New constraints on biological production and mixing  processes in the South China Sea from triple isotope  composition of dissolved oxygen

Jurikova, Hana; Abe, Osamu; Shiah, Fuh-Kwo; Liang, Mao-Chang

doi:https://doi.org/10.5194/bg-19-2043-2022

Articles | Volume 19, issue 7

https://doi.org/10.5194/bg-19-2043-2022

© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/bg-19-2043-2022

© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 19, issue 7

Research article

|

14 Apr 2022

Research article |

| 14 Apr 2022

New constraints on biological production and mixing processes in the South China Sea from triple isotope composition of dissolved oxygen

Hana Jurikova, Osamu Abe, Fuh-Kwo Shiah, and Mao-Chang Liang

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Final revised paper (published on 14 Apr 2022)
Supplement to the final revised paper
Preprint (discussion started on 15 Jan 2021)
Supplement to the preprint

Interactive discussion

Status: closed

RC1:
'Comment on bg-2020-448', Anonymous Referee #1, 07 Feb 2021

The comment was uploaded in the form of a supplement: https://bg.copernicus.org/preprints/bg-2020-448/bg-2020-448-RC1-supplement.pdf

Citation: https://doi.org/10.5194/bg-2020-448-RC1
- AC1: 'Reply on RC1, RC2 and RC3', Hana Jurikova, 26 May 2021
  
  The comment was uploaded in the form of a supplement: https://bg.copernicus.org/preprints/bg-2020-448/bg-2020-448-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/bg-2020-448-AC1
RC2:
'Comment on bg-2020-448', Anonymous Referee #2, 09 Mar 2021

The comment was uploaded in the form of a supplement: https://bg.copernicus.org/preprints/bg-2020-448/bg-2020-448-RC2-supplement.pdf

Citation: https://doi.org/10.5194/bg-2020-448-RC2
- AC1: 'Reply on RC1, RC2 and RC3', Hana Jurikova, 26 May 2021
  
  The comment was uploaded in the form of a supplement: https://bg.copernicus.org/preprints/bg-2020-448/bg-2020-448-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/bg-2020-448-AC1
RC3:
'Comment on bg-2020-448', Anonymous Referee #3, 11 Mar 2021

Review of “New constraints on biological production and mixing processes in the South China Sea from triple isotope composition of dissolved oxygen” by Hana Jurikova, Osamu Abe, Fuh-Kwo Shiah and Mao-Chang Liang

Summary:

In this manuscript, the authors present triple oxygen isotope data from the SouthEast Asian Time-series Study (SEATS, 18ËN, 116ËE) in the South China Sea. The samples were taken during three different years and three different states of the monsoon in the area. Based on this data and O2/Ar measurements, they determine gross primary production and net community production rates.

General Comments:

There are a number of severe points that need to be addressed before a possible publication. Most of these are covered by the two already submitted, detailed referee comments. Generally, this study lacks detailed description about how the sampling and analysis was conducted (e.g. the missing Chl a sampling in the methods section) and a proper error analysis.

The other main critique point, that I want to stress, is that this study is lacking a discussion about whether or not the sampled profiles are representative for the region and the season. This study is based on triple oxygen isotope measurements from three different seasons and three different years: 1 cast in October 2013 (11 samples from 5 to 500m), 2 casts on consecutive days from August 2014 (24 samples between 5 and 3500m) and 2 casts on consecutive days in April 2015 (21 samples between 5 and 3500m). O2/Ar data is only available for the stations in 2014 and 2015.

This is a very small amount of data to base such a study on. The authors need to give a detailed discussion about why they think that the presented profiles are representative for the area and the season. This could for example be done by comparing the measured profiles of temperature, chlorophyll and dissolved oxygen with previous observations in the area.

Minor comment:

Figure 4 needs to be changed. Especially for the shown oxygen data, the chosen diagram type and colorbar is not suited. It would also be interesting to see oxygen saturation data.

