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Simon Cook, Aberystwyth University (United Kingdom)
Zoe Robinson, Keele University (United Kingdom)
Ian Fairchild, University of Birmingham (United Kingdom)
Peter Knight, Keele University (United Kingdom)
Richard Waller, Keele University (United Kingdom)
Ian Boomer, University of Birmingham (United Kingdom)
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The occurrence of metres-thick sequences of debris-laden basal ice at temperate glaciers has been considered problematic. The process of glaciohydraulic supercooling may explain such basal ice thicknesses although there is strong debate as to how significant this process might be in this regard. This paper assesses the contribution of supercooling to basal ice formation at Svínafellsjökull and Skaftafellsjökull, southeast Iceland, both of which are known to experience supercooling. Five sub-facies (A, B, C, D and E) have previously been identified within the basal ice of Svínafellsjökull but the origins of the individual sub-facies have not been identified. We present new stable isotope data (ä18O and äD) alongside existing information on basal ice distribution, and physical character to assess the origins of these individual sub-facies. Two populations of basal ice emerge: one that has few characteristics consistent with an origin through glaciohydraulic supercooling, and one that does appear to have been formed by supercooling.
In addition to this, one sub-facies in particular, sub-facies C, shares almost all its geographical, physical, and stable isotope characteristics with frazil and anchor ice (vent ice facies) growing around vents of supercooled subglacial discharge, and has consistent characteristics at both glaciers studied. Sub-facies C can therefore be considered as an ice facies diagnostic of supercooling and may represent a means by which to identify the significance of supercooling at other glaciers. Sub-facies C accounts for around 46% of stratified facies basal ice across the margin of Svínafellsjökull, or 57% across areas where there is evidence for supercooling. Similar approximations at Skaftafellsjökull were not made due to limited exposure of basal ice. So although supercooling is very significant for basal ice formation, our results suggest that it cannot account for all the basal ice at such glaciers, contrary to previous research findings. Supercooling does, therefore, have important impacts on glacier sediment flux, the generation of ice-marginal landforms, and basal ice rheology and glacier behaviour, although is less significant than previously envisaged.
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