Discussion of the relationship between dustfall grain size and the desert border, taking the southern border of the Tengger Desert and the southern dust deposit area as an example
Abstract In northern China, high spatial and temporal instability exists in the southern desert border. Since the region is very sensitive to the changes of global climate and the migration of the southern desert border threatens the survival of surrounding inhabitants, it is very important to strengthen the research about the migration of the southern desert border of northern China. The dust in the downwind of the desert contains relevant information of the desert evolutionary history. In order to investigate the relationship between dustfall grain size and the southern border of northern China desert, we collected 56 eolian surface soil samples from the south of the Tengger Desert, selected two near north–south transects from these samples and used the grain size class-standard deviation method. We finally obtained three sensitive grain size components (ranking by degree of sensitivity from high to low): 61.8–185.4 μm, 18.2–61.8 μm and 2.3–18.2 μm. The values of the three sensitive grain size components from the 56 eolian surface soil samples and the three commonly used grain-size indicators, which are the median grain size, > 20 μm and > 63 μm particle content, have been converted to the grain-size contour figures. In the six grain-size contour figures, the contour of the 61.8–185.4 μm particle content component has the highest degree of similarity with the southern border of the Tengger Desert, followed by the > 63 μm particle content component, and then the components of the median grain size, 18.2–61.8 μm particle content, > 20 μm and 2.3–18.2 μm particle content in turn. Relative to the > 20 μm and > 63 μm particle content indicators, the indicator of 61.8–185.4 μm particle content is not only the most sensitive one in theory, but also has the highest degree of similarity between its contour and the southern desert border in practical terms. Moreover, this indicator is further defined as the upper limit of coarse grain size. Since the coarse grains in the eolian deposits are mainly from the near-source desert, the component of 61.8–185.4 μm particle content within the loess to the south of the Tengger Desert could be regarded as the indicator of the migration of the southern desert border, which could be used to quantitatively reconstruct the desert palaeo-border in the future.