Variation of soil Δδ13C values in Xifeng loess-paleosol sequence and its paleoenvironmental implication

The carbon isotopic compositions of soil organic matter （SOM） and total carbonate （TC） in Xifeng Ioess-paleosol sequence have been studied. The δ^13CsoM values vary from -23.8‰ to -20.2‰, which are higher in interglacial than in glacial stages. Contrary to δ^13Csoi values, the δ^13CTc values vary from -8.5‰ to -3.6‰ and are lower in interglacial than in glacial stages. The differences （△δ^13C） between the δ^13CsoM and δ^13CTc values vary from 14.1‰ to 19.4‰. Our results from the Xifeng loesspaleosol sequence indicate that the △δ^13C values represent the ratio of primary carbonate （PC） to secondary carbonate （SC）. The △δ^13C values were high in the loess stages, and the maximal PC-to-SC ratio can reach 6：4. But in the paleosol stages, the △δ^13C values were low, with a small proportion of PC. The △δ^13C values in Ioess-paleosol sequence also indicate the contributions of the dust to the loess sediment in the Chinese Loess Plateau because the dust contains the PC.     

δ13CSC values of the loess-paleosol sequence in Dali area, Shaanxi Province, China, and paleoenvironmental implications

The carbon isotopic ratios of carbonate in the two profiles of the Dali area were analyzed and some new understandings on the influencing factors of the δ^13Csc value of the Iocss-paleosol sequence and its paleoenvironmental implications were discussed preliminarily in this report. The δ^13Csc value of the Dali Ioess-paleasol sequence is synchronizing with the variance of magnetic susceptibility basically and the negative peaks of the δ^13Csc curves are corresponding to the different developmental periods of the paleosol. It is believed that the intervention of the CO2 produced by plants will cause the decrease of the δ^13Csc value, the amplitude of which may be relevant to the paleovegetation density and the ancient humidity. The relative biomass of C4 plants in the vegetation will affect the sublevel change of the δ^13Csc. Low δ^13Csc value by and large indicates the environmental conditions of the relatively abundant vegetation and humid climate. During the last 250000 years, the period with the sparsest vegetation and the most arid climate is the phase of the loess in L2 depositing and the period with the most abundant vegetation and the most humid climate is the last interglacial period. The δ^13Csc curves of Dali also show that the High Temperature and Large Precipitation Event of the Qinghai-Tibetan Plateau during 40-30 kaBP had affected the Central Shaanxi Plain with relatively humid climate, and had apparent influence on the local vegetation and humidity.     

Original component of grain size index in core sediment from southwestern slope of the South China Sea and its paleoenvironmental implication

Traditional grain size analysis was basically used to discriminate sediment type based on its particle dimension for sedimentary naming[1,2] and to analyze the dynamic feature of transport medium, including water current and wind strength[3―5]. Recently, some patency advances havebeen made by using different methods to separate different grain sizes in various original composition from sediments for searching a new way of paleoenvironmental study[6―8]. Grain size analysis is even playing an …     

δ~(13)C difference between plants and soil organic matter along the eastern slope of Mount Gongga

Carbon isotope ratios (δ 13C) of plants, litter and soil organic matter (0–5 cm, 5–10 cm and 10–20 cm) on the eastern slope of Mount Gongga were measured. The results show that δ 13C values of plants, litter and soil organic matter all decrease first and then increase with altitude, i.e. δ 13C values gradually decrease from 1200 to 2100 m a.s.l., and increase from 2100 to 4500 m a.s.l. The δ 13C altitudinal variations are related to the distribution of C3 and C4 plants on the eastern slope of Mount Gongga, ...     

Partial anhysteretic remanent magnetization (pARM) of synthetic single-and multidomain magnetites and its paleoenvironmental significance

Mineral magnetism is an inexpensive, efficient and non-destructive tool to decode paleoclimatic signals re- corded in natural sediments. However, this approach has often been hampered by its inherent complexities because the bulk magnetic signals could be contributed from a magnetic assemblage including both ferromagnetic (FM) (e.g., magnetite and/or maghemite) and antiferromagnetic minerals (AFM) (e.g., hematite and/or goethite) covering a wide range of grain size distribution. Therefore, t…     

Mid-Late Quaternary loess-paleosol sequence in Lantian’s Yushan,China: An environmental magnetism approach and its paleoclimatic significance

