The Evolution Of East Asian Summer Monsoon During Mid Holocene Recorded By A High-resolution Stalagmite From Fujian

The East Asian Summer Monsoon（EASM）is one of the most important components of the global monsoon system,which brings a large amount of moisture and influences the lives of millions of people in this region.Improving the understanding of the EASM variability during the Mid-Holocene Climatic Optimum is crucial to understanding the underlying mechanism and assessing its future behavior.Studies have shown that East Asia experienced several abrupt centennial-scale weak monsoonal events in the mid-Holocene,such as the―6.3 ka‖and―5.5 ka‖events.However,the timing,structure and geographical extent of these climate events remain unclear due to the lack of precisely dated and highly resolved records.With advantages of accurate U-Th dating and high-resolution paleoclimate reconstruction,stalagmites are widely used to study abrupt Holocene monsoon events.Yet existing stalagmite records covered the mid-Holocene are mainly concentrated in central and southwestern China,with few records from southeastern China.In this study,we present precisely dated and high-resolution EASM records derived from two well-duplicatable stalagmite（CXY1708 and XYⅢ-33）isotope sequences from Xianyun Cave,southeastern China.These 3-year resolved EASM records,covering the interval of 6.70～4.53 ka BP,supply an opportunity to investigate the timing,structure,and mechanism of abrupt monsoon events on decadal to centennial time scales during the mid-Holocene.The Xianyun Cave stalagmiteδ¹⁸O values range from-8.83‰to-7.32‰,with an amplitude of 1.51‰.Our stalagmiteδ¹⁸O record shows four weak summer monsoon events at 6.3,5.9,5.3,4.8 ka BP,which are also reflected in other stalagmite records in the Asian monsoon region.The―6.3 ka‖event occurred from 6.53～6.22 ka BP for～310 yr,with an amplitude of0.66‰.The―6.3 ka‖event is characterized by a slow weakening and an abrupt termination,accompanied by decadal to multi-decadal scale fluctuations.The―5.9 ka‖weak monsoon event spanned from 5.92 to 5.70 ka BP,which is different from other stalagmite records in the Asian monsoon region.The reasons for the discrepancy remain unclear,which may partly relate to age uncertainty,sample resolution or different regional responses.In addition,The 5.3 ka event occurred between 5.37 ka BP and 5.26ka BP.Both of the two events have an amplitude of 0.74‰.To clarify these events,more high-resolution records are needed.By comparing with other records,we found that theδ¹⁸O sequence of Xianyun Cave stalagmite is in good comparison with total solar irradiance,SST of equatorial eastern Pacific and ENSO records.Meanwhile,the power spectrum analysis results also show a significant solar activity cycle（542-yr and 197-yr）.The results indicate that the centennial and decadal monsoon changes of the Mid-Holocene in Fujian are mainly influenced by solar activities and sea-air processes（El Nino,etc.）.In addition,the high-resolution records of EASM reconstructed by stalagmiteδ¹⁸O in Xianyun Cave provide a reference for the climatic background of Qiaoqiutou and Tanshishan Cultures.In the mid-Holocene,the relatively warm climatic conditions and geographical location of the southeast coastal area enabled the ancestors of the region to form an economic form of gathering,fishing and hunting,which effectively reduced the negative impact of weak monsoon events.