General Comments

This study uses in-situ observations to identify the subsurface signal of the intense and long-lasting Mediterranean Sea marine heatwave of 2022. Beyond merely providing a description, the study links the propagation of MHWs by quantifying stratification and explaining the local dynamics (e.g., convection, upwelling). I find this study to provide convincing evidence of the vertical penetration of heat during the MHW, with new results on the depths influenced by these events. For example, an important distinction is made between the anomalous warming of 2022 and the long-term warming trend, which influence results on the deep profiles. While other referenced studies begin to study general characteristics of subsurface MHWs, this case study, performed by authors who display strong understanding of their study zone, is a welcome addition to the literature.

I agree with the publication of this manuscript after some minor corrections are made regarding clarity and communication. Generally, the figure quality could be improved. The manuscript is readable but would benefit from a grammar check (I provide technical corrections only for the abstract, for now).

Specific Comments

• Abstract: should mention the distinction between long-term warming signals and the 2022 anomalous warming. You mention the thermocline but do not refer to it or its depth in the main text. The last sentence is very vague.
• Figures: inconsistency between fonts styles and size, map outlines and land colors.
• Introduction: there is no mention of why it is important to look at subsurface penetration of MHWs, especially at the depths you study here.
• Table 2 is blurry.
• Line 39: “among others” is either lazy or unfair.
• Line 125: Could homogeneous warming be a sign that it is linked more to long-term warming than the 2022 event?
• In general, the paragraph separation could be improved to make the manuscript flow better. Line 140 is an example of an abrupt change.
• Line 235. This should be mentioned earlier in the results. As I was reading, I kept thinking “couldn’t the deep warming just be long-term climate change signals”? It is best to tackle that doubt early.
• Line 237: “A matter of fact” seems too confident to use generally. Possibly true in some places (e.g., SAP).
• Line 240 is the same vague line found in the abstract.

Technical Corrections

• Line 11: Argo float in-situ observations
• Line 13: Pelops Gyre and southern Adriatic Sea
• Line 14: T’ – remove the apostrophe
• Line 14: remove comma after “periods”
• Line 20: unclear why is SAP the exception.

overall quality

The manuscript studies the marine heatwave event that occurred in summer 2022 in the Mediterranean Sea using ARGO floats data. It first computes Ocean Heat Content anomaly (OHCA )for the surface, intermediate and deep layers for the year 2022 to determine regions that experienced strong warming. It then characterizes the vertical structure of the MHW event for each of those 5 regions using temperature anomaly profiles obtained from the ARGO floats during spring-summer 2022, to calculate the MHW depth that is then used to classify the MHW into 3 depth categories: surface, intermediate and deep. It concludes that different regions experienced MHWs with different vertical characteristics, with some regions showing MHWs constrained to the surface, and others MHWs propagating to intermediate and deeper depth. Authors state that the heat penetration can be explained by the dominant physical processes – whether stratification, advection, convection or upwelling – at play in each particular region.

The study provides insight into the vertical structure of MHWs by documenting MHWs beyond their surface signature, it also links the observed heat propagation to known regional ocean dynamics of the different regions however without support of an in-depth investigation for the hypotheses made. In the current state I would therefore not accept the manuscript for publication without substantial corrections; namely to carry out the evaluation of physical processes involved to support hypotheses, or to limit the scope of the study to the characterization of MHW with explanations of potential reasons for the observed signature.

Specific comments

On the calculation of the 2022 OHCA, why is the OHCA calculated over the full 2022 year to determine study regions, when we know it is during the months of May to September that the MHW occurred? Why not just use the spring-summer period? If not, how can we ensure that the obtained OHCA₂₀₂₂ value is not affected by a seasonal signal as a result of floats having heterogeneously sampled the region (e.g. only winter months)? Does an OHCA for summer months only lead to the same 5 regions?

Also, the product used is from International Argo Program; why not use CORA product from the Copernicus marine service?  

What is the justification for building an OHC climatology using argo data only? The presence of spatial gaps suggests limited data availability, how does this impact the calculation of OHC anomaly and associated uncertainties. Why not use a dataset containing more temperature data (like the Sea data Cloud dataset used later)?

It would be informative to associate uncertainties to the OHCA, by knowing how many profiles are used for the calculation in each 1x1 degree gridcell when calculating the OHC climatology. Similarly for the OHC for spring-summer 2022. As additional plots may not be possible I would suggest to add an extra paragraph in the discussion.

