Intraseasonal Variability and Eddy-Induced Structural Modulation of the North Pacific Intermediate Water Revealed by Multi-Mooring Observations

Ren, Qiang; Liu, Yansong; Tu, Shumin; Huang, Wei; Nan, Feng; Wang, Ran; Diao, Xinyuan; Wang, Jianfeng; Liu, Xinchuang; Chen, Zifei; Yu, Fei

doi:10.5194/egusphere-2025-6538

Preprints

https://doi.org/10.5194/egusphere-2025-6538

Preprints

28 Jan 2026

| 28 Jan 2026

Intraseasonal Variability and Eddy-Induced Structural Modulation of the North Pacific Intermediate Water Revealed by Multi-Mooring Observations

Qiang Ren, Yansong Liu, Shumin Tu, Wei Huang, Feng Nan, Ran Wang, Xinyuan Diao, Jianfeng Wang, Xinchuang Liu, Zifei Chen, and Fei Yu

Abstract. The North Pacific Intermediate Water (NPIW) plays a crucial role in modulating oceanic thermohaline circulation and biogeochemical processes. However, limited continuous observations have hindered the understanding of its short-term variability and structural response to mesoscale processes. This study investigates the intraseasonal structural variability of the NPIW and its modulation by mesoscale eddies, based on long-term mooring observations from three sites (M1–M3) across the western Pacific. The thickness of the NPIW displays substantial intraseasonal variability, dominated by an approximately 80-day period that is coherent among all mooring sites. Unlike previous studies that mainly focused on temperature and salinity anomalies, this work introduces NPIW thickness as a new structural diagnostic parameter to capture the vertical compression and expansion of the intermediate layer induced by eddy activity. The analysis identifies a strong inverse correlation between layer thickness and isopycnal-averaged salinity, demonstrating that anticyclonic (cyclonic) eddies correspond to thinner (thicker) and more saline (fresher) intermediate layers. Spatial composites further reveal that thickness variability is most pronounced near the western boundary, which may be associated with locally complex water mass exchange and mixing driven by eddies. These findings provide the first quantitative evidence of intraseasonal variability in NPIW thickness and highlight its role as a key indicator for diagnosing mesoscale–intermediate layer interactions in the North Pacific.

Received: 30 Dec 2025 – Discussion started: 28 Jan 2026

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.

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Journal article(s) based on this preprint

17 Aug 2026

Intraseasonal variability and eddy-induced structural modulation of the North Pacific intermediate water revealed by multi-mooring observations

Qiang Ren, Yansong Liu, Yansheng Zhang, Shumin Tu, Wei Huang, Feng Nan, Ran Wang, Xinyuan Diao, Jianfeng Wang, Xinchuang Liu, Zifei Chen, and Fei Yu

Ocean Sci., 22, 2449–2469, https://doi.org/10.5194/os-22-2449-2026,https://doi.org/10.5194/os-22-2449-2026, 2026

Short summary

Qiang Ren, Yansong Liu, Shumin Tu, Wei Huang, Feng Nan, Ran Wang, Xinyuan Diao, Jianfeng Wang, Xinchuang Liu, Zifei Chen, and Fei Yu

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2025-6538', Anonymous Referee #1, 03 Feb 2026

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2026/egusphere-2025-6538/egusphere-2025-6538-RC1-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2025-6538-RC1
- AC1: 'Reply on RC1', ren qiang, 24 May 2026
  
  Dear Professor
  We sincerely thank you for your careful evaluation and constructive comments provided earlier in the review process. We apologize for the delay in our response. Since the comments from the other reviewers were received in late April and early May, we revised the manuscript after considering all comments together, so that overlapping issues could be addressed consistently and comprehensively. We greatly appreciate your valuable suggestions, which have helped improve the clarity and scientific rigor of the manuscript.
  
  We have consolidated the comments from the Editor and all reviewers and provided point-by-point responses with corresponding revisions in the manuscript. The attached ZIP file includes the integrated response file and the revised manuscript. We would greatly appreciate it if you could kindly review the materials. We sincerely thank you again for your careful evaluation and constructive suggestions.
  
