Upwelling characteristics in the Gulf of Finland (Baltic Sea) as revealed by
Ferrybox measurements in 2007–2013

Kikas, Villu; Lips, Urmas

doi:https://doi.org/10.5194/os-12-843-2016

Articles | Volume 12, issue 3

https://doi.org/10.5194/os-12-843-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/os-12-843-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 12, issue 3

Research article

|

01 Jul 2016

Research article |

| 01 Jul 2016

Upwelling characteristics in the Gulf of Finland (Baltic Sea) as revealed by Ferrybox measurements in 2007–2013

Villu Kikas and Urmas Lips

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Final revised paper (published on 01 Jul 2016)
Preprint (discussion started on 20 Nov 2015)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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- Supplement

RC C1329: 'Review of “Upwelling characteristics in the Gulf of Finland (Baltic Sea) as revealed by Ferrybox measurements in 2007–2013”', Anonymous Referee #1, 20 Dec 2015
- AC C1653: 'Response to Anonymous Referee #1', Villu Kikas, 02 Mar 2016
RC C1567: 'referee comment', Anonymous Referee #2, 03 Feb 2016
- AC C1654: 'Response to Anonymous Referee #2', Villu Kikas, 02 Mar 2016

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by Villu Kikas on behalf of the Authors (18 Mar 2016) Author's response Manuscript

ED: Referee Nomination & Report Request started (21 Mar 2016) by Mario Hoppema

RR by Anonymous Referee #1 (13 Apr 2016)

Suggestions for revision or reasons for rejection

Review of
Upwelling characteristics in the Gulf of Finland (Baltic Sea) as revealed by Ferrybox measurements in 2007–2013

The paper is now much better to read and less cluttered. However, I feel that it still needs more work, especially the discussion section. The authors should be commended for including more physics in this version of the paper as compared to the previous version. The authors have several hypotheses to explain the different wind strengths needed for the N and S shore upwelling and to explain the spatial variability in the structure of the upwelling. I feel that the authors can improve on this, as their arguments are not yet clear. It would be helpful to the reader to include some conceptual diagrams that explain their hypotheses. Are there any references that have looked at this in other straits elsewhere on this planet?

