Extent and dynamics of ice on the southeast Pacific margin of West Antarctica during the Last Glacial Maximum, and its subsequent retreat history

• Main Authors: Larter, R. D., Hillenbrand, C. D., Smith, J. A., Graham, A. G. C., Deen, T. J., Dowdeswell, J. A., Evans, J., Gohl, Karsten, Kuhn, Gerhard, O'Cofaigh, C., Pudsey, C. J.
• Format: Conference Object
• Language: unknown
• Published: 2008
• Subjects: Amundsen Sea; Antarc*; Antarctic; Antarctic Peninsula; Antarctica; Iceberg*; West Antarctica
• Online Access: https://epic.awi.de/id/eprint/18673/; https://hdl.handle.net/10013/epic.30316

Marine geoscience data indicate that during the Last Glacial Maximum (LGM) grounded ice extended to the shelf edge along most, if not all, of the 2500 km-long continental margin from the northern Antarctic Peninsula to the Amundsen Sea. Past extent of grounded ice is indicated by swath bathymetry data from the outer parts of cross-shelf troughs, which reveal relict elongated subglacial bedforms. The bedforms show that the troughs were paths of fast-flowing (streaming) ice. Geomorphological evidence regarding the nature of ice flow over intervening outer shelf banks has been erased through pervasive post-glacial ploughing by icebergs. However, seismic profiles across the banks reveal widespread shelf edge progradation and numerous glacial unconformities that indicate grounded ice has extended across them many times during the Pleistocene, and before. Subglacial tills in the outer parts of shelf troughs are overlain by up to 2 m of postglacial sediments, which are no older than the LGM in any core yet dated. A layer of soft, intermediate shear strength (12¬25 kPa) till, interpreted as deformation till, underlies the postglacial sediments in cores in the troughs. These observations are consistent with the interpretation that streaming ice extended along the troughs during the LGM, but the duration of such flow, and whether or not it spanned the entire period when ice extended to the outer shelf remains undetermined.To determine when, and how rapidly, ice retreated from the continental shelf, ages of core samples from near the base of postglacial sediments in several troughs have been determined by AMS radiocarbon dating. Samples to constrain glacial retreat have been taken from either the base of muds deposited in seasonally open-marine conditions similar to today, or underlying sandy muds interpreted as having been deposited close to the grounding line. Modern sea-floor sediments on some parts of the margin contain sufficient calcareous microfossils for dating to constrain the local marine 14C reservoir ...