A potential explanation for the anomalously low nitrate to phosphate ratio in the well-oxygenated East/Japan Sea

Kim, Hyo-Ryeon; Lim, Jae-Hyun; Jung, Hae-Kun; Shim, Jeong-Min; Kim, Ju-Hyoung; Kim, Seo-Young; Kim, Il-Nam

doi:10.5194/egusphere-2025-5184

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https://doi.org/10.5194/egusphere-2025-5184

Preprints

01 Dec 2025

| 01 Dec 2025

A potential explanation for the anomalously low nitrate to phosphate ratio in the well-oxygenated East/Japan Sea

Hyo-Ryeon Kim, Jae-Hyun Lim, Hae-Kun Jung, Jeong-Min Shim, Ju-Hyoung Kim, Seo-Young Kim, and Il-Nam Kim

Abstract. The East/Japan Sea (EJS), a well‑oxygenated marginal sea, exhibits an anomalously low nitrate (NO₃⁻) to phosphate (PO₄³⁻) ratio (~ 2.6:1), diverging from the canonical Redfield ratio (16:1). To resolve this long‑standing biogeochemical enigma, we examined nitrogen (N) cycling genes and bacterial communities across depths and seasons. External phosphorus inputs – riverine, atmospheric, and crustal – were insufficient to explain the imbalance. Instead, high abundances of N‑reducing genes and affiliated taxa suggest a plausible role for bacterially mediated N loss throughout the water column. We propose that N removal may occur within particle-associated microenvironments (i.e., oxygen-depleted microzones inside sinking organic aggregates), despite oxygen-rich conditions. A dual-scale feedback – short-term anthropogenic N deposition enriching surface waters (i.e., increasing NO₃⁻:PO₄³⁻ ratio in the upper waters) and longer-term deoxygenation, driven by the weakening of deep-water formation, potentially favoring subsurface N loss (i.e., decreasing NO₃⁻:PO₄³⁻ ratio in the deep waters) – may promote a vertically stratified NO₃⁻:PO₄³⁻ regime in the future EJS. Our findings highlight the EJS as a sentinel system for how combined anthropogenic and climatic forces could reshape marine nutrient balances.

Received: 20 Oct 2025 – Discussion started: 01 Dec 2025

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Journal article(s) based on this preprint

09 Jul 2026

A potential explanation for the anomalously low nitrate to phosphate ratio in the well-oxygenated East/Japan Sea

Hyo-Ryeon Kim, Jae-Hyun Lim, Hae-Kun Jung, Jeong-Min Shim, Ju-Hyoung Kim, Seo-Young Kim, and Il-Nam Kim

Biogeosciences, 23, 4719–4733, https://doi.org/10.5194/bg-23-4719-2026,https://doi.org/10.5194/bg-23-4719-2026, 2026

Short summary

Hyo-Ryeon Kim, Jae-Hyun Lim, Hae-Kun Jung, Jeong-Min Shim, Ju-Hyoung Kim, Seo-Young Kim, and Il-Nam Kim

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2025-5184', Anonymous Referee #1, 22 Jan 2026

