HR: 11:35h
AN: C12B-06    [Abstracts]
TI: Monitoring Iceberg B15a With Airborne Radar Sounding
AU: * Blankenship, D D
EM: blank@ig.utexas.edu
AF: Institute of Geophysics, Jackson School of Geosciences,University of Texas at Austin, 4412 Spicewood Springs Road #600, Austin, TX 78759-8500 United States
AU: Young, D A
EM: duncan@ig.utexas.edu
AF: Institute of Geophysics, Jackson School of Geosciences,University of Texas at Austin, 4412 Spicewood Springs Road #600, Austin, TX 78759-8500 United States
AU: Peters, M E
EM: mattp@ig.utexas.edu
AF: Institute of Geophysics, Jackson School of Geosciences,University of Texas at Austin, 4412 Spicewood Springs Road #600, Austin, TX 78759-8500 United States
AU: Kempf, S D
EM: scottk@ig.utexas.edu
AF: Institute of Geophysics, Jackson School of Geosciences,University of Texas at Austin, 4412 Spicewood Springs Road #600, Austin, TX 78759-8500 United States
AU: Smith, D
EM: diana.smith@lpl.arizona.edu
AF: Lunar & Planetary Lab, University of Arizona, 1629 E. University Blvd., Tucson, AZ 85721-0092 United States
AU: Lindzey, L
EM: lindzey@its.utexas.edu
AF: California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125 United States
AU: Carver, K
EM: kevin.carver@gmail.com
AF: Institute of Geophysics, Jackson School of Geosciences,University of Texas at Austin, 4412 Spicewood Springs Road #600, Austin, TX 78759-8500 United States
AU: Holt, J W
EM: jack@ig.utexas.edu
AF: Institute of Geophysics, Jackson School of Geosciences,University of Texas at Austin, 4412 Spicewood Springs Road #600, Austin, TX 78759-8500 United States
AB: Understanding the migration, ablation and disintegration of large tabular icebergs requires knowledge of their thickness and basal character over time. In 2000, the ~5000 square km iceburg B15a calved off the western edge of the Ross Ice Shelf. The University of Texas, Institute for Geophysics (UTIG) first acquired phase-coherent radar imaging of iceberg B15a along with laser altimetry for accurate surface elevations during the early austral summer of 2001/02. At that time, the 20-month old iceberg was in one piece and was lying nearly perpendicular to the front of the Ross Ice Shelf north of Ross Island. A 140 km profile was flown parallel to and about 10 km from the then-recent ice shelf break, while an adjacent 160 km profile bisected the iceberg. These two profiles were connected with two shorter profiles (approximately 35 and 45 km) running perpendicular from the shelf break to the former shelf edge. Our objective of simultaneously imaging high-resolution surface and bottom scattering as well as the extremely subtle englacial layering was achieved. Ice thickness and internal layering implied B15a was subject to heterogeneous basal melting prior to calving from the Ross Ice Shelf. Also, major vertical cracking extending from the surface to the base was identified at only a single site (where the iceberg subsequently split) whereas basal cracking was pervasive over approximately two thirds of the iceberg base. On the two shorter profiles, maximum ice thicknesses ranged from 285 meters to 279 meters. Three years later, when a second survey opportunity arose, the iceberg had fragmented into three major pieces, B15a, B15j and B15k. During this field season, UTIG acquired new radar sounding data over the three-iceberg suite, with the goal of repeating the previous profiles as closely as possible; the objective was to detect any changes in ice thickness due to melting as well as to monitor the state of the stress-induced basal fractures. At the time of the most recent data acquisition, the largest portion (B15a) had drifted northward to between Franklin Island and Beaufort Island, large chunk B15j was rotated in place where the Ross Ice Shelf meets Ross Island, and sliver B15k had drifted westward from B15a. Due to relatively rapid iceberg rotation, precisely repeating the lines was impossible; cross-overs, minimum and maximum ice thicknesses were obtained, as well as the freeboard from laser altimetry. The repeated shorter lines had maximum thickness of 266 meters and 274 meters, respectively, compatible with several meters of ablation.
DE: 0732 Icebergs
DE: 0738 Ice (1863)
DE: 1621 Cryospheric change (0776)
DE: 4207 Arctic and Antarctic oceanography (9310, 9315)
DE: 4540 Ice mechanics and air/sea/ice exchange processes (0700, 0750, 0752, 0754)
SC: Cryosphere [C]
MN: Fall Meeting 2005