Although the development of Gobi Desert in central and eastern Asia has greatly affected the regional and even the global climate, its precise origin and evolution have yet to be determined. The ...three preconditions for the formation of Gobi Desert are: i) a dry climate, ii) basin landforms and iii) abundant sediment production. In this study, we present a synthesis of both new and published data on the formation and evolution of Gobi Desert in central and eastern Asia. We conclude that the combined effects of mountain building, the mid-latitude westerly circulation and changes in the Asian monsoon, accompanied by global cooling, were principally responsible for the formation of modern Gobi Desert landscapes in central and eastern Asia during the late Pliocene. The arid climate in central and parts of eastern Asia probably developed in the early Cenozoic, from ~50 Ma. Related events included the collision of the Indian and Asian plates, the closure and complete retreat of the Paratethys Ocean from central Asia, and the growth of the Himalayas and the Tibetan Plateau in the Eocene through late Miocene, which blocked the water vapor supply and intensified the aridification of the Asian interior. Superimposed on the topographic changes was the process of stepwise global cooling since the early Oligocene, and in particular since the late Miocene, which controlled the formation and evolution of the Gobi Desert landscape. Global cooling weakened the Asian monsoon circulation, strengthened the westerly circulation and enhanced physical weathering processes in mountain areas, which together promoted both the aridification of the Asian interior and sediment production. These processes finally resulted in the establishment of the modern Gobi Desert landscape in the late Pliocene. We estimate that the modern Gobi Desert landscape was formed at ~2.6 Ma and was the result of the stepwise evolution of Asian topography and climate during the Cenozoic, dominated by Asian tectonic deformation and uplift, and the evolution of Asian monsoon climate and the westerly circulation, forced by global temperature change.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Quantitatively reconstructing precipitation is an important component of paleoclimate research. The mean annual precipitation (MAP) of a closed-basin lake can be estimated by the energy–water balance ...model (EWBM). The EWBM can be divided into linear and nonlinear models, with determination of evaporation over water and land surface being the main components. However, the influence of vegetation changes on different models and the potential of the models to reconstruct vegetation remain unclear. Dali Lake, a closed-basin lake in the marginal region of the East Asian summer monsoon (EASM), is selected as the study region to test the feasibility of a new algorithm, i.e., the comparative method. This method is performed by comparing the reconstructed MAPs given by linear and nonlinear models for each stepwise reduced or increased forest fraction until both MAPs are approximately equal within the error range. The results indicate that the linear model is more sensitive to vegetation changes than the nonlinear model; however, both linear and nonlinear models can obtain the modern MAP correctly. Additionally, the comparative method can successfully determine the vegetation cover. Using the reported paleolake levels of Dali Lake, we calculate the Holocene MAP and vegetation of the Dali Lake basin. The results show that the early and middle Holocene MAP obtained by the comparative method is ∼10 mm higher than that obtained by the nonlinear model, while the difference in the late Holocene is not insignificant. The reconstructed vegetation is generally consistent with the pollen-indicated vegetation changes in the Dali Lake region and the monsoon marginal zone in North China. Our study suggests that both linear and nonlinear models can provide reliable MAP values for basins with known vegetation. For basins with unknown vegetation, the nonlinear model with variable parameters or the more advantageous comparative method is preferred. In cases where the basin mainly consists of two vegetation types, the comparative method enables to reconstruct the fraction of two vegetation types.
•Linear energy-water balance model is more sensitive to catchment vegetation.•New algorithm combines linear and nonlinear energy-water balance models.•Comparative method can reconstruct Holocene precipitation and forest fraction.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•Quartz SAR OSL and K-feldspar pIRIR290 methods were used to date loess in SE China.•Feldspar pIRIR290 yielded an age of ~200 ka for loess in the basal part of the deposits.•Loess ...from different sites in SE China have different sedimentation rates.•Deposition and preservation of loess are related to local depositional environments.
