Teleconnection Responses Of Stalagmite Records To ENSO Signals In The Middle And Lower Reaches Of The Yangtze River

The Yangtze River Basin makes a significant contribution to the sustainable development of China's economy and ecology,both spatial and temporal changes of precipitation in this region will significantly affect the spatiotemporal distributions of water resources,thus leading to the occurrence of droughts or floods and having impact on society and regional economies.In recent years,El Nino/Southern Oscillation(ENSO)activity plays an important role in the process of modern meteorological change,paleoclimate evolution and precipitation pattern change.It is very important for social and economic development to understand the trend of its change with global warming.Here,we derive a precisely ²³⁰Th-dated and high-resolution stalagmite?¹⁸O record from the Luoshui cave(29°44?N,109°7?E;1071m),Yongxing cave(31°35?N,111°14?E),Enshi,Hubei Province,Central China.The stalagmite(LS45)was collected in the chamber with a total length of about 237mm.This sample is divided into two sections of 0?130mm and 130?237mm because of growth hiatus at the depth of 130mm,so,the section of 0 mm to 130mm is the research area.Besides,the growth rate is stable throughout the entire stalagmite,as is by the ²³⁰Th dating results.And the stalagmite(YX230)was collected in the chamber with a total length of about 305mm,opalescent/dark layer can be clearly seen on the polished surface,which is basically judged as annual lamination,the section of 10mm to 305mm is the research area because of growth hiatus at the depth of 10mm.This paper stalagmite YX230 year time scale is established based on the annual lamina count and the absolute dating results.When halved and polished,it is composed of pure and transparent calcite with homogeneous lithological characteristics.We present a continuous high-resolution record of East Asian Summer Monsoon(EASM)evolution from 280 A.D.to 1850 A.D.,roughly contains three periods of Dark Times Cold Period(DACP),Medieval Warm Period(MWP)and Little Ice Age(LIA).The dating measurements were then conducted by multi-collector inductively coupled plasma mass spectrometer(MC-ICP-MS)at the Isotope Laboratory of Nanjing Normal University,and isotope geochemistry laboratory at the Earth Observatory of Singapore,Nanyang Technological University,Institute of Global Environmental Change,Xi'an Jiaotong University,Department of Earth and Environmental Sciences,University of Minnesota,the error is±2 sigma.The oxygen isotopic analyses were run at the Isotope Laboratory of Nanjing Normal University with Finnigan MAT-253 mass spectrometer.Precisions for?¹⁸O is±0.06‰and±0.05‰for?¹³C.The ?¹⁸O values of the stalagmite(LS45)vary from-8.2‰?-7.3‰and its maximum amplitude is close to 0.9‰,the average value is about-7.7‰,and the overall fluctuation range is small.The average?¹⁸O Values during the periods of 800?1400A.D.is negative,implying relatively stronger ASM and corresponding to the period of MWP.And the average?¹⁸O values during the periods of 280?800 A.D.and 1400?1850A.D.is positive,implying relatively weaker ASM,corresponding to the period of DACP and LIA respectively.The general trend of?¹⁸O record from stalagmite LS45 is temporally consistent with the stalagmite records from the Heshang Cave in Hubei,the Wanxiang Cave in Gansu,the Dandak Cave in India and red color in Laguna Pallcacocha within dating errors.The LS45 ?¹⁸O record shows that the intensity of Asian summer monsoon(ASM)has decreased in the past 2000 years in general.Three episodes reflected in our record show weak-strong-weak pattern of monsoon,and is punctuated by several centennial-interannual scale oscillations throughout the entire studied interval.It is observed that ASM is strongly weakened during the DACP and LIA.However,we found that DACP and LIA were not continuous cold periods lasting for several centuries,and there were regular secondary fluctuations of warm and cold times within them.These two episodes,also recognized in other stalagmite records,corresponds to weak solar activities.But the factors of the monsoon system on the centennial-decadal scale are very complicated.Besides,at the transition from DACP to MWP,ASM strengthened abruptly,taking place in about 40 years,indicating a rapid atmospheric circulation transition.This fast process is also mirrored in Heshang Cave,Wanxiang Cave,Dandak Cave records and red color in Laguna Pallcacocha,within dating errors.The abrupt monsoonal shift is consistent with a fast warming in the Atlantic sea surface temperature(SST),shift of Intertropical Convergence Zone(ITCZ)and Northern Hemisphere temperature,a sharp strengthening of both El-Nino activities and solar activities,this indicates that this mutation process is related to the increase of solar activity,ITCZ,Atlantic Multidecadal Oscillation(AMO)and the increase of ENSO activity.In addition,ENSO and AMO may be important amplification mechanisms and transmission mechanisms of solar activity signals regulating the East Asian summer monsoon.Based on the three stalagmites from Yongxing cave in the middle and lower reaches of the Yangtze River(YX230 as the data,18 ²³⁰Th ages and 306 sets of oxygen and carbon isotope data),the monsoon evolution sequence with an average resolution of 1.8 years in recent 1200 years is reconstructed.The?¹⁸O values of the stalagmite(YX230)vary from-9.5‰?-7.7‰and its maximum amplitude is close to1.5‰,the average value is about-8.7‰,and the overall fluctuation range is large.The ?¹⁸O records of the stalagmite YX230 and the Palmyra coral records have high similarity in the interdecadal scale.The power spectrum analysis shows that the stalagmite records have similar cycle changes with ENSO records.The above studies indicate that the?¹⁸O records of the stalagmite in the middle and lower reaches of the Yangtze River have the characteristics of ENSO activity evolution,which is also proved by the intensity index of the Meiyu front in the middle and lower reaches of the Yangtze River.The changes of EASM over the middle and lower reaches of the Yangtze River are correlated with ENSO activities on different time scales.On the interdecadal scale,when EASM-ENSO is significantly correlated,the ENSO-related circulation anomalies show an East Asia/Pacific(EAP)teleconnection,which is related to the enhancement(suppression)of rainfall anomaly over the western North Pacific and the north-south displacement of westerly jet.Meanwhile,it is also driven by ENSO and PDO,indicating that the seasonal precipitation in the middle and lower reaches of the Yangtze River is significantly affected by the ocean-atmosphere correlation.ENSO and PDO mainly influence the intensity of the EASM through the position and intensity of the Western Pacific Subtropical High(WPSH).