HR: 08:00h
AN: C21A-01 INVITED     [PDF]
TI: Ice stream D, West Antarctica, subglacial conditions from a combined seismic reflection, refraction, gravity and radar survey
AU: * Anandakrishnan, S
EM: sak@essc.psu.edu
AF: EMS Environment Institute and Dept. of Geosciences, Pennsylvania State University, University Park, PA 16802 United States
AU: Morse, D L
AF: Institute of Geophysics, University of Texas at Austin, Austin, TX 78759 United States
AU: Smith, A M
AF: British Antarctic Survey, Madingley Rd, Cambridge, CB3 0ET United Kingdom
AU: Blankenship, D D
AF: Institute of Geophysics, University of Texas at Austin, Austin, TX 78759 United States
AU: Alley, R B
AF: EMS Environment Institute and Dept. of Geosciences, Pennsylvania State University, University Park, PA 16802 United States
AU: Winberry, J P
AF: EMS Environment Institute and Dept. of Geosciences, Pennsylvania State University, University Park, PA 16802 United States
AU: Peters, L E
AF: EMS Environment Institute and Dept. of Geosciences, Pennsylvania State University, University Park, PA 16802 United States
AU: Voigt, D E
AF: EMS Environment Institute and Dept. of Geosciences, Pennsylvania State University, University Park, PA 16802 United States
AU: King, E C
AF: British Antarctic Survey, Madingley Rd, Cambridge, CB3 0ET United Kingdom
AU: Miranov, A
AF: Institute of Geophysics, University of Texas at Austin, Austin, TX 78759 United States
AB: A high resolution reflection seismic profile on ice stream D, West Antarctica, has revealed the presence of dilatant till beneath the far upstream sections of the ice stream. The characteristics of the reflection from the base of the ice stream (such as phase, magnitude, angle-dependence of amplitude, etc.) are clear indicators of the acoustic impedance of the material beneath the ice. We detect an extremely low acoustic impedance (product of density and seismic velocity) over much of the region, which we interpret as dilatant, actively deforming till. This discovery is particularly surprising given the location of the experiment: in the ``tributary'' region of the ice stream, 10s of kilometers upstream of the location where the ``onset of ice streaming'' has been hypothesized to occur. Our experiment was conducted in the region of moderate flow speeds ($<100$ m$\cdot$a$^{-1}$), and suggests that the onset region of the ice stream could be substantially farther upstream than previously thought. We combine the reflection seismic work with phase-coherent radar data to differentiate between basal roughness and subglacial acoustic impedance. In addition, we use refraction and gravity data to constrain deeper structure. A joint reflection/refraction seismic and gravity experiment successfully imaged sedimentary basins beneath the ice stream that are clearly associated with locating the boundaries of the ice stream. Finally, we report on the expanded capabilities that are possible with a new shothole drill, ranging from high resolution internal layer imaging to Moho reflections.
DE: 0935 Seismic methods (3025)
DE: 1827 Glaciology (1863)
SC: Cryosphere [C]
MN: 2003 Fall Meeting