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61.
通过对贵州龙里高山草原泥炭进行加速器(AMS)14C测年和有机碳的测定,获得泥炭层底部0.90 m和0.55 m处年龄分别为(7 933±33)a B.P.和(7 733±28)a B.P.,计算出泥炭层堆积速率为1.75 mm/a。获得泥炭层δ13C为-28.9‰~-26.6‰,平均为-27.8‰,说明植被以C3植物为主,与现在坪台沼泽上苔藓繁盛相似。结合其他地区的气候记录推断,研究区泥炭发育于相对温暖湿润的气候环境,是全新世大暖期的第一个暖湿期形成的产物。 相似文献
62.
随着分析技术的进步,δ13C观测在全球碳循环研究中越来越受到重视。在讨论关于碳循环中δ13C的Suess效应、分布特征和同位素分馏等基本概念的基础上,结合现有的观测事实,介绍应用δ13C辨别碳的源汇问题的方法,通过比较不同KeelingPlot方法分析该方法在研究大气CO2背景特征中的意义。着重讨论δ13C在研究大气C... 相似文献
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65.
Relocation of the Yellow River as revealed by sedimentary isotopic and elemental signals in the East China Sea 总被引:3,自引:0,他引:3
Weifeng Yang Min Chen Guangxue Li Zhigang Guo Jiang Liu 《Marine pollution bulletin》2009,58(6):923-927
The Yellow River (YR) supplies a large amount of nutrients and fresh water to the northern Chinese marginal seas, and greatly influences the ecosystem and current patterns. The relocation of the YR outlet from the southern Yellow Sea (YS) to the Bohai Sea in 1855 was demonstrated using northern East China Sea (ECS) sediment characteristics. Both isotopic (δ13C, δ15N) signals and C/N ratios in the organic matter (OM) indicate that prior to 1750, the predominant source of OM to the sediments was terrestrial. The terrestrial influences continuously weakened until 1855, when the YR estuary moved; after 1855, the OM was characterized by oceanic sources. Major elements (Al, Ti, Fe, Mn) and trace elements (Ni, Cr, Cu, Pb) had a much closer association with Malan loess prior to 1855, as >90% of the YR sediment was loess-derived. These results reveal that the relocation of the YR induced significant changes in the current patterns of the northern China Seas in the last 250 years; however, more studies are needed to further examine these linkages. 相似文献
66.
Combined with quantitative determination of concentration and isotopic composition of petroleum hydrocarbons, weathering simulation experiments on artificially mixed oils and their two end-member oils are performed for identification and quantification of mixed sources. The >C18n-alkanes show no appreciable losses during a short-term weathering process. An approach based on distribution of long-chain n-alkanes (>C18) is suggested for estimating the contribution proportion of each source in mixed oils. Stable carbon isotope profile of individual n-alkanes is a powerful tool to differentiate sources of oil spills, but unavailable to accurately allocate each contribution due to a relatively large analytical error. 相似文献
67.
GuoLiang Zhang ZhiGang Zeng XueBo Yin DaiGeng Chen XiaoYuan Wang XiaoMei Wang 《中国科学D辑(英文版)》2008,51(12):1786-1801
Thirty-six basalt samples from near East Pacific Rise 13°N are analyzed for major and trace elements. Different types of zoned plagioclase phenocrysts in basalts are also backscatter imaged, and major element profiles scanned and analyzed for microprobe. Basalts dredged from a restricted area have evolved to different extents (MgO=9.38wt%—6.76wt%). High MgO basalts are modeled for crystalliza-tion to MgO of about 7wt%, and resulted in the Ni contents (≈28 ppm) that are generally lower than that in observed basalts (>60 ppm). It suggests that low MgO basalts may have experienced more intensive magma mixing. High MgO (9.38wt%) basalt is modeled for self-"mixing-crystallization", and the high Ni contents in low MgO basalts can be generated in small scale and periodical self-mixing of new magma (high MgO). "Mixing-crystallization" processes that low MgO magmas experienced accord with recent 226Ra/230Th disequilibria studies for magma residence time, in which low MgO magmas have experi-enced more circles of "mixing-crystallization" in relatively longer residence time. Magma mixing is not homogeneous in magma chamber, however, low MgO magmas are closer to stable composition pro-duced by periodical "mixing-crystallization", which is also an important reason for magma diversity in East Pacific Rise. Zoned plagioclase phenocrysts can be divided into two types: with and without high An# cores, both of which have multiple reversed An# zones, suggesting periodical mixing of their host magmas. Cores of zoned plagioclase in low MgO (7.45wt%) basalt differ significantly with their mantle in An#, but are similar in An# with microlite cores (products of equilibrium crystallization) in high MgO (9.38wt%) basalt, which further shows that plagioclase phenocryst cores in low MgO basalts may have formed in their parental magmas before entering into the magma chamber. 相似文献
68.
