The effect of changing seawater Ca and Mg concentrations upon the distribution coefficients of Mg and Sr in the skeletons of the scleractinian coral Pocillopora damicornis

Sharmila J. Giri; Peter K. Swart; Quinn B. Devlin

doi:10.1016/j.gca.2017.11.011

The effect of changing seawater Ca and Mg concentrations upon the distribution coefficients of Mg and Sr in the skeletons of the scleractinian coral Pocillopora damicornis

Sharmila J. Giri, Peter K. Swart, Quinn B. Devlin

Marine Geosciences

Research output: Contribution to journal › Article › peer-review

6 Scopus citations

Abstract

The skeletal composition of calcifying organisms, in particular Mg/Ca and Sr/Ca ratios, have been widely used to understand fluctuations in seawater chemistry throughout the Phanerozoic. While the success of applying these data to the geologic record depends on a knowledge of the distribution coefficients for these elements (D_Mg and D_Sr), there are scarcely any studies which have described how these values vary as a result of changing seawater Mg/Ca ratios. To address this, we have cultured the scleractinian coral, Pocillopora damicornis, in seawater with ranges of Mg and Ca concentrations. Here, we demonstrate that Mg/Ca and Sr/Ca ratios of coral skeletons correlate with total seawater Mg/Ca and Sr/Ca molar ratios, but that apparent D_Mg and D_Sr values do not remain constant across the range of experimental seawater treatments, with D_Mg values significantly increasing with seawater Mg/Ca ratios and D_Sr values significantly increasing with seawater Ca concentrations. These trends are not rate dependent and may be best explained by a Rayleigh distillation model, in which the calcifying space is semi-isolated from seawater during skeletogenesis (i.e. leaky). As there is a slight increase in D_Mg and decrease in D_Sr values between our “Jurassic” and “Modern” seawater treatments, the application of a constant distribution coefficient to estimate changes in ancient seawater chemistry may underestimate seawater Mg/Ca ratios and overestimate Sr/Ca throughout the Mesozoic and Cenozoic. We suggest that interpretations of seawater chemistry from fossil corals may be improved by using the relationships derived for skeletal and seawater Mg/Ca and Sr/Ca ratios established by our experiments, as they incorporate the effect of seawater Mg/Ca ratios on skeletal Mg/Ca and Sr/Ca ratios.

Original language	English (US)
Pages (from-to)	535-549
Number of pages	15
Journal	Geochimica et Cosmochimica Acta
Volume	222
DOIs	https://doi.org/10.1016/j.gca.2017.11.011
State	Published - Feb 1 2018

Keywords

Aragonite
Calcium
Coral
Distribution coefficients
Element partitioning
Mg/Ca
Sr/Ca

ASJC Scopus subject areas

Geochemistry and Petrology

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title = "The effect of changing seawater Ca and Mg concentrations upon the distribution coefficients of Mg and Sr in the skeletons of the scleractinian coral Pocillopora damicornis",

abstract = "The skeletal composition of calcifying organisms, in particular Mg/Ca and Sr/Ca ratios, have been widely used to understand fluctuations in seawater chemistry throughout the Phanerozoic. While the success of applying these data to the geologic record depends on a knowledge of the distribution coefficients for these elements (DMg and DSr), there are scarcely any studies which have described how these values vary as a result of changing seawater Mg/Ca ratios. To address this, we have cultured the scleractinian coral, Pocillopora damicornis, in seawater with ranges of Mg and Ca concentrations. Here, we demonstrate that Mg/Ca and Sr/Ca ratios of coral skeletons correlate with total seawater Mg/Ca and Sr/Ca molar ratios, but that apparent DMg and DSr values do not remain constant across the range of experimental seawater treatments, with DMg values significantly increasing with seawater Mg/Ca ratios and DSr values significantly increasing with seawater Ca concentrations. These trends are not rate dependent and may be best explained by a Rayleigh distillation model, in which the calcifying space is semi-isolated from seawater during skeletogenesis (i.e. leaky). As there is a slight increase in DMg and decrease in DSr values between our “Jurassic” and “Modern” seawater treatments, the application of a constant distribution coefficient to estimate changes in ancient seawater chemistry may underestimate seawater Mg/Ca ratios and overestimate Sr/Ca throughout the Mesozoic and Cenozoic. We suggest that interpretations of seawater chemistry from fossil corals may be improved by using the relationships derived for skeletal and seawater Mg/Ca and Sr/Ca ratios established by our experiments, as they incorporate the effect of seawater Mg/Ca ratios on skeletal Mg/Ca and Sr/Ca ratios.",

keywords = "Aragonite, Calcium, Coral, Distribution coefficients, Element partitioning, Mg/Ca, Sr/Ca",

author = "Giri, {Sharmila J.} and Swart, {Peter K.} and Devlin, {Quinn B.}",

note = "Funding Information: We thank P. Gillette and T. Capo for allowing us to conduct this work in the University of Miami{\textquoteright}s experimental hatchery. We also thank K. Erceg, S. Shedd, B. Hall, S. Ahearn, D. Stommes, T. Longbottom, A. Bardales, K. Galvez, and S. Billings for their help with aquarium maintenance and coral rearing and A. Saied, P. Staudigel, M. Arienzo, S. Murray, and C. Kaiser for their help with sample preparation and analyses. The JCp-1 standard was generously supplied by B. Linsley. The authors are indebted to M. Bender for encouragement to undertake these experiments and to N. Allison and two anonymous reviewers for their critical evaluation of this manuscript. Support for this research was provided by Sigma Xi Grants-in-Aid , the Geological Society of America , and by the Stable Isotope Laboratory at the University of Miami . Publisher Copyright: {\textcopyright} 2017 Elsevier Ltd",

year = "2018",

month = feb,

day = "1",

doi = "10.1016/j.gca.2017.11.011",

language = "English (US)",

volume = "222",

pages = "535--549",

journal = "Geochmica et Cosmochimica Acta",

issn = "0016-7037",

publisher = "Elsevier Limited",

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TY - JOUR

T1 - The effect of changing seawater Ca and Mg concentrations upon the distribution coefficients of Mg and Sr in the skeletons of the scleractinian coral Pocillopora damicornis

AU - Giri, Sharmila J.

