中国黄土粒度的双峰分布及其古气候意义

Bimode Grain-Size Distribution of Chinese Loess and Its Paleoclimate Implication

中国黄土的粒度分布由分布峰度较高、分选较好的粗粒组分和分布峰度较低、分选较差的细粒组分叠加组成 ;前者代表了冬季风盛行季节近距离低空搬运的粉尘物质 ,其粒度指示了东亚冬季风所主导的近地面气流的强度 ,它在全样中的含量可能反映了冬季风粉尘的沉积通量 ;细粒组分可能主要为常态存在的、由高空气流搬运的远源粉尘 ,代表了黄土高原原始粉尘的本底 ,它的粒度特征与北太平洋西风带粉尘基本一致 ,可能指示了主要由西风带控制的高空气流的强度。黄土的粒度分布函数可用代表这两个组分分布的两个WEIBULL函数的和函数表示。用实测粒度分布数据对分布函数进行拟合可计算出该分布函数的各参数 。

Grain-size distribution of Chinese loess consistently shows bimode spectrum, which is composed of two distinct components. The main component is coarse grain size with, large kurtosis and narrow distribution range,makes up main part of loess material. This main component is likely produced in the season when winter monsoon dominate the paleoclimate of loess plateau, and therefore its grain size indicates East Asia winter monsoon strength. The other grain size component has a wide distribution range, lower kurtosis and fine average grain size. This fine component probably represents the general dust base level of atmosphere over loess plateau, which prevails in most of the season. In some extension, it is genetically connected to the Northern Hemisphere westerly. Grain size distribution function of Chinese loess can be expressed with a sum of two Weibull distribution functions that represent two components of loess grain size. By fitting measured grain-size data to proposed distribution function, all parameters of the function can be estimated. Meanwhile, distribution function as well as the ratio of the two components can also be obtained.