Book excerpt: The vertical temperature structure of ice in Greenland’s ablation zone is influenced and modified by variable surface and basal boundary conditions and englacial heat sources as ice moves from the central ice divide to the margin. Numerous heat sources exist that warm the ice as it moves from the central divide towards the margin, such as strain heat from internal deformation, latent heat from refreezing meltwater, the conduction of geothermal heat across the ice-bedrock interface. However, other than conduction of heat into the cold central core of the vertical ice column, mechanisms that serve as heat sinks and allow the ice to cool as it moves towards the margins remain difficult to identify. Nine boreholes drilled in the southwestern ablation zone of the Greenland Ice Sheet were instrumented with digital temperature sensors, which recorded full-depth ice temperature between July 2014 and July 2017. We examine the temporal evolution of ice temperatures to better constrain mechanisms of heat transfer at our field location. All boreholes cool near the bed, with most cooling occurring in the lowest third of the ice column. After eliminating possible mechanisms that could result in cooling in ice with the thermal structure observed at our field site, we suggest that basal crevasses are likely features that produce the temporal trends and temperature profile shapes found in the data. This work indicates that basal crevasses alter the thermal structure of ice in Greenland’s ablation zone and may influence the growth of basal temperate ice layers.