the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Using specularity content to evaluate five geothermal heat flux maps of Totten Glacier
Yan Huang
Liyun Zhao
Yiliang Ma
Michael Wolovick
John C. Moore
Abstract. Geothermal heat flux (GHF) is an important factor affecting the basal thermal environment of an ice sheet and crucial for its dynamics. But it is notoriously poorly defined for the Antarctic ice sheet. We compare basal thermal state of the Totten Glacier catchment as simulated by five different GHF datasets. We use a basal energy and water flow model coupled with a 3D full-Stokes ice dynamics model to estimate the basal temperature, basal friction heat and basal melting rate. In addition to the location of subglacial lakes, we use specularity content of the airborne radar returns as a two-sided constraint to discriminate between local wet or dry basal conditions and compare them with the basal state simulations with different GHF. Two medium magnitude GHF distribution maps derived from seismic modelling rank best at simulating both cold and warm bed regions well, the GHFs from Shen et al. (2020), and from Shapiro and Ritzwoller (2004). The best-fit simulated result shows that most of the inland bed area is frozen. Only the central inland subglacial canyon, co-located with high specularity content, reaches pressure-melting point consistently in all the five GHFs. Modelled basal melting rates there are generally 0–5 mm yr−1 but with local maxima of 10 mm yr−1. The fast-flowing grounded glaciers close to Totten ice shelf are lubricating their bases with melt water at rates of 10–400 mm yr−1.
Yan Huang et al.
Status: open (until 17 Jul 2023)
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CC1: 'Comment on tc-2023-58', Maximilian Lowe, 25 May 2023
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This paper evaluates different geothermal heat flux models and their influence on icesheet modelling, which is a crucial scientific question. Therefore, I wonder what the rational was for not considering the latest Antarctic geothermal heat flow models in this study? The latest open access continent wide geothermal heat flux models are:
Stål et al. (2021), G-Cubed https://doi.org/10.1029/2020GC009428
Lösing and Ebbing (2021), JGR Solid Earth, https://doi.org/10.1029/2020JB021499
Haeger et al. (2022), G-Cubed, https://doi.org/10.1029/2022GC010501
Furthermore, the manuscript misses citations for key review papers on Antarctica’s geothermal heat flow:
Reading et al. (2022), Nature Reviews Earth & Environment, https://doi.org/10.1038/s43017-022-00348-y
Burton-Johnson et al. (2020), The Cryosphere, https://doi.org/10.5194/tc-14-3843-2020
Citation: https://doi.org/10.5194/tc-2023-58-CC1 -
RC1: 'Comment on tc-2023-58', Anonymous Referee #1, 02 Jun 2023
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The paper takes a thoughtful approach to assess a collection of Geothermal Heat Flux (GHF) using two sets of radar sounding observations: the detection of subglacial lakes and bed echo specularity content. The authors rightly point out that “one-sided” tests using either observable will result in the selection of the highest GHF values. The authors are thoughtful about where they do and do not apply the specularity content in terms of upstream and downstream portions of the catchment. The authors are also thoughtful about the difference between how the lakes and specularity observations are used in terms of “one-sided” vs. “two-sided” constraint. However, the authors seem to view the choice as either a “one-sided” approach that only evaluates if the lakes/high-specularity correspond to thawed areas or a “two-sided” approach in which that comparison is combined with evaluation of “no lake”/low-specularity correspond to cold areas. However, it seems like there’s another option. To “reward” the match between lakes/high-specularity and thawed areas as in the “one-sided” and then to “penalize” a mismatch between lakes/high-specularity and cold areas. This seems like more than the “one-sided” approach and like it might not be vulnerable to the same preference for the highest meld as the pure “one-sided” approach. However, it also seems like it has the benefit of applying to both lakes and specularity. It has the additional benefit of allowing the specularity to be used in all regions of the catchment. This seems additionally important because, just as the authors describe for lakes, it’s not the case that low-specularity areas have to correspond to cold areas, it can correspond to thawed areas where water is not pooled in sufficient quantities to be specular and/or form a lake. As a result, this intermediate between “one-sided” and “two-sided” metrics could apply to both observables.
Citation: https://doi.org/10.5194/tc-2023-58-RC1
Yan Huang et al.
Yan Huang et al.
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