The paper «A potential explanation for the anomalously low nitrate to phosphate ratio in the well-oxygenated East/Japan Sea » by Kim et al. attempt to explore the contribution of bacterially mediated N loss for explaining the low N:P ratio encountered in the East/Japan Sea. The study is based on the hypothesis that N reducing pathways, i.e. nitrate reduction and denitrification, may occur at relevant magnitude in their study area (despite the well oxygenated conditions encountered), enough to explain low NO3-PO4 ratios. To test their hypothesis, the authors use sequencing data from samples collected between the surface and 1000 m depth during 5 cruises in the EJS, between February and October 2021. 16S sequencing was used to build up a taxonomic classification of bacterial communities at the order level. Furthermore, they applied a computational tool to infer functional properties of the obtained bacterial communities in an attempt to analyse the relative abundance of N-reducing genes.
I am not a specialist in genomics approaches but (or maybe because of that) I find that the Methods section lack literature references (with doi) for applied protocols, bioinformatics tools/pipelines and used databases. Hopefully, other reviewers more proficient in the field may assess whether the used methodology is sound.
This said, the main and critical caveat of this work is, in my opinion, that the conclusions are not supported by the data and the interpretation of the results is sometimes way too speculative. The authors base their conclusions in a series of numbers (percentages of N-reducing genes and associated bacterial communities) which do not give sufficient quantitative information. Throughout the manuscript, the authors state that they found « high » abundances of N-reducing genes ; but high compared to what ? And how can we know that the obtained percentages are « enough » to explain the observed N:P ratios ? Moreover, seasonal and vertical variability is presented without really assessing the reasons and consequences of this variability.
Nutrient data collected during the cruises are exploited only superficially although they should be at the center of their study. In the current version, all nutrient data have been merged to produce a unique value of NO3:PO4 ratio which is not presented in the results section but in the introduction. I strongly suggest to present the nutrient profiles for each cruise to explore seasonal and vertical variability in the same way as the genomics data. This may allow to compare the variability between nutrients and genomics data which may help assessing the role of N-reducing pathways in N loss in the water column.
The Results and Discussion section reads more like a literature review of the factors that may drive N:P ratios in the study area and I found that the results are not discussed enough. Moreover, there are a number of inconsistencies in the arguments given. For instance, the first part of the section claims that external phosphorus inputs are insufficient to explain low N:P ratios but later on, the authors state that N-enriched atmospheric deposition is responsible for high N:P ratios in surface waters. Again, presenting nutrient profiles will be very useful to understand whether N:P ratios are indeed higher in the surface that in deeper waters.
All the above are suggestions to help the authors derive clear findings from their hypotheses and data, and present substantial scientific insights. I suggest a thorough revision of the paper, particularly the Results and Discussion section, but I must say that I am not sure if such a thorough revision will finally make the manuscript suitable for publication in Biogeosciences.
Specific comments:
Lines 57-59. If low N:P ratios are a known feature of the EJA, I suggest the authors refer to literature data in the introduction and present their own data in the results section in a more detailed way.
Lines 64-66. Since genomics-based techniques are experiences rapid advances, the authors may want to cite more recent references.
Line 81. I guess it was filters and not filtered samples that were frozen and used for DNA extraction.
Line 83. Same comment as above.
As said before, the results and discussion section is awkward. Indeed, only 3.2. sub-section is properly results and a bit of light discussion. Sub-section 3,1 reads more like a literature review.
Lines 139-140. Please, add references for the selected biomarker genes.
Figure 2. Is there a possibility of adding error bars?
Line 169. Aren’t some of these orders (e.g. Alteromonadales, Pseudomonadales) ubiquitous in the ocean?
Line 178-179. The statement that proportions of 37.7% of N-reducing genes and 20.0% of taxa indicate the potential for bacterially mediated N loss is not very convincing. How these numbers compare with other regions?

Citation: https://doi.org/10.5194/egusphere-2025-5184-RC1
- AC1: 'Reply on RC1', Hyoryeon Kim, 17 Mar 2026
  
  We thank Reviewer #1 for the careful reading of our manuscript and for the constructive and insightful comments.
  We carefully considered each comment and prepared detailed, point-by-point responses. Accordingly, the manuscript has been revised to improve both structure and interpretation. In particular, we incorporated depth-resolved nutrient data at the same resolution as the genomic dataset, strengthening the data-driven basis of our analysis. We also reorganized the Results and Discussion to establish a clearer nutrient–genomic linkage framework. In addition, wording has been refined and relevant literature incorporated to ensure more precise and balanced interpretation. We believe these revisions have substantially improved the clarity and robustness of the manuscript. Detailed responses to each comment are provided in the attached PDF.
  
  Citation: https://doi.org/10.5194/egusphere-2025-5184-AC1
RC2:
'Comment on egusphere-2025-5184', Anonymous Referee #2, 18 Feb 2026

In this manuscript, Kim et al. explore the possible causes for the relatively low NO3:PO4 ratio in a well-oxygenated water column in the East/Japan Sea. They collected water samples from different depths over five months to understand microbial N cycling. They measured the abundance of N-reducing genes and the distribution of functionally grouped N-reducing bacterial communities. Based on these (non-quantitative) sampling results, they conclude that there is dual feedback driving the low NO3:PO4, i.e., enrichment in NO3 due to atmospheric N deposition and reduction of NO3 in low-oxygen microenvironments. They conclude that in the future, this process will prevail, as subsurface N removal associated with climate-driven deoxygenation, and the EJS can potentially serve as a sentinel for biogeochemical response in other regions.

Major comments
Overall, the paper is well written and clear. However, I think that the evidence given in the manuscript does not justify the conclusion. First, the water column in the EJS is well oxygenated (Fig. 1B). So, even a proposed reduction in 20 M O₂ will not make the deep ocean anoxic. Therefore, the proposed dual-scale feedback seems to be irrelevant to the EJS.
The author also mentions in the abstract that low NO3:PO4 in the well-oxygenated EJS is a “long-standing biogeochemical enigma”. This is the first time I have heard of this interesting enigma, and I would like to understand more about how past studies have approached it. The authors only provide a general statement (“Much of our current understanding of marine N cycling ...” LN 50). It is missing to understand what has been done until today.
P-balance: The riverine P balance has not been sufficiently analyzed. I would like to get more quantitative information about the riverine input – when was the dam constructed? What is the NO3:PO4 in the CDW? What do you mean by “confined to surface layers”? It is possible that the low NO3:PO4 is due to past influx? I would like more quantitative information on the long-term NO3:PO4 balance for the EJS. Furthermore, what about the release of P from anoxic sediment?
I am not so familiar with the sequencing protocol, so I am unable to evaluate it. However, to gain more quantitative intuition into the significance of the N-reducing genes, it would be beneficial to compare them with other locations. Perhaps other studies showed the relationship between N-reducing genes and rates?
Is it possible to plot NO3:PO4 vs. depth?
Minor comments
line 35 - > cite Tyrell ‘The relative influences of nitrogen and phosphorus on oceanic primary production’ (1999)
Line 50 -> cite Martiny et al., ‘Strong latitudinal patterns in the elemental ratios of marine plankton and organic matter’, 2013.
Line 50: What do you mean by “circulation terminates”?
Line 60: “Much of our current understanding of marine N cycling...” is it a general statement or is it specific to the EJS?

Citation: https://doi.org/10.5194/egusphere-2025-5184-RC2
- AC2: 'Reply on RC2', Hyoryeon Kim, 17 Mar 2026
  
  We thank Reviewer #2 for the constructive and insightful comments.
  We carefully considered the points raised and revised the manuscript accordingly to improve clarity and consistency of interpretation. In particular, we strengthened the quantitative assessment of phosphorus sources using additional literature, clarified the distinction between short- and long-term (dual timescale) processes, and refined the associated interpretations. We also expanded the Discussion by placing our results in the context of other regions while acknowledging the characteristics of our dataset. We believe these revisions have improved the clarity and robustness of the manuscript. Detailed, point-by-point responses are provided in the attached PDF.
  
  Citation: https://doi.org/10.5194/egusphere-2025-5184-AC2

Peer review completion

AR – Author's response | RR – Referee report | ED – Editor decision | EF – Editorial file upload

ED: Reconsider after major revisions (13 Apr 2026) by Frédéric Gazeau

AR by Hyoryeon Kim on behalf of the Authors (16 Apr 2026) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (17 Apr 2026) by Frédéric Gazeau

RR by Anonymous Referee #2 (18 May 2026)

Suggestions for revision or reasons for rejection

The paper has improved overall. However, I have significant concerns about the proposed “dual feedback” mechanism that should be addressed before publication. As stated in the title, the authors provide a potential explanation for the low NO3:PO4 ratio in the East Japan Sea and have overall improved the manuscript. However, I still have one major concern that should be addressed before the publication. Specifically, the authors do not adequately justify the proposed “dual feedback” mechanism for future conditions. The authors argue that a reduction in O2 “driven by the weakening of deep-water formation, potentially favoring subsurface N loss”. However, the authors did not justify this conclusion. To support this claim, the authors need to show a correlation between O2 concentration and the abundance of N-reducing genes using their data samples. Alternatively, they should provide a correlation between O2 concentration and the extent of O2-depleted microenvironments. If the authors cannot provide this evidence, I propose to tone down or remove claims about the projection of this dual feedback (specifically from the abstract and Section 3.5).

Specific comments:
• Line 65: “physical circulation and remineralization” - Please explain how these processes contribute to the low NO3:PO4 ratio.

• Line 65: “possible denitrification” – how was this concluded? observations?

• Line 85 (0m) - add a space between the ‘0’ and the ‘m’ (i.e., "0 m" not "0m").

• Line 95 - Remove the unnecessary gap after "After quality control,”

• New Section 3.1 - great addition to the paper.

