Observations of cross-shelf transport due to internal wave pumping on the Bay of Biscay shelf

Moncuquet, Adèle; Jones, Nicole L.; Bordois, Lucie; Dufois, François; Lazure, Pascal

doi:10.5194/os-21-3375-2025

Articles | Volume 21, issue 6

https://doi.org/10.5194/os-21-3375-2025

© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/os-21-3375-2025

© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 21, issue 6

Research article

|

10 Dec 2025

Research article |

| 10 Dec 2025

Observations of cross-shelf transport due to internal wave pumping on the Bay of Biscay shelf

Adèle Moncuquet, Nicole L. Jones, Lucie Bordois, François Dufois, and Pascal Lazure

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Final revised paper (published on 10 Dec 2025)
Supplement to the final revised paper
Preprint (discussion started on 26 May 2025)

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2025-2072', Anonymous Referee #1, 24 Jun 2025

This paper applies a volume transport decomposition to identify the relative importance of Eulerian and Stokes’ transports to the next cross shelf transport in the Bay of Biscay. They focus on the role of the Stokes’ transport by the linear internal tide and demonstrate that the derived transports fit well with theoretical understanding and are the dominant driver of cross shelf transport for some locations and times. Additionally, they highlight times when the transport is significantly modified by non-linearity. The transport across the shelf edge is an important problem and the role of the linear internal tide is not well understood with very few (only 2 others to my knowledge) observational studies. The paper is well written and clear with results that will be of interest to the readers of Ocean Science, as a result I recommend publication of the manuscript. I have made a few minor suggestions below that the authors may wish to consider.

Fig 1. It would be interesting to see the mooring derived profiles alongside some higher resolution ship profiles if you have any (e.g. from the MVP) to understand how well the resolution of the thermistors is capturing the stratification. From the figure I expect it is doing a good job but would be great to check.

Line 197 – I agree that the Franks derivation is clear however it is far from the first paper to show this result (as acknowledged by the authors). I think it first appears in an appendix of Thorpe 1968, so I would reference that here also.

Thorpe, S.A. 1968. On the shape of progressive internal waves. Philosophical Transactions of the Royal Society A 263(1145):563–614, https://doi.org/ 10.1098/rsta.1968.0033.

Fig 2c – The caption lists different isotherms to the ones labelled in the figure (the caption says 14,16,18,20 and the figure shows 13,15,17)

Line 319 – Typo Qr1

Citation: https://doi.org/10.5194/egusphere-2025-2072-RC1
- AC1: 'Reply on RC1', Adèle Moncuquet, 28 Aug 2025
  
  Thank you for reviewing our manuscript. We appreciate your precise feedback.
  
  Fig 1. It would be interesting to see the mooring derived profiles alongside some higher resolution ship profiles if you have any (e.g. from the MVP) to understand how well the resolution of the thermistors is capturing the stratification. From the figure I expect it is doing a good job but would be great to check.
  We thank the referee for this comment. First, we would like to highlight that Figure 1 provides an initial overview of the mean temperature profile. This averaged temperature profile was not used in the computations. We have previously compared the MVP to the high temporal resolution mooring data in Figure 7 from the following paper: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2024JC021021. Here we present the evolution of the temperature field over the course of a day, using both MVP measurements and mooring data. The comparison demonstrates that the mooring data has adequate vertical resolution.
  Line 197 – I agree that the Franks derivation is clear however it is far from the first paper to show this result (as acknowledged by the authors). I think it first appears in an appendix of Thorpe 1968, so I would reference that here also. Thorpe, S.A. 1968. On the shape of progressive internal waves. Philosophical Transactions of the Royal Society A 263(1145):563–614, https://doi.org/ 10.1098/rsta.1968.0033.
  We have now added the original reference.
  Fig 2c – The caption lists different isotherms to the ones labelled in the figure (the caption says 14,16,18,20 and the figure shows 13,15,17)
  Thank you for catching this error it has now been corrected.
  Line 319 – Typo Qr1
  The typo has been modified. Thank you.
  
