Hydrologic monitoring of supercooled meltwater from Icelandic glaciers

Knowledge of how glaciers entrain sediment is central to understanding processes of glacier movement and products of glacial sediment deposition. Previous work has shown that if the total hydraulic potential of subglacial meltwater increases more rapidly than the resulting mechanical energy can be transformed into sensible heat, then supercooling and ice growth will result. This process causes frazil ice to grow onto adjacent glacier ice, which acts to trap sediment in flowing meltwater eventually producing sedimentary inclusions within glacier ice. Supercooling has been recognised as a sediment entrainment mechanism at glaciers in Alaska, and more recently at several temperate Icelandic glaciers. Here we present short-period temperature measurements and field evidence of glaciohydraulic supercooling from three Icelandic glaciers. Temperature measurements demonstrate that supercooling occurs over a range of hydrological conditions and that the process does not operate continuously at all instrumented sites. Measurements of supercooling during a small jökulhlaup are also presented. Progressive accretion of supercooled meltwater creates sediment-laden ice exposures adjacent to active artesian vents. Understanding controls on the efficacy and pervasiveness of hydraulic supercooling is important for decoding the sedimentary record of modern and ancient glaciers and ice sheets.