Macro-scale bed roughness of the Siple Coast ice streams in west Antartica

Subglacial bed conditions are key to understanding ice stream behaviour and evolution, with bed roughness reflecting substrate composition and flow resistance. Here we present an analysis of bed roughness in the Siple Coast region of West Antarctica from airborne radio-echo sounding data. The ice streams are associated generally with low bed roughness values, which decrease downstream. The bed of the slow-flowing Ice Stream C (∼10 000 km²) is also characterized by being smooth at all scales (wavelengths ranging from 5 km to in excess of 40 km). Furthermore, the bed is smooth either side of Ice Stream C. This suggests the location of the ice stream is controlled by internal ice sheet dynamics rather than by bed morphology. If the ice stream were encouraged to migrate laterally, when active, there would be little resistance offered by the subglacial morphology. Other inter-ice stream regions are rough, however, indicating a subglacial topographic influence on ice stream position. Bed roughness increases up-flow of ice streams, which unless the bed is modified, may limit the inland migration of these systems.