Vegetation and environmental changes in western Chinese Loess Plateau since 13.0 ka BP

Pollen records from the Chinese Loess Plateau revealed a detailed history of vegetation variation and associated climate changes during the last 13.0 ka BP. Before 12.1 ka BP, steppe or desert-steppe vegetation dominated landscape then was replaced by a coniferous forest under a generally wet climate （12.1-11.0 ka BP）. The vegetation was deteriorated into steppe landscape and further into a desert-steppe landscape between 11.0 and 9.8 ka BP. After a brief episode of a cool and wet climate （9.8-9.6 ka BP）, a relatively mild and dry condition prevailed during the early Holocene （9.6-7.6 ka BP）. The most favourable climate of warm and humid period occurred during mid-Holocene （7.6-4.0 ka BP） marked by forest-steppe landscape and vegetation alternatively changed between steppe and desert-steppe from -4.0 to -1.0 ka BP.

Cenozoic Ephedraceae adaptation to global cooling in northwestern China

Ephedraceae has been applied largely as a drought indicator to reconstruct Cenozoic paleoenvironment and paleoclimate. However, temperature indication of Ephedraceae has been largely ignored. Here, we provide a record of Ephedraceae percentage spanning from the Early Eocene to Middle Miocene （52-17 Myr B.P.） in the Xining Basin, northeastem Tibetan Plateau. This record is comparable to a compiled Cenozoic Ephedraceae record from five other basins in northwestern China. Both records show Ephedraceae percentages were high during the Early Eocene, and decreased gradually from the Middle Eocene to Late Oligocene, then maintained a stable level since the Late Oligocene. By comparing these two Ephedraceae records with the marine oxygen isotope record, we discuss the variation of Ephedmceae percentage in Middle Cenozoic in response to global temperature change. Ephedraceae percentage was high in the Early Paleogene, associated with subtropical or tropical vegetation types in a global greenhouse climate, and decreased in Early Oligocene, associated with global cooling, suggesting that Ephedmceae is warm-tolerant during the Paleogene. The low Ephedraceae percentages in the Late Oligocene and Miocene were uncoupled with global warming, which may imply that Ephedraceae began to adapt to a eurythermic climate in the inland desert environment of westem China. Such adaptation may be a response to the high topography of the Tibetan Plateau.

Quantitative Analysis of Paleoatmospheric CO2 Level Based on Stomatal Characters of Fossil Ginkgo from Jurassic to Cretaceous in China

A better theoretical and practical understanding of the linkage between paleo-CO2 and climate during geological history is important to enhance the sustainable development of modern human society. Development in plant physiology since the 1980s has led to the realization that fossil plants can serve as a proxy for paleoatmosphere and paleobiosphere. As a relict gymnosperm with evolutionary stasis, Ginkgo is well suited for paleoenvironmental reconstruction. This paper analyzes fossil Ginkgo species from integrated strata in the north of China using anatomic data of plant physiology. Using stomatal parameters, a trend for the paleo-CO2 level during the Early-Middle Jurassic and the Early Cretaceous was obtained, which is consistent with the estimates by GEOCARB. The trend is also similar to that of Mean Global Surface Temperature in geological time. Compared with three other atmospheric CO2 concentration parameters, the trend of paleo-CO2 level based on the stomatal parameter of the fossil Ginkgo specimens from three contiguous strata is more exact.

Surface energy balance of Bayi Ice Cap in the middle of Qilian Mountains,China

Energy balance at the glacier surface is important for understanding the impacts of climate change on glaciers. Here, we analyzed the characteristics of the glacier surface energy fluxes along with their contributions to glacier melt on Bayi Ice Cap in Qilian Mountains by using a point-scale energy balance model. The half-hourly meteorological data from an automatic weather station(AWS) located on the glacier was used to drive the energy balance model. The model simulated results could accurately represent the mass-balance observations from the stake near the weather station during summer 2016. Our results showed the net radiation(86%) played an important role in the surface energy balance, and the contribution of the turbulent heat fluxes(14%) to the energy budget was relatively less important. A distinct behavior of energy balance, as compared to other continental glaciers in China(e.g., two adjacent glaciers Laohugou No. 12 Glacier and Qiyi Glacier), is the fact that a sustained period of positive turbulent latent flux exists on Bayi Ice Cap during August, causing faster melt rate in the month of August. Our study also presented the effect of frequent summer snowfall in slowing down surface melt by changing the surface albedo during the beginning of the melting season.

