HR: 0830h
AN: C31B-0399    [PDF]
TI: Basal Water Flow, Melt and Accumulation in the Dome C "Lake District", Antarctica, Using Airborne Radar Profiling of Bed Echo Character and Internal Layering.
AU: * Carter, S P
EM: sasha@ig.utexas.edu
AF: The University of Texas at Austin The John A. and Katherine G. Jackson School of Geosciences Institute for Geophysics, 4412 Spicewood Springs Rd., Bldg. 600, Austin,, TX 78759-8500
AU: Blankenship, D D
EM: blank@ig.utexas.edu
AF: The University of Texas at Austin The John A. and Katherine G. Jackson School of Geosciences Institute for Geophysics, 4412 Spicewood Springs Rd., Bldg. 600, Austin,, TX 78759-8500
AU: Morse, D L
EM: morse@ig.utexas.edu
AF: The University of Texas at Austin The John A. and Katherine G. Jackson School of Geosciences Institute for Geophysics, 4412 Spicewood Springs Rd., Bldg. 600, Austin,, TX 78759-8500
AU: Peters, M
EM: mattp@ig.utexas.edu
AF: The University of Texas at Austin The John A. and Katherine G. Jackson School of Geosciences Institute for Geophysics, 4412 Spicewood Springs Rd., Bldg. 600, Austin,, TX 78759-8500
AB: Using airborne radar we infer the presence of subglacial water by three physical conditions: A high amplitude basal reflector, a local minimum on a potentiometric surface obtained by adding bed elevation to the thickness of the overlying ice cover times its density, and a deformation of internal layers consistent with melt at the base of the ice sheet. The coefficient of reflection at the base is calculated by solving the radar equation and correcting for temperature dependant dielectric loss. The temperature profiles used to obtain this correction are highly sensitive to two poorly constrained parameters: accumulation history and geothermal flux. Improved estimates for accumulation, and melt rate can be obtained by obtaining a best fit of these parameters as well as shear layer thickness to Fahnestock's modification of the Dansgaard-Johnsen equation relating age and depth. Five internal layers of ages ranging between 53 ka and 291 ka have been traced through 5000 line km of UTIG airborne radar profiles, and then fit to this age versus depth equation to obtain shear layer thickness, accumulation and melt rate. The accumulation figure obtained by this fit is then used to calculate a one dimensional temperature profile to correct our basal reflection coefficients. The reflector corresponding to Lake Concordia is well defined and consistent with a potentiomeric low. While melting occurs over the lake, the area of heaviest melt is centered on the Southeast shore of the lake, not in the center of this body. The maximum melt rate here is on the order of 6 mm/yr. A valley extends southward of Lake Concordia which contains moderately bright reflectors consistent with saturated sediment. Our one dimensional temperature profiles are also consistent with the ice being at the pressure melting point in this area. At the southern part of this valley, 40-50 km from lake Concordia we see refection coefficients on the order of those associated with water. However since these reflections are up potential from the lake an additional source of melt is required to sustain their existence. The necessary melt occurs directly along an escarpment located 5 km to the west of our strong echoes. This escarpment forms a boundary between strong bed echoes and weak bed echoes and also represents an abrupt increase in relative shear layer thickness. Given the combination of strong bed echoes, a downward sloping potentiometric gradient between these upper lakes and Lake Concordia and the likelihood that warm ice is present throughout the valley, it is likely that a significant subglacial water system forms a hydraulic connection between these systems.
UR: http://www.ig.utexas.edu/people/students/sasha/index.htm
DE: 1827 Glaciology (1863)
DE: 1863 Snow and ice (1827)
DE: 2199 General or miscellaneous
DE: 3354 Precipitation (1854)
DE: 6900 RADIO SCIENCE
SC: Cryosphere [C]
MN: 2003 Fall Meeting