Review of the paper “A missing link in the carbon cycle: phytoplankton light absorption under RCP scenarios”  

General comments

 I have completed the review of the manuscript egusphere-2023-921. The manuscript shows some interesting results, somehow scientifically soundings. At the same time, I found that the manuscript has several issues that the Authors should address before a possible publication of their work. Thus, I asked major revisions for this work.

Major comments 

1. The manuscript shows several typos. See for example “phytopankton” at line 8. Please consider a strong editing of text.
2. There is a lack in explaining the purpose and the methodology followed in the study.
3. Along the text the Authors mention the “primary production”. Do you mean “net primary production” (gross pp minus respiration) or the gross pp? please specify since they are different things that can lead to a different interpretation of your outcomes.
4. There is a lack in the manuscript in the description of the modeling tool and forcing adopted in the simulations. For example, I do not understand why using such old values for wind forcing (Trenberth; 1989) since you run long term simulations covered several centuries, eventually covered by CMIP models.
5. I’m puzzled about the fact that chl-a is not transported by ocean currents. Is it your model result? Is it an assumption of the analysis or a constrain in your numerical simulations? Please explain better. Phytoplankton (and chl-a) could be considered a passive tracer (as it is  in many coupled models). Thus, in marine environment it can transported by advection or diffusion processes.
6. The explanation provided by the Authors related to the increase in the vertical velocity (see also my comment on Appendix D) looks to me weird (maybe I’m missing something in their reasoning and so please help me to understand). If someone warms/cools the upper/bottom of the water column I would expect an increase of the vertical stratification and thus lower vertical transport and vertical mixing (as predicted by several studies discussing the future climate projections). The Authors talk about an increase in the vertical velocity because of the difference in temperature. I do not think this is correct. Please explain better this point.

Specific comments

Line 2: I would say influence not impact.

Line 8-12: Please explain better how the light absorption would weaken the carbon pump.

Line 16-19: This part is not very clear and should go at the end of the introduction as purpose of the work.

Line 25-35. There is a dependence of the projections for the net primary production on the parametrization adopted and how they are influenced by the temperature. In the Mediterranean sea there is an extensive review on this topic by Richon et al., 2019 and Reale et al., 2022. Please consider to add a sentence about.

Line 33-35: how? Please explain

Line 38 and line 55: On what? Please explain

Line 68 e Fig.2: The RCP scenarios do not “describe possible future climate system” but hypothetical temporal evolution of greenhouse gases emission in the atmosphere. Please correct this statement and the caption.

Line 81-82-89: What do you mean with “association”, “intermediate” and “related to climate processes”?

Figure: is there a coupler managing the exchange of fields (arrows) among the components of the modeling tools? Please specify

Line 101: I see that the purpose of the work is not to validate your simulations but please add some quantitative information to your discussion (under/over estimation is too generic).

Line 123: Why do not you consider Nitrate? Please specify.

Line 145: DIC as nutrient sounds to me weird since it involves different chemical species (CO2aq, HCO3, CO3 and so on). Could you please add some references or explain better this point?

Line 169: What are the criteria to choose the sixth layer as limit for light?

Line 196: Why just one year (2050) instead of the entire period?

Line 200: It would be nice to see the spatial distribution of these differences that could explain the differences among the different scenarios instead of a single value that is meaningless

Line 226: I do not think that chl-a is a climate variable

Line 229: How? Please explain

Line 230-235: see my major point 6

Line 266: what do you mean with underestimation of the oceanic circulation?

Line 269: What do you mean “The missing….model setup”. Please explain

Line 274-276: Please rephrase.

Line 342-342: Not clear. Please rephrase

Appendix D: It would be better to have a map to show the global distribution of this quantity. Maybe the results in the Chilean area could be associated with La Nina/El nino pattern. Did you check that?