Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (5) Citing Articles via Google Scholar Google Scholar Articles by Ries, J. B. Articles by Hardie, L. A. Search for Related Content GeoRef GeoRef Citation

Scleractinian corals produce calcite, and grow more slowly, in artificial Cretaceous seawater

¹ Morton K. Blaustein Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, Maryland 21218, USA
² Department of Geology and Geophysics, University of Hawaii, 1680 East-West Road, Honolulu, Hawaii 96822, USA
³ Morton K. Blaustein Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, Maryland 21218, USA

The mineralogies of most biotic and abiotic carbonates have alternated in synchroneity between the calcite (hexagonal) and aragonite (orthorhombic) polymorphs of CaCO₃ throughout the Phanerozoic Eon. These intervals of calcite and aragonite production, or calcite seas and aragonite seas, are thought to be caused primarily by secular variation in the molar magnesium/calcium ratio of seawater (mMg/Ca > 2 = aragonite + high-Mg calcite; mMg/Ca < 2 = low-Mg calcite), a ratio that has oscillated between 1.0 and 5.2 throughout the Phanerozoic. In laboratory experiments, we show that three species of scleractinian corals, which produce aragonite in modern seawater and which have flourished as important reef builders primarily during aragonite seas of the past, began producing calcite in artificial seawater with an ambient mMg/Ca ratio below that of modern seawater (5.2). The corals produced progressively higher percentages of calcite and calcified at lower rates with further reduction of the ambient mMg/Ca ratio. In artificial seawater of imputed Late Cretaceous composition (mMg/Ca = 1.0), which favors the precipitation of the calcite polymorph, scleractinian corals produced skeletons containing >30% low-Mg calcite (skeletal mMg/Ca < 0.04). These results indicate that the skeletal mineral used by scleractinian corals is partially determined by seawater chemistry. Furthermore, slow calcification rates, resulting from the production of largely aragonitic skeletons in chemically unfavorable seawater (mMg/Ca < 2), probably contributed to the scleractinians' diminished reef-building role in the calcite seas of Late Cretaceous and early Cenozoic time.

Key Words: scleractinian corals • calcification • calcite seas • aragonite seas • biomineralization • seawater Mg/Ca • reef building

This article has been cited by other articles:

				J. R. WHEELEY, L. CHERNS, and V.P. WRIGHT Provenance of microcrystalline carbonate cement in limestone marl alternations (LMA): aragonite mud or molluscs? Journal of the Geological Society, January 1, 2008; 165(1): 395 - 403. [Abstract] [Full Text] [PDF]

				J. Stolarski, A. Meibom, R. Przenioslo, and M. Mazur A Cretaceous Scleractinian Coral with a Calcitic Skeleton Science, October 5, 2007; 318(5847): 92 - 94. [Abstract] [Full Text] [PDF]

				L. Pomar and P. Hallock Changes in coral-reef structure through the Miocene in the Mediterranean province: Adaptive versus environmental influence Geology, October 1, 2007; 35(10): 899 - 902. [Abstract] [Full Text] [PDF]