Stable isotopic composition of riverine dissolved inorganic carbon of the Xijiang River Inner Estuary

For researching the spatio-temporal variation of the stable isotopic composition of the riverine dissolved inorganic carbon（DIC）,we had carried out a survey throughout the hydrologic year during which theδ^13CDIC of the surface water and its physicochemical parameter were examined along the Xijiang River Inner Estuarine waterway from September 2006 to June 2007.There was a striking seasonal variation on the averageδ^13CDIC,as the averageδ^13CDIC in summer（-13.91‰）or autumn（-13.09‰）was much less than those in spring（-11.71‰）or winter（-12.26‰）.The riverineδ13C DIC was controlled by decomposed condition of the riverine organic matter linking the seasonal variation of the physicochemical parameter in the surface water according to the correlation analysis which indicated notable relations betweenδ^13CDIC and water temperature（p=0.000;r=-0.569）or betweenδ^13CDIC and oxide-reduction potential（p=0.000;r=0.646）.The striking positive correlation between δ^13CDIC and the sampling distance happened in the summer rainy season,while striking negative correlation happened in the spring dry season,indicating that river-sea interaction influenced water physicochemical parameters and controlled the riverine DIC property in the survey waterway.In view of the riverineδ^13CDIC decreasing for the decomposition of the terrestrial organic matter in the rainy season in summer and increasing for the briny invaded zone extending in the spring dry season along the waterway from the Makou gauging station to the Modaomen outlet,theδ^13CDIC spatio-temporal variation was closely related to the geographical environment of the Xijiang drainage basin.

Oxygen Stable Isotopic Ratio in Precipitations in Niigata Prefecture, Japan

Time-course of oxygen stable isotopic ratios （i.e., δ^18O） as well as seasonal variation of δ^18O has been examined to investigate the characteristics, sources and the passing route of precipitations in Niigata Prefecture. The precipitation samples have been mainly collected with a filtrating bulk sampler at the rooftop of Niigata University. Furthermore, backward trajectories analyses have been also conducted for these samples taken sequentially for a short period. Consequently, the following features have been mainly clarified for the precipitations in Niigata Prefecture： （1） the δ^18O values varied between -14.57%o and -3.86%0 in the precipitations of Niigata University; （2） as for the comparison among sampling points, the mean value of δ^18O at seaside spots （i.e., Niigata City： -6.93%0） is larger than that of inland spots （Sanjyo City： -8.68%0）; （3） δ^18O value was generally small in the rainy or typhoon season, and relatively large in summer; （4） decreasing δ^18O content with time is a predominant feature of sequentially sampled rainfalls as predicted by Rayleigh models of atmospheric vapor condensation.

Simulations of Stable Isotopic Fractionation in Mixed Cloud in Middle Latitudes-Taking the Precipitation at Urumqi as an Example

The introduced mathematical model takes into account the role of the kinetic fractionation effect in a supersaturation environment at the ice surface as liquid and solid phases coexist in mixed cloud. Using the model, the temperature effect of stable isotopes in precipitation is simulated under different cooling conditions. The rate of change of δ18O against temperature in the process of wet adiabatic cooling is smaller than in the process of isobaric cooling under the same humidity. The increasing supersaturation ratio at the ice surface, Si, leads to the strengthening of the kinetic fractionation effect. The kinetic fractionation function makes the synthesis fractionation factor decreased and the change of δ18O with temperature flatted, compared with that in the equilibrium state. The simulated results show that the slope parameter b and the intercept d of the meteoric water line (MWL), 6D = bδ18O+d, in wet adiabatic cooling are both greater than those in isobaric cooling. The global MWL lies between the two MWLs simulated under wet adiabatic and isobaric cooling processes, respectively. The magnitudes of 6 and d are directly proportional to Si. The greater the Si, the stronger the kinetic fractionation effect, and thus the greater the 6 and d, and vice versa. However, 6 and d have low sensitivity to the liquid-water contents in the cloud. Using the kinetic fractionation model, the variation of stable isotopes in precipitation at Uriimqi is simulated. The simulated stable isotopic ratio vs temperature and the SD vs δ18O curves are very consistent with the actual regressions and MWL at Uriimqi, respectively.

