Impact of wind variations on surface variability over the Patagonian Continental Shelves

Urricariet, M. Milagro; Ruiz-Etcheverry, Laura; Piola, Alberto Ricardo

doi:10.5194/egusphere-2026-873

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https://doi.org/10.5194/egusphere-2026-873

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24 Feb 2026

| 24 Feb 2026

Impact of wind variations on surface variability over the Patagonian Continental Shelves

M. Milagro Urricariet, Laura Ruiz-Etcheverry, and Alberto Ricardo Piola

Abstract. We study the impact of wind variability on sea surface temperature (SSTa), sea surface salinity (SSSa), and sea level anomaly (SLAa) over the Patagonian shelves around southern South America using satellite observations and the ERA5 reanalysis. Using Empirical Orthogonal Function (EOF) analysis, we identify the dominant patterns of variability in surface ocean properties and winds and assess their interconnections through correlation and composite maps. Zonal and meridional wind anomalies modulate the variability of sea level anomaly with distinct spatial signatures. Meridional wind variability emerges as the dominant driver, exerting a strong influence on sea surface temperature, salinity, and sea level, generating coherent patterns across the southeast South Pacific and southwest South Atlantic continental shelves. Specifically, the leading mode of meridional wind is significantly correlated with the dominant modes of variability of SSTa, SSSa, and SLAa. Moreover, the spatial patterns emerging from the composites associated with the leading meridional wind mode are consistent with the dominant SSTa, SSSa, and SLAa variability patterns. These results suggest that southerly winds promote upwelling and offshore flow of low salinity waters over the Pacific shelf, weaken the southward flowing Cape Horn Current along the shelf break, and strengthen the northward transport of cold-salty subantarctic water over the Atlantic shelf. Northerly winds reverse these dynamics. This study provides evidence of wind-driven coupling of the shelf circulation on both sides of South America and the interocean exchanges between the Pacific and Atlantic continental shelves.

Received: 14 Feb 2026 – Discussion started: 24 Feb 2026

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M. Milagro Urricariet, Laura Ruiz-Etcheverry, and Alberto Ricardo Piola

Status: final response (author comments only)

RC1:
'Comment on egusphere-2026-873', Anonymous Referee #1, 21 Apr 2026
This manuscript presents a comprehensive and well-structured analysis of the impact of wind variability on surface ocean properties over the Patagonian continental shelves. The study addresses a relevant and timely topic, combining satellite observations and reanalysis data with a coherent methodological framework based on EOF analysis, spectral decomposition, and composite techniques. The results are internally consistent and provide a physically plausible interpretation of the link between wind variability and ocean surface response. In particular, the identification of the dominant role of meridional wind variability and its connection to large-scale patterns across both the Pacific and Atlantic shelves is an interesting and valuable contribution.
The figures are clear, well organized, and effectively support the results presented in the manuscript. The captions are detailed and informative.
Overall, the manuscript is clearly written and well organized, and it makes a solid contribution to the understanding of regional ocean dynamics. The following comments are intended to further improve clarity, consistency, and the physical interpretation of some aspects of the analysis.
Introduction
The introduction is well structured and the progression from the general context to the regional description and study objectives is clear. However, the use of subheadings within the introduction feels somewhat inconsistent. The subheadings (“The Pacific Patagonian Shelf” and “The Atlantic Patagonian Shelf”) appear mid-introduction without corresponding subheadings for the opening paragraphs or the closing section on objectives, which may interrupt the overall flow.
This is also slightly inconsistent with the structure adopted in later sections of the manuscript (e.g., Methods and Results), where a clear hierarchical organization with numbered subsections is used. A simple way to improve this would be to introduce a third subheading (e.g., “Aims of this study”) to clearly mark the transition to the objectives and maintain structural consistency throughout the manuscript. In this context, it may also be helpful to move lines 115–119 (where the proposed mechanism is introduced) to the beginning of this subsection, as they would provide a more natural motivation for the objectives.
Additionally, the first two paragraphs (L28–37) would benefit from the inclusion of references. In particular, a general reference supporting the role of wind forcing on continental shelf dynamics (L31), as well as citations supporting the statements regarding previous studies and remaining knowledge gaps (L34 and L36–37), would strengthen the context and better position the study within the existing literature.
Results
Section 3.1
This section provides a useful and clear overview of the mean fields and variability patterns, effectively preparing the reader for the EOF analysis.

SSS variability (around line 263):

The discussion of nearshore SSS variability could benefit from a clearer distinction between physically meaningful variability and potential artefacts or uncertainties associated with satellite-derived salinity products in coastal regions. In this context, it may also be useful to explicitly acknowledge that satellite-derived salinity products can present systematic uncertainties near the coast and in regions with strong gradients, which could influence the interpretation of the spatial variability patterns.

