Variations In Carbon Isotopic Composition Research Articles

Excellent source rocks found along the margin of a large lacustrine basin: Case study from the Ordos Basin, China

Whether the Chang 6 oil pools of the Triassic Yanchang Formation in the Ansai-Yanchang (AY) oil province on the Yishan slope of the Ordos Basin formed from near source rock or far source rock has long been debated. An understanding of the source rock's position will impact the formation mode and distribution of accumulations in this area. Based on the geochemical data of the Chang 7 source rock in six wells and 18 crude oil samples, the geochemical characteristics of Chang 7 source rock and its relationship with Chang 6 crude oil were studied. There are two types of source rocks, namely, black shales and dark mudstones, present in the AY area. The gross thickness of the Chang 7 black shale is 3.0–19.7 m, with a distribution area of 5500 km2. It has an average total organic carbon (TOC) content of 3.34%, with a chloroform bitumen “A" content of 0.512%, indicating good to excellent source rock potential. The kerogen assessment with core samples shows mixed type I-II1, and has reached peak oil generation, maximum pyrolysis temperatures (Tmax) ranging from 445 to 458 °C. In contrast, the average TOC content of the dark mudstone in Chang 7 is 0.91%, chloroform bitumen “A” is 0.079%, the main type of kerogen is type II2-II1, and Tmax varying from 446 to 461 °C, indicating only fair source rock potential overall. The Chang 7 source rocks in the AY area have a gammacerane index of 0.07–0.38, with an average value of 0.21, which reflects a low-salinity fresh to brackish water environment. The relative abundances of C27, C28, and C29 steranes are 29.7%, 23.1% and 47.2%, respectively, indicating that terrestrial higher plants and aquatic organisms provide similar contribution in the Chang 7 source rocks. Oils produced from the AY area of the Chang 6 member have similar geochemical signatures, but are significantly different from the Chang 6 crude oils in the Daozhen (DZ) area of Ganquan County and the Huaishuzhuang (HSZ) area of Fuxian County, which are located in the center of the lacustrine basin. They differ in terms of the maturity of the oil samples and the microscale composition of the parent material type. The closer the wells are to the center of the lacustrine basin, the higher the maturity of the source rock and the greater the contribution of aquatic organisms. The variation of carbon isotopic composition of Chang 6 crude oil in AY area is consistent with that of Chang 7 shale locally, but opposite to that of Chang 6 crude oil in DZ area. The ratios of nC21-/nC22+, tricyclic terpane/hopane and C29 sterane ββ/(ββ+αα) biomarker parameters of Chang 6 crude oils in AY area are similar to those of Chang 7 shale in local area, but deviate from those of DZ and HSZ area. These data results reveal that the Chang 6 crude oils in the AY oil province are dominated by the local Chang 7 excellent source rocks rather than by the long-distance migration of oils from the basin center.

INTERREGIONAL CORRELATION OF THE MIDDLE FRASNIAN (UPPER DEVONOIAN) OF THE NORTH-WEST OF THE RUSSIAN PLATE AND THE EAST OF THE PECHORA PLATE: AN ECOGEOCHEMICAL ASPECT

The paper provides an example of the first stratigraphic application of ecogeochemical method based on the analysis of the carbon isotope values in conodont elements. The method is based on hypothesis of almost isochronic regime change (at least within the basin) in isotope fractionation of carbon in pelagic ecosystems which is reflected and kept in carbon isotope composition of conodont elements. This method has been used to compare between different facial Frasnian sequences of the northwestern Russian Plate (coastal marine facies) and eastern Pechora Plate (depression facies). There were traces of three isotope excursions: negative in the vicinity of the MN5 zone basement (domanic horizon basement), negative at the boundary between the MN5 and MN6 zones, and double positive excursion in the upper MN6 zone. The amplitude of excursions is usually much less in the deep-water facies. The similarity of variations in carbon isotope composition of conodont elements in geographically remote and facially different Fransnian sedimentary sequences of the northwestern Russian Plate and eastern Pechora Plate confirms the possibility of using this parameter for stratigraphic correlation.

