Role of glaciohydraulic supercooling in the formation of stratified facies basal ice: Svínafellsjökull and Skaftafellsjökull, southeast Iceland

There is need for a quantitative assessment of the importance of glaciohydraulic supercooling for basal ice formation and glacial sediment transfer. We assess the contribution of supercooling to stratified facies basal ice formation at Svinafellsjokull and Skaftafellsjokull, southeast Iceland, both of which experience supercooling. Five stratified basal ice subfacies have previously been identified at Svinafellsjokull, but their precise origins have not been determined. Analysis of stratified basal ice stable isotope compositions (delta 18O and delta D), spatial distribution and physical characteristics demonstrates that two subfacies present at both glaciers are consistent with supercooling. These 'supercool' subfacies account for 42% of stratified facies exposed at Svinafellsjokull, although estimates at Skaftafellsjokull are precluded by limited basal ice exposure. Owing to their high debris contents, supercooling-related facies contribute a debris flux of 4.8 to 9.6 m3 m-1 a-1 at Svinafellsjokull (83% of the stratified facies debris flux). Other stratified subfacies, formed by non-supercooling processes, account for 58% of the stratified basal ice at Svinafellsjokull, but only contribute a debris flux of 1.0 to 2.0 m3 m-1 a-1 (17% of the stratified facies debris flux). We conclude that supercooling has a significant role in glacial sediment transfer, although in stratified basal ice formation its role is less significant at these locations than has been reported elsewhere.