•High enrichments of As, Cd, Cs and Pb in the sediments should be of concern.•Lower part of Yarlung Tsangpo River (YTR) sediments source from local felsic bedrocks.•Surface sediments underwent ...incipient chemical weathering in the lower part of YTR.•Elevated heavy metals in early-mid-Holocene associated with warmer and wetter climate.
Loess-like deposits and soils distribute extensively along the wide valleys across the Yarlung Tsangpo River (YTR) catchment in southern Tibetan Plateau. They provide insights into pedogenetic processes and environmental changes. The climate of the low reach area of the YTR catchment is currently relatively wet and warm compared with the middle and upper reaches. To reconstruct climate and environmental changes in the source region, we carried out major and trace elements measurements on various types of sediments collected from the catchment of the lower part of YTR and its tributaries, i.e., Nyang, Po, Yigong and Parlung Tsangpo river (YPT). We find that CaO and MgO are more enriched in the YPT catchment than in the upper continental crust (UCC). Surface and profile sediments across the lower reach of the YTR show elevated As, Cd, Pb and Cs levels, which present potential health risks to local residents and should be considered in health policies. We also found that the sediments are predominantly sourced from local felsic bedrocks. Across the lower part of the YTR, surface sediments only underwent incipient chemical weathering. Steep slopes and heavy precipitation likely removed the sediments quickly and minimized the exposure of minerals to chemical weathering. Elevated As, Pb and Cs contents were found in sediments deposited during the wetter and warmer period from the early-middle Holocene compared with those deposited in modern times. Thus, climate might be an important factor for heavy metals release into the soils of southern Tibetan Plateau by modulating the extent of chemical weathering of their parent rocks.
The Yellow River Basin (YRB) is characterized by active geological and tectonic processes, rapid geomorphological evolution, and distinct climatic diversity. Correspondingly, major disasters in the ...YRB are characterized by varied types, extensive distributions, and sudden occurrences. In addition, major disasters in the YRB usually evolve into disaster chains that cause severe consequences. Therefore, major disasters in the YRB destroy ecologies and environments and influence geological and ecological safety in the basin. This paper systematically reviews research on geological and surface processes, major disaster effects, and risk mitigation in the YRB, discusses the trends and challenges of relevant research, analyzes the key scientific problems that need to be solved, and suggests prospects for future research based on the earth system science concept. Themes of research that should be focused on include geological, surface and climatic processes in the YRB and their interlinking disaster gestation mechanisms; formation mechanisms and disaster chain evolutions of giant landslides in the upper reach of the YRB; mechanisms and disaster chain effects of loess water-soil disasters in the middle reach of the YRB; occurrence patterns and amplifying effects of giant flood chains in the lower reach of the YRB; and risk mitigations of major disasters in the YRB. Key scientific problems that need to be solved are as follows: how to reveal the geological, surface and climatic processes that are coupled and interlinked with gestation mechanisms of major disasters; how to clarify the mutual feedback effects between major disasters and ecology; and how to develop a human-environmental harmony-based integrated risk mitigation system for major disasters. Prospects for future studies that follow the earth system science concept include the following: highlighting interdisciplinary research to reveal the interlinked disaster gestation mechanisms of the geology, surface and climate in the YRB in the past, present, and future; forming theories to clarify the regional patterns, dynamic mechanisms, and mutual-feedback effects between disaster chains and ecology in the YRB on land and in rivers in the region; solving technological bottlenecks to develop assessment models and mitigation theories for integrated risks in the YRB by following the human-environment harmony concept; and finally, establishing a demonstratable application pattern characterized by “whole-basin coverage” and “zonal controls”, thereby guaranteeing ecological and geological safety in the basin and providing scientific support for ecological conservation and high-quality development of the YRB.
Dust Storms in Northern China Guan, Qingyu; Sun, Xiazhong; Yang, Jing ...
