Grounding-zone wedges on the West Greenland shelf imaged from multibeam and seismic data

Abstract

Grounding-zone wedges (GZWs) are asymmetrical depocentres built up beneath the grounding zone of marine-terminating ice streams through the delivery of soft, deforming subglacial till from upglacier. They are typically tens of metres thick, tens of kilometres in length and usually form subdued transverse-to-flow ridges across the long axes of fjords and cross-shelf troughs on high-latitude continental shelves (e.g. Dowdeswell & Fugelli 2012; Batchelor & Dowdeswell 2015). The ridges, representing the relatively steeper ice-distal face of the wedge, usually appear as small scarps or steps in multibeam imagery. The wedges thin in an ice-proximal direction, often becoming difficult to identify except by using acoustic-stratigraphic methods. Relatively large sedimentary wedges have been identified in multibeam data from several Greenland cross-shelf troughs (e.g. Dowdeswell et al. 2014). The features generally have a scarp at their ice-distal end, and a subdued, low-gradient ice-proximal slope which makes their termination difficult to pinpoint from bathymetric data. Where a basal reflection can be identified, there is some evidence that the wedges thin progressively over a few tens of kilometres away from the former ice margin and have a characteristic asymmetry along trough axes. A multibeam image of a modern wedge from the outer shelf of …