of the Late Weichselian Greenland Ice Sheet across the adjacent continental margin, and that the ice sheet was far more extensive in north-east Greenland during the Last Glacial Maximum than the previous terrestrial–glacial reconstructions showed.
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