Variation in carbon isotope composition of plants across an aridity gradient on the Loess Plateau, China

Carbon isotope composition (indicated by leaf δ13C) reflects plants' strategies to balance carbon acquisition and water loss, which is directly linked to water use efficiency. At a large scale, leaf δ13C has been demonstrated to be closely related to climate and plant functional types; however, at a regional scale, its variation across an aridity gradient and species categories and its covariation with traits in leaf economic spectrum (LES) traits are still unclear. Here, a multivariate statistical analysis was carried out with 271 observations of leaf δ13C from 22 sampling sites on the Loess Plateau. Our results showed that (1) mean leaf δ13C did not differ significantly among life forms in C3 plants, with the maximum mean values occurring in geophytes (−26.31‰) and the minimum values occurring in lianas (−28.29‰); (2) the leaf δ13C responses of different life forms, families and species categories to climates were consistent for C3 plants, namely, they presented similar response rates to changes along the aridity gradient (represented by the moisture index); (3) climate, soil, species category, and leaf economic spectrum traits jointly explained 78.4% of the variation in leaf δ13C for C3 plants. Species category was the largest determinant of leaf δ13C variations for both C3 and C4 plants. Revealing the variation in leaf δ13C of the Loess Plateau plants not only helps us to understand plant adaptation strategies under arid conditions but also provides scientific support for ecological management in vegetation restoration regions.

Compound-Specific Stable Isotope Analysis of Amino Acids in Pelagic Shark Vertebrae Reveals Baseline, Trophic, and Physiological Effects on Bulk Protein Isotope Records

Variations in stable carbon and nitrogen isotope compositions in incremental tissues of pelagic sharks can be used to infer aspects of their spatial and trophic ecology across life-histories. Interpretations from bulk tissue isotopic compositions are complicated, however, because multiple processes influence these values, including variations in primary producer isotope ratios and consumer diets and physiological processing of metabolites. Here we challenge inferences about shark tropho-spatial ecology drawn from bulk tissue isotope data using data for amino acids. Stable isotope compositions of individual amino acids can partition the isotopic variance in bulk tissue into components associated with primary production on the one hand, and diet and physiology on the other. The carbon framework of essential amino acids (EAAs) can be synthesised de novo only by plants, fungi and bacteria and must be acquired by consumers through the diet. Consequently, the carbon isotopic composition of EAAs in consumers reflects that of primary producers in the location of feeding, whereas that of non-essential amino acids (non-EAAs) is additionally influenced by trophic fractionation and isotope dynamics of metabolic processing. We determined isotope chronologies from vertebrae of individual blue sharks and porbeagles from the North Atlantic. We measured carbon and nitrogen isotope compositions in bulk collagen and carbon isotope compositions of amino acids. Despite variability among individuals, common ontogenetic patterns in bulk isotope compositions were seen in both species. However, while life-history movement inferences from bulk analyses for blue sharks were supported by carbon isotope data from essential amino acids, inferences for porbeagles were not, implying that the observed trends in bulk protein isotope compositions in porbeagles have a trophic or physiological explanation, or are suprious effects. We explored variations in carbon isotope compositions of non-essential amino acids, searching for systematic variations that might imply ontogenetic changes in physiological processing, but patterns were highly variable and did not explain variance in bulk protein δ13C values. Isotopic effects associated with metabolite processing may overwhelm spatial influences that are weak or inconsistently developed in bulk tissue isotope values, but interpreting mechanisms underpinning isotopic variation in patterns in non-essential amino acids remains challenging.

Carbonization of Carbonates and Fractionation of Stable Carbon Isotopes in a Dynamic Slip Zone

Data obtained on carbonates and metaterrigenous rocks of the Devonian complex of the Sultan-Uizdag Range, northwestern Uzbekistan, which are carbonized in local deformation zones, are used in a generalized interpretation of the genesis of carbonaceous matter by means of decomposition of carbonates under the effect of seismogenic movements. The release of free carbon is facilitated by synchronous Fe–Mg metasomatism and by the reducing conditions in the presence of hydrogen. Based on literature data on experimental modeling of carbonization processes at high-speed shear deformations of carbonates in a hydrogen medium, a possible scenario is considered for the generation of hydrogen on the surfaces of quartz dislocations in the presence of water in metaterrigenous rocks in association with carbonates. The variation of carbon isotope composition over the volume of the carbonate and terrigenous rocks is extremely heterogeneous, with the 13C isotope enriched in the fracture zones and 12C enriched in the near-fracture volumes of decompression-damaged rocks. It is hypothesized that deformations can affect the fractionation of stable carbon isotopes. With regard for literature data, it is demonstrated that isotope exchange can proceed between the free carbon and carbonate carbon. Various aspects are discussed of the influence of mineral-phase and structural–textural transformations of carbonate rocks at their thermomechanical decomposition under shearing on the geomechanical behavior of the fracture, manifestations of mechanical instability in it, and causes of frictional weakening.

