this paper is clear and well written  ; it is novel and useful to the community ; the first figure is pedagogical

I recommend publication after addressing a few minor comments

1) what is the influence of the vertical mixing coefficient in the models, on the results ?

2) in a 1D hydrological (large-scale) model, potential vorticity PV will be directly related to N^2 but in a 3D model

it has dynamical components; they may be of use in characterizing the MW in the 3D model simulations ; have you

evaluated PV  in the 3D model in the MWL - and its gradients above and below ?

3) concerning the difference between 1D and 3D results (fig.5-6) it may be of interest to plot MKE and EKE next to

these figures to assess the local importance of horizontal advection

4) in your equation (1) you merge the thermal and haline contributions to buoyancy ; what are their respective roles

in MW formation and disappearance ; how uniform are T and S when rho is constantvertically ?

5) you mention barrier layers in relation with BBW; this latter flows along the eastern boundary of the AS ; how extended

geographically (away from the coast) is the influence of these barrier layers on MW ?

This paper uses Argo observations alongside one- and three-dimensional models to examine the formation mechanisms of Arabian Sea High Salinity Water, one of the key water masses in the upper Indian Ocean. ASHSW formation is found to be atmospherically driven in the main, although there are regions where ocean processes exert an appreciable influence.

The formation of ASHSW received a fair bit of attention a few decades ago: it is nice to see the topic revisited with new observations and tools, and a fresh approach. I have a few comments and questions below, but this is a well-written paper with nice figures, and I suspect that the revisions I’ve suggested are fairly minor.

Line 27. “… Over the Argo era…” – give the year, just for clarity?

Line 39. The paper has a lot of acronyms in it: I might not use one for Arabian Sea.

Line 42. Comma after mass?

Line 62. Acronym already defined, so should be OMZ.

Line 68. My feeling is that this sentence should be the start of a new paragraph – perhaps joined with the one after?

Line 85. The number of profiles for half-degree bin: is this over the whole time period?

Line 145. Is mode water thickness defined on depth or density? The upper and lower boundaries are defined in density – but is this then converted into a depth? Either is fine, but would be good to state clearly.

Line 147. Have the authors done any sensitivity analysis on these definitions? For instance, does choosing 30 days give very different results to choosing 20? Or 40?

Line 172. I think the paper would be clearer if the authors referred to the monsoons either as summer and winter, or north-east and south-west.

Line 182. “Equatorial”?

Line 185. “It’s”?

Line 191. “Monsoons”?

Line 192. I’m not quite sure what this sentence is trying to say – and especially because “the importance of the north” has not yet been demonstrated.

Line 195. Is there a typo in this equation? ImpactFactor_region appears on both sides and so, as written, should cancel… Also, what does region mean? I assume northern and southern Arabian Sea but, as written, it’s not crystal clear. Also, if ImpactFactor is volume over area, could it be described as a scale depth of the mode water later, perhaps?

Line 199. This sentence makes no sense.

Figure 3. Panels (o)  and (p) – say north and south, to match the names for the regions used in the text (if I’ve understood the text correctly), rather than re-stating the definition. And plotting things against day/week or year is one of my personal bug-bears – plotting against month is much more straightforward. (See also Figures 4, 8 and 9.)

Line 226. Again, this sentence makes no sense. I have turned the phrase “latitudinal regionality” over and over, but I cannot understand it.

Line 228. “collocated”: co-located? Does this involve interpolation, or do the authors just pick the closest ERA5 grid point?

Line 270. Seasons haven’t been defined? Does this mean “per three month period”?

Line 298. “… simplifying dynamics to their maximum”. This is a pretty vague phrase – might be good to be a little more specific?

Line 306. I’m not sure that I understand the logic here: surely the existence of a regionally invariant bias would suggest limitations in the ability of a one-dimensional model to replicate mixed-layer processes?

Line 362. Modulate ASHSW how?

Line 452. I’m not sure reminiscence is what you mean here?

Line 529. More important than what?

Line 544. ESM – acronym not defined? Also I’m pretty sure “impotence” is a typo…?!

