General comments:

The manuscript descibes and validates a modeling framework for investigating transient ocean climate change in the IPSL model. In general, the paper does a good job describing the model. However, some parts of the validation (particularly the Passive Tracers part, section 5) need more validation. It would also be helpful to the reader if the authors included more details on the scientific goals of this model. This seems to be mainly included in a separate, in review article. However, without some idea of the scientific goals, it is difficult to assess if the model set up can achieve those goals. For example, the authors do not include interactive sea ice, and yet they are investigating the timing of trends in temperature and salinity. I would expect that melting sea ice impacts T and S trends, at least in some regions. The authors need to better justify why sea ice would not impact whatever question they are investigating. The formatting and writing of the manuscript are clear. With revisions, the manuscript could be publishable. 

Specific comments: 

Line 65: The authors do not use coupled sea ice in the model. Perhaps this is ok, depending on the scientific question, but it is difficult to evalulate as they never state a scientific question. More details on the intended use of this model is would be helpful. 

Line 70: Is the 2000 years the spin up, or is it run for 2000 years after spin up? 

Line 71: what is ssp245? Perhaps include a citation

Line 72: "isolate the mechanims responsible for temperature and salinity TRENDS"? Not sure what this sentence means without "trends" added to it

Line 77-79: Why is it crucial to compare simulations with the same background internal variability? Perhaps it is important for what the authors are investigating, but I do not know what they are investigating so this statement confused me. It seems to me that it would be much more realistic to couple the ocean to the atmosphere. Please provide more justification for why this scientific question cannot be done with a coupled atmosphere. 

Line 90: Why monthly-mean anomalies? Again, this may be appropriate for the scientific question, but I don't know what the scientific question is. 

Line 96-98: Are you assuming that HEAT, STRESS, and WATER are all linear? 

Line 141: Is this slight difference in a figure somewhere? 

Figure 2: There are many acronyms on this that I cannot find defined in the paper (e.g. ORCHIDEE, PISCES, LIM3, LMDz, OPA). Please define in the figure caption, or somewhere else in the manuscript. 

Figure 2: Is the Chlorophyll forcing used? I thought that biogeochemistry was not included in the model version used (e.g. line 65) 

Line 169: Does use of monthly means make a difference for ALL? 

Line 251: What are the "scientific questions we aimed to answer" ? I would expect that the timing of things like warming of the ocean may depend on having interactive sea ice. Please provide justification that no sea ice is needed for the scientific questions. 

Line 310: What is the "purpose of the intended study"? 

Figure 7: Differences appear very large in some areas (mostly Arctic, as well as high latitude N Atlantic and some of the Pacific). It is difficult to assess if this matters since I do not know exactly what the authors intend to investigate as their scientific question. 

Line 423-425: What is this work designed to study? 

Line 434-435: Are there cirations of these previous experiments? 

Section 5 ("passive tracers"): This section is intended to validate the passive tracers. However, there are no figures to illustrate that the tracers work as intended. Recommend adding at least one figure to illustrate that the passive tracers work as they are meant to. 

Line 553-554: You have different scientific questions that FAFMIP. What are your scientific questions? What are those of FAFMIP? How are they different? 

Line 561: "This question of timescales is precisely the novel aspect we aim to tackle with this present study": timescales of what? Will sea ice melting potentially impact this timescale? What region are you planning to look at? 

I selected "poor" for reproducibility as the manuscript currently does not comply with the journal's "Code and data availability" policy.

In this manuscript, a modeling framework is designed to investigate the transient ocean climate change and the effects of different surface flux perturbations on it. Validations of designed experiments but not all are provided based on the results from the IPSL model. Overall, the manuscript is well organized in format and the writing is clear. The idea about the application of the hist+ssp245 scenario to the ocean-only model is also interesting here. However, I think the scientific goals are still vague, as also mentioned by another reviewer, especially when I compare this modeling framework with the FAFMIP&Ocean-only FAFMIP experiments. The interactive sea ice could be an issue here, but since another reviewer has raised several questions about that, I mainly provided some comments on the treatment and interpretation of internal variability and externally forced responses. Revisions are necessary to make the manuscript publishable.

Major Comments:

1.    I think the key to making this modeling framework different from the ocean-only FAFMIP is the usage of hist+ssp245. However, the manuscript took me a while to confirm the guess when I read it. It would help readers understand this work better if the authors can mention this difference in the abstract and at the beginning of the manuscript. 

2.    In the abstract, you mentioned “The question of timescales … is lacking” and may imply that these designed experiments are helpful to solve this. Is it a scientific goal here? However, I didn’t find any related investigation or discussions in the main body. I believe that the validations under different timescales are needed if it is the scientific goal. 

3.    I agree that the usage of the large ensemble can help obtain the forced responses. However, the multi-model mean variables used in FAFMIP also do the same thing. Are there other aspects to show the advantage of using large ensemble simulations in this study?

