HR: 0800h
AN: U31B-0299 [Abstracts]
TI: Radar detection of the meteoric-accreted ice boundary over Lake Vostok
AU: * MacGregor, J A
EM: joemac@u.washington.edu
AF: University of Washington
Department of Earth and Space Sciences, Box 351310, Seattle, WA 98195, United States
AU: Matsuoka, K
EM: matsuoka@ess.washington.edu
AF: University of Washington
Department of Earth and Space Sciences, Box 351310, Seattle, WA 98195, United States
AU: Studinger, M
EM: mstuding@ldeo.columbia.edu
AF: Columbia University
Lamont-Doherty Earth Observatory, 61 Rte., 9W, Palisades, NY 10964, United States
AB:
Airborne radar data collected over Lake Vostok, East Antarctica, show a reflector that approximately intersects the
Vostok ice core near the depth of the meteoric--accreted ice boundary. Here we evaluate the hypothesis that this
reflector is due to the meteoric--accreted ice boundary. Using ice-core-chemistry and borehole-temperature data,
we seek possible causes of reflection that replicate the observed radar reflectivity (about -60 dB). Ice-core
data show large variations in the number density of inclusions, chloride-ion concentration ([Cl-]), and ice-
crystal size near the meteoric--accreted ice boundary. We estimate the reflectivity due to insoluble mineral
inclusions to be -120 dB, based on a likely range of permittivity and inclusion-diameter values. An impurity-
and temperature-dependent ice-conductivity model predicts a reflectivity of -68 ± 4 dB due to the large
contrast in the concentration of soluble Cl- ions incorporated into the ice lattice near the top of the accreted ice.
These results suggest that mineral inclusions do not contribute the reflection found in the radar data and that the
[Cl-] contrast is likely the primary cause. The discrepancy (about 4--12 dB) between the radar-derived and
[Cl-]-induced reflectivities suggests that a crystal-fabric change may also be present at the meteoric--accreted
ice boundary. We argue that the observed reflection is caused by the [Cl-] contrast associated with the
meteoric--accreted ice boundary, and we interpret this result together with the spatial patterns of the detection of
the boundary, accreted-ice thickness, and echo intensities.
DE: 0726 Ice sheets
DE: 0746 Lakes (9345)
DE: 9310 Antarctica (4207)
SC: Union [U]
MN: 2007 Fall Meeting