С21n‑alkylbenzene and 1‑n‑alklylnaphthalene in Oils: Isotope Effect during Cyclization/Aromatization?

Abstract—Carbon isotope composition was analyzed in С21n‑alkylbenzene and n‑alklylnaphthalene from five Upper Devonian oils of the Timan–Pechora Basin. In spite of the variations in carbon isotope composition, the difference in δ13C between n‑alkylbenzene and n‑alklylnaphthalene is relatively constant and accounts for, on average, 2.7‰. It is generally accepted that these compounds were derived from a common source. Thus, the revealed carbon isotope fractionation is related to the cyclization and aromatization of aliphatic chain.

Mineral and fluid inclusions in diamonds from the Urals placers, Russia: Evidence for solid molecular N2 and hydrocarbons in fluid inclusions

The compositions of mineral inclusions from a representative collection (more than 140 samples) of diamonds from the placer deposits in the Ural Mountains were studied to examine their compositional diversity. The overwhelming majority of rounded octahedral and dodecahedral stones typical of placers contain eclogitic (E-type) mineral inclusions (up to 80%) represented by garnets with Mg# 40–75 and Ca# 10–56, including the unique high calcic “grospydite” composition, omphacitic pyroxenes containing up to 65% of jadeite, as well as kyanite, coesite, sulfides, and rutile. Peridotitic (P-type) inclusions are represented by olivine, subcalcic Cr-pyrope, chrome diopside, enstatite and magnesiochromite that are typical for diamonds worldwide. Comparing the chemical composition of olivine, pyrope and magnesiochromite in diamonds of the Urals, north-east of the Siberian platform placers and Arkhangelsk province kimberlites show striking similarity. There are significant differences only in the variations of carbon isotopic composition of the diamonds from the placers of the Urals and north-east of the Siberian platform. One typical rounded dodecahedral diamond was found to contain abundant primary oriented submicrometer-sized (<3.0 µm) octahedral fluid inclusions identified by transmission electron microscopy, which caused the milky color of the entire diamond crystal. The electron energy-loss spectrum of a singular inclusion has a peak at ∼405 eV, indicating that nitrogen is present. The Raman spectra with peaks at 2346–2350 cm−1 confirmed that nitrogen exists in the solid state at room temperature. This means that fossilized pressure inside fluid inclusions may be over 6.0 GPa at room temperature, so the diamond may be considered sublithospheric in origin. However, identification of unique fluid inclusions in one typical placer diamond allows one to expand the pressure limit to at least more than 8.0 GPa. The volatile components of four diamonds from the Urals placers were analyzed by gas chromatography–mass spectrometry (GC–MS). They are represented (rel. %) by hydrocarbons and their derivatives (14.8–78.4), nitrogen and nitrogenated compounds (6.2–81.7), water (2.5–5.5), carbon dioxide (2.8–12.1), and sulfonated compounds (0.01–0.96). It is shown that high-molecular-weight hydrocarbons and their derivatives, including chlorinated, nitrogenated and sulfonated compounds, appear to be stable under upper mantle P-T conditions. A conclusion is drawn that Urals placer diamonds are of kimberlitic origin and are comparable in their high E-type/P-type inclusion ratios to those from the northeastern Siberian platform and in part to diamonds of the Arkhangelsk kimberlite province.

Spatial heterogeneity in the relationship between precipitation and carbon isotopic discrimination in C3 plants: Inferences from a global compilation