4.    Some figures about perturbation experiments show the anomalies over the period when the CO2 forcing is quite large, for example, the 2040-2059 average in Fig. 11. When the external forcing is strong, isolating forced response from internal variability is easier. Hence, I am wondering if the differences between ALL and IPSL ensemble mean are still small and insignificant when you look at the period when CO2 forcing is not that strong, such as around the mid-20th century. In addition, how will it become when you only look at the difference in one year, not the average of 20 years or so. 

In other words, can this only one realization in ALL (HEAT, STRESS…) capture the result from the ensemble mean of 32 or 11 members at all time steps? Some validations are needed. 

5.    How many ensemble members are sufficient to obtain the forced surface flux perturbation? Are 11 members also fine? In particular, there are only 11 realizations after 2060 but 32 before that. Could you show a map about the difference in perturbation between the 32-member-mean and 11-member-mean in the year 2059 (and 1959 when CO2 forcing is weak)?

Could you also discuss the effects of ensemble size on your results in ALL, etc.?

6.    The results from HEAT, STRESS, and WATER are not shown. At least, the sum of them should be compared with ALL in a figure. If possible, HEAT, STRESS, and WATER may be comparable to the corresponding runs from ocean-only FAFMIP. For the passive tracers runs, the sum of added and redistributed terms should be compared with the HEAT or WATER in a figure, at least. 

Minor comments:

Title and Abstract: “large coupled ensembles” in the title is better to be also mentioned in the abstract. 

Line 33: What do you mean by “decomposition of mechanisms”?

Lines 35-36: “remain unclear” to “are not fully understood”? There are some findings from previous studies. 

Figure 5d,e,f: use dashed curve for CTL? 

Line 291: I feel the warming in the Pacific is not “slightly”.

Line 294: “…than the piControl interannual variability” but in Figure 7 you use 2 x STDDEV. 

Line 366: “Differences may …”. Does this difference represent ALL-CTL minus ensemble mean anomaly or ALL-CTL? 

Fig. 10a, c: Are these full-depth averages?

Line 408: “by twice the intermember standard deviation”. I’m not sure whether the uncertainty range is too wide.

Fig. 11: similar to major comment #4, how about the results after 2060?

Line 438: “This paper …” means this manuscript or the Silvy et al., in revision?

General comments:

This manuscript presents a modeling framework for investigating the effect of individual surface flux perturbations on transient ocean climate change, specifically focused on temperature and salinity trends. The modeling framework is implemented for the IPSL-CM6A-LR model such that the ocean component is forced with perturbations extracted from the historical+ssp245 ensemble of coupled model simulations. Overall, the structure and writing of the manuscript are clear, and most of the set-up is well validated. However, as discussed by previous reviewers, the scientific question that the new modeling framework seeks to address needs to be made more explicit. Choices for the framework set-up should be justified more clearly in the context of the scientific questions. Finally, the section on passive tracers should include validation plots, and passive anomaly salinity needs to be more thoroughly described. This manuscript could be publishable after revisions.

Specific comments: 

Line 65: What is scientifically added by using fixed fluxes from sea ice rather than coupling the sea ice model? Is this the same justification for not coupling to the atmosphere - i.e. to prevent retroactions that may change the phase of the internal variability? 

Line 94: Include validation on going from 32 members to 11 members after 2060, such as a plot showing mean and variability of forcings. As reviewer 2 asked, how many members are necessary to obtain the forced surface flux perturbation?

Section 3.5.2/Fig 4: Here, validation of the method for prescribing the chlorophyll field is by comparing global SST for each option. Does temperature in the vertical agree?

Line 250: It would be helpful to have more details here on why the unconstrained case is better for the scientific questions.

Fig 7d shows that for most depths below 1000-2000m, the zonal mean salinity difference is larger than 2 times interannual standard deviation of piControl. More justification on why this still validates the CTL experiment for the intended use would be helpful.

Line 361: Some mismatch between ALL and the fully coupled ensemble could also be due to eliminating atmosphere-ocean feedbacks. If the goal for the ALL experiment is to simulate a climate consistent with the coupled model ensemble, is this a limitation of this framework?

Fig 9c and 9d: Visually, the freshwater fluxes for this study appear to be stronger than the FAFMIP anomalies especially in the Arctic. Is this due to a stronger model response than the CMIP5 ensemble mean or due to other differences in experimental set-up?

Line 423-425: There are also some significant differences in salinity in the Southern Ocean between ALL and the coupled model (Fig 11f and l)

Line 428: This manuscript just shows results from ALL. It is stated that comparing HEAT+WATER+STRESS with ALL is in the companion paper, but it would be helpful to show it here.

Line 436: Which studies were compared to?

Sec 5: Validation plots for passive tracers needed.

Line 495 to 500: Equations equivalent to Equations 6 and 7 for salt and PAS would help for understanding the additional complexities here.

Line 505: Similar to for PAT, is there PAS in all experiments which experiences F’? If so, make this a bit clearer.

Technical corrections:

Line 21: “associated with” rather than “associated to”

Line 125: “bears similarities” rather than “bares similarities”

Line 266: capitalize “deacon”

Line 293: says stipples represents less than piControl interannual variability in Fig 7 but the figure caption says 2 times interannual standard deviation

Line 610: “worse” rather than “worst”

Line 628: “constraints” rather than “constrains”