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

Research output: Contribution to journalArticlepeer-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 (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.

Original languageEnglish (US)
Pages (from-to)535-549
Number of pages15
JournalGeochimica et Cosmochimica Acta
Volume222
DOIs
StatePublished - Feb 1 2018

Keywords

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

ASJC Scopus subject areas

  • Geochemistry and Petrology

Fingerprint Dive into the research topics of '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'. Together they form a unique fingerprint.

Cite this