Mean oxygen-isotope signatures in Porites spp. corals: inter-colony variability and correction for extension-rate effects

Abstract

The assessment of inter-colony variability in the mean skeletal δ18O signatures of modern Porites spp. corals is a prerequisite for the estimation of past mean climate conditions based on fossil colonies. Here we show that the mean δ18O signatures of Porites spp. corals from the northern end of the Gulf of Aqaba (Red Sea) with mean extension rates between 0.2 and 1.5 cm/year can have an inter-colony variability as large as 1.28‰. At extension rates of less than 0.6 cm/year the mean coral δ18O values of the individual colonies are strongly dependent on the mean extension rate, with increasingly higher δ18O values corresponding to decreasing extension rate. This suggests that extension-rate-related kinetic isotope disequilibrium effects are responsible for a large proportion of the inter-colony differences in the mean coral δ18O signatures. A correction procedure for these effects based on the relationship between mean δ18O values and mean extension rate reduces the variability of mean coral δ18O values among the individual colonies to 0.43‰. Although certainly not perfect, the correction procedure enables a better assessment of mid-Holocene climate conditions at this location based on Porites spp. with mean extension rates of less than 0.6 cm/year.