Evaluation of the effects of microscale chemical and isotopic heterogeneity of coral skeleton on conventional Sr/Ca and $\updelta^{18}$ O paleothermometers

Abstract

Recent studies using secondary ion mass spectrometry revealed microscale heterogeneity of Sr/Ca and $\updelta^{18}$ O in shallow-water coral skeletons, i.e., Sr/Ca and $\updelta^{18}$ O differ significantly between two basic microfeatures of the skeleton: the center of calcification (COC) and surrounding fibrous skeleton (SFS). The COC, in contrast with the SFS, consists of highly irregular crystals intermingled with significant amount of organic matter; therefore, analyzing the SFS only would probably be favourable for paleotemperature reconstruction. Conventional Sr/Ca and $\updelta^{18}$ O paleothermometers are, however, based on the analysis of the mixture of the COC and SFS, and thus may be significantly affected by the above-mentioned heterogeneity. In this study, I have evaluated the heterogeneity-induced effects on the conventional paleothermometers of Porites skeletons using published Sr/Ca, $\updelta^{18}$ O and volume-fraction data of the COC and SFS and published observations of seasonal variability of bulk skeletal density. Results indicate that the effects may yield significant or serious errors in paleotemperature reconstruction.