the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 21 Oct 2024
Intraseasonal variability of North Pacific Intermediate Water induced by mesoscale eddies
Abstract. The North Pacific Intermediate Water (NPIW) is one of the most crucial water masses in the global ocean, significantly impacting physical, biological, chemical, and ecological processes. The challenges inherent in direct continuous observation of NPIW have been limiting the understanding of its short-term variability. Utilizing 14 months of data from three moorings (146° E, 25° N, M1; 122.6° E, 22.3° N, M2; 126° E, 18° N, M3), this study reveals the characteristics of the NPIW and its consistent intraseasonal variability from 60 to days across a range of latitudes and spatiotemporal scales. Direct measurement show depth variations at 700 m, 600 m, and 550 m for M1, M2, and M3, respectively. The analysis reveals a significant association between NPIW variation and mesoscale eddies, evidenced by lead-lag coefficients of 0.6, 0.5, and 0.55 for SLA and salinity at M1, M2, and M3. During anticyclonic (cyclonic) eddies, a positive (negative) SLA corresponds to relatively warm (cooler) and saline (fresh) characteristics of NPIW. Further analysis has shown that due to the inverse S-shaped structure of salinity in the North Pacific region, the vertical movement of water masses within mesoscale eddies leads to inverse phase changes between the NPIW and deeper water. Also the circulation and water masses near the western boundary are relatively complex, mesoscale eddies also induce mixing of the surrounding water masses and thus modify the NPIW properties. The result found that under the influence of the eddy, the change in salinity in the intermediate layer can reach to 0.3 psu, and the depth of the low-salt core can vary by hundreds of meters. Therefor studying the variability of NPIW is crucial for accurately predicting mesoscale eddy transport of heat and energy to ocean's intermediate layer, and understanding its response to climate change, its role in the global carbon cycle, and its impact on marine ecosystems.
- Preprint
(3491 KB) - Metadata XML
- BibTeX
- EndNote
Status: open (until 03 Jan 2025)
-
RC1: 'Comment on egusphere-2024-3227', Anonymous Referee #1, 25 Nov 2024
reply
Review of “Intraseasonal variability of North Pacific Intermediate Water induced by mesoscale eddies” by Qiang et al.
Recommendation: A rejection of the current version and a possible resubmission of a revised version
Major comments
This manuscript presented data analyses from the three specific moorings located in different places of the North Pacific. The water mass, North Pacific Intermediate Water (NPIW), is the focus of this study. The manuscript showed results of the underwater thermohaline measurements. The authors argued that the observed intrasasonal variability shown in the data can be attributed to mesoscale eddies. This is the central theme throughout the manuscript.
Overall, I found the content was difficult to follow and felt that the authors did not convey strong enough evidence guiding the readers. The scientific story is also weak. My major comments will be elucidated in the following paragraphs.
Major comments 1: Poor English.
The English writing is very poor and there are many obvious grammatical errors shown in the manuscript. Word usages are confusing which makes the reading difficult. For example: the authors wrote “…and in some cases even thousands of meters of the seafloor…” (Lines 165 – 166). I do not understand at all this sentence. Another example is “…Multi Observation Global Ocean 3D Temperature Salinity Height Geostrophic
Currents and Mixed Layer Depth (MLD)…” (Lines 226 – 228). It looked like the authors seemed to copy and paste these text from a table from the CMEMS, this is obvious that this sentence is not written in formal English. Sometimes the authors used a symbol for sigma theta and describe a sentence like “the isopycnals of 26.2 – 26.7 sigma_thata…” (Lines 349) and “…26.8sigma_theta isopycnal…” (Line 255). I believe there must be a more proper and consistent way describing an isopycnal. I would suggest the authors consult with a native English editor first before submitting their work.
Major comments 2: Incoherent introduction.
