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 Dom e, West Antarctica. and under the dormant ice streams on its flanks. The RE S-detected bed-reflection power: corrected for the effects of instrumentati on and ice-thickness variation. is nearly constant across Siple Dome at a v alue suggesting spatially homogenous basal properties of ice frozen ta bedr ock. 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 S tream C suggests that they are underlain by either a thin (<0.05 m) water l ayer or a thick (>1m) thawed or frozen till layer. The evidence that the do rmant 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 b asal 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.