No abstract

The evolution and driving factors underlying dust activity in central Asia remain controversial, particularly in its effects on downwind regions. We present a Holocene dust storm activity record retrieved from the Tarim Basin (TB) and perform linear and nonlinear analyses on dust records from the TB and the Greenland areas. The results indicate a similar response of dust activities to total solar irradiance in both areas, and an outbreak of dust storms in the TB at ~3.5 kyr BP. We suggest that decreasing temperature in high northern latitudes, aided by solar activity change, reached a critical threshold near ~3.5 kyr BP. The resulting steepening of the meridional temperature gradient would have facilitated strengthening and southward shift of the Northern Hemisphere westerly jet, leading to the outbreak of dust storms through intensification of low level wind intensity and prolonged spring conditions in the Asian interior.

[1] Considerable attention has recently been paid to the magnetic properties of loess deposits in Central Asia. However, paleoenvironmental interpretations of magnetic properties of loess deposits in South Tajikistan, the Ili Basin, and the Tarim Basin remain controversial. Current meteorological observations demonstrate that the mean annual precipitation in the Junggar Basin exceeds that in the Tarim Basin and falls below that in the Ili Basin and South Tajikistan. This study of rock magnetism in loess from the Junggar Basin improves our understanding of the complicated relationships between magnetic properties, climate, and source materials for loess deposits of Central Asia. This study involved multiparameter investigations of rock magnetism in a 71 m loess section in the Dongwan area, on the northern slope of the middle Tian Shan (in the Junggar Basin). Variations in concentration of coarse eolian ferrimagnetic minerals appear to provide the main control over the magnetic properties of loess in this area. The contribution of ultrafine pedogenically produced magnetic grains to the magnetic susceptibility (c) is minimal. Furthermore, long-term increasing trends in the c and the saturation isothermal remanent magnetization (SIRM) were found in the Dongwan loess section. These trends may be linked with intensified aridification of Central Asia in the mid-Pleistocene. This study suggests that reduced precipitation of westerly moisture from Tajikistan into the Tarim Basin might play a critical role in the paleoenvironmental interpretations of magnetic properties in the loess deposits of Central Asia.