Carbon isotope (δ<sup>13</sup>C) excursions suggest times of major methane release during the last 14 kyr in Fram Strait, the deep-water gateway to the Arctic

Consolaro, C.; Rasmussen, T. L.; Panieri, G.; Mienert, J.; Bünz, S.; Sztybor, K.

doi:https://doi.org/10.5194/cp-11-669-2015

Articles | Volume 11, issue 4

https://doi.org/10.5194/cp-11-669-2015

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

https://doi.org/10.5194/cp-11-669-2015

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

Articles | Volume 11, issue 4

Research article

|

17 Apr 2015

Research article |

| 17 Apr 2015

Carbon isotope (δ¹³C) excursions suggest times of major methane release during the last 14 kyr in Fram Strait, the deep-water gateway to the Arctic

C. Consolaro, T. L. Rasmussen, G. Panieri, J. Mienert, S. Bünz, and K. Sztybor

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Final revised paper (published on 17 Apr 2015)
Supplement to the final revised paper
Preprint (discussion started on 24 Oct 2014)
Supplement to the preprint

Interactive discussion

Status: closed

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

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- Supplement

RC C1875: 'Toward a more powerful paper', Gerald Dickens, 08 Nov 2014
EC C1888: 'invitation to respond', Appy Sluijs, 10 Nov 2014
SC C2020: 'review of Consolaro et al. by Lennart de Nooijer', Lennart de Nooijer, 03 Dec 2014
- RC C2024: 'Review of Consolaro et al. by Lennart de Nooijer'', Lennart de Nooijer, 04 Dec 2014
AC C2285: 'Answers to referees' comments', Chiara Consolaro, 04 Feb 2015

Peer-review completion

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

AR by Chiara Consolaro on behalf of the Authors (04 Feb 2015) Author's response

ED: Referee Nomination & Report Request started (16 Feb 2015) by Appy Sluijs

RR by Lennart de Nooijer (26 Feb 2015)

RR by Gerald Dickens (11 Mar 2015)

Suggestions for revision or reasons for rejection

Consolaro and colleagues have significantly improved their original submission, and have addressed my original comments satisfactorily.

I think they need to do much more work to convince the broad community that they have interpreted things correctly, and even if so, to understand how the purported methane release would have occurred. However, the current version is for the most part now scientifically sound and well written.

I have a few comments (below) that they should consider and address. I would accept with minor revisions.

Sincerely,

Gerald (Jerry) Dickens

General Comment: I would remove the Sun and Turchyn (2014) reference from text and caption, as the authors do not consider methane and AOM. There are, however, much better papers on the topic of methane derived authigenic carbonate (e.g., Greinert et al., 2001), including some that even suggest that it represents a significant sink of CaCO3 (e.g., Snyder et al., DSR, 2007).

-- Page 2 --
Line 19: This is awkward. Probably should be “emissions from the seafloor through time, especially in relation to past climate change and with a focus on periods of climate warming.”

Line 21: Change to “… along continental margins within a gas …”

Line 22: This is not entirely true and should be rewritten. In my mind, a BSR only occurs when pore space with free gas is in contact with pore space with gas hydrate; certainly, there are locations with gas hydrate and no BSR. (see Dickens, Org. Geochem., 2001 as to discussion of the GHSZ and its relation to gas hydrate distribution).

Lines 23-27: This text and referencing is somewhat misleading. To my knowledge, the community is unclear on how gas passes through a REGIONAL GHSZ (for example, see discussion in Milkov et al., EPSL, 2004).

-- Page 3 --
Lines 1-3: This is awkward as written, because Equation 2 does not consume methane; that is, the second equation comes after the next sentence. In any case, neither reference is very good, as these authors did not originally describe the reactions.

Line 5: Avoid Latin abbreviations in the middle of sentences, because it is sloppy writing. Such abbreviations should only come in parentheses.

Line 6: Whiticar 1999 is not a good reference here, as the paper is not really about authigenic carbonate. Greinert et al., in Natural Gas Hydrates, 2001 is a much better reference for this statement. There are numerous other papers, too.

Line 7: Should be plural (“tests”).

Line 9: Should be “the pore space of surrounding sediments”.

Line 11: Remove second “the”.

Line 12: Borowski et al. (1996) is not a great reference here, as while a good paper on the topic, does not pertain to seeps and show this effect nicely. Other papers, such as Paull et al., GML, 2005; Castellin et al., Chem Geol., 2006, etc. are much better.

-- Page 4 --
Line 27: “Induced” is the wrong word choice here. Rewrite the sentence.

-- Page 5 --
Line 26: What reference core? This should be shown on Figure 1 and stated.

-- Page 8 --
Line 20: Presumably should be “no negative oxygen isotope excursions”

-- Page 9 --
Line 31: I think the original argument for this concept was in Dickens, G3, 2001.

-- Page 10 --
Line 1: Here and elsewhere, I would avoid adding the MDAC acronym, as this is not common usage.

Line 23: Change “are” to “is” or somehow pluralize silica.

Line 26: The authors might want to modify the statement, because AOM does not increase pH per se.

Line 28: Avoid starting sentences with abbreviations (e.g., Mg).

-- Page 11 --
Lines 22-25: There are multiple papers that now clearly show this effect, including across seeps. In other words, it is beyond “according to Borowski” - the ideas he presented are really obvious.

-- Page 12 --
Lines 9-12: Authigenic carbonate precipitation at or near the seafloor happens at many seep locations, not just Hydrate Ridge.

Line 19: Avoid MDAC and should not be plural given the verb.

-- Page 13/14 --
Lines 23 (page 13) – 4 (Page 14): I do not follow the first paragraph. First, I think it needs to state “… registered also in benthic foraminiferal records at sites in the region away from seep sites.” It then needs rewording at the end so as to emphasize that this is consistent with the idea that CH4 is rapidly oxidized in the water column such that any addition of CH4 derived carbon is diluted across a broader region. The problem here is that this now conflicts with the next paragraph. Bottom line, this part needs some rewriting to clarify.

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ED: Publish subject to minor revisions (review by Editor) (11 Mar 2015) by Appy Sluijs

AR by Chiara Consolaro on behalf of the Authors (18 Mar 2015) Author's response Manuscript

ED: Publish as is (27 Mar 2015) by Appy Sluijs

AR by Chiara Consolaro on behalf of the Authors (02 Apr 2015)

Short summary

A sediment core collected from a pockmark field on the Vestnesa Ridge (~80N) in the Fram Strait is presented. Our results show an undisturbed sedimentary record for the last 14 ka BP and negative carbon isotope excursions (CIEs) during the Bølling-Allerød interstadials and during the early Holocene. Both CIEs relate to periods of ocean warming, sea-level rise and increased concentrations of methane (CH4) in the atmosphere, suggesting an apparent correlation with warm climatic events.

Carbon isotope (δ13C) excursions suggest times of major methane release during the last 14 kyr in Fram Strait, the deep-water gateway to the Arctic

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Carbon isotope (δ¹³C) excursions suggest times of major methane release during the last 14 kyr in Fram Strait, the deep-water gateway to the Arctic