Correcting for vital effects in coral carbonate using triple oxygen isotopes

Carbonate oxygen isotopes ( 18 O/ 16 O) are a valuable tool for estimating palaeotemperatures, but their accuracy can be limited by so called vital effects that influence the isotope composition of biomineralised hard parts.In this study, we analysed the triple oxygen isotope composition ( 18 O/ 16 O and 17 O/ 16 O) of cold-and warm-water corals to demonstrate how such data can be used to identify and correct for vital effects.We found that the observed slopes in triple oxygen isotope space between the measured and expected equilibrium compositions are mainly controlled by CO 2 absorption, although there is a possibility of additional isotope fractionation effects from processes such as CO 2 (aq) diffusion through the cell membrane.We corrected these effects using an empirical vital effect slope and obtained accurate coral growth temperatures.The precision of reconstructed temperatures, considering the measurement error only, is ±5 °C.