Fine-scale vertical structure of sound-scattering layers over an east border upwelling system and its relationship to pelagic habitat characteristics

Diogoul, Ndague; Brehmer, Patrice; Perrot, Yannick; Tiedemann, Maik; Thiam, Abou; El Ayoubi, Salaheddine; Mouget, Anne; Migayrou, Chloé; Sadio, Oumar; Sarré, Abdoulaye

doi:https://doi.org/10.5194/os-16-65-2020

Articles | Volume 16, issue 1

https://doi.org/10.5194/os-16-65-2020

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

https://doi.org/10.5194/os-16-65-2020

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

Articles | Volume 16, issue 1

Research article

|

13 Jan 2020

Research article |

| 13 Jan 2020

Fine-scale vertical structure of sound-scattering layers over an east border upwelling system and its relationship to pelagic habitat characteristics

Ndague Diogoul, Patrice Brehmer, Yannick Perrot, Maik Tiedemann, Abou Thiam, Salaheddine El Ayoubi, Anne Mouget, Chloé Migayrou, Oumar Sadio, and Abdoulaye Sarré

Download

Final revised paper (published on 13 Jan 2020)
Supplement to the final revised paper
Preprint (discussion started on 08 Apr 2019)
Supplement to the preprint

Interactive discussion

Status: closed

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

- Printer-friendly version

- Supplement

RC1: 'os-2019-23 Fine scale vertical structure', Dr. Heino Fock, 19 Jun 2019
- AC1: 'Reply to referees for the manuscript “Fine-scale vertical structure of sound scattering layers over an east border upwelling system and its relationship to pelagic habitat characteristics” by Diogoul et al.', Ndague DIOGOUL, 10 Aug 2019
RC2: 'Review of Diogoul et al., "Fine-scale vertical structure of sound scattering layers..."', Anonymous Referee #2, 17 Jul 2019
- AC2: 'Reply to referee #2 for the manuscript “Fine-scale vertical structure of sound scattering layers over an east border upwelling system and its relationship to pelagic habitat characteristics” by Diogoul et al.', Ndague DIOGOUL, 10 Aug 2019

Peer-review completion

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

AR by Ndague DIOGOUL on behalf of the Authors (27 Aug 2019)

ED: Referee Nomination & Report Request started (02 Sep 2019) by Mario Hoppema

RR by Anonymous Referee #2 (20 Sep 2019)

Suggestions for revision or reasons for rejection

I thank the authors for considering my suggestions and taking them into account when revising their paper, which has been significantly improved. However, I still feel it needs some further work before it can be published. My main concern, that there was not enough information presented on the identity of the organisms in the scattering layer, still remains. In this light, I was especially surprised to see “Figure revision 2” in the responses to the reviewers’ comments—I did not realize you had multifrequency data available! This in fact allows you to say a lot about the animals making up the SSLs, even if you do not have direct sampling. Looking at the multifrequency echogram included in the response to the reviews, the main SSL scatters much more strongly at 38 kHz than at 70 or 120 kHz. This alone tells you that the scattering is probably dominated by animals with gas inclusions, such as swimbladdered fishes, or siphonophores. Why isn’t this information included? It would make for a much stronger paper.

Also along these lines, you can reject copepods as the cause of the SSLs at 38 kHz. Fluid-like zooplankton such as krill and copepods will scatter more strongly at higher frequencies than 38 kHz (i.e., Sv70 – Sv38 and Sv120 – Sv38 will both be negative). See e.g. Chapter 7 in Simmonds and MacLennan (2005). You can then focus your discussion on the likely scatterers: small fish or fish larvae. You can discuss some of the likely species, and reason more clearly about what they’re doing in relation to upwelling.

Some further comments:

A note on Choy et al. 2017: Jellyfish are in general weak sound-scatterers, so they do not typically show up as SSLs (unless they are physonect siphonophores, which have a gas bubble...). They also don't show up much in net tows, since they get torn up and fall apart. Choy et al. showed that jellies were important in midwater food webs, but not that they were important contributors to SSLs.

Figure 1: The revised version of this figure is much better and should be used in the main paper rather than the appendix. If the authors wish to increase the contrast around the upwelling zone, they could compress the color scale so that the limits are, say, 19 and 23 degrees. While the original color scale produces striking contrasts between the upwelling and non-upwelling areas, they would fall in completely different locations if the scale were shifted slightly. This is the advantage of using a perceptually uniform colorscale; differences in brightness remain proportional to differences in value even if the scale is shifted or compressed.

Figure 2: This figure has also been improved. However, I would still request that the authors add some horizontal scale, either as a scale bar, an additional set of labels on the x-axis, or simply a reference in the figure caption, such as “the total length of the transect in (a) is ….”

Figure 6: This figure is much improved! The only remaining suggestion I would suggest is to flip the y-axis so that “up is up.”

Appendix I, J, and K: The coefficient values from these tables should be included in the ANCOVA results in the main text

Hide

ED: Reconsider after major revisions (30 Sep 2019) by Mario Hoppema

AR by Ndague DIOGOUL on behalf of the Authors (16 Oct 2019)

ED: Referee Nomination & Report Request started (22 Oct 2019) by Mario Hoppema

RR by Anonymous Referee #2 (08 Nov 2019)

ED: Publish subject to minor revisions (review by editor) (14 Nov 2019) by Mario Hoppema

Dear Drs Diogoul, Brehmer and co-authors,

Thank you for the revision of the previous version of your manuscript and the extensive response to the reviewers. Your manuscript is almost ready for publication. Please see the list of my final comments below.

