HR: 0830h
AN: PP31C-0274    [PDF]
TI: Past Ice Flow in Pine Island Bay, West Antarctica, From Marine Geophysical Evidence
AU: * Dowdeswell, J A
EM: jd16@cam.ac.uk
AF: Scott Polar Research Institute, University of Cambridge, Cambridge, CB2 1ER United Kingdom
AU: Evans, J
EM: je10007@cam.ac.uk
AF: Scott Polar Research Institute, University of Cambridge, Cambridge, CB2 1ER United Kingdom
AU: O'Cofaigh, C
EM: co232@cam.ac.uk
AF: Scott Polar Research Institute, University of Cambridge, Cambridge, CB2 1ER United Kingdom
AU: Anderson, J B
EM: johna@rice.edu
AF: Dept. of Earth Science, Rice University, Houston, TX 77005 United States
AB: Marine geophysical and geological data from two recent cruises allow us to investigate the past extent and flow of a late Quaternary ice sheet in Pine Island Bay (PIB). Swath bathymetric data show that the shelf deepens inshore, and that cross-shelf troughs are present on both the inner and outer shelf. Three main types of sea-floor bedform were observed on the shelf. (a) Bedrock, with associated drumlinoid features probably formed by glacial erosion of the inner shelf. (b) Streamlined, elongate bedforms formed in soft sediments, found mainly in troughs on the mid and outer shelf and extending to the shelf edge. These features are interpreted as glacial lineations, inferred to be a product of soft-sediment deformation beneath former ice streams. They allow reconstruction of past ice-flow direction, and may also define former ice streams. Their presence at the shelf edge confirms that ice filled PIB at the last glacial maximum. Sub-bottom profiler records confirm that the sea floor is sedimentary and that there are in some places reflectors at a few metres depth defining an upper unit in whose surface the lineations are formed. Sometimes several reflectors appear to cross-cut one another, each with a similar acoustic unit above, suggesting shifting paleo-ice stream margins. (c) A highly irregular pattern of linear scour marks found in water depths $<$450-500 m, representing sediment reworking by iceberg keels produced from the 500 m or so thick floating tongues of the modern Pine Island and Thwaites glaciers. Geophysical evidence from the continental slope beyond PIB between 107§ to 115§W shows several sets of gullies or channels, up to about 100 m deep and 30 km long. The gullies are found mainly in two 50 km-wide groups at 113§20'W and 108§40'W. On the mid-slope and beyond, in over 2000 m of water, there is some evidence of wider channels, indicating that downslope transfer of glacier-derived sediments has taken place from the continental slope to the Amundsen Sea abyssal plain. During full-glacial conditions, sediments and meltwater would have been delivered from the ice front directly at the shelf break, leading to downslope mass-wasting, probably as turbidity currents and debris flows. It is likely that the gully or channel systems were formed by mass-flow activity, driven by either sediment-laden glacial meltwater or cold and saline water associated with sea-ice formation in a semi-permanent polynya at the former ice-sheet margin.
DE: 1635 Oceans (4203)
DE: 1827 Glaciology (1863)
DE: 3022 Marine sediments--processes and transport
DE: 3045 Seafloor morphology and bottom photography
DE: 4267 Paleoceanography
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting