No ion is an island: Multiple ions influence boron incorporation into CaCO3
No ion is an island: Multiple ions influence boron incorporation into CaCO3
Boron isotope ratios – as measured in marine calcium carbonate – are an established tracer of past seawater and calcifying fluid pH, and thus a powerful tool for probing marine calcifier physiology and reconstructing past atmospheric CO
2 levels. For such applications, understanding the inorganic baseline upon which foraminiferal vital effects or coral pH upregulation are superimposed should be an important prerequisite. Yet, investigations into boron isotope fractionation in synthetic CaCO
3 polymorphs have often reported variable and even conflicting results, implying our understanding of the pathways of boron incorporation into calcium carbonate is incomplete. Here we address this topic with experimental data from synthetic calcite and aragonite precipitated across a range of pH in the presence of both Mg and Ca. We observe coherent patterns in B/Ca and Na/Ca ratios that, we suggest, point to paired substitution of Na and B into the carbonate lattice to achieve local charge balance. In addition, we confirm the results of previous studies that the boron isotope composition of inorganic aragonite precipitates closely reflects that of aqueous borate ion, but that inorganic calcites display a higher degree of scatter, and diverge from the boron isotope composition of aqueous borate ion at low pH. With reference to the simultaneous incorporation of other trace and minor elements, we put forward possible explanations for the observed variability in the concentration and isotopic composition of boron in synthetic CaCO
3. In particular, we highlight the potential importance of interface electrostatics in driving variability in our own and published synthetic carbonate datasets. Importantly for palaeo-reconstruction, however, these electrostatic effects are unlikely to play as important a role during natural precipitation of biogenic carbonates.
Aragonite, Boron Isotopes, Calcite, Trace Element Incorporation, pH proxy, δ B
510-530
Henehan, Michael J.
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Klein Gebbinck, Christa D.
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Wyman, Jillian V.b.
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Hain, Mathis P.
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Rae, James W.b.
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Hönisch, Bärbel
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Foster, Gavin L.
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Kim, Sang-tae
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1 February 2022
Henehan, Michael J.
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Klein Gebbinck, Christa D.
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Wyman, Jillian V.b.
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Hain, Mathis P.
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Rae, James W.b.
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Hönisch, Bärbel
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Foster, Gavin L.
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Kim, Sang-tae
08eeeaf3-be2d-4cc1-85df-2f70b30e6fa8
Henehan, Michael J., Klein Gebbinck, Christa D., Wyman, Jillian V.b., Hain, Mathis P., Rae, James W.b., Hönisch, Bärbel, Foster, Gavin L. and Kim, Sang-tae
(2022)
No ion is an island: Multiple ions influence boron incorporation into CaCO3.
Geochimica et Cosmochimica Acta, 318, .
(doi:10.1016/j.gca.2021.12.011).
Abstract
Boron isotope ratios – as measured in marine calcium carbonate – are an established tracer of past seawater and calcifying fluid pH, and thus a powerful tool for probing marine calcifier physiology and reconstructing past atmospheric CO
2 levels. For such applications, understanding the inorganic baseline upon which foraminiferal vital effects or coral pH upregulation are superimposed should be an important prerequisite. Yet, investigations into boron isotope fractionation in synthetic CaCO
3 polymorphs have often reported variable and even conflicting results, implying our understanding of the pathways of boron incorporation into calcium carbonate is incomplete. Here we address this topic with experimental data from synthetic calcite and aragonite precipitated across a range of pH in the presence of both Mg and Ca. We observe coherent patterns in B/Ca and Na/Ca ratios that, we suggest, point to paired substitution of Na and B into the carbonate lattice to achieve local charge balance. In addition, we confirm the results of previous studies that the boron isotope composition of inorganic aragonite precipitates closely reflects that of aqueous borate ion, but that inorganic calcites display a higher degree of scatter, and diverge from the boron isotope composition of aqueous borate ion at low pH. With reference to the simultaneous incorporation of other trace and minor elements, we put forward possible explanations for the observed variability in the concentration and isotopic composition of boron in synthetic CaCO
3. In particular, we highlight the potential importance of interface electrostatics in driving variability in our own and published synthetic carbonate datasets. Importantly for palaeo-reconstruction, however, these electrostatic effects are unlikely to play as important a role during natural precipitation of biogenic carbonates.
