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the Creative Commons Attribution 4.0 License.
| 30 Jun 2026
Biogeochemistry of methane in Arctic waters: A multiyear synthesis (2014–2022) from the North Atlantic-Arctic sector and Barents Sea
Abstract. Methane seeping from numerous point sources at the seabed represents a biogeochemically constrained carbon source in the water column of the Arctic Ocean. Here, we compile and synthesise water-column data from 28 research cruises conducted between 2014 and 2022 to evaluate the spatial distribution and variability of methane across Arctic seep systems and to assess whether methane enrichment produces detectable changes in water-column biogeochemistry. Our synthesis shows that methane concentrations span five orders of magnitude, ranging from non-detectable levels (<0.52 nM) to 105 nM. Despite this distinct variability, continuous seeping of methane does not measurably alter bulk nutrient regimes, but it influences organic matter cycling through microbial methane oxidation (MOx). In contrast, nutrient and carbon biogeochemistry appear closely associated with seasonal patterns in primary production, showing typical vertical profiles, even in regions of maximum methane flux. This reflects the relatively low abundance of methane compared to other substrates, as nutrients and dissolved organic carbon concentrations remain one to two orders of magnitude higher even at peak methane levels. Consequently, methane-derived carbon constitutes only a minor fraction of total biogeochemical pools, constraining its effect on nutrient dynamics. However, methane exerts a cumulative influence by altering microbial processes and carbon transformation pathways, even in the absence of detectable changes in bulk nutrient concentrations.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Biogeosciences.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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RC1: 'Comment on egusphere-2026-3607', Anonymous Referee #1, 31 Jul 2026
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AC1: 'Reply on RC1', Muhammed Fatih Sert, 31 Aug 2026
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We would like to thank the anonymous reviewer for the time and effort devoted to reviewing our manuscript. We greatly appreciate the comments and valuable suggestions provided. We carefully considered all the points raised by the reviewer and addressed them in the revised manuscript. Below, please find point-by-point responses to the reviewer's comments.
Comment
Response
I was very disappointed with this manuscript which I believe fails in it's intention to address the "Biogeochemistry of methane in Arctic Waters". Though I accept that it does address the latter part of the title in presenting "A multiyear synthesis (2014-2022) from the North Atlantic-Arctic sector and Barents Sea".
We recognise the reviewer's comment that the first part of the original title, “Biogeochemistry of methane in Arctic waters,” may imply a broader analysis of Arctic methane biogeochemistry than our study provides. We intended to use this phrase to describe the broader scientific context, while the second part defined the geographical and temporal scope of the study. However, we agree that the title could more directly reflect the objectives of our manuscript. We have therefore revised the title to emphasise the source of methane. The title is now: "Biogeochemistry of methane from Arctic seabed sources: A multiyear synthesis (2014–2022) from the North Atlantic–Arctic sector and Barents Sea".
The manuscript is well presented and does offer a comprehensive description of variability in methane distribution but simply presenting this distribution alongside water column environmental variables does not deliver on any understanding of methane biogeochemistry that I can see, though estimates of methane oxidation and turnover do provide limited insight, despite the contention (Line 523-524) that these rates are specific to location.
We acknowledge the concern regarding the extent to which the original title reflected an investigation of methane biogeochemistry in a broader context than our study. We hope that the revised title better reflects the scope of the study and addresses this concern.
Lines 492-494 claims that the authors "evaluated whether methane enrichment produces detectable changes in water column biogeochemistry and which biogeochemical components might respond to elevated methane concentrations", I would argue that they simply compared profiles of variables with no defined protocol to what or why.
We acknowledge that a more standardised protocol would strengthen such assessment. However, given the heterogeneous nature of our dataset, which integrates observations collected across different regions, cruises, seasons, and hydrographic settings, applying a single predefined protocol is challenging. We have clarified that our evaluation represents a comparison rather than a controlled assessment of methane-induced biogeochemical responses. The text now reads: “In the present study, we compared methane enrichment with measured water-column biogeochemical variables to examine whether elevated methane concentrations were associated with detectable changes in these variables.”
