Seawater pH reconstruction using boron isotopes in multiple planktonic foraminifera species with different depth habitats and their potential to constrain pH and <i>p</i>CO<sub>2</sub> gradients

Guillermic, Maxence; Misra, Sambuddha; Eagle, Robert; Villa, Alexandra; Chang, Fengming; Tripati, Aradhna

doi:https://doi.org/10.5194/bg-17-3487-2020

Articles | Volume 17, issue 13

https://doi.org/10.5194/bg-17-3487-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/bg-17-3487-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 17, issue 13

Research article

|

08 Jul 2020

Research article |

| 08 Jul 2020

Seawater pH reconstruction using boron isotopes in multiple planktonic foraminifera species with different depth habitats and their potential to constrain pH and pCO₂ gradients

Maxence Guillermic, Sambuddha Misra, Robert Eagle, Alexandra Villa, Fengming Chang, and Aradhna Tripati

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Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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SC1: 'Comment on "Seawater pH reconstruction using boron isotopes in multiple planktonic foraminifera species with different depth habitats and their potential to constrain pH and pCO2 gradients" by Guillermic et al.', Michael Henehan, 26 Aug 2019
- AC2: 'Response to SC1 – Michael Henehan', Maxence Guillermic, 23 Oct 2019
RC1: 'Review of “Seawater pH reconstruction using boron isotopes in multiple planktonic foraminifera species with different depth habitats and their potential to constrain pH and pCO2 gradients” by Guillermic et al., submitted to Biogeosciences, by Jesse Fa', Jesse Farmer, 09 Sep 2019
- AC1: 'Response to RC1 – Jesse Farmer', Maxence Guillermic, 23 Oct 2019
RC2: 'Review', Anonymous Referee #2, 13 Sep 2019
- AC3: 'Response to RC2', Maxence Guillermic, 23 Oct 2019

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

ED: Reconsider after major revisions (28 Oct 2019) by Markus Kienast

AR by Maxence Guillermic on behalf of the Authors (12 Nov 2019) Author's response

ED: Referee Nomination & Report Request started (16 Nov 2019) by Markus Kienast

RR by Jesse Farmer (02 Dec 2019)

Suggestions for revision or reasons for rejection

Revision review by Jesse Farmer

Guillermic et al. have made great progress in revising their manuscript. The introduction, background, materials and methods and results are publishable with very minor revisions. However, the manuscript loses focus and cohesiveness in the discussion, where the text becomes quite difficult to read and understand in its current iteration. I do note that, to my reading, this is an issue only with the writing presentation; the technical aspects of the discussion are sound and the figures are generally excellent and supportive of the text. Still, unfortunately I cannot yet recommend this for publication until the discussion text is improved. I encourage the coauthors to churn through a few rounds of revision to the discussion, with a particular focus on English grammar, and have provided detailed comments below that hopefully aid their work. I look forward to approving the revised manuscript for publication.

L84. Change to “samples from sites that are currently in quasi-equilibrium with the atmosphere” (less ambiguous)

L125-127. Suggest change to “Furthermore, d11B differences between foraminifera species inhabiting waters of the same pH makes the acquisition of more coretop and culture data essential for applications of the d11B-pH proxy.”

L149. State here which fractionation value you use in this study, e.g., “We use the fractionation of 27.2 ‰ from Klochko et al. (2006) in this study.”

L176-177. Be a little more specific here, e.g., “The extent to which these results apply to the planktonic foraminifera studied here are not known. Nonetheless, pH modulation of the calcifying fluid may influence the d11B of planktonic foraminifera.”

Section 2.5. Please clarify- To what extent are these depth and habitat preferences global? Do foraminifera can show regional deviations in their depth & habitat preferences? Do we know? Many of the referenced studies of foraminifera habitats focus on the tropical/subtropical Atlantic.

L232. Change “drilled” to ”recovered” or “cored”. It is only appropriate to say “drilled” when a drilling system was used for core recovery (as is the case for ODP/IODP)

L255. Good points on the response to my comment; please incorporate your response into a sentence in the manuscript here.

L266. Typo, should read “3.5”

L269. Change to “70 uL of carbonate sample dissolved in 1N HCl was loaded...”. This gets around the ambiguity of acid used in my above comment on L256-257.