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Henehan 2022 No ion is an island - multiple ions influence boron incorporation into CaCO3
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Accepted/In Press date: 10 December 2021
e-pub ahead of print date: 17 December 2021
Published date: 1 February 2022
Additional Information:
Funding Information:
We thank Oscar Branson, Jesse Farmer and Joji Uchikawa for their helpful and open discussions throughout the drafting of this manuscript, and in particular Oscar Branson for assistance in implementing pitzer calculations via PHREEQCpy. We also thank Roberts Blukis for helpful discussion, Oded Nir, Yongliang Xiong and David Parkhurst for helpful insights in calculating aqueous chemical speciation, and Vasileios Mavromatis and Jelle Bijma for providing further information about previously published data. We are grateful for the editorial handling of associate editor Mariette Wolthers, and for helpful, insightful and constructive reviews from David Evans and two anonymous reviewers. The B-Team (in particular Joseph Stewart), Andy Milton, Matthew Cooper and Agnes Michalik at the University of Southampton are thanked for their help during these analyses. This research was supported by American Chemical Society – Petroleum Research Fund (ACS-PRF #50755-ND2), Natural Science and Engineering Research Council (NSERC) - Discovery Grants Program (386188-2010), Ontario Ministry of Research and Innovation - Ontario Research Fund (MRI-ORF #28001), Canada Foundation for Innovation - Leaders Opportunity Fund ( CFI-LOF # 28001) to S.-T. Kim
Funding Information:
We thank Oscar Branson, Jesse Farmer and Joji Uchikawa for their helpful and open discussions throughout the drafting of this manuscript, and in particular Oscar Branson for assistance in implementing pitzer calculations via PHREEQCpy. We also thank Roberts Blukis for helpful discussion, Oded Nir, Yongliang Xiong and David Parkhurst for helpful insights in calculating aqueous chemical speciation, and Vasileios Mavromatis and Jelle Bijma for providing further information about previously published data. We are grateful for the editorial handling of associate editor Mariette Wolthers, and for helpful, insightful and constructive reviews from David Evans and two anonymous reviewers. The B-Team (in particular Joseph Stewart), Andy Milton, Matthew Cooper and Agnes Michalik at the University of Southampton are thanked for their help during these analyses. This research was supported by American Chemical Society ? Petroleum Research Fund (ACS-PRF #50755-ND2), Natural Science and Engineering Research Council (NSERC) - Discovery Grants Program (386188-2010), Ontario Ministry of Research and Innovation - Ontario Research Fund (MRI-ORF #28001), Canada Foundation for Innovation - Leaders Opportunity Fund (CFI-LOF #28001) to S.-T. Kim
Publisher Copyright:
© 2021 Elsevier Ltd
Copyright:
Copyright 2022 Elsevier B.V., All rights reserved.
Keywords:
Aragonite, Boron Isotopes, Calcite, Trace Element Incorporation, pH proxy, δ B
Identifiers
Local EPrints ID: 456554
URI: http://eprints.soton.ac.uk/id/eprint/456554
ISSN: 0016-7037
PURE UUID: e572d762-54e4-4b30-a73a-5d1a3519e6dd
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Date deposited: 05 May 2022 16:30
Last modified: 17 Mar 2024 07:06
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Contributors
Author:
Michael J. Henehan
Author:
Christa D. Klein Gebbinck
Author:
Jillian V.b. Wyman
Author:
James W.b. Rae
Author:
Bärbel Hönisch
Author:
Sang-tae Kim
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