Preprints
https://doi.org/10.5194/tc-2021-179
https://doi.org/10.5194/tc-2021-179

  28 Jun 2021

28 Jun 2021

Review status: this preprint is currently under review for the journal TC.

Variability of Basal Meltwater Generation During Winter, Western Greenland Ice Sheet

Joel Harper1, Toby Meierbachtol1, Neil Humphrey2, Jun Saito2, and Aidan Stansberry2 Joel Harper et al.
  • 1Department of Geosciences, Univ. of Montana, Missoula, MT 59812, U.S.A.
  • 2Geology and Geophysics, Univ. of Wyoming, Laramie, Wyoming 82071, U.S.A.

Abstract. Basal sliding in the ablation zone of the Greenland Ice Sheet is closely associated with water from surface melt introduced to the bed in summer, yet melting of basal ice also generates subglacial water year-round. Assessments of basal melt rely on modelling with results strongly dependent upon assumptions with poor observational constraint. Here we use surface and borehole measurements to investigate the generation and fate of basal meltwater in the ablation zone of Isunnguata Sermia basin, Western Greenland. The observational data are used to constrain estimates of the heat and water balances, providing insights into subglacial hydrology during the winter months when surface melt is minimal or non-existent. Despite relatively slow ice flow speeds during winter, the basal meltwater generation from sliding friction remains many fold greater than that due to geothermal heat flux. A steady acceleration of ice flow over the winter period at our borehole sites can cause the rate of basal water generation to increase by up to 20 %. Borehole measurements show high but steady basal water pressure, rather than monotonically increasing pressure. Ice and groundwater sinks for water do not likely have sufficient capacity to accommodate the meltwater generated in winter. Analysis of basal cavity dynamics suggests that cavity opening associated with flow acceleration likely accommodates only a portion of the basal meltwater, implying a residual is routed to the terminus through a poorly connected drainage system. A forcing from cavity expansion at high pressure may explain observations of winter acceleration in Western Greenland.

Joel Harper et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on tc-2021-179', Martin Lüthi, 21 Jul 2021
    • AC1: 'Reply on RC1', Joel Harper, 25 Aug 2021
  • RC2: 'Comment on tc-2021-179', Samuel Doyle, 05 Aug 2021

Joel Harper et al.

Joel Harper et al.

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Short summary
We use surface and borehole measurements to investigate the generation and fate of basal meltwater in the ablation zone of Western Greenland. The rate of basal meltwater generation at borehole study sites increases by up to 20 % over the winter period. Accommodation of all basal meltwater by expansion of isolated subglacial cavities is implausible. Other sinks for water do not likely balance basal meltwater generation, implying water evacuation through a connected drainage system in winter.