the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 03 May 2024
Western Indian Ocean bottom water temperature calibration – are benthic foraminiferal Mg/Ca ratios a reliable palaeothermometry proxy?
Abstract. Mg/Ca ratios measured in benthic foraminifera have been explored as a potential palaeothermometry proxy for bottom water temperatures (BWT). Mg/Ca-BWT calibrations from the Indian Ocean are rare and comprise conflicting results. Inconsistencies between studies suggest that calibrations may need to be region specific. The aim of this study was to develop benthic foraminifera (Uvigerina peregrina, Cibicidoides wuellerstorfi and Cibicidoides mundulus) based Mg/Ca – BWT calibrations in the tropical western Indian Ocean. Testing variations of existing analytical protocols, aimed at optimising cleaning of the foraminifera while avoiding sample loss in the process, entailed that a previously established protocol by Barker et al. (2003) was the most suitable for our study. The majority of samples of Cibicidoides mundulus and Uvigerina peregrina, however, remained contaminated, rendering those data unusable for Mg/Ca core-top calibrations. Only Mg/Ca ratios in Cibicidoides wuellerstorfi allowed a tentative Mg/Ca - BWT calibration with the relationship being: Mg/Ca = 0.19 ± 0.02 ∗ BWT + 1.07 ± 0.03, 𝑟2 = 0.87. While this result differs to some degree from previous studies it principally suggests that existing core-top calibrations from the wider Indian Ocean can be applied to core-tops in the western Indian Ocean. The agreement of Mg/Ca ratios at lower temperatures in Cibicidoides wuellerstorfi, Cibicidoides mundulus and Uvigerina peregrina with Mg/Ca ratios reported for these species at low temperatures in other studies supports this conclusion. Many uncertainties surrounding the Mg/Ca proxy exist and more calibration studies are required to improve this method.
Competing interests: S. Jung is co-editor of the special issue dedicated to Dick Kroon and will not be involved in the handling of this manuscript. The other authors declare that they have no conflict of interest.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.-
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
(2234 KB)
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
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- BibTeX
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- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2024-979', Anonymous Referee #1, 30 May 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-979/egusphere-2024-979-RC1-supplement.pdfCitation: https://doi.org/
10.5194/egusphere-2024-979-RC1 -
AC1: 'Reply on RC1', Viktoria Larsson, 07 Sep 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-979/egusphere-2024-979-AC1-supplement.pdf
- AC4: 'Reply on RC1', Viktoria Larsson, 07 Sep 2024
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AC1: 'Reply on RC1', Viktoria Larsson, 07 Sep 2024
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RC2: 'Comment on egusphere-2024-979', Anonymous Referee #2, 21 Jun 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-979/egusphere-2024-979-RC2-supplement.pdf
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AC3: 'Reply on RC2', Viktoria Larsson, 07 Sep 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-979/egusphere-2024-979-AC3-supplement.pdf
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AC3: 'Reply on RC2', Viktoria Larsson, 07 Sep 2024
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RC3: 'Comment on egusphere-2024-979', Anonymous Referee #3, 26 Jun 2024
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.
Citation: https://doi.org/10.5194/egusphere-2024-979-RC3 -
AC2: 'Reply on RC3', Viktoria Larsson, 07 Sep 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-979/egusphere-2024-979-AC2-supplement.pdf
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AC2: 'Reply on RC3', Viktoria Larsson, 07 Sep 2024
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2024-979', Anonymous Referee #1, 30 May 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-979/egusphere-2024-979-RC1-supplement.pdf
-
AC1: 'Reply on RC1', Viktoria Larsson, 07 Sep 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-979/egusphere-2024-979-AC1-supplement.pdf
- AC4: 'Reply on RC1', Viktoria Larsson, 07 Sep 2024
-
AC1: 'Reply on RC1', Viktoria Larsson, 07 Sep 2024
-
RC2: 'Comment on egusphere-2024-979', Anonymous Referee #2, 21 Jun 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-979/egusphere-2024-979-RC2-supplement.pdf
-
AC3: 'Reply on RC2', Viktoria Larsson, 07 Sep 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-979/egusphere-2024-979-AC3-supplement.pdf
-
AC3: 'Reply on RC2', Viktoria Larsson, 07 Sep 2024
-
RC3: 'Comment on egusphere-2024-979', Anonymous Referee #3, 26 Jun 2024
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.
Citation: https://doi.org/10.5194/egusphere-2024-979-RC3 -
AC2: 'Reply on RC3', Viktoria Larsson, 07 Sep 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-979/egusphere-2024-979-AC2-supplement.pdf
-
AC2: 'Reply on RC3', Viktoria Larsson, 07 Sep 2024
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Viktoria Larsson
Simon Jung
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
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