Line 495 onward acknowledges that previous studies have failed to connect methane distribution to nutrient regimes and simply reconfirming this is not an investigation of methane biogeochemistry. The following lines indicate that a study of methane biogeochemistry needs to be focussed around the microbial cycling in deep waters and the last paragraph of the conclusion details what might be involved in such a study, unfortunately this was not done in the current manuscript.
A detailed investigation of microbial cycling was indeed beyond the scope of this study. However, by compiling and comparing methane concentrations, oxidation rates, and associated biogeochemical variables across different Arctic seep systems, our study provides an important baseline and lays the groundwork for more targeted process-based studies.
Further there are a number of statements which are simple supposition rather than supported fact: eg Line 515-516
This statement follows the findings of Sert et al. (2023), cited in the previous sentence, rather than from an unsupported assumption.
It should be noted in the title that a lot, if not all of the CH4 data presented results from sea-bed seeps
We have followed the reviewer’s suggestions (see also above) and changed the title accordingly. The title now reads "Biogeochemistry of methane from Arctic seabed sources: A multiyear synthesis (2014–2022) from the North Atlantic–Arctic sector and Barents Sea", which makes the focus on seabed sources explicit.
L60 is methane a micronutrient?
We wanted to mention that methane can be considered similarly to nutrients for the organisms that use it as a carbon and energy source. The sentence is updated.
L86 water mass structure is not shown in Fig 1a,b
We have changed the text to “[...] characterised by the prevailing water masses and circulation patterns (Fig. 1a, b).”
No methods are presented for DOP< PP, POC, PN, chlorophyll
We have added the description of the analysis for POC (note that we use the notation PC), PN, PP and Chla in section 2.3. Calculation for DOP and DON are described in section 2.4.
L410 MOx rate are in Fig 5
The figure reference has been corrected from Fig. 4 to Fig. 5.
Citation: https://doi.org/10.5194/egusphere-2026-3607-AC1
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AC1: 'Reply on RC1', Muhammed Fatih Sert, 31 Aug 2026
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RC2: 'Comment on egusphere-2026-3607', Anonymous Referee #2, 05 Aug 2026
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In the manuscript data on methane, oxidation rates and other biogeochemical variables from almost a decade of observations in the Arctic Ocean around Svalbard are presented. Most of the data, results and conclusions are based on previous papers of the CAGE group or other published studies. Unfortunately, new ideas or interpretations or new insights into the topic are missing. A main limitation of this study is stated by the authors at the end: ‘Future studies should also extend beyond observational water-column surveys of methane distributions and MOx rates.’. The proposed future research perspectives would indeed have the potential to provide new insights into the topic.
However, overall the manuscript is well written and the comprehensive summary presented here has its own merit and, I believe, warrants publication.
Editorial comments:
L51-65: The importance of water depth of seeps should be mentioned here as well. If seeping gas bubbles dissolve before reaching the mixed surface layer (50-100 m depending on wind/storm situation), atmospheric exchange will be limited – and MOx has sufficient time to consume the CH4. If the seep depth is shallower and bubbles reach the mixed layer, diffusive gas exchange with the atmosphere increases (e.g. Wanninkhof 1992) - partly because MOx then has less time to consume the CH4 before it is exchanged with the atmosphere.
L66: “Beyond its role as a greenhouse gas in submarine gas hydrates”. It is unclear to me what the authors want to imply here. In most areas of the world gas hydrates exist below water depths that prevent released CH4 from dissociating hydrates to reach the atmosphere. This is only relevant in some shallow water (<100 m) Arctic regions (see. Biastoch et al. 2011 and James et al. 2016). I suggest to be more specific in the formulation or drop it.
