the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 26 May 2025
Observations of cross-shelf transport due to internal wave pumping on the Bay of Biscay shelf
Abstract. Coastal cross-shelf transport drives the redistribution of sediment, nutrients and pollutants on continental shelves. Here, the cross-shelf volume flux is quantified from in situ measurements at two coastal sites on the Bay of Biscay (BoB) shelf. At both sites, a semidiurnal internal tide propagates onshore, and mode 1 nonlinear internal wave packets are observed. The Eulerian and Stokes drift contributions to the subtidal cross-shelf transport are estimated along density layers from ADCP, temperature sensors, and CTD measurements at 62 m water depth on the Landes plateau or SE-BoB (44° N) and 47 m water depth on the Armorican shelf or N-BoB (47° N). The Stokes drift transport has possible contributions from the internal tides, nonlinear internal waves and the surface waves and tide. At both sites, the vertical profile of the month-long averaged Stokes drift volume flux matches the shape of the semi-analytical Stokes drift volume flux due to a linear mode-1 internal tide. We demonstrate that nonlinear internal wave events can also contribute to the Stokes drift volume flux. We thereby attribute the Stokes drift volume flux at the study sites to internal wave pumping (IWP). At both sites, the IWP is responsible for a near-seabed onshore volume flux during stratified conditions and spring internal tides that is equivalent to an wind-driven upwelling event generated by a 4 m/s wind. At N-BoB (47° N), IWP is the main contributor to the total cross-shelf volume flux under stratified conditions and a spring internal tide. At SE-BoB (44° N), IWP augments the near-seabed onshore volume flux during upwelling events and maintains a near-seabed onshore volume flux even during downwelling events.
-
Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
-
Preprint
(29028 KB)
-
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(29028 KB) - Metadata XML
- BibTeX
- EndNote
- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2025-2072', Anonymous Referee #1, 24 Jun 2025
-
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
-
AC1: 'Reply on RC1', Adèle Moncuquet, 28 Aug 2025
-
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 toCitation: 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".
- AC3: 'Reply on RC2 2/2', Adèle Moncuquet, 13 Sep 2025
-
AC2: 'Reply on RC2 - 1/2', Adèle Moncuquet, 13 Sep 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
-
AC1: 'Reply on RC1', Adèle Moncuquet, 28 Aug 2025
-
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 toCitation: 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".
- AC3: 'Reply on RC2 2/2', Adèle Moncuquet, 13 Sep 2025
-
AC2: 'Reply on RC2 - 1/2', Adèle Moncuquet, 13 Sep 2025
Peer review completion
Journal article(s) based on this preprint
Viewed
| HTML | XML | Total | BibTeX | EndNote | |
|---|---|---|---|---|---|
| 775 | 118 | 24 | 917 | 17 | 35 |
- HTML: 775
- PDF: 118
- XML: 24
- Total: 917
- BibTeX: 17
- EndNote: 35
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1
Adèle Moncuquet
Nicole Jones
Lucie Bordois
François Dufois
Pascal Lazure
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(29028 KB) - Metadata XML
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