The paper by Zeising and co-authors, titled “Assessment of transparent exopolymer particles in the Arctic Ocean implemented into the coupled ocean–sea ice–biogeochemistry model FESOM2.1–REcoM3”, describes the new implementation of PCHO and TEP tracers and respective processes in a global ocean BGC model, which is calibrated for the Arctic Ocean. The model was integrated for 1958-2019 period where the results from the last three decades is analyzed. In addition to evaluating the performance of the simulated PCHO and TEP, they present the mean states and spatial distribution of the simulated phytoplankton-related carbon state variables, including the seasonal cycle, and comparison with observational-based estimates. It is nicely written and easy to follow with clear figures to illustrate key messages the authors try to convey. As a model description, the paper contains sufficient details and result presentations. I have a few comments that hopefully the authors can address to further improve the paper.

Main comments

Impacts of adding these new processes and state variables. The motivation is well outlined in the introduction, nevertheless, how do these new processes change the carbon/nutrient cycling/export production/PP/etc., as compared to the model’s reference configuration without these new tracers, are not so clear after reading the paper. The readers should get some insights whether these processes are indeed important and/or worth implementing in other models.

Assuming similar baseline experiments exist but without the new improvements, some figures or performance metrics could be useful to have. For instance, a climatological seasonal vertical profile of nutrients from models with and without this modification (compared with observations) could be interesting to see.

How much of the 662Pg DOC (L17) are PCHO based on your model simulation? How much are converted to POC or what is the new POC export rate? Can you stipulate how future climate change may alter this and the broader ocean carbon cycle?

The results seem to be quite sensitive to limiter function (eqs. 5-6). Please briefly describe how the threshold 0.2 and 0.151 was determined and if they are spatially varying?

As the authors stated, this is an important first step toward advancing the air-sea coupling (L39-41) in ESMs. Can you elaborate your plans in this direction? Is it feasible to simulate the marine TEP emissions? What would be the cloud feedback and radiation budget effect mentioned? Will it be similar to DMS (Schwinger et al., 2017 BG, https://doi.org/10.5194/bg-14-3633-2017)? Can the authors estimate the magnitude of this effect?

Most (if not all) of the presented analysis are for surface processes. Are TEP and PCHO in the model only exist near the surface layers and none below? Is that why the spin up was so short and if they exist below the mixed layer, are they in sufficiently steady state? Some discussions or presentations of impacts on interior biogeochemistry (if any) would be appreciated.

Minor comments:

Fig3 caption: mention that this is from model simulation. Why not add observations here?

Fig3 caption: remove extra ‘)’

L295: add space after period.

L306: describe SIC

Fig4: why are there ‘discontinuity’ in the red lines?

Fig5: Any observations that can be plotted together (e.g. in same color dashed lines)?

Why only eastern Fram Strait in Fig. 5, I would think showing the western Fram Strait or N. Barents Sea could be interesting, showing also the sea-ice concentrations.

L340: in the eastern Fram Strait(?)

L344: ”It peaks at 150 µg C L−1 in August and quickly declines thereafter“, this is inconsistent with Fig. 5.

Table 5: Eurasian Basin (3e-51): is this a typo?

L429: remove ‘)’

L461-4: Vertical profiles comparing model and observations would be useful.

L471: at the beginning of

L472: and decrease toward

L481: A scatter plots of TEP vs TChla (from Fig. 4), including DIN values could support this statement.

L493-6: The statement gives the impression that the correlation of 0.71 considers the data from Caitlin Ice Base, when in fact data less than 1umol is excluded (Fig. A4 caption). Please rephrase.

L581: 10-150 is not ‘agreeing well’ with 0-39. Please rephrase.

The article « Assessment of transparent exopolymer particles in the Arctic Ocean implemented  Into the coupled ocean–sea ice–biogeochemistry model FESOM2.1–REcoM3 » by Zeising and colleagues presents new developments within the coupled physics-biogeochemistry model FESOM-REcoM allowing the simulation of PCHO and TEP, which are essential molecules produced by phytoplankton that have an increasingly recognized role in ocean particle dynamics and aerosol formation. This model is currently parametrized for Arctic ecosystems, but the authors provide a short global picture of TEP and PCHO.

This article is overall well written and the model evaluation is quite comprehensive and complete. The topic of the study is timely and the model developments presented here represent a promising avenue of research.

I have one major comment regarding the presentation of model results and more minor comments regarding model evaluation and the presentation of results.

Major comment :

The lack of a control simulation without PCHO and TEP production makes it difficult to assess the impacts of these tracers on ocean biogeochemistry.

If I understand correctly, the modeled PCHO is produced from phytoplankton exudation. Phytplankton exudation gives both DOC and PCHO. Is the total exudation (DOC+PCHO) different in this version of the model than in previous versions without PCHO? If yes: then I think the current model should be compared to a control simulation without PCHO exudation. If not, then maybe the model has already been evaluated previously and Chla should be the same as in previous versions? Then, I think model evaluation could be limited to PCHO and TEP data.

When evaluating model performances based on Chla concentrations (in sections 3.1 and 4.1) , the model should be compared to satellite and to a control version.

In the results and discussion, the climatology of Chla is mentioned several times, I think that comparison of the climatology of Chla with satellite climatology would be strengthen your arguments.

Minor comments :

Intro lines 32-40: I am missing a little bit of numbers.

Maybe give some average concentrations of TEP measured? E.g. “remote marine regions, particularly the Arctic, organic compounds emitted from the upper ocean can serve as an important source of particles, thereby influencing the cloud feedback mechanisms and the  verall radiation budget (Hamacher-Barth et al., 2016; Goosse et al., 2018; Hartmann et al., 2020; Ickes et al., 2020).” Is there an estimate of the flux or the proportion of organic compounds in the Arctic aerosols?

You mention the PASCAL campaign several times, I think adding the location of the measurements on one of your maps would be good (e.g. On figure 1 or 4).

Paragraph lines 125-131: maybe add a simple schematics of the PCHO and TEP model?

Line 345 : you show the results of your simulations only for 0-30m, what do TEP and PCHO concentrations look like below ? Do they fall at 0 ?

Line 355 : you remind in this sentence that the model is optimized for the Arctic region, but also show global results. What are the implication of the Arctic parametrization on your global results ?

Line 515 : « TEP aids in the aggregation of other particles (the TEP dependency of the aggregation rate, Eq. 7), but is not itself transferred in the process » even though TEP itself is not sinking, does it have an effect on particles sinking and subsequent C export in your model ? Since this is a potential strong implication of this work, I would like to see it discussed. Again, a comparison with a simulation without TEP would strengthen the demonstration.