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

The assessment of inter-colony variability in the mean skeletal δ¹⁸O signatures of modern Parites 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 Parites 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.