In “Western Indian Ocean bottom water temperature calibration – are benthic foraminifera Mg/Ca ratios a reliable palaeothermometry proxy?” Larsson & Jung measure Mg/Ca ratios in benthic foraminifers across a depth / space transect in the Western Indian Ocean to determine if a local Mg/Ca-temperature calibration is appropriate. They also test several cleaning techniques to determine their effects on contamination, sample yield, etc.

I’m no expert in Mg/Ca paleothermometry, but it seems like the half of the paper devoted to cleaning procedures is thorough and useful (if a little hard to follow). The calibration, however, is based on very few points (and anchored by one high-temperature sample), which the authors acknowledge, and is not likely to be used on its own. I think the exercise is still valuable, given that most of their data fall in the Mg/Ca-temperature space in prior calibrations, but the manuscript needs a clearer through-line, e.g., “best” cleaning protocol established -> despite efforts, majority of the specimens contaminated -> resulting calibration is sparse, but (most of) the data seem reasonable and species- / habitat-specific contamination thresholds, calibrations, etc. are recommended.

I believe that this can be of use to the paleoceanographic community pending major revisions in terms of structure, organization, and clarity – I would also highly recommend a thorough grammatical overhaul, there are numerous minor issues only some of which I’ve noted below. I don’t believe further laboratory analyses are required, although there are one or two instances where they might be helpful.

General comments:

The title is rather vague and doesn’t reveal much about the study’s true findings. Maybe something like “Persistent contamination issues preclude a simple benthic Mg/Ca-temperature calibration in the Western Indian Ocean?” I’m sure you can come up with something better.

Your tests of the various cleaning procedure parameters are a major part of the paper, and I would mention it in the title. I think you need to emphasize that this is a valuable contribution to Mg/Ca thermometry, however – it reads to me like a sidenote compared to the calibration until you reach the later part of the manuscript.

If I missed this, I apologize, but any ideas as to why the other Indian Ocean calibrations didn’t have as extensive of contamination issues?

Overall, the figures are well-made and easy to understand. I’m unconvinced this is a good idea, but if you (very lightly) shaded the “contaminated zone” above the peach-colored line e.g., in Figure 6, would it help drive home that almost everything’s contaminated, or would it just add clutter?

Line by line comments:

Lines 24-31: This paragraph seems out of place; reading it, I thought this paper was about to go in a very different direction. I think you could start from line 32 and be fine.

Lines 94-97: This whole paragraph or a statement of this kind belongs further towards the beginning – maybe at the end of Section 1?

Line 121 (?): What is the small inset panel on the right? I assume it’s ship tracks but the information would be good to have in the caption.

Lines 153-216: Can you divide Experiments 1-3 into their own subheadings? I.e., “2.2.1. Preparation experiment 1: XYZ?” As it is now, it’s a massive section that’s difficult to follow. I could also see this being divided up where you explain the experiments simply and clearly in Section 2.2 and describe your findings in the Results.

Line 219: There’s inconsistency in foraminifera abbreviations: G. ruber vs. Cibicidoides wuellerstorfi, for example. I would go with the abbreviation, but be consistent either way.

Line 265: Where’s panel D?

Line 325: Capitalize “c” in “c. wuellerstorfi.”

Line 369: “Figure ???11”

Section 4.2. header: Not sure why this is blue?

Lines 467-472: Is there any support for this in the literature or is it speculation? I hate to ask, but any possibility of elemental mapping to support?

Lines 478-479: Missing parentheses.

Lines 484-493: I think Section 4.8 belongs in the introduction – it’s critical motivation for your cleaning tests but you don’t bring it up until the end.

Lines 495-521: This is too long of a block of text, it’s dense and hard to follow.

Lines 523-535: This is a great conclusion and summary! Bring some of this clarity to the introduction and method explanations.