  Ren Qiang
  
  Citation: https://doi.org/10.5194/egusphere-2025-6538-AC1
RC2:
'Comment on egusphere-2025-6538', Anonymous Referee #2, 28 Apr 2026

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2026/egusphere-2025-6538/egusphere-2025-6538-RC2-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2025-6538-RC2
- AC2: 'Reply on RC2', ren qiang, 24 May 2026
  
  Dear Professor,
  We sincerely thank you for your careful evaluation of our manuscript and for providing constructive and insightful comments. Your suggestions have been very valuable in helping us improve the manuscript.
  We have carefully consolidated the comments from the Editor and all reviewers and addressed them in a point-by-point manner. The attached ZIP file includes the integrated response file and the revised manuscript with corresponding revisions. We would greatly appreciate it if you could kindly review the materials. Thank you again for your valuable time and constructive suggestions.
  Ren Qiang
  
  Citation: https://doi.org/10.5194/egusphere-2025-6538-AC2
RC3:
'Comment on egusphere-2025-6538', Anonymous Referee #3, 13 May 2026

This manuscript investigates the intraseasonal variability of the North Pacific Intermediate Water (NPIW) using multi-mooring observations. Considering the limited availability of long-term in situ measurements in the intermediate ocean, the dataset presented here is valuable and provides useful observational constraints on subsurface variability. The analyses are generally reasonable and the results contribute to a better understanding of NPIW variability. The introduction of NPIW thickness as a structural indicator is particularly interesting and represents a useful extension beyond traditional thermohaline analyses. This perspective helps to better interpret the response of intermediate water to mesoscale processes. But I have a few comments regarding clarity of definitions, and methodological description that should be addressed.
Main Comments:
1. The definition of NPIW could be clarified. Different criteria are used in the manuscript (e.g., 34.3 psu isohaline vs. salinity minimum). It would be helpful to briefly explain why 34.3 psu is chosen to define thickness. Is this threshold robust across regions? Would similar results be obtained with a slightly different value? A short discussion would improve clarity.
2. In the Data and Methods section, three moorings are used. A schematic showing the vertical configuration of CTD sensors would be very helpful. This would allow readers to better evaluate whether the vertical resolution is sufficient. In addition, please provide a bit more detail on data processing (e.g., interpolation and filtering methods).
3. In Section 3.2, the salinity variability at M1 (34.12–34.16 psu) is much smaller than at M2 and M3. A brief explanation would be useful. This could be related to regional hydrographic conditions or differences in dynamical influence.
4. The variability is mainly attributed to mesoscale eddies, which is reasonable. However, it would strengthen the paper to briefly discuss other possible contributors. For example, could remotely forced signals (e.g., Rossby waves) also play a role at similar timescales? A short discussion would help justify the interpretation.
5. The discussion would benefit from a clearer assessment of the relative roles of vertical displacement (isopycnal heaving) and horizontal advection/mixing in driving the observed NPIW variability. In particular, can the authors further clarify under what conditions (or at which mooring sites) each mechanism is dominant? Additionally, are there observational indicators (e.g., phase relationships, vertical coherence, or spatial patterns) that could help distinguish between these processes?

Specific Comments：
1. The line color in Fig. 4b is inconsistent with Fig. 4a. Please revise for consistency.
2. In Fig. 3, the salinity shading at M1 appears discontinuous. This may be due to the sparse vertical resolution of the CTDs, which might not fully capture the salinity minimum. In this case, the averaged line may be misleading. It is suggested to reconsider or remove the averaged salinity line for clarity.
3. Line 438: the symbol “/” better replaced with “and”

Citation: https://doi.org/10.5194/egusphere-2025-6538-RC3
- AC3: 'Reply on RC3', ren qiang, 24 May 2026
  
  Dear Professor,
  We sincerely thank you for your careful evaluation of our manuscript and for providing constructive and insightful comments. Your suggestions have been very valuable in helping us improve the manuscript.
  We have carefully consolidated the comments from the Editor and all reviewers and addressed them in a point-by-point manner. The attached ZIP file includes the integrated response file and the revised manuscript with corresponding revisions. We would greatly appreciate it if you could kindly review the materials. Thank you again for your valuable time and constructive suggestions.
  Ren Qiang
  
