Methane dynamics in three different Siberian water  bodies under winter and summer conditions

Bussmann, Ingeborg; Fedorova, Irina; Juhls, Bennet; Overduin, Pier Paul; Winkel, Matthias

doi:https://doi.org/10.5194/bg-18-2047-2021

Articles | Volume 18, issue 6

https://doi.org/10.5194/bg-18-2047-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/bg-18-2047-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 18, issue 6

Research article

|

22 Mar 2021

Research article |

| 22 Mar 2021

Methane dynamics in three different Siberian water bodies under winter and summer conditions

Ingeborg Bussmann, Irina Fedorova, Bennet Juhls, Pier Paul Overduin, and Matthias Winkel

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Final revised paper (published on 22 Mar 2021)
Preprint (discussion started on 22 Apr 2020)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Review of "Seasonal methane dynamics in three different Siberian water bodies"', Anonymous Referee #1, 09 Jul 2020
- AC1: 'Response to referee 1', Ingeborg Bussmann, 02 Oct 2020
RC2: 'Major Revision', Anonymous Referee #2, 07 Sep 2020
- AC2: 'Response to referee 2', Ingeborg Bussmann, 02 Oct 2020

Peer-review completion

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

ED: Publish subject to minor revisions (review by editor) (02 Nov 2020) by Zhongjun Jia

ED: Reconsider after major revisions (04 Nov 2020) by Zhongjun Jia

AR by Ingeborg Bussmann on behalf of the Authors (06 Nov 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (16 Nov 2020) by Zhongjun Jia

RR by Anonymous Referee #1 (10 Dec 2020)

Suggestions for revision or reasons for rejection

The manuscript "Methane dynamics in three different Siberian water bodies under winter and summer conditions" by Bussmann et al. has been substantially revised by the authors and most of my previous comments have been taken into account.

I still think that the argumentation on the MOX rates could be further strengthened, however. The discussion of the manuscript heavily relies on the calculated MOX rates, and in my previous review of the manuscript my main criticism was that I missed a chain of arguments that justifies the calculation of MOX rates for all water types from the fractional MOX rates measured in ice core and river samples.

In their answer to my review, the authors agreed that their approach has some drawbacks but stated that due to the difficult logistics, transferring the MOX rates measured in the ice core and river waters to the other water bodies is the best they can do. While I understand that conducting MOX rate incubation experiments under field conditions is very challenging, I still think the authors need to discuss the limitations of their approach in the manuscript more clearly. In lines 449-454 the authors state that transferring the MOX rates from ice core and river data to the other bodies is justified due to the fact that MOX rates are generally low at low temperatures and due to the fact that the methanotrophic population (does this refer to the community composition?) of the ice cores is similar to the one measured in the water below. While I agree that the temperature dependence of the MOX rate indicates that MOX is low at low temperatures, I am not fully convinced that other factors have sufficiently been taken into account by the authors. Particularly the influence of CH4 concentrations on MOX rates may be of importance, as CH4 concentrations in the lake and the coastal embayment were significantly higher below the ice than in the river water.

I furthemore have some minor comments that should be taken into account:

Lines 34 and 36: replace "10-times" and "40-times" with “10 times”, “40 times”

Line 55: I guess it should read “from 2.2 ppb/yr to..."

Line 67: replace “concentration” by “mole fraction”

Lines 67-69: CH4 emissions from water bodies (incl. lakes, rivers, coastal waters) have not been mentioned in the introduction before. How significant are these emissions in relation to other sources in the northern latitudes?

Lines 189-193: if the samples are transferred to Nalgene bottles before filling the glass bottles, how is CH4 loss from the samples prevented?

Lines 313-315: “In Figure 3 the median concentrations in the … “: this formulation is somewhat strange. Please rephrase this sentence to something like “Figure 3 shows the median CH4 concentrations in the ice core and at in the water from the ice-water interface in…”

Lines 319-320: there seems to be something wrong with the reference that should be cited here.

Lines 328-329: can the authors give additional information on the CH4 concentrations in the samples that were used to determine MOX rates? Did the authors find any correlation between MOX rate and concentrations?

Lines 333-335: This sentence repeats the previous one.

Lines 337-340: Does this mean that an overall median MOX (mean of ice cores and water samples) is transferred to the entire dataset? If MOX in 73% of the ice cores is below the detection limit would the overall median value from the ice cores not be below detection limit, too? Would it not make more sense to transfer the MOX rates from only the water samples to the other water bodies?

Line 366: "lower than in summer"

Lines 618-619: this sentence is a repetition of lines 578-579.

Table 1: maybe the information on samplings for the MOX rate measurements can be added here? I think it is interesting to know where and when the authors took the samples for these incubations.

Figure 3: I would suggest to swap the data from Lake Golzovoye and Tiksi Bay, to show the Lake Golzovoye data next to the data from the separate ice core from the lake.

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ED: Publish subject to minor revisions (review by editor) (19 Dec 2020) by Zhongjun Jia

AR by Ingeborg Bussmann on behalf of the Authors (31 Dec 2020) Author's response Author's tracked changes Manuscript

ED: Publish subject to technical corrections (13 Feb 2021) by Zhongjun Jia

AR by Ingeborg Bussmann on behalf of the Authors (15 Feb 2021) Author's response Manuscript

Short summary

Arctic rivers, lakes, and bays are affected by a warming climate. We measured the amount and consumption of methane in waters from Siberia under ice cover and in open water. In the lake, methane concentrations under ice cover were much higher than in summer, and methane consumption was highest. The ice cover leads to higher methane concentration under ice. In a warmer Arctic, there will be more time with open water when methane is consumed by bacteria, and less methane will escape into the air.