L129: ‘spectrometer’ instead of ‘spectrometry’
L131: VPDB (Vienna Peedee Belemnite)
L132: ‘uncertainty’ refers to precision or accuracy?
L240: The authors mean dissociation of gas hydrates, not ‘dissolution’. The latter would not lead to gas formation.
Table 2 header, Figure 3 caption, L381, L467, L476: variable, not ‘parameter’
Fig.3: Why is dissolved oxygen not shown?
L489-501: This conclusion was already clear from decade-old studies on oceanic methane concentrations, e.g. reviewed by Reeburgh (2007). Unfortunately, the posed question if the ‘primary role may instead occur through microbial pathways and carbon processing’ is only raised but not addressed.
Various locations: If mean values are reported, please also state the 2-sigma standard deviation. Only report significant number of digits.
Mostly American English spelling is used, but occasionally also British spelling – please use consistent spelling.
Citation: https://doi.org/10.5194/egusphere-2026-3607-RC2 -
AC2: 'Reply on RC2', Muhammed Fatih Sert, 31 Aug 2026
reply
We would like to thank the anonymous referee for the time and effort devoted to reviewing our manuscript. We greatly appreciate the comments and valuable suggestions provided. We carefully considered all the points raised and addressed them in the revised manuscript. Here are point-by-point responses to all comments.
Comment
Response
In the manuscript data on methane, oxidation rates and other biogeochemical variables from almost a decade of observations in the Arctic Ocean around Svalbard are presented. Most of the data, results and conclusions are based on previous papers of the CAGE group or other published studies. Unfortunately, new ideas or interpretations or new insights into the topic are missing. A main limitation of this study is stated by the authors at the end: ‘Future studies should also extend beyond observational water-column surveys of methane distributions and MOx rates.’. The proposed future research perspectives would indeed have the potential to provide new insights into the topic.
However, overall the manuscript is well written and the comprehensive summary presented here has its own merit and, I believe, warrants publication.
As the reviewer points out, we acknowledge limitations of this study. This study aims to bring these observations together across regions and years to provide a broader synthesis of methane distributions, oxidation rates, and associated biogeochemical patterns in Arctic seep systems.
L51-65: The importance of water depth of seeps should be mentioned here as well. If seeping gas bubbles dissolve before reaching the mixed surface layer (50-100 m depending on wind/storm situation), atmospheric exchange will be limited – and MOx has sufficient time to consume the CH4. If the seep depth is shallower and bubbles reach the mixed layer, diffusive gas exchange with the atmosphere increases (e.g. Wanninkhof 1992) - partly because MOx then has less time to consume the CH4 before it is exchanged with the atmosphere.
We have updated the text as: “The fate of methane strongly depends on water depth. At deeper sites, free gas methane may dissolve below the mixed layer, increasing the residence time of dissolved methane and allowing more time for microbial oxidation. At shallower sites, both free gas and dissolved methane can more readily reach the mixed layer, increasing the potential for sea-air exchange (e.g. Wannikhof, 1992, James et al., 2016).”
L66: “Beyond its role as a greenhouse gas in submarine gas hydrates”. It is unclear to me what the authors want to imply here. In most areas of the world gas hydrates exist below water depths that prevent released CH4 from dissociating hydrates to reach the atmosphere. This is only relevant in some shallow water (<100 m) Arctic regions (see. Biastoch et al. 2011 and James et al. 2016). I suggest to be more specific in the formulation or drop it.
The reference is removed. The text now reads: “Beyond its climatic relevance as a greenhouse gas, methane exerts [...]”
L129: ‘spectrometer’ instead of ‘spectrometry’
The text is updated accordingly.
L131: VPDB (Vienna Peedee Belemnite)
We corrected as suggested
L240: The authors mean dissociation of gas hydrates, not ‘dissolution’. The latter would not lead to gas formation.
Mentioned wording was found in line number 250 and corrected as suggested
Table 2 header, Figure 3 caption, L381, L467, L476: variable, not ‘parameter’
We corrected as suggested
Fig.3: Why is dissolved oxygen not shown?