Detailed comments
Figure 1. If the colorbar at (b) does not apply to the colorbar at (a), please add colorbar to (a).
L102. Please mention how this paper addresses the unknowns in the literature regarding the upwelling. As it is stated now, the goal is to just present observations, but not really to explain them.
L215. Is UI computed using the deviation from the mean of the daily transects or the mean of one single transect? In Figure 2, L312 you use “daily transect mean”. It is somewhat confusing.
L243. Remind the reader again that PT100 is a temperature sensor.
L243-246. It is unclear what you say here regarding, precision, uncertainty, ’25 times’. Please omit or be clearer.
L248-258. This relates to my previous comments in the first round (see comment P10, L24). The authors can compute w=1/f*(dtau_y/dx - dtau_x/dy) and see how w compares to the w estimated from upwelling. The authors did not even come up with quantitative back of the envelope calculations and used qualitative arguments to reject this idea. I do not think it is hard to show quantitatively that wind shear does not play a role. Maybe the wind shear affects the frontal dynamics related to the discussion of Figure 8?
I still have some un-addressed questions regarding the wind. Why not use an area averaged wind speed locally at the ferry transect? Why not use the weather station instead of the model data if a model data point is chosen close to the weather station (L252)?
L256-258. The English is not clear in this sentence.
L210. ”longest” please specify how many days.
L307. Use of ‘course’ here and elsewhere sounds out of place. Maybe use ‘trends’?
L312. This is Figure 3.
L317. Is this the daily mean or transect-mean T?
L318. Please indicate how RMSE is computed (show a formula).
L389. The two subsequent dashes may be confusing?
L408. Use of ‘column’ is confusing. Use something like “top and bottom of each subplot”
L420. ‘was revealed’. English. It sounds like it was revealed in the past and not in this paper.
Figure 6. Maybe used dashed lines for the linear fits to emphasize the differences? Provide a correlation coefficient between CUI and CWS?
L466. You mean the annual ‘average values’. When using average and mean, please specify the period.
L471. ‘over the all’. Remove ‘the’.
L472-L474. ‘This estimate …. respectively’. I am not sure what you mean with this sentence. How do 8.8 days and mean stress values relate?
L474-L477. This is not clear either. The difference between the impulses is comparable to the average wind stress? Specify the difference. 0.71 - - 0.44? Or 0.71 + -0.44 = 0.27 N/m2? The mean would be 0.13 N/m2 (which is equally far removed from 0.71 and -0.44). This is 10 times larger than the mean of 0.015 N/m2.
L481-L484. Please explain the connection between daily measurements and the inertial period. This sentence is not clear. What is the link between this sentence and the rest of this paragraph that shows some examples of T and S for upwelling profiles?
L530-532. ‘not enough attention’. I think the installers know the fallacies, but you have to work with the ferry infrastructure. Changing this for the purpose of measurements is very costly. I suggest you remove this point.
L546. “We suggest that such coordinate correction procedure should be used in all Ferrybox systems”. I suggest you remove this point too. My experience is that these corrections are made to get the best georeferenced data (I certainly did that) – since everybody wants the best data. I think this point should not be one of the main conclusion of this paper. You should mention the most important findings first.
L570. What are ‘those values’
L583-585. Please explain the physics behind these reasons. Why are a deeper TC and topography reasons that explains the 0.71 vs -0.44 N/m2 difference?
L585-587. “However, one could suggest that the thermohaline structure of the Gulf of Finland is adapted to the general prevalence of westerly-south-westerly winds.” Ok this is not clear to me. How can there be a structure (TC slope) if the mean wind stress is almost zero (0.015 N/m2)? If it was 0.135 N/m2 your argument would be stronger. Please explain this better.
L588-591. “This suggestion … gulf” After rereading this sentence several times I still do not know what the authors want to say here. What does the comparison show?
L590. “for the all”. English!
L598. Please specify the general circulation scheme.
L616. “Since often the wind conditions were quite variable before the upwelling events, it was not possible to suggest any quantitative criterion for wind forcing generating one or the other type of temperature distribution.” If this is the case, what is the point of showing Figure 8. I suggest you remove this figure.
L625. ‘could be related’. Could the shear in windstress play a role? Do you have references that show that (sub)mesoscale variability (you mean eddies?) causes the steep fronts? So it is not really related to upwelling?
L626. “which are made visible if due to the slightly lower forcing the mesoscale dynamics do not fully dominate.” This is not clear. Explain better.
L632-634. ‘Thus ….. waters’ Again some more explanation is needed. Where does the deepening occur? On the north shore?
L642. Why not make this in a separate conclusion chapter?
L654. “deviation from the average”. The mean is 0.015 N/m2. So I do not think there is a strong horizontal thermocline slope associated with this value?
L658-661. Please specify what sub-mesoscale motions and how do they interact with the upwelling?

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ED: Reconsider after major revisions (13 Apr 2016) by Mario Hoppema

AR by Villu Kikas on behalf of the Authors (09 May 2016) Manuscript

ED: Referee Nomination & Report Request started (17 May 2016) by Mario Hoppema

RR by Anonymous Referee #1 (24 May 2016)

Suggestions for revision or reasons for rejection

Review of Upwelling characteristics in the Gulf of Finland (Baltic Sea) as revealed by Ferrybox measurements in 2007-2013

The paper is almost there. The authors did there best in making it more of a discussion with more physics. All the ingredients are there. However, their logic is sometimes hard to follow. The physics are still not well explained, although the authors now refer to the papers that discuss these upwelling mechanisms. The authors should better guide the reader and explicitly explain the physics, instead of leaving it to the reader to read these cited papers to complete the story. That leaves a somewhat unsatisfying feeling. The connection between the paragraphs is not always clear. Many of my suggestions relate to wording and clarity. The paper is also quite long. I made some suggestions here and there to shorten the text.

L64-l73. Since the paper is quite long, is this discussion on biochemical interaction relevant to this paper? I suggest to take it out.

L110. 'two coastal areas' Sometimes it is better to be specific (as elsewhere in the paper). You mean the north and south coasts?

L124. Instead of “is in use” use “has been in use”

L245-248. I am not sure if I understand this discussion on the accuracy. Also I am not sure if the calculation of the maximum uncertainty of 1.6 (40x0.04) is correct. Why not omit this?

L259. You mean there is a 20 degree bias that needs to be corrected for?

L334. “it was suggested”. Who suggested this? Incorrect English language usage.

L347. Incorrect English language usage: “so distinct than in”. You mean “distinct as the variability”?

L349. Use “at a distance of”

L371. “Exceeded”

L376-377. “Thus...C” Incorrect English language usage.