L289. Remove “internal”

L291. Change “boron isotopes liquid standard” to “boric acid standard”

L303. Again on the 1N HCl dissolution from L256-257. If I follow your protocol, you have a foram aliquot dissolved in 1N HCl, to which you have added HNO3 and HF for the ICP-MS measurement. Was HCl added to the standards to properly matrix-match? Or was the volume of HCl sufficiently small that you ignored it? Please specify.

L339. Suggest “during their growth” in lieu of “along their ontogeny”

L339-341. Are these uncertainties truly representative of foram depth migration during their lifespan, or are they more indicative of uncertainty in different measurements of foram depth habitats? Please specify.

Section 4.1. This is a fair response to my comment; please incorporate this response into the text by adding a paragraph in Section 3.8. It is certainly fine to use a best guess and reasoned approach to derive CDs, as long as the reader is aware of your approach. (Note- it might also help to mock up a figure showing the data in Tables S6 and S7).

Section 4.2
To what extent are your foraminifera samples and those from the literature in Fig. 5 from different size fractions? If so, given the noted d11B differences between size fractions, is it worth regressing against literature data from different size fractions? How much of the “large uncertainty given variability in the data” (L399) might reflect size class differences? Please address in the text.

Also, suggest changing “ fall (above/below) the 1:1 line” to “exhibit (higher/lower) d11B compared to expected d11B_borate at their collection location” throughout the text. It is less confusing and more precise. (see L396, 400)

Section 4.2.1 G. ruber. This section is confusing as currently written. Some rephrasing ideas:
• L383: Rephrase to “However, our two datapoints from d11B_borate < 19 ‰ are lower compared to previous studies.” “Lighter d11B” is not correct; use either “lighter B isotopic composition” or “lower d11B”.
• L383-384: Regarding the comment from M. Henehan and response, are your samples from different size fractions than
• L384-385: “Whilst...” Delete this unnecessary sentence.
• L385-386: “The positive offset from the 1:1 curve...” change to say elevated d11B foram values relative to d11B_borate
• If you want to discuss the properties of the calibration curves, you should state the curves in the text for the reader. You should say something like you do for T. sacculifer on L396-397: “Linear regression on our data alone yields a regression of ______. While this regression is not significantly different from a 1:1 line, the uncertainty terms are significant given limited data in our study. Therefore, our data are not inconsistent with the low sensitivity trend.... (append the rest of the paragraph as written)”.

L400. Remove “below the 1:1 line” as no data are significantly below this line.
“close to” is fine. Can you indicate the WEP samples on this plot with a star or other indication?

L408-409. Rephrase to “, and is not significantly different from (p >0.05) the O. universa calibration previously reported by Henehan et al. (2016) (0.95 ± 0.17).”

L413. “For O. universa and all deep-dwelling species,”

L417. Change “may remain” to “remains”

L430. Typo T. sacculifer (sacc)

L432-433. What do you mean by interspecific B/Ca ratios? Please elaborate. I do not think it comes as any surprise that B/Ca ratios are different in different foraminifera species.

L441-444. Confusing. Please split into two sentences, with one about core site depth and one about calcification depth. Also please note that you see a weak decrease in B/Ca with increasing calcification depth, although it is significant (p<0.05).

L454. Typo (w/o sacc)

L487-488. Instead of saying seasonality is not important, rephrase to “seasonality is of relatively minor impact on the carbonate system parameters at the sites we examined.”

L499-503. Specify symbiont photosynthesis

L502-503. lower/lowest

L508-549. This is difficult to understand as written and needs revising, otherwise these points will be completely lost by the reader.

L508-513. Present items in logical order: First what you observe (low d11B of deep-dwelling species relative to d11B borate), then context (lower symbiont density and photosynthetic activity in these forams), and combine this into an interpretation (lower symbiont activity leads to lower microenvironment pH and may explain the low d11B of these taxa).

L513. “and” instead of “et”

L514 and throughout. Do not use “they” or any pronouns, as it is not clear to what you are referring. Use the noun itself. Here, “they” = “symbionts”

L518. Be specific. “A deeper depth habitat will reduce the light intensity the symbionts receive, and as a consequence may lower symbiont photosynthetic activity, possibly reducing pH in the microenvironment surrounding the foraminifera”.

