In this work, the authors examine the marine subsurface heatwaves recorded in the Gulf of Lion in summer 2022. The analysis is run from observations and, most importantly, numerical modelling. The authors describe the physical processes involved in a sound manner, properly separating different types of warm events depending on the wind conditions, and the presence of upwelling or downwelling. They also describe some biological impacts of the warm events in benthic ecosystems. This last part is the one that seems to me to be the least developed. From the title I would expect more information and discussion on the impacts, section 4.4 is too short. Maybe the authors should slightly change the paper title.

For all those reasons, I want to congratulate the authors for the work and recommend the publication of the paper with some very minor changes or clarifications (see below).

Minor comments

Línea 129-130 “but proved sufficient to achieve our objective.” How was this proved? Did the authors run horizontal resolution sensitivity tests?

Lines 237-238: Change 4.4.X to 4.3.X (section numbers seem to be misleading)

Line 230 “A sensitivity study will explore the temperature response to an extension of the wind period”. What does this sentence mean? Does it refer to the next sections or to future work?

Lines 334-335: “During the summer of 2022, the atmospheric heatwaves that hit Western Europe gave rise to extreme marine heatwaves across the western Mediterranean”. Is this supported by the authors work or from recent literature? I am not saying I disagree with this sentence but that it should be supported somehow. In the introduction, the authors cite the work of Guinaldo, if this is the base of the sentence it should be properly attributed.

General remark for figures: I would change the font for the axis labels and scales to be clearer and more legible, but this is a matter of personal preference.

This work is an analysis of the atmospheric conditions and oceanic processes which define the extreme temperature conditions present in the summer of 2022 in the Mediterranean Sea. Using in-situ and model data to study regional-scale processes in the Gulf of Lion, the authors identify how the characteristics of the marine heatwave (duration, reoccurrence, depth and intensity) were shaped by local-scale processes (upwelling/downwelling and extension of currents).  Data on the impacts on benthic communities is also presented.

In my opinion, the work is novel and of interest to those who study the Mediterranean Sea and marine heatwaves in general. The identified processes provide more nuance to the discussion of marine heatwave drivers, showing for example that winds can both “stop” or “redirect” heating. For this, I congratulate the authors. Although it is an interesting read, the writing makes it difficult to follow. Therefore, I suggest some minor revisions before publication.

Specific comments

The authors should improve the writing. While the main messages are there, some key points are not immediately clear, for example when describing temperature increases. Sections 4.3.1 and 4.3.2, in which the two processes are described, need to be made more explicit in my opinion. Please see below for some suggestions.

The authors should provide more info on the ECMWF forecast model used.

Previous studies (see Darmaraki et al., 2024 and references therein) point to the crucial role of reduced latent heat anomalies, and to a lesser extent sensible heat, in the heat accumulation in the ocean (at least at the surface). Some data on latent heat during this event, if available at a suitable resolution,  would be welcome, to either complement or challenge what has previously been reported.

Moreover, Darmaraki et al., 2024 propose that intensified wind speeds are a driver of subsurface MHWs – the authors should discuss the importance of their findings in light of previous literature.

DARMARAKI, S., DENAXA, D., THEODOROU, I., LIVANOU, E., RIGATOU, D., RAITSOS, D., STAVRAKIDIS-ZACHOU, O.R.E.S.T.I.S., DIMARCHOPOULOU, D., BONINO, G., McADAM, R.O.N.A.N. and ORGANELLI, E., 2024. Marine Heatwaves in the Mediterranean Sea: A Literature Review. Mediterranean Marine Science, 25(3), pp.586-620.

Technical corrections

Abstract

Line 8: “an atmospheric situation” -> atmospheric conditions

Line 9: Mediterranean Sea

Line 10/11: “…down to depths of 30m which led to massive mortality…”

Intro

Line 36: Full stop, not :

2 Main characteristics of the study site

Line 83: low salinity

Line 84: “originally” from the Atlantic?

Line 105: Authors refer to a “A second type of wind” – this is confusing because two winds have already been discussed, and this “second type” is not shown on the map. Why not?

3 Material and Methods

Line 131: Why is the model driven by forecasts and not by analysis (if available)? How exactly are the forecasts used to drive the model (i.e. only lead time 0 is used)? Does this make the model a type of forecast itself or not?

Line 138-193: No need to mention the mortality event again.

4 Results

Line 170: “model bias is largest/greatest”

Line181: What does a “signature at 30m around +5oC” mean? An increase compared to what? The temperature increase in mid-August

seems closer to 10oC than 5oC.

Line 195: “ECMWF model”

Section 4.3: It is unclear which locations are being referred to here.

Line 243: “temperature at 5m increased by 4 to 7oC” makes is sound like the final temperature reached was 7, which is confusing. Please reword.

Sections 4.3.1 and 4.3.2: The writing is a bit convoluted and difficult to follow. I would suggest (1) beginning with sentences which summarise the findings of the roles of upwelling/currents.

Line 305: What was |well above average”? The downwelling?

Line 313: “the period of strengthened winds”

Line 331: “populations were less affected”

5 Discussion and perspectives

An interesting outcome of the study is that In the coastal environment, even nearby locations display very different MHW drivers and different responses to similar drivers – this could be highlighted.

Line 359: “a numerical simulation”

Line 370: “insights into”

Figures

2: ECMWF operational model is not described anywhere – is this the the same as the driver of the hydrodynamical model? Please add “Jun”, “Jul”, “Aug” etc to the x-axis labels, maybe adding vertical lines to denote the start of each month.

A1: What happened in summer 2014 to the data? I would change “data” to “in-situ”.