Impact of Dense Water Formation on the Transfer of Particles and Trace Metals from the Coast to the Deep in the Northwestern Mediterranean

Round 1

Reviewer 1 Report

In work entitled " Impact of dense water formation on the transfer of particles  and trace metals from the coast to the deep in the northwestern  Mediterranean" by Madron X. et al., the Authors analyzed the interannual variability of coastal dense water cascades and open sea convection in the Gulf of Lions (NW Mediterranean).  I have read the manuscript, and I saw that its results fall within the scope of the journal.  The authors have well written the manuscript and the figures are of good quality. However, need some minor modification and reformulation of sentences before its eventual acceptance.

Abstract:

Comment:1 Overall, the abstract is well written and summarizes the findings of the studies. However, has some scope for improvement to improve readability and also include more findings replacing the first 3 lines which are very general and part of the introduction.  

Comment 2: Trend should not be the keyword, as it is not much used in the manuscript.

Comment:3 Introduction needs to add recent references and includes some discussion of the motivation of the study at the end of the introduction.

Comment:4 Conclusion is too short. I would suggest adding more information.

Author Response

We thank the reviewer for his comments and suggestions which helped to clarify certain points and improve the manuscript. We recall here the different remarks of the reviewers and our answer to each one.

Reviewer #1

In work entitled " Impact of dense water formation on the transfer of particles and trace metals from the coast to the deep in the northwestern Mediterranean" by Madron X. et al., the Authors analyzed the interannual variability of coastal dense water cascades and open sea convection in the Gulf of Lions (NW Mediterranean). I have read the manuscript, and I saw that its results fall within the scope of the journal. The authors have well written the manuscript and the figures are of good quality. However, need some minor modification and reformulation of sentences before its eventual acceptance.

Abstract:

Comment:1 Overall, the abstract is well written and summarizes the findings of the studies. However, has some scope for improvement to improve readability and also include more findings replacing the first 3 lines which are very general and part of the introduction.

The abstract was slightly modified within the 200 words limit.

Comment 2: Trend should not be the keyword, as it is not much used in the manuscript.

We modify this term by “changes”

Comment:3 Introduction needs to add recent references and includes some discussion of the motivation of the study at the end of the introduction.

The references are up to date as far as we know. It is not clear which publications the reviewer is referring to. However, we have added two references, the first one from Millot (1990) that describes the regional circulation suggested by the reviewer#3, the second one from Garcia-Lorenzo et al. (2019) on heavy metals in the coastal zone on the Spanish margin, and Columbo et al. (2022) on the advective transport of particulate trace element.

For the motivation, the last part of the introduction was modified: “The implementation of numerous moorings equipped with sediment traps during this event allows us to assess for the first time the role of this type of events on the transfer of metals between the shelf and the slope, as well as in the basin, and to infer their interactions. For this, the discussion will focus on the study of: a) the temporal variability of mass fluxes (rivers, atmosphere, slope, basin) over the period 2010-2017; b) the key PTMs concentrations in the different matrices (rivers, atmosphere, suspended particles, sediments) during the Jan 2012 – Dec 2012 period, and c) the evaluation of the PTM fluxes transported during these events.”

Comment:4 Conclusion is too short. I would suggest adding more information.

The conclusion was developed to highlight the results on metals.

Reviewer 2 Report

Minor revisions, see attached file

Comments for author File: Comments.pdf

Author Response

We thank the reviewer for his comments and suggestions which helped to clarify certain points and improve the manuscript. We recall here the different remarks of the reviewers and our answer to each one.

Reviewer #2

This paper proposes a global analysis of recorded long-time (8 years, 2010-2017) data of temperature, currents, sediment and metal traces concentration at three main stations located in Gulf of Lion representative of coastal/ or open sea and of surface layer /or deep basin. The role of extreme dense shelf water cascading combined with convection events in sediment dispersion is illustrated. On the last part of period of monitoring, temperature increase of coastal water coincides with a period with no extreme deep cascading events suggesting that climate warming could modify the dynamics and the repartition of dispersed sediment in future. Comments are well referenced to previous works and illustrated by presented data.

Only minor revisions are needed.

Detailed comments

-  L. 4 “X. Durrieu de Madron, D. Aubert, ...”

Done

-  L. 45 “ ... were responsible for increased transfer ...

Done

-  L. 64 : omitted dot after [22].

Done

-  L.68 : “...during 8 year period (2010-2017)

Done

-  Several acronyms are used and should be expressed in first use
POC (L.162), SPM (L.165), DSWC (L.400, the acronym could be introduced L.54), ETM (L.438).

Done. For clarity, we specified in the introduction to the first appearance of the terms "Dense Shelf Water Cascading" and "open-ocean convection" that we will refer to them simply as "cascading" and "convection". The acronym DSWC has been removed from the text and figures.

