Stepwise expansions of C-4 biomass and enhanced seasonal precipitation and regional aridity during the Quaternary on the southern Chinese Loess Plateau

The expansion of C-4 plants is one of the most prominent vegetation changes in the global ecosystem during the Cenozoic Era. Although C-4 plant expansions in the latest Miocene have been widely reported, factors driving the expansions are still in debate, and the details of vegetation changes during the Quaternary have not been well studied. Here we present high-resolution carbon isotope time series of both organic matter and bulk carbonates, covering the past 2.58 Ma, derived from the loess-soil successions on the southern Chinese Loess Plateau. The organic matter delta C-13 values indicate stepwise C-4 plant expansions initiated at similar to 1.6 and at similar to 0.43 Ma, respectively. We conclude that such tectonic time scale C-4 plant expansions are controlled by enhanced seasonality of precipitation (relatively more precipitation in the warm growing season) as well as regional aridity, and this long-term fluctuation superimposes on the orbital scale variations of C-4 plants, while the latter appears phase-locked with cyclical changes of summer monsoon circulations.</p

Column-Integrated Aerosol Optical Properties during Summer and Autumn of 2012 in Xi'an, China

Column-integrated aerosol optical properties were derived systematically from measurements made in Xi&#39;an, which is located in Guanzhong Plain of central China with a ground-based CIMEL sun photometer from May to November 2012. Aerosol optical depths (AODs), Angstrom exponents, water vapor contents, and aerosol optical and micro-physical properties, including aerosol volume size distribution, complex refractive indices and single scattering albedo (SSA), were determined. Daily variations in AODs at 440 nm (tau(440)) generally followed those of the 24-hr PM2.5 mass concentrations, but there were differences in the relationships in summer and autumn. August showed the highest monthly tau(440) (1.13) while the largest monthly Angstrom exponent (alpha(440-870) = 1.30) and water vapor content (C-w = 4.28) both occurred in July. Monthly averages of the aerosol size distributions showed the dominance of coarse mode aerosols, except in July and August, when the contribution of the accumulation and coarse modes were fairly comparable. Monthly changes in the complex refractive index (including both real and imaginary parts) and SSA were also studied, including their wavelength dependences; these analyses implied changes in the abundances of the aerosol types. Finally, an episode involving urban and dust aerosols was analyzed using sun photometer aerosol retrievals; MODIS images captured by Aqua satellite and average wind vectors from the NCEP operational global analyses were also considered in the case study.</p

Atmospheric lead in urban Guiyang, Southwest China: Isotopic sourcesignatures

Total suspended particles (TSP) and their source-related samples from Guiyang, Southwest China, were collected and analyzed for their lead (Pb) concentrations and Pb isotopic compositions, to identify the sources of atmosphere lead in urban Guiyang. Coals from Guizhou Province had significantly high radiogenic Pb, different to those from North China. Local vehicle exhaust had similar Pb isotope ratios to those of other areas in China. Pb isotopic compositions of atmospheric aerosols, rainwaters, plant samples, and acid-soluble fraction of street dusts were similar to each other. The results clearly suggest that the PbeZn ore-related industrial emission, and/or vehicle exhaust, rather than the local coal combustion, are the main sources of atmospheric Pb in Guiyang. Furthermore, binary mixing model indicates that the contribution of coal combustion to the local atmospheric Pb decreased from about 40% in 1988 to about 10% in 2013.</p

Sedimentary history of the western Bohai coastal plain since the late Pliocene: Implications on tectonic, climatic and sea-level changes

Thick Cenozoic deposits from the western Bohai coastal plain, a tectonic-subsiding region, provide the potential to study the relations between sedimentary environments and tectonic, climatic and sea-level changes. However, sedimentary history of this region extending to the whole Quaternary, as well as their links to tectonic, climatic and sea-level changes are still poorly understood, mainly because of the lack of long-term records with well-constrained chronology. In this study, we present an integrated record based on sedimentology and proxies (grain-size and color reflectance) of a 203.6 m core recovered from the western Bohai coastal plain near Tianjin. The core was chronologically well constrained using paleomagnetic and optically stimulated luminescence dating methods. The results show that from the late Pliocene (similar to 3.3 Ma) to the late Pleistocene (similar to 0.10 Ma), the study region was mainly dominated by fluvial setting, and the extensive incursion of sea water into this region began during the last interglacial period (similar to 0.10 Ma). The sedimentology and the color index suggest that tectonic subsidence of the Bohai Basin during the Plio-Quaternary must have played a significant role in controlling the sedimentary environments in this region. The changes in base-level because of sea-level fluctuations during the Quaternary influenced the fluvial development greatly and led to the alternations of coarse crevasse splay/channel and finer floodplain deposits in the core sequence. In addition, climatic changes since the late Pliocene also have had significant effects on the sedimentary settings in the Bohai coastal plain by influencing the fluvial process with a series of mechanisms.</p

Multiple mineralization events of the Paleozoic Tuwu porphyry copper deposit, Eastern Tianshan: evidence from geology, fluid inclusions, sulfur isotopes, and geochronology

The Tuwu porphyry Cu deposit, located in Eastern Tianshan, NW China, is hosted by a plagiogranite porphyry and Carboniferous Qi’eshan Group volcanic rocks. Based on crosscutting relationships and mineral assemblages, hydrothermal alteration and mineralization processes at Tuwu can be divided into four stages: early propylitic alteration (stage I), porphyry mineralization (stage II), overprinting mineralization (stage III), and post-mineralization (stage IV). The porphyry mineralization stage (stage II) contributed to the majority of the Cu–Mo resource, with Cu mineralization occurring mainly as quartz-chalcopyrite veins. Stage III also produced minor Cu mineralization, characterized by chalcopyrite–anhydrite–chlorite–calcite assemblages. Fluid inclusion (FI) study reveals that stage II is characterized by a high-temperature, high-salinity, highly oxidized, and K-rich H2O–NaCl–CaCl2 fluid. Fluid boiling and mixing likely occurred during the porphyry mineralization stage, leading to the precipitation of chalcopyrite and pyrite. Alteration and mineralization in stage III were derived from a S-rich H2O–NaCl–CaCl fluid, with fluid boiling leading to the precipitation of chalcopyrite. The d34S values of chalcopyrite from stages II and III are - 0.8–0.6 ‰ and 1.1–1.3 ‰, respectively, suggesting magmatic sources for the ore-forming components of both stages. 40Ar/39Ar dating indicates that stage II likely occurred at 328.1 ± 1.4 Ma, around the age emplacement of the causative plagiogranite porphyry (ca. 337.7–330.3 Ma). We suggest the overprinting mineralization event occurred at ca. 323 Ma, spatially and genetically related to the emplacement of the quartz albite porphyry at 323.6 ± 2.5 Ma. [Figure not available: see fulltext.]