Greenland and Canadian Arctic ice temperature profiles

Løkkegaard, Anja; Mankoff, Kenneth D.; Zdanowicz, Christian; Clow, Gary D.; Lüthi, Martin P.; Doyle, Samuel; Thomsen, Henrik S.; Fisher, David E.; Harper, Joel T.; Aschwanden, Andy; Vinther, Bo M.; Dahl‐Jensen, Dorthe; Zekollari, Harry; Meierbachtol, Toby; McDowell, Ian; Humphrey, Neil; Solgaard, Anne; Karlsson, Nanna B.; Khan, Shfaqat Abbas; Hills, Benjamin H.; Law, Robert; Hubbard, Bryn; Christoffersen, Poul; Jacquemart, Mylène; Fausto, Robert S.; Colgan, William

doi:10.5194/tc-2022-138

Cited by 3 publications

(5 citation statements)

References 55 publications

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“…In order to verify local GHF structures, local information such as magnetic data or radar data should be included in the calculation in addition to more direct GHF observations such as the not yet published EastGRIP point. Furthermore, heat flow modelling could be improved by including the temperature at the top of the bedrock, derived by ice temperature profiles from Yardim et al (2021) and Løkkegaard et al (2022). Using the different HF maps in connection with the ice temperature profiles within the 1D stationary HF equation could provide information on the reliability of the HF maps.…”

Section: Discussionmentioning

confidence: 99%

Statistical Appraisal of Geothermal Heat Flow Observations in the Arctic

Freienstein,

Szwillus,

Wansing

et al. 2023

Preprint

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Abstract. Geothermal heat flow is an important boundary condition for ice sheet, affecting for example basal melt rates, but for ice covered regions we only have sparse heat flow observations with partly high uncertainty. In this study, we first investigate the agreement between such point-wise heat flow observations and Solid Earth models, applying a 1D steady state approach to perform a statistical analysis for the entire Arctic region. We find that most of the continental heat flow observations have a high reliability and agreement to Solid Earth models, except a few data points, as for example the NGRIP point in Central Greenland. For further testing, we perform a conditional simulation with focus on Greenland, in which the local characteristics of heat flow structures can be considered. Simple kriging shows that including or excluding the less reliable NGRIP point has a large influence on the surrounding heat flow. The geostatistical analysis with the conditional simulation supports the assumption that NGRIP might not only be problematic for representing a regional feature but likely is an outlier. Basal melt estimates show that such a local spot of high heat flow results in local high basal melt rates, but leads to less variation than existing geophysical models.

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Section: Discussionmentioning

confidence: 99%

Statistical Appraisal of Geothermal Heat Flow Observations in the Arctic

Freienstein,

Szwillus,

Wansing

et al. 2023

Preprint

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“…Strain rates and stresses are calculated from long term average ice velocities. This may not accurately reflect the conditions under which crevasses were formed since trends or seasonal variability in ice flow are unaccounted for (Grinsted et al, 2022;Solgaard et al, 2022) (elaborated on below). We therefore separately examine onset regions with steady flow, defined as fulfilling V peak /V winter < 2 and v < 2 m a −2 .…”

Section: Regions Of Interestmentioning

confidence: 99%

“…It is, however, not clear whether this model is accurate, and there will likely be regional biases in the modelled temperature. Further, ice temperatures at depth may deviate from surface temperatures due to advection and redistribution of energy via melt and refreezing (Løkkegaard et al, 2022). We gauge the sensitivity of our stress estimates to temperature by calculating (A(T 1 )/A(T 2 )) 1/n (see eqn.…”

Section: Uncertaintiesmentioning

confidence: 99%

“…Understanding the mechanics of ice fracture is important for predicting the stability of ice sheets and glaciers, since fractures lead to crevassing, calving, and moulins (Colgan et al, 2016): calving is a major component of the mass budget of ice sheets and a potential source of rapid unstable retreat; crevassed and damaged ice is expected to flow more readily (Borstad et al, 2013;MacAyeal et al, 1986;Albrecht and Levermann, 2014;Sun et al, 2017b); moulins couple basal conditions to surface conditions (Das et al, 2008) by channeling warmer surface melt water through the englacial system and potentially accelerating rates of ice loss (cryohydrologic warming; e.g. Phillips et al (2010);Solgaard et al (2022)). Yet in spite of the broad literature on glacier ice, important material properties that constrain ice fracturing remain under-studied.…”

