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Volume 12, issue 10 | Copyright
The Cryosphere, 12, 3215-3227, 2018
https://doi.org/10.5194/tc-12-3215-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 08 Oct 2018

Research article | 08 Oct 2018

Processes influencing heat transfer in the near-surface ice of Greenland's ablation zone

Benjamin H. Hills1,2, Joel T. Harper2, Toby W. Meierbachtol2, Jesse V. Johnson3, Neil F. Humphrey4, and Patrick J. Wright5,2 Benjamin H. Hills et al.
  • 1Department of Earth and Space Sciences, University of Washington, Seattle, Washington, USA
  • 2Department of Geosciences, University of Montana, Missoula, Montana, USA
  • 3Department of Computer Science, University of Montana, Missoula, Montana, USA
  • 4Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming, USA
  • 5Inversion Labs LLC, Wilson, Wyoming, USA

Abstract. To assess the influence of various heat transfer processes on the thermal structure of near-surface ice in Greenland's ablation zone, we compare in situ measurements with thermal modeling experiments. A total of seven temperature strings were installed at three different field sites, each with between 17 and 32 sensors and extending up to 21m below the ice surface. In one string, temperatures were measured every 30min, and the record is continuous for more than 3 years. We use these measured ice temperatures to constrain our modeling experiments, focusing on four isolated processes and assessing the relative importance of each for the near-surface ice temperature: (1) the moving boundary of an ablating surface, (2) thermal insulation by snow, (3) radiative energy input, and (4) subsurface ice temperature gradients below the seasonally active near-surface layer. In addition to these four processes, transient heating events were observed in two of the temperature strings. Despite no observations of meltwater pathways to the subsurface, these heating events are likely the refreezing of liquid water below 5–10m of cold ice. Together with subsurface refreezing, the five heat transfer mechanisms presented here account for measured differences of up to 3°C between the mean annual air temperature and the ice temperature at the depth where annual temperature variability is dissipated. Thus, in Greenland's ablation zone, the mean annual air temperature is not a reliable predictor of the near-surface ice temperature, as is commonly assumed.

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At its surface, an ice sheet is closely connected to the climate. Assessing heat transfer between near-surface ice and the overlying atmosphere is important for understanding how the ice sheet is melting at the surface. We measured ice temperature within 20 m of the surface of the Greenland Ice Sheet. Resulting ice temperatures are warmer than the air, a peculiar result which implies the role of some nonconductive heat transfer processes such as latent heating by refreezing meltwater.
At its surface, an ice sheet is closely connected to the climate. Assessing heat transfer...
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