Rectified tidal transport in Lofoten–Vesterålen, northern Norway

Børve, Eli; Isachsen, Pål Erik; Nøst, Ole Anders

doi:https://doi.org/10.5194/os-17-1753-2021

Articles | Volume 17, issue 6

https://doi.org/10.5194/os-17-1753-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/os-17-1753-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 17, issue 6

Research article

| Highlight paper

|

02 Dec 2021

Research article | Highlight paper |

| 02 Dec 2021

Rectified tidal transport in Lofoten–Vesterålen, northern Norway

Eli Børve, Pål Erik Isachsen, and Ole Anders Nøst

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Final revised paper (published on 02 Dec 2021)
Preprint (discussion started on 26 May 2021)

Interactive discussion

Status: closed

RC1:
'Comment on os-2021-41', Anonymous Referee #1, 25 Jun 2021
Review comments to Rectified tidal transport in Lofoten-Verstalen, Northern Norway by Eli Borve et al.

In this work the authors examine tracer dispersal due to tidal processes around the Lofoton-Vesteralen with the motivation of determining the importance of tides modulating the dispersal of cod eggs and larvae from spawning to nursery areas. They focus on two non-linear tidal processes, namely tidal pumping and tidal rectification. FVCOM is run with an unstructured grid 2D setup for tides only and subsequent tracer releases are analysed. The authors then analyse the relative importance of each process in driving the exchange of waters in and out of Vestfjorden through a number of different straits.

The paper is well written, clear and nicely presented. My comments are generally related to the presentation of the results and how they could be made more easily to understand.

Introduction:

L.18 – 21: could do with a few additional references

L 50-65: It would be nice to have a diagram to illustrate this process. You could move Figure 9 to the intro and refer to it here as it greatly adds to the intuitive understanding of the process.

L 68-83: Again, it would be nice to have the diagram for this in the intro.

Methods:

L 118: Why do you use TPXO7.2? The latest version is 9 and is available as a higher resolution dataset. This is likely to affect your results. By how much do open boundary forcing values differ between the two datasets?

Model validation:

It would be nice to see some numerical values so that the reader can assess the performance of the model in absolute terms. Could you add a table with the amplitudes, phases, and amplitude and phase errors for each station for M2 and K1? You could also report mean errors for each constituent analysed.

Tidally driven tracer transport:

L.177: Why do you show results only for 3 and 4.5 hours? It would be good to see the process through the tidal cycle at e.g. hourly intervals.

Rectified tilde currents:

L.335: I’m not sure this sentence fully makes sense? Which mechanism dominates and is responsible for the net flux or how does each process contribute?

343: How will your choice of linear bottom friction impact your results? Is this the same bottom friction used in the tide model? It may be an issue if they are not consistent?

375: How does the choice of filter impact the curves? It would be nice to see 1 tidal cycle values as well.

440: I’m not sure I understand how you define the topographic length scale

445: Where do you define L_B and what is it? How does it differ from L?

Summary and conclusion:

L.492L ‘But not all straits are created equal’ – reword to something more specific.

General: Given that your introduction talks about cod quite a lot, the reader feels a little let down in the conclusions. How important are these tidal processes for the dispersal of the Arctic cod?

How do the observed processes compare to other regions in the world and different observations? It would be nice to see this work be put into context of other previous work in this section.

Figures:

Figure 2: It would be nice to have more information with this figure: e.g. (a) how do the two figures differ? (I guess it’s the phase of the tide); (b) the velocity front is identified – why is this relevant and what does it mean for this study?

Figure 4: how about plotting observed values on top as shaded circles on top of the model results? Also, plot against latitude and longitude rather than distance.

Figure 6, l.5: do = does

Figure 7: Could you take your panels a bit further south? At 10.5 hours you are missing part of the incoming waters

Figure 9: Panel b: Why is us Ae in the sink region? Should it not be in the jet? It would be nice to illustrate all of the length scales on this plot (as far as possible)

Figure 10: Not all marker labels are visible. Also, you could increase the intuitiveness of the plot by adding labels such as an arrow with ‘more asymmetric’ along the axis y axis and doing the same for the x-axis.

Figure 11: Mention what each non-dimensional parameter is in words either on the axis or in the legend.

Figure 13: What do you mean by ‘sets of closed contours’? Could you show these on a map?

Figure 14: It would be nice to add the positive/negative vorticity gains in the diagram – it would make it even more intuitive. You could also explicity include the words squeezing and stretching in the diagram.

Minor comments:

Generally, watch out for the use of commas. E.g. Here, … In this study,…

l.16: rises = raises

l.54: is = are

59: what = which

102: no comma needed

425: ‘is down the’ = is down to the

520: appears = appear
Citation: https://doi.org/10.5194/os-2021-41-RC1
- AC1: 'Reply on RC1', Eli Børve, 12 Jul 2021
  
  We thank the referee for good comments and suggestions regarding our manuscript.
  
  Please find our answers in the attached file.
  
  Kind regards,
  
  Eli
  
  Citation: https://doi.org/10.5194/os-2021-41-AC1
RC2:
'Comment on os-2021-41', Anonymous Referee #2, 11 Jul 2021

This paper discusses two physical processes, tidal pumping and tidal rectification, that may be relevant to the dispersion and transport of cod eggs and larvae in the Lofoten - Vesteralen area, Northern Norway.

The geographical and ecological settings, as well as the physical processes and numerical techniques used to address the questions involved in larvae and cod egg transport and spreading are well described. The paper comes to a clear conclusion regarding the relevance of tidal pumping, and provides welcome suggestions for further investigation of the process of tidal rectification.

