Eight years of continuous Rockall Trough transport observations using moorings and gliders

Burmeister, Kristin; Fraser, Neil James; Jones, Sam C.; Cunningham, Stuart A.; Drysdale, Lewis A.; Inall, Mark E.; Dotto, Tiago S.; Holliday, N. Penny

doi:https://doi.org/10.5194/egusphere-2025-3167

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https://doi.org/10.5194/egusphere-2025-3167

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25 Jul 2025

| 25 Jul 2025

Status: this preprint is open for discussion and under review for Ocean Science (OS).

Eight years of continuous Rockall Trough transport observations using moorings and gliders

Kristin Burmeister, Neil James Fraser, Sam C. Jones, Stuart A. Cunningham, Lewis A. Drysdale, Mark E. Inall, Tiago S. Dotto, and N. Penny Holliday

Abstract. The Rockall Trough (RT) channels an important branch of the North Atlantic Current (NAC), transporting heat from the Gulf Stream toward the Nordic Seas, and the European Slope Current (ESC) which flows northward along its eastern boundary. Variability in the NAC influences poleward heat transport and the strength of the Atlantic Meridional Overturning Circulation, while the ESC plays a key role for the oceanic conditions on the European shelf and the North Sea. Here we present observed volume, heat, and freshwater transports through the Rockall Trough from 2014 to 2022, using data from Ellett Array moorings (operational since 2014) and gliders (deployed from 2020 onward). Although gliders provide high-resolution spatial data in the ESC, their inconsistent temporal coverage complicates their integration into RT transport estimates. We develop a methodology to merge mooring and glider observations into a unified, high-resolution time series, producing—for the first time—a continuous ESC transport dataset spanning nearly a decade. This demonstrates the effectiveness of heterogeneous observing arrays and provides a transferable framework for sustained ocean transport monitoring.

Received: 02 Jul 2025 – Discussion started: 25 Jul 2025

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Kristin Burmeister, Neil James Fraser, Sam C. Jones, Stuart A. Cunningham, Lewis A. Drysdale, Mark E. Inall, Tiago S. Dotto, and N. Penny Holliday

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RC1:
'Comment on egusphere-2025-3167', Anonymous Referee #1, 10 Sep 2025 reply
Burmeister et al. present a new method of resolving spatiotemporal differences in sampling between moorings and gliders at the Rockall Trough sector of the Ellett Array. This region is one of repeat monitoring and an important region for North Atlantic circulation. With greater integration of autonomous platforms (gliders, AUVs) to traditional repeat monitoring methods (fixed moorings), the authors are tackling a very relevant problem to the community. While the science is worthwhile, we have concerns about the paper itself and suggest major revisions are needed before this manuscript can become a suitable paper.



Major comments:

The overall structure of the paper is inconsistent and confusing, taking focus from the science and making it very difficult to read. The paper lacks well defined methods, results, and discussion sections. Throughout the paper, the authors seem to jump between methods, results, and discussions no matter the actual location in the paper. I would highly recommend the authors follow a more traditional paper structure.

The paper relies extremely heavily on a previous paper from the second author (Fraser et al., 2022). The paper doesn’t seem to sufficiently introduce this paper in a clear manner. Currently, to understand the full context of Fraser et al., and how their method differs from this previously published method, the reader needs to go and seek out Fraser et al. Additionally, we noticed some portions of the text between the two papers was very, very similar with only a word or two of difference between the two. We suggest that the authors take care not to copy themselves.

Please keep consistency in grammar, capitalization, etc. throughout the paper. For example, figure captions are sometimes “longitude”, “lon”, “Longitude [degE]”, or “Longitude [ºE]”.

The authors only briefly mention an important difference between the model and observation output; the model does not capture the extreme events that the glider does. In a region like the North Atlantic that is known to be physically dynamic (Holliday et al., 2006; Johnson et al., 2024), this difference is noteworthy and the implications of such should be discussed more. Can you explore the implications of this more? One method could be to calculate monthly and annual budgets with and without the extreme events to better understand the net impact they have?

The Discussion reads like a conclusion, and much of what should be included in the Discussion is throughout. Currently, the paper ends abruptly and the “why should you employ this method” is missing.



Line by line comments:

Line 13: What is European temperature? Temperature of Europe?

Line 15: Does order one mean “first order”? Can the authors clarify what they mean by this sentence?

Line 31: Presumably some of the observational difficulty in this region stems from ship traffic. Has there been any effort to integrate commercial shipping data?

Line 31-32: I would suggest putting part about RTADCP into methods and add abbreviation definition

Line 40: Perhaps change “amassed” to “completed”?

Line 41: The reader needs more information on Fraser et al method without having to chase it down themselves.