Citation: https://doi.org/10.5194/bg-2020-448-RC3
- AC1: 'Reply on RC1, RC2 and RC3', Hana Jurikova, 26 May 2021
  
  The comment was uploaded in the form of a supplement: https://bg.copernicus.org/preprints/bg-2020-448/bg-2020-448-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/bg-2020-448-AC1

Peer review completion

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

ED: Reconsider after major revisions (08 Jun 2021) by Carol Robinson

AR by Hana Jurikova on behalf of the Authors (24 Sep 2021) Author's response Author's tracked changes Manuscript

EF by Sarah Buchmann (24 Sep 2021)

ED: Referee Nomination & Report Request started (25 Sep 2021) by Carol Robinson

RR by Anonymous Referee #1 (09 Dec 2021)

Suggestions for revision or reasons for rejection

I appreciate the authors following the recommendations made during the first revision of this manuscript. The manuscript is now more structured and easier to read. The authors included more references sustained with data for comparison to other studies and addressed uncertainties in their calculations.
I still have some comments (annotated in the pdf of the revised ms) and recommendations listed below, that I hope help the authors to further improve their manuscript for its publication in Biogeosciences.
Main comments:
1) Despite the authors mentioned in their response that the revised manuscript went through a thorough English edition, I still found places where there are typos or grammar mistakes. I only marked some of them as annotated comments in the revised manuscript. I strongly recommend the authors to check again the English before final publication.

2) The review of the revised manuscript, could have been also facilitated if the authors would have included in their response file the exact paragraphs that were modified in the revised text, or pointing out to the location where the changes were made. Instead, the response is filled with words like “clarified”, “modified”, etc.

3) I find certain contradictions between the individual response to the reviewers and what is actually written in the manuscript. Specifically concerning the possible upward contribution of O2-rich water (and Chl-a maximum horizon) from below the thermocline into the mixed layer during October 2013. The authors replied that they “did not find any significant upwelling of water and therefore this component of mixing from the deep layer might have not been relevant”. However, in numerous places in the revised manuscript, they agree that this process might have been relevant due to the elevated 17 signal measured below the mixed layer in the sampling representing winter, e.g. Discussion section 4.1: “The high mixed layer values therefore seem to reflect transient increase in biological O2 due to upward flux of dissolved O2 from the Chl−a maximum horizon.”, or in section 4.3.: “Generally, we would, however, expect higher rates at SEATS, where both seasonal monsoon forcing and/or episodic typhoon events induce sufficient vertical mixing to bring nutrients to the mixed layer and stimulate primary production.”. There is no further comment to fix anything in this regard in the manuscript itself, however I recommend the authors to corroborate their individual answers with their actual manuscript content before submitting a response, hence the need to fulfill my comment no. 2 above.

4) The comparison between 14C-PP values from previous works and the NOP presented in this work, merits further discussion. I have added a review note in the annotated pdf file (last paragraph of section 4.2. of discussion)

Referee Report: PDF

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RR by Anonymous Referee #2 (21 Jan 2022)

ED: Publish subject to minor revisions (review by editor) (21 Jan 2022) by Carol Robinson

AR by Hana Jurikova on behalf of the Authors (15 Feb 2022) Author's response Author's tracked changes Manuscript

EF by Sarah Buchmann (15 Feb 2022)

ED: Publish as is (02 Mar 2022) by Carol Robinson

AR by Hana Jurikova on behalf of the Authors (08 Mar 2022) Manuscript

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Short summary

We studied the isotopic composition of oxygen dissolved in seawater in the South China Sea. This tells us about the origin of oxygen in the water column, distinguishing between biological oxygen produced by phytoplankton communities and atmospheric oxygen entering seawater through gas exchange. We found that the East Asian Monsoon plays an important role in determining the amount of oxygen produced vs. consumed by the phytoplankton, as well as in inducing vertical water mass mixing.