the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Responses of fossil coccolith morphology to preservation conditions in the deep ocean
- 1Oceanographic Institute, University of São Paulo, São Paulo, Brazil
- 2Geological Institute, ETH Zurich, Zurich, Switzerland
- 3Center for Marine Studies, Federal University of Paraná, Pontal do Paraná, Brazil
- 4State Key Laboratory of Marine Geology, Tongji University, Shanghai, China
- 1Oceanographic Institute, University of São Paulo, São Paulo, Brazil
- 2Geological Institute, ETH Zurich, Zurich, Switzerland
- 3Center for Marine Studies, Federal University of Paraná, Pontal do Paraná, Brazil
- 4State Key Laboratory of Marine Geology, Tongji University, Shanghai, China
Abstract. Understanding the variations in past ocean carbonate chemistry is critical in elucidating the role of the oceans in balancing the global carbon cycle. The fossil shells from marine calcifiers present in the sedimentary record are widely applied as past ocean carbon cycle proxies. However, the interpretation of these records can be challenging due to the complexity physiological and ecological response to the carbonate system during organisms' life cycle, as well as the potential for preservation at the sea-floor. Here we present a new dissolution proxy based on the morphological attributes of coccolithophores from the Noëlaerhabdaceae family (Emiliania huxleyi and Gephyrocapsa spp., > 2 µm). To evaluate the influences of coccolithophore calcification and coccolith preservation on fossil morphology, we measured morphological attributes, mass, length, thickness, and shape factor (ks), of coccoliths in a laboratory dissolution experiment and surface sediment samples in the South China Sea. The coccolith morphological data in surface sediment were also analyzed with environment settings, namely surface temperature, nutrients, pH, chlorophyll-a concentration, and carbonate saturation of bottom water by a redundancy analysis. Statistical analysis indicate that carbonate saturation of the deep ocean explains the highest proportion of variation in the morphological data instead of the environmental variables of the surface ocean. Moreover, the dissolution trajectory in the ks vs length of coccoliths is comparable between natural samples and laboratory dissolution experiments, emphasizing the importance of carbonate saturation on fossil coccolith morphology. However, the mean ks alone cannot fully explain all variations observed in our work. We propose that the mean ks and standard deviation of ks (σ) over the mean ks (σ/ks) could reflect different degrees of dissolution and size-selective dissolution, influenced by the assemblage composition. By applying together with the σ/ks ratio, the ks factor of fossil coccoliths in deep ocean sediments could be a potential proxy for a quantitative reconstruction of past carbonate dissolution dynamics.
Amanda Gerotto et al.
Status: final response (author comments only)
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RC1: 'Comment on egusphere-2022-1329', Anonymous Referee #1, 23 Jan 2023
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.
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.
Could elaborate on species/assemblage influence – fragility due to size, crystal composition etc. this is left rather vague.
How might this measurement influence global records of coccoliths?
Specific comments by line:
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, 20009)
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?
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
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 ?
Sea floor or sea-floor?
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RC2: 'Comment on egusphere-2022-1329', Anonymous Referee #2, 24 Jan 2023
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
Figure 1 – Include a larger inset map; In captions remove source of the data and direct the reader to M&M
- 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.
- Mention in the discussion the environmental data used was not obtained in-situ but from climatologies including interpolations, etc.
- It’s possible to evaluate how well your proxy predict bottom omega calcite using an independent dataset?
107 - Remove (n = 28) from the Introduction
360 – It’s seemed a word as “caused” is missing
451 - Replace “environmental conditions” by “nutrients conditions”
465 – 466 elaborate better the question “…to trace their evolution safely, or instead be a good…”
476-479 – Elaborate better the end of this paragraph
520 – Maybe “complementarity” could be more precise than “complexity”
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RC3: 'Comment on egusphere-2022-1329', Anonymous Referee #3, 24 Jan 2023
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.
- 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.
- 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.
Technical corrections
- 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.
- 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.
- 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”
- 287: be consistent when using “versus” along the entire text. I suggest to always use vs.
- 338: Change with “comparison”
- 376: species differenceà probably meaning “assemblage composition”? Please be more specific.
- 383-384: change “coccolith” with assemblages
- 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.
- 411 and 435: ECSà state the acronym when mentioned for the first time, but I guess that the authors meant SCS.
Amanda Gerotto et al.
Data sets
Morphological measurements of coccoliths from surface samples of South China Sea Gerotto, A., Zhang, H., Nagai, R. H., Stoll, H. M., Figueira, R. C. L., Chuanlian, L., Hernández-Almeida, I https://doi.org/10.5281/zenodo.7271441
Amanda Gerotto et al.
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