Stable Isotopic Variations in Precipitation in Southwest China

This study analyzes .the relationships of stable isotopes in precipitation with temperature, air pressure and humidity at different altitudes, and the potential influencing mechanisms of control factors on the stable isotopes in precipitation in Southwest China. There appear marked negative correlations of the δ^18 in precipitation with precipitation amount, vapor pressure and atmospheric precipitable water （PW） at the Mengzi, Simao and Tengchong stations on the synoptic timescale; the marked negative correlations between the δ^18 in precipitation and the diurnal mean temperature at 400 hPa, 500 hPa, 700 hPa and 850 hPa are different from the temperature effect in middle-high-latitude inland areas. In addition, the notable positive correlation between the δ^18 in precipitation and the dew-point deficit ATd at different altitudes is found at the three stations. Precipitation is not the only factor generating an amount effect. Probably, the amount effect is related to the variations of atmospheric circulation, and vapor origins. On the annual timescale, the annual precipitation amount weighted-mean δ^18 displays negative correlations not only with annual precipitation but also with annual mean temperature at 500 hPa. It can be deduced that, in the years with an abnormally strong summer monsoon, more warm and wet air from low-latitude oceans is transported northward along the vapor channel located in Southwest China and generates abnormally strong rainfall on the way. Meanwhile, the abnormally strong condensation process will release more condensed latent heat in the atmosphere, and this will lead to a rise of atmospheric temperature during rainfall but a decline of δ^18 in the precipitation. On the other hand, in the years with an abnormally weak summer monsoon, the precipitation and the atmospheric temperature during rainfalls decrease abnormally but the δ^18 in precipitation increases.

Stable isotopic composition of otoliths in identification of stock structure of small yellow croaker(Larimichthys polyactis) in China

Oxygen and carbon isotope ratios（δ^（18）O and δ^（13）C） in otoliths were used to identify the stock structure of small yellow croaker,Larimichthys polyactis.Otoliths were collected from fish at five locations across the Yellow Sea and the Bohai Sea representing most of their distributional range and fisheries areas.The significant differences in the isotopic signatures showed that the five locations could be chemically distinguished and clearly separated,indicating stock subdivision.Correlation of δ^（18）O and δ^（13）C values suggested that population of L.polyactis could be divided into the Bohai Sea group,the southern Yellow Sea group and the central Yellow Sea group.Discriminant analysis of δ^（18）O and δ^（13）C values demonstrated a high significant difference with 85.7% classification accuracy.The spatial separation of L.polyactis indicated a complex stock structure across the Yellow Sea and the Bohai Sea.These results indicate that optimal fisheries management may require a comprehensive consideration on the current spatial arrangements.This study has provided further evidence that measurement of the stable isotopes ratios in otolith can be a valuable tool in the delineation of fishery management units.

Variations of methane stable isotopic values from an Alpine peatland on the eastern Qinghai-Tibetan Plateau

Isotopic signature is a powerful tool to discriminate methane(CH_(4)) source types and constrain regional and global scale CH_(4) budgets.Peatlands on the Qinghai-Tibetan Plateau are poorly understood about the isotopic signature of CH_(4) due to the limited experimental conditions.In this study,three campaigns of diurnal air samples spacing 2-3 h were taken from an alpine peatland on the eastern Qinghai-Tibetan Plateau to investigate its source signal characteristics.Both CH_(4) concentration and its stable carbon isotope(δ^(13)C-CH_(4)) were measured to derive the carbon isotopic signature of the CH_(4) source using the Keeling plot technique.Diurnal variation patterns in CH_(4) concentration and δ^(13)C-CH_(4) were observed during summertime,with depleted δ^(13)C-CH_(4) signals and high CH_(4) concentration appearing at nighttime.The δ^(13)C-CH4 signature during summer was calculated to be-71 % ± 1.3%,which falls within the range of other wetland studies and close to high-latitude peatlands.The boundary layer dynamic and CH_(4) source were supposed to influence the measured CH_(4) concentration and δ^(13)C-CH_(4.)Further investigations of CH_(4) isotopic signals into the nongrowing season are still needed to constrain the δ^(13)C-CH_(4) signature and its environmental controls in this region.