Journal of climate,
09/2017, Letnik:
30, Številka:
17
Journal Article
Recenzirano
Odprti dostop
Airborne dust derived from desertification in northern China can be transported to East Asia and other regions, impairing human health and affecting the global climate. This study of northern China ...dust provides an understanding of the mechanism of dust generation and transportation. The authors used dust storm and climatological data from 129 sites and normalized difference vegetation index (NDVI) datasets in northern China to analyze spatiotemporal characteristics and determine the main factors controlling dust storms occurring during 1960–2007. Dust storm–prone areas are consistent with the spatial distribution of northern China deserts where the average wind speed (AWS) is more than 2 m s−1, the mean annual temperature (MAT) ranges from 5° to 10°C, and the mean annual precipitation (MAP) is less than 450 mm. Dust storms commonly occur on spring afternoons in a 3-to 6-h pattern. The three predominant factors that can affect DSF are the maximum wind speed, AWS, and MAT. During 1960–2007, dust storm frequency (DSF) in most regions of northern China fluctuated but had a decreasing trend; this was mainly caused by a gradual reduction in wind speed. The effect of temperature on DSF is complex, as positive and negative correlations exist simultaneously. Temperatures can affect source material (dust, sand, etc.), cyclone activity, and vegetation growth status, which influence the generation of dust storms. NDVI and precipitation are negatively correlated with DSF, but the effect is weak. Vegetation can protect the topsoil environment and prevent dust storm creation but is affected by the primary decisive influence of precipitation.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
It is generally assumed that increased dust accumulation rate (DAR) on the Chinese Loess Plateau (CLP) is associated with intensified inland Asian aridification. However, the timescales and area that ...any such association operates over is unclear. In this study, we demonstrate a lack of correlation between the southern CLP loess DAR variations and aridification over the past 130 ka, which does not support a direct link between high DAR and intensified inland Asian aridification over millennial to tens of millennial timescales. Instead, we propose that loess DAR variation is more likely determined by wet‐dry cycles and associated loose sediment production and availability via fluvial and glacial processes.
Plain Language Summary
Aridification is a global challenge facing humanity. As such, there is a pressing need to understand changes in aridification over a range of scales, as well as their causes. Arid inland Asia is the largest middle‐latitude arid region, and mineral dust emitted from here is found downwind in the Chinese Loess Plateau (CLP) loess, North Pacific Ocean sediments, and even Greenland ice. As a result, North Pacific and CLP sediments are frequently used to infer inland Asian aridification history. Underpinning this is the assumption that faster dust accumulation corresponds to increased inland Asian aridification. By contrast, here we demonstrate that fast dust accumulation during cycles within the Ice Age on the southeastern CLP correspond instead to periods of increased East Asian river erosion associated with intensified dry‐wet climatic contrasts. Thus, dust accumulation is decoupled from inland Asian aridification variations. This challenges one of the most basic foundations in inland Asian aridification research. This study has broad implications for understanding the responses and feedbacks of atmospheric dust in climate systems, dust‐climate modeling assumptions, understanding of inland Asian aridity history and its causes, and interpretations of far field dust accumulation records in, for example, North Pacific sediments and Greenland ice‐cores.
Key Points
Sedimentary evidence is utilized to systematically test the role of inland Asian aridification in Chinese Loess Plateau (CLP) dust accumulation
Inland Asian aridification is not the dominant control on CLP dust deposition at millennial and tens of millennial timescales
This underscores the important role of fluvial sediments in supplying sediments to the CLP and local impacts on dust deposition
This study illustrates the textural, mineralogical and geochemical signatures of sediments from the upper Yellow River. Sediments of major tributaries have also been examined to study the influence ...of provenance, weathering intensity, and hydraulic sorting on the spatial compositional variability of sediments. Similarly to floodplain sediments, riverbed deposits are strongly depleted in MgO and Na2O, and enriched in CaO and Si2O relative to the upper-continental-crust standard. The pattern of rare earth elements (REE) indicates LREE enrichment and negative Eu anomaly (Eu/Eu* = 0.54–0.68). Low CIA (Chemical Index of Alteration) values indicate that the sediments from the trunk-river channel, floodplain, and major tributaries have not experienced intense chemical weathering in arid to semi-arid climatic conditions. The distribution of chemical elements shows a significant increase of Zr and Hf with coarsening of grain-size, whereas Rb, Ni, and V are associated with finer sediment fractions supplied by adjacent dune fields and tributaries. The Al/Si ratio (a proxy for grain size) correlates positively with CIA, Fe2O3, MgO, and K2O, but not with Na2O, reflecting grain-size control. Clay mineral assemblages in the upper Yellow River and in tributaries draining the Loess Plateau (e.g., Qingshui and Zuli Rivers) are dominated by illite and chlorite, whereas the abundance of smectite characterizes the middle reaches of the Yellow River and the Ten tributaries draining the Ordos Plateau.
