Interannual and decadal variability of the western Pacific sea surface condition for the years 1787-2000: Reconstruction based on stable isotope record from a Guam coral

We present a monthly resolved, 213-year stable isotope time series from a coral from Guam (13°N, 145°E), which is located on the northern edge of the western Pacific warm pool. Oxygen isotopic composition of the coral skeleton (δ ¹⁸O_coral) shows seasonal, interannual, and decadal variability, which documents significant oceanographic changes related to thermal and hydrologic variations in this region. The δ¹⁸O_coral anomaly reflects sea surface temperature (SST) anomaly and sea surface salinity (SSS) anomaly with significant r values of -0.69 and 0.49, respectively, which are strongly linked to oceanographic changes that occur during El Niño-Southern Oscillation (ENSO) warm and cool phases. We identified 46 ENSO warm (El Niño) and 53 cool phases (La Niña) in the coral record, which are consistent with those phases reconstructed by Niño 3.4 SST anomaly. Spectral analyses of the δ ¹⁸O_coral anomaly record for the years 1790-1999 identified significant peaks around ∼3 to ∼7 years. These results indicate that the Guam coral has recorded ENSO periodicity. The δ¹⁸O_coral anomaly shows decadal variability of ∼15- to ∼45-year periodicity with significant shifts (<0.2‰) from warmer to cooler condition and vice versa. An accumulative decrease in δ ¹⁸O_coral time series may imply ∼0.75°C warming of SST and ∼0.23‰ freshening of seawater δ¹⁸O, corresponding to a decrease of SSS by ∼0.85, in the northwestern tropical Pacific over the last 2 centuries.