Effect of dietary stable isotopic ratios of carbon and nitrogen on the extent of their incorporation into tissues of rats

This study was conducted to investigate the effect of different dietary ratios of 13C to 12C or 15 N to 14N on their relative incorporation into tissues. Eighty male rats were used in two 21-day feeding trials in which they were fed diets with either high δ13C levels （δ13C=-13.89%o and δ15N =2.37%o in experiment 1 and δ13C=-19.34%o and δ15N = 4.73%o in experiment 2） or low 613C levels （δ13C =-17.90%o and δ15N = 3.08%o in experiment 1 and δ13C =-21.76%o and δ15N = 0.53‰ in experiment 2）, meanwhile, the dietary δ15N levels were designed to two ranks Blood, liver, adipose and muscle tissues were collected on day 0, 3, 7, 14, and 21 for determination of 13C, 12C, 15N and 14 N isotopes. Rat growth rate, antioxidant capacity and metabolic parameters were also assessed. The results indicate that adipose tissue tend to deplete 13C before the stable isotopic ratios achieved final equilibrium. Therefore, feeds with different isotopic signatures had different incorporation rates into tissues. Low dietary 13C levels decreased tissue δ13C values whereas high dietary 13C levels did not alter tissue δ13C values during the 21-d experiment. Blood δ15N values were a reliable parameter in assessing the relative contribution of dietary nitrogen to tissues. This study revealed a relationship between dietary tissues. However, more studies are needed to illustrate the sotopic signatures and their incorporation rates into rat mechanism through which dietary isotopic ratios nfiuence the extent of isotopic incorporation into the tissues

Multivariate statistical analysis of chemical and stable isotopic data as indicative of groundwater evolution with reduced exploitation

Groundwater resources in the North China Plain(NCP)are undergoing tremendous changes in response to the operation of groundwater exploitation reduction(GWER)project.To identify groundwater evolution in this complex context,hierarchical cluster analysis(HCA)and principal component analysis(PCA)were combined to interpret an integrated dataset of stable isotopes and chemical data from four sampling campaigns in a pilot area of groundwater control.We proposed a novel HCA approach integrating stable isotopes and chemical signals,which successfully partitioned the groundwater samples into the unconfined and the confined water samples.Stable isotopic evidence showed that the lateral inflow and the surface water may contribute more to groundwater recharge in this region than local modern precipitation.The unconfined water's main hydrochemical types were Na type with mixed anions,and Na-Cl-SO_(4)type,while the confined water was mainly Na-Cl and Na-SO_(4)types.Geochemical processes mainly involved the dissolution/precipitation of halite,gypsum,Glauber's salt,feldspar,calcite and dolomite,as well as the cation exchange.PCA results showed that water-rock interaction(i.e.,salinity-based and alkalinity-based processes)predominated the hydrochemical evolution,along with local nitrate contamination resulting from fertilizers and domestic sewage.The GWER project regulated the natural evolution of unconfined water chemistry,and significantly reduced the unconfined water's salinity(mainly Na^(+),Mg^(2+),SO_(4)^(2-)).This may be attributed to upward leakage from low-salinity confined water at some parts of the aquifer.Additionally,insignificant changes in the confined water's salinity reflected that the impact of GWER on the confined aquifer was negligible.This study facilitates the groundwater classification effectively in the areas lack of geological data,and enhances the knowledge of groundwater chemical evolution in such a region where groundwater restoration is in progress,with important implications for groundwater sustainable management in similar basins worldwide.