L521. What does “basically support” mean? Either the trend supports the fact or it does not.

L524. Start a new paragraph here. “To test if the d11B signature was inferred to a light driven”- what does this mean?

L524-525. change to “we have independently calculated foraminifera (calcification?) dpeth based on various light insolation culture experiments and the microenvironment ∆pH derived from our data”.

L535. Change to Microenvironment ∆pH

L537-541. Please rephrase these sentences. I think this may be a key point, but I cannot follow it as currently written.

L542. Change to “G. menardii and G. tumida are similar...”

L547-549. Need to add some commas here to make this understandable.

L555-557. “more borate ion may be incorporated.... more boric acid may be incorporated.” This is just a hypothesis.

L560-572. Again, this is difficult to read as currently written. Please revise and particularly correct English grammar.

L582. Change to “which supports previous paleo-reconstructions using existing calibrations of d11B_carbonate to d11B_borate”.

L583. Which observations are these from Henehan et al. (2016)? Be specific.

L590-592. Please rephrase and be much much more specific, I have no idea what you are trying to say here. What do you mean “add a weight/shell”? Is 11 µg per shell small or large? Context needed!

L594. What correction? What coretop study?

L597. Typo on species

References. Please double check these and their formatting. Some citations missing and formatting issues.

Figures.
Fig. 2. Change figure and caption to B(OH)3 and B(OH)4- to match main text. Note typo on Figure α, should be 1.0272.

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RR by Anonymous Referee #2 (02 Dec 2019)

Suggestions for revision or reasons for rejection

This is my second review of this MS. As it stands, the edits are generally ok, but in some cases the authors chose to only reply to edits in the response and not always insert their response into the MS. Sometimes this was ok, but if a reviewer requests an explanation, the response should generally be incorporated into the manuscript. Reviewer 1 should also review the edits as some of Dr. Farmer's suggestions were also not implemented into the revised MS. I have specific comments below. The new section on symbiosis and the findings of Tagaki was very poorly written and should be edited prior to final publication.

As an aside: please do not assume that anonymous reviewers are CIS gendered males. The opening response to my review was “We wish to thank this reviewer for HIS thorough review of our manuscript and HIS helpful comments”. Instead: We thank the reviewer for helpful comments and suggestions.

There is no evidence that foraminifers change their symbiont assemblages to ones more similar to what are found in deeper dwelling species. In addition, the paragraph beginning on line 195 where differences in the boron isotope data between T. sacculifer, G. ruber, and O. universa is explored states that O. universa exhibits lower d11B because it lives deeper in the water column, but the depth habitats chosen for these species IN THIS STUDY overlap or are at the same depth according to table S7.

Line 176: Change: “We acknowledge this is speculative as it is based upon benthic foraminifer experiments” to “We acknowledge this process may not be the same for planktic species as these findings were based upon benthic foraminifer experiments”

Section 3.3: the reviewers responded to my comment but did not add any additional text to the MS. The reason the full reductive cleaning protocol was used should be included in this paragraph so that other readers are aware of the study by Misra 2014 and the purpose of the full cleaning protocol.

Line 339: I suggest removing the clause “As foraminifera can migrate in the water column along their ontogeny” because it is misleading. Foraminifers can occupy a deeper depth habitat at the end of their ontogeny, but as written it still seems to imply that foraminifers migrate up and down, which they likely do not. Removing this clause bears no impact on the rest of the sentence.

Line 456: Again: I think this should be more carefully written. The use of the word “migrate” with foraminifer depth habitats usually implies that they move up and down in the water column, which they do not. This should be reworded to state that at the end of their life cycle they often transition to deeper waters prior to gametogenesis.

Line 495: G. ruber, T. sacculifer and O. universa do not have chrysophyte algal symbionts, only dinoflagellates. There is no mention of chrysophytes in the Anderson and Be paper nor in Spero 1987. N. dutertrei has pelagophyte symbionts not chrysophytes, confirmed using genetics, see Bird et al., 2018.

Paragraph beginning line 500 is poorly worded.
Line 509: have microenvironments with lower “pH” than ambient seawater (insert pH)
Line 513: ‘et’?

