HR: 1340h
AN: C43A-0220    [Abstracts]
TI: GPS and GPR Profiles of Snow Megadunes in East Antarctica
AU: * Bauer, R
EM: bauerr@kryos.colorado.edu
AF: National Snow and Ice Data Center, CIRES, University of Colorado, 449UCB, Boulder, CO 80309 United States
AU: Scambos, T
EM: teds@icehouse.colorado.edu
AF: National Snow and Ice Data Center, CIRES, University of Colorado, 449UCB, Boulder, CO 80309 United States
AU: Haran, T
EM: tharan@kryos.colorado.edu
AF: National Snow and Ice Data Center, CIRES, University of Colorado, 449UCB, Boulder, CO 80309 United States
AB: Global Positioning System (GPS) and ground-penetrating radar (GPR) profile data were acquired over a series of snow megadunes about 400 km southeasst of Vostok Station (80.78 S, 124.5 E) in November 2002 and January 2004. GPS profiles (110 km total) acquired in the mean wind direction (bearing 225) show the topographic characteristics of the dunes: 3 to 7 meters relief, with short, steep windward faces and longer, shallower lee surfaces relative to regional along-wind slope. Regional absolute slope in this area is nearly perpendicular to wind flow, i.e. nearly parallel to dune crests. GPS-derived mean ice velocity is 4 +/- 0.2 m/yr at bearing 130, with little regional gradient. GPR profiles (total of 60 km) were acquired at two frequencies, 100 MHz and 250 Mhz, providing information on snow layering to about 80 meters. Megadune regions are composed of stacked sequences of fore-set, windward-accreted snow layers, 8 to 15 meters thick, separated by lee-side layer sections showing near-zero accumulation (and possibly some erosion). Buried lee faces of the dunes, characterized by mono-layer ice 'glazes' on the surface are represented by 1- to 4meter thick zones of reduced reflection amplitude. Dune sequence layering can be detected at up to 70 meters depth, implying that dunes have been present for several millennia. Comparison with a shallow ice core drilled at the Megadunes camp indicates that interpreted buried glaze/lee surfaces coincide with anomalous low density regions in the firn. A separate profile of a region showing a transition from megadune terrain to a non-undulating, low slope plateau surface shows that megadunes became lower in amplitude, and intervening glazed-surface regions showed more evidence of accumulation as slope decreased to near-zero. At depth (20 - 40 meters), dunes structures underlay the smooth plateau surface, possibly due to advection. Details of the shape of the accretionary section of the windward face of the dunes and the arrangement of stacked dune sequences at depth will be used to constrain models of dune formation.
DE: 9310 Antarctica
DE: 1827 Glaciology (1863)
DE: 1863 Snow and ice (1827)
DE: 1894 Instruments and techniques
SC: Cryosphere [C]
MN: 2004 AGU Fall Meeting