East Asian Summer Monsoon Variability Over The Last Millennium Recorded By Stalagmite In Cave Shuidong, Liaoning Province

Asian summer monsoon（ASM） contributes most of precipitation totals in Asia and provides the water required for all agriculture activities. A better understanding of the nature of the ASM is necessary to improve our adaptability to extreme climate, especially under the background of ongoing global warming. The stalagmite oxygen isotope has been a valuable strategy in the studying of EASM. However, until now most of stalagmite records of EASM were derived from Northern China, where the local climate also influenced by India Summer mosoon more or less. In this study, stalagmite TW705 in Northeastern China, caves Miao Dong and ShuiDong of Benxi Liaoning Province, will be chosen to reconstruct high resolution proxy index of EASM during the last millennium, based on MC-ICP-MS-230 Th dating and high resolution stable oxygen isotope analysis. The second purpose of this study is to discuss the nature of decade-scale and century-scale variability of the EASM and its forcing mechanism.The cave Miaodong is located in northeastern China, a northern margin region of the East Asian Summer Monsoon（EASM）. Its Climate is sensible to oscillation of EASM. High-resolution stalagmite δ¹⁸O record in this area is important for understanding the evolution and mechanism of EASM. However, interpretation of stalagmite δ¹⁸O is never straightforward due to complex karst processes. Thus, knowledge about transfers of seasonal isotopic variability among meteoric precipitation, drip-water and its calcite deposition is crucial for better understanding of stalagmite δ¹⁸O. To this end, sub-monthly in situ monitoring of δ¹⁸O in the meteoric precipitation, drip-water and calcite deposition rate was carried out at cave Miaodong, Liaoning province, through two hydrological years（from January 2012 to December 2013） to determine the seasonal variability and mechanisms of oxygen isotopic transfer in Miaodong. In this research, drip water δ¹⁸Ow response to rainfall δ¹⁸O well,and snowfall contribute much less to the drip water.Stalagmite TW705, from Shuidong and a length of 186 mm, based on 13 high-precision U/Th dates and a total of 371 isotope measurements, with δ¹⁸O values ranging from-9.20‰ to-7.57‰, provides a continuous history of the Asian monsoon over the past 1000 years. According to the above study, the TW705 δ¹⁸O record is a proxy for Asian Summer monsoon intensity（rainfall amount）. The δ¹⁸O curve shows Asian summer monsoon variability on inter-decadal to century scale. The oxygen isotope profile clearly shows that Medieval Warm Period fluctuated from a stronger monsoon（from AD842¹008）to a weaker monsoon（from AD1008¹224）.The Little Ice Age is mainly characterized by a strong monsoon event, which is interrupted by weaker monsoon events during later Ming dynasty（from AD1503¹670）. Power spectrum analysis of the δ¹⁸O records shows significant 7, 10, 11, 402 year periodicities. According to investigate primary research on short-term and long-term driving mechanisms over the past millennium, this dissertation inferred the variability of Asian summer monsoon correlates with the ocean-atmosphere interactions interfered by external factors.