The introduction is poorly written. The first paragraph of the introduction listed points and previous studies, but in a superficial way. I was expecting that the authors would provide the state of the arts in the NPIW. For example, what is the spatial distribution of the NPIW and what are they related to the three deployed moorings? Why do we care about the NPIW? Are the depths of the NPIW the same at the three deployed moorings? Why do we care about the variability at a time scale of < 100 days? Why does the time scale of < 100 days be associate with mesoscale eddies? Without these information and the latest status of the NPIW research, the introduction is just like a memo listing old papers.
One important argument connecting eddies to the observed T/S variability is that eddies can influence at deeper depths. How can an eddy influence the water layers at deeper depths (via observations or numerical simulations)? However, the readers cannot understand how eddies make a contribution at the ocean interior. Following this argument, how can this eddy-driven change at deeper depths link to the mooring data? There are too many oceanic phenomena causing interior T/S changes from mooring data. Low-frequency internal waves can be also a natural candidate, can’t they? The linkage between observed T/S variability and eddies is not convincing. The authors used satellite SLA data and inferred these SLA data as eddies. Note that you are directly relating surface signatures with underwater mooring data. There are no qualitative (or quantitative) explanations (or showing some previous studies that had linked SLA to underwater T/S data) how you can proceed such an analysis in the introduction.
Major comments 3: Loosely defined NPIW.
Definition of the NPIW is not clear nor consistent in the manuscript.
The authors declared that the sigma theta raging 26.7 – 26.9 kg m-3. But later terminologies “Kuroshio Intermediate Water (KIW)”, “Intermediate Water”, and South “China Sea Intermediate Water (SCSIW)” also appeared in the manuscript. As these water masses should have their own T/S ranges, a further explanation is needed.
There should be more precise definitions for NPIW rather than sigma theta. However, “low salinity” later becomes a criterion for the appearance of NPIW. The choice of this low salinity criterion was not clearly explained in the manuscript (in what value of the salinity can be called “low”?). The moorings are located in three different places. How can be a criterion (either sigma theta, or low salinity) applied to these different places without additional considerations? All of these drawbacks largely reduce the convincingness.
Also, some figures shown in the manuscript are depth-averaged values at the depth range 500 – 800 m depth. This is another criterion using a depth-averaged value that has not been gone through a clear definition. I don’t know why averaged values within 500 – 800 m depth can represent NPIW at the all of the three mooring locations. No evidence or explanation are given.
Major comments 4: SLA and eddies.
The authors applied a passed band of 20 – 100 day to SLAs and tried to connect the correlation of SLA to band-passed T/S fields shown in the mooring data. I don’t see any words or evidence that can guide me why SLAs with energy at 20 – 100 day (e.g., Figure 6) are related to underwater salinities with energy at 40 – 100 day (e.g., Figure 5).
As an eddy passes by the mooring site, it is expected to observe long-lived, short-lived, fast-propagating and slow-propagating eddies. Some eddies are quite big, several times the size of the local Rossby radius, while other eddies can be quite small. As these different types of eddies can have particular effects on the observed mooring data, I don’t see the manuscript carefully differentiate these issues, but simply relate everything to eddies. I am not convinced.
Again, why are only eddies with energy at 40 – 100 day important? Aren’t those with energy at < 40 days not important? Perhaps the authors made this decision of a passed band by Figure 4. Again, as my other question, why does the spectrum need to be calculated using depth-averaged salinities within 500 – 800 m depth?
SLAs with energy at 20 – 100 day could be also signatures of westward propagating Rossby waves. This part is not even discussed at all. This question makes me wonder that “how can you really make sure that an eddy indeed passed by the mooring site?”
Major comments 5: Low and high salinity events. (Line 559)
This part is very confusing. The addressed low and high salinity events are relative, no arguments are provided why such a salinity change has to be eddy-driven. There are also no definitions showing how these low/high salinity events are defined.
Major comments 6: The literature seems to be out of date.
There is only one paper regarding NPIW published after 2021, Ren et al. (2022). This is very surprising because this paper is the first-author’s paper. I don’t think this kind of literature review can help the readers.