L379-429. This section has a lot of boring statistics (boring to the average reader). Can these be transferred to a table and then only discuss the ones most relevant to the main story?

L471. Here you say that the mean for 2007, 2009 and 2012 is 0.029 N/m2. Is that correct?

L478-480. “It can be … region” I do not understand this sentence. What are the differences? What is the mean value. Where are they discussed in the text?

Figure 7. The lines are too thin and the colors are to similar. You can also use dashed lines.

L519. Why the use of “obviously”?

L576-L577. “analysis of wind data”. Be more precise here and better guide the reader. You mean that up-estuary wind stresses are larger than down-estuary stresses (as found in this study and elsewhere) and that this should result in stronger upwelling along the northern coast?

L584-L590. These arguments are not clear to me. How does Laanemets arguments explain the difference in north-south upwelling? How does “the steeper slope and greater” make “the upwelling outcome [...] more intense in the southern Gulf”? Please explain in terms of physics.

L585. Please be precise and explain in phyiscal terms how the slope can affects upwelling. Is this through bottom drag?

L586. Is this the along-channel or cross-channel return flow?

L592. An “alternative” to what? You mean the “the higher position of the thermocline, steeper bottom slope and greater depths in the southern part”? It is not yet clear. Can this also be an “additional” explanation?

L595. Please explain how the southwesterly wind forcing and rotation cause the horizontal cyclonal circulation?

L596-L598. “Such circulation … of the gulf” To me if there is cyclonal circulation in a geostrophic balance both (out) sides should have a higher water levels and deepere thermoclines (and the center SSH depression and a shallow thermocline). But this is not the case.

What is the role of estuarine circulation in this? Geostrophy pushes the outflowing freshwater against the northern coast, deepening the thermocline there. Are you trying to say this? I do not understand your explanation of cyclonal circulation due to wind.

See also this paper and references therein:

Thomson, R. E., S. F. Mihaly, and E. A. Kulikov (2007), Estuarine versus transient flow regimes in Juan de Fuca Strait, J. Geophys. Res., 112, C09022, doi:10.1029/2006JC003925
(http://onlinelibrary.wiley.com/doi/10.1029/2006JC003925/pdf)

The deeper thermocline then requires a stronger SW wind impulse to cause upwelling along the north shore.

L609. “If the strong southwesterly winds prevail, a downward movement of the thermocline in the gulf as a whole occurs”. You mean that there is a “bunching” of water in the upper layer as the estuarine outflow (part of the “estuarine circulation”) is countered by the wind driven circulation?

L611. “In contrary, the down-estuary winds cause a general upward movement of the thermocline in the gulf.” Because now all the water in the surface layer is pushed out due to the wind and estuarine circulation acting in concert?

These in phase and out of phase forcings enhance southern and counter northern upwelling, correct? Then explicitly say so.

L625. What is the “general circulation scheme”. The estuarine circulation modified by rotation? Did you discuss this earlier?

L642. To what does the “latter” refer? 'Gradual fronts'. Pleas say so. What are upwelling filaments? Do they only occur with gradual fronts and not sharp ones? Can you indicate the filaments in Figure 7?

L651. You do not have a lot of data points that confirm the relation between sharp/gradual fronts and wind strength. Maybe shorten this discussion and omit Figure 8?

L656-L679. What is the purpose of these two sections? Do you want to explain why two easterly wind events corresponded to two southern gradual fronts? That is not very clear now.

L658. Please explain to the reader what “squirts” are.

L665. Where and what is the upwelling jet? You implicitly suggest it has been discussed earlier?

L670. What do you mean with “when the thermocline had a deeper position that might enhance the influence of the bottom irregularities to the upwelling dynamics.” ?

L673 'deepening' this is related to the 'bunching' (L607-619)?

L697. Maybe say (just be clearer and more precise): “a stronger southwesterly wind impulse to cause upwelling along the northern coast as compared to a weaker northeasterly impulse to cause upwelling along the southern coast”

L704. What is the “latter”?

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ED: Publish subject to minor revisions (Editor review) (25 May 2016) by Mario Hoppema

AR by Villu Kikas on behalf of the Authors (30 May 2016) Manuscript

ED: Publish subject to technical corrections (09 Jun 2016) by Mario Hoppema

AR by Villu Kikas on behalf of the Authors (10 Jun 2016) Author's response Manuscript