山西公海湖泊沉积物记录的大气粉尘现代过程

The Modern Processes of Atmospheric Dust Recorded by Sediments from Gonghai Lake,Shanxi,China

湖泊粉尘记录是研究区域大气粉尘演化历史的重要载体,而现代过程研究是定量提取湖泊沉积物中粉尘信号的重要基础。对山西公海湖泊沉积岩芯样品及周边不同类型的表土样品开展了粒度分析,并对岩芯样品进行粒度组分的定量分离。结果表明:全新世湖泊岩芯样品以黏粒(<2μm)、细粉砂(2~19μm)和粗粉砂(19~78μm)为主,粗粉砂组分的粒度特征与湖泊沉积物中的石英颗粒、黄土样品中的粗粒组分及现代大气降尘的粒度特征相似,石英颗粒的表面微形态也具有典型风成特征。因此,公海湖泊沉积物中粒径19~78μm的粗粉砂组分可用来代表大气粉尘的变化,这与湖泊沉积物中粗粉砂组分是大气尘暴降尘主要组分的认识一致。另外,公海湖泊冰面粉尘样品的平均粒径还具有从西北向东南递减的趋势,表现出与冬季风方向一致的特征,进一步表明公海湖泊沉积物中粗粉砂组分可以代表东亚冬季风强度的变化。因此,公海湖泊岩芯中的粗粉砂组分可用来重建全新世大气粉尘变化以及可能的东亚冬季风强度演化历史。

Lacustrine dust record is one of important documents for studying the evolution history of reginal dust, while the study of modern deposition processes of dust is the key basis to quantitatively extract dust signal from lake sediments. In the present paper, we analyzed the grain-size distributions of lacustrine sedi- ments from Gonghai Lake and different types of modern surface deposits from the catchment. In addition, we further quantitatively separated grain-size components of sedimentary core from Gonghai Lake. The re- sults indicate that lacustrine sediments from Gonghai Lake during the Holocene are mainly composed of clay （~2 t^m）, fine silt （2.19 t^m） and coarse silt （19--78 t^m）, and the grain-size distribution of the coarse silt is similar with that of the isolated quartz particles in the sediments, coarse component of loess and mod- ern atmospheric dust. Moreover, the surface of lacustrine quartz particles is characterized by typical aeolian features. Hence we conclude that the variation of coarse silt component in lake sediments from Gonghai Lake can be used to indicate the evolution of atmospheric dust, which is consistent with the knowledge that coarse silt component of lake sediments could be regarded as the main component of dust storm. In addition, the mean grain size of ice-trapped aeolian dust from lake-ice surface of Gonghai Lake decreases from northwest to southeast, and this direction is consistent with prevailing wind direction of winter monsoon, thus further indicating that the content of coarse silt component in sediments from Gonghai Lake can represent the varia- tion of East Asian winter monsoon. Therefore, it is suggested that the coarse silt component of sediments from Gonghai Lake can be used to reconstruct the variation of atmospheric dust and the possible evolution history of East Asian winter monsoon during the Holocene.