  Citation: https://doi.org/10.5194/egusphere-2025-6538-AC3
RC4:
'Comment on egusphere-2025-6538', Anonymous Referee #4, 24 May 2026

I have carefully read the revised manuscript and the authors' responses to the previous reviewers. First, I would like to commend the authors on presenting a highly valuable and interesting dataset. Long-term, high-frequency mooring observations of the North Pacific Intermediate Water (NPIW) are rare. The manuscript has been improved during the revision process (at least on 25th May); however, I believe there are still a few critical points that need to be addressed to further strengthen the scientific validity and depth of the discussion.

Below are my major comments, which build upon and extend some of the concerns raised in the previous review round.
1. Quantitative Comparison with CMEMS Data (Related to the general validation of reanalysis data and Reviewer 2's concerns regarding analytical rigor)

In the revised manuscript, the authors added T-S scatter plots using CMEMS data (Figure 7d-f) to validate its consistency with the in-situ observations. While this is a good addition to demonstrate qualitative agreement (e.g., the positive correlation between SLA and temperature/salinity), it currently lacks a quantitative comparison of the variation amplitudes. For instance, the mooring at M2 observed large salinity fluctuations (e.g., a standard deviation of 0.7 psu). The authors should quantitatively discuss how well the CMEMS data reproduces the actual magnitude of these variations. Comparing the amplitude or variance between the observations and the CMEMS data would provide a more rigorous justification for using the reanalysis data to explain the physical mechanisms in Section 4.3.

2. 3D Structure of Eddies and Phase Relationships using CMEMS Data (Directly related to Reviewer 1's comment on 3D lens-shaped structures and Reviewer 3's comment on using phase relationships to distinguish mechanisms)

In response to Reviewer 1 (regarding 3D eddy structures) and Reviewer 3 (who perceptively asked if "phase relationships" could help distinguish between vertical displacement and horizontal advection/mixing), the authors stated that their 1D mooring observations limit such 3D or quantitative separations. While this is true for the mooring data alone, the authors incorporate 3D CMEMS reanalysis data in Section 4.3, meaning this limitation no longer fully applies. Currently, Figures 12-14 only show 2D horizontal composite maps at specific depth ranges. To convincingly demonstrate the structural modulation by eddies, the authors should utilize the 3D nature of the CMEMS data to present vertical cross-sections (zonal and/or meridional composites) across the eddy center. Furthermore, by investigating the time lags relative to the SSHA peaks (e.g., creating cross-sectional composites before, during, and after the passage of SSHA peaks), the authors could effectively examine the phase differences between isopycnal heaving and the lateral intrusion of high-salinity waters. Addressing this would directly answer Reviewer 3's excellent point and allow for a much more conclusive, quantitative discussion on the mechanisms driving the anomalies at different sites.
3. Implications of Non-overlapping Observation Periods (A crucial point largely overlooked in the previous review round) The observation periods for the three moorings do not overlap: M3 (2016-2017), M1 (2017-2018), and M2 (2019-2020).

The manuscript currently attributes the differences in NPIW variability among the sites entirely to spatial heterogeneity (i.e., open ocean vs. western boundary). However, because the measurements were taken in completely different years, there is a strong possibility that interannual variability (e.g., different climate phases, background hydrographic shifts, or year-to-year differences in regional eddy kinetic energy) also contributes to the observed differences. While this does not negate the study's general findings regarding the eddy-induced modulation, the potential influence of interannual variability due to the asynchronous observation periods must be explicitly acknowledged and discussed in the Discussion section to ensure scientific rigor.

