The Anthropogenic Footprint of Physical Harm on the Seabed of Augusta Bay (Western Ionian Sea); A Geophysical Investigation

Round 1

Reviewer 1 Report

The study examines anthropogenic-driven impact on the seafloor of Augusta Bay in the western Ionian Sea by using a combination of seismic Chirp, sidescan sonar and bathymetric data. Seafloor samples and at least one core were also examined. The authors look at the signal of seven different indicators (or footprints) of human activity in order to ultimately produce a stress map for the entire area. Their study is highly relevant and adaptable in other areas of the world. However, there is room for improvement.

First and foremost, I would like to say that the article is very interesting and there is a logic to the way it is formulated.

Over all, the English is not bad but should be improved. I have made some suggestions, but stopped at some point and then only pointed out glaring mistakes.

Figures 1a and 1b need scale bars and coordinates as well as a depth bar (color scale).

Figure 2 –on the top image, the text on the color bar and horizontal scale is small and fuzzy. It is hard to read and impossible to see on the scale bars in the subsequent table (sidescan images, bathymetry, sediment). Same with Figure 5.

Sidescan data can be tricky to interpret. I would like to see a little more information on how the different features were recognized and categorized. One example of what I mean is in Figure 3 – how do you distinguish current furrows from trawl marks if they are in the same direction? Please provide as much details as possible of the factors that led to your characterizations when discussing the SSS data.

Figure 3 – text on scale bars is impossible to read

Figure 4B – the vertical scale should be the same for all three – I know this will cause a problem but it is the only way the reader can compare the images and get an idea of scale

4c – impossible to see black writing on blue background

4d– hard to see white dashed and solid lines on 4D. It would be beneficial for the reader if you enlarged the central area (the “mound”) so it is easier to see what you are talking about.

Supplementary map – could not find the generic target on it.

Paragraph beginning on line 425 – please rule out a bottom current deposit such as a mounded drifts instead of dump

Paragraph beginning on line 436 is a repletion of information presented in the Results. Since this is the Discussion – I would expect here some kind of interpretation or insights based on this information.

Please explain in more detail how you obtain the date of the dump once you have the annual sediment deposition rate. It took me a long time to figure out that what you were saying is that given the thickness of the sediments covering the pile – you can date the top of the pile by knowing sedimentation rate. If it was not clear enough to me right away, it may not be clear enough to others.  In addition, I take it you are assuming that there is no change in currents, and thus in sedimentation rate, due to the presence of the pile on the seafloor. This is not exactly true but you have no way of knowing this. I think you should mention this assumption in the text – it will show the reader that you are thinking of all possible scenarios and are aware of your limitations.

Table 2 is not clear to me at all.

Please see additional comments and remarks on the annotated manuscript. 

Comments for author File: Comments.pdf

Author Response

• Reviewer n.1

The study examines anthropogenic-driven impact on the seafloor of Augusta Bay in the western Ionian Sea by using a combination of seismic Chirp, Side-scan Sonar and bathymetric data. Seafloor samples and at least one core were also examined. The authors look at the signal of seven different indicators (or footprints) of human activity in order to ultimately produce a stress map for the entire area. Their study is highly relevant and adaptable in other areas of the world. However, there is room for improvement.

First and foremost, I would like to say that the article is very interesting and there is a logic to the way it is formulated.

Reply: Many thanks, we are very glad for this comment!

• Over all, the English is not bad but should be improved. I have made some suggestions, but stopped at some point and then only pointed out glaring mistakes.

Reply: All the corrections were accepted and many others were added to improve the readability of the text, following the English mother-tongue revision.

• Figures 1a and 1b need scale bars and coordinates as well as a depth bar (color scale).

Reply: This point has been fixed

• Figure 2 –on the top image, the text on the color bar and horizontal scale is small and fuzzy. It is hard to read and impossible to see on the scale bars in the subsequent table (sidescan images, bathymetry, sediment). Same with Figure 5.

Reply: This point has been fixed. Figures 2 and 5 became 3 and 6, respectively.

• Sidescan data can be tricky to interpret. I would like to see a little more information on how the different features were recognized and categorized. One example of what I mean is in Figure 3 – how do you distinguish current furrows from trawl marks if they are in the same direction? Please provide as much details as possible of the factors that led to your characterizations when discussing the SSS data.