SLA variability (around line 293):

The persistence of the spatial structure of SLA variability after removing the seasonal cycle is an interesting result. Since this is later explained in terms of intraseasonal wind forcing and geostrophic adjustment (Sections 3.3 and 4), a brief forward reference here, for example, noting that non-seasonal wind variability is explored in subsequent sections, would help the reader anticipate the physical interpretation and improve the flow of the manuscript.

Wind (around line 295) :

The relatively large variability of the meridional wind component compared to its mean—implying frequent reversals—is an important result. Since meridional wind variability is later identified as a key driver of ocean variability, it would be helpful to more explicitly highlight its physical implications here and briefly anticipate its role in modulating cross-shelf transport and surface properties.

Section 3.2.1 (EOF analysis)
The EOF analysis is well implemented and provides a useful framework to describe the dominant patterns of variability. Some aspects of the interpretation could be further refined. In particular, it would be useful to acknowledge that EOF modes represent statistical modes and are not necessarily associated with independent dynamical processes, especially when assigning physical meaning to them. Additionally, some modes (e.g., SSSa) explain a relatively small fraction of the total variance, their robustness and physical relevance could be further discussed. Also, a clearer connection between the spatial patterns and the dominant temporal scales identified in the spectral analysis would strengthen the interpretation.
In addition, it may be helpful to briefly discuss the sensitivity of the identified modes to the preprocessing choices (e.g., filtering and detrending), as these steps can influence the variance distribution and spatial patterns. Clarifying this would help assess the robustness of the EOF-based interpretation.
It may also be useful to briefly discuss the sensitivity of the results to the temporal filtering applied, as this could influence the variability patterns identified.
Section 3.3.2 (Composites)
This section provides a coherent and well-structured analysis linking wind variability to ocean surface properties through composite patterns. The results are internally consistent and physically plausible. However, some aspects of the interpretation could be slightly tempered. In particular, it would be helpful to more clearly distinguish between statistical consistency and physical causality when attributing changes to wind forcing.
Discussion (Section 4)
For consistency with the structure used in previous sections, it may be helpful to introduce subsection numbering in Section 4 (e.g., 4.1, 4.2, etc.), rather than using only informal subheadings.
SSSa: The discussion of SSSa variability is generally cautious but could be further refined. In particular, the leading EOF modes explain a relatively small fraction of the total variance, and the correlations with wind are relatively weak, suggesting a more complex and possibly multi-factorial control. Additional processes such as mixing, advection, and freshwater inputs may also play a role and could be more explicitly considered. Furthermore, the known limitations of satellite-derived salinity products, especially in coastal regions, should be more clearly taken into account when interpreting these patterns.
Citation: https://doi.org/10.5194/egusphere-2026-873-RC1
- AC1: 'Reply on RC1', Maria del Milagro Urricariet, 09 Sep 2026
  
