Systematic Relationships between Carbon and Oxygen Isotopes in Carbonates Deposited by Modern Corals and Algae

Science  22 Oct 1965:
Vol. 150, Issue 3695, pp. 498-501
DOI: 10.1126/science.150.3695.498


Analyses of organic carbonates from Jamaican coral reefs show a positive correlation between the O18: O16 ratio and the C13 C12 ratio in some taxonomic groups of corals and algae, but essentially no correlation (nearly constant O18) in one suborder of reef-building corals. The strontium and magnesium contents apparently are controlled mainly by skeletal mineralogy and show no correlation with carbon or oxygen isotopic composition. The observed positive correlations between C13 and O18 content may be due to calcification processes utilizing carbon-oxygen compounds from two isotopically different sources or utilizing selected portions of a wide spectrum of carbon-oxygen compounds in which there is a positive correlation between C13 C12 and O18;O16 ratios. Coral and algal carbonates from Jamaican waters, with an annual temperature range of only about 4°C, exhibit a total δC13 range of more than 13 per mil and a σO18 range of more than 4 per mil. The wide isotopic variability resulting from vital effects of calcifying organisms must be taken into account in applying isotopic analysis to the study of sedimentary carbonate rocks which may include reef-derived carbonates.