HR: 14:25h
AN: C43A-04    [Abstracts]
TI: Buoyancy Distribution Around Ice Sheet Grounding Zones in the Western Amundsen Sea Embayment, Antarctica: Results from the AGASEA Survey
AU: * Young, D A
EM: duncan@ig.utexas.edu
AF: Institute for Geophysics, Jackson School for Geosciences, Uinversity of Texas at Austin, 4412 Spicewood Springs #600, Austin, TX 78759-8500 United States
AU: Blankenship, D D
EM: blank@ig.utexas.edu
AF: Institute for Geophysics, Jackson School for Geosciences, Uinversity of Texas at Austin, 4412 Spicewood Springs #600, Austin, TX 78759-8500 United States
AU: Vaughan, D G
EM: DGV@bas.ac.uk
AF: British Antarctic Survey, National Environment Research Council, High Cross, Magingley Road, Cambridge, CB3 0ET United Kingdom
AU: Holt, J W
EM: jack@ig.utexas.edu
AF: Institute for Geophysics, Jackson School for Geosciences, Uinversity of Texas at Austin, 4412 Spicewood Springs #600, Austin, TX 78759-8500 United States
AB: Exposed grounding lines abutting Antarctica's relatively warm Amundsen Sea may represent an important locus of ice sheet erosion. Recent satellite remote sensing has indicated both expansion and retreat of active grounding lines in the region, with implications for global sea level change. As part of the 2004/05 AGASEA project, the University of Texas Institute for Geophysics (UTIG) surveyed Thwaites Glacier and Smith Glacier, two major marine outlet glaciers on the Amundsen Sea coast, using an aerogeophysical platform configured for simultaneous glaciological and geological investigations. The primary glaciological tools were a high-power coherent radar sounder and a laser altimeter, positioned by dual carrier phase GPS. Coverage of the Thwaites Glacier grounding line includes nine longitudinal radar and laser altimetry profiles collected by UTIG, two longitudinal radar profiles collected by the British Antarctic Survey, and three transverse radar and laser altimetry profiles collected by UTIG. Grid spacings for Thwaites Glacier were ~15km. The Smith Glacier grounding line location is constrained by two converging longitudinal profiles and three transverse lines at 15 km spacing, all five of which are UTIG radar and laser altimetry profiles.Surface elevations and ice thicknesses were derived from these data. These laser/radar profiles allow us to analyze buoyancy across the Smith Glacier and Thwaites Glacier grounding line zones. We use laser altimetry across sea ice to establish local sealevel to within a meter, and using this reference, predict from glacier surface elevations apparent hydrostatic compensation depths. Correspondence between the apparent compensation depth and the observed ice thickness allow us to identify floating ice, and thus allow a direct determination of the upstream limit of hydrostatic equilibrium. We compare this result to published tidal hinge lines delineated by satellite-based interferomic imaging radar between 1992 and 2000. The two methods match at the center of main trunk, but diverge considerably at the shear margins, which other work has suggested may be actively migrating. The reason for this divergence may be substantial retreat of the grounding line at the shear margins since 2000. An alternative explanation may be a systematic seaward offset of the tidal hinge line from the grounding line in thinner ice. The main trunk of Thwaites Glacier floats at a relatively shallow depth, and a broad lateral sill appears to localize the grounding line. Smith Glacier's grounding line is much deeper, and lacks a confining sill.
DE: 0720 Glaciers
DE: 0728 Ice shelves
DE: 0762 Mass balance (1218, 1223)
DE: 0794 Instruments and techniques
DE: 4540 Ice mechanics and air/sea/ice exchange processes (0700, 0750, 0752, 0754)
SC: Cryosphere [C]
MN: Fall Meeting 2005