MS No.: egusphere-2026-189

MS type: Technical note

Major comments :

This technical note addresses the question of how to correct vertical variations in sensor position

between closely distributed moorings with adequate instrumentation (here RBRs) in a deep-sea

environment. Though it seems to concern only very specific network of moorings, it could be useful to

other users. Therefore, I am favorable to a publication after bringing some clarifications in the

manuscript.

Detailed comments:

paragraph 3.1: Parabola model (l.121 – 139)

- The 5° starting assumption relies on a test as I understand (from fig. 3 caption). How was that test

conducted? Additional information is need in the text.

- I’m not an expert in net deformation. Parabola shape seems intuitive given that each net node support

the same tension from each top-mooring buoyancy.... but are there any references? Are blue and red

curves the only possibilities?

-What guarantees that the outer pipe remains circular?

- Is the maximum 5° parabola better consistent with the expected elongation of the steel grid? I guess

the results (° more, less) depends on the tensioning of the grid lines and the fact that the outer pipe

remains more ore less circular?

Paragraph about slanted warm episodes (l.182 – 190)

I do not necessarily see why the parallel with slanted convection. Here, we have warm water intrusion

from above in the domain of the T-sensor cube. It's not cold water from convection as mentioned at

lines 190... Does the 3D-view from the cube exhibit systematic slanted warm ‘intrusions’?

Temperature sensor spectra (l. 191-197)

It would be quite informative then to show and comment the contrast between the typical averaged

spectra when homogeneous conditions occur vs stratified conditions associated with warm water events

as in Fig. 7 & 8.

l. 199: band-pass -filter and Fig. 8

I'm a bit lost with this paragraph:

A you referring to another spectrum? I don't see any example of spectrum using a band-pass filter

applied to theta(z,t).

We just have Fig. 8 with light smoothing of spectral rays at low frequencies and heavier smoothing

between spectral rays at high frequencies (which is not what I would call a band-pass filter).

Are you pointing Fig. 8 with the buoyancy (cyan-dashed) and inertial (black-dashed) slopes?

Please add the values of the slopes on Figure 8 and in the text + add references for such slopes in the

text.

Inertial and buoyancy subranges (l. 202): need a clarification

If I try to understand the point, the author wants to contrast the high frequency behavior of

thermistances that are close to the bottom (6, 20 m) with other that are farther (40 m, 120 m).

Those farther clearly align with the inertial black dashed line (-5/3 slope?), while the closest to the

seafloor seems 'closer' to the buoyancy cyan dashed line (-1 slope?).

My interpretation is different. At high frequencies (> 100 or 1000 cpd), all spectra follows a -5/3 slope,

but for the two sensors closest to the seafloor, that slope is shifted toward higher energy levels due to

energy input around 100 cpd @ 20 m high, and around 300-900 cpd @ 6 m high. Above those

frequencies of energy input, the inertial slope fits the high frequency part of 6 and 20 m sensors. To me,

there is no real evidence of a buoyancy subrange with those spectra (Fig. 8).

l. 205: ‘ Future investigations will be directed to improve statistics ...’: agree - difficult to tell which of

inertial or buoyancy lines better fits the spectra between 10 and 100 cpd. The difference in slopes

between those subranges is too tenuous with your illustration.

l. 207: temperature variance

Please indicate how it is calculated: Is it the variance, calculated over 1.3 day in physical space, of the

600-1800 cpd-band-pass filtered temperature time series?

About the height pattern (Fig. 10 and associated text)

Results (Fig. 10 vs 6) are convincing but...

Is there an assumption behind that the temperature field, or more exactly, the temperature variance field

has to be horizontally homogeneous across your sensor network, at a given depth, to be able to convert

temperature variance differences with the reference line to height using the 45-line variance average?

If yes, you should state it and you have to comment on the realism of the homogeneity assumption,

given the fact that, warm water events are transitory and are advected across the mooring network,

which may induce heterogeneity between neighboring lines.

In the same vein, I'd be curious to see the variability of Fig. 10 using other periods of warm water

events.

l. 243 comparison with ‘... open-ocean values observed in stratified waters well away from

boundaries’

Here, it would be fair to remind the reader that your experiment was located close to the shelf break,

where the strong Liguro-Provençal current flows. This contrasts with open-ocean dynamics.

Appendix A, l. 306: Define NTC where it first appears.

l. 319: addition: Low-pass time filtering, with a cut-off frequency of 500 cpd, does not reduce these

l. 319: ‘... but additional vertical filtering adequately removes the bias (Fig. A1c,f)’. Information

missing: impossible to reproduce, not enough details. What type of 10-m-vertical filter is used (Fig.

A1-cf)?

l. 342: ‘...temperature spectra become horizontal following buoyancy-subrange scaling, rather

abruptly.’

This rather true for old, but not for new sensors. For new sensors, green and magenta evolves

consistently from 50 (first crossing) to 100 cpd (last crossing). From 100 to 300 cpd, the green remains

flat and is consistent with a buoyancy subrange typical slope. Above 300 cpd, the slope gradually

increases towards a white noise slope (+1 on this scaled loglog plot).

l. 344: ‘... was no longer dominant at frequencies higher than that of the crossing, more so in Fig. A2a

than in Fig. A2b.’

I just wrote the opposite! A2a (new sensors) remains consistent with buoyancy subrange after crossing!