As a consequence, it is recommended that the paper is published provided it addresses the few minor issues discussed next.

Line 53 : waters => water

Caption Fig. 2: instruments => instrument

Line 127: drop ‘the’

Line 404: The along-isobath velocity scale U may be much stronger than the cross-isobath current used in the previous scaling (line 403).

How is the value of R motivated?

Closer to islands, D decreases. So, how appropriate is a choice D=50m?

Line 443: chances => changes

Line 462: dynamically => dynamical

Line 519: Bottom intensification of tidally-rectified flows and concomitant vertical circulation cells (Maas et al 1989) might possibly be of relevance for the transport and spreading of marginally sinking larvae and cod eggs.

Figures A1 and A2 have interchanged captions.

Reference:

L. R. M. Maas & J. T. F. Zimmerman (1989) Tide-topography interactions in a

stratified shelf sea II. Bottom trapped internal tides and baroclinic residual currents, Geophysical & Astrophysical Fluid Dynamics, 45:1-2, 37-69, DOI: 10.1080/03091928908208892

Citation: https://doi.org/10.5194/os-2021-41-RC2
- AC2: 'Reply on RC2', Eli Børve, 18 Aug 2021
  
  We thank the referee for good comments and suggestions regarding our manuscript.
  Please find our answers in the attached file.
  
  Kind regards,
  
  Eli
  
  Citation: https://doi.org/10.5194/os-2021-41-AC2
- AC3: 'Reply on RC2', Eli Børve, 23 Aug 2021
  
  Here are some additional comments to the reviewer's question regarding the scaling of the vorticity production terms in Line 404:
  
  "The along-isobath velocity scale U may be much stronger than the cross-isobath current used in the previous scaling (line 403)".
  
  We calculated the along- and cross-isobath velocities (u and v, respectively) around the depth contours encircling the two island groups. Taking the contour-mean amplitude of the two oscillating velocity components, the along-slope velocity component U is only up to 1.6 times the amplitude of the cross-slope velocity component V.
  The mean ratio U/V around Røst is 1.4 and around Mosken/Værøy is 1.2. This ratio (U/V) varies off course somewhat around the contours and may be up to almost 3 at some places, which certainly increases importance of the bottom frictional torque. However, the over-all impression, is that a scaling assuming U and V has similar magnitude is a reasonable assumption.
  Comparing the U/V ratios with Figure 1 in our previous answer, we still, in general, have a weak dominance of the vorticity generation by squeezing and stretching even if we assume U/V = 1.5.
  
  We will include these results and discuss this more carefully in the revised manuscript.
  
  Citation: https://doi.org/10.5194/os-2021-41-AC3

Peer review completion

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

AR by Eli Børve on behalf of the Authors (04 Oct 2021) Author's response Author's tracked changes Manuscript

ED: Publish subject to technical corrections (25 Oct 2021) by Joanne Williams

Dear authors,

Thank-you for the revised manuscript and response to reviewers. My apologies again for the delay at this editorial stage, but I'm glad I took the time to reread your interesting paper. There are just a few small corrections I noticed, then it can go forward for typesetting & final proofs. Line numbers refer to the latest version.

Line 54: Delete "clearly"

Paragraph from line 47: I agree with the reviewer that the diagrams would help a lot at this early stage, especially as Fig 1 doesn't include the tidal pumping mechanism. Please move fig 9 and fig 14 to this paragraph (they could be combined as two panels of one figure if you prefer). I understand your argument about the notation but it is easier to refer back to a diagram on the first or second page having already grasped the physical picture than forwards several pages.

Line 122 It might not affect the results, but what phase was the tide at the point of tracer release?

Fig 4 top right the label K1 has gone wrong.

Equation 4 is incorrect, a font problem I think. Please check.

The fit in Fig 10 is a bit unconvincing, especially on a log-log axis. But I don't think it necessarily damages your later argument.

Fig 13 needs a legend. Also "encricling"-> "encircling" in the caption.

Line 420: Tidy. "Even though the latter term is not necessarily negligible, we will omit it in the following for simplicity..."

Fig 15: If you haven't already, please check this colour scheme: https://www.color-blindness.com/coblis-color-blindness-simulator/

Fig 17 needs a legend.

I hate to say it but "data available on request" is not enough, and not much help to a researcher in ten years time if you have a new job and don't answer your emails! Please consider uploading model results to a public archive server. If uploading the whole model run is impossible, you should at least make public the data necessary to reproduce the figures. See https://www.ocean-science.net/submission.html#assets

Data used for model boundary conditions must be included in Acknowledgements, using the data statement as provided with the data, as should the satellite images (people who fund satellites like to run searches to see their money is being well spent). And the bathymetry. Oh, and the tide stations in figure 5 - where is their data hosted please?

Ocean Science now has the capability to host a video abstract to help promote and explain your paper. It isn't compulsory, and you can return to it later, but animations from the model would be very well suited to this, so you might like to consider it.

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AR by Eli Børve on behalf of the Authors (03 Nov 2021) Author's response Manuscript

Short summary

Non-linear tidal dynamics can produce prominent time-mean transport in coastal regions where strong tidal currents interact with topography. We investigate tidal-induced transport using a tidally driven ocean model for Lofoten–Vesterålen in northern Norway and find that both tidal pumping and tidal rectification can play an important role for time-mean transport in the region. The study emphasizes the importance of non-linear tidal dynamics for time-mean transport in complex coastal regions.