Precipitation changes in the western tropical Pacific over the past millennium

摘要

Modern seasonal and inter-annual precipitation variability in Palau is linked to both meridional movement of the Intertropical Convergence Zone (ITCZ) and changes in the Pacific Walker Circulation (PWC) associated with the El Nino-Southern Oscillation. Thus, Palau's hydroclimate should be sensitive to mean shifts in the ITCZ and PWC on decadal to centennial time scales. Using compound-specific hydrogen isotope ratios (delta H-2) of dinosterol in lake sediments, we generated a decadal-resolution proxy record of hydroclimatic variability in Palau spanning the past 800 yr. Results indicate a drying trend during the Little Ice Age in Palau, consistent with a southward displacement of the ITCZ. In addition to the secular drying trend, there are persistent large (similar to 20%) multi-decadal to centennial oscillations in the delta H-2 record, the most recent of which indicates an abrupt shift to drier conditions in the mid-1970s that coincides with a decadal-scale negative shift in the Southern Oscillation Index.