Rising utilization of stable isotopes in tree rings for climate change and forest ecology

Analyses of stable isotopes(C,O,H)in tree rings are increasingly important cross-disciplinary programs.The rapid development in this field documented in an increasing number of publications requires a comprehensive review.This study includes a bibliometric analysis-based review to better understand research trends in tree ring stable isotope research.Overall,1475 publications were selected from the Web of Science Core Collection for 1974-2023.The findings are that:(1)numbers of annual publications and citations increased since 1974.From 1974 to 1980,there were around two relevant publications per year.However,from 2020 to 2022,this rose sharply to 109 publications per year.Likewise,average article citations were less than four per year before 1990,but were around four per article per year after 2000;(2)the major subjects using tree ring stable isotopes include forestry,geosciences,and environmental sciences,contributing to 42.5%of the total during 1974-2023;(3)the top three most productive institutions are the Chinese Academy of Sciences(423),the Swiss Federal Institute for Forest,Snow and Landscape Research(227),and the University of Arizona(204).These achievements result from strong collaborations;(4)review papers,for example,(Dawson et al.,Annu Rev Ecol Syst 33:507-559,2002)and(McCarroll and Loader,Quat Sci Rev 23:771-801,2004),are among the most cited,with more than 1000 citations;(5)tree ring stable isotope studies mainly focus on climatology and ecology,with atmospheric CO_(2) one of the most popular topics.Since 2010,precipitation and drought have received increasing attention.Based on this analysis,the research stages,key findings,debated issues,limitations and direc-tions for future research are summarized.This study serves as an important attempt to understand the progress on the use of stable isotopes in tree rings,providing scientific guid-ance for young researchers in this field.

Determinant variables on the isotopic values of particulate organic matter in a neotropical floodplain

Particulate organic matter(POM)is an important energy source for aquatic consumers,understanding its origin and composition is essential for understanding the energetic dynamics of aquatic environments.The aim of this study was to analyze the relationship between POM and phytoplankton(isotopic values and chlorophyll concentration)and abiotic variables during dry and rainy seasons.Sampling was conducted in rivers and lagoons in the floodplain of the Upper ParanáRiver.We found a greater difference in ^(δ13)C values of POM between sampling points than between seasons,indicating that the composition of regional sources influences the composition of POM more than dry and rainy seasons.In addition,the concentration of chlorophyll during the dry season was positively correlated with ^(δ13)C values during that rainy period.Additionally,we found a relationship between factors limiting the growth of phytoplankton and ^(δ13)C values of POM,such as phosphate ions,indicating that variables that regulate phytoplankton growth tend to influence the composition of POM in river floodplains.Therefore,maintaining the variables that regulate the phytoplankton community is of fundamental importance for the composition of POM,an important energy source in aquatic environments.

Distribution and sources of sedimentary organic matter in different aquaculture areas of northeastern Zhanjiang Bay using stable carbon and nitrogen isotopes

