科研之友
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摘要
Independent dust provenance data play an important role in understanding changes in the atmospheric dust loading over geological time. Major elemental compositions and grain-size characteristics of the aeolian deposits (Xiangshan (XS) section) at the southeastern margin of the Tengger Desert in northwestern China demonstrate that the deposits are an intermediate product of the transportation of aeolian materials from the dust source area (deserts) to the dust depositional regions (Chinese Loess Plateau) that were likely formed by dust storm processes. The >40 mu m and 63-178 mu m fractions and the ratio of SiO(2)/TiO(2) of the XS section were used as proxies to reconstruct the surface wind regime over the last 20 kyr. The results show that the surface winds were much stronger and fluctuate acutely from 19.1 to 11.4 kyr. The winds gradually attenuated after the beginning of the Holocene and reached a minimum between 4.0 and 3.5 kyr BP. A sharp increase in surface winds occurred after 2.5 kyr BP. The surface winds in the Asian dust source area are largely consistent with the changes in winter monsoon strength documented by the Chinese loess deposits. Also, the stronger surface winds from 19.1 to 11.4 kyr coincide with the high mineral dust concentration determined from the Greenland ice core, except for the period of Bolting-Altered (B/A), when the atmospheric dust may have been washed out by enhanced global hydrological cycles although dust was still emitted from source areas. This suggests that the stronger surface winds in dust source areas can enhance the atmospheric dust loadings during the late glacial. The weakening surface wind regime during the Holocene may have greatly contributed to the decrease in dust concentration of the remote dust records. The paleo-environmental changes in the study area since 42.5 kyr BP are broadly in agreement with other adjacent records. However, the possible warm and humid spell of 42.5-19.1 kyr BP still requires verification.