Local Mode Water dynamics are critical for understanding the physical oceanography (and thus the biogeochemical oceanography) of the Arabian Sea. The understanding of these dynamics contributed by the manuscript is valuable for understanding ventilation of the Arabian Sea OMZ, and will help in evaluating future ocean and climate model representations of Arabian Sea ventilation. The manuscript highlights significant and bimodal contributions of the southern Arabian Sea to MW formation, when previous literature has focused on northern winter MW formation.

The analysis performed in this study is thorough, and draws upon the relevant physical frameworks for analyzing changes in stratification related to Mode Water Formation. The use of both observations and models is a strength of the manuscript. I believe that the comparison of the 1D and 3D model to infer the importance of horizontal dynamics is sound, though I have some questions about the role of turbidity in the comparison. 

The takeaway messages are clear, but some sections could be more concise or clearly structured, and some figures more clearly introduced.

I recommend minor revisions, with specific points listed below. In the points below, I also include a one or two new pieces of analysis that I would be interested in seeing. However, the manuscript already contains sufficient results, and no new results are necessary for the manuscript to be fit for publication. Overall, I think that the manuscript makes valuable contributions to the topic.

Specific points:

Lines 135-145: To clarify, this algorithm is strictly one-dimensional, correct? So if a MWL exists at a given point, but was formed elsewhere, it would not appear in e.g. Figure 3c-n? Do you think that this may lead to cases where a MWL seems erroneously eroded, if it remains intact but advected to a location that did not have a MW formation event?

Lines 144-145: In Figure 1, sometimes the MWD is above the bottom of the MWL, including in the schematic in Figure 1b. So, the physical intuition for these metrics is a bit fuzzy. Can you clarify this? How is it that the Mode Water layer can extend deeper than the deepest surface mixed layer? Is the 0.05 kg/m3 threshold universally justified, or does it break down in some regions?

Results 4.1: this section is quite hard to follow because the text jumps between Figures 2,3 and 4 without actually introducing any of them. I think that Figure 2 is a clear and simple starting point for contrasting the North, Central and South Arabian Sea, but it doesn’t really get any attention or explanation. Also perhaps a separate color scheme for the samples in each section would highlight the regional contrast.

Lines 303-310: May strengthen your argument to touch upon some things that the models represent well, in addition to biases. For example, the 3D model capturing the summer mixed layer depth

Lines 318-319: This is a really nice point. MLD is much easier to diagnose in models than the Mode Waters themselves, and I would be interested in seeing if any more quantitative connections can be made. For example, you could look at a few timeseries for different regions to show how the MLD biases lag the MWT biases and how the magnitudes compare. Is it pretty consistent? Does it change by region?

Line 322: “major differences and various dynamics” reads a bit clunkily here

Lines 356-357: I’m missing the connections here that lead to the takeaway that the MWs are “driven by the build-up of upper ocean stratification during spring-summer from ocean heat gain”. The reasoning in this paragraph is a bit unclear

Line 369: “In the Central…”

Lines 397-403: consider moving to Discussion

Section 4.4.3: The argument based on water type representation should be set up more clearly earlier on in the manuscript. The water types and absorption coefficients are alluded to in the methods but not explained (Line 107). Up until this point, the reader is under the impression that comparisons between the 1-D and 3-D models basically isolate horizontal advection and eddies. However, suddenly there is this other factor that has not been considered in the previous comparisons, which leads to questions about whether water types can also explain differences in other three test regions. If the absorption coefficients are referring to chlorophyll shelf-shading effects, I would think they could be important in all of the regions. If it is referring to the suspension of sediments, etc., then I would be skeptical of their influence this far from the shelf. 

Lines 440-465: I would argue that oxygen content below the mixed layer is more relevant here for ventilation and biogeochemical impacts. Is there a reason why you don’t use the results excluding the mixed layer for Figure 9, instead of the 0-250m results? 

Lines 523-537: It may be worth clarifying here that you are only discussing the impacts of locally formed MWs in the Arabian Sea. This may cause some confusion because remotely formed mode waters in the southern hemisphere likely join the Central Waters in the western boundary current and play a significant role in ventilating the AS OMZ as well.

Line 562: Briefly, what are the expected precipitation changes in the AS with warming? Does it follow the “wet gets wetter, dry gets drier” paradigm (e.g. Held and Soden 2006).