Zhanjiang Bay is a major aquaculture area in China with many types of mariculture products(such as oysters,fish,and shrimp).The culture area and shrimp output in Zhanjiang Bay are ranked first in China.We investigated the total organic carbon(TOC),total nitrogen(TN),TOC/TN ratio,and stable isotopes(δ^(13)C and δ^(15)N) of the fish and shrimp feed,fish and shrimp feces,and sedimentary organic matter(SOM) in and around different aquaculture areas of northeastern Zhanjiang B ay to study the impact of aquaculture activities on SOM.The average TOC contents of fish and shrimp feed were 39.20%±0.91% and 39.29%±0.21%,respectively.The average TOC content in the surface sediments of the oyster culture area,the mixed(fish and shrimp) culture area,and the cage fish farm area were 0.66%,0.88%±0.10%,and 0.58%±0.19%,respectively,which may indicate that mixed culture had a greater impact on SOM.The relatively high TOC and TN contents and relatively low TOC/TN ratios,and δ^(15)N values in the upper layer of the core sediment in the mixed culture area could also support the significant influence of mixed culture.The average δ^(13)C and δ^(15)N values of fish and shrimp feed were -20.6‰±2.2‰ and 1.8‰±1.2‰,respectively,which were different from the isotopic values of SOM in the study area.δ^(13)C and δ^(15)N values for SOM in different aquaculture areas were different from those of nearby reference stations,probably reflecting the influence of aquaculture.The δ^(13)C and δ^(15)N values in the oyster culture area(-25.9‰ and6.0‰,respectively) seemed to have reduced δ^(13)C and enriched δ^(15)N relative to those of the reference station(-24.6‰ and 5.8‰,respectively).This may reflect the influence of organic matter on oyster culture.The δ^(15)N value of the station in the mixed culture area(7.1‰±0.4‰) seemed to be relatively enriched in δ^(15)N relative to that of the reference station(6.6‰).Sedimentation and the subsequent degradation of organic matter from mixed cultures may have contributed to this phenomenon.The surface sediment at the cage fish farm area seemed to be affected by fish feces and primary production based on the indication of δ^(13)C and δ^(15)N values.The sediment core at the mixed culture region(NS6) had lower TOC/TN ratios and more positive δ^(13)C and δ^(15)N values than the sediment core at the oyster culture area,suggesting a higher proportionate contribution of marine organic matter in the mixed culture area.In summary,oyster culture,mixed culture,and cage fish culture in northeastern Zhanjiang Bay had a certain degree of impact on SOM,and mixed culture had more significant influences on SOM based on the high TOC contents and the significant vertical variations of TOC/TN ratio and δ^(15)N value in the sediment of this area.This study provides new insights into the impact of aquaculture activities on SOM content.

Effects of thinning and understory removal on water use efficiency of Pinus massoniana:evidence from photosynthetic capacity and stable carbon isotope analyses

Understanding the relationship between forest management and water use efficiency(WUE)is important for evaluating forest adaptability to climate change.However,the effects of thinning and understory removal on WUE and its key controlling processes are not well understood,which limits our comprehension of the physiological mechanisms of various management practices.In this study,four forest management measures(no thinning:NT;understory removal:UR;light thinning:LT;and heavy thinning:HT)were carried out in Pinus massoniana plantations in a subtropical region of China.Photosynthetic capacity and needle stable carbon isotope composition(δ^(13)C)were measured to assess instantaneous water use efficiency(WUE_(inst))and long-term water use efficiency(WUE_(i)).Multiple regression models and structural equation modelling(SEM)identified the effects of soil properties and physiological performances on WUE_(inst)and WUE_(i).The results show that WUE_(inst)values among the four treatments were insignificant.However,compared with the NT stand(35.8μmol·mol^(-1)),WUE_(i)values significantly increased to 41.7μmol·mol^(-1)in the UR,50.1μmol·mol^(-1)in the LT and 46.6μmol·mol^(-1)in HT treatments,largely explained by photosynthetic capacity and soil water content.Understory removal did not change physiological performance(needle water potential and photosynthetic capacity).Thinning increased the net photosynthetic rate(A_n)but not stomatal conductance(g_s)or predawn needle water potential(ψ_(pd)),implying that the improvement in water use efficiency for thinned stands was largely driven by radiation interception than by soil water availability.In general,thinning may be an appropriate management measure to promote P.massoniana WUE to cope with seasonal droughts under future extreme climates.