Why the region centred on 28W 36N, south of Türkiye was not included in study as it seems affected by large anomalies (surface and middepth) and presents floats for both periods?

Method for computing Ta. I am not a specialist but I wonder if there is a continuity between Argo data and SDC dataset so to ensure difference taken between float profile and mean SDC profile is meaningful?

To evaluate the mean shape of MHW2022 vertical Ta profiles, a mean Ta profile is calculated using all floats for the season during year 2001-18. It is stated that this negative anomaly is not observed in the clim Ta profile (line 152), it would be useful to plot an uncertainty associated with the mean clim Ta profile, to get a better feeling of the spread of Ta with depth.

For each region a proportion of Ta profiles for each categories should be given

In SAP region, how are Ta profiles categorized if (as suggested by mean profiles fig 2e) no negative anomalies are observed? Mean profiles for Category 1 and 3 seem identical, what makes them fall into different categories.

purely technical corrections

General writing would benefit from being more precise, English could also be improved

Abstract

Abstract could overall be improved,

line 13 to 17: the two sentences are counter intuitive and should be rewritten. First one mentions C1 has shallow heat penetration (0-150m) and the second sentence says C1 shows negative anomalies in that depth range (50-150) without mention of positive anomalies (at very near surface).Such info should be added.

line 18: study does not mention thermocline except for the abstract

line 19-20: Unclear whether message conveyed is valid for both period studied or just summer (unlike the next sentence). Please clarify.

‘All sectors show similar warming’, be more specific, in particular because a comparison is then made with SAP region. Unclear for reader what similar characteristics are observed and how this is different for SAP region.

Line 20: SAP use of acronym not yet defined

Line 22: remove ‘s’ to scenarios

Intro:

Line 28: change to ‘the frequency of MHW events has increased by 50%...’

Line 29: ‘across latitude’ strange use of term in this contect

Line 33: strong increase in MHWs, unclear number of MHWs??

Line 34: ‘facing’ do you mean addressing?

Line 34: confine to and not in

Line 40: propagate? I think the use of propagate is not appropriate, it suggests that warm anomalies travel from surface to deeper depth, when this may not be necessarily the only case with other mechanisms are also at play (lateral advection). This is also raised by the authors at the end of the paragraph with often no surface signature of mhws occurring at subsurface. Please rephrase.  

Line 43: registered, do you mean occurring?

Line 45: ‘were’ detected

Line 71: calculated instead of computed, changes in and not of,

Line 72-75: a bit of a drafty sentence, please reword

Methods:

Line 76-80: a brief  

Line 80: Argo product from the International Argo Program is not referenced in Table1 (or is it product 1?),

Line 89: ‘and better sampled by floats’, but also sufficiently sampled by floats

Selected areas are referred to as region or sectors, please be consistent across manuscript in the term chosen

Line 90: The T_a , please introduce before use

Line 93: what’s the vertical resolution of SDC product?

Line 103: Z_N not ZN

Definition of Z_N line 104: if it’s the temperature anomaly that is used in the expression it should be written as T_a(z) and not T(z)

Same for CT_a

Line 108: by spatially

Line 110-111: please rephrase as not english

Line 114-116: please explain why was N² calculated

Results:

Line 130: specify in the text that profiles in fig2 correspond to those from the spring summer period.

Line 140-147 seems more part of a discussion aspect to me.

Line 159-160: should be in discussion part, and needs elaborating.

Line 161-166: should not be in results but in discussion

Line 168: ‘decreasing warming’ specify the decrease is with depth

Line 174-176: same, description of area should not be in results

Line 180: this is not true for Category 2 whose mean profile suggests a progressively decreasing Ta with depth.

Line 180: sentence starting with ‘All five sectors’ is beginning of new paragraph

Line 181: All five sectors showed a larger warming than the float clim: not the case for Cat1 in PG which is lower.

Line 181-188 should be part of the discussion

Caption fig 3: (e) Daily Sea Surface Temperature (°C) in the ION sector (black box) for late November and (f) early December 2022.

Line 196: refer to relevant figure associated with statement

Line 200: attribution to an upwelling event also evidenced in N2 anomaly for the region in December

Note: mean Ta(z) are available for fall period, but not for summer period (available only for each category) which makes it difficult to visualize the seasonal change.

References: Check formatting, presence of inconsistencies between citations (e.g. first names, …)