Finally, I feel the manuscript is confusing and is also not well written at this stage. The whole content needs to be re-arranged thoroughly. To summarize what I have read so far, NPIW, eddies, SLA, and low salinity, and various depth ranges for NPIW are not presented in a coherent and clear story. The authors kept using vague sentences without providing definitive values or evidence. The term “variability” should reflect important aspects of the NPIW, such as its volume, its layer thickness, at which depth ranges it distributed, strength of stratification, …etc, and the manuscript did not discuss how these variabilities change with eddies in an intraseasonal time scale. The manuscript, however, only told the readers that eddies can result in salinity change by 0.3 and the low-salinity core can situate in a depth range of hundreds of meters. Can these statements apply to different seasons or different locations? What kind of eddies can cause a meaningful or a statistically-significant impact on NPIW? I do not see a broader and scientific story from the current version of the manuscript, unfortunately.
I don’t think a major revision can be a viable option because there are many issues needed to be clarified and examined, and it will take a lot of time. There should be a better version of the manuscript based on these unique data sets. To my conclusion, I think the current manuscript should be rejected without further considerations. The editorial office may ask the authors to resubmit their work once the major comments and issues are revised.
Some other important issues (they are still many of them…)
Line 60: What is “low-salt”? I believe this is not a formal English writing.
Line 99 – 104: The text describe variabilities of NPIW, but did not make it clear what these variabilities actually are.
Lines 131 – 138: It is not clear why salinity anomalies in the Kuroshio Extension have something to do at the mooring sites.
Lines 157 – 158: not always. This is for mid-latitude, but eddies at high-latitudes will be nuch smallers.
Lines 169 – 170. I don’t understand what you tried to say.
Line 206. Since WOA 2023 has been announced. WOA13 is very out of date.
Lines 238 – 242: This part looks like introduction.
Line 258: How can we see NPIW disperse southward and westward from Fig. 1?
Line 261: No definition for the “edge” of the NPIW.
Lines 272 – 275: This interpretation comes from nowhere, right? Please provide more evidence.
Line 281: What is “discontinuities”.
Lines 309 – 311: Why do we need to care about KIW and SCSIW? And what are their relationships with NPIW?
Line 346: Here you defined NPIW sign salinity and depth range. But your Figure 1 emphasized sigma theta.
Line 349: But here you used signa theta again but using “intermediate waters”. Is this the same as NPIW? The depth range is also different here.
Lines 358 – 359: …”…relatively faster”. I don’t understand at all.
Lines 369 – 370: stronger signals, weaker signals, these text are very vague.
Line 374: “inverse phase change”, what is this?
Lines 363 – 365, and Figure 5: The salinity anomalies have to be related to NPIW, why?
Figures 6 – 7: They should be in the result section.
Lines 477 – 482: Why?
Lines 491 – 493: SLA and geostrophic currents are daily data. But your analyses on mooring data have been low-passed. How can they be comparable with other?
Figures
Some figures (Figures 9, 11 – 13) are hard to see the shading and vectors.
Citation: https://doi.org/10.5194/egusphere-2024-3227-RC1 -
AC1: 'Reply on RC1', Ren Qiang, 16 Dec 2024
reply
Dear reviewers
Thank you very much for your valuable suggestions on my paper. I have made careful corrections based on your suggestions, and the attached is my answers to the relevant questions you have commented. Please review it again.
-
AC3: 'Reply on RC1', Ren Qiang, 21 Dec 2024
reply
Dear reviewer：
Thank you very much for your careful review of my manuscript and for suggesting some important comments that could significantly improve and increase the value of my manuscript.
Recently, I have carefully considered and revised my manuscript in response to your comments, but I received a second reviewer's comments yesterday, so I will take both your and his suggestions into account and revise my manuscript in the coming days. I will resubmit the revised manuscript and ask you to review it again.Thanks again to you and the second reviewer for your constructive comments on my manuscript.