A bulk extraction method to determine the stable isotope ratios of iron,nickel,copper,zinc,and cadmium in seawater using multi-collector inductively coupled plasma mass spectrometry

The oceanic trace metals iron(Fe),nickel(Ni),copper(Cu),zinc(Zn),and cadmium(Cd)are crucial to marine phytoplankton growth and global carbon cycle,and the analysis of their stable isotopes can provide valuable insights into their biogeochemical cycles within the ocean.However,the simultaneous isotopic analysis of multiple elements present in seawater is challenging because of their low concentrations,limited volumes of the test samples,and high salt matrix.In this study,we present the novel method developed for the simultaneous analysis of five isotope systems by 1 L seawater sample.In the developed method,the NOBIAS Chelate-PA1 resin was used to extract metals from seawater,the AG MP-1M anion-exchange resin to purify Cu,Fe,Zn,Cd,and the NOBIAS Chelate-PA1 resin to further extract Ni from the matrix elements.Finally,a multi-collector inductively coupled plasma mass spectroscope(MC-ICPMS)was employed for the isotopic measurements using a doublespike technique or sample-standard bracketing combined with internal normalization.This method exhibited low total procedural blanks(0.04 pg,0.04 pg,0.21 pg,0.15 pg,and 3 pg for Ni,Cu,Fe,Zn,and Cd,respectively)and high extraction efficiencies(100.5%±0.3%,100.2%±0.5%,97.8%±1.4%,99.9%±0.8%,and 100.1%±0.2%for Ni,Cu,Fe,Zn,and Cd,respectively).The external errors and external precisions of this method could be considered negligible.The proposed method was further tested on the seawater samples obtained from the whole vertical profile of a water column during the Chinese GEOTRACES GP09 cruise in the Northwest Pacific,and the results showed good agreement with previous related data.This innovative method will contribute to the advancement of isotope research and enhance our understanding of the marine biogeochemical cycling of Fe,Ni,Cu,Zn,and Cd.

Variation characteristics of stable isotopes in atmospheric precipitation in Adelaide,Australia

Background,aim,and scope Stable isotope in water could respond sensitively to the variation of environment and be reserved in different geological archives,although they are scarce in the environment.And the methods derived from the stable isotope composition of water have been widely applied in researches on hydrometeorology,weather diagnosis,and paleoclimate reconstruction,which help well for understanding the water-cycle processes in one region.Here,it is aimed to explore the temporal changes of stable isotopes in precipitation from Adelaide,Australia and determine the influencing factors at different timescales.Materials and methods Based on the isotopic data of daily precipitation over four years collected in Adelaide,Australia,the variation characteristics of dailyδD,δ^(18)O,and dexcess in precipitation and its relationship with meteorological elements were analyzed.Results The results demonstrated the local meteoric water line(LMWL)in Adelaide,wasδD=6.38×δ^(18)O+6.68,with a gradient less than 8.There is a significant negative correlation between dailyδ^(18)O and precipitation amount or relative humidity at daily timescales in both the whole year and wither/summerhalf year(p<0.001),but a significant positive correlation between dailyδ^(18)O and temperature in the whole year and the winter half-year(p<0.001).Discussion The correlation coefficients betweenδ^(18)O and daily mean temperature didn’t show a significant positive correlation,which may be attributed to that the precipitation in Adelaide area in January was mainly influenced by strong convective weather,and the stable isotope values in precipitation were significantly negative.Furthermore,this propose was also evidenced by the results from dexcess of precipitation with larger value in the winter half-year than that in the summer half-year,which may be resulted from the precipitation events in winter are mostly influenced by oceanic water vapor,while the sources of water vapor in summer precipitation events are more complicated and influenced by strong convective weather.On the other hand,the slope and intercept of theδ^(18)O—P regression lines in the summer months(-0.41 and 0.50‰)are larger and smaller than those in the winter months(-0.22 and-2.15‰),respectively,indicating that the precipitation stable isotopes have a relatively stronger rainout effect in the summer months than in the winter months.Besides,the measured values ofδ^(18)O in daily precipitation have a good linear relationship with our simulated values ofδ^(18)O,demonstrating the established regression model could provide a reliable simulation for theδ^(18)O values in daily precipitation in Adelaide area.It’s worth noting that the precipitation events with low precipitation amount,low relative humidity and high temperature,usually had relatively small slope and intercept of MWL,implying that raindrops may be strongly affected by sub-cloud secondary evaporation in the falling process.Conclusions The variation ofδ^(18)O in daily precipitation from Adelaide region was controlled by different factors at different timescales.And the water vapor sources and the meteorological conditions of precipitation events(such as the degree of sub-cloud secondary evaporation)also played an important role on the variation ofδ^(18)O.Recommendations and perspectives Stable isotope in daily precipitation can provide more accurate information about water-cycle and atmosphere circulation,it is therefore necessary to continue to collect and analyze daily-scale precipitation data over a longer time span.The results of this study will provide the basis for the fields of hydrometeorology,meteorological diagnosis and paleoclimate reconstruction in Adelaide,Australia.

