Basal roughness of the Institute and Möller Ice Streams, West Antarctica: process determination and landscape interpretation

We present a detailed analysis of bed roughness beneath Institute and Möller Ice Streams, West Antarctica, using radio-echo sounding data (RES) acquired in the austral summer of 2010/11. We assess roughness using a two-parameter approach, and also assess the directionality of roughness relative to present day ice flow. Our work highlights the wealth of additional information that resides in analyses of bed roughness, and also serves to stress the importance of exercising caution in interpreting such data where flightline orientation is sub-optimal (i.e. neither flow parallel or flow-orthogonal). Employing these multiple approaches we show that spatially-variable roughness patterns are partly a consequence of the ability of flowing ice not only to smooth the bed but also to redistribute and remove sediments, and to do this along-flow. Accordingly, we identify some fast-flow tributaries underlain by topography which has been streamlined, and other tributaries which are underlain by sediments. We also identify locations that are currently protected from erosion, but where more ancient erosion may once have occurred, as well as terrain which we interpret to be a preglacial landscape. We conclude that the roughness of an ice-sheet’s bed should be viewed as the consequence not only of ancient marine sedimentation, but also as a product of more contemporary erosion and redistribution of sediments, as well as bedrock-smoothing that is ongoing because of continuing dynamic activity. In this way, basal roughness has the potential to evolve continually with ice sheet form and flow, and should not be viewed simply as a snapshot of either present day, or palaeo-basal conditions.