• Line 200: Please separate "1000" from "m" (i.e., "1000 m" not "1000m").

• I suggest moving the Section ‘External phosphorous input cannot explain the low NO3:PO4 ratios” to its earlier position (i.e., after Section 3.1)

Hide

RR by Anonymous Referee #3 (05 Jun 2026)

Suggestions for revision or reasons for rejection

This revised manuscript provides an innovative and compelling biogeochemical rationale for the persistent low NO₃⁻:PO₄³⁻ ratio in the oxygenated water column of the East/Japan Sea (EJS). The authors have successfully integrated constructive feedback from the previous review, significantly strengthening the logical foundation of the study. In particular, the newly added depth-resolved nutrient distributions and the quantitative exclusion of external sources such as riverine and sedimentary inputs provide strong support for the main conclusions of the manuscript. Consequently, the revised manuscript is considered to be of sufficient merit for publication, pending a few minor technical revisions. For example:
Revision (p. 2, line 36): The reference “Tyrell, 1999” appears to be a typographical error and should be corrected to “Tyrrell, 1999”.
Revision (Figure 2, p. 6): The sentence “The dashed gray line indicating the canonical Redfield ratio (16:1)” lacks a main verb.
Revision (Figure 2, p. 6): The expression “below 0.05 < µmol L⁻¹” is redundant in its notation.
In addition, I recommend a thorough final proofreading of the manuscript to ensure consistency in spelling and proper alignment of all references.
Finally, while this study provides important insights into nutrient stoichiometry and microbial responses in the EJS, it is limited by the specific sampling period. To better understand the long-term impacts of environmental variability and climate change on nutrient distributions, future research should be considered to require long-term observational datasets, together with high-resolution numerical modeling and autonomous observing platforms, in order to quantitatively resolve the relative contributions of physical transport and biological processes.

Hide

ED: Publish subject to minor revisions (review by editor) (10 Jun 2026) by Frédéric Gazeau

AR by Hyoryeon Kim on behalf of the Authors (12 Jun 2026) Author's response Author's tracked changes Manuscript

ED: Publish as is (24 Jun 2026) by Frédéric Gazeau

AR by Hyoryeon Kim on behalf of the Authors (25 Jun 2026) Manuscript

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2025-5184', Anonymous Referee #1, 22 Jan 2026

The paper «A potential explanation for the anomalously low nitrate to phosphate ratio in the well-oxygenated East/Japan Sea » by Kim et al. attempt to explore the contribution of bacterially mediated N loss for explaining the low N:P ratio encountered in the East/Japan Sea. The study is based on the hypothesis that N reducing pathways, i.e. nitrate reduction and denitrification, may occur at relevant magnitude in their study area (despite the well oxygenated conditions encountered), enough to explain low NO3-PO4 ratios. To test their hypothesis, the authors use sequencing data from samples collected between the surface and 1000 m depth during 5 cruises in the EJS, between February and October 2021. 16S sequencing was used to build up a taxonomic classification of bacterial communities at the order level. Furthermore, they applied a computational tool to infer functional properties of the obtained bacterial communities in an attempt to analyse the relative abundance of N-reducing genes.
I am not a specialist in genomics approaches but (or maybe because of that) I find that the Methods section lack literature references (with doi) for applied protocols, bioinformatics tools/pipelines and used databases. Hopefully, other reviewers more proficient in the field may assess whether the used methodology is sound.
This said, the main and critical caveat of this work is, in my opinion, that the conclusions are not supported by the data and the interpretation of the results is sometimes way too speculative. The authors base their conclusions in a series of numbers (percentages of N-reducing genes and associated bacterial communities) which do not give sufficient quantitative information. Throughout the manuscript, the authors state that they found « high » abundances of N-reducing genes ; but high compared to what ? And how can we know that the obtained percentages are « enough » to explain the observed N:P ratios ? Moreover, seasonal and vertical variability is presented without really assessing the reasons and consequences of this variability.
Nutrient data collected during the cruises are exploited only superficially although they should be at the center of their study. In the current version, all nutrient data have been merged to produce a unique value of NO3:PO4 ratio which is not presented in the results section but in the introduction. I strongly suggest to present the nutrient profiles for each cruise to explore seasonal and vertical variability in the same way as the genomics data. This may allow to compare the variability between nutrients and genomics data which may help assessing the role of N-reducing pathways in N loss in the water column.
The Results and Discussion section reads more like a literature review of the factors that may drive N:P ratios in the study area and I found that the results are not discussed enough. Moreover, there are a number of inconsistencies in the arguments given. For instance, the first part of the section claims that external phosphorus inputs are insufficient to explain low N:P ratios but later on, the authors state that N-enriched atmospheric deposition is responsible for high N:P ratios in surface waters. Again, presenting nutrient profiles will be very useful to understand whether N:P ratios are indeed higher in the surface that in deeper waters.
All the above are suggestions to help the authors derive clear findings from their hypotheses and data, and present substantial scientific insights. I suggest a thorough revision of the paper, particularly the Results and Discussion section, but I must say that I am not sure if such a thorough revision will finally make the manuscript suitable for publication in Biogeosciences.
Specific comments:
Lines 57-59. If low N:P ratios are a known feature of the EJA, I suggest the authors refer to literature data in the introduction and present their own data in the results section in a more detailed way.
Lines 64-66. Since genomics-based techniques are experiences rapid advances, the authors may want to cite more recent references.
Line 81. I guess it was filters and not filtered samples that were frozen and used for DNA extraction.
Line 83. Same comment as above.
As said before, the results and discussion section is awkward. Indeed, only 3.2. sub-section is properly results and a bit of light discussion. Sub-section 3,1 reads more like a literature review.
Lines 139-140. Please, add references for the selected biomarker genes.
Figure 2. Is there a possibility of adding error bars?
Line 169. Aren’t some of these orders (e.g. Alteromonadales, Pseudomonadales) ubiquitous in the ocean?
Line 178-179. The statement that proportions of 37.7% of N-reducing genes and 20.0% of taxa indicate the potential for bacterially mediated N loss is not very convincing. How these numbers compare with other regions?