  We thank you for the time devoted to reviewing the manuscript and providing feedback that has improved its overall quality. Below, each comment is followed by our response (in bold).
  We noticed that the Results, Discussion, and Conclusions sections and the subsections within them were incorrectly numbered in the preprint. The correct section numbers are 4, 5, and 6, respectively. To avoid confusion, below we corrected the section numbers indicated by the reviewers.
  This manuscript presents a comprehensive and well-structured analysis of the impact of wind variability on surface ocean properties over the Patagonian continental shelves. The study addresses a relevant and timely topic, combining satellite observations and reanalysis data with a coherent methodological framework based on EOF analysis, spectral decomposition, and composite techniques. The results are internally consistent and provide a physically plausible interpretation of the link between wind variability and ocean surface response. In particular, the identification of the dominant role of meridional wind variability and its connection to large-scale patterns across both the Pacific and Atlantic shelves is an interesting and valuable contribution.
  The figures are clear, well organized, and effectively support the results presented in the manuscript. The captions are detailed and informative.
  Overall, the manuscript is clearly written and well organized, and it makes a solid contribution to the understanding of regional ocean dynamics. The following comments are intended to further improve clarity, consistency, and the physical interpretation of some aspects of the analysis.
  Thanks for your positive remarks about the manuscript. We have implemented the changes suggested; they are described one by one below.
  Introduction
  The introduction is well structured and the progression from the general context to the regional description and study objectives is clear. However, the use of subheadings within the introduction feels somewhat inconsistent. The subheadings (“The Pacific Patagonian Shelf” and “The Atlantic Patagonian Shelf”) appear mid-introduction without corresponding subheadings for the opening paragraphs or the closing section on objectives, which may interrupt the overall flow.
  This is also slightly inconsistent with the structure adopted in later sections of the manuscript (e.g., Methods and Results), where a clear hierarchical organization with numbered subsections is used. A simple way to improve this would be to introduce a third subheading (e.g., “Aims of this study”) to clearly mark the transition to the objectives and maintain structural consistency throughout the manuscript. In this context, it may also be helpful to move lines 115–119 (where the proposed mechanism is introduced) to the beginning of this subsection, as they would provide a more natural motivation for the objectives.
  Thanks. As suggested, we have numbered the subheadings (1.1 and 1.2), inserted a third subsection, 1.3 Aims of this study and reorganized the text in the revised version of the Introduction.
  Additionally, the first two paragraphs (L28–37) would benefit from the inclusion of references. In particular, a general reference supporting the role of wind forcing on continental shelf dynamics (L31), as well as citations supporting the statements regarding previous studies and remaining knowledge gaps (L34 and L36–37), would strengthen the context and better position the study within the existing literature.
  We have inserted references supporting the statements in the first and second paragraphs of the Introduction.
  Results
  Section 4.1
  This section provides a useful and clear overview of the mean fields and variability patterns, effectively preparing the reader for the EOF analysis.
  SSS variability (around line 263): The discussion of nearshore SSS variability could benefit from a clearer distinction between physically meaningful variability and potential artefacts or uncertainties associated with satellite-derived salinity products in coastal regions. In this context, it may also be useful to explicitly acknowledge that satellite-derived salinity products can present systematic uncertainties near the coast and in regions with strong gradients, which could influence the interpretation of the spatial variability patterns.
  We have added a cautionary note in Sect. 2.2 on reduced sensitivity in cold waters and land contamination near the coast. Section 4.1.2 also discusses coastal data limitations and freshwater inputs, with additional references.
  SLA variability (around line 293): The persistence of the spatial structure of SLA variability after removing the seasonal cycle is an interesting result. Since this is later explained in terms of intraseasonal wind forcing and geostrophic adjustment (Sections 4.3 and 5), a brief forward reference here, for example, noting that non-seasonal wind variability is explored in subsequent sections, would help the reader anticipate the physical interpretation and improve the flow of the manuscript.
  Thanks for the suggestion. We have added a sentence anticipating the analysis at the end of Sect. 4.1.3.
  Wind (around line 295): The relatively large variability of the meridional wind component compared to its mean—implying frequent reversals—is an important result. Since meridional wind variability is later identified as a key driver of ocean variability, it would be helpful to more explicitly highlight its physical implications here and briefly anticipate its role in modulating cross-shelf transport and surface properties.
  We have inserted a sentence highlighting the possible relevance of the meridional wind reversals at the end of Sect. 4.1.4.
  Section 4.2.1 (EOF analysis)
  The EOF analysis is well implemented and provides a useful framework to describe the dominant patterns of variability. Some aspects of the interpretation could be further refined. In particular, it would be useful to acknowledge that EOF modes represent statistical modes and are not necessarily associated with independent dynamical processes, especially when assigning physical meaning to them.
  We have clarified in Sect. 3.3.1 that EOF modes do not necessarily represent independent physical processes.
  Additionally, some modes (e.g., SSSa) explain a relatively small fraction of the total variance, their robustness and physical relevance could be further discussed.
  We have revised Sects. 4.2.1 and 5.2 to emphasize the low variance explained by the SSSa modes (14 and 7 %), their noisy patterns and shorter record. We also clarify the regional relevance of EOF2-SSSa, which captures energetic intraseasonal variability in the southern Pacific.
  Also, a clearer connection between the spatial patterns and the dominant temporal scales identified in the spectral analysis would strengthen the interpretation.
  We have expanded the description of the spectral variability in Sects. 4.2.1 and 4.2.2 and added a summary comparing the dominant ocean and wind timescales. Section 5.2 also discusses the temporal resolution of the SSS product and the increase in SSSa–wind correlations when wind variability shorter than 40 days is filtered out.
  In addition, it may be helpful to briefly discuss the sensitivity of the identified modes to the preprocessing choices (e.g., filtering and detrending), as these steps can influence the variance distribution and spatial patterns. Clarifying this would help assess the robustness of the EOF-based interpretation.
  We repeated the EOF analysis using alternative low-pass filters and seasonal-cycle removal methods (Sect. 3.2.2). Linear detrending was kept unchanged in these tests. Detrending was carried out in all calculations to minimize the impact of long-term warming and associated sea level rise. These is clarified in the revised text.
  It may also be useful to briefly discuss the sensitivity of the results to the temporal filtering applied, as this could influence the variability patterns identified.
  This is covered by the tests described above, which include three different low-pass cutoff periods (10, 20 and 30 days) and two different filter families (Butterworth and Lanczos), as well as two alternative ways of removing the seasonal cycle. In addition, the sensitivity of the SSSa–wind relationship to the cutoff period is examined explicitly in Sect. 5.2, as described above.
  Section 4.3.2 (Composites)
  This section provides a coherent and well-structured analysis linking wind variability to ocean surface properties through composite patterns. The results are internally consistent and physically plausible. However, some aspects of the interpretation could be slightly tempered. In particular, it would be helpful to more clearly distinguish between statistical consistency and physical causality when attributing changes to wind forcing.
  We have clarified at the beginning of Sect. 4.3.2 that composites describe statistical associations and do not establish causality on their own. We have also revised the wording in Sect. 4.3.1 and the Conclusions to reflect this distinction. The composite subsections are now numbered consistently.
  Discussion (Section 5)
  For consistency with the structure used in previous sections, it may be helpful to introduce subsection numbering in Section 5 (e.g., 5.1, 5.2, etc.), rather than using only informal subheadings.
  The subheadings were numbered as suggested.
  SSSa: The discussion of SSSa variability is generally cautious but could be further refined. In particular, the leading EOF modes explain a relatively small fraction of the total variance, and the correlations with wind are relatively weak, suggesting a more complex and possibly multi-factorial control. Additional processes such as mixing, advection, and freshwater inputs may also play a role and could be more explicitly considered. Furthermore, the known limitations of satellite-derived salinity products, especially in coastal regions, should be more clearly taken into account when interpreting these patterns.
  Section 5.2 now discusses the limitations of the SSSa analysis, the potential contributions of advection and freshwater inputs, and uncertainties in coastal satellite retrievals. We emphasize that SSSa signals near the Strait of Magellan require cautious interpretation and confirmation with in-situ observations.
  
