We would like to thank the reviewers and editor for the valuable comments and suggestions. We have taken into consideration both questions and specific review concerns. The questions were answered below each reviewer's comment. Considering RC1 specific comments we followed all the reviewer's advice. To address them changes were made throughout the text.

RC1

The project is well designed and has produced some interesting results along with a well-written manuscript to accompany it. The project has identified a novel proxy for quantifying rates of carbonate dissolution with valid methods clearly outlined. Results are clearly displayed in figures and tables with strong explanations of the proxy application as well as cautions.

Questions for authors to address if they feel it would add to the story:

It would be helpful to hear whether these were the results expected by the authors.

Authors response: The expected dissolution pattern results (mean ks) were described in lines 216-220. However, to complement this topic, additional remarks regarding the expected results regarding dissolution primarily affecting the morphology of coccoliths were added between lines 403 and 405. The relationship between bottom water carbonate chemistry/dissolution and coccolith morphology is as what we expected. Before carrying out the RDA, we thought the surface processes’ impacts could be larger, but the results indicated that coccolithophore growth in the surface ocean only plays a limited role in coccolith thickness on a basin scale.

The abstract mentions that degree of dissolution and size-selective dissolution is influenced by assemblage composition but this is not fully addressed in the text.

Authors response: We complement the paragraph between lines 386 and 389 highlighting the role of assemblage composition on the degree of dissolution according to the large geographical variability influencing the coccolithophore calcite production during its life cycle.





Could elaborate on species/assemblage influence – fragility due to size, crystal composition etc. this is left rather vague.

Authors response: We did not carry out any dissolution experiments on the species’ influence. We only evaluated the role of the assemblage composition, as testing the effect of crystal composition with requires additional analyses and instrumentation that was beyond the original goal of this study.  But we believe that the species/assemblage difference could be mainly caused by the fragility difference between G. oceanica and E. huxleyi. We made this hypothesis clear in lines 174., 305, and 347. The downcore assemblage differs from the surface sediment samples in their higher proportion of the thicker coccolithophore species G. caribbeannica,  compared to the thinner G. oceanicaand E. huxleyi.

How might this measurement influence global records of coccoliths?

Authors response: Mean ks combined with σ/ks vs. ks can be applied to global records since this new index considers the different compositions of assemblages according to geographical variability. We suggest the principle rule described in our work should be universal in other basins. However, caution still should be kept in mind. For example, the assemblage measured in this work was mainly composed by E huxleyi and G oceanica. How the ks and σ/ks behave in coccolithophore assemblages characterized composed by different species (today or in the past) should be tested. Moreover, should we use a mono-species morphology parameter, or we can mix all coccoliths even from different family? These should be done in the future works in the next few years.

Specific comments by line:

Authors response: All the following suggestions have been accepted, or replied to if a longer explanation was needed.

11 – critical to elucidating

14 – complex not complexity

15 – during an organism’s life cycle

21 – samples from the South China Sea

22 – surface sediments were

24 – statistical analysis indicates that

39 – ocean CO₂ is influenced (atmospheric CO₂ = pCO₂)

42-43 – concentration, and carbonate

56 – variations in the ocean carbon

65-66 – provides a quantitative

73 – called coccoliths. Coccoliths

74 – up to 80 % of deep-sea

75 – changes in coccolith morphology are believed

89 – there has been no study

96 – between coccolithophore biometry

97 – building on these results

99 – it has also been demonstrated

104 – studies that systematically explore the drivers

 121 – by shallow passages to the north and south

122 – water exchange between

125 – East Asian Monsoon (EAM; Wang and Li, 2009)

148-149 – relatively low DIC and TALK and high pH

 169 – add reference for smear slide preparation technique

170 – dissolution experiments using

171 – obtained from a Late Pleistocene

173 – what is the thinner species that is being referred to?

Authors response: We added in the text “compared to the thinner species (e.g. E. huxleyi)”

175 – suspension was separated into

176 – each with a volume

177 – has traditionally been used

198 – parameters of coccoliths in the

209 – calculated using the formula by Young

210 – obtained from C-Calcita

229 – coccolithophorid is observed in

 306-307 – between several coccolith morphological parameters and bottom

360-361 – rephrase

Authors response: We fixed a typo in the sentence. Now it reads “Second, changes in the σ/ks ratio in the dissolution experiment reflect a slight and gradual increase in dissolution and then a decrease with the highest concentrations of Calgon® (Fig. 2C).”

427-428 – deep ocean deposits with lower sedimentary

442 – coccolith dissolution in different

444 – ks of coccolith is a more

465 – variation of coccoliths be employed

470 – to trace evolutionary trends

488 – focusing on coccolithophore evolutionary histories

493 – increase in dissolution

494 – interpreted as dissolution

 514 – more prone to dissolution (without “suffer”)

Continuity:

Vs or vs.? Should it not be versus/vs ?

