This study uses a combination of satellite observations and ocean reanalysis data to research the characteristics and trends of marine heatwaves on the northwest European Shelf.  Spatial variations of the marine heatwave metrics and their trends are emphasized. The author further looked into the relationship between the marine heatwaves and water column stratification on the shelf and they have found a decreasing trend of the stratification despite the increasing surface marine heatwaves. It is an interesting study, however, some further analyses are necessary to support the conclusion from the study, so I would suggest major revisions before a publication can be considered.

The authors use two datasets but there is a lack of cross-validation of the two. Also, for the ocean model data, some validation for the research region is necessary. 

The authors propose some subsurface warming causes the opposite trends between marine heatwaves and stratification. However, the subsurface data is now shown in the study, which is necessary to confirm the conclusion. 

In lines 118-119, the authors suggest that there is a periodicity of 7-10 years in regard to the MHWs occurrences. This is not obvious in Fig. 1. There needs to be more statistical analysis on that statement. 

Line 134-136: This is an interesting finding. Is there a climate driver or dynamic process that drives this spatial variation?

line 158: Are all shelf regions present summer stratification? 

The Norwegian Trench is not shown in Fig. 1.

Line 206 and 214: what is "SST intensification"?

Line 238-239: a scatter plot may show the relationship better. 

Review of Is the North West European Shelf becoming more stratified with the occurrence of marine heatwaves? by Wei Chen and Joanna Staneva

This works looks at an interesting process: the possible changes in stratification of the water column that may occur with the increasing frequency and intensity of marine heat waves. As such the works lacks to settle which temporal scales the authors are working with. Is the average stratification over the year, or the stratification surrounding a MHW event? It is not clear how long the enhanced stratification caused by a MHW event would last in a region subject to strong tidal currents. The authors find that indeed, stratification appears to be weakening, which may appear counter-intuitive but I think it stems from the temporal scale mentioned above.

I am not a huge fan of questions in titles, and in this case, in which the answer appears to be negative, I would suggest to rephrase the title so that it is more informative.

I include here below a few comments that could maybe help in improving this work.

The main comment, as mentioned above, would be to establish from the beginning at which temporal scales do the authors think the MHWs would have an effect on stratification, and perform tests at different time scales to assess how long the effects of MHWs are felt in the water column. As the place is limited I would suggest to cut on the part of the MHW description, as there is already previous work on that on this region (e.g. Mohamed et al 2023) and focus more on the stratification part.

Detailed comments:

The Abstract contains a last part with too general wording (starting at "The outcomes of this research transcend theoretical confines...") that I don't think belong to an abstract (-> Conclusion?)

line 67: 1982 - 2022 I guess?

line 178: salinity is related to salt and freshwater discharges. But in figure 4, last row, there is no signal of the many rivers (Scheldt-Rhine-Meuse, Thames, Elbe?) that flow into the North Sea. How is this possible? It may be that the signal is too weak compared to the offshore signals (Norwegian coast, Atlantic Sea), so maybe it would be good to limit these figures to the North Sea Shelf. Otherwise it is only the offshore features that can be discussed.

Figure 1. It is confusing that there are numbers in the panel a and b but they do not refer to the same things. The dotted line in panel a is difficult to see. Is the panel b a global assessment of MHWs in the whole domain? Not very informative as almost all signals are damped down by the averaging. Panels c to f: the individual lines are impossible to see.

Figure 3. This should be a central figure of this paper, as it presents the evolution of stratification over time, which is what the title claims the paper is about. But it is just slightly mentioned in the text, and in fact as the data are presented I think it is difficult to extract meaningful information. The text says "During summer, higher SST enhances the density stratification, leading to ø in summer approximately twice as high as the annual mean" but the lines in figure 3 (all panels) look quite homogeneous and no intra-annual variations are observed. I think the authors could get rid of figure 2 (and refer to results in literature) and expand figure 3 in two figures, maybe doing a short-term analysis of the effects of MHWs in the stratification and another with longer-term trends (i.e. your figure 3) but which would present the data more clearly: add grid lines, maybe a line showing the average value, and explain better what the green and black lines are (the caption says "The green and black dashed curves are similar as the red and blue curves, but for different subdomains" which I do not understand). 

Figure 5. As for figure 4, in figure 5 variations at the Norwegian trench overshadow variations over the shelf. Also, the colorbar goes up to 2 but I would say 1.5 would be better?