Abstract
Abstract. Temperature sensors installed in a grid of nine full-depth boreholes drilled in the southwestern ablation zone of the Greenland Ice Sheet recorded cooling in discrete sections of ice over time within the lowest third of the ice column in most boreholes. Rates of temperature change outpace cooling expected from vertical conduction alone. Additionally, observed temperature profiles deviate significantly from the site-average thermal profile that is shaped by all thermomechanical processes upstream. These deviations imply recent, localized changes to the basal thermal state in the boreholes. 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 near-basal ice. Thermal decay after latent heat is released from freezing water in basal crevasses is the most likely mechanism resulting in the transient evolution of temperature and the vertical thermal structure observed at our site. We argue 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.
Highlights
Rates of ice deformation and the onset of basal sliding are regulated by the thermal regime of ice sheets (Hooke, 1981; Weertman, 1957), which makes ice temperature an important physical variable to be measured in the field and modeled to determine current and future ice motion
As ice moves from the central divide towards the margins, heat is conducted into the ice column from the surface and basal boundaries and is introduced through sources such as energy released by internal deformation and refreezing of meltwater (Cuffey and Paterson, 2010)
We are interested in the thermal behavior of ice in the region of a basal crevasse at times much longer than the crevasse remained open, so we model the crevasse as an instantaneous planar heat source, considering only the total latent heat released during the refreezing
Summary
Rates of ice deformation and the onset of basal sliding are regulated by the thermal regime of ice sheets (Hooke, 1981; Weertman, 1957), which makes ice temperature an important physical variable to be measured in the field and modeled to determine current and future ice motion. Mechanisms of heat transfer and heat sources in Greenland’s ablation zone have been investigated by comparing sparsely collected temperature profiles to output from thermomechanical models (e.g., Iken et al, 1993; Funk et al, 1994; Lüthi et al, 2002; Harrington et al, 2015; Lüthi et al, 2015; Poinar et al, 2017). Previous modeling and observational studies highlight the appreciable influence of refreezing meltwater as a source of latent heat in Greenland’s ablation zone (e.g., Phillips et al, 2013; Harrington et al, 2015; Lüthi et al, 2015; Poinar et al, 2017; Seguinot et al, 2020; Thomsen et al, 1991). Outside of Greenland, observations of englacial warming from latent heat sources have been demonstrated as early as the 1970s (Jarvis and Clarke, 1974)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