Authors response: We chose to use vs. and changed it throughout the text.

Sea floor or sea-floor?

Authors response: We chose seafloor and changed it throughout the text.

We want to thank the reviewer for their valuable comments and suggestions. We have considered them and made modifications to the manuscript to improve it. To address the reviewers’ specific comments changes were made throughout the text. Specific questions were answered detailed below the reviewer’s comment.

RC2

General comments:

In this manuscript, Gerotto et al. make use of dissolution lab experiments and sediment samples for develop a proxy for the reconstruction of past carbonate dissolution dynamics. For do that, they compare morphological measurements of coccoliths came either from modern surface sediments along basin-scale environmental vertical gradients as those resulting from dissolution experiments using sediment samples taken elsewhere on the Pacific. The thematic thread conveys the reader naturally to the theme under study. The Theoretical background is comprehensive but concisely enough to give support to the discussion. The methods are described in-depth and are suitable for addressing the aim of the study. The Results are properly weighted into a well-structured Discussion. They properly recognize in M&M and Discussion that the sensitivity resulted from dissolution experiments and modern samples cannot be compared directly, as well as, has critically described the effects of Calgon^® solution in carbonate particles. Therefore, after minor reviews posted below are addressed, I find this manuscript is suitable for publication in Egusphere.

Specific comments:

Title – Much more straightforward if it includes that a new proxy was developed

Authors response: To address this comment, we have modified the manuscript title to “Fossil coccolith morphological attributes as a new proxy for deep ocean carbonate chemistry”.

Figure 1 –Include a larger inset map; In captions remove source of the data and direct the reader to M&M

Authors response: We have modified the figure and caption.

- In the RDA model it’s appear to be redundant variables (ex. the TA-Sal, pH-pCO2 and N-P pairs of variables are expected to be strongly autocorrelated as Fig. 5a actually shows) that might be introducing statistical noise and eventually reducing % of explained variance and/or impeding a more direct evaluation of mayor environmental drivers on coccolith morphology. If you think it could be the case, apply a test for identify redundant variables (ex. varclus procedure in RStudio) and redo the RDA analysis including only non-redundant variables.

Authors response: We performed a correlation test at the beginning of the statistical analysis between temperature, salinity, phosphate, nitrate, silicate, alkalinity, dissolved inorganic carbon (TCO₂), pH, fugacity of CO2 (FCO₂), partial pressure of CO₂ (pCO₂), HCO₃, CO₃, CO₂, Total Boron, OH, revelle factor, chlorophyll-a concentration, photosynthetic active radiation, and omega calcite in the bottom. We removed some of these variables due to autocorrelation. We chose to keep some autocorrelated variables as they strongly influence coccolith morphology during the life-cycle (Chen et al., 2007; Jin et al., 2016).

- Mention in the discussion the environmental data used was not obtained in-situ but from climatologies including interpolations, etc.

Authors response: We carefully described the feature of data in the method section. We  now specify at the end of line 228 and referring to the environmental data “ were extracted from different databases, interpolated to the geographical location of the surface sediment samples.”

- It’s possible to evaluate how well your proxy predict bottom omega calcite using an independent dataset?

Authors response: Unfortunately there are not independent datasets using the same morphological parameters in coccoliths (ks) with the same method (circular polarization and C-Calcita) in modern samples which could be used to validate our proxy. We should keep in mind that this proxy would not work in samples located along small gradients of deep water carbon chemistry, well above the lysocline, as it is mentioned in section 5.2. In addition, there are other potential drivers of coccolith dissolution (and variation of morphological parameters) such as changes in the DIC as the result of organic matter respiration at the seafloor, so the application of this parameter to another dataset can not be done without considering these other factors.

107 - Remove (n = 28) from the Introduction

Authors response: Changed.

360 – It’s seemed a word as “caused” is missing

Authors response: ‘Caused’ has been added.

451 - Replace “environmental conditions” by “nutrients conditions”

Authors response: Changed.

465 – 466 elaborate better the question “…to trace their evolution safely, or instead be a good…”

Authors response: We changed the text to “can the morphological variation of coccoliths be employed to trace their evolution safely, or instead be a good proxy for carbonate preservation?”

476-479 – Elaborate better the end of this paragraph  

Authors response: We found there was a typo in the original manuscript and that is why it was not clear. Now the end of this paragraph reads as follows “with strong selective pressure from CO₂ declines as a potential mechanism.”

520 – Maybe “complementarity” could be more precise than “complexity”

Authors response: We changed to “complexity”.

We would like to thank the reviewer’s valuable comments and suggestions. We have taken into consideration both specific comments and technical corrections. To address them changes were made throughout the text. Some specific comments were answered detailed below the reviewer’s comment.

