Stable isotopes in a branching coral monitor seasonal temperature variation

Abstract

Reef corals, both fossil and recent, are potentially useful monitors of the surface ocean ‘climate’. Because coral reefs flourish only in relatively warm water^1,2, the very presence of reef corals constrains the estimation of local temperature ranges. Studies of hermatypic corals have shown that coral growth rate^3–8, density band formation (in some species)^9–15, and stable isotopic composition^14–23, all respond to variations in water temperature and light intensity. We have measured the stable isotopic composition of specimens of the branching reef coral Pocillopora damicornis which have grown in the field while seawater temperatures were continuously recorded. Detailed oxygen isotope profiles of branches of this species indicate that seasonal changes in temperature and seawater isotopic composition are precisely recorded. Isotopic profiles may be used to estimate growth rates of branching corals, which lack annual density banding. The method provides a technique for high resolution palaeoclimatic reconstruction of seasonal temperature ranges and accurate estimation of rates of reef carbonate production.