Citation: https://doi.org/10.5194/egusphere-2025-5184-RC1
- AC1: 'Reply on RC1', Hyoryeon Kim, 17 Mar 2026
  
  We thank Reviewer #1 for the careful reading of our manuscript and for the constructive and insightful comments.
  We carefully considered each comment and prepared detailed, point-by-point responses. Accordingly, the manuscript has been revised to improve both structure and interpretation. In particular, we incorporated depth-resolved nutrient data at the same resolution as the genomic dataset, strengthening the data-driven basis of our analysis. We also reorganized the Results and Discussion to establish a clearer nutrient–genomic linkage framework. In addition, wording has been refined and relevant literature incorporated to ensure more precise and balanced interpretation. We believe these revisions have substantially improved the clarity and robustness of the manuscript. Detailed responses to each comment are provided in the attached PDF.
  
  Citation: https://doi.org/10.5194/egusphere-2025-5184-AC1
RC2:
'Comment on egusphere-2025-5184', Anonymous Referee #2, 18 Feb 2026

In this manuscript, Kim et al. explore the possible causes for the relatively low NO3:PO4 ratio in a well-oxygenated water column in the East/Japan Sea. They collected water samples from different depths over five months to understand microbial N cycling. They measured the abundance of N-reducing genes and the distribution of functionally grouped N-reducing bacterial communities. Based on these (non-quantitative) sampling results, they conclude that there is dual feedback driving the low NO3:PO4, i.e., enrichment in NO3 due to atmospheric N deposition and reduction of NO3 in low-oxygen microenvironments. They conclude that in the future, this process will prevail, as subsurface N removal associated with climate-driven deoxygenation, and the EJS can potentially serve as a sentinel for biogeochemical response in other regions.

