This is a review of the work «Implementation of an intermediate complexity snow-physics scheme (ISBA-Explicit Snow) into a sea-ice model (SI³): 1D thermodynamic coupling and validation», which I believe to be a necessary and relevant study. However, there are several concerns regarding the realism and presentation of the model and its outputs. There are large sections of the manuscript that need additional explanation of the choices in parameterization. In addition, the manuscript requires significant formatting improvements as the current presentation of this manuscript gives the impression of a rushed or incomplete submission.

The model includes a high level of complexity, incorporating parameters such as albedo, grain size, radiation extinction coefficient, compactive viscosity (accounting for snow overburden), thermal conductivity, snowfall density, and wind-driven snow compaction. Given this complexity, the density outputs appear overly simplified and do not justify the inclusion of so many detailed processes. While the average densities presented appear realistic, the vertical profile of densities on sea ice is not. Typically, a natural sea ice snowpack features a low-density depth hoar layer beneath a higher-density wind slab, which you address later in the manuscript on L403. This stratification is not represented in the model outputs. Nonetheless, the model seems to realistically simulate the evolution of snow depth and temperature relative to SHEBA, but since the publication of this SHEBA data, the thermal conductivity measurements have been questioned. I address this again below.

The model appears tailored specifically to snowpacks on level sea ice, where dynamic processes are minimal. This limited scope should be clearly acknowledged. If this is, in fact, the case, then SHEBA measurements made only on level ice need to be incorporated. I don’t believe this is addressed in the manuscript.

In addition, it would be nice to read more about the parameterizations used, e.g., Anderson snow grain size. Can more details be given as to why and how this was used? At the moment, the text is quite vague, and I had to jump between references. Another example is the use of Royner (2021) parametrization for snowfall density, in which the density max is 600. How is this feasible for snowfall? Why was this chosen?

I would also consider removing the snow-ice conversion section as there is already a lot to unpack in this manuscript and introducing this quickly at the end required new model configurations and new locations is not necessarily contributing to the paper’s conclusions. Unless significant snow-ice was measured during SHEBA, but I think this could even be added to another manuscript.

Please check for colorblind-friendly figures. For example, figures 2,3, 7b, and 8 have green and red plots together.

Minor comments

Please check the formatting of units throughout the text eg. g/m3 should be  g/m³

L23 please add «thermal» conductivity. Here, conductivity can also refer to ionic conductivity

L111 «We assume that snow covers the whole mesh in the presence of snow» seems self-explanatory; consider re-writing this. Do you mean that there is no snow-free ice in winter?

L127 upper layer thickness is bounded so that its thickness does not exceed 0.2m. Please elaborate on this reasoning in addition to referencing Boone and Etchevers (2001)

L134 Why did you choose the Brun et al (1989,1977) scheme? Please explain the reason behind this decision.

Eqtn 2 W_l seems to be referenced as W₁ ensure the same symbols/fontare used throughout

L147 Tf needs to have subscript f

L154 subscripts needed here

Eq9 c_w  incorrectly subscripted

L190 _tΓ_i,drift . There is no t and the k is replaced with i in the equation. Please check this.

L194 «which should be more suited to the Arctic region.» why is this? What is your reasoning for this?

L198 Since the work of Sturm there have been further work on the snow thermal conductivity. For example Riche 2013 showed there is likely an underestimate in this scheme due to the measurement bias. Is there a reason for this choice of parameterization? Consider looking into Calonne (2019)/ Macfarlane (2023). Would this make a difference in your ice growth estimates?

L212 formatting of p_s,k and h_s,k

L214 there is no enthalpy in equation 14. Consider moving this to line 218

L218 Soce and Si are the salinities of seawater and ice respectively. If these are fixed values please provide them here

L235 «subscript sn» are you referring to the subscripts s here? There is no sn!

L236 formatting of K_s-i  from here onwards I will stop pointing out each parameter formatting but please go through the text for the next submission version to correct all these formatting mistakes.

L259 magnaprobes spelling

L261 In Persson et al. 2002, they mention that «Ts was measured at the radiometer stand (or the Barnes radiometer stand) where the snow was significantly shallower, so the Ts values used may be slightly different than the actual surface temperature above the Tice and ds measurements. These factors must be considered when making conductive flux estimates from these measurements». It would be good to mention these uncertanties and how the snow-ice interface temperatures need using with care, it’s hard to identify in thermistor profiles. Unless an alternative method was used? Please clarify this

L268 Does ERA need caps here?

L276 marginal «ice» zone

Figure 2 top: the different thickness of lines means that it’s really hard to see the difference between ERA5 and MERRA2. Please consider changing this or adding a relative difference plot between the two

Figure 2 bottom legend capitalise SHEBA (and fig 3). Are the observed (black dots) a daily average? If so, please include this information in the caption.

L303 Calculation incorrect here, 0.153 x 191 does not equal 50.5. I also got a little lost here with parameters used, why are you referring to mass per unit area? Can you clarify and also bring this into Table 2?

