摘要
以洛川黄土剖面中 >30 μm的粗颗粒含量作为东亚冬季风强度代用指标 ,根据模式并结合绝对年代控制点建立了较精确的独立的时间标尺。对该时间序列进行了小波变换分析和频谱分析。结果表明 ,最近 10 2 4ka以来东亚冬季风变化在 12 8ka和 6 4ka时间尺度上幅度最大 ,更短或更长的时间尺度冬季风变化幅度减小。东亚冬季风变化的 10 0 ka和 2 1ka等周期可能受地球轨道运动驱动的太阳辐射量变化控制 ,而 5 7ka和 33ka等周期的驱动机制还有待于进一步查明。
The loess paleosol deposit at Luochuan,central Chinese Loess Plateau,was investigated in order to obtain pattern and frequency of the monsoon climate change in the Pleistocene on 10 4～10 5 year time scale.The deposits in thick profiles were sampled at interval of 5～10 cm,and all the samples were measured for grain size distribution using FRITSCH A22 laser particle sizer(LU et al,1999).The >30μm coarse fraction of grain size distribution was employed as a proxy index of East Asia winter monsoon strength.An absolute and detailed time scale for the loess deposit was obtained by citing the palaeomagnetic results which offer an age control(Kukla and AN,1989),and interpolating age of each sampling level by a sediment grain size model(Porter and AN,1995).Thus,a time series representing the winter monsoon change in the past one million years have been obtained.Wavelet and spectral analyses were performed on this time series,showing that the winter monsoon strength presents higher fluctuation amplitude on 128 ka and 64 ka time scale than that on shorter or longer time scale,indicating that the fluctuation amplitude was gradually reduced on both the shorter and longer time scale.And the variability of the winter monsoon strength represents different patterns due to different time scales:high frequency on the shorter time scale but lower frequency on the longer one.The spectral analysis shows that there exist 100 ka and 21 ka periodicities which should be related to the ice volume variations induced by the solar radiation changes.The origins of periodicities of 57 ka and 33 ka in this time series are still unclear,they may be in harmony with the orbital frequencies and/or a product of interaction of the monsoon system.This study preliminarily examines the East Asian winter monsoon changes by wavelet technique,but further research is needed to develop the application of the wavelet analysis to palaeoclimatic study.
出处
《海洋地质与第四纪地质》
CAS
CSCD
北大核心
2000年第2期79-82,共4页
Marine Geology & Quaternary Geology
基金
中国科学院"九五"重大项目!( KZ95 1-A1-4 0 2 )