There is much info on the precision and accuracy of the different methods presented, which is good. Missing I think is a final estimate of uncertainty of SSL data.

Please check whether the data are correctly cited, and if and how the data originators wish to be acknowledged: Global High Resolution Sea Surface Temperature (GHRSST) data extracted from daily outputs by the Regional Ocean Modeling System group at NASA’s Jet Propulsion Laboratory (JPL OurOcean, 2010). Daily SST data (GHRSST Level 4 G1SST Global Foundation Sea Surface Temperature Analysis)

L36 „unexpectedly reported“ This is very strange and does not belong here. It should be deleted.

L44 delete columns
L48 delete that

L48-49 “and that animals making up SSLs can be all kinds of different things” This is not correct. As written animals are similar to things. Please rephrase.

L52 I think with “Zooplankton” a new paragraph should start.
L64 Change sentence to: DHM, like DVM, which often occur concurrently, helps organisms to find food …

L72-73 “Upwelling fronts are by now a very well recognized part of the coastal upwelling process.” This is textbook knowledge and is not necessary here.

L76 driven (not drifted)
L79 please define SST with first use

L109 Please use SI units for oxygen concentration – or at least give it besides the unit you use

L124 define IRD
L136 Not sure if “structuration” is a correct word. It is often used as in “structuration theory” but that has nothing to do with SSLs

L167 hydrographic (not hydrologic)
L173 define DO here

L175 Winkler titrations (not Winkler test)
L178 Please use SI units for oxygen concentration

L195 define SA and Sv here (Sv is defined in L201)
L209 define HCA here

L210 define PCA here
L243 there is one “stations” too many here.

L269 Earlier the transects are indicated as T1-T3
L274, 276 Please be consistent with naming the transects

L309 Appendix G occurs twice
L347 Change to: Upwelling is a key process …

L358 … carrying nutrients to the coast which is separated by water mass fronts.
L384 … and a well-mixed surface layer.

L384-385 In the inshore area it is likely that …
L443 … which may have biased the observed …

L448 hydrographic (not hydrologic)
L466-467 “Despite hypoxia local condition found in some stations (DO <1.42 ml l-1), SSLs appeared.” This sentence is not clear. Please rephrase and use SI units for oxygen.

L468 delete: from waters
L480 present (instead of distributed)

L490 What is clines?
L503 delete led

L518 feature

There are many appendices. I think most should be moved to the supplementary material, in particular A, B, C, D, E, F, and G. Please note that in appendix G some of the same comments hold as for Figure 2. When A-G are moved to the supplementary material, also change the reference to it in the main text.

References
P45, L92-93 Mar Ecol Prog Ser occurs double
P45, L95 Deep Sea Res. Part I (I missing)

L46, L121-122 Please add city where symposium took place
L130 Please write out journal Fish and Fisheries

L138 idem
P47, L156 Complete reference: Front. Mar. Sci., 4:25. doi: 10.3389/fmars.2017.00025

P48, L198 Mar Ecol Prog Ser occurs double
L218 Deep Sea Res. Part I (I missing)

P49, L226-227 Any more info about this? Publisher, city?
L244 volume number not correct

P50, L270 Deep Sea Res. Part I (I missing)
P51, L327 Deep Sea Res. Part I (I missing)

Figure 1: Please indicate Cap Vert in the figure. In the caption a horizontal black line is mentioned; it is not present in the figure. It is not clear where the northern border of Gambia is. The transects are mentioned R1-R3 in the caption; this is not how they are shown in the figure. Stations of group 1 are not blue, but white. Please indicate in the caption that SST is shown in the figure. Please indicate what the white dashed lines indicate and what the numbers mean.

Figure 2 (at the location depicted by the red vertical line in top panels) (add: at the location)
What do the horizontal dashed lines in all profile diagrams show?
The unit for oxygen concentration is not a SI unit, please modify.

Figure 3 Please use a) and b) instead of 1) and 2)
In the 1) part of the figure: What exactly was done here? Method? What is the height on the y-axis show or represent?

Figure 4 T1, T2, T3 mentioned here do not occur in Figure 1.
Again the unit of dissolved oxygen is not correct.
The diagrams are called vertical profiles. This is not correct. They are contour plots.
“with positions of vertical probe stations CTD in the inshore area (vertical line in blue (G1)) and the offshore area (vertical line in red (G2)).” The positions of the stations are not at all clear. The blue and red vertical lines are not present.

Thanks and best wishes
Mario Hoppema

Hide

AR by Ndague DIOGOUL on behalf of the Authors (20 Nov 2019)

ED: Publish as is (25 Nov 2019) by Mario Hoppema

AR by Ndague DIOGOUL on behalf of the Authors (30 Nov 2019) Manuscript

Short summary

We characterized the water masses of the Senegalese Petite Côte and described spatial and temporal variations of SSLs in relation to their environment. SSL distributions were mainly structured by bottom depth, diel period, and the level of vertical stratification in the water column. This study serves as a precursor in the field of SSL study in the Senegalese Petite Côte and even West African coasts, hence the importance of this work.