L324 How does it compare well? What are the errors associated with the models? The line seems to lie on the average but the snow melt and the thickness decrease is not well represented. Are all SHEBA datasets on level ice? Or are also the thicknesses measured, including ridged areas? This refers back to my previous comment about this model being tailored to level-ice areas. Maybe only using SHEBA data collected on level ice actually improves the comparison between models as there is likely to be less variability in snow thickness.

L325, if ERA5 underestimates snow thicknesses, then the ISBA-ES looks to also underestimate. Also, the 3.5 cm in the text is listed as 3.4 cm in Table 3. Please check this and also add a reference to Table 3 on L326.

Figure 4a, can you include the density evolution measurements made on SHEBA rather than the average? This would provide a lot more necessary information to the reader.

L369 snow persists until the end of the melting season in the observations. Maybe this includes snow in ridged areas? What about a surface scattering layer that develops? The observations might include this which is trypically approx. 2-10cm. This also relevant for your final sentence in this paragraph, L379. An important process that needs adressing in this discussion!

L391 Denser snow associated with a thinner snowpack? Really? Can you include a reference for this statement?

L410 lacks accurate representation of the wind slabs. In my opinion, the model also lacks accurate representation of the lower depth hoar formation. If this is the case, I’m struggling to convince myself that this 1D  model is useful. Please can you comment on this? Why not just look statistically at the data, and are the over-simple representations of snow cover worse than this?

Figure 6 and 7a, it’s hard to see the data in both of these plots, can you consider changing the line thickness or colors or elongating the plot?

L422, include a reference for this statement

L423 Check units throughout W /mK

L425 very low conductivities are used here especially for a bulk conductivity. 0.1 is more likely a conductivity for fresh snow with low density, see Calonne (https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019GL085228)  a reason for this is the likely underestimation of k from the snowfork see Riche 2013 (https://tc.copernicus.org/articles/7/217/2013/) which explains why the conductivity estimates are low on SHEBA. I would consider rewording this and including the newer references.

L443 The lower snow surface temperature in Figure 7a (although it is hard to see) combined with the low thermal conductivity means that the snow-ice interface temperatures will be warmer. As a result it is hard to draw direct conclusions about this in the model. Can you include a model run with the SHEBA snow surface temperatures as an input?

L458 albedo of 0.83 is consistent with observations at the tower. Where is this seen? Can you include a reference to this statement?

L478 Why is snow-ice conversion important specifically during the Jan 11993-Jun1993 period? Please provide details

Review of “Implementation of an intermediate complexity snow-physics scheme (ISBA-Explicit Snow) into a sea-ice model (SI³): 1D thermodynamic coupling and validation” by Brivoal et al.

In this manuscript, Brivoal et al. describe the implementation of the detailed snow physics scheme ISBA-Explicit Snow (ISBA-ES) into the SI³ sea-ice model, which is part of the forthcoming CNRM-CM climate model configurations. The ISBA-ES scheme enables the simulation of realistic snowpack characteristics - including density, grain size, and thermal conductivity - offering a significant advancement over the simpler slab snow model originally used in SI³. Notably, the integration is achieved directly, without a coupler, by compiling ISBA-ES within the SI³ framework.

The study is a valuable contribution to the field of snow and sea ice modeling and falls well within the scope of the journal. However, I believe that substantial revisions are necessary before the manuscript can be recommended for publication.

Major Comments

1. Justification for Using SHEBA Observations
   
   The manuscript does not sufficiently explain why the SHEBA dataset was selected for model evaluation. Given the availability of the more recent MOSAiC dataset which is (i) publicly accessible, (ii) covers a different region of the Arctic, and (iii) spans a full annual cycle, it would be highly beneficial to include a comparison using MOSAiC data in your analysis.

2. Impact on Sea Ice Thickness Evolution
   
   While the results are clearly presented, they lack a critical assessment of how the new snow representation affects sea ice thickness. I strongly recommend including a comparative analysis between the updated SI³ model (with ISBA-ES) and the original version, ideally benchmarked against observed sea ice thickness data from relevant Arctic field campaigns.

3. Relevance of the Snow-Ice Section
   
   The discussion on snow-ice formation currently feels disconnected from the rest of the study. If the intention is to explore this process in depth, I suggest using data from campaigns where snow-ice formation was directly observed, such as N-ICE2015, or from ice mass balance buoys that have recorded such events.

Minor Comments

• Please ensure the manuscript undergoes thorough English language proofreading.
• Line 35: Replace “accumulated” with “accumulates”.
• Lines 85–86: The thermodynamic component of CICE, Icepack, includes many snow processes mentioned here. Please cross-check and clearly specify what aspects are novel in your implementation.
• Line 110: Capitalize “turbulent” to “Turbulent”.
• Line 111: Replace “2m temperature” with “2m air temperature”.
• Line 259: Correct “magnoprobes” to “magnaprobes”.
• Line 297: A parenthesis is left open, please close it.
• Lines 300–301: Why was SnowModel-LG used for initial snow density instead of SHEBA observations? Please clarify.
• Figure 4a: The SHEBA observational line is not visible. Consider improving its visibility.
• Lines 422–424: Move the phrase “but in ISBA-ES” to follow “by Sturm et al. (2002)” for better clarity.
• Line 472: Replace “freeboard” with “ocean surface”.