|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.
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.
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”?
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.
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.
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)