Abstract Understanding the causes of large variations in carbon isotopic composition of C3 plants (δ13CC3) is a key challenge for paleoenvironmental reconstruction. Several investigations have attempted to study the global patterns in the δ13CC3 values and their correlation with the precipitation variability. Sparse representation of dataset from low-latitude and equatorial regions in the existing global compilation hinders to understand the precipitation-δ13CC3 gradient at different latitudinal-bands. In the present study, available global compilation has been extended with the newly measured dataset, and the new compilation (ca. 1.5 times larger than previous dataset) comprises results from 720 sites across the world. All the δ13CC3 values have been converted to carbon isotopic discrimination between air and leaf (Δair-leaf). Mann-Whitney analysis indicates distinct region-specific distribution of the Δair-leaf values. The average Δair-leaf value in mid-latitude region of the Northern Hemisphere is ca. 2‰ lower than equatorial sites. Multiple linear models have been used to investigate relative influence of climatic (precipitation and temperature) and geographical factors (altitude and latitude) on the Δair-leaf values. This analysis shows that precipitation controls the Δair-leaf values in every latitudinal-bin though the effect of precipitation is negligible beyond 1500 mm. Furthermore, the Δair-leaf-precipitation gradient has a large spatial variability and the most prominent changes in the Δair-leaf values have been observed at arid regions in mid-latitudes of the Southern Hemisphere (maximum 1.3‰ 100 mm−1). Region-specific distribution of δ13C values of plant and Δair-leaf-precipitation gradient prompt to recalculate the relative abundance of C3–C4 plants in the Siwalik sections of the Himalayan foreland basin. Our results show that earlier investigations in the Siwaliks for the Middle-Late Miocene have underestimated the abundance of C4 plants by ca. 20%. The recalculation shows that C4 plants existed in these regions earlier (ca. 17 Ma) than the previously proposed timings.

Improvements in Drill-Core Headspace Gas Analysis for Samples from Microbially Active Depths

The IsoJar™ container is widely used in headspace gas analysis for gases adsorbed on cuttings or bore cores from oil and gas fields. However, large variations in the carbon isotopic ratios of CH4and CO2are often reported, especially for data obtained from depths of &lt;1000 m. The IsoJar™ method leaves air in the headspace that allows microbial oxidation of CH4to CO2, meaning that isotopic fractionation occurs during storage. This study employed the IsoJar™ method to investigate the causes of differences inδ13C data reported by previous studies in the Horonobe area of Japan. It was found that after 80 d storage,δ13CCO2values decreased by ~2‰, whileδ13CCH4values increased by &gt;30‰, whereas samples analyzed within a week of collection showed no such fluctuations. The conventional amount of microbial suppressant (~0.5 ml of 10% benzalkonium chloride (BKC) solution) is insufficient to suppress microbial activity if groundwater is used as filling water. The significant variations in carbon isotopic compositions previously reported were caused by microbial methane oxidation after sampling and contamination by groundwater from different depths. To avoid these problems, we recommend the following: (1) if long-term sample storage is necessary, &gt;10 ml of 10% BKC solution should be added or &gt;0.3% BKC concentration is required to suppress microbial activity; (2) analyses should be performed within one week of sampling; and (3) for CO2analyses, it is important that samples are not contaminated by groundwater from different depths.

Genotypic differences in agro-physiological, biochemical and isotopic responses to salinity stress in quinoa (Chenopodium quinoa Willd.) plants: Prospects for salinity tolerance and yield stability

Quinoa is an important nutritive crop that can play a strategic role in the development of marginal and degraded lands. Genotypic variations in carbon isotope composition (δ13C), carbon isotope discrimination (Δ13C), ratio of intercellular to atmospheric CO2 concentration (Ci/Ca), intrinsic water use efficiency (iWUE), seed yield and grain protein contents were analyzed in 6 quinoa cultivars grown in the field under saline conditions (0, 10, 20 dS m−1). Significant variations occurred in dry biomass, seed yield, plant height, number of branches, number of panicles, panicle weight, harvest index, N and C content. Some genotypes produced yields with values significantly higher than 2.04 t ha−1 (Q12), with an average increased to 2.58 t ha−1 (AMES22157). The present study indicates a large variation in Δ13C for salinity treatments (3.43‰) and small magnitude of variations among genotypes (0.95‰). Results showed that Δ might be used as an important index for screening, and selection of the salt tolerant quinoa genotypes with high iWUE. Quinoa genotypes differs in foliar 13C and 15N isotope composition, which reflected complex interactions of salinity and plant carbon and nitrogen metabolisms. Grain protein contents were found higher in Q19 and Q31 and lowest in Q26. The study demonstrates that AMES22157 and Q12, were salt tolerant and high yielder while the AMES22157 was more productive. This study provides a reliable measure of morpho-physiological, biochemical and isotopic responses of quinoa cultivars to salinity in hyper arid UAE climate and it may be valuable in the future breeding programs. The development of genotypes having both higher water use efficiency and yield potential would be a very useful contribution for producers in the dry region of Arabian Peninsula.

