Provenance of Aeolian Dust Revealed by (234U/238U) Activity Ratios in Cryoconites From High‐Altitude Glaciers in Western China and Its Transport and Settlement Mechanisms

Asian dust has significant impacts on atmospheric systems and global biogeochemical cycles. In this study, we applied the U isotopic method to trace sediments based on their comminuting age, analyzing the uranium isotopes of cryoconite samples from various glaciers in western China, including the Tibetan Plateau (TP) and Tianshan Mountains. We aimed to explore the spatial variability of the (U-234/U-238) activity ratio and residence time, as well as the transport mechanism of the dust cycle in the region. Additionally, we used Nd-Sr isotopes data from our previous work to jointly determine the provenance. Our results indicate that the average (U-234/U-238) activity ratios in southern TP glaciers are higher, with mean range of 0.981-0.993, while those in northeastern TP locations are lower, with mean of 0.974. This suggests a decreasing trend from south to north. In the Tianshan region, the (U-234/U-238) activity ratio is higher in central areas compared to eastern areas, with a mean range of 0.984-0.996, indicating a decreasing trend from west to east. U-Sr-Nd isotopes analysis showed that dust provenance is from multiple sources, including long-range transported and local dust inputs from the glacier basins, mainly originating from the TP surface and central Asian arid regions. Using the end-member mixing model analysis and meteorological data, we interpret that the cryoconite dust in eastern Tianshan and Qilian Mountains comes from a complex mixture of the southern Gobi, northern TP surface dust, and Taklimakan and Alxa arid deserts. In contrast, the glacial dust in southern TP locations originates mainly from the plateau surface dust. Our findings suggest that the uranium isotopes in high-altitude glaciers are primarily influenced by the origins of dust, which are affected by related atmospheric circulation. We also developed a conceptual model to illustrate the complete process of U isotopic fragmentation and migration changes during dust production, transport, and deposition in the TP region.