Citation: https://doi.org/10.5194/egusphere-2025-6538-RC4
- AC4: 'Reply on RC4', ren qiang, 28 May 2026
  
  Dear Professor,
  We sincerely thank you for the careful reading of our revised manuscript and for the constructive and insightful comments. We greatly appreciate your recognition of the value of the long-term, high-frequency mooring observations of the NPIW and the improvements made in the previous revision. The additional comments are very helpful for further strengthening the quantitative rigor, physical interpretation, and scientific balance of the manuscript.
  Please refer to the attached zip file for your suggested revisions and manuscript edits.
  We sincerely thank you for your review again.
  Ren Qiang
  
  Citation: https://doi.org/10.5194/egusphere-2025-6538-AC4

Peer review completion

AR – Author's response | RR – Referee report | ED – Editor decision | EF – Editorial file upload

AR by ren qiang on behalf of the Authors (04 Jun 2026) Author's response Author's tracked changes

EF by Polina Shvedko (04 Jun 2026) Manuscript

ED: Referee Nomination & Report Request started (17 Jun 2026) by Benjamin Rabe

RR by Anonymous Referee #3 (20 Jun 2026)

RR by Anonymous Referee #2 (27 Jun 2026)

RR by Anonymous Referee #1 (30 Jun 2026)

ED: Publish subject to minor revisions (review by editor) (30 Jun 2026) by Benjamin Rabe

Dear Dr. Ren and coauthors,
Thank you for your comprehensive response and revised manuscript.
Three of the reviewers are now satisfied with your revision, and the points by reviewer #4 also seem to be satisfied. Reviewer #2 points out a few technical details that need correcting:
"1. The subplot in Figure 1a should include explicit labels for both the x-axis and y-axis to ensure clarity. Please label the axes to indicate what variables they represent.
2. L382. classical -> typical
3. Figure 10, 12–14 should include a legend for the current vectors to clarify the magnitude of the ocean currents."

I have a couple of remaining points, though, that I have mentioned before and that I think have not been adequately addressed: One relates to the layer thickness of NPIW, where you write "To obtain uniformly gridded vertical profiles for subsequent analyses including contour plots and depth-dependent temperature/salinity variability, the observations were linearly interpolated between vertically adjacent CTD measurements on the same mooring line onto a common set of standard depth levels. In addition, local linear interpolation was applied between vertically adjacent CTD sensors on the same mooring line that bracketed the 34.3 psu value to estimate the depths of the upper and lower isohalines used for NPIW thickness calculation."
This means that you use linear interpolation to estimate the exact layer thickness. Each of your instruments are around 100 m apart on each mooring line (see Figure 2), yet, you show variability as small as 50 m within one month (Figure 4) and subsequently analyse using linear regression with gradients as small as 50 m thickness over the whole range of isopycnally-averaged salinities at M1 (Figure 8a). Ideally, you would show a CTD-Profile taken at deployment and/or recovery of the mooring that illustrates why linear interpolation is appropriate here; e.g. are the profiles approximately linear or do they show strong changes in gradient within the NPIW range (or just above/below in the water column). At least I would expect a paragraph estimating the potential accuracy or error in your NPIW layer thickness, given that you use time series at discrete depths further apart than some of the signal you analyse.

Data: You give two DOI in the Data Availability section, yet, you do not cite them. Please cite with an entry in the reference list that contains each DOI (e.g. for the Copernicus data, as under https://help.marine.copernicus.eu/en/articles/4444611-how-to-cite-copernicus-marine-products-and-services?pk_vid=926987ee88e2d6571782844875ebffa3 , and as listed under "For a specific product's citation").
Further, you state"Researchers interested in accessing the mooring data may contact the corresponding author, who will facilitate access through a formal data request procedure. If required by the journal, the authors commit to coordinating with the data owner to deposit the dataset in a publicly accessible repository and to provide a DOI upon acceptance." Please provide a doi and cite it in the text with reference to an entry in the reference list, so that the data is publicly accessible and any reader can follow-up what you have done in your work.

Minor comments:
Figures 12/13/14: Those are showing CMEMS data, correct? Please note this in the figure captions (you did note it in the caption of Figure 15, for example). Further, I would call the arrows in those figures black, not blue (or if they're blue than a very dark shade of blue) -- perhaps that will make it more clear to the reader, as the colour-scale includes blue shading.
Colour scales: Did you check if your figures are suitable for colour-blindness? Guidelines can be found here: https://www.ocean-science.net/submission.html#figurestables .