Dissolved oxygen was initially separated for a different CTD figure during an earlier version of the manuscript. As the figure was subsequently reorganised, the dissolved oxygen profile was inadvertently omitted from the final version. We have now corrected this and included the dissolved oxygen in the vertical profiles in Figure 3.
L489-501: This conclusion was already clear from decade-old studies on oceanic methane concentrations, e.g. reviewed by Reeburgh (2007). Unfortunately, the posed question if the ‘primary role may instead occur through microbial pathways and carbon processing’ is only raised but not addressed.
We agree with the reviewer that the role of methane-associated metabolic pathways and carbon processing is not yet fully understood and requires more targeted data. We have therefore revised Lines 492–493 to clarify that our study examined the associations between methane enrichment and water-column biogeochemical variables, rather than direct methane-induced responses or microbial processes. The broader role of microbial pathways and carbon processing cannot be directly addressed with our current dataset. However, we have referred to relevant previous studies in the following two paragraphs and highlighted these processes as an important direction for future research.
Various locations: If mean values are reported, please also state the 2-sigma standard deviation. Only report significant number of digits.
We agree that reporting the 2-sigma values can provide additional information on data variability. However, the full ranges of the measurements for the respective regions are already provided in Table 2 (Table 3 in the revised manuscript) and at the corresponding locations in the text, allowing the reader to assess the variability of the observations. In addition, histograms for all variables are provided in the Supplementary Material (Fig. S2) for further assessment of the data distributions. To avoid further complicating the text with additional statistical values, we have retained the current presentation of the mean values. We have also reviewed the reported values and adjusted the number of significant digits where necessary to avoid unnecessary precision.
Mostly American English spelling is used, but occasionally also British spelling – please use consistent spelling.
We homogenised the text to British spelling.
Citation: https://doi.org/10.5194/egusphere-2026-3607-AC2
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AC2: 'Reply on RC2', Muhammed Fatih Sert, 31 Aug 2026
reply
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RC3: 'Comment on egusphere-2026-3607', Damian Leonardo Arévalo-Martínez, 07 Aug 2026
reply
Please see attachment.
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AC3: 'Reply on RC3', Muhammed Fatih Sert, 31 Aug 2026
reply
We would like to thank Dr Arevalo-Martinez for the time and effort devoted to reviewing our manuscript. We greatly appreciate the comments and valuable suggestions provided. We carefully considered all the points raised and addressed them in the revised manuscript. Here are point-by-point responses to all comments.
Comment
Response
The topic of the manuscript is relevant, entails an impressive compilation of in-situ observations and it is generally well written. Nonetheless, in my opinion there are several caveats that would need to be revised before considering publication. One of the major issues I see is that the novelty does not come across clearly. Such a data compilation for the region is new and valuable or course, but the conclusions that the water column biogeochemistry (especially in deep water areas) is not noticeably affected by methane release, and that the sedimentary emissions are highly heterogeneous are not precisely new.
We thank the reviewer for recognising the value of this comprehensive dataset. As the reviewer notes, our main contribution is not that the individual observations regarding methane release, water-column biogeochemistry, or sedimentary emissions are entirely new. Rather, the novelty of this study lies in the compilation and synthesis of a decade-long dataset collected across numerous, often difficult-to-access regions of the Arctic Ocean and its integration into a broader biogeochemical context. The dataset is highly heterogeneous in terms of sampling locations, sampling depths, environmental conditions, and also observational approaches. This makes a comprehensive synthesis challenging. Although some components of the dataset are from published works, a substantial proportion -particularly from the more recent Eastern Barents Sea cruises- are presented here for the first time (Table 1). By bringing these observations together, our study provides a regional perspective across the Arctic–North Atlantic sector.
Furthermore, while clearly the observations provide a comprehensive overview of the regional distribution, I could not identify substantial evidence in direct support of the arguments regarding methane-derived carbon in the system (most arguments were drawn based on literature).