AU - Swart, Peter K.

AU - Devlin, Quinn B.

N1 - Funding Information: We thank P. Gillette and T. Capo for allowing us to conduct this work in the University of Miami’s experimental hatchery. We also thank K. Erceg, S. Shedd, B. Hall, S. Ahearn, D. Stommes, T. Longbottom, A. Bardales, K. Galvez, and S. Billings for their help with aquarium maintenance and coral rearing and A. Saied, P. Staudigel, M. Arienzo, S. Murray, and C. Kaiser for their help with sample preparation and analyses. The JCp-1 standard was generously supplied by B. Linsley. The authors are indebted to M. Bender for encouragement to undertake these experiments and to N. Allison and two anonymous reviewers for their critical evaluation of this manuscript. Support for this research was provided by Sigma Xi Grants-in-Aid , the Geological Society of America , and by the Stable Isotope Laboratory at the University of Miami . Publisher Copyright: © 2017 Elsevier Ltd

PY - 2018/2/1

Y1 - 2018/2/1

N2 - The skeletal composition of calcifying organisms, in particular Mg/Ca and Sr/Ca ratios, have been widely used to understand fluctuations in seawater chemistry throughout the Phanerozoic. While the success of applying these data to the geologic record depends on a knowledge of the distribution coefficients for these elements (DMg and DSr), there are scarcely any studies which have described how these values vary as a result of changing seawater Mg/Ca ratios. To address this, we have cultured the scleractinian coral, Pocillopora damicornis, in seawater with ranges of Mg and Ca concentrations. Here, we demonstrate that Mg/Ca and Sr/Ca ratios of coral skeletons correlate with total seawater Mg/Ca and Sr/Ca molar ratios, but that apparent DMg and DSr values do not remain constant across the range of experimental seawater treatments, with DMg values significantly increasing with seawater Mg/Ca ratios and DSr values significantly increasing with seawater Ca concentrations. These trends are not rate dependent and may be best explained by a Rayleigh distillation model, in which the calcifying space is semi-isolated from seawater during skeletogenesis (i.e. leaky). As there is a slight increase in DMg and decrease in DSr values between our “Jurassic” and “Modern” seawater treatments, the application of a constant distribution coefficient to estimate changes in ancient seawater chemistry may underestimate seawater Mg/Ca ratios and overestimate Sr/Ca throughout the Mesozoic and Cenozoic. We suggest that interpretations of seawater chemistry from fossil corals may be improved by using the relationships derived for skeletal and seawater Mg/Ca and Sr/Ca ratios established by our experiments, as they incorporate the effect of seawater Mg/Ca ratios on skeletal Mg/Ca and Sr/Ca ratios.

AB - The skeletal composition of calcifying organisms, in particular Mg/Ca and Sr/Ca ratios, have been widely used to understand fluctuations in seawater chemistry throughout the Phanerozoic. While the success of applying these data to the geologic record depends on a knowledge of the distribution coefficients for these elements (DMg and DSr), there are scarcely any studies which have described how these values vary as a result of changing seawater Mg/Ca ratios. To address this, we have cultured the scleractinian coral, Pocillopora damicornis, in seawater with ranges of Mg and Ca concentrations. Here, we demonstrate that Mg/Ca and Sr/Ca ratios of coral skeletons correlate with total seawater Mg/Ca and Sr/Ca molar ratios, but that apparent DMg and DSr values do not remain constant across the range of experimental seawater treatments, with DMg values significantly increasing with seawater Mg/Ca ratios and DSr values significantly increasing with seawater Ca concentrations. These trends are not rate dependent and may be best explained by a Rayleigh distillation model, in which the calcifying space is semi-isolated from seawater during skeletogenesis (i.e. leaky). As there is a slight increase in DMg and decrease in DSr values between our “Jurassic” and “Modern” seawater treatments, the application of a constant distribution coefficient to estimate changes in ancient seawater chemistry may underestimate seawater Mg/Ca ratios and overestimate Sr/Ca throughout the Mesozoic and Cenozoic. We suggest that interpretations of seawater chemistry from fossil corals may be improved by using the relationships derived for skeletal and seawater Mg/Ca and Sr/Ca ratios established by our experiments, as they incorporate the effect of seawater Mg/Ca ratios on skeletal Mg/Ca and Sr/Ca ratios.

KW - Aragonite

KW - Calcium

KW - Coral

KW - Distribution coefficients

KW - Element partitioning

KW - Mg/Ca

KW - Sr/Ca

UR - http://www.scopus.com/inward/record.url?scp=85035755624&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85035755624&partnerID=8YFLogxK

U2 - 10.1016/j.gca.2017.11.011

DO - 10.1016/j.gca.2017.11.011

M3 - Article

AN - SCOPUS:85035755624

VL - 222

SP - 535

EP - 549

JO - Geochmica et Cosmochimica Acta

JF - Geochmica et Cosmochimica Acta

SN - 0016-7037

ER -

The effect of changing seawater Ca and Mg concentrations upon the distribution coefficients of Mg and Sr in the skeletons of the scleractinian coral Pocillopora damicornis

Abstract

Keywords

ASJC Scopus subject areas

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