Basal conditions on Rutford Ice Stream, West Antarctica, from seismic observations

A seismic reflection profile, perpendicular to the ice flow direction has been acquired on Rutford Ice Stream, Antarctica. An interpretation of both the amplitude and phase of the seismic reflections from the ice-bed interface has been made to investigate the properties of the sub-ice material. The interpretation assumes that acoustic impedance can be used to imply subglacial sediment porosity. Multiple reflections from the ice-bed interface on a number of seismic wide-angle lines allowed a calibration of the reflection coefficient at the bed. This enabled the acoustic impedance of the bed material to be calculated from the seismic reflection data. Mean acoustic impedance in the different sections of the bed ranges from 2.70x10(6) kg m(-2) s(-1) to 4.31x10(6) kg m(-2) s(-1). Almost three quarters of the ice stream bed at this site appears to be saturated, deforming sediments. The rest of the bed is probably also saturated sediments, but they are not deforming to any significant degree. Ice flow could include a combination of subglacial deformation and basal sliding. Localized regions which support disproportionately high amounts of basal shear stress may also occur. From the seismic data, it is not possible to apportion relative amounts of restraint to these different processes. There does not appear to be any correlation between the different sections identified on the ice stream bed with either satellite images or nearby surface velocity data. A feature which is interpreted as a subglacial drumlin is seen on the seismic section.