Regional calibration of coral-based climate reconstructions from Palau, West Pacific Warm Pool (WPWP)

Stable isotopic and trace element records from corals collected within the West Pacific Warm Pool (WPWP) are well suited to examine interannual to decadal climate variability associated with the El Niño-Southern Oscillation (ENSO) phenomenon. The most commonly used climate recorder in corals is δ18O (δ18OCRL), a parameter subject to multiple regional and local environmental influences. Location-specific calibration of δ18OCRL is a necessary first step for developing long-term paleoceanographic reconstructions. Here we present four new coral δ18O stratigraphies from the Republic of Palau (7.5°N 134.5°E), and compare our records with instrumental measurements for the period 1950-2008. We also compare our results with a previously published coral record from Palau. We employ a new sea surface salinity (SSS) product and validate its utility for coral-based paleoclimate calibrations. We not only examine differences among the records but also identify strong and regionally coherent environmental signals. We find that SSS variability is the dominant influence on δ18OCRL in Palau, while sea surface temperature (SST) is of secondary importance. Our results show that time-averaging multiple δ18OCRL records into a single composite series produce greater correlations with instrumental data and indices than individual stratigraphies alone. Our results are consistent with observations of a strengthening of the hydrological cycle in the WPWP region over the past 50 years, though the magnitudes of long term linear trends differ among the different Palau δ18OCRL records. Interannual and interdecadal variabilities between the Palau δ18OCRL records are more consistent than the long term linear trends. Monthly Palauan δ18OCRL anomalies capture strong El Niño events with high fidelity over the calibration period. This study provides constraints for future paleoenvironmental investigations in Palau using longer coral records.