Bed properties of Siple Dome and adjacent ice streams, West Antarctica, inferred from radio-echo sounding measurements

We have used ground-based radio-echo, sounding (RES) profiles to reveal the spatial distribution of basal and internal ice properties across Siple Dome, West Antarctica. and under the dormant ice streams on its flanks. The RES-detected bed-reflection power: corrected for the effects of instrumentation and ice-thickness variation. is nearly constant across Siple Dome at a value suggesting spatially homogenous basal properties of ice frozen ta bedrock. Till. if present under the dome. must be thin (<0.1 m). The high basal reflectivity measured under now dormant "Siple Ice Stream" (SIS) and Ice Stream C suggests that they are underlain by either a thin (<0.05 m) water layer or a thick (>1m) thawed or frozen till layer. The evidence that the dormant SIS is not frozen directly to underlying bedrock (but is separated by a water or till layer) is a further indication that it was once an active ice stream. and suggests that streaming motion may have ceased before the basal layer was frozen. The absence of a thick till layer beneath Siple Dome is consistent with its apparent stability as an inter-ice-stream ridge in the past and may suggest that it will remain as a stable limitation of ice-stream width in the future.