Storm-Related Rhodolith Deposits from the Upper Pleistocene and Recycled Coastal Holocene on Sal Island (Cabo Verde Archipelago)

Round 1

Reviewer 1 Report

The manuscript is very well presented and organized. I have made corrections and proposed changes in the attached pdf file.

Sincerely yours.

Comments for author File: Comments.pdf

Author Response

The authors are grateful to Reviewer #1 for providing an annotated copy of our manuscript showing where words and phrases might best be eliminated and tags at crucial places with notes about additional factors that ought to be considered, as well as references to published papers that back-up those oversights.

Foremost among the changes made to our submission, we have added all three of the references recommended by Reviewer #1 (Bassi et al. 2020; Matsuda and Iryuy, 2011), and Checconi et al., 2010).  The first author was aware of the paper by Bassi et al. (2020) only after the manuscript was submitted to the editors and it was recognized as relevant to our story.  But we are grateful to the other two papers, which were unknown to us.  Incorporation of these articles into the text makes good sense.

Before going further, an apology is due to the fact that an entire section of the manuscript (5.4. Sal Island Rhodolith Deposits Compared to Others in the North Atlantic) was omitted from the submitted paper.  When adjusting for the new references added to the paper, it was discovered that some of the previous references listed in the bibliography were nowhere to be found in the text.  We hope that the restoration of this section helps to bring proper closure to the manuscript.

Reviewer #1 pointed out that rhodoliths from deeper water settings often show growth that is more ellipsoidal and discoidal.  These growth forms are not nearly as likely to be rolled shoreward by storm waves of hurricane intensity capable of feeling bottom to greater depths.  This was worth pointing out.

Almost all of the words or phrases marked in red with strike-out lines have been removed.  In a few cases, we felt it necessary to retain the adjective “spherical” from place to place.

A revised Figure 3 has been added to the paper in order to substitute the word “deposit” for “shelf” as questioned by Reviewer #1.  However, two other places marked with tags were not adjusted and we hope our explanation for not doing so will makes sense.  Three tags were attached to Fig. 8.  The tags for Figs. 8a and 8d relate to our labels for small organic cobbles.  Technically, cobbles range in diameter size from 6.4 to 25.6 cm.  The largest rhodoliths plotted do not exceed 15.5 cm in diameter and most of them are in the range of 6.6 to 8 cm.  Therefore, we feel we are correct in referring to these as “small organic cobbles.”.  The tag for Fig. 8c suggests that the label might be changed by adding the word “Holocene.”  We wish to leave the label as it is, because the rhodoliths in question are not actually Holocene in age.  They are Pleistocene rhodoliths that were reworked later on sometime during Holocene time.  Especially in the results section of the paper, we wanted to avoid making a judgement on the age of these particular rhodoliths. 

A tag added to Table 1 suggests that the locality names be added to the table caption.  However, we note that the locality names are clearly shown in the left-side column.

Aside from these differences of opinion, we have adopted all suggestions by Reviewer #1.

Reviewer 2 Report

Overall this is a well written paper and explores an interesting hypothesis about the origin, transport and deposition of coastal rhodolith beds on a high energy windward shore. However, I would like to see it beefed up in a number of ways to make it a more useful and interesting paper.

1) the algae responsible for the rhodoliths do not appear to have been identified. Can this be done (at least to generic level)

2) what is the known about the distribution of these live algae within the area, or offshore distribution of the rhodoliths?

3) If wind speeds and wave heights are known from this area, and frequency of hurricanes, then bottom oscillatory currents can be calculated. Is this sufficient to move the (largely spherical) rhodoliths of this size and density?

Having said this I am sure the general story you have of offshore  rhodolith growth and transport and deposition onto storm ridges is likely to be correct.

Comments for author File: Comments.pdf

Author Response

The authors are grateful to Reviewer #2 for providing an annotated copy of our manuscript showing where words and phrases might best be eliminated and tags at crucial places with notes about additional factors that ought to be considered.

Before going further, an apology is due to the fact that an entire section of the manuscript (5.4. Sal Island Rhodolith Deposits Compared to Others in the North Atlantic) was omitted from the submitted paper.  Reviewer #2 noticed that some of the references listed in the bibliography were not covered in the text. We hope that the restoration of this section helps to bring proper closure to the manuscript, as we intended.

Most of the word changes suggested by Reviewer #2 have been adapted, as can be reviewed in the track changes to our manuscript.  However, it must be acknowledged that difficulties arise in balancing the editing by two different reviewers.  In combination, we believe that the paper reads better with the combined suggestions of both reviewers.

The various tags also inserted on the ms. were helpful, but in some cases not addressed the way the reviewer may have wished.  For example, the tag attached to Figure 1a requested that the dotted line around the North Atlantic islands be identified.  However, we feel that this “insert” is much too small to add the necessary label.  Instead, we have added to the Figure caption text that the dotted line represents the 4,000 m line of bathymetry shared by these various island groups.

Otherwise, tags concerning other issues are addressed directly on the body of the text.

Elsewhere on the journal’s evaluation form, Reviewer #2 listed three questions for further consideration.  The first of these asked whether or not the lab work might be done to identify at least to generic level the kind of rhodloths found at our two study locations.  The fourth author invited to participate in this work has been “locked out” of her work place due to the coronavirus pandemic and has been working from home.  Thus, it was not possible to do this work in a timely fashion and still meet the deadline for submission to the Special Issue of “Geosciences.”  This obstacle has held up progress on other papers without such a deadline.  As it is, we were very fortunate that access to Sal Island was possible during the pandemic, so that the necessary measurements on rhodoliths could be made.

Regarding the second question about the status of biological survey work in the waters around Sal Island (also marked by a tag on the ms.), we have nothing to add beyond what is already stated in the mansuscript.  The Republish of the Cabo Verde Islands is poor in resources and little outside help has been offered by oceanographic organizations to rectify this situation. 

We are aware of one published account that deals with corals in a completely different island, but it does not include rhodoliths.

Lastly, the third question concerns the possibility of doing more to appraise “bottom oscillatory currents” to better address the energy levels moving rhodoliths.  The first author has applied the equations by Nott (2003) to estimate wave forces moving rocky shore clasts elsewhere in the Americas and in the Azores.  An attempt was made to test the applicability of these work to the fossil rhodliths (as mentioned in the text), but abandoned.  I’m afraid that further considerations of this kind are beyond our capabilities.

We appreciate the effort made by the reviewer and hope that our efforts to improve the paper will be found adequate.