the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 22 Jan 2026
Three-dimensional structure of sub-mesoscale eddies on the continental shelf
Abstract. Sub-mesoscale eddies are oceanic features crucial for energy transfer processes, transport of heat and biogeochemical tracers, and for promoting diversity in marine ecosystems. Their small length scales (<20 km) and short lifespans (O~days), make their characterization challenging using field measurements. In this paper, we combined remote sensing, ocean glider, shipborne, and mooring data to investigate the internal structure and dynamical properties of sub-mesoscale eddies and peddies ('petite' eddies; diameters ≤10 km extending through the water column) along the Wadjemup (Rottnest) Continental Shelf (WCS), Western Australia. Data collected in August 2010 showed an anti-cyclonic mesoscale eddy spawning several cyclonic, cold core sub-mesoscale eddies that promoted upwelling (vertical extension ~185 m) with maxima in chlorophyll concentration at the centre. Results suggested that sub-mesoscale eddies drive chlorophyll advection either at (in) their periphery (centre) of cyclonic eddies, or at their interfaces. In general, cyclonic eddies promoted upwelling and anti-cyclonic eddies promoted downwelling; however, our data also showed that upwelling conditions could also occur in anti-cyclonic eddies. Winds were found to affect the internal structure and lifecycle of sub-mesoscale eddies, particularly under strong wind (speeds > 7 ms-1) conditions, through upwelling and/or vertical mixing. In the presence of dense shelf water outflows along the continental shelf, sub-mesoscale eddies were found to trap, upwell, and transport denser nearshore waters off the continental shelf. This unique dataset provided a detailed picture of the three-dimensional structure of sub-mesoscale eddies, including the characterization of sub-surface eddies, and contributes to the understanding of their role in chlorophyll advection in shelf and coastal environments.
Competing interests: At least one of the (co-)authors serves as editor for the special issue to which this paper belongs.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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Status: open (until 19 Mar 2026)
- RC1: 'Comment on egusphere-2025-6559', Anonymous Referee #1, 22 Feb 2026 reply
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RC2: 'Comment on egusphere-2025-6559', Anonymous Referee #2, 03 Mar 2026
reply
This manuscript presents a very interesting dataset showcasing multiple eddies along and across the continental shelf of Western Australia. It is relatively rare to see such detailed three-dimensional observations of very small (“petite”) eddies, and this aspect alone makes the study valuable. Moreover, the authors combine multiple observational platforms, which is never trivial, and the effort to bring them together into a coherent description of the eddy structure is appreciated.
That said, I found the manuscript difficult to follow and lacking a clear central objective. Beyond illustrating the diversity of eddies observed, the main scientific question is not clearly articulated. What is the overarching goal of the study? Is there a way to compare the eddies more objectively and derive a set of characteristic properties, or process understanding, rather than listing and describing them individually? A clearer framing of the aims, together with a more structured comparison among cases, would greatly improve the manuscript.
In its current form, the analysis remains largely descriptive and somewhat shallow. While the observational detail is valuable, the manuscript misses an opportunity to move beyond description and extract more general insights into eddy structure and their biogeochemical impacts. A more synthetic analysis, identifying commonalities and differences, quantifying key metrics, and situating the results within the broader literature, would substantially strengthen the contribution of the study.The presentation itself also requires improvement. Several figures are difficult to interpret (e.g., missing axis labels, incomplete captions, inconsistent spatial or temporal extents, fragmented panels). In most cases, it is not easy to identify or track the eddies along the time or space axes. Improving figure clarity and consistency, and more clearly highlighting the eddies within the visualizations, would greatly enhance readability and accessibility.
In conclusion, the dataset is interesting and potentially important. However, in its current form, the manuscript remains primarily descriptive and lacks a clear, well-developed scientific focus. I therefore recommend rejection at this stage, to give the authors the opportunity to substantially restructure the manuscript, clarify its main objectives, and develop a stronger and more synthetic analysis.
More suggestions and line by line comments are below.
Main specific comments:
Regarding the lack of story, here are potential suggestions. First, chlorophyll seems to be a focus of the manuscript. One interesting angle could be to investigate the advection versus production of chlorophyll through eddy uplift, or even wind-driven upwelling. A clear quantification (relative to seasonality), and clear identification of the bloom location (centre versus periphery), and whether this changes over time would be adding to the current knowledge on the topic.
The manuscript mentions a few time upwelling/ downwelling, both from the wind, and within the eddies. Is it possible to infer something about their relative importance in the region? There seem to be anticyclonic eddies with upwelling winds, which is interesting. Although table 2 is missing the eddy rotation direction.
