Modelling the transfer of supraglacial meltwater to the bed of Leverett Glacier, Southwest Greenland

Clason, C. C.; Mair, D. W. F.; Nienow, P. W.; Bartholomew, I. D.; Sole, A.; Palmer, S.; Schwanghart, W.

doi:https://doi.org/10.5194/tc-9-123-2015

Articles | Volume 9, issue 1

https://doi.org/10.5194/tc-9-123-2015

© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/tc-9-123-2015

© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 9, issue 1

Research article

|

22 Jan 2015

Research article |

| 22 Jan 2015

Modelling the transfer of supraglacial meltwater to the bed of Leverett Glacier, Southwest Greenland

C. C. Clason, D. W. F. Mair, P. W. Nienow, I. D. Bartholomew, A. Sole, S. Palmer, and W. Schwanghart

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Final revised paper (published on 22 Jan 2015)
Preprint (discussion started on 29 Jul 2014)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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SC C1444: 'Flow law parameter A', Martin Lüthi, 30 Jul 2014
- SC C1454: 'Interactive comment on “Modelling the transfer of supraglacial meltwater to the bed of Leverett Glacier, southwest Greenland” by C. C. Clason et al.', Caroline Clason, 31 Jul 2014
SC C1506: 'Recent article', Neil Arnold, 11 Aug 2014
RC C1705: 'Review of “Modelling the transfer of supraglacial meltwater to the bed of Leverett Glacier, southwest Greenland”', Anonymous Referee #1, 04 Sep 2014
RC C2151: 'Review of `Modelling the transfer of supraglacial meltwater to the bed of Leverett Glacier, southwest Greenland' by Clason et al.', Anonymous Referee #2, 25 Oct 2014
AC C2353: 'Response from the authors to anonymous referees 1 and 2', Caroline Clason, 17 Nov 2014

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by Caroline Clason on behalf of the Authors (17 Nov 2014) Author's response Manuscript

ED: Referee Nomination & Report Request started (22 Nov 2014) by G. Hilmar Gudmundsson

RR by Anonymous Referee #1 (05 Dec 2014)

Suggestions for revision or reasons for rejection

---General Comments---

The revised paper “Modelling the transfer of supraglacial meltwater to the bed of Leverett Glacier, southwest Greenland” by Clason, et al. has addressed most of the issues raised in my initial review.

One of my two primary concerns was the lack of a control simulation; this has been added and I think it contributes strongly to the paper. The increasing importance of the englacial/routing model at higher elevations is clear from the revised Figure 8. I think this is an important finding of the paper and it gives future researchers a guide to where including these processes is critical and where it might safely be ignored. I might even suggest the authors consider mentioning this in the abstract. For example, the sentence at p11/22-24 could be modified like “At these higher elevations, the delay between modelled melt generation and subsequent delivery of melt to the bed matches the observed delay between the peak air temperatures and subsequent velocity speed ups”… “while the instantaneous transfer of melt to the bed in a control simulation does not.”

My other primary concern was regarding the prescription of supraglacial lake locations. The authors have adjusted the text to make this point more obvious and acknowledged its limitations. In their response they have also pointed out the fact that though lake locations are prescribed, the drainage of those lakes is not. They have also added a qualitative description of validation of the timing of lake drainage by comparing model results to MODIS observations by Bartholomew et al. (2011). As this is a valuable validation for this component of the model, it would more fully address this issue to include a quantitative figure in addition to the general description, if possible. If it is possible to get the data for lake drainage timing/volume/elevation from Figure 2a in Bartholomew et al. (2011) (which seems likely given the authorship of the two papers), that could simply be overlaid on the modeled version of lake drainages shown in Figure 3a.

I had also made a point that it would be nice to see more information about the calibration of tensile strength to the distribution of visual surface crevassing on satellite imagery. The sentence the authors added to Appendix A is pretty vague. I still think it would be valuable to include a figure showing the spatial overlap of regions where surface tensile stress exceeds the chosen tensile strength and where surface crevassing was mapped from imagery. This could logically be a Figure 2b, or alternatively, this information could be conveyed as overlaid histograms of calculated surface stress for cells where crevassing was mapped and cells where it was not. I’d expect a lot of overlap between the two distributions, but I’d also hope to see a clear separation of the modes of the two distributions. Given this is calibration of an important model parameter, I think a somewhat more rigorous presentation is warranted. Additionally, the relationship between surface crevassing and tensile strength in real glaciers and ice sheets is a worthwhile topic that has received limited attention (e.g., Catania et al., 2008), and the authors could clearly make a contribution here.

---Other Specific Science Comments and Technical Corrections---

p21/9: Should this be figure 4a instead of 3a?

p24/16: The very recent paper by Andrews et al. (2014) strongly supports the assertion here that in the mid-ablation zone there will be “considerable heterogeneity in subglacial drainage system evolution.”

---References Cited---
Andrews, L. C., Catania, G. A., Hoffman, M. J., Gulley, J. D., Lüthi, M. P., Ryser, C., Hawley, R. L. and Neumann, T. A.: Direct observations of evolving subglacial drainage beneath the Greenland Ice Sheet, Nature, 514(7520), 80–83, doi:10.1038/nature13796, 2014.
Bartholomew, I., Nienow, P., Sole, A., Mair, D., Cowton, T., Palmer, S. and Wadham, J.: Supraglacial forcing of subglacial drainage in the ablation zone of the Greenland ice sheet, Geophys. Res. Lett., 38(8), n/a–n/a, doi:10.1029/2011GL047063, 2011.
Catania, G. A., Neumann, T. A. and Price, S. F.: Characterizing englacial drainage in the ablation zone of the Greenland ice sheet, J. Glaciol., 54(187), 567–578, 2008.

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ED: Publish subject to minor revisions (Editor review) (09 Dec 2014) by G. Hilmar Gudmundsson

AR by Caroline Clason on behalf of the Authors (12 Dec 2014) Author's response Manuscript

ED: Publish as is (24 Dec 2014) by G. Hilmar Gudmundsson