Size-dependent geochemical characteristics of Asian dust - Sr and Nd isotope compositions as tracers for source identification

Aerosol samples, which are dust suspended in the atmosphere, were collected in Qira, Aksu, and Shapotou in 2001 and Qira, Dunhuang and Shapotou in 2002, which are located between north-western and central China, one of the possible source areas of Asian dust. Their chemical and isotopic compositions, mainly Sr and Nd isotopic compositions, in the total suspended particles (TSP) and finer fraction (phi < 5 mu m) in the TSP were analysed. There is a slight difference in the chemical compositions of TSP and the phi < 5 mu m fraction that can probably be attributed to the relative increase of silt and/or clay in the phi < 5 mu m fraction. Sr-87/Sr-86 ratios were 0.71770-0.72030 in the TSP and 0.72349-0.72737 in the phi < 5 mu m fraction over all sampling sites, although epsilon(Nd)(0) values were relatively constant, from - 11.3 to -9.3. The isotopic characteristics due to the variation of particle size are clearly seen in Rb-Sr and Sr-Nd isotopic correlation diagrams, which are useful aids to identify the sources of Asian dust. In addition to the possible isotopic change with particle size, results of Sr and Nd isotopic measurements suggest that the broad area from the north-western to the central part of China, i.e. from the Taklimakan Desert to the Central Loess Plateau, is characterized as a single possible source component of Asian dust. Clarifying the correlation between geochemical features and particle size is an important requirement that may allow the correlation of long-range transported Asian dust to possible source materials.