The Stalagmite In Longfugong Cave Records The Asian Monsoon Abrupt Event From The Late MIS3 To The Early Holocene

The unstable climate and the catastrophic events of the last glacial period is worth researching.It is helpful to understand the inner mechanism of climate and to predict the future environment.Longfugong Cave(110°47'E,31°43'N;500m above sea level)is located at Mt.Shennongjia,Hubei Province,central China.The cave is approximately 400m in length,and the relative humidity inside is close to 100‰.The mean annual precipitation at this site ranges between 1500mm and 2000mm with the strong influence of the East Asian monsoon,60%of which falls during summer from June to September.Two stalagmites of LFG(LFG20,LFG21)were collected in the deep chamber of the cave.A total of 2294 subsamples were obtained along the growth axis,and the stable isotopic analysis was performed on a MAT-253 mass spectrometer fitted with a Kiel Carbonate Device.Thirty-five subsamples for U/Th dating were drilled,processed and measured on a Thermo Fisher Neptune Multi-collector Inductively Coupled Plasma Mass Spectrometer(MC-ICP-MS).All the measurements were conducted at the Isotope Laboratory of the College of Geography,Nanjing Normal University.We present a high-resolution record of Asian Summer Monsoon evolution over a period from 28.2 to 7.2ka B.P.,through the late episode of marine isotope stage 3(MIS3)to the early Holocene.The ?18O values range from-10.3‰ to-6.0‰,and the amplitude is small.The ?68O records of two stalagmites have a good reproducibility from the late episode of marine isotope stage 3(MIS3)to Last Glacial Maximum(LGM).The overall pattern and the abrupt change events in ?18O record,agrees well with speleothem records from Hulu Cave and other geological records.These two features indicate the accuracy of the experimental data and equilibrium deposition of the stable isotopes of LFG.The climate of the late episode of marine isotope stage 3(MIS3)is warm and moist,but LGM is very cold.Power spectrum analysis of episode in ?18O data identifies intense solar activity cycles with 133a,116a,79a,73a,69a,42a,38a,37a,28a,25a,20a.At the beginning phase of H1 event,the EASM is characterized with two monsoon weakening,consistent with Hlb and H1a presented in ice rafted debris records and other speleothem records.During the early stage of the H1,the ITCZ shifts southward,leading to the abrupt EASM weakening at about 17 ka B.P.And the second evidently weak Asian Monsoon event,with a duration of 80 years,also occurred at about 15.6 ka B.P.,coinciding with the 'drought-wet' transition reconstructed from New Mexico's Lake Estancia in America This may be associated with a southerly migration of ITCZ,caused by the extension of sea ice around North Atlantic Ocean.A positive shift of ?18O values from-8.6‰ to-7.9‰ at around 11.71 ka B.P.,which is also mirrored in the carbon isotope composition with ?13C values from-7.4‰ to-6.0‰,indicates a?200a monsoon failure within the YD.The structures and transitions of YD event in LFG?18O record are equally registered by the ?18O record of the H1 event(Heinrich 1)from Hulu Cave,possibly implying the same forcing mechanism.The calcite ?18O record,which presents abrupt fluctuations and detailed instabilities in monsoon over the studied interval,shows coherence with ice-core ?18O record from Greenland,supporting the direct linkage between Greenland climate and monsoonal circulation.Basing on the comparison with the bulk sedimentary titanium(Ti)records from the Cariaco Basin,we attribute the internal centennial monsoon failure to the southward displacement of the Intertropical Convergence Zone(ITCZ).The statistically significant periodicities of?128a(?13C)and?200a(?18O)from the wavelet analysis likely indicate the role of solar activity playing in monsoon,and this is further supported by the 10Be flux record derived from ice core.