Line 514: insert ‘a’ between also and function.
Line 515: Should “for the purpose of this study” be a new sentence?
Line 537: Tagazaki should be Tagaki.
Line 540: specie is spelled incorrectly

Paragraph beginning on line 540: O. universa in this study occupy similar depths to the G. ruber and G. sacculifer. Thus, I do not agree with the discussion here.

Section 5.4 is very confusing. It seems haphazardly put together and some sentences are poorly structured.

Paragraph 580 could be deleted.

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RR by Michael Henehan (20 Dec 2019)

Suggestions for revision or reasons for rejection

Review Guillermic et al.

The manuscript is greatly improved from its previous incarnation. Although it is for the previous reviewers to judge whether their comments are adequately dealt with, my sense is that they seem to be largely adequately discussed.

I am personally still a bit unconvinced in the point of plotting a calibration line through data that come from different size fractions for G. ruber and T. sacculifer, when there is clearly a known size fraction effect which is muddling the pH (/borate) signal and potentially influencing the slope. I guess particularly also in this study using such wide size fractions (perhaps by necessity due to sample limitations) means that there is always the possibility that the size distribution could have varied within this range and introduced inter-site differences that change the slope. The authors now provide some shell weight data to inform a little as to the possibility of there being inter-site differences in the sampled shell size fraction – I presume because there are no photos of the samples to measure the actual size distribution. This is at least something, but just telling us that the average shell weight varied is only of limited use- why not give us this data in the tables, so we can see if those boron samples that diverge most strongly from the existing calibration line of ruber/sacculifer were indeed on average the smallest test sizes? It would be helpful.

There are also still quite a few oddities in sentence structure, word choice, spelling/typos which I will outline below.

Otherwise, with these edits/additions, I have no objections the paper being published. Congratulations to the authors on some nice work.

Line 94: Anagnostou et al. (2016) also did this for core-top and Eocene samples.

Line 144: B(OH)3 and B(OH)4-, as used here, are the more common notations for these aqueous species.. I would favour using these. But then for whatever reason in Fig. 2 and its caption (but I think nowhere else?) you have called them H4B(OH)3 etc. I think you should be consistent so the unfamiliar reader can relate what you are talking about better. Why not stick to what you have here to be more consistent with the literature?

Line 157: as far as I am aware Noireaux et al 2015 did not look at taxonomic differences in forams- rather inorganic carbonate polymorphs. Either rephrase the sentence or delete the reference.

Line 196: within the parentheses, insert comma after the subscript borate, followed by ‘hereafter’

Line 204: Note that the culture slopes of T. sacculifer and O. universa are also within error of 1, when one propagates the error on each datapoint (which for universa in particular is rather large).

Line 273: I may be being ignorant, but I have never heard of H or X sample cones, only skimmer cones. Is this correct here?

Line 282: delete ‘the’ before 11B.

Lines 285, 293, possibly elsewhere: Inconsistent nomenclature of JCp-1 coral standard. How I just wrote it is the official notation.

Line 300: Subscript needed for 3 on nitric acid.

Line 329: ‘prerequisite’ would be a better word than ‘postulate’.

Line 331: apostrophe after the ‘s’ of species.

Line 426: typo in obliquiloculata.

Line 427: What do the authors mean by ‘This study supports interspecific B/Ca ratios’.. ? Rewrite.

Line 451: correct names are ‘Kemle-von Mücke and Oberhänsli’

Line 486: Is this statement really true? See Shaked and de Vargas (2008), doi:10.3354/meps325059

Line 517-518: Sentence poorly written. Not exactly sure what it is the authors want to say.

Line 532: missing s on species.

Line 537: ‘deep-dwelling species’ or ‘deeper-dwelling species’, not ‘deep dweller species’

Line 546: Joji Uchikawa, not Ushikawa.

Lines 550-551: Not sure it’s wise to pool all different size fractions like this- what does this truly tell you about pH?

Line 552: missing ‘and’ before ‘the observation’? Also ‘is’, not ‘are’.

Line 567-568: “the main interest with utilizing boron-based proxies relates to the…” poorly written sentence. “The main aim of utilizing” or “The primary applications of boron-based proxies are”?