Kind Regards, Benjamin Rabe

Hide

AR by ren qiang on behalf of the Authors (10 Jul 2026) Author's response Author's tracked changes Manuscript

ED: Publish subject to technical corrections (11 Jul 2026) by Benjamin Rabe

AR by ren qiang on behalf of the Authors (12 Jul 2026) Author's response Manuscript

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2025-6538', Anonymous Referee #1, 03 Feb 2026

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2026/egusphere-2025-6538/egusphere-2025-6538-RC1-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2025-6538-RC1
- AC1: 'Reply on RC1', ren qiang, 24 May 2026
  
  Dear Professor
  We sincerely thank you for your careful evaluation and constructive comments provided earlier in the review process. We apologize for the delay in our response. Since the comments from the other reviewers were received in late April and early May, we revised the manuscript after considering all comments together, so that overlapping issues could be addressed consistently and comprehensively. We greatly appreciate your valuable suggestions, which have helped improve the clarity and scientific rigor of the manuscript.
  
  We have consolidated the comments from the Editor and all reviewers and provided point-by-point responses with corresponding revisions in the manuscript. The attached ZIP file includes the integrated response file and the revised manuscript. We would greatly appreciate it if you could kindly review the materials. We sincerely thank you again for your careful evaluation and constructive suggestions.
  
  Ren Qiang
  
  Citation: https://doi.org/10.5194/egusphere-2025-6538-AC1
RC2:
'Comment on egusphere-2025-6538', Anonymous Referee #2, 28 Apr 2026

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2026/egusphere-2025-6538/egusphere-2025-6538-RC2-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2025-6538-RC2
- AC2: 'Reply on RC2', ren qiang, 24 May 2026
  
  Dear Professor,
  We sincerely thank you for your careful evaluation of our manuscript and for providing constructive and insightful comments. Your suggestions have been very valuable in helping us improve the manuscript.
  We have carefully consolidated the comments from the Editor and all reviewers and addressed them in a point-by-point manner. The attached ZIP file includes the integrated response file and the revised manuscript with corresponding revisions. We would greatly appreciate it if you could kindly review the materials. Thank you again for your valuable time and constructive suggestions.
  Ren Qiang
  
  Citation: https://doi.org/10.5194/egusphere-2025-6538-AC2
RC3:
'Comment on egusphere-2025-6538', Anonymous Referee #3, 13 May 2026

This manuscript investigates the intraseasonal variability of the North Pacific Intermediate Water (NPIW) using multi-mooring observations. Considering the limited availability of long-term in situ measurements in the intermediate ocean, the dataset presented here is valuable and provides useful observational constraints on subsurface variability. The analyses are generally reasonable and the results contribute to a better understanding of NPIW variability. The introduction of NPIW thickness as a structural indicator is particularly interesting and represents a useful extension beyond traditional thermohaline analyses. This perspective helps to better interpret the response of intermediate water to mesoscale processes. But I have a few comments regarding clarity of definitions, and methodological description that should be addressed.
Main Comments:
1. The definition of NPIW could be clarified. Different criteria are used in the manuscript (e.g., 34.3 psu isohaline vs. salinity minimum). It would be helpful to briefly explain why 34.3 psu is chosen to define thickness. Is this threshold robust across regions? Would similar results be obtained with a slightly different value? A short discussion would improve clarity.
2. In the Data and Methods section, three moorings are used. A schematic showing the vertical configuration of CTD sensors would be very helpful. This would allow readers to better evaluate whether the vertical resolution is sufficient. In addition, please provide a bit more detail on data processing (e.g., interpolation and filtering methods).
3. In Section 3.2, the salinity variability at M1 (34.12–34.16 psu) is much smaller than at M2 and M3. A brief explanation would be useful. This could be related to regional hydrographic conditions or differences in dynamical influence.
4. The variability is mainly attributed to mesoscale eddies, which is reasonable. However, it would strengthen the paper to briefly discuss other possible contributors. For example, could remotely forced signals (e.g., Rossby waves) also play a role at similar timescales? A short discussion would help justify the interpretation.
5. The discussion would benefit from a clearer assessment of the relative roles of vertical displacement (isopycnal heaving) and horizontal advection/mixing in driving the observed NPIW variability. In particular, can the authors further clarify under what conditions (or at which mooring sites) each mechanism is dominant? Additionally, are there observational indicators (e.g., phase relationships, vertical coherence, or spatial patterns) that could help distinguish between these processes?

