Influence of intraseasonal eastern boundary circulation variability on hydrography and biogeochemistry off Peru

Lüdke, Jan; Dengler, Marcus; Sommer, Stefan; Clemens, David; Thomsen, Sören; Krahmann, Gerd; Dale, Andrew W.; Achterberg, Eric P.; Visbeck, Martin

doi:https://doi.org/10.5194/os-16-1347-2020

Articles | Volume 16, issue 6

https://doi.org/10.5194/os-16-1347-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Special issue:

Ocean deoxygenation: drivers and consequences – past, present...

https://doi.org/10.5194/os-16-1347-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 16, issue 6

Research article

|

09 Nov 2020

Research article |

| 09 Nov 2020

Influence of intraseasonal eastern boundary circulation variability on hydrography and biogeochemistry off Peru

Jan Lüdke, Marcus Dengler, Stefan Sommer, David Clemens, Sören Thomsen, Gerd Krahmann, Andrew W. Dale, Eric P. Achterberg, and Martin Visbeck

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Final revised paper (published on 09 Nov 2020)
Preprint (discussion started on 05 Aug 2019)

Interactive discussion

Status: closed

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

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RC1: 'Review of "Influence of intraseasonal eastern boundary circulation variability on hydrography and biogeochemistry off Peru" By J. Lüdke et al.', Anonymous Referee #1, 12 Sep 2019
- AC1: 'Response to Reviewer 1', Jan Lüdke, 13 Feb 2020
RC2: 'Comments on “Influence of intraseasonal eastern boundary circulation variability on hydrography and biogeochemistry off Peru”', Anonymous Referee #2, 02 Oct 2019
- AC2: 'Response to Reviewer 2', Jan Lüdke, 14 Feb 2020

Peer-review completion

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

AR by Jan Lüdke on behalf of the Authors (16 Mar 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (29 Mar 2020) by Minhan Dai

RR by Anonymous Referee #2 (07 Apr 2020)

Suggestions for revision or reasons for rejection

The authors conducted extensive field observations of flow, hydrographic conditions and the concentration of biogeochemical substances over the shelf and slope off Peru. They combined the satellite remote-sensed SLA and SST and the field observations to investigate the causes of the intra-seasonal variabilities of, for example, DO in the water column and qualitatively discussed the characteristics of the propagating CTW, and those of the variant types of nutrients and DO, as well as oscillation in OMZ. This manuscript is extensively condensed and improved from its previous OSD version with great improvement in the scientific focus. This manuscript is well-written, and the reflected sciences are well presented. I thereafter intend to suggest an “minor revision”. However, since I still have serval suggestions for the authors to consider, I thereby suggest a major revision to let the authors think more in depth into the dynamics they proposed.
1) The authors revised the manuscript from their last submission to the OSD journal, and there are typos left. I suggest the authors to go through the entire manuscript very carefully. For example, L265, the last “maintaining” should be “maintain”. L280, 6 month should be “months”. L305, what does this “not inconsistent” mean? “consistent”? I didn’t see any verb in this sentence. I stop here, but it is the duty of the authors to check the expressions sentence by sentence.
2) Too many citations in the introduction section. I suggest you to just preserve the most representative ones, and reduce the number of references substantially. Obviously, you didn’t discuss all those studies. And I can not find Winkler 1888 (L130)?
3) L190, what does the exact meaning of the long sentences starting with “The data were …” I can understand that you did spatial smoothing but the description here is very confusing.
4) You clarified the respective roles of wind stress curl and wind stress itself. In section 4.2.1. This is good, but could you please also show in the response (you may don’t want to include them into the revised manuscript) about the role of tides? You don’t need to discuss the flood-ebb tides, but spring-neap tides may play some roles?
5) Still, section 4.4 is too descriptive. This is important, since that massive and systematic observations are new to us to understand the background and variabilities. However, it is still your obligation to help the readers to get insight into your science. I thereby strongly suggest the authors to include a schematic plot for different patterns of the CTWs propagation, changes in the shelf currents and the responses of the nutrients and DO you show in section 5. You cited too much of some others studies in the section 5, and some contents can be extracted from your own observation. I may suggest you to further condense and deepen the sciences in section 5 by your own data, although the current arrangement of logics looks sensible. This is the core of my major concern.

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RR by Anonymous Referee #3 (22 May 2020)

Suggestions for revision or reasons for rejection

I read the revised manuscript and the authors’ responses to the comments. Overall, following both reviewers’ comments, the authors have made adequate modifications to the deficiencies, especially the unclear explanation on physical processes, in the first draft. The revised paper have discussed the possible effects of various dynamic factors, including CTWs, local winds, topography, eddies etc., on the intraseasonal strengthening of PCUC. The comprehensive analyses of these potential factors indicate the essential role of CTWs in modulating the variability of sea level and PCUC. Although the authors has not carried out further numerical simulation, the existing data analysis results still provide a lot of valuable information on dynamic processes and physical-biogeochemical interactions. These interesting results are worthy of further quantification through the numerical experiments of coupling models in the future. At the same time, I also noticed that some new errors were introduced during the modification. Thus, I suggest that the authors read through the text and revise it carefully. Detailed comments are the following:

1) The authors modified the order of some figures, but the text part was not completely revised accordingly. As a result, some figures do not match the corresponding discussions in the text.
For example: l 284-288: Fig. 7 should be Fig. 6. The descriptions of Figures 8, 9 and 10 in Sections 4.3-4.4 actually correspond to figures 9, 10 and 11 in the list.

2) Section 4.1.3 should be Section 4.2.3.

3) P7, L272-274: “…… However, during the later period the strong acceleration of the poleward flow occurred, requiring an intensification of alongshore wind stress.” It is difficult to imagine why the intensification of alongshore wind will accelerate the poleward undercurrent. To my understanding, given that the prevailing winds are southeasterly along the Peruvian coast, the weakening of local southeast trade winds will excite poleward-propagating downwelling CTWs, similar to those driven by the equatorial westerly winds. In fact, some studies on the coastal El Nino in spring 2017 have shown that the northerly coastal wind anomalies and the equatorial westerly winds anomalies are both important in maintaining the high sea level along the Peruvian coast (e.g. Peng et al., 2019).
Peng, Q., Xie, S., Wang, D. et al. Coupled ocean-atmosphere dynamics of the 2017 extreme coastal El Niño. Nat Commun 10, 298 (2019). https://doi.org/10.1038/s41467-018-08258-8.

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ED: Reconsider after major revisions (24 May 2020) by Minhan Dai

AR by Jan Lüdke on behalf of the Authors (06 Jul 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (20 Jul 2020) by Minhan Dai

RR by Anonymous Referee #2 (27 Jul 2020)

RR by Anonymous Referee #3 (01 Aug 2020)

ED: Publish as is (20 Aug 2020) by Minhan Dai

Short summary

We analyse the intraseasonal variability of the alongshore circulation off Peru in early 2017, this circulation is very important for the supply of nutrients to the upwelling regime. The causes of this variability and its impact on the biogeochemistry are investigated. The poleward flow is strengthened during the observed time period, likely by a downwelling coastal trapped wave. The stronger current causes an increase in nitrate and reduces the deficit of fixed nitrogen relative to phosphorus.