Another angle that could be explored is the isotherm uplifts, which, in addition to the Rossby number and eddy radius, is the only quantification provided. It would be nice to compare these values, and try to extract something general, ideally in a figure (maybe isotherm uplift versus chlorophyll anomaly, Rossby number or eddy radius)? I am sure the authors can come up with other ideas to give some depth to the manuscript.The other processes that are mentioned are eddy generation (“spawned eddies”) and evolution, but it feels like these are not clearly supported by the dataset, which is a shame.
Regarding the Rossby number, I understand why different methodologies are used to estimate it, but it needs a sensitivity study. Is at least one eddy which was observed by multiple datasets could be used as a test case to quantify the impact of the method used.
For a manuscript largely on sub-mesoscale, it is frustrating to see the lack of consistency in the suggested definition (20km in the abstract, <50 km page 2 and 4, then <20km diameter page 4, <50km diameter p. 9). I would also expect a mention of the Richardson number for sub-mesoscale.
Finally, some work needs to be done on the formatting and presentation. Table 1 has a whole useless column for units, which could be replaced by the depth of measurements. Table 2’s last column has different formats for dates and radii and misses an opportunity to list the rotation direction and other parameters (e.g. isotherm uplift). Figures are hard to follow. Please specify the event number in the caption, and please add a line to show the eddy timing.
Specific comments to the authors
l. 30-50: There is a transition missing between the general sentence in oceans and cross-shore transport which specifically refers to continental shelves.
Fig. 1: How is along-shelf velocity defined?
Fig 1. The colourbar for glider missions is confusing: it looks like e.g. “7” in red means that there are 7 missions along that line.
l. 73: Explain why the current is “anomalous”.
l. 76: which remote forcing?
l. 78. Is this daily maximum wind speed?
l. 100: Please avoid the sentences with contrasting ideas in brackets.
l. 140: Specify which year.
l. 154: These mooring names are very confusing (WATR40 in 40m, WATR05 in 50m)! Too late to change?
l. 168: 1000x1000 grid… which resolution?
l.145. Low-pass filter for which frequency?
l.182. Is it not level 4 product? Skin or foundation SST?Section 2.8. Please re-order: as it states, it starts with the Rossby number, then vorticity, than Rossby, then finally explained the notation line 211… It is very confusing.
3. Results
l. 230: Do you really have eddies of 1km diameter? Would that be 4 grid point with the greater resolution you have (glider)?
l. 235. Any insight on the “appearance” of the peddie? Specify the year.
l. 245. It also looks like high DO in the peddie. Why?
l. 247: I can’t see the vertical uplift.
l. 250: Why would upwelled water have high DO?Fig.2: Please show the centre of the eddy and specify the eddy event in all captions (and eddy number when there are many).
Fig.3: Add the mooring location (same for each figure which showcases mooring data). The caption does not mention the velocity vectors in panel a).
Fig.4: Missing the year. I struggle to see the timing of the eddy.l. 289: Why a downwelling signature with southerly winds?
l. 298: I can’t see the 100 m uplift.
l. 300 paragraph. Very hard to follow with all these eddies not marked in the figure.
Fig. 6: Surprisingly elongated Rossby numbers, as opposed to circular eddies. Are they really matching?l. 346 “A glider… was”
Fig. 12: I am not sure what to get from this figure.
Fig. 15: missing x-axis labels.
l. 376: Maybe I am looking at the wrong time, but I can’t see chlorophyll uplifted in figure 14 during the eddy.The discussion is very general and just lists possibility of scenarios.
l.425. Rewrite the sentence, I think it is unfinished.
l.430: You did not show the destabilization, nor eddy shape evolution, even less how it is linked to the wind evolution.
l. 445: That is interesting, although very hard to infer from the multiple figures. If you add the Rossby number, eddy rotation direction, and vertical uplift in the table 2, maybe it will be clearer.l. 453. “High horizontal shear areas” and “life-cycle”: none of them were explicitly shown.
“Anti-cyclonic eddies promote both downwelling and upwelling”: interesting, but not obvious in the manuscript with the current organisation.Citation: https://doi.org/10.5194/egusphere-2025-6559-RC2
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- 1
This work brings together data from multiple platforms to characterise the structure of submesoscale dynamics along the Wadjemup Continental Shelf and their impact on biogeochemical tracers of chlorophyll and oxygen. I commend the authors for assembling a diverse observational dataset that provides multiple lines of evidence for submesoscale features and their biogeochemical signatures. I believe this work provides a useful contribution to the way that we observe submesoscale processes and their connection with atmospheric forcing. My main concern is about clarity of the message/text. While in many places the writing was clear, I found numerous instances, where the presentation of the results was rather challenging to understand and interpret. Additionally, the discussion could be improved with more connection to what this work advances. Still, I feel that this work can be published in Ocean Sciences after addressing the comments below.