Loess deposits in Xiashu are representative of such deposits in Southeastern China that are mainly distributed in the middle and lower reaches of the Yangtze River valley. These loess-paleosol sequences provide a key archive of past climate change in humid, subtropical regions. However, the ages of the sequences are not well constrained. In this study, the standard quartz single-aliquot regenerative (SAR) dose optically stimulated luminescence (OSL) and K-feldspar post-infrared infrared stimulated luminescence (post-IR IRSL; pIRIR290) methods are used to date two loess sequences in Nanjing region. Our results show that quartz SAR OSL and K-feldspar pIRIR290 ages are more or less indistinguishable from one another up to ∼50 ka. Beyond this age, the K-feldspar pIRIR ages increased systematically with deposition depth, agreeing well with the expected ages as far as ∼200 ka. On the basis of a fully independently-dated timescale, we are therefore able to propose, for the first time, a new age model for the Xiashu Loess deposits accumulated since the penultimate interglacial period. Using our newly obtained luminescence dating ages, we observe a marked difference between the loess accumulation rates in the two sequences, potentially forced by regional depositional processes and loess preservation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Effective management of municipal solid waste (MSW) is essential for the conservation of ecosystems in the Qinghai-Tibetan Plateau (QTP). Considering the landfill is the major method of MSW ...management, the factors influencing groundwater contamination near MSW landfill sites in the QTP were studied, based on field investigations, environmental impact assessment, and meteorological and hydrogeological analyses. Results indicated that the groundwater was contaminated heavily by nitrate (PI = 7.5), particularly in the landfill without an anti-seepage system, followed by nitrite (PI = 3.5) and heavy metals including arsenic (PI = 4.1) and hexavalent chromium (PI = 2.8). Total hardness, total dissolved solids, nitrate, and lead in the groundwater near the investigated landfill sites were significantly different between the monsoon and the cold seasons. Both the rainfall infiltration and the leachate infiltration were considerably limited by environmental characteristics in the QTP, including high evaporation, low rainfall, and the presence of permafrost. Soil sample contamination near landfill sites was considered as moderate (28.6% of the soil samples) and moderate to heavy (71.4% of the soil samples), based on the geoaccumulation index of mercury. However, comparatively low generation and concentrations of leachate and good topsoil quality (PI = 0.84) reduced the quantity of pollutants infiltrating into the groundwater. The alkaline leachate (pH = 7.45–9.23) and soil (pH = 7.08–8.72) also considerably decreased the concentrations of contaminants dissolved in the infiltrated rainfall and leachate. Additionally, low groundwater level can delay preferential flow and enhance attenuation. Therefore, the groundwater contamination near the landfill sites was simply point pollution, which was influenced by leachate, soil, climate, and hydrogeology characteristics in the QTP. The anti-seepage system is a potential strategy for use in the prevention of groundwater contamination by MSW landfills in the QTP.
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•Groundwater was contaminated heavily by nitrate in landfills without anti-seepage system.•Significant differences of TDS, nitrate, lead occurred between monsoon and cold season.•Rainfall and leachate infiltration were restrained by the climate characteristics in QTP.•Low pollutant concentration in leachate and topsoil reduced pollutants infiltration.•Low groundwater level, alkaline leachate and topsoil enhanced pollutant attenuation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In this study, NiCoCrAlYSi coatings prepared via laser cladding were modified using a high-current pulsed electron beam (HCPEB) technique. The microstructural modifications and the effects that the ...HCPEB treatment had on the high-temperature oxidation resistance were investigated. Microstructural observations reveal that the cladding coating surface, which was initially porous and composed of dendritic segregations, was totally changed after HCPEB irradiation; specifically, the microstructure became rather dense, and the composition became uniform. The grain refinement and high density of dislocations were obtained in the remelted layer. After oxidation for 100 h, the original coating showed relatively poor oxidation resistance, presented as severe internal oxidation. After HCPEB irradiation, the modified coating samples promoted the rapid formation of a stable, continuous, and slow-growing α-Al2O3 scale, which effectively prolonged the high-temperature life of the cladding coating.
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•NiCoCrAlYSi laser cladding coating was irradiated via a HCPEB technique.•Original micro-pores and segregation were eliminated and the remelted surface became compact and uniform.•Dislocations and nano-crystalline structures were obtained after HCPEB irradiation.•Restructuring of surface contributed to a very stable, continuous, slow-growing, and uniform α-Al2O3 scale.•HCPEB technique is an effective way to improve the service life of MCrAlYX-type coatings.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
C0 = sequentially anaerobic/semi-aerobic bioreactor (SASAB); C1, C2, and C3 = reactors forming the spatiotemporally anaerobic/semi-aerobic bioreactor (STASAB).
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•The STASAB takes full ...advantages of anaerobic and semi-aerobic bioreactors.•It eliminates acidogenic and ammonia inhibition during the anaerobic phase.•It enhances the rate and extent of waste decomposition.•It achieves zero leachate discharge (excluding rainfall infiltration).•It rapidly starts methanogenesis, enhancing methane generation.