  Citation: https://doi.org/10.5194/egusphere-2025-2072-AC1
RC2:
'Comment on egusphere-2025-2072', Anonymous Referee #2, 08 Jul 2025

Review of "Observations of cross-shelf transport due to internal wave pumping on the Bay of Biscay shelf" by Moncuquet et al.
The authors study observed cross-shelf volume transports associated with mode-1 internal tides and high-frequency Nonlinear Internal Waves (NLIWs) in two contrasting mid-shelf locations. The vertical structure of the Stokes drift profiles Qr is a particular focus, with monthly-averaged volume transport estimates of ~0.1-0.2 m2/s in different parts of the water column. Comparison with theoretical predictions for the shape of Qr suggest this is a significant cross-shelf transport mechanism in the Armorican and Aquitaine shelves. Interaction with the wind-driven upwelling/downwelling Eulerian circulation is also discussed.
The text and figures are mostly clear, though figure labels are sometimes hard to read. I appreciate the comparison between the two different regimes and the Stokes volume transport estimates, since this is a difficult process to measure, and is not present in most full-complexity numerical models.
I see some major and minor issues with the manuscript in its present form, which I detail below. Briefly, I feel that a couple of sources of instrumental error (random instrumental noise and the assumption of flow homogeneity across the ADCPs' beam separation) need to be examined to add more confidence to the results.
Major points:
M1: Since the transports Q, QEu and Qr (and other quantitative estimates) are based on measurements which contain random error, it is important to have error bounds derived from the propagation of the instrumental noise. This would add confidence to the results, for example the comparison between experimental and theoretical Stokes drift fluxes in Section 4.1. Figures 1(c,e), 6, 9, and 10 would also benefit from this analysis.
M2: The lagged arrival times of short-wavelength signals at different beams of an ADCP can cause substantial differences in measured velocities due to the beam-to-Earth coordinate transformation. In this dataset, the presence of NLIWs and tidal bores can add spurious transport to the raw time series. Scotti et al. (2005, https://doi.org/10.1175/JTECH1731.1) propose a method to correct for these efects, which I think is necessary here. This would eliminate potentially spurious NLIWs and tidal bore signals in the raw velocity records that could affect the total Q estimates (and hence Qr). This could change the interpretation of the Qr profiles' shapes, e.g., the discussion in lines 449-463.
M3 (Line 132): It is worth checking that the 24 h cutoff period effectively filters all major tidal constituents. I wonder if it might leak some M2 variance, as M2 is the most energetic constituent and has a period that is not a multiple of 24 h.
M4 (Lines 192-193, 301): I understand the Stokes drift from the other processes listed, but why would density-driven mean flows have a Stokes component? It is not an oscillatory process.
Minor points:
m1 (line 54): "The southern shelf of the BoB presents the smallest barotropic tide of the shelf". This statement could use a reference.
m2 (Line 79): "on average the regional circulation is less than 2.5 cm/s". Is this a typical along-shelf or cross-shelf velocity, or a speed?
m3 (96-97): It would be helpful to include the temperature and pressure sensors' specifications such as manufacturer and model.
m4 (Line 98-99): What is the source for the 0.15 degrees C accuracy of the temperature sensor?
m5 (Line 100-101): Same as in m4, it would be good to include the ADCP's single-ping standard deviation for error propagation.
m6 (Lines 136-137): "We then solved the Sturm-Liouviille equation (4) and... and amplitude." This sentence might read more naturally if it is after equation 4 is introduced.
m7 (Line 426): "...Peru shelf, a location with a strong internal wave field". A reference for this statement would be helpful. I do not think Lentz and Chapman (2004) mention this.
m8: The axis labels and some of the annotations in most figures are too small to read without zooming in.
Typos/minor edits
Line 11: an -> a

Line 38: transportation -> transport

Line 89: over -> in

Line 159: of the -> the

Line 189: in the next -> in

Line 197: this -> that

Line 250 isotherms -> isotherm

Line 281: maxima -> maximum

Line 297: dominate -> dominant

Line 301: waves -> wave

Line 306: height -> heights

Line 319: Qr1 -> Qr

Line 321: T > 15°C -> T < 15°C; dominatly -> dominantly

Line 352: drove Q_A asymmetry -> caused Q_A's asymmetry

Lines 358, 387, 389, and elsewhere: NLIW -> NLIWs

Line 361: time series -> the time series

Line 387 attributed -> attributed to

Citation: https://doi.org/10.5194/egusphere-2025-2072-RC2
- AC2: 'Reply on RC2 - 1/2', Adèle Moncuquet, 13 Sep 2025
  
  Thank you for reviewing our manuscript. We are also grateful for the discussion you have initiated. We have answered the comments in two files, which are linked to the discussion. M1.pdf addresses the first major comment regarding the propagation of uncertainty measurements. Comments on the rest of the manuscript are gathered in "comments_R2.pdf".
  