Major comments
Overall, the paper is well written and clear. However, I think that the evidence given in the manuscript does not justify the conclusion. First, the water column in the EJS is well oxygenated (Fig. 1B). So, even a proposed reduction in 20 M O₂ will not make the deep ocean anoxic. Therefore, the proposed dual-scale feedback seems to be irrelevant to the EJS.
The author also mentions in the abstract that low NO3:PO4 in the well-oxygenated EJS is a “long-standing biogeochemical enigma”. This is the first time I have heard of this interesting enigma, and I would like to understand more about how past studies have approached it. The authors only provide a general statement (“Much of our current understanding of marine N cycling ...” LN 50). It is missing to understand what has been done until today.
P-balance: The riverine P balance has not been sufficiently analyzed. I would like to get more quantitative information about the riverine input – when was the dam constructed? What is the NO3:PO4 in the CDW? What do you mean by “confined to surface layers”? It is possible that the low NO3:PO4 is due to past influx? I would like more quantitative information on the long-term NO3:PO4 balance for the EJS. Furthermore, what about the release of P from anoxic sediment?
I am not so familiar with the sequencing protocol, so I am unable to evaluate it. However, to gain more quantitative intuition into the significance of the N-reducing genes, it would be beneficial to compare them with other locations. Perhaps other studies showed the relationship between N-reducing genes and rates?
Is it possible to plot NO3:PO4 vs. depth?
Minor comments
line 35 - > cite Tyrell ‘The relative influences of nitrogen and phosphorus on oceanic primary production’ (1999)
Line 50 -> cite Martiny et al., ‘Strong latitudinal patterns in the elemental ratios of marine plankton and organic matter’, 2013.
Line 50: What do you mean by “circulation terminates”?
Line 60: “Much of our current understanding of marine N cycling...” is it a general statement or is it specific to the EJS?

Citation: https://doi.org/10.5194/egusphere-2025-5184-RC2
- AC2: 'Reply on RC2', Hyoryeon Kim, 17 Mar 2026
  
  We thank Reviewer #2 for the constructive and insightful comments.
  We carefully considered the points raised and revised the manuscript accordingly to improve clarity and consistency of interpretation. In particular, we strengthened the quantitative assessment of phosphorus sources using additional literature, clarified the distinction between short- and long-term (dual timescale) processes, and refined the associated interpretations. We also expanded the Discussion by placing our results in the context of other regions while acknowledging the characteristics of our dataset. We believe these revisions have improved the clarity and robustness of the manuscript. Detailed, point-by-point responses are provided in the attached PDF.
  
  Citation: https://doi.org/10.5194/egusphere-2025-5184-AC2

Peer review completion

AR – Author's response | RR – Referee report | ED – Editor decision | EF – Editorial file upload

ED: Reconsider after major revisions (13 Apr 2026) by Frédéric Gazeau

AR by Hyoryeon Kim on behalf of the Authors (16 Apr 2026) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (17 Apr 2026) by Frédéric Gazeau

RR by Anonymous Referee #2 (18 May 2026)

Suggestions for revision or reasons for rejection

Hide

RR by Anonymous Referee #3 (05 Jun 2026)

Suggestions for revision or reasons for rejection

Hide

ED: Publish subject to minor revisions (review by editor) (10 Jun 2026) by Frédéric Gazeau

AR by Hyoryeon Kim on behalf of the Authors (12 Jun 2026) Author's response Author's tracked changes Manuscript

ED: Publish as is (24 Jun 2026) by Frédéric Gazeau

AR by Hyoryeon Kim on behalf of the Authors (25 Jun 2026) Manuscript

Journal article(s) based on this preprint

09 Jul 2026

A potential explanation for the anomalously low nitrate to phosphate ratio in the well-oxygenated East/Japan Sea

Hyo-Ryeon Kim, Jae-Hyun Lim, Hae-Kun Jung, Jeong-Min Shim, Ju-Hyoung Kim, Seo-Young Kim, and Il-Nam Kim

Biogeosciences, 23, 4719–4733, https://doi.org/10.5194/bg-23-4719-2026,https://doi.org/10.5194/bg-23-4719-2026, 2026

Short summary

Hyo-Ryeon Kim, Jae-Hyun Lim, Hae-Kun Jung, Jeong-Min Shim, Ju-Hyoung Kim, Seo-Young Kim, and Il-Nam Kim

Supplement

https://doi.org/10.5194/egusphere-2025-5184-supplement

Hyo-Ryeon Kim, Jae-Hyun Lim, Hae-Kun Jung, Jeong-Min Shim, Ju-Hyoung Kim, Seo-Young Kim, and Il-Nam Kim

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The well-oxygenated East/Japan Sea shows a low NO₃⁻:PO₄³⁻ ratio (12.6:1), below the Redfield ratio (16:1). External P inputs cannot explain this. Abundant N-reducing genes and bacteria indicate microbial N loss within oxygen-poor microzones in sinking particles. A dual feedback is proposed: surface N enrichment from atmospheric deposition and deep N loss from deoxygenation, forming a vertically stratified nutrient regime under future change.


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