Environmental and biological effects on the stable oxygen isotope records of corals in the northern Gulf of Aqaba, Red Sea

Monthly 18 O records of 2 coral colonies (Porites cf. lutea and P. cf. nodifera) from different localities (Aqaba and Eilat) from the northern Gulf of Aqaba, Red Sea, were calibrated with recorded sea surface temperatures (SST) between 1988 and 2000. The results show high correlation coefficients between SST and 18 O. Seasonal variations of coral 18 O in both locations could explain 91% of the recorded SST. Different 18 O/SST relations from both colonies and from the same colonies were obtained, indicating that 18 O from coral skeletons were subject to an extension rate effect. Significant 18 O depletions are associated with high extension rates and higher values with low extension rates. The relation between coral skeletal 18 O and extension rate is not linear and can be described by a simple exponential model. An inverse relationship extends over extension rates from 1 to 5 mm yr -1 , while for more rapidly growing corals and portions of colonies the relation is constant and the extension rate does not appear to have a significant effect. We recommend that 18 O values be obtained from fast-growing corals or from portions in which the isotopic disequilibrium is fairly constant (extension rate > 5 mm yr -1 ). The results show that interspecific differences in corals may produce a significant 18 O profile offset between 2 colonies that is independent of environmental and extension-rate effects. We conclude that the rate of skeletal extension and the species of coral involved have an important influence on coral 18 O and must be considered when using 18 O records for paleoclimatic reconstructions.