High-resolution Oxygen And Carbon Isotope Recording Of Stalagmites In The Mid-Holocene

As the most recent interglacial in the cycles of the Quaternary glacial interglacial,Holocene is an important period for the development of human social civilization.The character of climate change is extremely unstable.In this thesis,one stalagmite was collected from a cave in Jiangsu province,the Yangtze River's downstream and east of China.Based on the 3 U/Th dates,1452 annual layers,3064 oxygen and carbon isotopic data and 7611 trace element data,we reconstruct seasonal-annual resolution monsoon climatic history.The average resolution is 0.47 year.The stalagmite(ML13)cover a time span of 6100-4500a and the stalagmite ?180 record ranges from-9.70‰ to-5.58‰,with an average amplitude of 0.435‰ among neighboring data point.By Hendy test,the amplitude of the isotope changes in the same growth layer appears small and the weak correlation between ?180 and ?13C(R2=0.0921)indicates that carbon isotopes and oxygen isotopes are not highly correlated through kinetic fractionation.In addition,a good replication is observed between the stalagmite ML 13 and other stalagmite 8180 records in Asia.Therefore,it has been concluded that the stalagmite ML13 grew under the condition of isotopic equilibrium and the ?180 record of ML13 can be used as a reliable proxy for the reconstruction of the paleo-climate and paleo-environment.The ?13C record is coincident with the trace element Mg/Ca value in peaks and valleys;and their variation shows the corresponding relationship with annual layers in the season scale.On the one hand,it shows that the climate proxy has high reliability,on the other hand,it shows the common response mechanism of climate change:biomass of surface vegetation and soil possibly have a direct effect on the seasonal changes of the stalagmite ?13C record.In the areas influenced by the Asian Monsoon,the climate becomes warm and wet,the vegetation covered on the top of the cave develop rapidly,resulting in the much biomass and the strong oxydic dissolution of the residues and the related decrease of the ?13C values in the stalagmite;whereas the cold and dry climate in the winter contribute to the withered vegetation over the cave and the decreased biomass,and the roots respiration and the oxidation of the vegetation wracks become weak,finally resulting in the heavy isotope values.The results of power spectrum and wavelet analysis show that the 2-6a common cycle which is agree with the ENSO cycle,indicating that the ENSO cycle in the Pacific Ocean near the equator has a distant correlation with the precipitation in the east of China through the coupled atmosphere-ocean system;the cycles of 11a?21?22a?91a and 200a is in accordance with the cycles of solar activity,indicating that the dominate role of the solar activity in the Asian Monsoon system.The results from the wavelet also suggest that the detected cycles of 50-70a is in accordance with the cycle of Pacific Decadal Oscillation(PDO),which indicates that the correlation between the components of the climate system,and the PDO maybe control the Asian monsoon variation,such as the precipitation and the intensity.