| 18 Dec 2025
Year-Round Characterization of Upwelling Along the Uruguayan Coast Using a High-Resolution Regional Ocean Model
Abstract. Upwelling along the Uruguayan coast has largely been interpreted as a summertime process, primarily based on surface temperature signals. Here, we investigate coastal upwelling year-round using a high-resolution regional ocean model (Coastal and Regional Ocean Community, CROCO), with the aim of reassessing how upwelling manifests across seasons under contrasting thermohaline conditions. The seasonal covariability between daily winds and sea surface salinity anomalies was analyzed through a Maximum Covariance Analysis, revealing upwelling signatures during spring, autumn, and summer, marked by positive sea surface salinity anomalies (SSSa) along the Uruguayan coast. Summer upwelling events were characterized by positive SSSa and negative sea surface temperature anomalies (SSTa), indicating that both are reliable upwelling proxies during this season. In contrast, during spring and autumn, SSSa resulted in a better proxy. In this regard, upwellings were clearly marked by increments in SSSa, but the SSTa pattern in the coast was variable due to differences in thermal vertical profiles. Based on the thermal properties of the upwelled waters, three upwelling regimes can be identified: cold-water upwellings associated with warm-season stratified conditions, transitional upwelling events occurring under weak or absent thermal stratification, and warm-water upwellings linked to cold-season conditions, characterized by inverse thermal stratification. Overall, our results highlight that upwelling events along the Uruguayan coast cannot be described by a single thermal signature, but rather by seasonally dependent thermohaline regimes.
The manuscript addresses a relevant and timely topic: the year-round characterization of coastal upwelling along the Uruguayan coast. It convincingly proposes the use of sea surface salinity as an alternative proxy to sea surface temperature outside the summer season. The ocean model appears to be well configured, the methodological basis is solid, and the analysis is extensive. Overall, the study has clear potential and could make a valuable contribution to the understanding of coastal upwelling processes in the region.
However, the manuscript presents several issues related to structure, focus, and scientific positioning that currently weaken its overall impact. In many passages, the text reads more like a technical report or a project deliverable than a scientific article oriented toward hypothesis-driven research, critical comparison, and discussion of results in the context of existing literature.
The Introduction section, in particular, is not clearly closed. It is difficult to identify where the introduction ends and where the methodology begins (around lines 75–90, when the description of CROCO and the model setup starts). The introduction would benefit from a more explicit motivation for the modeling approach adopted, a clearer justification for the use of this specific tool, and a more precise formulation of the study objectives and its novel contributions. I would expect to find a paragraph explaining why this type of model is needed, what gap in current knowledge it addresses, and what questions this study is able to resolve, followed by a clear statement of objectives. In addition, heat fluxes are discussed and analyzed in the Results section; however, the “Methodology” does not describe how these heat fluxes were calculated. The manuscript should clearly specify which heat flux formulation or parameterizations were used in CROCO.
More generally, the manuscript would benefit from a clearer and more conventional scientific structure, with well-defined sections (e.g., Introduction, Methodology, Results, Discussion, and Summary and Conclusions). At present, the boundaries between sections are not always clear, making it difficult to distinguish between background information, methodological descriptions, results, and interpretation. This also affects the readability of the manuscript and the clarity of its main messages.
The comparison with previous studies is rather limited. While there is some discussion of the water column structure, there is little quantitative comparison with existing literature or independent datasets, particularly regarding the validation of vertical velocities and the vertical structure of temperature and salinity. As a result, it is not always clear whether the simulated values are realistic. The limited use of references to benchmark the results also makes it difficult to clearly identify the novelty of the study beyond its descriptive analysis.
The methodology section requires more technical detail, especially for shallow bathymetric regions. For instance, the minimum and maximum depths considered in the simulations should be explicitly stated. In addition, the description of the forcing needs to be more detailed, particularly regarding freshwater inputs and tidal forcing.
Several figures and figure captions also require corrections to improve clarity, consistency, and organization. Some figures show inconsistencies between what is described in the caption and what is actually displayed, while others would benefit from clearer panel labeling and ordering.
Specific comments:
The paragraph around line 45 requires additional references to support the statements made. The material presented between lines 75 and 90 would be more appropriate in the Methodology section rather than in the Introduction.
Regarding Figure 1 (lines 105–110), according to the caption, CL and TR should be indicated in the figure to identify the coastal location and the transect, respectively. However, in the figure only “IF” and “Transect” appear. This should be corrected for consistency, especially since IF (Isla de Flores) is referenced later in the text. In addition, if abbreviations are used for cities (e.g., Mvd, PdE), the corresponding abbreviation for PP should also be included.
Around lines 115–120, it appears that only two river inputs are included. Please clarify whether these are the only freshwater sources considered in the simulation. Furthermore, the tidal forcing should be specified more clearly, including which tidal model or tidal constituents were used.
In Figure 2 (around line 160), the panel labels (a, b, c, etc.) should be placed outside the title, particularly for panels e and f, where the letters appear to be part of the title. It is recommended to place the panel labels as text positioned, for example, in the upper-left corner of each panel.
For Figure 3 (around line 175), I suggest adding a vertical profile from the nearest GLORYS grid point to provide a clearer reference and vertical validation of the model results.
In Figure 5 (around line 210), please revise the order of the panel labels so that the left panels are labeled a, b, c, d, and the right panels e, f, g, h, to improve clarity and consistency.
Finally, in the caption of Figure 7 (around line 240), the word “upwelling” is repeated twice and should be corrected.
In summary, while the study has clear potential for publication, it requires substantial revisions in terms of structure, clarity, and scientific positioning, rather than minor corrections.