Sensor calibration and data processing
It is not clear whether calibration was carried out for all sensors, particularly the oxygen. Please state the calibration procedures used, including for which instruments and when these were performed.
Apart from the reference to the glider data processing, there is very little information on how data from the different platforms were processed. For reproducibility, please describe the key processing steps for all platforms (glider, moorings, ship-based measurements, radar, etc.).
The method used to derive velocity from the glider data should be explicitly described (including assumptions, vertical averaging, and any quality control or smoothing applied).
Use and presentation of mooring data
L247: The location of the mooring relative to the peddie is not shown. Please clarify the role of the moorings in this context and show their positions relative to the eddies.
L286: Mooring sites are not indicated on the corresponding figure. Readers should not need to translate GPS coordinates from the methods into figure locations; please add the mooring positions directly to the maps.
L319: The locations of the moorings are again unclear at this point; please ensure all relevant figures clearly show them (including on Figure 1c).
Clarity and readability of results
I found the results section, and in particular Event 2, difficult to follow because the text frequently refers to multiple different figures for a single point, and many figures lack clear labels. This made it challenging to track where the eddies and moorings are and to interpret the data. For all events, please ensure that all glider, mooring and ship locations are shown on the relevant maps and clearly referenced in the captions.
For Event 2, I suggest revisiting the structure of the section. Try to make it clear in each step where the eddies are and which observations are being used. For instance, use the eddy‑tracking algorithm described in the methods to plot eddy positions/contours directly on the figures.
Consider combining some figures so that the reader can see all relevant information (eddies, moorings, glider tracks, etc.) on fewer pages. I regularly had to assess figures on 2/3 different pages to understand a single point. This would improve the readability.
Provide enough information in the captions so that each figure is understandable without extensive cross‑referencing (see detailed figure comments below).
Figure axes, symbols and labelling
Many figures (e.g. Figures 5, 9, 10, 14) lack x‑axis labels. Please indicate what the x‑axis represents (time, distance, etc.), including units. This is essential for interpreting the oscillations and spatial/temporal scales shown.
Figure 5: Could you please comment on whether the oscillations shown are at all related to internal tides or gravity waves.
Figure 6: Please explain what the circles and contours represent.
Figure 8 and 9: Consider combining these and reducing the total number of maps if possible; do all nine panels need to be shown to demonstrate the eddy?
Figures 9 and 10 (and others): Ensure that all axes are labelled with quantity and units, and that any symbols (squares, circles, ellipses, white squares, etc.) are clearly explained in the captions.
Physical interpretation and novelty of the results
L363: The “peddie” referred to here cannot be clearly identified in the glider data as presented. Please show more explicitly how this structure appears.
L414: You state that the eddies are in cyclostrophic balance. Can you provide more evidence for this. Please provide the diagnostics used or otherwise justify this statement more quantitatively.
Overall, the discussion currently reads largely as a summary of the results. It would be strengthened by making clearer what is new about these observations compared to previous work on submesoscale eddies, emphasising how combining multiple observational platforms advances understanding of submesoscale processes and their biogeochemical impacts, and clarifyin, where possible, the connection between submesoscale upwelling/eddy activity and dense shelf water outflows; the current link is rather qualitative and vague.
Check the definition and consistent use of DWST across the manuscript.
Specific line‑level comments
L252: There is no M‑Chl data shown, although it is mentioned; this appears to have been omitted. Please include it or revise the text.
L131, L164, L280, L303, L424 and Table 1: Several typographical or grammatical errors were noted here; please proof‑read these and the rest of the manuscript carefully.
Figures
Please make figure captions fully standalone. Each caption should clearly describe the variables plotted, contours, markers and symbols, units, dates/time period, platforms and data sources, and any key processing choices.
Figure 1c: Please add the mooring locations here to help orient the reader.
Figure 2: The caption refers to a red line in Fig. 2c and a black square in Fig. 2f, but these are not visible; please either add them or correct the caption.
Figure 10: The colour scheme used for temperature differs from the map and sections; please use a consistent palette for the same variable throughout the manuscript, and explain what the squares in the map represent.
Figure 12 is currently not referenced in the text.
Figure 14: It is not clear whether this is glider data, what the x‑axis represents, or where the glider was deployed. These need to be specified.
Please consider using colour‑blind‑friendly colour schemes for all figures and avoid divergent colour maps for variables that are not naturally centred around zero, as these can be visually misleading. Sequential colour maps or perceptually uniform schemes are more appropriate for strictly positive variables such as salinity or chlorophyll.
The abbreviation for metres per second is inconsistent (ms‑1 vs m s‑1). Please apply m s‑1 uniformly. Check all units again.
There is inconsistent spacing between numbers and units (e.g. “200m” vs “200 m”). Please adopt the journal convention and apply it throughout.