Лëд и снег (Dec 2021)
Late Pleistocene glaciation and retreat of ice sheet on the shelf of the South Orkney Plateau, West Antarctica
Abstract
The research aims to provide insight into reconstruction of the Late Pleistocene glaciations and ice retreat that followed the Last Glacial Maximum. The study is based on multi-channel seismic profiling and multibeam survey conducted on the shelf during the 63-rd Russian Antarctic Expedition (2018) on RV «Akademik Alexander Karpinsky». The 560-channel, 7000-m-long streamer and the Atlas Hydrosweep MD-3/30 multibeam echo-sounder were used for seismic and multibeam survey, respectively. In addition, previously collected seismic data available from the Antarctic Seismic Data Library System and bathymetry data from the «International Bathymetry Chart of the Southern Ocean» (IBCSO) Project were involved for interpretation. The multibeam survey was carried out within the Signy Trough and its flanks with depths ranging from 180 to 400 m, and covered the area of about 1500 km2. The data were collected along 43 profiles spaced at 750 m to ensure enough overlap between swaths. Variety of submarine glacial landforms formed by grounded ice was identified on shelf of the South Orkney Plateau with use of seismic and multibeam data. The most prominent of these features is the large terminal moraine at the middle shelf (previously described as the mid-shelf break) marking the greatest ice extent at the LGM. Oceanward of the large terminal moraine, the plateau-like feature (delineated by 350 and 425 m isobaths) with relatively steep outer slope is recognized from seismic data and interpreted as the distal terminal moraine formed during the pre-LGM Pleistocene glaciation. Within the Signy Trough, submarine glacial landforms mapped by multibeam survey, reflect ice retreat after the LGM; these landforms include: subglacial lineation at the western flank of the northern Signy Trough indicating fast flowing grounded ice, transverse recessional moraine ridges, lateral shear moraine on the western flank and lateral marginal moraine on the eastern flank of the Trough, two grounding zone wedges, streamlined features (drumlins) and an ice-proximal fan (presumably). The end moraine was also identified in the eastern flank of Signy Trough. It is thought to be formed due to ice (outlet glacier) re-advance during the Antarctic Cold Reversal. Numerous iceberg plough-marks were observed at least down to 370 m water depths.
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