  Citation: https://doi.org/10.5194/egusphere-2026-873-AC1
RC2:
'Comment on egusphere-2026-873', Anonymous Referee #2, 06 Sep 2026

“Impact of wind variations on surface variability over the Patagonian Continental Shelves”
By M. Milagro Urricariet, Laura Ruiz-Etcheverry, Alberto R. Piola
This article presents an analysis of the impact of wind variability on anomalies of the sea surface temperature, salinity and height over the Patagonian shelves in South America. The authors find a strong modulation of the circulation by the meridional winds with southerly winds promoting upwelling and offshore flow of fresher waters over the Pacific shelf and strong flow of cold-salty water over the Atlantic shelf with northerly winds reversing this pattern. The study shows the interconnection of the regions by the winds filling an observational gap and addressing the PCS system as a whole.
The article is well written, and I only have minor corrections and suggestions. Also, I would like the authors to clarify on potential uncertainties in the use of satellite altimetry over shallow waters. Subject to the authors adequately addressing the concerns raised in this review, I recommend the manuscript for publication.
Important remarks
Comment on SLA in coastal regions and its uncertainty? See Birol et al., (2025). Understanding uncertainties in the satellite altimeter measurement of coastal sea level: insights from a round-robin analysis.
You mentioned the unreliability of the data in line 267 when referring to SSS within 40-100 km from land and in line 498 mentioning “near-shore altimetric limitations associated to the geophysical corrections”. While the manuscript does discuss the SLAa results in depth and compares results with reanalysis data, there is only brief mention of potential uncertainties associated with altimetry measurements in waters shallower than 200 m, which are typically found over continental shelves. It would be beneficial to highlight this limitation early in the discussion to make readers aware of potential data caveats and to provide appropriate context for the interpretation of the results.
Minor suggestions and fixes
Introduction
Line 84. Replace “characterize” by “characterized”.
Line 107. Remove brackets from reference in narrative citation i.e., Juhl et al. (2024) demonstrate …
Data
Line 146. Remove “,” after “2025”.
Methods
Line 215. Identify all terms in eq. 1
Line 222. Fix “revision mode” after “functions of the …”
Results
Line 233. This section starts with a figure and no description or introduction to lead result. Perhaps move the figure to section 3.1.1 or break the composites for each of the sections 3.1.X as done in section 3.2.1
Line 303. I don’t see a “white” dashed line, just a black one. Similarly in line 333 I don’t see “Gray” line. Check other similar figures.
Discussion
Line 530. Fig 5?