-Fig.4a : Leucate is not located in figure 1.

Done

- L.219 Cap de Creus canyon is not located in figure 1

Done

- Figure 5c, there is a shift on date axis (abscissa) compared to the four other figures 5.

Corrected

- L. 257: The figure index is missing.

Several references to figure 5 were missing or wrong in this paragraph. It has been corrected. A sentence describing the figure 5c was added.

- What does represent the open circles in figures 6?

Open circles represent outliers. The meaning of the box and whisker plots is given.

Each box encloses 50% of the data (between the upper and lower quartiles) with the median value of the variable displayed as a line. The length of the whiskers is restricted to a maximum of 1.5 times the interquartile range. That is, the whisker reaches the value that is the furthest from the center while still being inside a distance of 1.5 times the interquartile range from the lower or upper quartile. Data points that are outside this interval are represented as points on the graph and considered potential outliers.

- L. 282: “Box and Whisker plots”

Done

- L. 294 : NW to N continental winds (Tramontane and Mistral)

Done

- L. 296-L. 300 : These explanations concerning the dynamics that induces the cascades of dense shelf water should be given in the introduction.

Several sentences, which were initially located at the beginning of the discussion, have been moved to the introduction to explain the origin of these processes: “Among those phenomena, the formation of dense water, produced in winter by heat loss associated with northern continental winds (Tramontane and Mistrals), is central. The coastal waters are cooled, homogenized and densified.  They propagate mainly along the western coast of the Gulf of Lion, in a cyclonic manner driven by wind-induced winds, and are exported from the shelf at the level of its SW end incised by the Lacaze-Duthiers and Cap de Creus canyons. There, they cascade down the slope, sometimes to more than 2000 m for the most intense events. This dense shelf water cascading process is called simply cascading hereafter. In the basin, open-ocean convection involves a progressive deepening of the upper oceanic mixed layer, which first reaches the intermediate water and eventually extends to the bottom, if the atmospheric forcing is sufficiently intense. This process is typically composed of three phases: the preconditioning phase, the intense mixing phase, and the restratification-spreading phase {13}. During the fall and early winter preconditioning, northern winds strengthen the cyclonic circulation in the Gulf of Lions, which traps and upwells surface and intermediate waters in the centre of the basin. During the intense winter mixing phase, the high atmospheric heat loss makes the surface water dense enough to sink to depth and form a homogeneous convective patch of dense water. Finally, during the restratification-spreading phase, the patch of dense water sinks and spreads out at depth while the lighter surrounding waters reinvest the area.”

- Figures 7b and 7c, in legend (4) : “Resuspension and material transport ...”

Corrected

Is the “insert” announced in L. 361-363 the same as figure 8 since no insert is visible in figure 7 ? If so, L. 361-363 could probably be suppressed.

There was an error in the legend for Figure 7. The intended insert is shown in Figure 8. The reference to the insert has been removed

-L.420 , write “DSWC” and not DSCW.

Done, this acronym has been replaced by the term “cascading”

- L. 433, write “PTMs” and not TMPs.

Done

Reviewer 3 Report

My first suggestion, if the authors believe it necessary, for those who do not know the area well, concerns the addition of a sentence on the circulation of water in the area, perhaps with an indication to add to figure 1, but just suggestion. 

In line 89 - 1.50 m (add space).

In line 257 the reference to the figure is missing.  

In Fig 6 Sed is reported but in text is SED with caps and caption of the figure not very clear, I would add an explanation of the acronyms

The reference in the text of figure 7 is missing, mayby in line 305  is reported Figure 6  instead of Figure 7.

In  Figure 7 in  the text (4) is written "materal"

Author Response

We thank the reviewers for his comments and suggestions which helped to clarify certain points and improve the manuscript. We recall here the different remarks of the reviewers and our answer to each one.

Reviewer #3

My first suggestion, if the authors believe it necessary, for those who do not know the area well, concerns the addition of a sentence on the circulation of water in the area, perhaps with an indication to add to figure 1, but just suggestion. 

A reference to the synthesis paper of Millot (1990) describing the regional circulation and the major hydrodynamical processes has been added in the introduction

In line 89 - 1.50 m (add space).

Done

In line 257 the reference to the figure is missing.

Corrected.

In Fig 6 Sed is reported but in text is SED with caps and caption of the figure not very clear, I would add an explanation of the acronyms

Sed is an acronym for “sediment”. Acronyms used in Figure 6 have been clarified in the caption.

The reference in the text of figure 7 is missing, mayby in line 305  is reported Figure 6  instead of Figure 7.

Indeed, there was a wrong reference to figure 6 instead of Figure 7. This has been corrected.

In  Figure 7 in  the text (4) is written "materal"

Corrected.