('more so' refers to no longer dominant after crossing)

Dear Dr. van Haren,

Please find here my review of the manuscript entitled "Technical note: turbulence demonstrates height variations in closely spaced deep-sea mooring lines". This short note aims to determine that height variations in moorings lines relative to the seafloor (due to the deformation of a round grid made of steel cables under vertical pull by floatation) can be calculated. Three methods are considered, but the author demonstrates that the one based on turbulence variance is the more appropriate. Preliminary turbulence statistics are also presented at the end of the note (although the methodology for this part if not explain, see one comment below).

This is a very technical paper, but in itself the science is sound, although the manuscript would benefit from some clarifications. Since the data are from a unique mooring design, I doubt of the widespread applicability of this study: the error correction is only relevant to reference multi-lines moorings to one another, and this error in vertical position would be negligible for a single line mooring. 

I do think that the analysis here could have also been contained in an appendix of another related study (at the end, only one method is really working, so the description of the failed attempts could have been avoided).  For example, I note that the same author already has 2 other Technical Notes submitted to OS using the same data (and some figures are shared) and one paper accepted in GRL using also the same data set. I wonder why the current technical notes was not added to one of those studies in an appendix, but I am not overly worried if the Editor decides to leave it separate. If the Editor is fine with the observations I make above, I suggest the potential publication of the technical notes after some text-related changes.

---- Main Comments ----

L. 87-96, the whole paragraph: "In addition, because vertical temperature (density) gradients are so small in the deep Mediterranean, so that buoyancy frequency N = O(f) where f denotes the inertial frequency, reference was made to periods of typically one-hour duration that were quasi-homogeneous with temperature variations smaller than instrumental noise level (van Haren, 2022). Such >125-m tall quasi-homogeneous periods existed on days 350 (in 2020), 453, and 657 (-366 in 2021) in the records. This secondary drift correction allowed for proper calculations of turbulence values using the method of Thorpe (1977) under weakly stratified conditions. As will be demonstrated in Appendix A, under very weakly stratified conditions a tertiary correction involved low-pass filtering of data."

-> This whole section is not clear. It looks like something is missing from the first sentence and then "this secondary drift correction" seems to refer to a part that was not introduced... I suggest re-writing that paragraph.

L. 111: "Eight 'corner-lines'... "

-> I suggest identifying them in Figure 1.

L. 132 - 139: This part is not clear and very confusing.

In addition: "pushing it to the seafloor from the low side" -> What does it mean?

I suggest re-writing this part.

L. 175: "Unexpectedly, such a method is not found during a near-homogeneous period."

-> What "found a method" means? and why "unexpectedly"?

Do you mean "this method does not work"?

L.207: "During such a period of warm waters from above, temperature variance may be relatively low closest to the seafloor, but it increases to high levels well above common interior-values in the first O(10)m above seafloor (Figs 8, 9)."

-> It is unclear because at 2500m depth, O(10)m above bottom is relatively close to the seafloor... Please clarify.

L. 214: dz = 2 is a constant in the equation? Please clarify.

L. 234: "Coarsely every two hours, 124-m vertically averaged turbulence dissipation rate peaks, indicating the largest overturns being about 100 m in height, given a waterflow speed of 0.03 m s-1."

-> This is really unclear. Please explain.

L. 241: The method to derive turbulence variables is not explained. I understand that this may be described in other papers, but I think it is important to recall it here if some results are presented.

L. 216: "Here, the pattern is given for height determination by computing across the largest gradient of temperature-variance, between T-sensors #2 and #3 from the seafloor."

-> It is the first times #2 and #3 are introduce. What it means?

L.261: "Instead, a mooring-height determination was *found* during a period of relatively large stratification"

-> Was achieved? (check also the rest of the text)

Data availability statement:

Note to the Editor: Is this acceptable to just say that the data are too complex to be shared or used by someone else? 

Figure 6: A divergent colormap (centered at zero) would be more appropriate here.

---- Minor Comments ----

Title: I personally find the title difficult to understand. I suggest something more straightforward such as "Determination of the height of mooring lines above seafloor using turbulence measurements"

The author uses a lot of unnecessary parentheses. I would personally remove. 

E.g. L. 88: "In addition, because vertical temperature (density) gradients are so small ..." While I understand what the author means, but it could be more explicit: "... vertical gradients of temperature, and thus density, are so small ..." 

Similar (unnecessary) parentheses are used elsewhere in the text Lines 92, 121, 166, 184, 275, 449

Also Lines 457: what is meant by "(sic!)" in the caption?

L. 124: "the models start from there"

-> You mean it is the "zero-crossing value"? If so, please be more specific.

L. 125: "angle of 5 deg. (green model in Fig. 3)"

-> add angle in Figure 3.

L. 234: why "values" with quotation marks?

L. 246: "Although the warm-water event of Fig. 7 is relatively *strong*"

-> What "strong event" means?  I suggest using a more precise qualificative (e.g., event of strong turbulence?). 

L. 248: "This will be reported elsewhere in more detail..."

-> where? how? elsewhere in the text? other paper?

L. 255: "unmeasurably small"

-> Yet it was measured?

L. 267: "several-fold" is used, but the following text uses "first" and "second" only.

Section 3.2 (and elsewhere): Please consider using scientific notation for temperature variance/precision.