Interaction of DNA with aromatic hydrocarbons fraction in atmospheric particulates of Xigu District of Lanzhou,China

Voluminously epidemiological studies show that the relationships exist between the air pollution and human health and cancer. Aromatic hydrocarbons （AHs） in air form a large class of organic pollutants, which are widely in environment and many of them are known to be carcinogenic and/or mutagenic and contribute to ambient air pollution. In the past decades, bioassays mainly have been used to evaluate the toxicity of chemical mixtures in atmospheric particulates or aqueous environment. However, it is well known that the covalent complexes formed by carcinogens with DNA may be exert negative results in bioassay. So the main aim of this paper is to develop an evaluation method of toxicity effects of chemical mixtures in atmospheric particulates from chemical standpoint. In this study, the in vitro interaction of the AHs with DNA was investigated by absorption, fluorescence and resonance light scattering （RLS） spectroscopic techniques. The results showed that the AHs in the atmospheric particulates could combine with calf thymus DNA （ctDNA） and herring sperm DNA （hsDNA） without being activated or metabolized by organism, respectively. Intercalation may be present in the mechanism of interaction. The binding constants of the AHs with ctDNA and hsDNA were 2.5x102 and 2.0x103, respectively, which indicated that the interaction of the AHs with hsDNA is stronger than that with ctDNA. In addition, the relationships of dose-effect between the total mole concentration of chemical components and the ability of binding ctDNA and hsDNA were confirmed. This research made it possible to study the toxicity effects of chemical mixtures in atmospheric particulates by chemical method. It is believed that the composition and contents of unknown AHs and the interaction of DNA with AHs in atmospheric particulates of Xigu District of Lanzhou City, China are first reported in the past twenty years.

Cenozoic Stratigraphy Deformation History in the Central and Eastern of Qaidam Basin by the Balance Section Restoration and its Implication

The Qaidam Basin, located in the northern margin of the Qinghai-Tibet Plateau, is a large Mesozoic-Cenozoic basin, and bears huge thick Cenozoic strata. The geologic events of the Indian- Eurasian plate-plate collision since -55 Ma have been well recorded. Based on the latest progress in high-resolution stratigraphy, a technique of balanced section was applied to six pieces of northeast- southwest geologic seismic profiles in the central and eastern of the Qaidam Basin to reconstruct the crustal shortening deformation history during the Cenozoic collision. The results show that the Qaidam Basin began to shorten deformation nearly synchronous to the early collision, manifesting as a weak compression, the deformation increased significantly during the Middle and Late Eocene, and then weakened slightly and began to accelerate rapidly since the Late Miocene, especially since the Quaternary, reflecting this powerful compressional deformation and rapid uplift of the northern Tibetan Plateau around the Qaidam Basin.

The impacts of climate change on the Neolithic cultures of Gansu-Qinghai region during the late Holocene Megathermal

