Mesophotic Hardground Revealed by Multidisciplinary Cruise on the Brazilian Equatorial Margin

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Please see the file.

Comments on the Quality of English Language

The essay is generally fluent and natural in English.

Author Response

Reviewer #1

The authors performed the first scientific expedition on the Amapá continental shelf (ACS) and show the preliminary data on geophysical, geological and biological surveys were carried out within the ACS. For the cruise report, the quantity and quality of the data generally met the needs of the paper for publication. However, there are some issues with the interpretation of the data, the presentation of the conclusions, and the format of the writing, which the authors are advised to revise.

We sincerely appreciate all constructive comments of the reviewer and we accepted all of them.

 

#1. the interpretation of XRF data

As mentioned in Line 341, the XRF data should presented in “counts per second”. But in Line 506-514 and Figure 14, the XRF expression instead becomes a percentage. Generally, the natural logarithm of the XRF data can correspond well with tests for elemental content, but it cannot replace the latter in order to derive a quantitative percent content for an element. If similar studies have been published, please cite the relevant paper and describe them in the Methods section. If not, then it is best to use the natural logarithm of the XRF data as a qualitative index of elemental variation.

Thank you for highlighting this issue about the graphic representation of XRF data. We corrected Figure 14. It is now displayed to show the elements and their respective kilo counts per seconds (kcps).

 

#2. the interpretation of grain size data

In Line 515-519, authors report the grain size composition of the sediments. Further interpretation of the grain size data to determine the type of sediment (Folk classifications, Long, 2006; or Shepard classifications, Shepard et al., 1954) would be helpful in the derivation of subsequent conclusions.

Based on the Folk’s classification, the sediments from our study site is a clayey sand. However, we believe it is a silicon-carbonate hardground in agreement with other preliminary results that we show within the manuscript. Moreover, soon we will measure the amount of carbonate in our samples and are very confident that this result will strengthen our preliminary results.

 

 

#3. the source of the sediments

We cannot simply derive the source of the sediment from the mineral, grain size, and XRF data, as is the case with the statement made on Line 520-523 and Line 33(6). The determination of the source of the material requires data and interpretation of organic carbon isotopes or Sr/Nd isotopes.

We agree. We added uncertainty regarding whether the source of the material is the Amazon River and added a sentence “Further analysis on carbon organic matter and neodymium isotopes will be used to determine if the sediments derive from the Amazon River.”

 

#4. language expression

Line 24: “sweet/salt water equilibrium”, it is commonly expressed in environmental science as “fresh/salt water equilibrium”.

Thank you, we corrected this expression. Now it can be seen in line 29 as the following phrase: “fresh/salt water equilibrium with the Amazon River”. 

 

 

Line 524: “silicon-carbonate hardground or Beachrocks”, the current data are insufficient to define sediment as “silicon-carbonate”.

Thank you for the suggestion, we fixed this throughout the manuscript.

 

#5. Format of figures

Figure 1: The earth on the left should be round, not elliptical.

We corrected this issue in Figure 1.

 

Figure 2: Please keep the letter format (ABCD) in the upper left corner of Figure 2 the same as Figures 3-4, i.e., white letters with no background color.

In the new Figure 2, you can now see the same letter format as Figures 3 and 4.

 

#6. References format

Line 629: The position of the year.

Line 635, 654-655: The light gray shade of some words.

Line 711: The space between words.

Line 713, 715, 724: The year.

Line 717: The author's omission, unlike Line 687-691.

 

We corrected the mistakes pointed out above.

 

#7. Unit of measurement

Line 307: Unit of temperature in degrees Celsius.

We corrected this throughout the manuscript.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The report presents unpublished, interesting, and highly significant data for the region. However, further work is required to fully exploit the data and render it less incipient, thereby enhancing its scientific value.

Methodology - Given that this is a report, there is a need for more detailed information. It would be advantageous to present a flowchart that outlines the techniques employed and their rationale in this context.

Additionally, some examples of further required details: Did the separation of areas 1, 2 and 3 have any methodological implications for the geophysical data?

Software used to process the bathymetry and the corrections applied should be specified; additionally, a less simplistic definition of backscatter and the parameters and software used to process the backscatter (not even the frequency is mentioned) should be provided; software used to process the sidescan sonar data should be included.

A few minor suggestions:

- Figure 5: the bathymetry map could be superimposed on another bathymetric background (or isobaths), to show how the detail of the mapping has improved; indicate in figure 5 the features mentioned (lines 396/397); 7 points are not in the legend; indicate more adequately that there is a frame exemplifying the rock feature in three-dimensional form.

- Backscatter values appear to be up to 35 positive. Decibels are a logarithmic scale, so this would imply that the acoustic energy returned is greater than the energy than was emitted, or that some of the acquisition parameters have not been properly corrected. It is recommended that the scale of the values be left simply as High (whiter tones) or Low (darker tones). 

- Seismic with few examples, sidescan doesn't seem to have been analyzed at all.

- It is recommended that some methodological passages in the results be relocated (e.g. 540 - 545). Furthermore, it is advisable to avoid the use of maps displaying markedly disparate patterns (backgrounds, coordinate details, ticks and scales and grids...).

Author Response

Reviewer #2

The report presents unpublished, interesting, and highly significant data for the region. However, further work is required to fully exploit the data and render it less incipient, thereby enhancing its scientific value.

