The thermal oceanographic signal of El Niño reconstructed from a Kiritimati Island coral

Abstract

Central equatorial Pacific sea surface temperature (SST) anomaly is a critical predictor of basin‐wide oceanographic and atmospheric effects of the El Niño‐Southern Oscillation (ENSO) phenomenon. We employ two geochemical thermometers measured on coralline aragonite to reconstruct an independent proxy‐based measure of central equatorial Pacific sea surface temperature anomaly. In addition, we assess the observational error associated with extraction of large‐scale SST anomalies from δ18O and Sr/Ca measurements. On the basis of paired data for the 1981–1987 period, RMS error for the estimation of SST from Kiritimati coral δ18O is about 0.4°C, assuming no seawater δ18O influence; for Sr/Ca, the observational error is about 0.5°C. Singular spectrum analysis of the δ18O time series suggests that 1/3 of the variance is explained by SST anomaly and that this variance may be separated from other signals in the frequency domain. The interannual component of the δ18O record shares 70% variance with the interannual component of local SST anomaly estimates (ρ=−0.84) and correlates as highly with NINO3 region (150°W–90°W, 5°N–5°S) SST anomaly estimates; comparison of annual averages of the δ18O data with analyzed SST for 55 years suggests that the error in deriving annually averaged SST anomalies at Kiritimati is about 0.4°C. A global SST correlation analysis suggests significant correlation with the rest of the Pacific Basin and the tropical Indian and Atlantic sectors. The ocean‐wide level of correlation achieved using the coral data is indistinguishable from that achieved using the NINO3 SST anomaly index and suggests that a few well‐located coral reconstructions with low observational error may be sufficient to reconstruct the global SST anomaly field associated with ENSO activity.