Abstract
ABSTRACTThe spatial pattern and morphometry of bedforms and their relationship to sediment thickness have been analysed in the Marguerite Bay Palaeo-ice stream Trough, western Antarctic Peninsula. Over 17 000 glacial landforms were measured from geophysical datasets, and sediment thickness maps were generated from acoustic sub-bottom profiler data. These analyses reveal a complex bedform pattern characterised by considerable spatial diversity, influenced heavily by the underlying substrate. The variability in length and density of mega-scale lineations indicates an evolving bedform signature, whereby landforms are preserved at different stages of maturity. Lineation generation and attenuation is associated with regions of thick, soft till where deformation was likely to be the greatest. The distribution of soft till and the localised extent of grounding-zone wedges (GZWs) indicate a dynamic sedimentary system characterised by considerable spatio-temporal variability in sediment erosion, transport and deposition. Formation of GZWs on the outer shelf of Marguerite Trough, within the error range of the radiocarbon dates, requires large sediment fluxes (upwards of 1000 m3 a−1 (m grounding line width)−1), and a >1 m thick mobile till layer, or rapid basal sliding velocities (upwards of 6 km a−1).
Highlights
The drainage of continental ice sheets is organised into a series of tributaries that feed rapidly-flowing outlet glaciers known as ice streams (Bamber and others, 2000)
Due to their rapid flow, ice streams account for 50–90% of ice discharge from modern ice sheets and recent observations of their thinning and acceleration indicate that their contribution to sea level rise has increased over the past few decades (Pritchard and others, 2009; Moon and others, 2012)
Using a recent map presented by Livingstone and others (2013), our aim is to analyse the spatial pattern and morphometry of ice stream bedforms and their relation to till properties and thickness on the former Marguerite Bay ice stream (MBIS), western Antarctic Peninsula, to understand ice stream retreat patterns, sedimentary processes and bedform genesis
Summary
The drainage of continental ice sheets is organised into a series of tributaries that feed rapidly-flowing outlet glaciers known as ice streams (Bamber and others, 2000) Due to their rapid flow, ice streams account for 50–90% of ice discharge from modern ice sheets and recent observations of their thinning and acceleration indicate that their contribution to sea level rise has increased over the past few decades (Pritchard and others, 2009; Moon and others, 2012). The mechanisms driving these changes are likely to involve both atmospheric and oceanic warming, but evolving conditions on the beds of ice streams play a crucial role in modulating their behaviour Relatively few studies have undertaken comprehensive mapping and detailed quantitative/statistical analysis of palaeo-ice stream beds (e.g. Dowdeswell and others, 2004a; Livingstone and others, 2013; Stokes and others, 2013; Spagnolo and others, 2014; Klages and others, 2015), which are required to fully characterise their basal environment over large spatial scales
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