We agree with the reviewer that our direct evidence for methane-derived carbon is limited and that several of our interpretations are supported by previous studies, including marine omics studies from our group. These studies provide important evidence for the microbial processing of methane-derived carbon, but the underlying datasets are fundamentally different in nature from the hydrographic and biogeochemical observations compiled in the present study. Therefore, we could not directly make the integration into this manuscript. In addition, we aimed to maintain a consistent data scope across all regions, whereas the available methane-derived carbon and omics observations are restricted to a limited number of specific locations. Nevertheless, we consider the microbial processing of methane-derived carbon to be an important framework for interpreting the observed water-column dynamics of methane and related biogeochemical parameters. We have therefore retained this aspect in the discussion, while clarifying that these interpretations are based primarily on previous studies and cannot be directly demonstrated by the present dataset.
Another issue I see is the weight that is given to the regional variability in environmental conditions. Within the methods section (“2.1 Study Areas”), the authors provide an extensive description of the hydrographic and geological properties of the sub-regions they have identified. Yet, later in the manuscript the authors state that actually (based on their isotopic data) all sub-regions could be objectively clustered in two groups (“Atlantic” and “Barents Sea”). Knowing this, it appears unjustified to have all the details on all regions if the dynamics come down to the main water source. At the end,the large descriptions presented in the methods result being only loosely connected with the results and the conclusions of the study. In this regard, I wondered whether an angle that would emphasize the impact of this data compilation would be to aim exploring mechanistic explanations for the methane distribution based on the data at hand and compare the two main areas in view of projected changes (e.g. increased Atlantic inflow into the Arctic). For instance, if the methane filter is more effective in the Barents Sea, could it be that warmer waters form the Atlantic will make the filter weaker, leading to enhanced release? The ancillary data should allow checking for such a targeted comparison which would be, I think, insightful.Overall, I see this could be a valuable contribution, but I would recommend revising the framing of the study based on the type of observations that it comprises.
We agree that the water-column hydrographic and biogeochemical data reveal two major water-mass regimes that can broadly be clustered as Atlantic and Barents Sea, and this distinction is indeed reflected in our analysis of the vertical profiles. However, we believe that reducing the entire analysis to these two broad clusters would overlook an important aspect of our study: the regional geological and biogeochemical variability associated with individual methane-receiving environments. While hydrography and nutrient distributions show a strong water-mass control at the broader spatial scale, our assessment of methane concentrations, methane oxidation rates, and methane-turnover times indicates marked variability among the individual sub-regions. We therefore consider the geological framework essential for interpreting the observed methane dynamics. In particular, the regional differences are evident in Figures 4 and 5 and in the associated discussion, where we show that methane concentrations, MOx, and turnover times vary considerably among regions with different geological and microbial characteristics. Such variability is important because methane oxidation is influenced not only by the overlying water mass but also by local methane availability and microbial communities, which can vary over relatively small spatial scales.
In addition, as suggested by the other reviewers, we have revised the title of the manuscript to “Biogeochemistry of Methane from Arctic Seabed Sources:...” The updated title better emphasises the geological context of the study sites.
We appreciate the reviewer’s suggestion to investigate whether projected changes in Atlantic inflow could alter the efficiency of the methane filter. We consider this an interesting point that would be suited for a more targeted time-series study. However, directly testing such a mechanistic scenario with the present compilation would substantially change the scope and structure of the manuscript. Our objective here is instead to provide a comprehensive regional synthesis that preserves the geological context of the observations while assessing the relationships between methane and water-column biogeochemistry.
l. 46–50: This is a good point. However, as large as the data set is, it is also a collection of localized measurements that represent only a snapshot of what happens on a certain location. For instance,most data sets are confined to summer, which while understandable given the difficulties of sampling in the Arctic during winter, is not discussed here. I would argue that assessing mechanistic explanations for the methane (and oxidation rates) distribution could be a significant improvement,because it would provide insights on how the system might change under varying environmental conditions.