Section: Introductionmentioning

confidence: 99%

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Failure strength of glacier ice inferred from Greenland crevasses

Grinsted,

Rathmann,

Mottram

et al. 2023

Preprint

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Abstract. Ice fractures when subject to stress that exceeds the material failure strength. Previous studies have found that a von Mises failure criterion, which places a bound on the second invariant of the deviatoric stress tensor, is consistent with empirical data. Other studies have suggested that a scaling effect exists, such that larger sample specimens have a substantially lower failure strength, implying that estimating material strength from laboratory-scale experiments may be insufficient for glacier-scale modelling. In this paper, we analyze the stress conditions in crevasse onset regions to better understand the failure criterion and strength relevant for large-scale modelling. The local deviatoric stress is inferred using surface velocities and reanalysis temperatures, and crevasse onset regions are extracted from a remotely sensed crevasse density map. We project the stress state onto the failure plane spanned by Haigh–Westergaard coordinates, showing how failure depends on mode of stress. We find that existing crevasse data is consistent with a Schmidt–Ishlinsky failure criterion that places a bound on the absolute value of the maximal principal deviatoric stress, estimated to be (158 ± 44) kPa. Although the traditional von Mises failure criterion also provides an adequate fit to the data with a von Mises strength of (265 ± 73) kPa, it depends only on stress magnitude and is indifferent to the specific stress state, unlike Schmidt–Ishlinsky failure which has a larger shear failure strength compared to tensile strength. Implications for large-scale ice-flow and fracture modelling are discussed.

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“…While many boreholes have been drilled around the icesheet periphery, basal temperature and geothermal heat flow have only been directly sampled in the ice-sheet interior at six sites in the last 6 decades (Løkkegaard et al, 2022). These six sites denote the locations of the deep Greenland ice cores: Camp Century (1966), DYE-3 (1981), GISP2 (1993), GRIP (1998), NGRIP (2003), andNEEM (2010).…”

Section: Introductionmentioning

confidence: 99%

Design and performance of the Hotrod melt-tip ice-drilling system

Colgan

Shields

Тalalay

et al. 2023

Geosci. Instrum. Method. Data Syst.

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Abstract. We introduce the design and performance of an electrothermal ice-drilling system designed to insert a temperature sensor cable into ice. The melt tip is relatively simple and low-cost, designed for a one-way trip to the ice–bed interface. The drilling system consists of a melt tip, umbilical cable, winch, interface, power supply, and support items. The melt tip and the winch are the most novel elements of the drilling system, and we make the hardware and electrical designs of these components available open-access. Tests conducted in a laboratory indicate that the melt tip has an electrical energy to forward melting heat transfer efficiency of ∼35 % with a theoretical maximum penetration rate of ∼12 m h−1at maximum 6.0 kW power. In contrast, ice-sheet testing suggests the melt tip has an analogous heat transfer efficiency of ∼15 % with a theoretical maximum penetration rate of ∼6 m h−1. We expect the efficiency gap between laboratory and field performance to decrease with increasing operator experience. Umbilical freeze-in due to borehole refreezing is the primary depth-limiting factor of the drilling system. Enthalpy-based borehole refreezing assessments predict refreezing below critical umbilical diameter in ∼4 h at −20 ∘C ice temperatures and ∼20 h at −2 ∘C. This corresponds to a theoretical depth limit of up to ∼200 m, depending on firn thickness, ice temperature, and operator experience.

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Greenland and Canadian Arctic ice temperature profiles

Cited by 3 publications

References 55 publications

Statistical Appraisal of Geothermal Heat Flow Observations in the Arctic

Statistical Appraisal of Geothermal Heat Flow Observations in the Arctic

Failure strength of glacier ice inferred from Greenland crevasses

Design and performance of the Hotrod melt-tip ice-drilling system

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