In situ measurements of meltwater flow through snow and firn in the accumulation zone of the SW Greenland Ice Sheet

Clerx, Nicole; Machguth, Horst; Tedstone, Andrew; Jullien, Nicolas; Wever, Nander; Weingartner, Rolf; Roessler, Ole

doi:https://doi.org/10.5194/egusphere-2022-71

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https://doi.org/10.5194/egusphere-2022-71

Preprints

13 Apr 2022

| 13 Apr 2022

In situ measurements of meltwater flow through snow and firn in the accumulation zone of the SW Greenland Ice Sheet

Nicole Clerx, Horst Machguth, Andrew Tedstone, Nicolas Jullien, Nander Wever, Rolf Weingartner, and Ole Roessler

Abstract. The Greenland Ice Sheet is losing mass, part of which is caused by increasing runoff. The location of the runoff limit, the highest elevation from which meltwater finds its way off the ice sheet, plays an important role in the surface mass balance of the ice sheet. The recently observed rise in runoff area might be related to an increasing amount of refreezing: ice layer development in the firn hinders vertical percolation and promotes lateral runoff. To investigate meltwater flow near the runoff limit in the accumulation zone on the southwest Greenland Ice Sheet, we carried out in situ measurements of hydrological processes and properties of firn and snow. The hydraulic conductivity of icy firn in pre-melt conditions measured using a portable lysimeter ranges from 0.17 to 12.8 m hr^-1, with flow predominantly occurring through preferential flow fingers. Lateral flow velocities of meltwater on top of the near-surface ice slab at the peak of the melt season measured by salt dilution- and tracer experiments range from 1.3 to 15.1 m hr^-1. With these lateral flow velocities the distance between the slush limit, the highest elevation where liquid water is visible on the ice sheet surface, and the runoff limit could be up to 4 km in regions where near-surface ice slabs are present. These measurements are a first step towards an integrated set of hydrological properties of firn on the SW Greenland Ice Sheet, and show evidence that meltwater runoff might occur from elevations above the visible runoff area.

Received: 18 Mar 2022 – Discussion started: 13 Apr 2022

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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.

Journal article(s) based on this preprint

19 Oct 2022

In situ measurements of meltwater flow through snow and firn in the accumulation zone of the SW Greenland Ice Sheet

Nicole Clerx, Horst Machguth, Andrew Tedstone, Nicolas Jullien, Nander Wever, Rolf Weingartner, and Ole Roessler

The Cryosphere, 16, 4379–4401, https://doi.org/10.5194/tc-16-4379-2022,https://doi.org/10.5194/tc-16-4379-2022, 2022

Short summary

Nicole Clerx et al.

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2022-71', Sergey Marchenko, 15 May 2022

See comments in the enclosed file.

Citation: https://doi.org/10.5194/egusphere-2022-71-RC1
- AC1: 'Reply on RC1', Nicole Clerx, 24 Jun 2022
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-71/egusphere-2022-71-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2022-71-AC1
RC2:
'Comment on egusphere-2022-71', Anonymous Referee #2, 19 May 2022

Please see attached review.

Citation: https://doi.org/10.5194/egusphere-2022-71-RC2
- AC2: 'Reply on RC2', Nicole Clerx, 24 Jun 2022
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-71/egusphere-2022-71-AC2-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2022-71-AC2

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2022-71', Sergey Marchenko, 15 May 2022

See comments in the enclosed file.

Citation: https://doi.org/10.5194/egusphere-2022-71-RC1
- AC1: 'Reply on RC1', Nicole Clerx, 24 Jun 2022
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-71/egusphere-2022-71-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2022-71-AC1
RC2:
'Comment on egusphere-2022-71', Anonymous Referee #2, 19 May 2022

Please see attached review.