Experimental and Theoretical Evidence for Surface-Induced Carbon and Nitrogen Fractionation during Diamond Crystallization at High Temperatures and High Pressures

Isotopic and trace element variations within single diamond crystals are widely known from both natural stones and synthetic crystals. A number of processes can produce variations in carbon isotope composition and nitrogen abundance in the course of diamond crystallization. Here, we present evidence of carbon and nitrogen fractionation related to the growing surfaces of a diamond. We document that difference in the carbon isotope composition between cubic and octahedral growth sectors is solvent-dependent and varies from 0.7‰ in a carbonate system to 0.4‰ in a metal-carbon system. Ab initio calculations suggest up to 4‰ instantaneous 13C depletion of cubic faces in comparison to octahedral faces when grown simultaneously. Cubic growth sectors always have lower nitrogen abundance in comparison to octahedral sectors within synthetic diamond crystals in both carbonate and metal-carbon systems. The stability of any particular growth faces of a diamond crystal depends upon the degree of carbon association in the solution. Octahedron is the dominant form in a high-associated solution while the cube is the dominant form in a low-associated solution. Fine-scale data from natural crystals potentially can provide information on the form of carbon, which was present in the growth media.

Large Variation in Carbon Isotope Composition of Bulk Leaf Material of Rubber Trees from a Germplasm Collection: An Opportunity for Improving Water Use Efficiency in Breeding Programs

The rubber tree (Hevea brasiliensis) is an important economic crop, particularly in Thailand. As the plantations extend to new and drier areas, iriformation on physiological parameters such as water use efficiency (WUE) is required to help breeding for adapted genotypes. Carbon isotope composition of bulk leaf (~13C) can be used as an indicator of intrinsic water use efficiency (WUE) of plants. A prerequisite step is to analyse the genetic variability of o13C. We compared the carbon isotope composition of bulk rubber tree leaf (~13C) in rainy and dry seasons in a collection of 49 wild genotypes of rubber in Northern Thailand. There were large ~13C variations among the genotypes at all seasons. ~13C ranged between -33.3%0 to -30.0%0 in rainy season and -33.1%0 to -29.9%0 in dry season. ~13C was rather stable with a good correlation between rainy and dry season. In rainy season, there was a positive significant correlation between ~13C, leaf mass per area (LMA) and leaf nitrogen per area (N ). The average ~13C was significantly different between two genetic clusters previously identified in this population. The large genetic variability of ~13C in wild rubber population is promisingfor breeding genotypes using less water. (Resume d'auteur)

Combining carbon-13 and oxygen-18 to unravel triticale grain yield and physiological response to water stress

Water availability in semi-arid regions is increasingly becoming threatened by erratic rains and frequent droughts leading to over-reliance on irrigation to meet food demand. Improving crop water use efficiency (WUE) has become a priority but direct measurements remain a challenge. There is therefore a need to identify reliable proxies and screening traits for WUE. Carbon isotope discrimination (Δ13C) offers potential as a proxy for WUE, but its application is hindered by environmental factors and thus varies greatly among different studies. A two-year study was carried out with four moisture levels, ranging from well-watered (430–450mm) to severe stress (SS) (220–250mm), combined with four commercial triticale genotypes grown under field conditions in a hot, arid, steppe climate of Limpopo in South Africa. The study tested the use of Δ13C as a proxy of intrinsic WUE and grain yield of triticale. Second, δ13C and δ18O in combination with measured gas exchanges were used to test the functionality of the dual isotope model to interpret causes of variation in carbon isotope composition. Third, grain filling carbon assimilate sources were inferred from measured flag leaf and grain Δ13C.The results showed that moisture level significantly influenced grain yield, intrinsic WUE and Δ13C in triticale. Well-watered conditions increased grain yield, which ranged from 3.5 to 0.8tha−1 and 4.9–1.8tha−1 in 2013 and 2014 respectively. Δ13C was also high under well-watered conditions and decreased with decreasing moisture level while WUEintrinsic increased with decreasing moisture level. The relationship between Δ13C and grain yield was positive (P<0.01), but only significant under water stressed conditions, indicating dependence of the relationship on moisture level. The relationship between Δ13C and WUEintrinsic did not depend on the moisture level but showed a negative relationship when data for all moisture levels was combined. δ13C showed a negative relationship with photosynthetic rate (A), while the relationship between stomatal conductance (gs) and δ18O varied with season. Hence, the dual isotope model could only predict that variation observed in Δ13C and thus intrinsic water use efficiency was due to a concomitant decrease in both A and gs when transpiration was not limited by evaporative demand. Flag leaf Δ13C measured under SS at GS71 in the 2014 growing season, was significantly higher (2.2–3.6‰) than grain Δ13C, also measured under SS, suggesting minimal contribution of flag leaf photosynthesis to grain filling. No genotypic differences were observed in Δ13C, grain yield and WUEintrinsic, indicating a probable lack of diversity in the studied genotypes.The results of this study show that carbon isotope discrimination could be useful as a predictor of triticale grain yield in drought prone areas. Δ13C also offers potential as a proxy for WUEintrinsic and breeding for lower Δ13C values could result in varieties with higher WUEintrinsic in triticale. Flag leaf photosynthesis and pre-anthesis assimilates contribute much less carbon to grain filling under water stress than previously thought. Lastly, our results show that the dual isotope model is operational, but is not all encompassing but depends on evaporative demand.

