Geological evidence for past subglacial conditions: dry-based vs wet-based ice

gerhard.kuhn [ at ]


Amongst the geological community there is now consensus that the West Antarctic ice sheet reached outer continental shelf positions in most sectors during its last maximum extent. This conclusion is mainly formed on the basis of extensive palaeo-glaciological work that has been conducted during the past decade in various drainage sectors of the ice sheet. In these regions of the continental shelf, reconstructions of ice-sheet extent, relative flow velocities and retreat have mainly focused on deeper cross-shelf depressions, generally interpreted as pathways of fast-flowing palaeo-ice streams. Within these troughs, the prevalent glacial landforms consist of continuums of streamlined bedforms (e.g. mega-scale glacial lineations and drumlins) whose progressive increase in elongation is indicative of formation beneath wet-based streaming ice. However, extensive shelf areas surrounding these spatially restricted deeper corridors largely lack well-preserved glacial landforms, thereby inhibiting reliable shelf-wide ice-flow reconstructions. Recently, by analysing new high-resolution bathymetric data from these inter-ice stream ridges, former basal ice conditions could be illuminated for the first time. Subglacial landforms such as hill-hole pairs, sediment rafts and crevasse-squeeze ridges clearly indicate cold/dry-based, slow-flowing or even stagnant ice on the shelf areas outside the troughs. Here we present a new compilation of bathymetric datasets from the eastern Amundsen Sea Embayment covering both palaeo-ice stream troughs and adjacent inter-ice stream ridges. It allows a clear distinction between different basal ice regimes (dry-based vs wet-based) across the former ice-sheet bed. However, we additionally identified regions of apparent changes in basal conditions, i.e. regions where hill-hole pairs overprint mega-scale glacial lineations, thereby suggesting cold/dry-based basal conditions prior to final retreat rather than streaming flow. Generally, the ability to reconstruct the width and basal form of the West Antarctic ice sheet in this manner, across other parts of the Antarctic shelf, will greatly aid numerical ice-sheet models that aim to simulate past configurations of the ice sheet and its evolution to the present day.

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Conference (Poster)
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Event Details
International Symposium on Hydrology of Glaciers and Ice Sheets, 21 Jun 2015 - 27 Jun 2015, Höfn, Island.
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Klages, J. P. , Kuhn, G. , Graham, A. G. C. , Smith, J. A. and Hillenbrand, C. D. (2015): Geological evidence for past subglacial conditions: dry-based vs wet-based ice , International Symposium on Hydrology of Glaciers and Ice Sheets, Höfn, Island, 21 June 2015 - 27 June 2015 .

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