Ren Qiang
Citation: https://doi.org/10.5194/egusphere-2024-3227-AC3
-
AC1: 'Reply on RC1', Ren Qiang, 16 Dec 2024
reply
-
RC2: 'Comment on egusphere-2024-3227', Anonymous Referee #2, 20 Dec 2024
reply
This is my first review of a manuscript by Qiang et al. titled ‘Intraseasonal variability of North Pacific Intermediate Water induced by mesoscale eddies’ in which the authors use a series of moorings to study the intraseasonal variability of North Pacific Intermediate Water. I realize that the manuscript has already received the first reviews and the authors have responded to that, but I am still reviewing the first version of the manuscript. I have tried to avoid making the exact same comments as the first reviewer, but it might be that some of the comments are not relevant anymore as you have changed the manuscript already.
In any case, I had somewhat similar experience as the first reviewer. The introduction contains very old citations (nothing wrong with that, but I would think more research must have taken place in the last decade), and the motivation is given really only in one sentence (L87-L89) which doesn’t have any citation. Note that in principle it is also fine to build a motivation around a water mass that we just don’t know enough about, it doesn’t need to be the most crucial water mass in the global ocean to warrant a manuscript. My main issue is linked to the title and the analysis (see my major comment below), there is a difference in analyzing variations in water massess at a fixed locations (which is what they authors have done) and analyzing changes in properties of a water mass (which is what the title suggests the authors would do). The latter is worth publishing, whereas it is harder to see why the former would be worth publishing (in this case anyway).
Based on this version of the manuscript, I don’t think it has enough novel results to warrant a publication. However, there is enough material so that the authors could turn it into a valuable contributions with a bit of extra work. This could be seen as a major revision, although it may be best that the manuscript is rejected at this time, giving the authors enough time to make the required changes before resubmission.
Major comment:
The title is misleading. In principle, the authors don’t really analyze the intraseasonal variations of NPIW, they rather analyze the intraseasonal variations in water mass characteristics at their mooring sites. That is to say, there is a difference in saying that at one locations . The authors also use a lot of text and figures to argue that the variability is eddy driven, which is not really a surprise given the moorings are close the western boundary.
Towards the end the authors start to speculate on the role of the eddies in shaping NPIW, along the lines that the title promised. On line L696 they actually state that the eddies do influence NPIW but, I don’t think the authors actually demonstrated. However, I think that this would be easily done and that would turn the manuscript into a valuable contributions. Here’s what I would suggest:
- Keep the ‘The time series of NPIW from different mooring site’ section, but make sure you state the NPIW definition and mark the watermass boundaries in all relevant figures (see comments below)
- Have a section where you demonstrate that the water mass characteristics vary due to eddies (you can use some of the material you already have, but don’t need all of it)
- Then you could have a section called ‘Intraseasonal variations of NPIW’ but here you should really try to demonstrate that the properties of NPIW change, not that there are salinity changes at some depth level (interval). In Figure 1a we can clearly see that the NPIW salinities gradually increase (from locations of M1) towards the western boundary (where M2 and M3) are situated. Is this change due to horizontal or vertical mixing between the surrounding water masses? The authors seem to argue that it would be due to vertical mixing, and indeed in, for example, Fig. 2a, it does look like there is a diapycnal flux of higher salinity water across 26.4 kg/m3 and 27 kg/m3 density contours to the NPIW layer. Could the authors show that this is a true vertical flux (not horizontal variability), and quantify that flux? Such a result would be well worth publishing.
-
In addition to the mooring, it could help to bring in some Argo float observations or e.g. analyse the ARMOR3D dataset. Those could help create a bit more spatial awareness to the analysis
In general I think using results from M2 and M3 for looking at NPIW properties is more difficult, since the water mass seems to be present here only occasionally. However, one idea would be to compute how much (in say %) the NPIW properties change from M1 to M2/3.