We studied the physicochemical and molecular changes of compost during its maturation within 60, 90, and 150 days after the composting process. Moreover, the changes were also studied in compost residues after sequential removal of lipidic compounds. Infrared DRIFT spectrometry and 13C‐CPMAS‐NMR spectroscopy indicate that the molecular composition of compost changes dramatically during the stabilization period. The most decomposable components, mainly represented by bioavailable lipidic and peptidic structures, were progressively mineralized passing from 60 days to longer periods of compost stabilization. At increasing maturity stages, the composition of organic matter underwent a progressive enrichment in stable hydrophobic and ligno‐cellulosic material. The sequential extraction of lipidic compounds allowed an improved characterization of substrates and confirmed the outlined progressive transformation of compost. Compost may well be chosen on the basis of selected characteristics for environmental applications. 相似文献
69.
通过测定贵州省清镇市王家寨小流域内不同背景区(喀斯特与非喀斯特)土壤的含水量以及16种植物叶片的δ13 C值,比较了不同背景区从退化生态到非退化生态过程中各样地之间,以及石漠化和土山样地不同坡位之间土壤含水量与植物叶片δ13 C值的相关关系。研究结果表明,不管是喀斯特背景区还是非喀斯特背景区从退化到非退化的过程中,随着土壤含水量的逐渐增大,植物叶片的δ13 C值与土壤含水量呈现显著的负相关关系,即土壤含水量越大,植物的水分利用效率就越低;而从不同坡位土壤含水量与植物叶片δ13 C值的相关关系分析表明,石漠化样地植物叶片δ13 C值并不随坡位土壤含水量的不同呈现出规律性的变化,而坡位自上而下土山样地植物叶片的δ13 C值则表现出随土壤含水量的增大而逐渐趋负。这些研究结果均反映了植物叶片的δ13 C值对不同生境土壤水分条件的适应机制,其中石漠化样地上的植物对土壤含水量变化的响应最迅速和最敏感。 相似文献
70.
Pierre Giresse Makaya Mvoubou Jean Maley Alfred Ngomanda 《Journal of Paleolimnology》2009,41(2):369-392
Seven vibro-cores were collected from three shallow lakes of the Gabon (Kamalété, Nguène, Maridor) along a 300-km west–east
transect close to the Equator. These lakes are located in very distinct landscapes: coastal forest-savanna mosaic, rain forest
and savanna with colonising forest, respectively. Core chronologies were established by radiocarbon dating. Study of these
lacustrine archives (textural variables, clay minerals, organic matter components, δ13C, pollen) allowed comparison of late Holocene environmental changes recorded at each site and with results from other studies.
Lake Kamalété indicates minor climatic deterioration (increased drying and greater seasonality) between 1,410 and 500 cal.
years BP, which is also recognised in southern Cameroon and east-central Africa. Lake Nguène was surrounded by dense moist
forest throughout the last 4,110 years, but shows significant deterioration from ~2,800 cal. years BP, a phenomenon seen at
nearby sites. Lake Maridor shows a decline of forest initiated a little after 3,800 cal. years BP, which indicates timing
that is distinct from the two other sites. This was probably a response to local conditions (i.e. outlet damming). Although
the three lakes display generally parallel climatic trends perhaps linked to SST oscillations, there is not perfect coherence
between these three sites. Differences among the three basins may be attributable to local factors like groundwater hydrology
and slope instabilities of such shallow lake systems in this equatorial region. 相似文献