Ground ice, organic carbon and soluble cations in tundra permafrost soils and sediments near a Laurentide ice  divide in the Slave Geological Province,  Northwest Territories, Canada

Subedi, Rupesh; Kokelj, Steven V.; Gruber, Stephan

doi:https://doi.org/10.5194/tc-14-4341-2020

Articles | Volume 14, issue 12

https://doi.org/10.5194/tc-14-4341-2020

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

https://doi.org/10.5194/tc-14-4341-2020

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

Articles | Volume 14, issue 12

Research article

|

02 Dec 2020

Research article |

| 02 Dec 2020

Ground ice, organic carbon and soluble cations in tundra permafrost soils and sediments near a Laurentide ice divide in the Slave Geological Province, Northwest Territories, Canada

Rupesh Subedi, Steven V. Kokelj, and Stephan Gruber

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Final revised paper (published on 02 Dec 2020)
Supplement to the final revised paper
Preprint (discussion started on 10 Feb 2020)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Referee comment tc-2020-33', Anonymous Referee #1, 06 Mar 2020
- AC1: 'Reply to Anonymous Referee 1', Stephan Gruber, 29 Jun 2020
SC1: 'Subedi et al. (tc-2020-33) Comments', Stephen Wolfe, 27 Mar 2020
- AC3: 'Reply to Stephen Wolfe', Stephan Gruber, 29 Jun 2020
RC2: 'Review of tc-2020-33: Ground ice, organic carbon and soluble cations in tundra permafrost and active-layer soils near a Laurentide ice divide in the Slave Geological Province, N.W.T., Canada', Anonymous Referee #2, 09 Apr 2020
- AC2: 'Reply to Anonymous Referee 2', Stephan Gruber, 29 Jun 2020
- AC1: 'Reply to Anonymous Referee 1', Stephan Gruber, 29 Jun 2020
AC4: 'Summary of changes in revised manuscript', Stephan Gruber, 29 Jun 2020

Peer-review completion

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

ED: Reconsider after major revisions (further review by editor and referees) (09 Jul 2020) by Christian Hauck

Dear authors,

thank you very much for your detailed responses to the two reviewer reports and the additional short comment by S. Wolfe. In my view, they are adequately addressing all points raised - however, as many of these comments are very major and point to potential problems in the methodology as well as in interpretations and generalisations drawn from the results, you should make careful decisions how to incorporate the criticism and the many suggestions in your revised manuscript.

All comments highlight the value of the data set as such, although certain comments criticise some of the methodological steps, both regarding lay-out and analysis of the data. Obviously, regarding layout and some of the analyses, no changes can be made at this stage. Where methodological shortcomings (being intentional or unintentional) are present, they must be clearly stated and corresponding uncertainties should be named. If necessary, too speculative interpretations should be omitted.

A second group of critical comments addresses the generalisation of the findings and the description of their linkage to (a) regional/geologic/glaciological aspects and (b) material composition of other permafrost environments. In my opinion these comments reflect a certain ambiguity in the present manuscript, i.e. the necessity to show the usefulness of the data but also the necessity to state all methodological uncertainties and to admit that spatial heterogeneity on many scales may prohibit quantitative exploitation of the data for many research questions.

A solution could be to better highlight the fact that this study should be seen as one of many (future) steps towards the quantitative assessment of ground ice, carbon and soluble cation contents and their comparison to other environments. The study does not have to address all possible links in detail - where uncertainties are (still) too large, interpretations or generalisations should be avoided and can be omitted. The corresponding research questions can then be revisited in a future study with improved methodological design.

In this respect I am looking forward to your revised manuscript,

kind regards,
Christian Hauck

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AR by Stephan Gruber on behalf of the Authors (11 Jul 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (22 Jul 2020) by Christian Hauck

RR by Anonymous Referee #1 (10 Aug 2020)

Suggestions for revision or reasons for rejection

General comments

In my original review of this manuscript I suggested minor revisions. On the one hand, this study presents unique and highly valuable data on ground ice, organic carbon and soluble cation contents in permafrost cores of the Central Canadian Arctic. On the other hand, I had questions related to representativity of the study area for the wider region as well as the thoroughness of field and laboratory procedures. In my opinion, the overall value of the dataset outweighs uncertainties associated with some methodological shortcomings, which to a large extent cannot be corrected any longer.

