Anaerobic oxidation of methane alters sediment records of sulfur, iron and
phosphorus in the Black Sea

Egger, Matthias; Kraal, Peter; Jilbert, Tom; Sulu-Gambari, Fatimah; Sapart, Célia J.; Röckmann, Thomas; Slomp, Caroline P.

doi:https://doi.org/10.5194/bg-13-5333-2016

Articles | Volume 13, issue 18

https://doi.org/10.5194/bg-13-5333-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/bg-13-5333-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 13, issue 18

Research article

|

23 Sep 2016

Research article |

| 23 Sep 2016

Anaerobic oxidation of methane alters sediment records of sulfur, iron and phosphorus in the Black Sea

Matthias Egger, Peter Kraal, Tom Jilbert, Fatimah Sulu-Gambari, Célia J. Sapart, Thomas Röckmann, and Caroline P. Slomp

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Final revised paper (published on 23 Sep 2016)
Supplement to the final revised paper
Preprint (discussion started on 10 Mar 2016)
Supplement to the preprint

Interactive discussion

Status: closed

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

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RC1: 'Comments to the authors', Orit Sivan, 24 Mar 2016
- AC1: 'Reply to the review by Dr. Sivan', Matthias Egger, 18 May 2016
RC2: 'review of bg-2016-64', Anonymous Referee #2, 06 Apr 2016
- AC3: 'Reply to the review by Anonymous referee #2', Matthias Egger, 18 May 2016
RC3: 'Nice data, nice science, and nice writing. There is some room for model improvement.', Wei-Li Hong, 15 Apr 2016
- AC2: 'Reply to the review by Dr. Hong', Matthias Egger, 18 May 2016

Peer-review completion

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

ED: Reconsider after major revisions (19 May 2016) by Tina Treude

AR by Matthias Egger on behalf of the Authors (24 Jun 2016) Author's response Manuscript

ED: Referee Nomination & Report Request started (13 Jul 2016) by Tina Treude

RR by Wei-Li Hong (20 Jul 2016)

RR by Anonymous Referee #2 (03 Aug 2016)

Suggestions for revision or reasons for rejection

The authors have done an excellent job in revising the paper in response to the reviewers’ comments. Most importantly in my view, they have justified the assumptions and reasons for excluding organoclastic iron reduction in the methane zone, making it clear that the purpose of the study is to explore the potential for iron-dependent AOM rather than determining actual Fe-AOM rates. I only find one minor issue:

I still respectfully disagree with the use of the closed-system Rayleigh distillation model to determine fractionation factors for sulfate-AOM (l. 428-441). A remark is now included that determination of accurate factors require modelling, which is fine, but I am confused by the remark that “diffusion could be slower than oxidation”. This true in the sense that some methanogenesis occurs in the AOM zone, but AOM rates in the SMTZ are about an order of magnitude higher than methane production rates there (Fig. 6), so most of the methane must be supplied by diffusion – this is by no means a “quasi-closed system” as claimed in the text.

Just a remark: I my comments to the 1st version I had missed the fact that hydrogenotrophic methanogenesis in the model depends on the DIC concentration and not on the hydrogen concentration. This is a strange formulation since methanogens in sediments usually deplete hydrogen to the energetic threshold (see papers by Hoehler et al.) and thus, expectedly, are hydrogen limited (with hydrogen supply limited by the degradation of organic matter and, possibly, pyrite formation). Thus, the modelling of two separate methanogenic pathways is questionable, but this has no real influence on the paper now, because the authors have chosen to present the combined methane production.

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RR by Orit Sivan (03 Aug 2016)

ED: Publish subject to minor revisions (Editor review) (06 Aug 2016) by Tina Treude

AR by Matthias Egger on behalf of the Authors (07 Aug 2016) Author's response Manuscript

ED: Publish as is (17 Aug 2016) by Tina Treude

AR by Matthias Egger on behalf of the Authors (17 Aug 2016)

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Short summary

By combining detailed geochemical analyses with diagenetic modeling, we provide new insights into how methane dynamics may strongly overprint burial records of iron, sulfur and phosphorus in marine systems subject to changes in organic matter loading or water column salinity. A better understanding of these processes will improve our ability to read ancient sediment records and thus to predict the potential consequences of global warming and human-enhanced inputs of nutrients to the ocean.