HR: 08:15h
AN: C21A-02    [PDF]
TI: Subglacial Sediments as a Control on the Location of Ice Streams C and D, West Antarctica, from Seismic Refraction and Reflection Imaging
AU: * Peters, L E
EM: lpeters@geosc.psu.edu
AF: The Pennsylvania State University, Department of Geosciences, 503 Deike Building, University Park, PA 16802
AU: Anandakrishnan, S
EM: sak@essc.psu.edu
AF: The Pennsylvania State University, Department of Geosciences, 503 Deike Building, University Park, PA 16802
AU: Winberry, J P
EM: winberry@essc.psu.edu
AF: The Pennsylvania State University, Department of Geosciences, 503 Deike Building, University Park, PA 16802
AU: Alley, R B
EM: ralley@essc.psu.edu
AF: The Pennsylvania State University, Department of Geosciences, 503 Deike Building, University Park, PA 16802
AU: Blankenship, D D
EM: blank@ig.texas.edu
AF: The University of Texas at Austin, Institute for Geophysics, 4412 Spicewood Springs Rd., Bldg. 600, Austin, TX 78759
AU: Morse, D L
EM: morse@ig.texas.edu
AF: The University of Texas at Austin, Institute for Geophysics, 4412 Spicewood Springs Rd., Bldg. 600, Austin, TX 78759
AU: Smith, A M
EM: amsm@bas.ac.uk
AF: British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 0ET United Kingdom
AU: King, E C
EM: ecki@bas.ac.uk
AF: British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 0ET United Kingdom
AB: Ice streams discharge a majority of the inland ice from the Ross Embayment of West Antarctica. This increased ice flow is believed to be aided by a dilatant subglacial till, but the mechanisms controlling the initiation of streaming flow within the ice sheet are uncertain. The focus of our study is to image the presence of subglacial sediments and interpret their importance in ice stream velocity and location. We present the results of two refraction seismic experiments in the onset regions of ice streams C and D during the 2002 - 2003 Antarctic field season that were performed to image subglacial geology and develop a better understanding of its role in initiating ice streaming. The refraction experiments consisted of a 31.2km longitudinal profile of ice stream C (C1B) and a 34.5km transverse profile of ice stream D (DT1), giving the opportunity to image the shallow (upper 1-2km) subglacial geology in the onset regions of these two Ross ice streams. Coupled with reflection seismic data, gravity (for DT1), and GPS data, the inverse modeling of the refraction data imaged the presence of sedimentary basins in both locations. The C1B results reveal a thin ($<$50m) cover of sediments in the upstream (non-streaming ice) portion of the longitudinal profile that quickly thickens into a $\sim$600m sedimentary basin in the downstream (streaming ice) reaches. The DT1 results reveal a large sedimentary basin extending across the width of the ice stream, with a maximum thickness of $\sim$600m near the center of the ice stream. We determined these sediment thicknesses by creating a 2D model consisting of a sedimentary layer, whose velocity ranges from 2400m/sec to 2500m/sec, between the ice and the underlying bedrock. The thick sedimentary basins along both C1B and DT1 also correspond with increased ice velocities along the two profiles. Our results reveal that the presence of sediments is a necessary requirement for initiating ice streaming in the onset regions of the Ross ice streams. Thick sedimentary basins at the onset provide a source for the dilatant subglacial till that acts as a lubricant in aiding ice flow along the length of the ice streams. It appears that tributary C1B of ice stream C has reached the inland extent of subglacial sediments, which may mark the paleo-shoreline of the West Antarctica during complete deglaciation (presumed to have occurred within the last 600,000 years). This sediment boundary may also outline the maximum inland extent of the Ross ice streams.
DE: 0935 Seismic methods (3025)
SC: Cryosphere [C]
MN: 2003 Fall Meeting