Reply: New evidence has been added to clarify our interpretations: see chapter 4.1.1

Basically, trawl marks are characterized by acoustic facies made up of sharp, thin and long-linear stripes with an overall pattern ranging from subparallel to slightly diverging and occur also in sheltered seafloor;  some tracks show wide-radius bends for reversing in the direction of navigation. On the contrary, current furrows consist of blurred long-linear striations, show an overall coherent pattern due to physical morphological constraints (e.g., rocky outcrop; contour and gradient trends). However, some sectors are characterized by the coexistence of both trawl marks and current furrows. A further piece of description has therefore been added to chapter 4.1.1

• Figure 3 – text on scale bars is impossible to read

Reply: This point has been fixed

• Figure 4B – the vertical scale should be the same for all three – I know this will cause a problem but it is the only way the reader can compare the images and get an idea of scale.

Reply: Topographic profiles are indeed in scale, both horizontally that vertically.

• 4c – impossible to see black writing on blue background

Reply: This point has been fixed

• 4d– hard to see white dashed and solid lines on 4D. It would be beneficial for the reader if you enlarged the central area (the “mound”) so it is easier to see what you are talking about.

Reply: An inset with a zoomed and un-interpreted view of the mound has been added to the figure; fonts in fig. 4E have been enlarged.

• Supplementary map – could not find the generic target on it.

Reply: This point has been fixed. The layer “generic target” was switched off.

• Paragraph beginning on line 425 – please rule out a bottom current deposit such as a mounded drifts instead of dump

Reply: This point has been fixed. To motivate more convincingly why the deposit cannot be anything but a dumping deposit, we added to the morphological and stratigraphic motivations, already present in the text, some other stratigraphic considerations (lack of onlap terminations on discontinuities, lack of truncations of underlying reflectors against the seabed, lack of moats) and geometrical characteristic of the deposit (cumuli are round-shaped in plan view and lack of geometrical asymmetries that might indicate the direction of bottom currents), reinforcing our considerations. Few more literature works have been cited. 

• Paragraph beginning on line 436 is a repletion of information presented in the Results. Since this is the Discussion – I would expect here some kind of interpretation or insights based on this information.

Reply: We removed the paragraph, keeping just one sentence and moving it to results, chapter 4.1.3

• Please explain in more detail how you obtain the date of the dump once you have the annual sediment deposition rate. It took me a long time to figure out that what you were saying is that given the thickness of the sediments covering the pile – you can date the top of the pile by knowing sedimentation rate. If it was not clear enough to me right away, it may not be clear enough to others.  In addition, I take it you are assuming that there is no change in currents, and thus in sedimentation rate, due to the presence of the pile on the seafloor. This is not exactly true but you have no way of knowing this. I think you should mention this assumption in the text – it will show the reader that you are thinking of all possible scenarios and are aware of your limitations.

Reply: The paragraph has been improved with a step by step explanation of the conceptual flow; limitations of the procedure were also clarified. See chapter 5.3 - 6th paragraph

• Table 2 is not clear to me at all.

Reply: Table 2 reports the ensemble of indicators used to quantify the damage at each discretized seafloor cells (each of 500 m side) and the relative score.  If more than one indicator is present within a cell, its overall score is raised by a linear-incrementing value, in order to enhance the increased hazard associated with the coexistence of different impacting activity, with unpredictable effects on the environment. The resulting scores help define a semi-quantitative assessment of the physical harms for each cell. Accordingly, a more detailed explanation of the adopted criteria is now given in chapter 5.4, 5^th and 6^th paragraph.

• Please see additional comments and remarks on the annotated manuscript. 

Reply: All of them were accepted

Author Response File: Author Response.pdf

Reviewer 2 Report

Recommendation：Major Revision.

This study represents an interesting survey of physical harm to the seabed. The following issues should be addressed before being accepted.

(1) Ln 26-30, it is difficult to understand, it describes the anthropogenic footprints, why this sentence by “ originated by natural processes” to end. Please clarify the meaning of sentence carefully.

(2) the correspondence between Figures and context is not well. Some key information is not shown in the figures, such as the different data spatial distribution, in the MS, the side-scan sonar and sub-bottom chirp sonar survey has same legend. The data size is different in the context description.

