A Coral Diagenesis and Physiology Framework for Improving Coral δ 18 O Paleoclimate Reconstructions

Abstract Reef‐building corals provide seasonally resolved records of past climate variability based on the oxygen isotope composition (δ 18 O) of their skeletons. However, many non‐climatic factors can alter coral δ 18 O values. These include coral biomineralization and post‐depositional alteration of the coral skeleton, which can add uncertainty to coral based paleoclimate reconstructions. These uncertainties are apparent in mean climate reconstructions developed from coral δ 18 O values. We present a framework to minimize this uncertainty in mean coral δ 18 O records using a multi‐variate regression model that incorporates four commonly measured properties in coral δ 18 O records. We test the ability of the model to reduce variability in a Holocene climate reconstruction comprised of 37 coral δ 18 O records from Kiritimati. 38% of the variance in the mean coral δ 18 O values across the Holocene is accounted for by a combination of four predictors: (a) mm‐scale variability in coral δ 18 O, (b) the mean coral δ 13 C value, (c) the mean coral extension rate, and (d) the extent of diagenetic alteration identified in Scanning Electron Microscope images. Once these non‐climatic artifacts are minimized in the reconstruction, the weighted variance of the Holocene data set is reduced by 43% and the uncertainty in the trend of mean coral δ 18 O is reduced by 18%. The model is validated using three well‐characterized modern coral records with pristine and altered sections. These results have important implications for the climate interpretation of this Holocene data set. This framework also has the potential to improve other paleoclimate reconstructions based on ensembles of mean coral δ 18 O records.