The Holocene Megathermal is divided into early, middle and late periods, each having different impacts on the Neolithic cultures due to their different climate changing trends This study is based on a comparative analysis of the environmental evolution information recorded in the Qinghai Lake, the western edge of the Loess Plateau and Zoige and the spatial distribution of Neolithic sites of the Gansu-Qinghai region. Results show that the early and middle periods towards warm and humid promoted the development of Neolithic cultures with agriculture as the main sector in the Gansu-Qinghai region, furthermore a heyday of Yangshao Culture prosperity emerged. The Holocene entered the late period after the cold climate event at 5.9 ka BP in the Gansu-Qinghai region. Later the climate began to turn cold. However, at the 5.8-4.2 ka BP a relatively stable warm and humid climate created the conditions for the development of Majiayao Culture of the Neolithic Age in this region, thus the distribution of its cultural heritage sites expanded towards high altitudes and high latitudes. From 4.2 ka BP onwards, the climate became cold and dry, which had a significant influence on the Neolithic cultures of the Gansu-Qinghai region, leading to a dramatic change in the cultural characters and spatial distribution of Qijia Culture around 4.2 ka BP. After a nearly 300 years of cold and dry period, the unified Neolithic farming culture completely collapsed. Afterwards an industrial division of animal husbandry and farming and regional multiple cultures formed, and ultimately led to the end of primitive society and the starting of a civilized society.

Ecological risk assessment of the Gannan Plateau,northeastern Tibetan Plateau

Desertification, soil salinization and grassland degradation are the major environmental hazards faced by the Gannan Plateau, northeastern Tibetan Plateau. Ecological risk assessment plays an important role in formulating environmental management strategies yet little attention to this region. In this study, we established an ecological risk assessment index system based on 30 evaluation indices in the categories of hydrometeorology, ecological environment, ground surface disturbance, and society and economy for the Gannan Plateau. An entropy method was used to calculate an index weight,and subsequently the matter-element method was used together with extension theory to establish a matter-element extension model of ecological risk. We assessed the ecological risk in this region by calculating the degree of association between index layer, system layer and target layer, and the cumulative ecological risk index. The degrees of ecological risk for the counties of the region were determined by using Arc GIS which would represent a spatial heterogeneity of the risk grade in production. Our results showed that the areas of high ecological risk were in Zhouqu County and Zhuoni County, and others were of low risk(Hezuo City, Diebu County, Xiahe County and Lintan County) or intermediate risk(Maqu County). The results of the assessment were in accord with the actual observed situation. Thus, our ecological risk assessment index system is appropriate for this region and suggests that high risk counties need a priori ecological protection. Such research could provide a technological support which would potentially prevent or reduce disasters by establishing an ecological barrier to promote the sustainable development of Gannan Plateau.

Compound-specific hydrogen isotopes of long-chain n-alkanes extracted from topsoil under a grassland ecosystem in northern China

To investigate characteristics of H isotope variation in long-chain n-alkanes （δDn-alkanes） from higher plants in surface soils under a single ecosystem, 12 samples from a basalt regolith were randomly collected from Damaping in Wanquan County of Zhangjiakou in North China. Molecular distribution and C （δ^13Cn-alkanes） and H isotopes of long-chain n-alkanes, as well as C isotopes of TOC （δ^13CTOC）, were analyzed. Both δ^13CTOC and δ^13Cn-alkanes values from four representative dominant long-chain n-alkanes （n-C27, n-C29, n-C31, n-C33） derived from terrestrial higher plants show minor variations among the 12 samples, indicating the major contributor is from local grasses with a uniform C3 photosynthetic pathway. In contrast, variations in δ^13Cn-alkanes values of the four long-chain n-alkanes are relatively large, with the more abundant homologs generally showing more negative δDn-alkanes values and less variation. However, variation of 〈30‰ among weighted averaged δDn-alkanes values of the four long-chain n-alkanes is not only less than that among δDn-alkanes values for different modern terrestrial C3 grasses from the specific locations, but also less than the literature values of δDn-alkanes of long-chain n-alkanes for single species over different seasons. Thus, because the sources of long-chain n-alkanes in surface soils and sediments are similarly from multiple individual plants, our results are significant in confirming that paleoclimatic, paleoenvironmental and paleohydrological information can be interpreted more accurately from δDn-alkanes values of long-chain n-alkanes from sediments, particularly terrestrial sediments with organic matter derived from in-situ plants.