The fate of upwelled nitrate off Peru shaped by submesoscale filaments and fronts

Hauschildt, Jaard; Thomsen, Soeren; Echevin, Vincent; Oschlies, Andreas; José, Yonss Saranga; Krahmann, Gerd; Bristow, Laura A.; Lavik, Gaute

doi:https://doi.org/10.5194/bg-18-3605-2021

Articles | Volume 18, issue 12

https://doi.org/10.5194/bg-18-3605-2021

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

https://doi.org/10.5194/bg-18-3605-2021

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

Articles | Volume 18, issue 12

Research article

|

17 Jun 2021

Research article |

| 17 Jun 2021

The fate of upwelled nitrate off Peru shaped by submesoscale filaments and fronts

Jaard Hauschildt, Soeren Thomsen, Vincent Echevin, Andreas Oschlies, Yonss Saranga José, Gerd Krahmann, Laura A. Bristow, and Gaute Lavik

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Final revised paper (published on 17 Jun 2021)
Supplement to the final revised paper
Preprint (discussion started on 14 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 "The fate of upwelled nitrate off Peru shaped by submesoscale filaments and fronts"', Takeyoshi Nagai, 01 Jun 2020
- AC1: 'Response to review of "The fate of upwelled nitrate off Peru shaped by submesoscale filaments and fronts"' by Takeyoshi Nagai', Jaard Hauschildt, 29 Sep 2020
RC2: 'Review of “The fate of upwelled nitrate off Peru shaped by submesoscale filaments and fronts” by Hauschildt et al.', Anonymous Referee #2, 24 Jul 2020
- AC2: 'Response to review of "The fate of upwelled nitrate off Peru shaped by submesoscale filaments and fronts"' by Anonymous Referee #2', Jaard Hauschildt, 29 Sep 2020

Peer-review completion

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

ED: Reconsider after major revisions (03 Oct 2020) by Aninda Mazumdar

AR by Jaard Hauschildt on behalf of the Authors (13 Oct 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (30 Oct 2020) by Aninda Mazumdar

RR by Anonymous Referee #2 (01 Dec 2020)

Suggestions for revision or reasons for rejection

Review of “The fate of upwelled nitrate off Peru shaped by submesoscale filaments and fronts” by Hauschildt e al.

General comment

The revised paper by Hauschildt e al. is more complete than the previous version and it is clear that the authors added quite some information to it and reorganized the results. I appreciate the new model evaluation section, and really like the new tables in the text, which help to understand the many results from the study.
However, I still find it difficult to read. The English is not polished and the new sections read badly. The structure of the paper is also odd, with the supplement consisting in one single plot without any commentary.
My suggestion is to publish the manuscript after minor revisions (especially on the writing) are done.
I will list below my comments.

Major comments

1) English and length
- I acknowledge the overall improvement in the paper, but I still find several of its portions really difficult to read, especially the new paragraphs in bold. I really encourage all of the authors to re-read these paragraphs as well as the whole paper, and improve the quality of the writing. Otherwise, I suggest to have a mother-tongue read it and correct the writing, as this would help quite a lot to deliver the message.
I am not going to provide a full list of corrections to the writing, but I will focus on a few critical points in the detailed comments list. It is on the authors to improve the rest of the paper.
- The manuscript is also really long, and much of the new text still includes numbers and many many details that are already provided in tables and plots. I strongly suggest that the authors make an effort to streamline and shorten the paper, where the information is already provided in plots and tables.
At the present moment, the combination of length and quality of the writing makes it very difficult to read through the entire manuscript.

2) Model evaluation
I really appreciate that the paper now includes a model evaluation to give context to the results. This subsection may be moved to the Methods rather than the Results, so to keep the real results more in focus.
However, as the other “new” parts of the paper (bold parts), also this section is not quite well written and should be improved. As a general note about the content of the evaluation, the text could and should focus more on what is relevant for the present study (see comments below): it should constitute a reference to then discuss strengths and shortcomings of the model results in the discussion. It is way more important to spend more words on these relevant aspects of the model performance, than to repeat in detail in the text all the numbers of the Taylor diagrams which already provide the information.
As the supplement consists in only one figure, I think this should rather be in an appendix to the main manuscript and not in a supplement. A supplement should be something more substantial than one spare plot.
It is good practice that, when using data (eg. AVHRR, CARS…), the authors also include the references to the relevant publications for that dataset.
In terms of the content of the model evaluation:
- Please, indicate biases in absolute values rather than percentages. The plot that is currently in the supplement doesn’t include difference plots, therefore this is even more important. How many degrees is the max positive SST bias, how many the negative? How many meters the MLD bias? And same for the other mentioned variables.
- Given the focus of this paper is on the lateral and vertical transport, wouldn’t it be appropriate to show a 2D map of the total velocity field and of the small scale variability of the flow (eg. standard deviation of SSH of the daily data or EKE)? This figure could also go in an appendix.
- The authors mention the upwelling being too strong in the model, and this is also visible in panels a,b,c of the supplement. This should be discussed in the model evaluation before than in the discussion.
- Regarding the figure in the supplement, I think comparison plots should show the difference plot (at least for the crucial 1/45o run), as without the difference the eye can easily be driven to find general similarities, but it’s very difficult to see biases in a quantitative way.

