Overview and general recommendation:

This manuscript examines the variation in surface area and latitude of ocean provinces, which are defined by three environmental variables closely linked to micronekton biomass. The topic is very interesting and valuable for marine and climate change policy-making. However, issues related to clarity, methodological transparency, and result interpretation significantly undermine the scientific rigor and credibility of the study. Therefore, I recommend a major revision.

Below are the detailed comments and suggestions:

Specific comments:

1. A major concern is that the entire study extends from an unpublished paper currently "under review," as mentioned over ten times throughout the manuscript. However, the authors provide no additional materials to clarify the methodology or findings of the prior study. Without access to this prior work, the present study lacks context and transparency. For example, the methodology is frequently referenced as "see the previous unpublished study", but the reader know nothing about that. I attempted to locate the referenced study (Albernhe et al., 2024) online to find whether it is published so I will understand what authors talking about. Fortunately, it is published. If this study heavily depends on the unpublished paper, I suggest waiting for its publication or providing supplemental materials to ensure reviewers and readers fully understand the background and methodology.
2. Lines 56-59: The authors mention that micronekton observations primarily rely on trawl sampling, which can introduce biases, and then abruptly shifts to ecosystem and population models. The connection is unclear. Why are numerical models, such as spatial ecosystem and population models, complementary tools? Please elaborate and provide supporting details.
3. Lines 63-64: The authors state that "catch per unit of effort of commercial fisheries" and "multi-expertise discussions" are environmental forcings. However, these appear to be more related to human or economic activities. Please clarify or revise.
4. Lines 70-84: This paragraph is confusing. The statement, "The ambition of this work was to identify..." seems to describe the prior study rather than the present one. After multiple readings, it appears the authors are referencing the previous work. I suggest revising this section to explicitly distinguish between the goals of the prior study and the current one.
5. Lines 114-116: I understand that authors used the same methodology as the prior study. However, the main difference is the period of input data (1998-2019 vs. 1998-2023). Despite conducting a new training phase with updated data, the authors still used k=6 for clustering, as in the prior study. It is necessary to show the results of clustering and PCA in the Result part or Supplementary materials.
6. Line 122: Authors mentioned they are using monthly time series of biophysical biomes that captures seasonal and interannual variability, but I cannot see any detailed description in the whole manuscript and Supplementary about that. Also, this is my another main concerned of the study. Please see the comment point 7.
7. Lines 136-150: The authors used linear regression (R² and slope) to analyze trends in surface area and poleward shifts, but this approach raises several issues:

First, there is insufficient information on how surface area and poleward shifts vary annually. Scatterplots showing surface area and average latitude trends, with fitted regression lines, should be included in the Results or Supplementary Materials.

Second, low R² values (approaching zero) suggest poor linear regression fits. Statistical significance of the regression should also be reported. Seasonal and interannual variations may not follow a simple linear relationship. The observed dynamics could involve regular or cyclical changes over time, which are not captured by linear regression.

Third, Conclusions based on a comparison of 1998 and 2023 alone are unconvincing. Given the low R² values, comparing other years (e.g., 1998 vs. 2022 or 2021) could yield opposite conclusions for some provinces.

So, I recommend using more sophisticated methods, such as Generalized Additive Models (GAMs), Multivariate Adaptive Regression Splines (MARS), Seasonal Autoregressive Integrated Moving Average (SARIMA), or machine learning approaches, to analyze seasonal and interannual variations. These methods could also help identify the significance of different environmental variables and their roles in driving variations in surface area and poleward shifts, enhancing the study's credibility and depth.

1. Lines 172-175: Authors mention seasonal variability and regional phenomena (e.g., ENSO events) but does not describe specific patterns or results. It is not reasonable to ask readers to infer patterns from figures or videos. Providing a detailed explanation would greatly improve the study's readability.
2. Lines 214-218 and Figure 3: Why do neighboring provinces (e.g., 405 and 203) exhibit opposite patterns in average latitude evolution? This requires further explanation in the Discussion section.
3. Line 217: Authors consider a ±0.5° poleward shift over the study period as "stable." Please provide evidence or references to support this criterion.
4. Discussion section: The results are interesting, but the discussion lacks depth. I suggest the following improvements:

Lines 270-271: Further discussion is needed to explore why the area has shrunk. Based on the results of this study, what are the main environmental variables driving the reduction? How do changes in those three environmental variables lead to the shrinking of provinces? Similarly, why have some areas expanded? This is unlikely to be a simple consequence of spatial redistribution. A deeper analysis could provide valuable insights for climate change policy-making.

Lines 273-275: I suggest the focus of the discussion should be shifted to the characteristics of productive provinces and subpolar provinces, providing a detailed explanation of the reasons behind their expansion. This section could be combined with the discussion in the previous paragraph. Additionally, sufficient literature references are needed to support the arguments with robust evidence.

Lines 280-282: The results are highly promising; however, the discussion is overly simplistic and superficial. A more thorough comparison with other studies is needed. Based on the findings of this study, the reasons behind poleward migration should be clarified. While the discussion briefly mentions temperature changes, this study also considers NPP. Are there any interactive effects between these two factors? Furthermore, the potential connections between changes in external environmental variables and micronekton should be explored. For instance, how does micronekton respond to temperature changes, what are the underlying mechanisms, and how does it influence the variation of ocean province definition?

Technical corrections:

Line 18: Avoid including references in the Abstract.

Line 111: Specify “stratification” of what?

Figure 1: The color area for "602" is unclear. Only the number is visible in the top right.

Line 222: Correct “VGMP” into “VGPM”

Line 231: Please ensure consistent section numbering. Change "II.1" to "2.1."

Please provide the citation for the Albernhe et al., (2024) if it has been published.