 

Methodology - Given that this is a report, there is a need for more detailed information. It would be advantageous to present a flowchart that outlines the techniques employed and their rationale in this context.

Additionally, some examples of further required details: Did the separation of areas 1, 2 and 3 have any methodological implications for the geophysical data?

The preliminary data presented in our manuscript is an institutional partnership among a great petroliferous Brazilian company (Petrobras), the University of São Paulo, the Brazilian Navy and other Brazilian universities. All the three study areas were delimited by Petrobras in order to be mapped through geophysics methods (mainly multibeam and SBP). However, due the shallow depth of study area 1 (~190 - 280 m), the geophysics team from Petrobras decided to also map this area with the available side scan sonar. Thus, the subdivision of study areas was carried out due to pre-cruise planning from Petrobras, which was agreed by the other institutions aforementioned, without prior information regarding what would be found on the seafloor in those areas.

 

Software used to process the bathymetry and the corrections applied should be specified; additionally, a less simplistic definition of backscatter and the parameters and software used to process the backscatter (not even the frequency is mentioned) should be provided; software used to process the sidescan sonar data should be included.

To process the bathymetry data and apply the appropriate corrections, we used the CARIS Hips software (version 12). Such data was processed on Brazilian Navy licensed computers throughout the research cruise on board. The backscatter data was extracted from the same software.  

 

 

We provided the frequencies associated with the multibeam in line 189, which now it can be read as following: “Multibeam bathymetric data were acquired throughout the study region using EM-710 (70 – 100 kHz) and EM-122 (12 kHz) echosounders”.

 

We better define the backscatter methodology, parameters and software used to process its data in the lines 193 to 218 as following: “The multibeam echosounder also generates backscatter data, which provides valuable insights into substrate composition as it is an important tool for seabed mapping subtract. This methodology involves the generation of an initial acoustic pulse (~80 µs). This signal return to the multibeam echosounder and is analyzed based on the intensity of the sonar pulse amplitude. A weak return signal (low amplitude) indicates the presence of a soft bottom substrate, while a strong return signal (high amplitude) suggests the presence of hard bottom substrate [36]. Multibeam bathymetric data and backscatter data were acquired through the software Seafloor Information System (SIS, version 5.9.1). Both data were processed and analyzed within the software CARIS Hips (version 12). The correction of tide was made manually by the Navy surveyor on board. As the study region is very dynamic, it was necessary to use different data to validate and correct the sound velocity value in the water, which was used to calibrate the multibeam bathymetric and backscatter data. The sound velocity was corrected through the expendable bathythermograph (XBT) and expendable sound velocity (XSV) and moving vessel profiler (MVP) (showed in the section 3.1.4).”

 

We specify the software used to acquire and process sonar side scan data in lines 253-255, as following: “The data generated from the SSS was acquired and processed within the software SonarWiz (version 5). These preliminary data were analyzed during the expedition.”

 

 

A few minor suggestions:

- Figure 5: the bathymetry map could be superimposed on another bathymetric background (or isobaths), to show how the detail of the mapping has improved;

We completely agree with you that by adding a bathymetric background (or isobaths), we can show how the mapping has improved, however it is not possible to do this during the review period. In the future (in the second semester of 2024), all geophysics data will be analyzed in detail by other undergraduate, master and PhD students.

 

Indicate in figure 5 the features mentioned (lines 396/397);

In the previous version of our manuscript, we have mentioned the presence of pockmarks and in the new Figure 5, we highlighted this feature.

 

 

7 points are not in the legend;

In the legend of the new Figure 5, we explain more clearly that those seven black dots represent the seven sites that we collected sediments through use of a box corer. 

 

Indicate more adequately that there is a frame exemplifying the rock feature in three-dimensional form.

In the legend of the new Figure 5, we explain that the right upper panel shows the three-dimension of hardground structure that was found in study area 1 (lines 1116-1119).

 

- Backscatter values appear to be up to 35 positive. Decibels are a logarithmic scale, so this would imply that the acoustic energy returned is greater than the energy than was emitted, or that some of the acquisition parameters have not been properly corrected. It is recommended that the scale of the values be left simply as High (whiter tones) or Low (darker tones).

Thank you for the suggestion, now we present a corrected version of Figure 6 following your instructions.

 

- Seismic with few examples, sidescan doesn't seem to have been analyzed at all.

The seismic lines showed in Figure 7 were obtained within study area 1 and these lines were chosen to show the hardground structure (rough surface). As these results are preliminary, they will be analyzed in detail in the future. Thus, the seismic results from study area 2 and 3 will be addressed in other manuscripts, as this area will be part of undergraduate, master and PhD studies in the second semester of 2024.

 

- It is recommended that some methodological passages in the results be relocated (e.g. 540 - 545).

Thank you for drawing this to our attention. We moved some information into the methods, clarified one sentence and moved the position to make it more clear what result was being reported, and reordered several other sentences in this section to clarify the text following these changes, also removing some redundancy.

 

Furthermore, it is advisable to avoid the use of maps displaying markedly disparate patterns (backgrounds, coordinate details, ticks and scales and grids...).

Thank you for the suggestion, we improved it.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Thank you for your clarifications, and I wish you success in continuing the next analyses and publications regarding this hard-working fieldtrip.

Author Response

Thanks!