  Citation: https://doi.org/10.5194/egusphere-2025-2072-AC2
- AC3: 'Reply on RC2 2/2', Adèle Moncuquet, 13 Sep 2025
  
  The linked file 'M1-1.pdf' presents an analysis of the propagation of uncertainty measurements.
  Best wishes
  
  Citation: https://doi.org/10.5194/egusphere-2025-2072-AC3

Peer review completion

AR – Author's response | RR – Referee report | ED – Editor decision | EF – Editorial file upload

AR by Adèle Moncuquet on behalf of the Authors (02 Oct 2025) Author's response Author's tracked changes Manuscript

ED: Publish subject to minor revisions (review by editor) (11 Oct 2025) by John M. Huthnance

Dear Authors
Thank-you for your responses to referees and the revised manuscript. I think you have largely responded appropriately to the referee comments but in some cases I would like to see better representation of your response in the revised manuscript. If readers have a similar comment it is better to give them easy access to some form of response, either directly in the manuscript or by reference. This applies to the first three items below. The other “Detailed comments” are minor but are intended to improve clarity in a revised version which I would like to see.
Yours sincerely
John Huthnance (Editor)

Regarding Ref 1 comment on Fig. 1 and comparison between mooring and MVP data, I think you should consider including a summary of your response in the final manuscript.

Regarding Ref 2 comment M1, I think you should consider including your response “M1.pdf” as a linked supplement and also include its results briefly in the main text with reference to the supplement. Please note however that supplements are not copy-edited.

Regarding Ref 2 comment M3 about the 24 h filter cutoff, I think you should consider including a summary of your response in the final manuscript.

Detailed comments
Line 38 end. “boluses”?
Line 102. “so that the horizontal” needs completion or deletion.
Line 108. Better “between 48.5°N and around 46.5°N” or “from 48.5°N to around 46.5°N”. Similarly for line 251 dates.
Lines 130-131. I think you rotated the co-ordinates, not the currents.
Line 162. “an” implies just one “NLIW” (omit “an” if more than one) whereas “NLIWs” implies more than one.
Line 200. Does “that paper” refer to Franks et. al (2020) or Thorpe (1968)? Better to be explicit.
Line 230. “offshore” –> “onshore”?
Line 231. “August 10” is long before the start of figure 2b.
Line 241 end. Better “between 20 and 15 mab.” or “at 20-15 mab.”
Line 251. C.f. line 108 comment.
Lines 268-269. I suggest “flow; Lentz” and “2004) from July 12- Figure 4a,b.”
Lines 271-272. Just before July 27 as well? “increase of the temperature . . . warming of the near seabed temperature” – duplication.

Line 303: “internal waves solitons, surfaces wave,” –> “internal wave solitons, surface waves,”
Line 311. “on” –> “to”
Line 315. Better “. . 15 °C; QEu was small . .”
Line 353: “drove” -> “caused”
Line 377. “. . (Figure 7a,b). . .”
Line 467. “. . NLIWs on the different components . .”?
Line 472. “. . tides and NLIWs . .”?
Lines 491-493. “using” three times in the sentence. It is not clear what two variables the regression is between.

M1.pdf
1 Context. “This supplement aims . . comment: “Since . . fluxes.” would suffice for the final publication.
2.2 first sentence. “. . error of a quantity . . combination . .”
Second line after (3). “. . formula is in . .”
2.3 before (4) and 2.3.1 before (5). “. . transport is expressed as . .”
Second line after (4). “. . independent and collocated . .”
Third line after (4). “. . represents low-pass filtering.”
Line after (6) I think you want the definition of δh here.
Line before 2.4 and line of 2.4.1. “uncertainty in”
Line before (9). “interpolated” (spelling). “expressed as”.

2.4.2 line 1. Better to mention “low pass” here as well as in the figure 1 caption.
Line 3 and Figure 1 caption. “cutting” –> “cut-off”? Line 3 also “1/(24 hours)”.
Figure 1 should give units for frequency.

Line after (13). “explicited” –> “described”
2.6 second sentence. “untrustable” –> “uncertain”?
3.1.1 lines 4-5. “can dominate”.
3.1.1 2nd paragraph 2nd sentence. “. . before 17th July, when the transport reached a maximum”
3.2 line 5: “. . reduced: σ . .”
3.2.1 line 6. Omit first “mostly”. Line 7. “NaN”

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AR by Adèle Moncuquet on behalf of the Authors (28 Oct 2025) Author's response Author's tracked changes

EF by Polina Shvedko (29 Oct 2025) Manuscript Supplement

ED: Publish subject to technical corrections (11 Nov 2025) by John M. Huthnance

AR by Adèle Moncuquet on behalf of the Authors (13 Nov 2025) Manuscript

Short summary

Internal waves along the Bay of Biscay coast transport water distinctly: surface and seafloor water moves shoreward while mid-depth water moves offshore, matching linear internal tide theory. This transport equals effects of moderate winds that typically dominate. Internal waves were the main transport at one site and enhanced shoreward flow near the seabed at another. Understanding these patterns could explain movement of nutrients, sediments, and pollutants affecting coastal ecosystems.