the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Lagoon hydrodynamics of pearl farming islands: the case of Gambier (French Polynesia)
Oriane Bruyère
Romain Le Gendre
Vetea Liao
Serge Andréfouët
Abstract. Between 2019 and 2020, the Gambier lagoon was instrumented over a period of 9 months with a large array of autonomous oceanographic instruments measuring temperature, pressure and current. Two deployments were conducted, respectively from June 2019 to October 2019 (Leg1) and from late October 2019 to late February 2020 (Leg2). A total of sixteen instrumented locations were spread across the lagoon and on the forereef. Physical parameters were measured to characterize the wave climate, tide and surges, lagoonal circulation, and spatial and vertical temperature variabilities. Those observations were part of the ANR-funded MANA project (2017–2022) and its derivatives that aimed to improve knowledge of processes influencing the spat collection of Pinctada margaritifera oysters that are used for black pearl farming and production. This data set was a prerequisite for the development of a high resolution biophysical model on Gambier lagoon which aims at tackling the connectivity oyster larvae. The sampling strategy focused on the northern region of Gambier lagoon and especially on the sub-lagoon of Rikitea which is a prime spat collection site. The data set was post processed, quality controlled and is archived in a dedicated repository with a permanent DOI into the SEANOE marine data platform.
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Oriane Bruyère et al.
Status: open (until 06 Nov 2023)
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RC1: 'Comment on essd-2023-302', Stuart Pearson, 18 Sep 2023
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General Comments
This manuscript presents a hydrodynamic dataset for the Gambier Islands (French Polynesia) in the Pacific Ocean, detailing waves, currents, temperature, and water levels at multiple locations around an atoll for 9 months in 2019-2020. The entire atoll seems well-instrumented, with instruments suitable to capture a wide range of hydrodynamic phenomena.
This article furthers ESSD’s goals of clearly presenting and documenting a high quality earth science dataset. The authors’ dataset is unique, capturing the hydrodynamics of a remote coral atoll in with relatively wide spatial coverage and fine temporal resolution. Such a dataset is not trivial to produce and will provide a valuable addition to the scientific literature. The dataset is also useful in itself for understanding atoll hydrodynamics, but has already apparently been used as a basis for model validation (Bruyere et al 2023b). I have made many comments below but I believe they are mostly minor in scope and in the spirit of helping a strong dataset and manuscript shine brighter.
As coral atolls are at high risk to the effects of climate change, such a dataset provides a welcome snapshot of a vulnerable location that may be valuable for researchers in other fields (e.g., ecology, coastal engineering) or studying other atolls. I can think of several colleagues who may be interested in using this dataset for their research on coral reef hydrodynamics (including myself), although it seems strange to filter out low-frequency wave data from this dataset if it was measured (see detailed comments below). As far as I can tell, the dataset here is complete and makes a coherent collection, and is sufficiently presented by this manuscript.
Data quality
The data is very clearly available in well-formatted netcdf files from the website. I downloaded several of the files to check the metadata and accessibility of the data, and it was very easy to find what I was looking for. I will actually share this with my students as an example of good practice for sharing research data.
However, I think that more attention to error/uncertainty estimates and processing procedures should be given in the manuscript (see detailed comments below). The current quality control section (Section 4.5) is only two sentences long and would benefit from more detail. There was not much discussion of errors or data cleaning/processing, beyond some mentions of unlinked Python datasets.
Presentation quality
The article is not too long and is clearly written, covering most of the major questions that I had when I started reading. The figures are all generally clear and well-formatted. Overall the presentation quality is good.
As per ESSD guidelines, “The authors should point to suitable software or services for simple visualization and analysis, keeping in mind that neither the reviewer nor the casual "reader" will install or pay for it.” Perhaps then Section 6 (Data Availability) should here indicate again that the data is stored as NetCDF files and that they can be readily analyzed and visualized using a wide range of freely available code/software packages, or something along those lines.
Specific Comments
- L149-151: General question: how were your instruments mounted? E.g., were they placed on frames, laid directly on the seabed, bolted to a reef, weighted down? If placed on a metal frame, were your compasses calibrated and did you account for interference from the metal frame (e.g. for ADCP current direction)?
- L167: Can you provide more detail on the processing (“processed with Python routines”)? Is the code available online? If so, that would be good to mention here and link.
- L178/184: How were your pressure/wave data processed? Can you provide more details?
- L182: Why did you use a constant atmospheric pressure to offset your wave gauges instead of measurements from the nearby weather station? What are the limitations of this assumption?
- L184: You only examine waves with periods 3-25 s, but infragravity (25-250 s) and very low-frequency (>250 s) waves are often very important on coral reef flats. Why did you make this choice? Is the lower-frequency data still available? This data would be extremely valuable for e.g. predicting flooding on atoll islands and validating existing theories about low frequency wave hydrodynamics on coral reefs. If you still have the raw data at these frequencies, I would strongly encourage you to add it to your dataset as I can think of quite a few people (myself included) who would find it useful.