Some anthropogenic footprints should mark in the figures, such as Dredging in Section 4.1.2, some descriptions, I cannot find the corresponding information in the figures.

(3) what are the contributions of samples? Please give a clear description.

(4) add the full text of abbreviation, such as DTM,DEM

 

(5)Some writing error should be checked carefully, such as, Ln 48 some case->some cases Ln 53 high-resolution seismic investigations we surveyed the-> high-resolution seismic investigations, we surveyed the; Ln 194 20 km2on the whole -> 20 km2 on the whole. 

Author Response

Reviewer n. 2

Recommendation：Major Revision.

This study represents an interesting survey of physical harm to the seabed. The following issues should be addressed before being accepted.

• Ln 26-30, it is difficult to understand, it describes the anthropogenic footprints, why this sentence by “originated by natural processes” to end. Please clarify the meaning of sentence carefully.

Reply: The paragraph has been modified to improve its readability.

 

• the correspondence between Figures and context is not well. Some key information is not shown in the figures, such as the different data spatial distribution, in the MS, the side-scan sonar and sub-bottom chirp sonar survey has same legend. The data size is different in the context description.

Reply: This objection is not clear to us

 

• Some anthropogenic footprints should mark in the figures, such as Dredging in Section 4.1.2, some descriptions, I cannot find the corresponding information in the figures.

 

Reply: The dredged area is very small, it is located at the entrance of Levante inlet and it has been evidenced in the map of Supplementary material.

 

• what are the contributions of samples? Please give a clear description.

 

Reply: box-cores and grabs samples served to calibrate the SSS imagesand to define the sediment texture, habitat and colonization in the areas not affected by dumping. Surface samples are necessary to develop a thematic cartography of the seabed. The gravity core is fundamental to depict the subsurface sediment in the dredge spoil pile and to highlight the anomalous stratigraphic signature. Additional explanations are given in figs. 3 and 6, chapter 3.3, chapter 4.2 - 2^nd paragraph, chapter 5.3 - 6^th paragraph

 

• add the full text of abbreviation, such as DTM,DEM

 

Reply: We checked throughout the ms: DTM is not used, DEM has been defined in chapter 3.4 once introduced for the first time.

 

• Some writing error should be checked carefully, such as, Ln 48 some case->some cases Ln 53 high-resolution seismic investigations we surveyed the-> high-resolution seismic investigations, we surveyed the; Ln 194 20 km2on the whole -> 20 km2 on the whole. 

Reply: Typos were fixed

Author Response File: Author Response.pdf

Reviewer 3 Report

Authors investigated the extent of human-driven physical impact on the continental shelf outside the Rada di Augusta, by means of acoustic remote data (using a Multibeam echosounder, Side scan sonar and Sonar Chirp profiler) and direct seabed samplings. The impact is identified using the following foot-prints shown on sea floor, and they are anchor grooves and scars, excavations, trawl marks, targets, marks from bilge drains, isolated dumping and dumping cumuli.

But to classify those marks, most of them were identified using side-scan sonar images. As to other acoustic methods, including using soil samples, did not provide favorable evidence to convince the reader of their views. Even those side-scan images are not convincing in their descriptions of targets on the seabed. For example, anchor scars spread in limited and sporadic waters and distributed in depths greater than 50 meters (usually ships rarely drop anchor at this depth); bilge drains marks, it's hard to imagine this bilge waste, mainly composed of water, fuel, solvent, chemicals, particles etc., will descend and leave marks on the seabed at a depth of more than 50 meters.

Therefore, the content of the article does not convince me to believe the conclusion of the article. For improvement, in this article, at least there is one chapter shall provide strong optical evidence for the identification of all targets, such as the use of ROV to all identification as the production of photography. In archaeological surveys, side-scan sonar images have always been the most efficient tools for finding targets, but the identification of targets still needs to be confirmed by optical images.

My recommendation is to return the manuscript with this current format, because it is a very subjective, but lack of scientific evidence of the investigation report.

Author Response

Reviewer n. 3

Authors investigated the extent of human-driven physical impact on the continentalshelfoutside the Rada di Augusta, by means of acoustic remote data (using a Multibeamechosounder, Side scan sonar and Sonar Chirp profiler) and direct seabed samplings. The impact is identified using the following foot-prints shown on sea floor, and they are anchor grooves and scars, excavations, trawl marks, targets, marks from bilge drains, isolated dumping and dumping cumuli.