As the reviewer points out, most of the measurements were collected during the summer months due to the logistical challenges of Arctic winter sampling. This limitation is discussed in the second paragraph of Section 5.3, although the discussion there was primarily focused on nutrient distributions rather than the methane cycle. We also agree that mechanistic assessment regarding temperature changes, tidal variability, and density-driven changes can influence methane release and oxidation in seep environments. These mechanisms have been addressed in previous studies from our group and elsewhere (e.g., Ferré et al., 2019; Silyakova et al., 2020; Steinle et al., 2015), and we have incorporated these studies into our discussion. However, we consider that a detailed mechanistic assessment of these processes is beyond the scope of the present regional synthesis. Such an assessment would ideally require temporally resolved observations at individual seep sites or time-series measurements that can capture changes in methane release, hydrography, and microbial methane oxidation over time. This is particularly important because methane seeps and their surrounding environments can undergo substantial temporal and spatial variability, including changes in the composition and activity of methane-oxidising microbial communities. Our objective in the present study is therefore to characterise the regional distribution of methane and its relationship with available environmental and biogeochemical parameters across a large number of Arctic sites, rather than to derive site-specific mechanistic relationships.
l.57: There is also the paper by Thornton et al. (2020; Science Advances, DOI:10.1126/sciadv.aay7934). Perhaps the authors might consider citing it in this context.
We added suggested reference to the manuscript.
l.122 and ff.: Basic data on accuracy and calibration procedures for the methane measurements is missing. In particular, with regards to calibration, it is unclear which reference gases were used and the calibration scales to which those can be traced back to. Considering that the dataset contains samples that span nearly a decade, I doubt the same reference gases have been used. However, in any case it is important to mention this to show the extent at which data are comparable.
Additional details on the analytical procedures, including the calibration approach, reference gases, and laboratory conditions, are provided in the revised text. Although the dataset covers nearly a decade, the methane samples were analysed using the same analytical methodology and under comparable laboratory conditions, with calibration performed using reference gases. This was feasible because of the ten-year run of the CAGE project.
l.128: A note indicating that isotopic oxygen measurements are being used as a water mass tracer would be useful for the reader.
Oxygen isotope data were obtained during only a limited number of cruises and do not cover all sampling points and areas included in our compilation. Therefore, it is not sufficiently comprehensive in our case to assess water-mass changes systematically across the different regions and depth levels based on isotope results.
l. 147–149: This is also an instance in which it would be important to provide details on how the data was quality-controlled and harmonised before being combined.
We added further details on the quality-control procedures and analytical considerations in Section 2.3 of the revised manuscript.
l. 152–153: The details of this are essential for the interpretation of the methane data in this study. As such, there should be clarity on how this background concentration was computed.
We added further details to Section 2.4 describing how the background methane concentration was determined. In addition, the R scripts used for data processing and plotting are provided as supplementary material.
l.166: To my understanding, works in preparation are not allowed as references.
Unpublished citation is removed from the manuscript.
l. 205–207: A table would be clearer for presenting all these values.
A table is added to summarise water mass properties as suggested
l. 205–213: Also, perhaps the authors could consider replacing the T-S in figure 2 by a T-S plot in which methane is depicted as 3 (z) axis, such that the large-scale distribution can be more clearly seen.
We would like to retain the T-S diagram in Figure 2 because it provides a consistent representation of the regional water-mass properties and the T-S boundaries used throughout the manuscript. This also allows the hydrographic context to be presented consistently with the subsequent analyses. In addition, such a visualisation, as seen in the attached figure, does not clearly reveal the large-scale methane distribution. Methane concentrations in our dataset span several orders of magnitude, and even when displayed on a logarithmic scale, the resulting distribution is strongly dominated by the low-concentration samples. High concentrations, on the other hand, are predominantly associated with the deepest sampling points and localised deep-water environments, which would make the overall spatial pattern difficult to distinguish in a T-S representation.
l. 216–217: For the reader it would be easier to see a column with the numbers of the regions according to Fig.1.
