Hf-Nd-Sr isotopic fingerprinting for aeolian dust deposited on glaciers in the northeastern Tibetan Plateau region

摘要

This study investigated the isotopic compositions of Hf, Nd, and Sr in aeolian dust deposited in several glacier basins of the northeast Tibetan Plateau in order to trace the source and provenance of long-range transported (LRT) dust in the region. Transmission electron microscope (TEM) and energy dispersive X-ray spectrometer (EDX) measurements and dust size distributions both indicated that LRT dust was dominant in glacier cryoconite and snowpacks. Isotopes of Hf-Nd-Sr exhibited a generally heterogeneous geographic distribution that varied from north to south. The northern sites (e.g. Miaoergou Glacier) in the Tianshan Mountains showed much higher epsilon(Nd) and epsilon(Hf) values, whereas the southern sites (e.g. Yuzhufeng Glacier) in the Kunlun Mountains had lower epsilon(Nd), with the Hf isotope exhibiting two parts: one positive epsilon(Hf) section and one negative epsilon(Hf) section. Lower Sr-87/Sr-86 ratios were apparent in the Miaoergou Glacier compared to other locations. In general, the Miaoergou Glacier had similar Hf-Nd-Sr isotopic compositions to those of southern Mongolian Gobi and Taklimakan Deserts. By contrast, Qilian Mountain locations exhibited similar Hf, Nd, and Sr isotopic compositions to those of the north Tibetan Plateau soil crust and Chinese Gobi Deserts. However, the Yuzhufeng Glacier, located in the hinterland of the Tibetan Plateau, had LRT dust that was derived predominantly from the north Tibetan Plateau desert and surface crust, but also partly from the Taklimakan desert. Compared with Nd-Sr isotopes, Hf-Nd isotopes provided new evidence for LRT dust transport. For example, the Yuzhufeng and Miaoergou Glaciers had similar Hf-Nd isotopes to those of the Taklimakan Desert and Mongolian Gobi, respectively, implying the potential LRT dust source and atmospheric transport routes. The marked spatial differences in LRT dust source were mainly caused by large-scale atmospheric circulation interactions (e.g. the Mongolian High and Westerlies) during spring and summer. Wind stream analysis and MODIS AOD also demonstrated the potential differences in the sources of dust and the routes taken between northern and southern locations. This work provides new evidence and a more complete view of aeolian transport over the northeast Tibetan Plateau region under the current climate.