Tree-ring δ~(18)O based PDSI reconstruction in the Mt. Tianmu region since 1618 AD and its connection to the East Asian summer monsoon

摘要

Previous studies on tree-ring stable oxygen isotopes (delta O-18) in the monsoon region of China have rarely involved in variations of the East Asian summer monsoon (EASM) and its rainbelt. In this study, a tree-ring delta O-18 chronology of Cryptomeria fortune at Mt. Tianmu, located south of the Yangtze River lower reaches, was developed and applied to reconstruct the local June-October Palmer Drought Severity Index (PDSI6-10) during the 1618-2013 AD period. The reconstruction explains 40.5% of the observational PDSI6-10 variances during 1951-2013, captures the actual variation features at both high and low frequencies, largely represents the PDSI6-10 in the middle and lower reach regions of the Yangtze River and further south, and the reconstruction is well-compared with other existing proxies. The reconstruction reveals that the durations of 1620 s-1660 s, 1680 s-1700 s, 1810 s-1830 s, 1850 s, 1900 s-1940 s, and 1960 s were drought periods, while wet durations were 1730 s-1770 s, 1790 s-1800 s, 1860 s-1870 s, 1950 s, and 1980 s-1990 s. Based on the meteorological re-analysis data and new EASM definitions, the reconstructed PDSI6-10 correlates with the meiyu rainbelt precipitation and EASM intensity during May-June, which is when Mt. Tianmu is affected by the EASM rainbelt. The Mt. Tianmu tree-ring delta O-18 chronology exhibits significantly positive correlations with El Nino-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). The relationship of the tree-ring delta O-18 chronology with the PDO could be due to EASM associations, while it is not clear to explain the mechanism of ENSO connecting to the tree-ring oxygen isotope.