Sr–Nd isotope evidence for modern aeolian dust sources in mountain glaciers of western China Jianzhong XU, 1 Guangming YU, 1 Shichang KANG, 2 Shugui HOU, 1,3 Qianggong ZHANG, 2 Jiawen REN, 1 Dahe QIN 1 1 State Key Laboratory of Cryospheric Sciences, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou, China E-mail: jzxu@lzb.ac.cn 2 Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, China 3 MOE, Key Laboratory for Coast and Island Development, School of Geographic and Oceanographic Sciences, Nanjing University, Nanjing, China ABSTRACT. In order to apportion the dust sources of mountain glaciers in western China, the Sr–Nd isotopic compositions of insoluble particles were determined in snow samples collected from 13 sites. The combined plot of 87 Sr/ 86 Sr and " Nd (0) demonstrates a distinctive geographic pattern over western China, which can be classified into three regions from north to south. Samples from the Altai mountains show the lowest 87 Sr/ 86 Sr ratio and the highest " Nd (0) value, similar to the data of deserts in the north of China such as the Gurbantunggut desert. Samples from the southern Tibetan Plateau (TP) and Himalaya show the highest 87 Sr/ 86 Sr and lowest " Nd (0) values, resembling the local and regional dust sources found in the southern TP and Himalaya–India region. Samples from the Tien Shan and northern Tibetan Plateau exhibit intermediate 87 Sr/ 86 Sr and " Nd (0) values, similar to the data reported for the northern margin of the TP (NM_TP). However, three sampling sites, JMYZ (Jiemayangzong) located in the Himalaya and ZD (Zadang) and YL (Yulong) located in the southeast TP, presented distinctive Sr–Nd isotopic signatures typical of the NM_TP, suggesting potential long-range and high-altitude dust transport across the TP. 1. INTRODUCTION Glaciers in the mountains of western China are unique recording media of paleoclimate and paleoenvironment in mid-latitudes (e.g. Thompson and others, 2000). Based on particle concentrations in ice cores, researchers can back- calculate the historical aerosol loadings and composition, which reflect environmental change, such as historical dust- storm frequencies (Xu and others, 2007), extreme drought events (Thompson and others, 2000) and anthropogenic impacts (Hong and others, 2009; Kaspari and others, 2011) in the source area. Yet the connection between dust sources and sinks remains uncertain. For example, there is little knowledge of how dust gets lost and is altered during and after transportation. In the past decade, isotopic and geochemical methods have been developed to address these uncertainties. The strontium–neodymium (Sr–Nd) iso- topic composition was found to be particularly important as different source materials have unique profiles reflecting their origins and ages, and these profiles undergo little change during weathering, transportation and deposition (Biscaye and others, 1997; Grousset and Biscaye, 2005; Bory and others, 2010). Arid and semi-arid areas in Central Asia including the Taklimakan, Gobi and Thar deserts make up the second largest dust source on Earth. There has been increasing focus on the dust transportation and deposition from these areas due to the large amount of emitted dust and its significant climatic and environmental impacts (Duce and others, 1980; Huang and others, 2010). For instance, there is growing concern regarding dust emission due to its effect on glacier melting and alteration of biogeochemical cycles (Fujita, 2007); however, available datasets in these areas remain limited to the identification and distinguishing of dust sources. The Sr–Nd isotopic method has only been applied at a few sites in the mountain glaciers of these areas to trace the dust sources (Xu and others, 2009; G. Wu and others, 2010). The goal of this study is to characterize the dust sources and investigate the transport of dust in these areas utilizing a more comprehensive Sr–Nd isotopic dataset. 2. SAMPLING SITES AND METHODS Between September 2008 and November 2010, 15 snow pits were collected from 13 mountain glaciers in western China (Fig. 1). Table 1 presents the details of sampling location, collection time and snow-pit depth. At each sampling site, snow samples were collected from the snow pit at a vertical resolution of 5–20 cm, following the clean- hands-and-dirty-hands protocol with sampling personnel wearing integral Tyvek 1 bodysuits, non-powdered gloves and masks to avoid possible contamination (Fitzgerald, 1999). All sampling sites except Yala were chosen from the accumulation area of glaciers, and most snow pits have accumulated for more than 1 year (Zhang and others, 2012). The Yala samples were collected from the terminus of a glacier due to its harsh condition. Insoluble particles in the snow samples for each research site were obtained by centrifugation (15 000 rpm) and heating evaporation. After each centrifugation cycle (30 min), the supernatant was discarded using a syringe, and the remaining water (10 mL) was evaporated in a class 100 laminar flow box. Extracted particles were dissolved in an HF–HClO 4 mixture, and kept at 100–1208C for 7 days. Taking into account the low quantity of the samples, the Sr–Nd separation and purification were carried out following the low-background method. Briefly, rubidium (Rb)–Sr and light Journal of Glaciology, Vol. 58, No. 211, 2012 doi: 10.3189/2012JoG12J006 859