Review Reports

Round 1

Reviewer 1 Report (Previous Reviewer 2)

Comments and Suggestions for Authors

The authors have addressed or responded to all the comments I made on a previous version of this paper, so it is now suitable for publication.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report (New Reviewer)

Comments and Suggestions for Authors

Role of Lee Wave Turbulence in the Dispersion of Sediment Plumes

The authors use a high-resolution LES (Oasis solver) over a realistic seamount bathymetry in the Lofoten Basin, track Lagrangian particles representing several sediment size groups, and report that coarse particles mostly settle within 50–200 m while fine particles (groups 5–6) can remain suspended and be diluted to <1 ppm at ~2 km in many scenarios. These are useful first-order results that would interest both physical oceanographers and impact-assessment practitioners.

However, the following issues need to be addressed before it can be considered for publication:

 

- Please define Lee-wave in the introduction

-Define "ppm" and units when first used (p.342–353)

- This is a numerical study. However, there is not a single equation in the whore manuscript. In particular for the particle settling model, as well as the universal law for sand.

-How Is the particle release specified?

-Provide the full particle properties table (density, shape factor, settling law used)

-The time steps used are too big for LES model. Please provide justification for that.

-No grid independence study is presented to be confident about the results. Please provide a clear table of grid spacing (Δx, Δy, Δz) as function of depth and lateral position, as well as a quantified statement of the smallest resolved eddy scale (and corresponding Reynolds number).

- This is important as no validation against experimental data is carried out. Although you say that “We here predict that 95% of the sediments settle within 200 meters. These results are consistent with in-situ experiments from [3] where 92-98% of sediments settled within the first hundred meters.” This is not shown in the manuscript

- Table A1 should be in the manuscript not in the appendix, as this is very relevant to understand the problem

- In section 2.2.2 says 20m and 50m. However, figure A1 gives other dimensions. Also, this figure should be placed within the relevant text.

 

-Discuss the physical effects of fixed top boundary on vertical exchange and whether the domain height (3000 m) is adequate with those BCs.

- Please separate the section discussion and conclusions to make it clear what the conclusions are.

Overall, the manuscript is well written, but figures and methods need more detail in order to have confidence in the results

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report (New Reviewer)

Comments and Suggestions for Authors

The issues have been addressed satisfactorily. I recommend the manuscript publication.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have meticulously described the model, indicating various weaknesses. The objectives are well-explicated and well written.

However I found some serious flaws:  The model are calibrated with sediments from other area (Canary islands); the model simplify the flow dynamic deliberately neglected the Coriolis effect and tides effect. The fluctuations caused by eddies have scales of 10 meters, which is the scale of the model.

The model results show the expected outcomes (these conclusions do not necessarily require modelling): coarse particles are deposited over short distances, while fine particles are transported over longer distances; the simulations show that turbulent processes spread the plumes as a function of grain size. 

In my opinion, the article adds little to the existing knowledge on the dynamics of plumes caused by deep-sea mining.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

The authors use an LES model to study flow around a real isolated sea mount, incorporating a sediment model to consider how plumes of sediment from deep sea mining would disperse and settle.  A particular focus is on the turbulence generated by sea mounts and how this affects the sediment distribution.  The model is described carefully, and the results presented clearly.  Overall the writing is clear but there are some aspects the authors should consider.

There is some justification of the mesh size by using Pope's criterion, but otherwise the justification or validation of the chosen mesh sizes is rather limited.  Could this be enhanced in some way?

The simulated boundary condition flows are simplified - while this captures the basic features of the real local flow field (part of a gyre) some discussion of more varying or realistic flow fields (e.g. due to variations on tidal or seasonal time scales) would be good, even if just as possible future extensions to the work. Similarly, while leaving out Coriolis may be justified for an initial look at flows on short time scales, some more discussion of how this might affect the flows and sediment distributions (again, possibly as future work) would be good.

line 113: you describe the sea mount as "almost circular" and this and other parts of the description in the text leads the reader to expect a much simpler geometry than is revealed in Fig 1b (looks more like a diamond to me!).  A couple of cross sections (e.g. NW-SE and SW-NE) might be good.

I think most of the figures from the Appendix should be in the main text.  Note figs A4-A11 could be a single figure, with a single caption (and multiple plots).

Author Response

Please see the attachment.

Author Response File: Author Response.docx