Citation: https://doi.org/10.5194/egusphere-2026-873-RC2
- AC2: 'Reply on RC2', Maria del Milagro Urricariet, 09 Sep 2026
  
  We thank you for the time devoted to reviewing the manuscript and providing feedback that has improved its overall quality. Below, each comment is followed by our response (in bold).
  We noticed that the Results, Discussion, and Conclusions sections and the subsections within them were incorrectly numbered in the preprint. The correct section numbers are 4, 5, and 6, respectively. To avoid confusion, below we corrected the section numbers indicated by the reviewers.
  This article presents an analysis of the impact of wind variability on anomalies of the sea surface temperature, salinity and height over the Patagonian shelves in South America. The authors find a strong modulation of the circulation by the meridional winds with southerly winds promoting upwelling and offshore flow of fresher waters over the Pacific shelf and strong flow of cold-salty water over the Atlantic shelf with northerly winds reversing this pattern. The study shows the interconnection of the regions by the winds filling an observational gap and addressing the PCS system as a whole.
  The article is well written, and I only have minor corrections and suggestions. Also, I would like the authors to clarify on potential uncertainties in the use of satellite altimetry over shallow waters. Subject to the authors adequately addressing the concerns raised in this review, I recommend the manuscript for publication.
  Thank you for the positive assessment. We agree that the uncertainties of satellite altimetry over the shelf deserved a more explicit treatment, and we have revised the manuscript accordingly. We have implemented the changes suggested; they are described one by one below.
  Important remarks
  Comment on SLA in coastal regions and its uncertainty? See Birol et al., (2025). Understanding uncertainties in the satellite altimeter measurement of coastal sea level: insights from a round-robin analysis.
  You mentioned the unreliability of the data in line 267 when referring to SSS within 40-100 km from land and in line 498 mentioning “near-shore altimetric limitations associated to the geophysical corrections”. While the manuscript does discuss the SLAa results in depth and compares results with reanalysis data, there is only brief mention of potential uncertainties associated with altimetry measurements in waters shallower than 200 m, which are typically found over continental shelves. It would be beneficial to highlight this limitation early in the discussion to make readers aware of potential data caveats and to provide appropriate context for the interpretation of the results.
  We have added a cautionary note in Sect. 2.2 on the limitations of SLA data in coastal regions and a discussion at the beginning of Sect. 5, citing Birol et al. (2025) and Ballarotta et al. (2019). We also expanded the caveat in Sect. 4.3.2.2 to identify the relevant sources of uncertainty.
  Minor suggestions and fixes
  Introduction
  Line 84. Replace “characterize” by “characterized”.
  Corrected (Sect. 1.2).
  Line 107. Remove brackets from reference in narrative citation i.e., Juhl et al. (2024) demonstrate …
  Corrected.
  Data
  Line 146. Remove “,” after “2025”.
  Corrected.
  Methods
  Line 215. Identify all terms in eq. 1
  All the terms are now defined immediately after Eq. (1). We have also named the upper limit K of the summation in Eq. (2), which was the only term of that equation left undefined.
  Line 222. Fix “revision mode” after “functions of the …”
  Corrected.
  Results
  Line 233. This section starts with a figure and no description or introduction to lead result. Perhaps move the figure to section 4.1.1 or break the composites for each of the sections 4.1.X as done in section 4.2.1
  We have added an introductory paragraph at the beginning of Sect. 4.1.
  Line 303. I don’t see a “white” dashed line, just a black one. Similarly in line 333 I don’t see “Gray” line. Check other similar figures.
  We have corrected the colour descriptions in the figure captions.
  Discussion
  Line 530. Fig 5?
  We have added the reference to Fig. 5d: “This mode is weakly but significantly correlated with the first mode of meridional wind variability (Fig. 5d, Table 1) and emerges prominently in the EOF1-Va composites (Fig. 6a and b).”
  
  Citation: https://doi.org/10.5194/egusphere-2026-873-AC2

M. Milagro Urricariet, Laura Ruiz-Etcheverry, and Alberto Ricardo Piola

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https://doi.org/10.5194/egusphere-2026-873-supplement

M. Milagro Urricariet, Laura Ruiz-Etcheverry, and Alberto Ricardo Piola

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Short summary

Wind variability drives coherent variability in surface temperature, salinity, and sea level across the Patagonian shelves of South America. Our findings suggest that southerly winds enhance Pacific coastal upwelling, export fresh waters offshore, weaken the Cape Horn Current, and strengthen northward transport of cold, salty subantarctic waters over the Atlantic shelf, while northerly winds reverse these patterns, revealing wind-driven modulation of shelf circulation and interocean exchanges.


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