The Geomorphology of Ice Stream Beds: Recent Progress and Future Challenges

English Abstract:

Ice sheets primarily lose mass by melting and discharge via rapidly-flowing ice streams. Surface and basal melting (e.g. of ice shelves) are closely linked to atmospheric and oceanic conditions, but the mechanisms that drive changes in ice stream discharge are more complex, and influenced by conditions at their bed, which may act to sustain, enhance or inhibit their motion. Although explicit comparisons are rare, the ice-bed interface is similar to the ‘boundary layer’ in fluvial and aeolian environments, where shear stresses (both basal and lateral in the case of ice streams) oppose the flow of the overlying medium. The analogy extends further because processes within the boundary layer create a distinctive geomorphology that is often characterised by subglacial bedforms that resemble features in fluvial and aeolian environments. Their creation results from erosion, transport and deposition of sediment which, in turn, is intimately linked to the mechanisms of ice stream flow. The study of ice stream geomorphology is, therefore, critical to our understanding of their dynamics. Despite difficulty observing the subglacial environment, our understanding of ice stream geomorphology has grown rapidly in the last three decades, from almost complete ignorance to a reasonably detailed knowledge of their geomorphological imprint. This has been brought about by two main approaches: (i) geophysical investigation of modern (active) ice streams, and (ii) sedimentological and geomorphological investigation of well-preserved palaeo-ice stream beds. The aim of this paper is to review progress in these two main areas; highlight the key questions that remain; and discuss the key opportunities that are likely to arise that will enable them to be addressed. It becomes clear that whilst each of these two main approaches have led to important advances, they have often been viewed as separate sub-disciplines, with minimal cross-pollination of ideas and concepts, particularly with respect to how landforms can be securely linked to process. However, it is argued that future surveys of modern-ice stream beds are likely to offer unprecedented opportunities to study ice stream geomorphology that will require the convergence of ideas from each of these two main approaches, together with a third approach – numerical modelling.