To meet the requirements of domestic solid waste treatment and technological upgrading of bioreactors, a spatiotemporally anaerobic/semi-aerobic bioreactor (STASAB) was designed. The STASAB took full advantages of anaerobic and semi-aerobic bioreactors by the sequential alternation of anaerobic and semi-aerobic operation and by recirculation of mixed leachate from different-stage bioreactors. Results indicated that after the start-up stage, the pH of leachate in the STASAB always remained higher than 6.88, even in the hydrolysis and acidogenesis stage. The maximum total nitrogen concentration in the STASAB was 1461 mg·L−1, which was merely half that of the sequentially anaerobic/semi-aerobic bioreactor (SASAB) and had no adverse effects on the anaerobic process. Nitrogen removal in the STASAB reached 92.3%–95.5% when operated in the semi-aerobic phase and even reached 49.4% when operated in the anaerobic phase. The peak concentration of chemical oxygen demand was much lower and the anaerobic digestion lag time was much shorter in the STASAB than in the SASAB. The period of rapid biogas production in the STASAB was double that of the SASAB, which resulted in a 70% increase in biogas generation. Moreover, leachate could be exhausted by evaporation in just 3–5 months during the semi-aerobic phase. Therefore, the STASAB can eliminate acidogenic and ammonia inhibition during solid waste treatment, enhance the rate and extent of organic waste decomposition, rapidly initiate methanogenesis, enhance methane generation, and achieve zero leachate discharge (excluding rainfall infiltration). The STASAB is an efficient and feasible technique for treating domestic solid waste in rural areas.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Reconstructing the Plio-Pleistocene sedimentary history of the Yellow Sea, is important for understanding the long-term influence of the Yellow River (Huanghe) and/or Yangtze River (Changjiang) on ...the Asian marginal seas and to further constrain any links between river development, regional paleoenvironmental change, tectonic deformation and/or global climate change. Here we present the first high-resolution clay mineral record combined with Sr-Nd isotopic compositions from a 300-m long sediment core recovered in the western South Yellow Sea. Our study suggests that large-scale transgression in the Yellow Sea occurred after ∼0.8 Ma, possibly related to tectonic subsidence of eastern China coast and the Min-Zhe Uplift. In contrast, the sedimentary environment of Bohai and Yellow Seas was mainly dominated by fluvial/lacustrine deposits at 3.5–0.8 Ma. Provenance analysis suggests a major change in sediment provenance from the Yangtze River to the Yellow River at ∼0.8 Ma, which corresponds to the timing of the final integration of the Yellow River in its present form. At the same time the major channels of the Yangtze River migrated from the South Yellow Sea to the modern Yangtze River delta due to the subsidence of east China coast. The consistence in timing of the provenance transition and large-scale regional marine transgression suggests that tectonic deformation, rather than climate change, is the first-order control on the evolution of the Yellow and Yangtze Rivers and sedimentary environmental change in the Bohai and Yellow Seas.
•A major change in sediment provenance in South Yellow Sea from the Yangtze River to Yellow River occurred at 0.8 Ma.•Large-scale transgression in the Yellow Sea began at 0.8 Ma, possibly related to subsidence of the Min-Zhe Uplift.•Tectonic deformation, rather than climate change, is the major control on the evolution of the Yellow and Yangtze Rivers.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The cycle of precipitation change is key to understanding the driving mechanism of the East Asian summer monsoon (EASM). However, the dominant cycles of EASM precipitation revealed by different proxy ...indicators are inconsistent, leading to the "Chinese 100 kyr problem". In this study, we examine a high-resolution, approximately 350,000-year record from a low-latitude loess profile in China. Our analyses show that variations in the ratio of dithionite-citrate-bicarbonate extractable iron to total iron are dominated by the ~20-kyr cycle, reflecting changes in precipitation. In contrast, magnetic susceptibility varies with the ~100-kyr cycle and may be mainly controlled by temperature-induced redox processes or precipitation-induced signal smoothing. Our results suggest that changes in the EASM, as indicated by precipitation in this region, are mainly forced by precession-dominated insolation variations, and that precipitation and temperature may have varied with different cycles over the past ~350,000 years.
Parabolic dunes can transform from and into other types of dunes in response to environmental changes. The sand hills, including some parabolic dunes, on the shore of Poyang Lake mainly accumulated ...during the Last Glaciation and are rare inland aeolian landforms in the humid monsoon climate zone in East China. However, the characteristics, distribution and formation of the parabolic dunes in this region are still not clear. Three sand hills with similar scales and wind regimes at Shaling, Jishan and Songmenshan were selected as the research targets. Integrating topographical, hydrological, vegetation and wind data, we found that the development of the parabolic dunes was effectively controlled by both the vegetation cover of the sand hills and the space available downwind of the sand hills. No parabolic dunes were found at Songmenshan and Shaling; the former has too little vegetation cover, favouring the formation of blowouts, and the latter lacks available space since Shaling is surrounded by villages and farmlands. Three types of parabolic dunes that developed sequentially in the downwind direction, namely, type A, type B and type C dunes, are observed at Jishan, and their formation is related to a narrowly unimodal and high-energy wind regime. Different from existing models, type A dunes are found to originate from the wedge-shaped depositional lobes of trough blowouts; type B dunes transform from type A dunes after migration; and type C dunes develop from very low sand drifts. Composite parabolic dunes are formed when the sand supply is plentiful, while simple parabolic dunes appear when the sand supply is limited. The formation of the parabolic dunes occurred approximately 250 years ago, which is close to the documented time when the sand hills were reactivated due to the vegetation being anthropogenically damaged. Therefore, anthropogenic destruction of vegetation is a trigger for producing parabolic dunes in this humid area. This study may shed light on the evolution of aeolian landforms in humid monsoon climate zones.
•Both simple and composite parabolic dunes develop on the shore of Poyang Lake.•Formation models of three types of parabolic dunes in this humid area are proposed.•Anthropogenic destruction of vegetation is a trigger for producing parabolic dunes.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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