Coral-Thermometry: A Method for Determining Past Surface Water Temperature Variations

Montastrea annularis, collected from the reefs off Barbados, Jamaica, and Bermuda and the uplifted Pleistocene reefs of Barbados, were analyzed for oxygen isotopes. Annual growth bands were transected and appoximately fifteen evenly spaced samples were analyzed for each year of growth. Systematic oxygen isotope fluctuations occur with an annual periodicity. The lightest Ȣ18O values coincide with dense skeletal bands which form annually during warmest water temperatures. A comparison of the annual oxygen isotope record of the modern specimens to local temperature records demonstrates the temperature dependence of the oxygen isotopic composition, although isotope values are systematically offset from equilibrium values for inorganically preciptated calcium carbonate. Coral-thermometry has applications in the fields of coral ecology, Holocene and Pleistocene climatology, and as a stratigraphic tool for use in geochemical studies