Landscape evolution models (LEMs) are essential tools for analyzing tectonic-climate interactions and reproducing landform-shaping processes. In this study we used a LEM to simulate the evolution of ...the mountains from the central Hexi Corridor in the northeastern Tibetan Plateau, where the climate is arid and the surface processes are relatively uniform. However, there are pronounced differences in the topography between the mountains around the central Hexi Corridor. The East Jintanan Shan, West Jintanan Shan and Heli Shan are located in the northern part of the corridor; and the Yumu Shan in the southern part. Firstly, several representative areas were selected from these mountains to analyze the topographic characteristics, including the uniform valley spacing, local relief, and the outlet number. Secondly, a LEM for these areas was constructed using the Landlab platform, and the landscape evolution was simulated. With uniform valley spacing and other topographic characteristics as the criteria, we compared the realistic and simulated terrain for different model ages. Finally, based on the similarity of the simulated and realistic terrain, we estimated the timing of the initial uplift and the uplift rate of the four mountain ranges. The results are consistent with previous geological and geomorphological records from these youthful stage mountains that have not yet reached a steady state. Our findings demonstrate that LEMs combined with topographic characteristics are a reliable means of constraining the timing of the initial uplift and the uplift rate of the youthful stage mountain. Our approach can potentially be applied to other youthful stage mountains and it may become a valuable tool in tectonic geomorphology research.
Marine accumulations of terrigenous sediment are widely assumed to accurately record climatic- and tectonic-controlled mountain denudation and play an important role in understanding late Cenozoic ...mountain uplift and global cooling. Underpinning this is the assumption that the majority of sediment eroded from hinterland orogenic belts is transported to and ultimately stored in marine basins with little lag between erosion and deposition. Here we use a detailed and multi-technique sedimentary provenance dataset from the Yellow River to show that substantial amounts of sediment eroded from Northeast Tibet and carried by the river's upper reach are stored in the Chinese Loess Plateau and the western Mu Us desert. This finding revises our understanding of the origin of the Chinese Loess Plateau and provides a potential solution for mismatches between late Cenozoic terrestrial sedimentation and marine geochemistry records, as well as between global CO2 and erosion records.
A central theme in geomorphology is the quantitative determination of the relationship between topography and its controlling factors, such as tectonics, lithology, and climate. However, rather than ...relief and slope, channel steepness (ksn) is a more effective metric for topography, and together with the abundance of beryllium‐10 (10Be) erosion rate data, it provides a more convenient means of quantitatively revealing the relationship between topography and its driving factors. A power‐law relationship between ksn and 10Be erosion rates has been widely demonstrated, which indicates the dominant control of tectonics on topography, while the dominant control of climate has not been clearly revealed. In this study we selected nine tectonically active regions, comprising 241 catchments, covering a wide range of mean annual precipitation values, and by extracting ksn values and hypsometric curves, we obtained the relationship between ksn and erosion rates. The results show that the power‐law relationship differs between regions, largely due to differences in the erosion coefficient, K. After separating the influences of lithology and climate, we found that although soft sedimentary rocks will increase the erosion coefficient, precipitation plays the main role in controlling the erosion coefficient, resulting in a linear relationship between precipitation and K. This relationship clearly demonstrates the occurrence of higher relief under a drier climate, even with similar rates of tectonic uplift.
Our compilation of river topographic indicators (ksn) and beryllium‐10 (10Be) erosion rates shows that the topographic relief is different, even under the same uplift rate. We show that the topography is mainly controlled by the erosion coefficient, K. Via its influence on K, a drier climate leads to higher channel steepness and thus to greater topographic relief. This result provides empirical support for the long‐standing conceptual model in geomorphology of how climate affects topographic evolution.
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