Line 567-575: Odd paragraph separation, and first line of second paragraph in line 572 isn’t particularly self-contained. In line 574: ‘which is also supporting of’ should be ‘which supports’.

Lines 576-578: I would suggest that Chalk et al. (2017)’s accurate downcore data would suggest there isn’t necessarily need for a calibration from the same location or setting? Is it fair to make such a bold statement, and advocate for every downcore reconstruction from now on to have a calibration point from the same setting, based on your sacculifer data alone (that could in theory be different in some places just because the size distribution isn’t exactly the same in all sample sites)?

Lines 579-580: What correction do you mean? And why? Correction relative to what, the culture calibration?

Lines 580-582: I think you could explain this a little better here.

Line 583: what is meant by ‘our sample add a weight/shell’?

Line 584: Suggest “Greater divergence” rather than “The higher divergence”

Line 588: insert ‘isotope-pH’ after boron.

Line 592 (and elsewhere): in situ is not hyphenated.

Lines 592-594: This sentence could be rewritten to explain a bit more clearly what you did.

Line 600: ‘Sparsest’ seems an odd choice of word- implies not only that there is more scatter, but there is also not as much data. ‘most scattered’ might be better?

Line 606: ‘can impact’ rather than ‘impacts’, as for example your deep dwellers are not very affected.

Line 614: insert ‘similarly’ before respiration

Line 617: “those calibrations” – which calibrations are you referring to?

Line 618: ‘taxon-specific’, not ‘taxa-specific’, I would think here?

Figure 5: Include the size fraction in each ruber and sacculifer dataset’s legend entry, not just one.. and why are the ruber culture data not plotted?

Figure captions: In general the figure and table captions are a little spartan, and could be a bit more in-depth and informative. Examples, for instance:
Fig. 4 caption, ‘Pre-industrial data’ is vague.. hydrographic data (also ‘for the sites’, rather than ‘of the sites’)? Are these actual measurements or interpolations? What are the dotted lines? Why are the temperatures seasonally defined but nothing else?
Fig.5 caption: d11Bborate was, not were. Are the measurements from core-tops, tows, cultures, etc? Are these just the MC-ICPMS data, if so state, so it’s clear why there’s no NTIMS measurements in here? How are the error bars defined, are they one sigma or two?
Fig. 6: ‘plotted’, not ‘plot’.
Fig. 8: watch your superscripts. Does the light attenuation coefficient have a unit? State how the calcification depth marked by the grey band was derived.
Fig. 10: say a little bit more about what the ‘reconstructed’ values come from and how they were calculated.

Table 2: Is it necessary to have a column for the cleaning method when it's the same for every sample?

Quick question- Site A14 (to a lesser extent also FC-02a) has a really weird vertical pH gradient.. any idea what causes this?

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ED: Reconsider after major revisions (20 Jan 2020) by Markus Kienast

AR by Maxence Guillermic on behalf of the Authors (09 Mar 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (20 Mar 2020) by Markus Kienast

RR by Jesse Farmer (25 Mar 2020)

Suggestions for revision or reasons for rejection

Review of Guillermic et al., “Seawater pH reconstruction using boron isotopes in multiple planktonic foraminifera species with different depth habitats and their potential to constrain pH and pCO2 gradients”, revised for Biogeosciences, by Jesse Farmer

This is now my nth review of the manuscript by Guillermic and colleagues, and I am pleased to report that the authors have made excellent progress in both the text and figure presentation. At this point, while I still have a laundry list of recommended changes, specifications and clarifications, I am comfortable with publication of this manuscript in principle. Nice work.

General comments:
I strongly recommend that the authors address the following issues to improve readability and precision of the manuscript. Note particularly three items:
1. Terms such as CD1 and d11B must be defined at their first use.
2. The readability of this manuscript suffers from a lack of specificity in multiple places. Pronouns and vague descriptions should be removed and replaced with specific terms at every possible instance.
3. Responses to previous reviewer comments are often in the location of the comment, and not the location in the text where the response would be most helpful to the reader. As a result, there is unnecessary overlap between Materials and Methods, Results, and Discussion that should be cleaned up for clarity.

Specific comments:

Title
A bit bulky; what about cutting the end and making this “Seawater pH reconstruction using boron isotopes in multiple planktonic foraminifera species with different depth habitats”?