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Detailed comments

Abstract: please add a comma after often in the second sentence “Often, studies…” or better replace with something more clear, such as “Most studies on this topic…”

Abstract: why are some sentences bold?

Page 2, line 5: the following sentence misses the verb in its second half “These Eastern
Boundary Upwelling Systems (EBUS) are found in all major ocean basins and named after the Canary, Benguela, California, and Peru-Chile current systems.”

Why are some parts of the “manuscript version 3” in bold? The uploaded manuscript shouldn’t be the track changes manuscript. Also, for future use, it would be nice to have the track changes manuscript at the end of the “Author’s answers” file showing both what was added and what was removed from the previous submitted manuscript version. This can be obtained using latexdiff in latex, or the track changes in word. I strongly encourage the authors to use one of these methods in the future.

Page 3, lines 6-8: The following sentence must be corrected, the English is not sound:
“For instance, if the time scale of nitrate uptake by PP was shorter than that of subduction, mainly organic matter produced in the surface layer would be subducted. If it were longer, mainly nitrate would be subducted.” The subordinate doesn’t read correctly. One should write “… , more organic matter than nitrate would be subducted” and then “…, the opposite would be true”.

Page 10, lines 22-27: This paragraph is really difficult to read, please correct the English, all of the three sentences are not clear.
The 2 year averaging period (last sentence here) corresponds to the analysis data, is this correct? The duration of spinup and analysis data can be mentioned in subsection 2.5 where the simulation is described, and here the authors can refer to the fact that they evaluate the mean of the 2 years of analysis data without need to mention the spinup.

Page 10 line 28: “The model fit of” is not a sound expression, this sentence should be rephrased.

Page 10, line 30: For me, it is not clear here what figure I should look at when the authors talk about “spatial patterns”. All the discussion on patterns and biases is not clearly referring to any figure. Please, refer to the right figure when discussing the patterns. If the figure is the one in the supplement, please move it to an Appendix and mention it in the evaluation where needed.

Subsection 3.2: This subsection sounds like another model evaluation, especially given the beginning and the new final sentence. However, as far as I understand, the authors are focusing on one particular simulated event and not an average performance of the model. This is still not clear in the text, it is only mentioned in the figure caption.
The initial sentence “The characteristic structure of coastal upwelling in the physical fields is well reproduced in our simulations” refers to figure 4, and that one single figure doesn’t say much about the simulation as a whole, it only shows a particular event, therefore its description in the text shouldn’t be so general. At line 32, when starting the discussion of the model data, the authors should state something like (please, rephrase better before using):
From the model simulation, we chose one particular event that reproduces physical conditions similar to those of the survey and assessed the ability of the model to reproduced the dynamics observed in situ.

Page 25, line 4: “negative SST bias of ~ −3%”, please, use absolute values in degrees. Same also a few lines after: there is a comparison between a percentage bias in nitrate and an absolute bias in previous literature. This is not good for readability. Please, include absolute values also for the biases in the present model.

Page 25, line 30: Please, reverse the words order: “of the nitrate upwelling fluxes” or “of the upwelling fluxes of nitrate”

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ED: Reconsider after major revisions (13 Dec 2020) by Aninda Mazumdar

AR by Jaard Hauschildt on behalf of the Authors (24 Feb 2021) Author's response Author's tracked changes Manuscript

ED: Publish as is (18 Mar 2021) by Aninda Mazumdar

AR by Jaard Hauschildt on behalf of the Authors (12 Apr 2021)

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Short summary

In this paper we quantify the subduction of upwelled nitrate due to physical processes on the order of several kilometers in the coastal upwelling off Peru and its effect on primary production. We also compare the prepresentation of these processes in a high-resolution simulation (~2.5 km) with a more coarsely resolved simulation (~12 km). To do this, we combine high-resolution shipboard observations of physical and biogeochemical parameters with a complex biogeochemical model configuration.