HR: 1340h
AN: G33A-0022    [Abstracts]
TI: Comparison of New Airborne Gravity Results and GRACE Anomalies in the Thwaites Glacier Catchment of the Amundsen Sea Embayment, West Antarctica
AU: * Diehl, T M
EM: theresa@ig.utexas.edu
AF: Institute for Geophysics, Jackson School of Geoscience, The University of Texas at Austin, 4412 Spicewood Springs Rd. Building 600, Austin, TX 78759-8500 United States
AU: Holt, J W
EM: jack@ig.utexas.edu
AF: Institute for Geophysics, Jackson School of Geoscience, The University of Texas at Austin, 4412 Spicewood Springs Rd. Building 600, Austin, TX 78759-8500 United States
AU: Blankenship, D D
EM: blank@ig.utexas.edu
AF: Institute for Geophysics, Jackson School of Geoscience, The University of Texas at Austin, 4412 Spicewood Springs Rd. Building 600, Austin, TX 78759-8500 United States
AU: Richter, T G
EM: tomr@ig.utexas.edu
AF: Institute for Geophysics, Jackson School of Geoscience, The University of Texas at Austin, 4412 Spicewood Springs Rd. Building 600, Austin, TX 78759-8500 United States
AU: Filina, I Y
EM: irina@ig.utexas.edu
AF: Institute for Geophysics, Jackson School of Geoscience, The University of Texas at Austin, 4412 Spicewood Springs Rd. Building 600, Austin, TX 78759-8500 United States
AB: The West Antarctic Ice Sheet is a marine ice sheet of which 75% is resting on bedrock below sea level. This situation is highly unstable and as the climate warms, the potential for rapid discharge of the ice sheet grows. Examining the areas of the ice sheet that are most likely to react to changing climate is essential. The Amundsen Sea Embayment contains two of the most important outlet glaciers in West Antarctica: Thwaites and Pine Island Glaciers. These two glaciers have among the highest discharge velocities in West Antarctica and they lack large protective ice shelves, making them susceptible to warming ocean waters. The area is currently a target of interest for both GRACE and GLAS, as well as future land- and air-based surveys. To date, we have conducted the only large-scale geophysical survey over the catchment of Thwaites Glacier: an airborne survey completed during the austral summer 2004-2005. Over 43,500 line-kilometers of data were collected with a geophysical platform that included ice-penetrating radar, gravity, magnetics, laser and pressure altimetry, and GPS. Free-air gravity, in conjunction with magnetics and radar-derived subglacial topography, is capable of delineating microplate and rift boundaries as well as basin and volcano locations. A free-air gravity map of these structures helps ascertain the contribution of subglacial geology to the ice sheet's decay in the Thwaites Glacier catchment. The acquisition, reduction, and initial results of the airborne gravity survey will be presented and then compared to GRACE gravity anomalies. Extreme relief in ice surface elevation across the survey area necessitated short, smooth vertical altitude changes at survey block boundaries to maintain adequate flight altitude for the onboard ice-penetrating radar systems. Weather conditions sometimes required additional elevation changes or course corrections, producing significant aircraft motion during data acquisition. The impacts of these aircraft motions on the gravity data are discussed. The combination of GPS-derived horizontal accelerations with meter-mounted accelerometer measurements allows for the direct calculation of platform leveling errors, including leakage of the horizontal accelerations into the measured vertical gravity. We examine the magnitude and significance of platform leveling errors in relation to the overall survey resolution. Power spectral analysis of the gravity illuminates differences in the anomaly detection threshold over thick ice like that near Byrd Subglacial Basin versus over thin ice like that near the Thwaites Glacier grounding line. Filtering requirements for this situation are discussed. A preliminary free-air gravity map for the Thwaites Glacier catchment is presented along with error analysis and initial structural interpretations. The interpretations of the airborne regional gravity will be compared to GRACE static gravity anomalies over the same area of the catchment.
DE: 0794 Instruments and techniques
DE: 1219 Gravity anomalies and Earth structure (0920, 7205, 7240)
DE: 1223 Ocean/Earth/atmosphere/hydrosphere/cryosphere interactions (0762, 1218, 3319, 4550)
DE: 1295 Integrations of techniques
DE: 8122 Dynamics: gravity and tectonics
SC: Geodesy [G]
MN: Fall Meeting 2005