Spatial variations in paleowind direction during the last glacial period in north China reconstructed from variations in the anisotropy of magnetic susceptibility of loess deposits

摘要

Anisotropy of magnetic susceptibility (AMS) of Chinese loess is considered to be an effective tool for determining paleowind direction. However, the relationship between AMS and the paleowind direction is still a matter of debate. This study reports the results of AMS measurements of Chinese loess deposited during the last glacial period on slopes of varying slope angles and orientations. The sites are located on the Chinese Loess Plateau, in West Qinling, and on the eastern margin of Qilian Mountain. The results show that within the same region, magnetic lineations are clustered along similar orientations despite differences in slope exposure and slope angle, but that different regions exhibit different directions of magnetic lineation. These results suggest that the alignment of themagnetic grains during deposition of the eolian deposits was determined by air circulation rather than bywater flowon the surface of the slopes, and therefore that the AMS of Chinese loess can be used to determine paleowind directions. In addition, our results indicate that the AMS of Chinese loess is determined mainly by the patterns of regional surface wind flow that occurred during dust accumulation rather than by the uniform pattern of large-scale atmospheric circulation. In addition, since wind direction is influenced significantly by regional topography, the AMS of Chinese loess may have the potential to detect significant changes in past regional topography.