- Figure 5: Is there any temporal lag in the two signals? They look very close, so it’s a bit hard to tell, but I think this is useful information.
- L182: How long were your bursts? (e.g. 20 mins every hour)?
- L209: See my earlier comments re: compass calibration if you used a metal frame.
- L221: Again, is this code available?
- L226: Please provide more detail on the data cleaning process.
- Section 7 (Conclusions): Something that I missed was a sentence or two describing how similar/different this location is to other sites (and therefore how can it be applied/useful for scientists/engineers at different locations besides the Gambier Islands)? Perhaps also circle back to the other French Polynesian sites mentioned in L43-53?
- Relatedly, a relatively limited pool of references was used, so I think the manuscript would benefit from a few additional references to other similar atoll measurements from other corners of the literature, such as:
- Rogers, J. S., Monismith, S. G., Koweek, D. A., Torres, W. I., & Dunbar, R. B. (2016). Thermodynamics and hydrodynamics in an atoll reef system and their influence on coral cover. Limnology and oceanography, 61(6), 2191-2206.
- Grimaldi, C. M., Lowe, R. J., Benthuysen, J. A., Cuttler, M. V. W., Green, R. H., & Gilmour, J. P. (2023). Hydrodynamic and atmospheric drivers create distinct thermal environments within a coral reef atoll. Coral Reefs, 1-14.
Technical Corrections
- L27: Cite Bruyère et al (2023a) here just to make it clear that the biophysical model is in that paper and not in the current manuscript.
- L27: Missing word à “connectivity [OF] oyster larvae”
- L42: Missing something here re: flushing vs stagnation- what’s most important for oyster larvae?
- L52: Add some words to clarify? “Similar data collected on [OTHER FRENCH POLYNESIAN] atolls…”
- L53: Maybe add something here about human influences (or lack thereof) on the atoll? E.g. have the channels between islands been dredged or land reclaimed for runways etc? This sort of information could also be appropriate elsewhere in Ch. 2.
- L83: Missing word – “Mean and maximum [DEPTHS] are…”
- Figure 2: Indicate location of weather station (and ERA reanalysis point) on map with a dot and label?
- L100: Indicate what the vertical datum is? (e.g. measurements relative to mean sea level or some other local datum?)
- L100: I know it’s in Figure 3 implicitly (and later in L124-125), but since this is the first time it comes up, I think you should explicitly state here in the text which dates your data spans during Leg 1 and 2.
- L112: Clarify “…probably related to wave events.” Is it worth mentioning the difference here between local wind waves and remotely-generated swell?
- L118 (and Figure 4): What is the (cross-shore) position on the reef? E.g., were you measuring on the shallow reef flats or deeper on the fore reef or in the lagoon etc?
- Figure 4: Could you add a sentence or two to the text of the manuscript about how Andrefouet & Bionaz (2021) did the seabed classification? E.g. was it just based on depth or also on ecological parameters?
- Table 1: Great, very comprehensive!
- L224: RIP P01. I am impressed that you only lost one instrument during such an extensive campaign, well done!
- L227: What is the range beyond which something was considered “out of range”?
- L238: Capitalize “python” à “Python”; can you cite the T-Tide package?
- Figure 6: Could you indicate the side of the atoll next to each station in the legend? E.g., “O03 (SE); O04 (N)”, etc. I think this would help the reader with interpretation, especially with connecting the long-period swell vs local sea in panel (C) with your text in Section 5.2.
- Highlight that this data could also be useful for flood hazard estimation or validation of early warning systems (see Winter et al…)
- L324: the delta T described here is with respect to time for a single sensor across the full period (i.e. max dT/dt), rather than the max temperature difference between the surface and bottom during the period (i.e. max dT/dz), correct? Some clarification here would be helpful.
- L347: Given that you describe thermally stratified conditions in L314 and Figure 9, how appropriate is it to show depth-averaged flow here? Is there any shear in the velocity? Perhaps it is good to mention in ~L211-216 whether only the depth-averaged flow is included in the ADCP dataset or if you have provided all the bins.
Once these comments have been addressed, I think that this manuscript will make a welcome addition to ESSD and the coral reef hydrodynamics community.
Sincerely,
Stuart Pearson
Citation: https://doi.org/10.5194/essd-2023-302-RC1
Oriane Bruyère et al.
Data sets
Lagoon hydrodynamics of pearl farming islands in French Polynesia : the case of Gambier Islands S. Andréfouët, O. Bruyère, V. Liao, R. Le Gendre https://doi.org/10.17882/94148
Oriane Bruyère et al.
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