Citation: https://doi.org/10.5194/egusphere-2022-71-RC2
- AC2: 'Reply on RC2', Nicole Clerx, 24 Jun 2022
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-71/egusphere-2022-71-AC2-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2022-71-AC2

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

ED: Publish subject to revisions (further review by editor and referees) (05 Jul 2022) by Kristin Poinar

AR by Nicole Clerx on behalf of the Authors (07 Aug 2022) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (09 Aug 2022) by Kristin Poinar

RR by Anonymous Referee #2 (26 Aug 2022)

RR by Sergey Marchenko (01 Sep 2022)

ED: Publish subject to revisions (further review by editor and referees) (07 Sep 2022) by Kristin Poinar

AR by Nicole Clerx on behalf of the Authors (07 Sep 2022) Author's response Author's tracked changes Manuscript

ED: Publish subject to minor revisions (review by editor) (16 Sep 2022) by Kristin Poinar

Dear Nicole Clerx and co-authors,

Thank you for your response to reviewers and corresponding revisions to your manuscript. I find it nearly ready to go, but I have a few suggestions to better incorporate the insights of Reviewer #1 to your manuscript. Given the state of our understanding and capability of observing meltwater flow through firn, I judge that the caveats pointed out by Reviewer #1 give valuable context to your measurements and findings, and should be incorporated into the manuscript itself (briefly is fine), rather than addressed solely in the review files, which will be publicly available but relatively buried to readers.

All of the line numbers below refer to the differenced version of your manuscript (ATC2).

A. line 253 "could be a lot higher" -- please provide an estimate (a rough estimate is okay) in place of "a lot".

B. line 335 -- Reviewer 1 commented that the timing is biased low, as the authors used time of first arrival, rather than time of peak concentration through. In their response, the authors pointed out that they did not measure concentrations (it was not possible with the methods/equipment they had), so the peak time could not be discerned. Nevertheless, the authors should comment on this timing bias —- it means their velocities are biased high. Comment here or in the discussion how this compounds or offsets other sources of error.

C. Reviewer 1 points out that the datum for the water table is the ice slab surface, which can undulate locally and is not likely to be level or even flat. The authors should comment on this -- probably in the discussion (lines 466-7), or alternately lines 307-8, where the water table measurement method is described, or lines 386-8. Because the authors are concluding no correlation between the local water table height and lateral flow velocity (stated on line 466), these undulations may well matter, and should be addressed.

D. Table 2 - unsaturated has no quotes, while 'saturated' has quotes. Why? Suggest to choose a style and apply to both for consistency.

With the above additions, I will be happy to see this work in The Cryosphere. I believe it will be a worthy contribution to the community's ongoing effort in the important problem to better quantify meltwater flow through firn. Thank you again for your work and attention to addressing the reviewers' comments.

Cheers,
Kristin Poinar

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AR by Nicole Clerx on behalf of the Authors (20 Sep 2022) Author's response Author's tracked changes Manuscript

ED: Publish as is (20 Sep 2022) by Kristin Poinar

AR by Nicole Clerx on behalf of the Authors (28 Sep 2022)

Journal article(s) based on this preprint

19 Oct 2022

In situ measurements of meltwater flow through snow and firn in the accumulation zone of the SW Greenland Ice Sheet

Nicole Clerx, Horst Machguth, Andrew Tedstone, Nicolas Jullien, Nander Wever, Rolf Weingartner, and Ole Roessler

The Cryosphere, 16, 4379–4401, https://doi.org/10.5194/tc-16-4379-2022,https://doi.org/10.5194/tc-16-4379-2022, 2022

Short summary

Nicole Clerx et al.

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Short summary

Meltwater runoff is one of the main contributors to mass loss on the Greenland Ice Sheet that influences global sea level rise. However, it remains unclear where meltwater runs off and what processes cause this. We measured the velocity of meltwater flow through snow on the ice sheet, which ranged from 0.17 to 12.8 m hr^-1 for vertical percolation and from 1.3 to 15.1 m hr^-1 for lateral flow. This is an important step towards understanding where, when and why meltwater runoff occurs on the ice sheet.


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