Specific Comments：
1. The line color in Fig. 4b is inconsistent with Fig. 4a. Please revise for consistency.
2. In Fig. 3, the salinity shading at M1 appears discontinuous. This may be due to the sparse vertical resolution of the CTDs, which might not fully capture the salinity minimum. In this case, the averaged line may be misleading. It is suggested to reconsider or remove the averaged salinity line for clarity.
3. Line 438: the symbol “/” better replaced with “and”

Citation: https://doi.org/10.5194/egusphere-2025-6538-RC3
- AC3: 'Reply on RC3', ren qiang, 24 May 2026
  
  Dear Professor,
  We sincerely thank you for your careful evaluation of our manuscript and for providing constructive and insightful comments. Your suggestions have been very valuable in helping us improve the manuscript.
  We have carefully consolidated the comments from the Editor and all reviewers and addressed them in a point-by-point manner. The attached ZIP file includes the integrated response file and the revised manuscript with corresponding revisions. We would greatly appreciate it if you could kindly review the materials. Thank you again for your valuable time and constructive suggestions.
  Ren Qiang
  
  Citation: https://doi.org/10.5194/egusphere-2025-6538-AC3
RC4:
'Comment on egusphere-2025-6538', Anonymous Referee #4, 24 May 2026

I have carefully read the revised manuscript and the authors' responses to the previous reviewers. First, I would like to commend the authors on presenting a highly valuable and interesting dataset. Long-term, high-frequency mooring observations of the North Pacific Intermediate Water (NPIW) are rare. The manuscript has been improved during the revision process (at least on 25th May); however, I believe there are still a few critical points that need to be addressed to further strengthen the scientific validity and depth of the discussion.

Below are my major comments, which build upon and extend some of the concerns raised in the previous review round.
1. Quantitative Comparison with CMEMS Data (Related to the general validation of reanalysis data and Reviewer 2's concerns regarding analytical rigor)

In the revised manuscript, the authors added T-S scatter plots using CMEMS data (Figure 7d-f) to validate its consistency with the in-situ observations. While this is a good addition to demonstrate qualitative agreement (e.g., the positive correlation between SLA and temperature/salinity), it currently lacks a quantitative comparison of the variation amplitudes. For instance, the mooring at M2 observed large salinity fluctuations (e.g., a standard deviation of 0.7 psu). The authors should quantitatively discuss how well the CMEMS data reproduces the actual magnitude of these variations. Comparing the amplitude or variance between the observations and the CMEMS data would provide a more rigorous justification for using the reanalysis data to explain the physical mechanisms in Section 4.3.

2. 3D Structure of Eddies and Phase Relationships using CMEMS Data (Directly related to Reviewer 1's comment on 3D lens-shaped structures and Reviewer 3's comment on using phase relationships to distinguish mechanisms)

In response to Reviewer 1 (regarding 3D eddy structures) and Reviewer 3 (who perceptively asked if "phase relationships" could help distinguish between vertical displacement and horizontal advection/mixing), the authors stated that their 1D mooring observations limit such 3D or quantitative separations. While this is true for the mooring data alone, the authors incorporate 3D CMEMS reanalysis data in Section 4.3, meaning this limitation no longer fully applies. Currently, Figures 12-14 only show 2D horizontal composite maps at specific depth ranges. To convincingly demonstrate the structural modulation by eddies, the authors should utilize the 3D nature of the CMEMS data to present vertical cross-sections (zonal and/or meridional composites) across the eddy center. Furthermore, by investigating the time lags relative to the SSHA peaks (e.g., creating cross-sectional composites before, during, and after the passage of SSHA peaks), the authors could effectively examine the phase differences between isopycnal heaving and the lateral intrusion of high-salinity waters. Addressing this would directly answer Reviewer 3's excellent point and allow for a much more conclusive, quantitative discussion on the mechanisms driving the anomalies at different sites.
3. Implications of Non-overlapping Observation Periods (A crucial point largely overlooked in the previous review round) The observation periods for the three moorings do not overlap: M3 (2016-2017), M1 (2017-2018), and M2 (2019-2020).

