The Variation Of East Asian Monsoon Over The Past Two Millennium From A Stalagmite Record,central Zhejiang Province

Recently,climate change in the past 2000 years has become a hot spot in paleoclimate research.Based on 9 ²³⁰Th ages and 300 oxygen isotopes of stalagmite SY6 from Songya Cave,Zhejiang province,we reconstruct East Asian summer monsoon record with 5.4 years resolution during 224?1862AD.SY6 stalagmite?¹⁸O record matches another stalagmite?¹⁸O from the same cave well,indicating stalagmite SY6 are basically deposited under isotope equilibrium fractionation.In order to test the climatic significance of stalagmite?¹⁸O,we compare the drought/flood index and instrumental summer rainfall?May to September?of Jinhua station with stalagmite SY6?¹⁸O record and find SY6?¹⁸O is conherent with them.Thus,stalagmite SY6?¹⁸O reflects the variation of the East Asian summer monsoon precipitation on centennial to decadal scale.The lower stalagmite SY6?¹⁸O values reflect increased East Asian summer monsoon precipitation,and vice versa.In Asian monsoon region,different stalagmites records behave a similar trend characteristic on the millennium to centennial scale.The regional precipitation discrepancy on the decadal scale may be related to the north-south movement of the westerly belt and the length of its residence time,causing monsoon precipitation spatial difference on the short scale.The growth period of stalagmite SY6 covers three climatic characteristic periods including Dark Ages Cold Period?DACP?,Medieval Warm Period?MWP?,and the Little Ice Age?LIA?.The East Asian monsoon precipitation showed increased first and then weakened slightly.The East Asian monsoon precipitation weakened slightly before 1750AD during LIA,monsoon precipitation weakened significantly since 1750AD.The stalagmite SY6?¹⁸O clearly depicts the significant weakend monsoon periods such as the Late Tang Weak Monsoon Period,the Northern Song Strong Monsoon Period,the Late Yuan Weak Monsoon Period and the Late Ming Weak Monsoon Period.Futhermore,we mark the major drought events,high-frequency war periods and well-known peasant uprisings on the stalagmite SY6 time scale.It was found that the above events all occurred in higher?¹⁸O phase,and the monsoon precipitation decreased,indicating that the evolution of civilization link the monsoonal climate tightly,and further confirm that the stalagmite SY6?¹⁸O singal captures the East Asian monsoon precipitation oscillation accurately on the decadal scale and shorter scale.The power spectrum analysis results show that stalagmite SY6 have significant cycles of 545,182,121,18,and 11?13 years.Except for the 545-year cycle,other cycles are close to 200,123,22,and 11 years cycles of solar activity,respectively.Wavelet analysis also shows significant periods of?11 years and 121?200 years cycles,suggesting solar activity had played an important role in regulating the East Asian monsoon climate over the past2000 years.The anti-phase relationship between the stalagmite SY6 and the ice cores ¹⁰Be record and the total solar irradiance record,which may be caused by the release of latent heat from the ocean in the southern hemisphere to affect the Asian monsoon in the northern hemisphere needs nearly 100 years.The stronger solar activity period corresponds to stronger East Asian monsoon precipitation period,which indicates that there is a lag in the regulation of solar activity on the East Asian monsoon on centennial to decadal scale.During strong volcanic activity periods,the climate is mostly cold,however the East Asian monsoon precipitation decreased was not significant.Instead,the monsoon precipitation record showed multi-second-order strong monsoon hydrological cycles,indicating the variation of temperature and precipitation in the different direction.The water vapor of monsoon precipitation in Songya Cave region mainly comes from the Pacific Ocean.This study found that the Intertropical Convergence Zone precipitation index and stalagmite SY6?¹⁸O sequence change basically synchronously.When the northward movement of the tropical convergence zone,the East Asian monsoon precipitation increased.The high-resolution ENSO records are consistent with stalagmite SY6?¹⁸O,and the comparsion shows a good coupled correlation on decadal scale.ENSO developed into El Ni?o status,accompanied by the increased monsoon rainfall in East Asia,and vice versa.In addition,the East Asian monsoon also closely linked to the Pacific Decadal Oscillation and Asian-Pacific Oscillations,and the Pacific moisture plays an important role in the East Asian monsoon climate.