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

McDowell, Ian; Humphrey, N. F.; Harper, Joel T.; Meierbachtol, Toby

doi:10.5194/tc-15-897-2021

Cited by 7 publications

(13 citation statements)

References 40 publications

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“…These sites are limited to western Greenland, where abundant surface meltwater is available (Iken and others, 1993; Harrington and others, 2015; Lüthi and others, 2015). Temperate ice thickness extending upward from the bed within an ice-stream shear margin could also result from upward heat transfer by meltwater infiltration through basal crevasses (McDowell and others, 2021), a process which is not included in our numerical model. This is a different mechanism than suggested by previous studies, which have indicated the possibility of significant temperate ice from strain heating.…”

Section: Discussionmentioning

confidence: 99%

Radar attenuation demonstrates advective cooling in the Siple Coast ice streams

et al. 2022

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Ice streams are warmed by shear strain, both vertical shear near the bed and lateral shear at the margins. Warm ice deforms more easily, establishing a positive feedback loop in an ice stream where fast flow leads to warm ice and then to even faster flow. Here, we use radar attenuation measurements to show that the Siple Coast ice streams are colder than previously thought, which we hypothesize is due to along-flow advection of cold ice from upstream. We interpret the attenuation results within the context of previous ice-temperature measurements from nearby sites where hot-water boreholes were drilled. These in-situ temperatures are notably colder than model predictions, both in the ice streams and in an ice-stream shear margin. We then model ice temperature using a 1.5-dimensional numerical model which includes a parameterization for along-flow advection. Compared to analytical solutions, we find depth-averaged temperatures that are colder by 0.7°C in the Bindschadler Ice Stream, 2.7°C in the Kamb Ice Stream and 6.2–8.2°C in the Dragon Shear Margin of Whillans Ice Stream, closer to the borehole measurements at all locations. Modelled cooling corresponds to shear-margin thermal strengthening by 3–3.5 times compared to the warm-ice case, which must be compensated by some other weakening mechanism such as material damage or ice-crystal fabric anisotropy.

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Section: Discussionmentioning

confidence: 99%

Radar attenuation demonstrates advective cooling in the Siple Coast ice streams

et al. 2022

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“…Injection of water-filled basal crevasses can locally modify the thermal profile of the ice sheet (Luckman and others, 2012) and is a potential explanation of the spatially-varying temperate ice layer. The thermal structure of basal crevassing, which is similar to that of dykes in rock (Daniels and others, 2014), has been modelled in several studies (Jarvis and Clarke, 1974; McDowell and others, 2021). Their approach recognises that water-filled basal crevasses in sub-temperate ice propagate on a short timescale, followed by rapid refreezing of water inside the crack.…”

Section: Discussionmentioning

confidence: 99%

Basal hydrofractures near sticky patches

et al. 2022

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Basal crevasses are macroscopic structural discontinuities at the base of ice sheets and glaciers that arise by fracture. Motivated by observations and by the mechanics of elastic fracture, we hypothesise that spatial variations in basal stress (in the presence of basal water pressure) can promote and localise basal crevassing. We quantify this process in the theoretical context of linear elastic fracture mechanics. We develop a model evaluating the effect of shear-stress variation on the growth of basal crevasses. Our results indicate that sticky patches promote the propagation of basal crevasses, increase their length of propagation into the ice and, under some conditions, give them curved trajectories that incline upstream. A detailed exploration of the parameter space is conducted to gain a better understanding of the conditions under which sticky-patch-induced basal crevassing is expected beneath ice sheets and glaciers.

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“…See Figure 1 Overall, 61 of the 85 profiles were available as tabulated temperature measurements (Heuberger, 1954;Classen, 1977;Stauffer and Oeschger, 1979;Clarke et al, 1987;Thomsen et al, 1991;Iken et al, 1993;Hansson, 1994;Cuffey et al, 1995;Thomsen et al, 1996;Cuffey and Clow, 1997;Dahl-Jensen et al, 1998;Fischer et al, 1998;Lüthi et al, 2002;Kinnard et al, 2006;Buchardt and Dahl-Jensen, 2007;Kinnard et al, 2008;Lemark and Dahl-Jensen, 2010;Rasmussen et al, 2013;Ryser et al, 2014;Harrington et al, 2015;Hills et al, 2017;Zekollari et al, 2017;Doyle et al, 2018b;Hubbard et al, 2021a;Harper and Meierbachtol, 2021;Law et al, 2021). The remaining 24 profiles were digitized from figures (Hansen and Landauer, 1958;Davis, 1967;Paterson, 1968;Classen, 1977;Paterson et al, 1977;Colbeck and Gow, 1979;Gundestrup and Hansen, 1984;Blatter and Kappenberger, 1988;Gundestrup et al, 1993).…”

Section: Methodsmentioning

confidence: 99%

“…This thermal disturbance of hot-water drilling often requires many months to fully dissipate, as the latent energy released by the refreezing borehole warms surrounding ice. Empirical cooling curves of temperature measurements collected multiple times post drilling can usually constrain this thermal disturbance effect to better than ±0.1°C (Humphrey and Echelmeyer, 1990;Ryser et al, 2014;McDowell et al, 2021).…”

Section: Sources Of Uncertaintymentioning

confidence: 99%

“…Several process-level studies of potential heat sources have been performed, which compare individual observed temperature profiles from local areas with temperature profiles modeled by a thermal, or themo-mechanical, ice flow model (Iken et al, 1993;Lüthi et al, 2002;Harrington et al, 2015;Lüthi et al, 2015;Meierbachtol et al, 2015;McDowell et al, 2021;Law et al, 2021;Maguire et al, 2021). Although these studies featured different local areas, the comparisons generally showed that models tend to underestimate englacial temperatures, and thus need to incorporate additional heat sources in order to reproduce observed ice temperature profiles.…”

Section: Sources Of Uncertaintymentioning

confidence: 99%

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Greenland and Canadian Arctic ice temperature profiles

Løkkegaard

Mankoff²,

Zdanowicz³

et al. 2022

Preprint

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Abstract. Here, we present a compilation of 85 ice temperature profiles from 79 boreholes from the Greenland Ice Sheet and peripheral ice caps, as well as local ice caps in the Canadian Arctic. Only 25 profiles (32 %) were previously available in open-access data repositories. The remaining 54 profiles (68 %) are being made digitally available here for the first time. These newly available profiles, which are associated with pre-2010 boreholes, have been submitted by community members or digitized from published graphics and/or data tables. All 85 profiles are now made available in both absolute (meters) and normalized (0 to 1 ice thickness) depth scales, and are accompanied by extensive metadata. This metadata includes a transparent description of data provenance. The ice temperature profiles span 70 years, with the earliest profile being from 1950 at Camp VI, West Greenland. To highlight the value of this database in evaluating ice flow simulations, we compare the ice temperature profiles from the Greenland Ice Sheet with an ice flow simulation by the Parallel Ice Sheet Model (PISM). We find a cold bias in modeled near-surface ice temperatures within the ablation area, a warm bias in modeled basal ice temperatures at inland cold-bedded sites, and an apparent underestimation of deformational heating in high-strain settings. These biases provide process-level insight on simulated ice temperatures.

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

Cited by 7 publications

References 40 publications

Radar attenuation demonstrates advective cooling in the Siple Coast ice streams

Radar attenuation demonstrates advective cooling in the Siple Coast ice streams

Basal hydrofractures near sticky patches

Greenland and Canadian Arctic ice temperature profiles

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