Could Coral Skeleton Oxygen Isotopic Fractionation be Controlled by Biology?

Abstract

During 1970s, coral skeleton oxygen isotope composition ( δ 18 O) was regarded as the isotopic thermometer following thermodynamic rules. Recently, coral aragonite oxygen isotopic fractionation could appear to be controlled by biology, its rate being accelerated by an enzyme (carbonic anhydrase or CA). Such a new concept results of an original approach involving coral culture in controlled conditions. Environmental factors, temperature and also light have been tested on macrosize scale samples (some mg), and δ 18 O revealed vital effects, anomalies compared with chemical and isotopic equilibrium, related to metabolic activity. δ 18 O analyses at microsize scale (some μ m), using ion microprobe, could display the mechanism of crystallisation, δ 18 O fractionation responding to biological kinetic effects. The understanding of coral aragonite δ 18 O is the absolute prerequisite to develop the first model of a coral proxy.