Stable isotope ratio variations in non-scleractinian coelenterate carbonates as a function of temperature
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Some coelenterates of the class Hydrozoa and some anthozoan coelenterates from the subclass Octocorallia secrete skeletons of calcium carbonate. Skeletal carbonates of three hydrozoans and of two octocorals were analyzed for the stable isotopes of carbon and oxygen. The results suggest that each of these coelenterates deposits CaCO3 in oxygen isotopic equilibrium with seawater, and that at least one octocoral, Heliopora, has skeletal carbon in apparent isotopic equilibrium with atmospheric CO2. Two of these coelenterates, Millepora and Helipora, are significant contributors to the construction of coral reefs. Whereas δ18O of these corals is temperature dependent, δ13C is not obviously related to temperature. The δ18O-temperature relationship is not significantly different from the oxygen isotope paleotemperature scale developed by Epstein et al. (1953). These findings contrast with numerous analyses of the carbonate in scleractinian coelenterates, which have long been reported to deposit CaCO3 skeletons whose carbon and oxygen isotopic compositions are not in equilibrium with the external sea-water environment.
KeywordsIsotopic Composition Stable Isotope CaCO3 Coral Reef Oxygen Isotope
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