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The Asian summer monsoon exerts a strong influence on the hydrologic cycle in East Asia. Moreover, the distribution of heavy precipitation in the Yangtze River basin, which covers a large area of South China, is sensitive to changes in monsoon intensity. Thus, the paleo-distribution of heavy precipitation in the Yangtze basin is key in reconstructing the paleo-monsoon intensity. In this study, we established proxies for distinguishing sediments from the northwestern and southeastern parts of the Yangtze River basin, with the goal of using them to reconstruct the paleo-distribution of heavy precipitation in the basin based on changes in the provenance of detrital sediments, as determined using sediment records at the river mouth. The proxies included the electron spin resonance (ESR) signal intensity and the crystallinity index (CI) of quartz in modern riverbed sediments along the mainstream and tributaries of the Yangtze River. The data revealed that the fine-silt fraction of the sediments (which represents suspended particulate matter, SPM) from each major tributary can be distinguished on the basis of ESR signal intensity and CI values. The values for each tributary reflect the age and type of bedrock in the tributary basin and show distinct regional variations according to the distribution of geological blocks within the Yangtze basin. In addition, the analyzed ESR signal intensity and CI values of the fine-silt fraction of riverbed sediments below mainstream-tributary junctions agree well with values calculated according to a simple mixing model of SPM discharged from the tributaries and the mainstream. [ABSTRACT FROM AUTHOR]

This study examines the effects of hydrologic sorting and mixing of sources on the Sr-Nd isotopic compositions of suspended sediments at different water depths. The samples were collected from three layers (surface, middle and bottom) at Datong hydrological station of Yangtze River during the flood season of 2010. Our results show that, Sr/Sr values decrease from surface to bottom, ranging from 0.730332 to 0.720857. ɛ(0) values range from −14.75 to −10.09, with surface sediments being the most negative. The isotope composition at the middle layer can best represent the mean isotopic composition of the total suspended sediments transported by a river. It is believed that the stratification of Sr-Nd isotope is attributable to mixing of sediments from different sources due to hydrological sorting. Sediments from the upper stream are found to be coarser, and tend to contribute more to the lower water column. Although Sr-Nd isotope is a well acknowledged tool to trace sediment provenance, the current study suggests that the grain size of the samples and the sampling locations should be taken into consideration when applying this method to provenance study. [ABSTRACT FROM AUTHOR]

A 10.35-m-long sediment core from the Luobei depression in Lop-Nur, Xinjiang, Northwest China, provides detailed information about environmental changes during the Late Pleistocene. The samples taken every 5 cm of the core were analyzed for 10 environmental proxies, including magnetic susceptibility, granularity, chroma, carbonate and loss on ignition (LOI), and pH value. The chronology data are provided by the uranium/thorium disequilibrium dates. The sediments of the section were deposited during the last 32000 years. The results of analysis of 10 proxies were examined using multivariate statistical analysis, and the principal components were calculated. According to the results, the Late Pleistocene sequence contains four climatic and environmental stages appearing in the cycles of cold-wet and warm-dry changes. During 10-9 ka BP, it was the earliest warm episode in the Holocene. Environmental changes in this district were restricted by global change, as suggested by the analysis of glacial-interglacial cycles. But it was different from the mutative trend of a monsoon region in East China because of its own characteristics, which was the situation of cold-wet and warm-dry climate-environment change. The candidate reason may be the uplift of the Tibet Plateau and the westerly wind circulation. [ABSTRACT FROM AUTHOR]

Abstract: A 9.35-m long sediment core, CK2, that covers the time span between 31.98 and 9.14 kilo annum before present (ka BP) at the Luobei Depression (Lop Nur, Eastern Xinjiang, Northwest China) was studied by pollen analysis. The pollen assemblages of coniferous trees, temperate deciduous trees, herbs, and shrubs can be divided into the following four stages: Zone I (31.98ka BP to 19.26ka BP) corresponds to a steppe or desert steppe landscape, which conforms to the cold-wet climatic environment of the Last Glacial Maximum; Zone II (19.26ka BP to 13.67ka BP) corresponds to a steppe–desert or desert landscape, which conforms to the warm-arid climatic environment of the transient interglacial period; Zones III (13.67ka BP to 12.73ka BP) and IV (12.73ka BP to 9.14ka BP) are similar to Zones I and II, respectively, corresponding to the late last glacial and post last glacial, i.e., Early Holocene, respectively. The climatic environment in Lop Nur was increasingly getting drier based on Artemisia/Chenopodiaceae ratios of ≤0.5 in Subzones IVa and IVc. The Heinrich cold events (H3, H2, H1, and YD) and the Dansgaard–Oeschger warm events (IS4, IS3, IS2, IS1) with millennial-scale changes appearing at high latitudes can also be found in the pollen records of Lop Nur. Results show that the climate characteristics of the Lop Nur region are mainly controlled by the westerly belt, as displayed in mainly cold-wet or warm-arid synchronization. These climate characteristics differ from those of the monsoon area, which are mainly displayed in cold-arid and warm-wet synchronization but also restricted by the atmospheric circulation at high latitudes. [Copyright &y& Elsevier]