Loggerhead Sea Turtles Hand-Reared in Captivity: Isotopic Insights into Their Inherent Dietary Variation

Stable isotope analysis is a widely used method for gathering ecological insights into the diet and feeding habitats of various species. While captive studies often limit lethal sampling and differ from wild conditions, they offer valuable insights into inherent isotopic variations among individuals, which are often assumed to reflect differences between natural populations. In the Sea Turtle Conservation Program, loggerhead turtle hatchlings from different nests were fed. Necropsies were conducted on turtles that died during this period, obtaining bone fragments for analysis. We evaluated the isotopic variation of carbon (δ13C) and nitrogen (δ15N) in bone tissue across six turtle nests (n = 66 samples) and assessed differences in Straight Carapace Length (SCL, n = 71 samples). Using SIBER and nicheROVER in R, we calculated niche width and overlap, while the simmr package determined primary prey assimilation. Despite feeding the hatchlings the same prey, we observed variations in nitrogen isotope assimilation between nests. Nests 4 and 6 had a niche width >1.8‰, indicating consistent consumption frequencies across all prey and >70% niche overlap with other nests. In contrast, nests 1 and 2 showed a narrower niche width (Mugil sp. constituted the primary diet component (>40%) across all groups. This study demonstrates how factors like competition or prey preference can influence the assimilation of diet, even when the source remains constant (inherent variation).

MATHEMATICAL MODELING OF VARIATIONS ON STABLE ISOTOPIC RATIOS IN FALLING RAINDROPS

The variations of stable isotopic contents in falling raindrops are not only influenced by the humidity conditions, but also by the stable isotopic contents in atmospheric vapor to a certain extent. If there is a difference between the isotopic contents in the vapor of the surrounding air and at the surface of the raindrops, the move of the isotopic contents from high to low values will be produced. Usually. influenced by the evaporation process, the stable isotopic ratios in raindrops are constantly increased in the unsaturated atmosphere. The less the atmospheric humidity, the more obvious the increased range. As the enrichment rate of stable isotopes in raindrops is equal to the outward isotopic move rate. the 'pseudo-equilibrium state' appears. The influence of evaporation on stable isotopic contents disappears in the saturated atmosphere, so that the magnitude of isotopic ratio in raindrops is dependent on the isotopic exchange between the raindrops and the surrounding atmosphere.

Stable Carbon Isotopic Composition of Black Carbon in Surface Soil as a Proxy for Reconstructing Vegetation on the Northern Slope of the Qinling Mountains

Because of the unique geographical location and important ecological effect of the Qinling Mountains, reconstruction of its vegetation and climate needs comprehensive research. We need to consider a multiple-proxy approach to gain more information on recovering the paleovegetation and climate in the Qinling Mountains. Black carbon （BC） is produced by the incomplete combustion of vegetation and fossil fuels, and is a good proxy, recording paleoenvironmental information. However, in the Qinling Mountains, what are the characteristics of the BC, and whether BC stable carbon isotope （δ^13CBc） can be used as a new proxy to study ancient vegetation, still need further study. In order to establish a sound basis for studying paleoenvironmental by BC proxy in the Qinling Mountains, we carried out systematic and detailed study on modern process of BC on the northern slope of the mountains. We analyzed stable carbon isotopes and carbon concentration of organic carbon （% SOC, δ^13Csoc） and BC （%BC, δ^13CBc）, and identified the pollen assemblages from systematically sampled surface soil. The results show that the calculated ratio of C4 plants in the vegetation （%C4） based on the δ13Csoc data reflects a similar distribution of C4 plants in the surface vegetation and the pollen assemblage. The δ^13Cac values have a strong positive correlation with δ13Csoc values, and their difference （△13CSOC-BC） is in the low range. These data indicate that δ^13CBC and δ^13CSOC have very similar characteristics. Surface soil δ13BC values can indicate surface vegetation as effectively as δ^13Csoc values, and the δ^13CBC proxy can be used effectively in paleovegetational research in the northern slope of Qinling Mountains.