Minor comments:
L129 Freshening during which period?
L157 I would suggest ‘survival period’ → ‘lifetime’
The multiple citations on the eddy studies are a bit odd (why this selection?).
L176 Arguably the timeseries are not very long
L221-222 Sentence about AVISO use cases seems out of place
L248 should this read: can be carried?
L347 – L350 why do the authors need to use a depth range to define the watermass? Is it not already well defined by the density and salinity criteria. Also, please plot a box in Figure 3 that defines the NPIW and maybe even color those dots that are within that definition.
L407 Which previous study?
L528 One might argue otherwise.
L580 Do the authors mean irreversible (diapycnal) mixing, or just vertical displacement of isopycnals?
L589 Here the authors seem to really suggest that the eddies cause diapycnal mixing?
Datasets:
World Ocean Atlas 2013 → there is a much newer dataset available, and I would suggest using the latest WOA2023, in Figure 1. Also, the authors should use the proper citation instead of just linking to the webpage (the citation is given at the top of https://www.ncei.noaa.gov/products/world-ocean-atlas)
L216-L235 The CMEMS data citations are a bit odd and I think the authors are also using ARMOR3D but there is no doi for that (should be https://doi.org/10.48670/moi-00052). I would suggest moving 234-235 to the data availability statement (and you should remove the ‘insert all relevant DOIs links here’ text and actually just put the DOIs there) and making the a data citation for each data as
"Product Title. E.U. Copernicus Marine Service Information (CMEMS). Marine Data Store (MDS). DOI: 10.48670/moi-xxxxx (Accessed on DD-MMM-YYYY)"
Which is the recommended citation (see https://help.marine.copernicus.eu/en/articles/4444611-how-to-cite-copernicus-marine-products-and-services). I would then suggest using these citations in
section 3. The Copernicus Marine Environment Monitoring Service (CMEMS) data.
FIGURES
Figure 1. It is perhaps a bit misleading that the colorbar is non-linear. Also, as the first reviewer pointed out, it is a bit unclear what the exact definition of the NPIW is. I would suggest that the authors state that somewhere, and then plot a corresponding contour/mask to Figure 1, so that the reader doesn’t have to guess.
Figure 2. I would suggest changing the colorbar to something else (jet is well known to be misleading). Then, it looks like the colorbar is continuous, but the actual plot shows more distinct contours (very visible in panel c). I would suggest double checking the plotting script, and I would encourage using just a few contour levels, otherwise it is very hard to distinguish anything from the plot. Also, I would suggest making the line plots (panels b, d, f) with dots such that one can actually see where the measurements are taken. Here again, it would be very helpful to plot the watermass boundaries in panels a, c, and e. At the moment it is not clear what counts as NPIW, but I am assuming the mostly the blue hues.
Figure 3a. Why are there dots so discontinuous at M1 in comparison to M2 and M3? Are the temperature measurements somehow further apart? Aslo, somehow this is not very visible in Figure 2a.
Figure 3 caption: ‘bule’ → ‘blue’.
Citation: https://doi.org/10.5194/egusphere-2024-3227-RC2 -
AC2: 'Reply on RC2', Ren Qiang, 21 Dec 2024
reply
Dear reviewer：
I have received your review comments yesterday, thank you very much for your very important comments in the areas that may improve the value of my manuscript, I will be in the next period of time to seriously consider your suggestions and make serious revisions to the manuscript.
I would like to thank you for your detailed suggestions once again, and I will ask you to review the manuscript after I have finished revising it.Ren Qiang
Citation: https://doi.org/10.5194/egusphere-2024-3227-AC2
Viewed
| HTML | XML | Total | BibTeX | EndNote | |
|---|---|---|---|---|---|
| 116 | 41 | 13 | 170 | 2 | 3 |
- HTML: 116
- PDF: 41
- XML: 13
- Total: 170
- BibTeX: 2
- EndNote: 3
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1