The cooling signature of basal crevasses in a hard-bedded region of the Greenland Ice Sheet

Abstract. Temperature sensors installed in a grid of 9 full-depth boreholes drilled in the southwestern ablation zone of the Greenland Ice Sheet consistently record cooling over time within the lowest third of the ice column. Rates of temperature change outpace cooling expected from vertical conduction alone. Additionally, observed static temperature profiles deviate significantly from modeled purely diffusional thermal profiles, implying strong non-conductive heat transfer processes within the lowest portion of the ice column. Although numerous heat sources exist to add energy and warm ice as it moves from the central divide towards the margin such as strain heat from internal deformation, latent heat from refreezing meltwater, and the conduction of geothermal heat across the ice-bedrock interface, identifying heat sinks proves more difficult. After eliminating possible mechanisms that could cause cooling, we find that the observed cooling is a manifestation of previous warming in basal ice. Thermal decay after latent heat is released from freezing water in basal crevasses is the most likely mechanism resulting in the temporal evolution of temperature and the vertical thermal structure observed at our site. Basal crevasses are a viable englacial heat source in the basal ice of Greenland's ablation zone and may have a controlling influence on the temperature structure of the near basal ice.