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.
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 -