In the revised version of the manuscript, the authors have addressed the representativity of the study area by comparing surface geology maps for the study area and two larger sheets. Unfortunately, the four landscape classes identified in this study cannot be directly linked to the units in the surface geology maps, and their proportional extent is unclear.

As stated above, many of the methodological issues cannot be remedied at this late stage, but the authors make generally a better case of identifying uncertainties derived from these shortcomings (e.g., lack of field volume for collected samples, a single LOI value for organic samples, volume occupied by large clasts, the role of the 0.5-5 mm fraction, etc.).

The added Supplement with individual core logs is highly valuable.

Specific comments

Title: The title has become too long and is partly inaccurate. It is unnecessary to add …, including preserved Laurentide basal ice, … The polygenetic nature of the ground ice is clearly explained in the abstract as well as in the results. There is nothing like … active-layer soils … It is implicit that a permafrost soil has an active layer. I suggest, therefore to change the title to ‘Ground ice, organic carbon and soluble cations in tundra permafrost soils and sediments near a Laurentide ice divide in the Slave Lake Geological Province, N.W.T., Canada’

Page 1, Line 13 (P1, L13): …, based on greater spatial and …
P1, L16: … lower than at previously studied …
P1, L18: No need to start a new paragraph
P1, L19: The last sentence is out of scope. This study does not present any evidence for buried paleosols of interglacial/interstadial age, which are not to be expected due to the (at times) warm-based erosive nature of the Ice Sheet in this region
P2, L23: ... It sampled the active layer and permafrost layer of soils and sediments and …
P2, L33+: … The area beneath the Keewatin Dome spreading centre (Fig. 1C, zone 1), …
P2, L36: … in the western Canadian Arctic (Fig. 1C, zone 3). Between both (Fig. 1C, zone 2) is an area of increasing …
P3, L62: ecological succession = peat accumulation
P5, Fig. 1: Explain zones 2 and 3 in caption figure 1C
P5, L123: Soil parent materials consist of …
P9, L196: ‘homogenized’. Here it should be explained that dried samples were crushed, and that any larger organic fractions (>0.5mm) like roots, plant remains are therefore part of the P0.5 sample analyzed for LOI (see answer of authors to my original question)
P9, L202: … This occurred only in the top 0.3m ? (but also in peat down to >2m ?)
P13, L266: It is not at all evident from figures 5 and 6 that cation values are lower in organic/active layer vs mineral/permafrost layer. Please check this sentence/these numbers
P15, L283: … Figure B2 panels B) and C) … Incomplete sentence
P16, L288: growth = accumulation
P17, L332: Using samples from the Greenland …
P19, L393: Table D1 compares the SOC storage in till soils (considered Turbels), esker soils (considered Orthels) and organic soils (considered Histels) to published values (Hugelius et al., 2014). This is useful but it should be considered that these are circumpolar mean values. A comparison with values reported for the study area would be more informative. It is unfortunate that the four landscape classes recognized in this study cannot be linked unambiguously to the surface geology map units, and therefore their proportional extent is unclear. However, given the low representation of the organic class in the study area, it is likely that the mean landscape values for 0-1m and 0-3m are quite similar to those reported in Hugelius et al. (2014)., which are 5-15 KgC m2 for 0-1m (one polygon in the NCSCD) and anything between 20-75 KgC m2 for the 0-3m (two polygons in the NCSCD). They are also quite similar to the Hossain et al. (2015) values reported next.
P19, L393-394: This is similar to … Check sentence
P21, L475-477: Out of scope (see my comment P1, L19)

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ED: Publish subject to minor revisions (review by editor) (23 Sep 2020) by Christian Hauck

AR by Stephan Gruber on behalf of the Authors (06 Oct 2020) Author's response Manuscript

ED: Publish as is (26 Oct 2020) by Christian Hauck

AR by Stephan Gruber on behalf of the Authors (26 Oct 2020)

Short summary

Permafrost beneath tundra near Lac de Gras (Northwest Territories, Canada) contains more ice and less organic carbon than shown in global compilations. Excess-ice content of 20–60 %, likely remnant Laurentide basal ice, is found in upland till. This study is based on 24 boreholes up to 10 m deep. Findings highlight geology and glacial legacy as determinants of a mosaic of permafrost characteristics with potential for thaw subsidence up to several metres in some locations.