The application of rock magnetism methods to investigating the variations of magnetic minerals in the sediments is an important approach to the reestablishment of paleoclimate evolution. Thus we performed fine magnetic measurements on the loess-paleosol sequence (from L15 upwards to S5, in which L is short for Loess, S is short for Paleosol, the same hereinafter) of Yushan stratigraphic section, which is on the southeastern margin of Chinese Loess Plateau, in Lantian County of China’s Shaanxi Province, and the thickness of which is ca. 40 m. Our study shows that the primary magnetic carriers of loess and paleosol in this section are magnetite, maghemite, hematite and goethite. Thermomagnetic analyses on the samples of representative horizons show that the higher pedogenesis degree of the sediments, the smaller variations of magnetization there will be before and after heating, probably related to the pedogenic alteration of loess sediments. Analyses of several magnetic parameters show a significant discrepancy between the paleoclimatic conditions recorded in the strata from the loess unit L15 upward to the paleosol unit S5 in the study area and those recorded in the relative strata of other sections on the Chinese Loess Plateau, and those recorded in marine sediments, indicating the great impact of regional geological background. Similarly, the rapid and intensive change recorded in the segment from L15 to S9-1, and the significant difference between the paleoclimate evolutions of the two periods before and after the change (from L15 to S9-1, and from L9 to the base of S6) indicate the strong alteration of magnetic carriers in the study area as a result of the alternations of summer and winter monsoons in East Asia.     

δ~(13)C and water-use efficiency indicated by δ~(13)C of different plant functional groups on Changbai Mountains, Northeast China

Leaf δ13C of different plant functional groups (trees, shrubs and forbs; evergreen and deciduous; annual, biennial and perennial) were examined on the Changbai Mountains, China. Life form has a significant influence on plant δ13C, suggesting that leaf δ13C is also ideal for distinguishing functional groups species in temperate and frigid zones with high humidity. Additionally, the difference of water-use efficiency (WUE) is significant among different plant functional groups. δ13C and WUE are in the followi...     

Different climatic controls of soil δ~(13)C_(org) in three mid-latitude regions of the Northern Hemisphere since the Last Glacial period

Paleoecological records of soil δ13Corg from three regions in the middle latitudes of the Northern Hemisphere, including the Chinese Loess Plateau (CLP), the Great Plains and adjacent areas of North America and northwestern Europe, showed different variations since the Last Glacial period. An at-tempt was made to evaluate the causes for the difference in δ13Corg on the basis of the modern climatic data collected in these regions and of the modern C3 and C4 plant distributions. The analysis indicates that temperature, especially the growing season temperature, has a dominant control on the growth of C4 plants. When the mean annual or growing season temperatures are below the "threshold value" , the growth of C4 plants is limited. When the temperature is above the "threshold value" , C4 plants can grow under a wide range of precipitation. However, when the precipitation is high enough to favor the growth of trees, the proportions of C4 plants in local biomass will decline. The implicit control factor recovered by sedimentary records is consistent with the control factor on modern C3/C4 distribution. Pure C3 plants have been dominating the local biomass since the Last Glacial period in European loess region, mainly owing to the low local temperature. The increases in C4 plants from the late Pleistocene to the Holocene in the Chinese Loess Plateau, the Great Plains and adjacent areas, mainly reflect the influ-ence of increasing temperature.     

Foliar δ^13C and δ^15N values of C3 plants in the Ethiopia Rift Valley and their environmental controls

The foliar C and N stable isotopic compositions （δ^13C and δ^15N） and the relationships between these compositions and environmental factors of C3 plants in the Ethiopia Rift Valley were investigated. There were three distribution patterns for foliar δ^13C with mean values of -26.7‰±0.4‰, -29.7‰ ±0.6‰ , and -26.9‰± 1.2‰ in cold-moist, temperate-moist, and arid-hot environments, respectively. The δ^15N values ranged from -1.4‰ ±1.7‰ to 14.3‰ ± 0.1‰, with higher values under arid-hot conditions and the lowest values in plants growing at higher altitudes under cold-moist conditions. A strong negative relationship between mean annual precipitation and δ^15N explained more than half of the observed variation in the δ^15N values （r2= 0.54, P 〈 0.001）; a modest positive relationship was also found between δ^15N and temperature （r2 = 0.32, P 〈 0.01）. A weakly positive relationship existed between δ^13C and temperature, and changes in δ^13C values with precipitation and altitude followed quadratic curves. This suggests a shift in the effects of water and heat conditions caused by altitude on carbon isotopic discrimination.     

