Corridor Aerogeophysics of the South East Ross Transect Zone (CASERTZ)Principle Investigator:
Don Blankenship,
University of Texas (in
collaboration with U.S. Geological Survey, Naval Research Laboratory
and Lamont-Doherty Earth Observatory) Background The CASERTZ scientific objective was to understand the lithospheric framework across the West Antarctic rift system in order to determine the geological controls on the dynamics of the West Antarctic Ice Sheet, the last marine ice sheet. These experiments included a suite of aerogeophysical measurements made within carefully chosen corridors. These corridors covered the eastern portion of the Interior Ross Embayment and encompassed: 1) the initiation zone and catchment regions of ice streams B and C and all of ice stream D from the ice divide to the grounding line (IRE, BSB, and TKD, respectively); and 2) the boundary between the broadly extended portion of the West Antarctic rift system within the Interior Ross Embayment and the crustal provinces dominated by the Whitmore Mountains and the Byrd Subglacial Basin (IRE and BSB, respectively). The experimental objective was to characterize and correlate the distribution of sedimentary basins, volcanic rocks and important ice dynamical boundaries within these corridors.
Technical DevelopmentTo achieve these objectives, CASERTZ required a system capable of simultaneously measuring the precise surface elevation and ice thickness needed for ice sheet studies, as well as the potential field observations necessary for inferring subglacial geology. UTIG, as lead institution for CASERTZ, benefited substantially from the expertise of its collaborating institutions, which included the USGS as well as the Naval Research Laboratory and Lamont Doherty Earth Observatory (NRL/LDEO). Initially, the CASERTZ instrumentation focus was only ice-penetrating radar, laser altimetry and magnetics in collaboration with the USGS but ultimately, with the assistance of NRL/LDEO, UTIG successfully developed an integrated aerogeophysical platform that included airborne gravity with carrier-phase GPS to support kinematic differential positioning. UTIG also developed flight structures for these instruments including an antenna system for radar sounding, access ports for laser altimetry, a towed magnetometer system and flight-certified equipment racking systems that placed the gravimeter near the aircraft's center of gravity. In parallel with the instrument integration, we also designed and implemented a comprehensive data management system to tightly couple time/position with the integrated aerogeophysical observations. During the initial two field seasons in West Antarctica, UTIG, with the assistance of the USGS and NRL/LDEO, used this system to collect 50,000 line km of geophysical observations within the region shown as IRE the coverage map. Details of the instrumentation can be found here. In 1994, in response
to the science proposal to complete the CASERTZ corridors, the National
Science Foundation's Office of Polar Programs requested that the aircraft
and its integrated instrumentation package be operated as a facility
with a mission of providing aerogeophysical observations to the broader
Antarctic science community. This request led to a Cooperative Agreement
between UTIG and NSF that created the Support
Office for Aerogeophysical Research (SOAR). ResultsVolcano figure Geological Controls on Ice StreamsAirborne geophysical results from the Interior Ross Embayment (IRE) from Blankenship et al., [2001]. (a) Surface topography from laser altimetry showing the steady downslope from the interior ice (along 105° W) to the onset regions of ice stream B and C branches B2, C1a, C1b and C2 as indicated by the white hatchure of crevasses identified by radar scattering. Superimposed with this figure are 50 and 100 kPa driving stress contours in blue and red, respectively. These bound the areas of ice stream onset; above 100 kPa ice flows by internal deformation, below 50 kPa rapid basal motion enabled by some process with an effectively weaker rheology than that of ice. (b) Bed elevation from radar sounding showing, in red, the Ellsworth-Whitmore Mountain Block and, in violet, troughs that locate the various ice stream tributaries. Contours of critical driving stress and the outline of the EWB from the subglacial topography are overlaid on maps of Bouguer gravity (c) and Magnetic field intensity (d).
From the analysis presented in Blankenship et al., [2001], we concluded that the only consistent control on the initiation of ice streaming in the IRE survey was the presence of a thin marine sediment drape that was deposited prior to West Antarctic glaciation. A follow-study by Studinger extended this conclusion to the BSB survey block as well. Selected Publications Morse, D. L.,
D. D. Blankenship, E. D. Waddington and T. A. Neumann. 2002. A site
for deep ice coring in West Antarctica: Results from aerogeophysical
surveys and thermo-kinematic modeling. Annals of Glaciology, 35, p.
36-44. Sweeney,
R. E., C. A. Finn, D. D. Blankenship, R. E. Bell and J. C. Behrendt.
Central West Antarctica aeromagnetic data: a web site for distribution
of data and maps. Open File Report 99-420, U. S. Geological Survey,
(1999). Behrendt, J.C., R. Saltus, D. Damaske, A. McCafferty, C.A. Finn, D.D. Blankenship and R.E. Bell. Patterns of late Cenozoic volcanic and tectonic activity in the West Antarctic rift system revealed by aeromagnetic surveys. Tectonics, vol. 15, no. 2, p. 660-676 (1996). Bindschadler, R., P. Vornberger, D. Blankenship, T. Scambos and R. Jacobel. Surface velocity and mass balance of ice streams D and E, West Antarctica. Journal of Glaciology, vol. 42, no. 142, p. 461-475 (1996).
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