Stable Carbon Isotopic Compositions of Methylated-MTTC in Crude Oils from Saline Lacustrine Depositional Environment:Source Implications

Significantly high abundant methyl-Methyl Trimethyl Tridecyl Chromans （MTTCs） have been detected in aromatic hydrocarbon fractions in crude oils from the Jizhong Depression and Jianghan Basin. The distribution of these compounds is dominated by methyl-MTTC and dimethyl- MTTC series, which indicate diagenetic products of a hypersaline depositional environment in the early stage and show a low degree of methylation. The occurrence of significantly high abundant methyl-MTTC depends mainly on good preservation conditions with a strongly reductive, hypersaline and water-columned depositional environment and subsequent non-intensive diagenetic transformations. The stable carbon isotopic compositions of the methyl-MTTCs and dimethyl-MTTCs in two samples are far different from the stable carbon isotopic composition of C30 hopane of apparent bacteria biogenesis （up to 4.11‰ and 5.75‰, respectively）. This obviously demonstrates that the methyl-MTTC and dimethyl-MTTCs cannot be of bacteria origin, which is different from the previous point of view about non-photosynthetic bacteria products or possible bacteria-reworked products. On the contrary, the stable carbon isotopic compositions of methyl-MTTC and dimethyl-MTTCs in the two samples were similar to that of the same carbon-numbered n-alkanes （nC27-nC28-nC29）, which indicates that they share the same source origin. Especially in the crude oil from the Zhao61 well, stable carbon isotopic compositions are also similar to that of the same carbon-numbered steranes with ααα- 20R isomer （mostly less than 0.4‰）. In consideration of the results of previous studies on saline lake ecological sedimentation, the authors hold that the methyl-MTTC and dimethyl-MTTCs in the saline lake sediments should be of algal biogenesis origin.

Variation of soil-plant-atmosphere continuum stable isotope and water source in Qinghai spruce forest of the eastern Qilian Mountains

Understanding the hydrogen and oxygen stable isotope composition and characteristics of different water bodies in soil-plant-atmosphere continuum is of significance for revealing regional hydrological processes and water cycle mechanisms.In this study,we analyzed the stable isotopic composition,relationship and indicative significance of precipitation,soil water(0~100 cm depth)and xylem water of Qinghai spruce(Picea crassifolia)forest in the eastern Qilian Mountains,and explored the circulation process among different water bodies.The results show that the stable isotopes of precipitation vary greatly during the entire observation period.The values ofδ2H andδ^(18)O in the precipitation in the warm season are richer than those in the cold season,and the slope and intercept of local meteoric water line(LMWL,δ2H=6.79δ18O+7.13)are both smaller than global meteoric water line(GMWL,δ2H=8.17δ18O+10.56).The stable isotopes of soil water at different depths underwent different degrees of evaporative fractionation,and theδ18O andδ2H of shallow soil water varied greatly,while the deep soil water tended to be similar.The topsoil(0~10 cm)can respond quickly to precipitation,and the response of the deep soil has a time lag.In the whole growing season,0~30 cm and 60~100 cm soil water are the main water sources of Qinghai spruce.The water source of Qinghai spruce was from all soil layers in May and September,mainly from the shallow soil layer(0~30 cm)in August and October,and mainly from the deep soil layer(60~100 cm)in June and July.