HR: 1340h
AN: C13B-1075    [Abstracts]
TI: Modeling englacial attenuation using ice-core data for radar sounding of basal conditions
AU: MacGregor, J A
EM: joemac@u.washington.edu
AF: Dept. of Earth and Space Sciences, University of Washington, Box 351310, Seattle, WA 98195 United States
AU: * Winebrenner, D P
EM: dpw@apl.washington.edu
AF: Applied Physics Laboratory and Dept. of Earth and Space Sciences, University of Washington, Box 355640, Seattle, WA 98195 United States
AU: Matsuoka, K
EM: matsuoka@ess.washington.edu
AF: Dept. of Earth and Space Sciences, University of Washington, Box 351310, Seattle, WA 98195 United States
AU: Conway, H
EM: conway@ess.washington.edu
AF: Dept. of Earth and Space Sciences, University of Washington, Box 351310, Seattle, WA 98195 United States
AU: Mayewski, P A
EM:
AF: University of Maine, Climate Change Institute, Orono, ME 04469 United States
AU: Clow, G
EM:
AF: US Geological Survey, Box 25046, MS980, Lakewood, CO 80225 United States
AB: Observation of the radar reflectivity of ice-sheet beds is a primary tool for discriminating wet from frozen beds, and for finding subglacial lakes. However, uncertainty in englacial radar attenuation and its spatial variation introduces corresponding uncertainty in estimates of basal reflectivity. Radio-frequency ice-sheet attenuation is dependent on the impurity (acidity and salinity) and temperature profiles in the ice column that is being probed. Modeling englacial radar attenuation using modeled temperature profiles and assumed, depth-averaged impurity concentrations reduces such uncertainties only modestly. Here we develop a physical attenuation model based on ice-core chemistry and temperature data that can be used, in conjunction with ice flow modeling, to estimate englacial attenuation over wide areas around an ice core (e.g., Vostok). We test the model initially at Siple Dome, West Antarctica, where both ice-core and independent radar attenuation data are available for comparison. The modeled depth-averaged attenuation rate there is 32 dB km^-1, which lies between values of 26 dB km^-1 and 35 dB km^-1 measured at Siple Dome [Winebrenner et al., Ann. Glaciol. 37, 226-232, 2003]. A synthesis of experimental conductivity data shows that uncertainty in computed attenuation rates depends on uncertainties in conductivity parameterizations, which increase with increasing impurity concentrations and decreasing temperature. When the ice temperature is below about -15°C, fine-depth-scale impurity variations (mostly acid) control the attenuation rate; above -15°C, the higher temperature controls the attenuation rate more strongly, as the attenuation increases with temperature following an Arrhenius relationship.
DE: 0724 Ice cores (4932)
DE: 0726 Ice sheets
DE: 0746 Lakes (9345)
DE: 0758 Remote sensing
DE: 0776 Glaciology (1621, 1827, 1863)
SC: Cryosphere [C]
MN: Fall Meeting 2005