Region numbers are added in parentheses to clarify in the text
l. 290–310: This section is fairly descriptive and in a way redundant considering Table 2 and Figure 3.
We have reorganised and condensed the corresponding text to reduce redundancy.
l. 325–326: In the methods there is no mention of ROV sampling. This should be revised.
We have added details on the ROV sampling procedures to the Methods section
l. 340–345: Along the lines of one of my comments above: if the data can be clustered in two groups (i.e.Atlantic-dominated and Barents Sea), it would be more consistent (and potentially clearer) to keep the separation in this figure instead of showing the individual sub-regions.
We would prefer to retain the figure in its original form, showing the individual sub-regions. Although the water-column properties broadly indicate two main clusters, there are still substantial spatial differences among the individual sub-regions. We believe that retaining the regional separation provides additional value by preserving the spatial resolution of the compilation and allowing readers to identify and compare specific regions of interest. This regional information may also be useful for researchers who wish to further investigate individual methane-bearing areas or use the compiled dataset in future studies.
l.384: It is not clear what is meant with “stable nutrient couplings”.
We intended to emphasise the strong correlations observed among nutrient concentrations. However, we agree with the reviewer that the meaning of this term was unclear. We have therefore omitted the statement from the revised manuscript.
l. 416–421: This paragraph is redundant with the introduction (c.f. l.61–64) and the connection with own data is not sufficiently clear. Also, given that this is an important argument in explaining the differences between conditions that foster methane accumulation vs rapid dilution and transport, I would kindly suggest exploring the possibility of computing a proxy for water column stability to better substantiate the interpretation.
We have rewritten this paragraph in the revised manuscript to reduce redundancy. Regarding the suggested proxy for water-column stability, we unfortunately do not have ADCP measurements incorporated into the current dataset to derive a consistent proxy for currents or water-column stability across regions. However, we have now incorporated relevant observations from previous studies at the investigated sites to provide additional context for interpreting the potential influence of currents, transport, and mixing on methane accumulation and dilution.
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AC3: 'Reply on RC3', Muhammed Fatih Sert, 31 Aug 2026
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I was very disappointed with this manuscript which I believe fails in it's intention to address the "Biogeochemistry of methane in Arctic Waters". Though I accept that it does address the latter part of the title in presenting "A multiyear synthesis (2014-2022) from the North Atlantic-Arctic sector and Barents Sea". The manuscript is well presented and does offer a comprehensive description of variability in methane distribution but simply presenting this distribution alongside water column environmental variables does not deliver on any understanding of methane biogeochemistry that I can see, though estimates of methane oxidation and turnover do provide limited insight, despite the contention (Line 523-524) that these rates are specific to location. Lines 492-494 claims that the authors "evaluated whether methane enrichment produces detectable changes in water column biogeochemistry and which biogeochemical components might respond to elevated methane concentrations", I would argue that they simply compared profiles of variables with no defined protocol to what or why. Line 495 onward acknowledges that previous studies have failed to connect methane distribution to nutrient regimes and simply reconfirming this is not an investigation of methane biogeochemistry. The following lines indicate that a study of methane biogeochemistry needs to be focussed around the microbial cycling in deep waters and the last paragraph of the conclusion details what might be involved in such a study, unfortunately this was not done in the current manuscript. Further there are a number of statements which are simple supposition rather than supported fact: eg Line 515-516
A small number of specific points:
It should be noted in the title that a lot, if not all of the CH4 data presented results from sea-bed seeps
L60 is methane a micronutrient?
L86 water mass structure is not shown in Fig 1a,b
No methods are presented for DOP< PP, POC, PN, chlorophyll
L410 MOx rate are in Fig 5