Introduction
L71. Change “utilizing” to “using”.
L74. Insert “available”: “one of the more robust available tools”.
L76. Change “ambient” to “solution”
L72 and thereafter: You need to define terms at their first use. For example, on L73 “the boron isotopic composition (expressed as d11B)…”
Related comment on L137-140: Here you define d11B in Equation 1. However, by this point you have already used d11B in the text without the definition. You should address this by either:
1. Move the equation and text on L137-140 up to L72, so that all instances of d11B occur after this equation. Or,
2. Keep the text and equation in place, use “boron isotope ratio” instead of d11B for all instances in the Introduction, and then use d11B after L140.

L84-86. You have not defined d11B_carbonate yet, and either way it is not specific enough for this sentence. Rephrase to “Values of pCO2 reconstructed from planktonic foraminifera d11B are indistinguishable…”

L87. Remove “therefore”; this does not logically follow the previous statement.
L90-91. Delete “in a few studies”.
L96. Suggest rephrase to “Here we add to the emerging pool of boron isotope data in planktonic foraminifera…”
L99. Add “analysis method for small samples (down to ~250 µg…)”
L100-101. End sentence at “planktonic foraminifera”. Start new sentence with “The studied sediment core-tops span a range…”.
L120. Important addition: “using d11B data from multiple taxa”. “Data” by itself is not specific and should be avoided without context.
L144. Add “NIST SRM 951 boric acid standard”
L149-150. Hopefully the third time on this terminology is a charm…. Fractionation factors are not in per mil units. Either change the text to “fractionation” or change “27.2‰” to “1.0272” to make this statement correct.
L178. Change “foraminiferal” to “foraminifera”
L184. Change “it” to “microenvironment pH”. Please avoid using pronouns.
L189. “but also depends on”
L228-229. Since you have not yet outlined the approach used in this study, you may wish to save this sentence for the discussion. Or else, add “as described below”.

Materials & Methods
L252. “, and from…”
L255 “dutertrei, and Pulleniatina…”
L258. How was the clay removed? Methanol? MQ water? Ultrasonication? Please add some brief details.
L261-262. Using reductive cleaning because the sites were not studied before is not a sufficient justification for using reductive cleaning. Please state why you used the reductive cleaning. Were you concerned about high Mn/Fe levels? Was this following typical laboratory protocols? (in which case, include reference). I agree with the authors that reductive cleaning should not make a huge difference for B, but it does for Mg (and hence your CDs), and so it needs justification.

L264-266. This is out of place as you have not yet defined or discussed CDs, and so this is very confusing to the reader. The answers to reviewers’ queries must be in the appropriate section. Please move this text to either Section 3.8 or Section 5.1.1.

L268-269. Matrix effects should not be addressed in the sample cleaning section. Again, the response to the reviewer comment is out of place. Please move to an appropriate text location.
L294-295. Change to “165 mV ± 5 mV, which closely matched…”
L297. Change to “and contributed less than….” (remove unnecessary parentheses)
L306. Call this NEP coral, as it is not a standard.
L307-308. Note either missing or extra parentheses.
L310-311. Also note the JCp-1 values published by Farmer et al. (2016) Chemical Geology here.
L317-138. For clarity, please make a different sentence; e.g., “Levels of remaining HCl in these diluted samples were negligible and did not contribute to matrix effects”.
L329-331. Are these uncertainties ± 2SD or the absolute 2SD range? For example, is it ±7 µmol/mol for B/Ca 2SD, or 7 µmol/mol B/Ca 2SD (±3.5 µmol/mol)? Please specify.
L336. Again, how was clay removed? If the same procedure was followed as for B analyses, please say so.
L338-339. Again, are uncertainties ± or absolute ranges?
L342-349. Please define your methods as CD1, CD2, and CD3 in the text. For example, “The first method (CD1) utilizes d18O measurements of the carbonate…”

L353-357. This approach is not clear, please rephrase. What is “that one”? What did you do if literature values were not available? How do you deal with reductive cleaning lowering Mg/Ca here?
L369. World Ocean Database (capital first letters).

