Radar derived Subglacial Properties and Landforms beneath Rutford Ice
Stream, West Antarctica
Abstract
Basal properties beneath ice streams and glaciers are known to be a
control for ice flow dynamics, hence knowledge of them is crucial for
predicting sea level due to changes in glacial dynamics. Basal
properties, processes and topography also drive the formation of
subglacial landforms. Bed properties beneath Rutford Ice Stream (West
Antarctica) have previously been described using seismic acoustic
impedance measurements at a sparse spatial coverage. Here, we derive bed
properties in a 15 x 17 km grid of surface radar data with coverage and
sampling much higher than previous seismic studies. Bed reflection
amplitudes in surface radar data were calibrated using sediment
porosities (ranging from 0.4 – 0.5) derived from seismic acoustic
impedance. We find the bed properties are spatially variable, consisting
of low porosity material in some areas and soft sediment in other areas.
Comparison of seismic and surface radar data imply the low porosity
material to be a consolidated sediment or sedimentary rock. Mega-scale
glacial lineations (MSGLs) are ubiquitous on the bed and consist of
soft, high porosity, probably deforming sediment, consistent with
previous interpretations of MSGLs. We find some MSGLs have high
reflectivity on their crest, interpreted as water bodies overlying high
porosity sediment, whereas the trough around and the upstream end of
some landforms consist of low porosity material. Integrating these
different observations, we place constraints on possible explanations
for the occurrence of water on the crest of landforms.