Diel variations in carbon isotopic composition and concentration of organic acids and their impact on plant dark respiration in different species.

Leaf respiration in the dark and its C isotopic composition (δ(13) CR ) contain information about internal metabolic processes and respiratory substrates. δ(13) CR is known to be less negative compared to potential respiratory substrates, in particular shortly after darkening during light enhanced dark respiration (LEDR). This phenomenon might be driven by respiration of accumulated (13) C-enriched organic acids, however, studies simultaneously measuring δ(13) CR during LEDR and potential respiratory substrates are rare. We determined δ(13) CR and respiration rates (R) during LEDR, as well as δ(13) C and concentrations of potential respiratory substrates using compound-specific isotope analyses. The measurements were conducted throughout the diel cycle in several plant species under different environmental conditions. δ(13) CR and R patterns during LEDR were strongly species-specific and showed an initial peak, which was followed by a progressive decrease in both values. The species-specific differences in δ(13) CR and R during LEDR may be partially explained by the isotopic composition of organic acids (e.g., oxalate, isocitrate, quinate, shikimate, malate), which were (13) C-enriched compared to other respiratory substrates (e.g., sugars and amino acids). However, the diel variations in both δ(13) C and concentrations of the organic acids were generally low. Thus, additional factors such as the heterogeneous isotope distribution in organic acids and the relative contribution of the organic acids to respiration are required to explain the strong (13) C enrichment in leaf dark-respired CO2 .

Variation in the carbon isotopic composition of alkanes during shale gas desorption process and its geological significance

Taking Chang 7 shale of the Yanchang Formation in the southeastern area of the Yishan slope of the Ordos Basin as our research subject, desorption experiments were performed on more than 30 shale samples that helped this study focus on the variation of carbon isotopic composition of alkanes during the desorption process of shale gas, the possible causes of this phenomenon and its geological significance will also be discussed as follows. It was found that carbon isotopic composition became higher by 9.2‰ (from −50.1‰ to −40.9‰) for methane desorbed gas (δ13C1), and it also became higher by 2.8‰ (from −35.5‰ to −32.7‰) for ethane (δ13C2), but there's barely any differences for propane during the desorption process. At room temperature or constant temperature, carbon isotopic composition for both methane and ethane (δ13C1 & δ13C2) increased continuously. The values of δ13C1 and δ13C2 were low at first and then it gradually became high whilst the desorption process of shale gas that was optimized with the aid of the increasing temperature. The reason for this phenomenon is most likely due to the main adsorption/desorption of shale gas and diffusion migration fractionation of isotope. Additionally, these variation characteristics of methane and ethane carbon isotope composition of shale gas may be a vital reason for the relatively low carbon isotopic composition of methane compared to δ13C calculated by means of the vitrinite reflectance (RO), and this may be applied to evaluate the remaining amount of shale gas resources.

Carbon isotope composition of latex does not reflect temporal variations of photosynthetic carbon isotope discrimination in rubber trees (Hevea brasiliensis).