The manuscript currently attributes the differences in NPIW variability among the sites entirely to spatial heterogeneity (i.e., open ocean vs. western boundary). However, because the measurements were taken in completely different years, there is a strong possibility that interannual variability (e.g., different climate phases, background hydrographic shifts, or year-to-year differences in regional eddy kinetic energy) also contributes to the observed differences. While this does not negate the study's general findings regarding the eddy-induced modulation, the potential influence of interannual variability due to the asynchronous observation periods must be explicitly acknowledged and discussed in the Discussion section to ensure scientific rigor.

Citation: https://doi.org/10.5194/egusphere-2025-6538-RC4
- AC4: 'Reply on RC4', ren qiang, 28 May 2026
  
  Dear Professor,
  We sincerely thank you for the careful reading of our revised manuscript and for the constructive and insightful comments. We greatly appreciate your recognition of the value of the long-term, high-frequency mooring observations of the NPIW and the improvements made in the previous revision. The additional comments are very helpful for further strengthening the quantitative rigor, physical interpretation, and scientific balance of the manuscript.
  Please refer to the attached zip file for your suggested revisions and manuscript edits.
  We sincerely thank you for your review again.
  Ren Qiang
  
  Citation: https://doi.org/10.5194/egusphere-2025-6538-AC4

Peer review completion

AR – Author's response | RR – Referee report | ED – Editor decision | EF – Editorial file upload

AR by ren qiang on behalf of the Authors (04 Jun 2026) Author's response Author's tracked changes

EF by Polina Shvedko (04 Jun 2026) Manuscript

ED: Referee Nomination & Report Request started (17 Jun 2026) by Benjamin Rabe

RR by Anonymous Referee #3 (20 Jun 2026)

RR by Anonymous Referee #2 (27 Jun 2026)

RR by Anonymous Referee #1 (30 Jun 2026)

ED: Publish subject to minor revisions (review by editor) (30 Jun 2026) by Benjamin Rabe

Hide

AR by ren qiang on behalf of the Authors (10 Jul 2026) Author's response Author's tracked changes Manuscript

ED: Publish subject to technical corrections (11 Jul 2026) by Benjamin Rabe

AR by ren qiang on behalf of the Authors (12 Jul 2026) Author's response Manuscript

Journal article(s) based on this preprint

17 Aug 2026

Intraseasonal variability and eddy-induced structural modulation of the North Pacific intermediate water revealed by multi-mooring observations

Qiang Ren, Yansong Liu, Yansheng Zhang, Shumin Tu, Wei Huang, Feng Nan, Ran Wang, Xinyuan Diao, Jianfeng Wang, Xinchuang Liu, Zifei Chen, and Fei Yu

Ocean Sci., 22, 2449–2469, https://doi.org/10.5194/os-22-2449-2026,https://doi.org/10.5194/os-22-2449-2026, 2026

Short summary

Qiang Ren, Yansong Liu, Shumin Tu, Wei Huang, Feng Nan, Ran Wang, Xinyuan Diao, Jianfeng Wang, Xinchuang Liu, Zifei Chen, and Fei Yu

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This study reveals how mesoscale eddies modulate the North Pacific Intermediate Water (NPIW) using three long-term mooring observations. By introducing “intermediate water thickness” as a new structural indicator, it shows that eddies compress or expand the NPIW layer, producing 60–80-day intraseasonal variability. Thickness and salinity are strongly inversely related, providing the first quantitative evidence of eddy-induced structural changes in mid-depth waters.

Intraseasonal Variability and Eddy-Induced Structural Modulation of the North Pacific Intermediate Water Revealed by Multi-Mooring Observations

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