L371-372. “Uncertainty… was similar to the one” I am confused, please rephrase. What one? Do you mean to say “Uncertainty… was similar to uncertainty calculated by…”?
L377. What is k? Please state/clarify for the reader.

Results.
L382-392. I still would like to see a small figure or a table in the main text with the calcification depths. But perhaps other reviewers feel differently.
L389. What are “both approaches”? Be specific.
L393-394. Which two calcification depth determination methods? You have three…
L403. Change to “where G. ruber shells”. Greater specificity would make this far easier to read.
L412. “by the high photosynthetic activity”…. Of what? Presumably of G. ruber symbionts? Please specify.
L414-417. Rephrase. “the uncertainty is significant given limited data in our study, and given this large uncertainty, our sensitivity of d11B_carbonate to d11B_borate is also consistent with the low sensitivity rend of culture experiments from…”
L419. Missing a closing parentheses
L423-426. This response to a reviewer comment should be included in the discussion. Here you should only present results, and you should not discuss why your data may (or may not) be different.
L437. Change to “When regressing data from the 250-400 µm size fraction, ...”
L449. “the points are in good agreement” what does that mean? What are points? Be specific.
L455-457. This statement is an interpretation of results and should be moved to the discussion.

Discussion
L511-512. This wording is awkward to me. I am not sure it is that “seasonality can have a major impact on hydrographic carbonate parameters”, as the authors state (Indeed, Gutjahr et al. (2018) argue otherwise). Instead, hydrographic parameters related to carbonate chemistry may change across seasons at a given water depth.

L541. “and in previous studies (reference list)”
L544. What do you mean by “mixed-dweller”? Do you mean “mixed-layer dwelling”? Please clarify.
L549. Comma use and grammar editing: “…photosynthetic activity, which may explain why P. obliquiloculata exhibited the lowest microenvironment pH as recorded by d11B.”
L563. Do you mean d11B? If ∆11B is correct here, please define what ∆11B means.
L573-577. This is still too confusing to be published as-is. How can a lower size fraction induce a change in photosynthetic activity? Do you not mean that a lower size fraction may have had lower photosynthetic activity and hence d11B?
Regardless, please change the final sentence to “Unfortunately, no weight per shell data were determined on foraminifera samples to constrain whether test size was significantly different across sites. Future studies could use shell weights to test these relationships.”

L583-584. Rephrasing: “which is supported by observation of a lower photosynthetic potential in O. universa than in T. sacculifer (Tagaki et al., 2019).”

L605-611. Add “In inorganic calcite, d11B_carboate and B/Ca have been shown to be sensitive….”. You must specify that these results are for inorganic calcite. Also, and I swear this is not personal bias, but Farmer et al. (2019) is missing from the references.

L644. Change “lighter” to “lower”
L651. “and coretop study will be determinant…”
L659-660. Which two approaches? Please specify.
L661-667. This section is difficult to follow as written; please reword.

Figure 1. To repeat myself once again, this figure is unnecessary and should be removed.
Figure 2. Change chemical formulae on figure to B(OH)3 and B(OH)4- for consistency with text.
Table 1. There is no such thing as a ∆14C age (unless you mean projection ages ala Adkins, and I doubt that you do). Please change to 14C. Also, some of these ages are in years, while others (Pacific Ocean) are in kyr. Please make consistent.
Table 2. You could make this table smaller by having separate uncertainty columns, and sharing one uncertainty column for d11B_C1 and d11B_C2 (as the uncertainties are exactly the same)

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ED: Publish subject to minor revisions (review by editor) (06 Apr 2020) by Markus Kienast

AR by Maxence Guillermic on behalf of the Authors (28 Apr 2020) Author's response Manuscript

ED: Publish as is (15 May 2020) by Markus Kienast

AR by Maxence Guillermic on behalf of the Authors (21 May 2020) Manuscript

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Boron isotope ratios (δ¹¹B) of foraminifera are a promising proxy for seawater pH and can be used to constrain pCO₂. In this study, we derived calibrations for new foraminiferal taxa which extend the application of the boron isotope proxy. We discuss the origin of different δ¹¹B signatures in species and also discuss the potential of using multispecies δ¹¹B analyses to constrain vertical pH and pCO₂ gradients in ancient water columns to shed light on biogeochemical carbon cycling in the past.