Latex, the cytoplasm of laticiferous cells localized in the inner bark of rubber trees (Hevea brasiliensis Müll. Arg.), is collected by tapping the bark. Following tapping, latex flows out of the trunk and is regenerated, whereas in untapped trees, there is no natural exudation. It is still unknown whether the carbohydrates used for latex regeneration in tapped trees is coming from recent photosynthates or from stored carbohydrates, and in the former case, it is expected that latex carbon isotope composition of tapped trees will vary seasonally, whereas latex isotope composition of untapped trees will be more stable. Temporal variations of carbon isotope composition of trunk latex (δ(13)C-L), leaf soluble compounds (δ(13)C-S) and bulk leaf material (δ(13)C-B) collected from tapped and untapped 20-year-old trees were compared. A marked difference in δ(13)C-L was observed between tapped and untapped trees whatever the season. Trunk latex from tapped trees was more depleted (1.6‰ on average) with more variable δ(13)C values than those of untapped trees. δ(13)C-L was higher and more stable across seasons than δ(13)C-S and δ(13)C-B, with a maximum seasonal difference of 0.7‰ for tapped trees and 0.3‰ for untapped trees. δ(13)C-B was lower in tapped than in untapped trees, increasing from August (middle of the rainy season) to April (end of the dry season). Differences in δ(13)C-L and δ(13)C-B between tapped and untapped trees indicated that tapping affects the metabolism of both laticiferous cells and leaves. The lack of correlation between δ(13)C-L and δ(13)C-S suggests that recent photosynthates are mixed in the large pool of stored carbohydrates that are involved in latex regeneration after tapping.

Variation in carbon isotopic composition over the past ca. 46,000 yr in the loess–paleosol sequence in central Kazakhstan and paleoclimatic significance

We present a high resolution record of δ13Corg variation from two loess sequences in central Kazakhstan. The variation shows that the vegetation was persistently dominated by C3 plants over the past ca. 46,000yr. The δ13Corg signature was most likely an indicator of moisture and the moisture variation in central Kazakhstan was associated with the precipitation in Western Europe. The δ13Corg indicated that moisture variation exhibited five stages: decreasing during stage 1 (ca. 46,000–ca. 31,500yr BP), increasing during stage 2 (ca. 31,500–ca. 25,500yr BP), again decreasing during stage 3 (ca. 25,500–ca. 19,000yr BP), fluctuating along a constant line during stage 4 (ca. 19,000–ca. 5000yr BP) and increasing during stage 5 (last ca. 5000yr). Our comparison demonstrated a general similarity between the δ13Corg-indicated moisture variation in central Kazakhstan and the reconstructed precipitation variation in Western Europe. The similarity implies that the moisture of the past ca. 46,000yr in central Kazakhstan has been controlled or modulated by westerlies that brought water vapor from the North Atlantic not only to Western Europe but also to central Kazakhstan.

Local variations of carbon isotope composition in diamonds from São-Luis (Brazil): Evidence for heterogenous carbon reservoir in sublithospheric mantle

Taking advantage of the common occurrence of superdeep mineral inclusion assemblages, we examined core-to-rim primary zonation in 69 diamonds from the alluvial deposits of the São-Luis River (Juina, Brazil). Syngenetic inclusions were represented by phases of superdeep paragenesis. The dominant inclusions are majoritic garnets, ferropericlases and CaSi- and CaSiTi-perovskites. Rare inclusions of MgSi-perovskites, olivines, clinopyroxenes, TAPP, phases of SiO2, kyanites, AlSi-phases, KFsp (K-hollandite?), CF, NAL, grossular, merwinite, native iron, Fe-sulphides, magnesite and CaCO3+CaMgSi2O6 (composite inclusions) were also found.The diamonds from São-Luis display wide variations in carbon isotopic compositions (δ13C), from +2.7 to −25.3‰. The diamonds with inclusions of ferropericlase have a very narrow range of δ13C values, from −2.1 to −7.7‰, which are close to the “normal” mantle values. In many cases, diamonds with inclusions of calcic majoritic garnet and CaSi- and CaSiTi-perovskites display marked differences from this range. Low δ13C values (−10 to −25 ‰) were observed exclusively in a series of diamonds with majorite garnets, Ca-silicates, aluminous silicates and SiO2. The δ13C values from the cores to rims in certain individual crystals varied substantially, indicating multiple stages of growth. The highly negative δ13C values in the cores (−20 to −25 ‰) potentially represent organic matter in metasediments of altered oceanic crust, and the lower δ13C values may represent mixing trends towards “normal” mantle compositions. In this study, we also found a set of diamonds that display an opposite trend of change of the carbon source, from primordial mantle to subducted/crust (either biotic or abiotic carbon).