• But to classify those marks, most of them were identified using side-scan sonar images. As to other acoustic methods, including using soil samples, did not provide favorable evidence to convince the reader of their views.

Reply: Primarily we do not use the bottom samples to prove the existence of human footprint, but to calibrate SSS imagery, defining sediment textures, presence of "bedrock" and types of bottom colonization, so as to develop the thematic cartography shown in Supplementary materials. Only the C2015 gravity core, taken from the dredged spoil mound, is used to highlight the stratigraphic anomalies accounted for by the anthropogenic nature of the deposit

• Even those side-scan images are not convincing in their descriptions of targets on the seabed. For example, anchor scars spread in limited and sporadic waters and distributed in depths greater than 50 meters (usually ships rarely drop anchor at this depth); bilge drains marks, it's hard to imagine this bilge waste, mainly composed of water, fuel, solvent, chemicals, particles etc., will descend and leave marks on the seabed at a depth of more than 50 meters.

Reply: From pilot books and navigation instruction manuals, it is often specified that large tonnage vessels stay at anchor between -30 and -80/-100 m. We find signs of anchorages in the range -40 /-75 m. We also emphasize in the submitted version of the manuscript (chapter 5.2, 3rd paragraph) that anchor furrows may be more frequent and evident at shallower depths as well, and specify the reasons why we probably do not see them.

Regarding bilge drains, unfortunately there is little literature, other than descriptions of the phenomenon, media documentation on how it occurs, methods of deterrence by using satellite imagery. Actually, we have not found any example of Side-Scan Sonar images ascribed to bilge drains. Although we stoutly believe in this hypothesis, since bilge drains do not only consist of oily materials or fluid components, but also of loose materials such as granular, residual sludge mixed to fine debris, that can quickly decant through the water column, but still, since we cannot prove it at the moment, we feel that we need to make changes to our initial draft, in accordance with what the reviewer suggested. For this reason, we propose a possible solution: we classify these footprints -which have their own specific characteristic and differ markedly from other dumping categories in backscatter and size-, as "dumping trails," i.e., aligned footprints of discharged materials, in line to the direction of ship movement. In doing so, we emphasize that these are still discharge practices -regardless of the material discharged- and that they are deployed by moving ships. We also emphasize, in this way, the differences with heaps and isolated dumping sites.

• Therefore, the content of the article does not convince me to believe the conclusion of the article. For improvement, in this article, at least there is one chapter shall provide strong optical evidence for the identification of all targets, such as the use of ROV to all identification as the production of photography.In archaeological surveys, side-scan sonar images have always been the most efficient tools for finding targets, but the identification of targets still needs to be confirmed by optical images.

Reply: Unfortunately, we do not have ROVs at present. Undoubtedly, if we had, we would have used them extensively with great benefit to the work.We totally agree with the Reviewer that direct images of the seafloor are the best way to calibrate features detected in SSS data, especially in case of small-sized objects. However, we also believe that for very large footprints ROVs images may not be directing, since the overall, distant view may be missing.

Having said that, we would like to emphasize that this work revises data acquired 20 years ago, as clearly stated in the Introduction and in Material and methods, based on which a detailed thematic mapping is developed.This is intended to represent a benchmark of the state of places against which new acquisitions (possibly calibrated by ROVs) can be compared. If we did ROVs now, to implement the SSS evidences, there might not be a match, since most of the footprints are ephemeral. Besides, there are several examples of this type of footprint in the literature and ample documentation in this regard. However, to avoid any possible ambiguity we modified the title by adding ": a geophysical investigations". With reference to the “targets”, we do have already specified in the submitted version of the text that their identification requires further investigation. This is also why they have been mapped as "generic targets", without giving them any interpretation, not even supposedly.

• My recommendation is to return the manuscript with this current format, because it is a very subjective, but lack of scientific evidence of the investigation report.

The nature of anthropogenic footprints is amply documented in the literature which we referred to. We also robustly documented the nature of the dumping mounds, using seismic acoustic data and direct sampling. Such a provision of converging data, also of excellent resolution and accuracy, reasonably prove the substance of our study and may also represents an acquisition standard for future investigations of physical environmental impacts.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

I agree to accept this MS for publication         

Reviewer 3 Report

I agree to accept this MS for publication