RC3

In this manuscript, the authors deepen on the issue of how the dissolution affects the coccolith morphology and calcification by using both targeted lab experiments and sediment-core sample from a natural setting. The experimental approach, as well as the statistical treatment of the data is accurate and well developed. This work brings out interesting results and useful insights for reflection when it comes to evaluate the role of coccolithophore within the carbonate production, as well as to use the fossil assemblages in reconstructing past evolution and/or oceanographic conditions. The outcomes are well displayed and robustly discussed in the manuscript. Although, I report below some specific comments to be addressed by the authors, and some technical corrections that need to be fixed in the text.

Some specific comments:

- The title should reflect better the novelty of this research, by adding a reference to the new index suggested here.

Authors response: To address this comment, we have modified the manuscript title to “Fossil coccolith morphological attributes as a new proxy for deep ocean carbonate chemistry”.



- 487-490: To observe the evolutionary trends it is important to study long-time intervals (see Beaufort et al 2022à 2 Myr, Bolton et al 2016à 15 Myr). How long can be the time covered by the shallow sediment cores? I think it is better to state that it is necessary to pay attention to the bias that can be introduced by the dissolution when it comes to use the ks factor and/or thickness for evolutive studies.

Authors response: The age of core top samples are less than two thousand year based on the report of Sonne cruises  95 and following publications (e.g. Wang et al., 1999). So, the feature of coccoliths in the surface sediment is mainly controlled by dissolution  in deep ocean and ecology in surface ocean (minor role). What we have emphasized in the Section 5.3 is that, for studies focusing on evolutions of coccoliths, it’s better to carefully check the preservation of coccolith before treating ks as a result of evolution. That’s also one of the main conclusions of our work.

Ref. Wang et al., 1999, Geophysical Research Letters, Holocene variations in Asian monsoon moisture: A bidecadal sediment record from the South China Sea,



- Suggestion: maybe the authors could take into account to attribute a specific short name to the new dissolution index “ratio σ/ks vs. mean ks”. The advantages would be: i) to characterize better the index and make it more “recognizable” among the community; ii) to make the text easier to read.

Authors response: We attribute the "normalized ks index" short name to the dissolution index.



Technical corrections

Authors response: These technical corrections have been accepted unless it is specified.



- 14: complex

- 26: vs has to be written in italics

- 75: coccoliths morphology, distribution and abundances

- 144: “ODV” State the entire “Ocean Data View” when mentioning it for the first time



- 172-174: specify the relative abundance of G. caribbeanica, what are the other “thinner” species anf their abundance.

Authors response: The Noelaerhabdaceae family coccoliths in the sample ODP 807 is composed by 41% G. oceanica (>4 μm), 34% G. caribbeanica (~3-4 μm) and 23% Gephyrocapsa <3μm. We add the percentages to the text and specify the thinner species found in the SCS in line 173: “The Noelaerhabdaceae family coccoliths in the sample ODP 807 is composed by 41% G. oceanica (>4 μm), 34% G. caribbeanica (~3-4 μm) and 23% Gephyrocapsa (<3 μm). Compared to the thinner Noelaerhabdaceae species found in the SCS (e.g. E. huxleyi, <4  μm), G. caribbeanica has the highest abundance in this sample.”



- 236: erase “extracted variables”

- 279: (e.g. 17930)



- Figure 3: I would change the x axis with the depth, instead of using the site ID, which is more meaningful for the discussion of the data. In this way I would erase also the arrow pointing the increasing depth. Then, recall the table 1 in the caption.

Authors response: We chose to apply color coding to the bars using the same pattern as in the following figures. In this way, the depth and the sample code can be identified easily in the figure. We also removed the arrow pointing to the increasing depth.



- 271: I would change the title of this section linking this more to the results, as it is it is more related to a discussion section connecting the morphological data directly with the environmental factors. Change with something more like “Morphological changes in natural conditions”

Authors response: We changed the 4.2 section title to “Variations in coccolith morphology in natural conditions”.



- 287: be consistent when using “versus” along the entire text. I suggest to always use vs.

Authors response: We chose to use vs. and changed it throughout the text.



- 338: Change with “comparison”

Authors response: Changed.



- 376: species differenceà probably meaning “assemblage composition”? Please be more specific.

Authors response: We changed to assemblage composition.



- 383-384: change “coccolith” with assemblages

Authors response: Changed.



- 391: I would not use the “life-cycle” in the section title as it is not discussed in depth, but just briefly mentioned. Please change the section title according to the main point presented in section 5.2.

Authors response: We have modified the section title to “Sedimentary record of coccolith morphology: calcification vs. dissolution factors”



- 411 and 435: ECSà state the acronym when mentioned for the first time, but I guess that the authors meant SCS.

Authors response: The acronym refers to the East China Sea. The full mention was included in line 411 when first mentioned.