Sub-permafrost methane seepage from open-system pingos in Svalbard

Hodson, Andrew J.; Nowak, Aga; Hornum, Mikkel T.; Senger, Kim; Redeker, Kelly; Christiansen, Hanne H.; Jessen, Søren; Betlem, Peter; Thornton, Steve F.; Turchyn, Alexandra V.; Olaussen, Snorre; Marca, Alina

doi:https://doi.org/10.5194/tc-14-3829-2020

Articles | Volume 14, issue 11

https://doi.org/10.5194/tc-14-3829-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/tc-14-3829-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 14, issue 11

Research article

|

09 Nov 2020

Research article |

| 09 Nov 2020

Sub-permafrost methane seepage from open-system pingos in Svalbard

Andrew J. Hodson, Aga Nowak, Mikkel T. Hornum, Kim Senger, Kelly Redeker, Hanne H. Christiansen, Søren Jessen, Peter Betlem, Steve F. Thornton, Alexandra V. Turchyn, Snorre Olaussen, and Alina Marca

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Final revised paper (published on 09 Nov 2020)
Preprint (discussion started on 03 Feb 2020)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'comments on Ms "pingos as hot spots of methane emissions"', Anonymous Referee #1, 18 Mar 2020
- AC1: 'Comments on ms by Referee 1', Andy Hodson, 30 Mar 2020
RC2: 'Comment on Hodson et al. "Open system pingos ..."', Anonymous Referee #2, 05 May 2020
- AC2: 'Comments on ms by Referee 2', Andy Hodson, 06 May 2020

Peer-review completion

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

ED: Publish subject to revisions (further review by editor and referees) (20 May 2020) by Peter Morse

AR by Andy Hodson on behalf of the Authors (09 Jul 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (30 Jul 2020) by Peter Morse

RR by Anonymous Referee #2 (05 Aug 2020)

Suggestions for revision or reasons for rejection

I thank the authors for their detailed response to my concerns and I have only one objection left after reading the revised version of the manuscript. Unfortunately, it is the main concern, which I also had with the original version of the manuscript. The authors have made a very interesting work under harsh conditions and present very valuable data on the origin and concentrations of methane in fluids of open system pingos. However, they have not presented enough data to calculate annual methane emissions from those pingos and an additional lake. They present about 25 data points of methane concentrations in five pingos and use these, together with data from an additional lake, not described in the manuscript, to calculate cumulative fluxes for a whole year using spring discharge measurements. It is unclear, how, when and how often these spring discharge measurements were done and how these relate to the presented methane concentrations. Still, a very large part of the discussion is about these very crude estimates, which are also used to support the final conclusion given in the abstract. I think, such a prominent presentation of these results is not justified considering the very sparse data these results are based on.

I still suggest the authors should either clearly explain that the annual methane flux estimates are only a simple back of the envelope calculation or present more data in the results section to substantiate these estimates. In this case, an error estimate of their calculated flux data should be included and it should be clearly explained how this was derived. In any case, the authors should explain how they calculated the discharge data presented in Tab. 3, how many measurements were done and how representative are these discharge data for the whole year. In Tab. 3, no attempt was done to include the uncertainty of the presented data. Hodson et al. (2019) e.g. shows in a detailed study on one of the pingos, also considered in this manuscript, a very high variability of methane emissions from this pingo during the year. I wonder how representative are four methane concentration data and an unfortunately unknown number of discharge data for the whole year methane discharge of this pingo? Which consequences does the variability of these fluxes have on the annual methane flux estimates?

Reference:

Hodson, A. J.; Nowak, A.; Redeker, K. R.; Holmlund, E. S.; Christiansen, H. H.; Turchyn, A. V., Seasonal Dynamics of Methane and Carbon Dioxide Evasion From an Open System Pingo: Lagoon Pingo, Svalbard. Frontiers in Earth Science 2019, 7, (30).

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RR by Anonymous Referee #1 (08 Sep 2020)

ED: Publish subject to minor revisions (review by editor) (09 Sep 2020) by Peter Morse

AR by Andy Hodson on behalf of the Authors (17 Sep 2020) Author's response Manuscript

ED: Publish subject to technical corrections (24 Sep 2020) by Peter Morse

AR by Andy Hodson on behalf of the Authors (30 Sep 2020) Manuscript

Short summary

Methane stored below permafrost is an unknown quantity in the Arctic greenhouse gas budget. In coastal areas with rising sea levels, much of the methane seeps into the sea and is removed before it reaches the atmosphere. However, where land uplift outpaces rising sea levels, the former seabed freezes, pressurising methane-rich groundwater beneath, which then escapes via permafrost seepages called pingos. We describe this mechanism and the origins of the methane discharging from Svalbard pingos.