Ecological basis of Alpine meadow ecosystem management in Tibet: Haibei Alpine Meadow Ecosystem Research Station

Alpine meadow and shrub are the main pasture types on the Tibetan Plateau, and they cover about 35% of the total land area. In order to understand the structural and functional aspects of the alpine ecosystem and to promote a sustainable animal production system, the Haibei Alpine Meadow Research Station was established in 1976. A series of intensive studies on ecosystem structure and function, including the energy flow and nutrient cycling of the ecosystem, were the main tasks during the first 10 years. Meanwhile, studies with 5 different grazing intensities on both summer and winter pasture have been conducted. In the early years of the 1990s, the research station started to focus its research work on global warming, biodiversity and sustainable animal production systems in pastoral areas. Various methods for improving degraded pasturelands have been developed in the region.

湘西地区上震旦统上部－下寒武统底部黑色岩系沉积学及地球化学

Widespread black chert-shales occur in the Ediacaran-Cambrian(E-C) boundary successions along the flank of Yangtze Platform, South China, remarkable changes in sedimentology, geochemistry and biology were recorded. Although extensive studies were carried out upon this boundary succession, the origin of black chert-shales still remain controversial. This paper focuses on the E-C black chert-shales in western Hunan, South China, upon which detailed depositional and geochemical changes are documented, accordingly a depositional model for black chert-shales is proposed. Stratigraphic anatomy across the depositional strike demonstrates that the shallow-water Dengying dolostone along the platform margin sharply pass basinward into the Liuchapo chert successions, which indicate syndepositional extensional faulting at depth could have occurred along the platform margin. The deep-water Niutitang phosphorite-rich black shales are either underlain by the Dengying dolostones on the platform margin toward platform interior or directly by the Liuchaopo chert successions farther basinwards. By detailed investigation, silica chimneys are firsly identified approximately in the chert along platform margin; two types of silica chimneys, including mounded and splayed/funnelized chert(generally brecciated) bodies are further sorted out. The mounded chert are exitbited by domed or hummocky surfaces on the top and irregular spongy to digitiform internal fabrics; within the silica mounds, abundant original vesicles/voids and/or channels were mostly plugged by initial chalcedony, quartze crystals with minor dolomite and bladed barite crystals. Splayed/funnelized brecciated chert “intrusion” cross-cut the uppermost dolostones capping to the horizon underneath, and are directly overlain by the Niutitang phosphorite-rich black shales. Their similarities to the silica chimneys reported from the oceanic spreading centres suggest a similar origin responsible for these unique silica bodies which is also supported by the microthermonmetric data and element geochemistry. High P, Ba, Fe contents and positive correlation between Fe and TOC concentrations in the Niutitang black shales indicate a high palaeo-productivity in the Early Cambrian ocean. The low Th/U and the high V/Cr, V/Sc, V/(V+Ni) ratios in the black shales suggest an anoxic water condition during this interval. Furthermore, Positive Eu anomalies and high Ba contents in the sediments also imply a hydrothermal influence on the formation of Niutitang black shales. To better constrain the placement of deep-water successions straddling the E-C boundary and the timing of hydrothermal silica chimneys, sensitive high-resoluton ion microprobe(SHRIMP) U-Pb dating of zircon grains from tuffs within the chert succession of Liuchapo Formation at Ganziping was conducted and yields a weighted-mean 206Pb/238Pb age at 536.6±5.5Ma, younger than E-C boundary age(542.0±0.3Ma). This age combined with carbon isotopic data is then proposed to correspond to the U-Pb age of zircons(538.2±1.5Ma) from the Zhongyicun member of Meishucun Formation at Meishucun in eastern Yunna, thus, the E-C boundary in Gazngziping was placed between the Dengying formations and Liuchapo formatioms. therefore, the silica chimneys took place at the beginning of the Cambrian period. The temporal coincidence of silica chimneys and negative excursions of δ13C and δ34Spy pairs suggest hydrothermal activities were likely responsible for the isotopic changes. Under such a circumstance, vast amounts of greenhouse gases(CO2, CH4, H2S), with highly 13C-depleted carbon and 34S-depleted sulfur would be released into the ocean and atmosphere. A positive shift in δ34Scas and Δ34S values from the late Ediacaran to the Early Cambrian could be a reflection of enhanced bacterial sulfate reduction(BSR), strengthened by the intensified oceanic anoxia stimulated by hydrothermal activities. Based on the analyses of sedimentology and geochemistry, a model- “oceanic anoxia induced by hydrothermal–volcanic activies” was proposed to responsible for the formation of black chert-shales during this E-C transition. Under this case, hydrothermal-volcanic activies could release large large amount of greenhouse into atmosphere and metal micronutrients into the ocean, which may lead to global warming, stratified ocean, thereby a high palaeoproductivity; on the other hand, the massive releasing of reduced hydrothermal fluids with abundant H2S, could have in turn enhanced the ocean anoxia. All of these were favourable the for preservation of organic matter, and subsequent extensive deposition of black silica-shales.

黄土中主要温室气体组分特征

Scientists have paid much attention to the greenhouse effects and the greenhouse gases for the fact of global warming. There are many uncertainties in the prediction of future climatic change. One of the important reasons causing the uncertainties is insufficient researches of the sources and sinks of greenhouse gases, especially, there is a missing sink in the global carbon cycle. The recent researches proposal that there may be an important carbon sink in the middle-latitude terrestrial ecosystems (vegetation and soil) in the North Hemisphere, despite that there is much disputation about its position and amplitude. Chinese loess is located in the middle latitude area in the North Hemisphere, what kind of role does it play in and how does it influence on the balance of the global greenhouse gases budget? For this reason, many samples were taken and analyzed from wide range and multi-stratum of Chinese loess to understand characteristics of major greenhouse gases in loess and loess possible effect on global greenhouse gas budget. Using self-made spiral corer, we totally took 81 gas samples and 65 soil samples from 7 loess profiles in China such as Zhaitang loess section of Beijing, Pianguan, Xingxian, Lishi, Puxian, Jishan loess section of Shanxi Province, and Luochuan loess section of Shaanxi Province. The gas concentrations for CO_2, CH_4 and N_2O, the contents of N_2, O_2 and carbonate, and the carbon isotopic compositions of CO_2 and carbonate in loess strata sequences are observed and measured. In addition, 19 gas samples data of the Weinan loess section, Shaanxi Province are combination with this research to study characteristics of greenhouse gases in loess. This research indicates that (1) the free gases in loess are neither paleo-atmospheric gases nor modern atmospheric gases; (2) the concentrations of CO_2, CH_4 and N_2O in loess are higher than atmospheric level; (3) the δ~(13)C of loess CO_2 shows that the CO_2 in loess mainly comes from the oxygenolysis of organic matters, but because of isotopic exchange with carbonate in loess, the carbon isotopic exchange with carbonate in loess, the carbon isotopic compositions of loess CO_2 are much more heavier than organic original CO_2; (4) the concentration of CH_4 in Malan loess is lower because it is not favorable for the decomposition of anaerobic bacteria in the Malan Loess; (5) estimation of the total amount of the carbonate in loess reveals that loess is a huge carbon reservoir (about 850PgC). In addition, the impact of the deuterogenic carbonatization during the loess accumulation on the global carbon cycle was discussed, and the preliminary conclusion is that the research work is still not enough to evaluate the effect of loess on the sources and sinks of the anthropogenic CO_2.