Fatty-acids and their δ~(13)C characteristics of seep carbonates from the northern continental slope of Gulf of Mexico

Here we reported the fatty-acids and their δ13 C values in seep carbonates collected from Green Canyon lease block 185 (GC 185;Sample GC-F) at upper continental slope (water depth:～540 m),and Alaminos Canyon lease block 645 (GC 645;Sample AC-E) at lower continental slope (water depth:～2200 m) of the Gulf of Mexico.More than thirty kinds of fatty acids were detected in both samples.These fatty acids are maximized at C 16.There is a clear even-over-odd carbon number predominance in carbon number range.The fat...     

醋杆多糖的~(13)C NMR研究

将淀粉控制酸水解成糊精溶液,继以用一种醋酸杆菌(Acetobactes)发酵得到一种新多糖、醋杆多糖(acetobaglucan,1)。该多糖的水溶液具有较好的流变性和剪切稀释能力,尤其是抗盐、钙污染的能力更为突出。在0.5％1的水溶液中加入30％氯化钠或65％氯化钙,其溶液的粘度不下降,也不发生凝聚和沉淀现象。初步应用试验表明,1在石油工业上有可喜的应用前景。     

Application of backflush and micro-flow techniques to the analysis of C_5—C_(13) hydrocarbons in crude oils and its geochemical significance

An Agilent 6890N GC equipped with both FID and Agilent 5975 MSD analyzer has been employed to analyze C5—C13 hydrocarbon fractions of crude oils. A technical combination of program temperature volatilizer injection, backflush and micro-flow controller afforded a fine separation of C5—C13 compounds on a PONA column with the heavy part of crude oils being cut off before entering the analytical column. Both GC-FID chromatogram and GC-MS mass chromatograms (MID and full scan) could be obtained at the same time. The retension time differences of nC6—nC13 alkanes between GC and TIC were in the range of 0.02—0.58 minutes. Totally 286 peaks have been assigned group compositions. Results on 8 typical oil samples from CNPC Key Laboratory Crude Oil Library showed that the characteristics of C6—C13 hydrocarbon group composition could be used in oil-oil correlation studies.     

多光子解离CHClF_2富集~(13)C

用无氦TEA CO_2激光器(9μm带谱线)辐照F-22,选择性激发~(13)CHClF_2,使其达到离解,得到~(13)C的富集。测得选择系数α的峰值位置在1047cm~(-1),相对于~(13)CHClF_2的线性吸收峰位置红移了36cm~(-1),α随激光能量密度、F-22气压的增高而降低。     

δ~(13)C_(carb) and Ce_(anom) excursions in the post-glacial Neoproterozoic and Early Cambrian interval in Guizhou, South China

Inordertounderstand paleoceanographicre spondstotheevolutionofearlymetazoans ,δ13Ccarbvariationsinthepost glacialNeoproterozoicandtheEarlyCambrianhavebeeninvestigatedintheYangtzeplatform ,wheremajoreventsofearlymetazoansaremuchmorecompletelyrecordedcomparedtoelse whereintheworld[1～ 4 ] .Thefirstδ13Ccarb profilewasreportedbyLambertetal.[1] fromtheDoushan tuoandDengyingFormationsintheYangtzeGorges .But ,theirδ13Ccarb valuesfromtheDoushantuoFor mationarewidelyvariable ,mostlikelyduetoea…     

固态高聚物的固体高分辩~(13)C核磁共振研究

本文描述了固体高分子在磁场中的行为.用固体高分辨~(13)C 核磁共振(NMR)研究了不同条件下结晶聚乙稀的多相结构.利用化学位移、各相中弛予时问T_(■e),T~(2■)的不同和不同的脉冲序列对结晶、界面、非晶相成分能够分别进行选择性观测.对定量测出的各成分量进行了讨论,并得到界面相厚度,和Flory 最近提出的格子模型理论计算值比较的结果说明:从较低分子量及稀溶液结晶的聚乙稀界面层厚度值和Flory 理论计算值一致.