Line 56: Please stay consistent with “Seaglider” or “glider”.

Line 69-70: Can you expand on this with how? I can see it is discussed below, but the how should come in the first sentence.

Line 70: The sentences “glider transects are invariably affected by the ocean velocity field and hence follow irregular and inconsistent trajectories. The different transects do not correspond spatially and do not in general have the same cross-sectional area” are a bit too close to Fraser et al. 2022: “However, glider transects are invariably affected by the ocean velocity field and hence follow irregular and inconsistent trajectories. As a result, different transects do not correspond spatially and, due to the variability in slope shape and steepness at different locations, do not in general have the same cross-sectional area.”

Line 76: Can you expand on what you mean by the correct isobath? Is this equivalent to essentially depth binning

Figure 1b : Please make the font larger.

Figure 1b: The black cross hatching is very difficult to see.

Figure 1b: What do the green triangles, blue boxes, and red circles represent? Please be explicit.

Figure 1a: Please remove the abbreviations if they are not mentioned.

Figure 1a: This panel is missing the ‘A’.

Line 104: What does “generally very high” mean? Please be explicit.

Line 107-108: This statement is redundant with the introduction and can likely be removed.

Line 105: Typo- “Gap filling”.

Figure 2: If you are going to include cruise IDs, those cruises need to be listed somewhere. Perhaps a table in the supplemental?

Figure 2: Please increase the font size.

Line 109: Do you mean “auxiliary data”?

Figure 2: Does the y-axis represent a fixed pressure? Why does this differ from the black lines when they are supposed to be the same variable?

Figure 3: Please define EOF in the caption.

Line 119-121: I appreciate the comparison of this “new” method to the previous method.

Line 125-126: I would suggest you contrast your method with the previously utilized method of Brandt.

Figure 4: This is a very nice figure.

Figure 4: Is ‘ADCP’ ‘RTADCP’? Please be consistent .

Lines 138-139: Please expand on this EOF analysis more.

Line 144: Should GLORYS2v12 be GLORYS2v1?

Equations 1 and 2: Shouldn’t this whole section be in a better-defined methods section?

Lines 149-154: Can you add significance tests to these correlations to further validate the approach?

Line 158-159: Can Section 3 be restructured so that “the volume, heat and freshwater transports are then calculated from the reconstructed eastern wedge velocity and hydrography sections using Equations 3-5” immediately precedes these calculations?

Line 157-158: It does not look like that reconstructed data is present in Fig 4b? Did you mean above 1000 m?

Line 157-158: What are the upper and lower bounds of depth bins?

Section 3.2: Much of this section could better fit in a proper Discussion section.

Lines 193-195: I find these sentences unnecessary, but that is personal preference.

Figure 5b: Please fix formatting of the legend so it does not cover part of the figure.

Figure 5: Please differentiate between a and b in the legend.

Figure 5: Somewhere, please mention/explain the glider data gaps.

Figure 5: Can you put a and b y-axes on the same scale?

Figure 5: Maybe chose different colours to make it more obvious when glider data is missing?

Figure 6: This is a nice figure.

Line 185: Can you provide the reference density and specific heat capacity?

Line 208: Can you please expand on the bias correction?

Lines 242-249: Comparisons between Fraser et al and this study should be better integrated.

Lines 251-255: The discussion does not need to begin with a recap of the study. This is redundant and would be better fitted as a single sentence in the start of the conclusion.

Figure 7: Please specify what red and blue shading are in the caption.

Line 263-264: Throughout, the authors will make statements like: “. . .declining northward transport in the mid-basin was counteracted by decreasing southward flow at the western boundary” but it would be good to have a figure showing these type of spatial trends.

Lines 269-270: If the ESC is “disproportionally important for poleward heat and freshwater fluxes”, it should be discussed more, and its importance should be brought up earlier in the paper. Is this from the literature or a finding?

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Citation: https://doi.org/10.5194/egusphere-2025-3167-RC1

Kristin Burmeister, Neil James Fraser, Sam C. Jones, Stuart A. Cunningham, Lewis A. Drysdale, Mark E. Inall, Tiago S. Dotto, and N. Penny Holliday

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https://doi.org/10.5194/egusphere-2025-3167-supplement

Kristin Burmeister, Neil James Fraser, Sam C. Jones, Stuart A. Cunningham, Lewis A. Drysdale, Mark E. Inall, Tiago S. Dotto, and N. Penny Holliday

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Short summary

The Rockall Trough carries key ocean currents that affect Europe’s climate and seas. Researchers combined data from underwater sensors and robotic gliders to track water, heat, and freshwater flow from 2014 to 2022. They created a new method to merge this data, producing the first long-term record of one important current. This improves ocean monitoring and helps us better understand climate-related changes.


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