Evolution of Radiocarbon in a Sandy Aquifer Across Large Temporal and Spatial Scales: Case Study from Southern Poland

We present the results of a comprehensive study aimed at tracing the evolution of carbon isotopic composition of the TDIC (total dissolved inorganic carbon) reservoir from the unsaturated zone down to the discharge area, in a sandy aquifer near Kraków, southern Poland. A multilevel well penetrating the unsaturated zone in the study area was equipped with horizontally mounted lysimeters with ceramic suction cups to collect samples of pore water and metal probes to collect soil air. Strong seasonal fluctuations were observed of soil pCO2 extending down to the water table, coupled with distinct, well-defined depth profiles of δ13CTDIC reaching approximately −10′ at 8 m depth and almost constant radiocarbon content in the TDIC pool, comparable to 14CO2 levels in the local atmosphere. Simple models (closed/open system) do not account for the observed depth variations of carbon isotopic composition of the TDIC pool. This suggests that the TDIC reservoir of pore waters is evolving under conditions gradually changing from an open towards a closed system. In order to explain 13C and 14C content of dissolved carbonates in groundwater in the recharge area of the studied aquifer, additional sources of carbon in the system are considered, such as organic matter decomposition accompanied by reduction of dissolved nitrates and sulfates. The piston-flow l4C ages of groundwater in the confined part of the studied system were calculated using 2 approaches: 1) the correction model proposed by Fontes and Garnier (1979) was used to calculate groundwater ages, utilizing the chemical and carbon isotopic data available for the sampled wells; and 2) inverse geochemical modeling was performed for selected pairs of wells using NETHPATH code. The calculated 14C ages of groundwater range from approximately 0.6 to 37.5 ka BP. Although both methods appeared to be in a broad agreement, NETHPATH calculations revealed that isotopic exchange processes between TDIC pool and solid carbonates present in relatively small amounts in the aquifer matrix play an important role in controlling the 13C and 14C signatures of the dissolved carbonate species in groundwater and should be taken into account when 14C ages are calculated.

Variations in carbon isotopic composition in the subcontinental lithospheric mantle beneath the Yangtze and North China Cratons: Evidence from in-situ analysis of diamonds using SIMS

The components and evolution of subcontinental lithospheric mantle beneath the North China Craton and the Yangtze Craton is a current topic in the geological study of China and the carbon isotopic composition of diamond is one of the most direct probes into cratonic lithospheric mantle processes. In this paper, in-situ SIMS (Secondary Ion Mass Spectrometry) techniques were used to analyze the carbon isotope compositions at different internal growth zones of diamonds from Shandong and Liaoning in the North China Craton and Hunan in the Yangtze Craton. It was found that the carbon isotopic range of diamonds from the North China Craton are rather distinct from those of the Yangtze Craton; the former has a range of −6.0/‰ to −2.0‰ (relative to VPDB) with an average value of −3.0‰ in their core areas, which is consistent with global peridotitic diamonds; the diamonds from the Yangtze Craton, however, have a carbon isotopic range from −8.6‰ to −3.0‰ with an average value of −7.4‰ in their core areas, being more consistent with global eclogitic diamonds. The variations of carbon isotope ratios between different internal growth zones in individual diamonds were different in the three diamond localities studied. There was a clear correlation between changes in carbon isotopic composition and phases of diamond dissolution and new growth, while no correlation was observed between δ 13C and internal inclusions. The variations suggest that the carbon isotopic compositions of mantle fluids were changing during the process of diamond crystallization, and that the heterogeneity of the carbon isotopic composition in mantle carbon reservoirs was a more important factor than carbon isotope fractionation in controlling the carbon isotopic compositions and their variation in diamonds. In addition, the preliminary results of in-situ nitrogen analyses demonstrated that the variation of carbon isotopic compositions between the core and outer growth zones does not correlate with nitrogen abundances, implying either that diamonds crystallized in an open environment or that the carbon isotopic composition and nitrogen contents in mantle fluids were controlled by other, not yet understood factors. The experimental results provide hints that the isotopic composition of carbon and its original sources were different in metasomatic fluids controlling diamond formation in the mantle beneath the North China Craton and the Yangtze Craton.