Assessment of sungkai tree-ring δ18O proxy for paleoclimate reconstruction in western Java, Indonesia

To assess the reproducibility of sungkai δ18O as paleoclimate proxies, we measured annual δ18O variations of two sungkai trees that had been collected in the same area as in a previous study. Two sungkai δ18O variations showed significant mutual correlation (r = 0.80; P < 0.001) and correlation with results of earlier analyses, suggesting that external climatic factors affect the δ18O values of sungkai. The annual δ18O of SungkaiNAN7 shows significant, positive correlation with temperature, sunlight hours, and air pressure. It shows significant, negative correlation with relative humidity and SOI. Moreover, the seasonal δ18O variation acquired during severe drought of the 1997-1998 El Niño event shows that the maximum δ18O value around 1997 latewood corresponds to the rainfall/relative humidity minimum and corresponds to the temperature/sunlight hours/air pressure maximum with a considerable time lag.