Average δ13C Research Articles

Chemical and isotopic characteristics of PM10 over the Bay of Bengal: Effects of continental outflow on a marine environment

Pollutants transport from South and Southeast Asia can profoundly affect the marine atmospheric boundary layer (MABL) over the Bay of Bengal (BoB). This study presents chemical and stable isotopic composition of PM10 collected at Port Blair Island (11.6°N, 92.7°E) located in the middle of the BoB during the late northeast monsoon (February–April), a period when the BoB receives considerable continental outflow. These samples (n = 50) were analysed for major ions, carbonaceous species, trace metals, and isotopic composition of total C, N, and S components. Mass concentration of PM10 ranged from 24 to 65 μg m−3 during the study period. The dominance of continental inputs over a marine realm was evident by a significant amount of non-sea-salt (nss)-SO42− (range: 1.8 to 16.9 μg m−3), which accounts for ~65% of the total water-soluble inorganic constituents. The impact of anthropogenic emissions was further evident from the widespread depletion of chloride (range: 57–100%, avg.: 98 ± 7%) from sea-salt aerosols. Carbonaceous species (elemental carbon and organic matter) contributed nearly 35% to PM10. Further, average δ13C (−25.6‰ ± 0.5) and δ34S (4.5‰ ± 1.3) values observed over the marine study region were similar to those found in typical urban environments. δ15N values (13.7‰ ± 5.1) show the significant presence of combustion sources along with the effect of atmospheric processing. Aerosol δ13C values correlate positively with the ratio of water-soluble organic carbon to total organic carbon, indicating the aging of organic aerosols during the transport. Chemical and isotopic data suggest that both biomass burning (BB) and fossil fuel burning (FFB) contributed to ambient PM10 with relatively more contribution of BB during February to early March and that of FFB during late March to middle of April. In aggregate, this study provides newer insights into sources of carbonaceous species and their chemical processing in MABL of BoB.

Kinetic isotope effects during CO2 hydration: Experimental results for carbon and oxygen fractionation

Kinetic isotope effects (KIEs) during the hydration of carbon dioxide (CO2) in aqueous solution are key to understanding various geochemical, physicochemical, and biological processes. Despite the growing interest in KIEs in natural systems (e.g., speleothem calcites, skeletal formation of corals, formation of cryogenic carbonates, and more), the currently available experimental data is limited to only a few studies. Here, we report results from laboratory experiments to constrain kinetic isotope fractionation (KIF) during the hydration of CO2. The experimental setup consisted of a stock solution vessel containing a NaHCO3 solution, a reaction chamber in which BaCO3 was rapidly precipitated from a Tris-buffered BaCl2 solution, and a pump to internally circulate gas throughout the system that was isolated from the ambient laboratory air. Resultant BaCO3 samples, as well as the NaHCO3 and deionized H2O used for our experiments were analyzed for stable carbon and oxygen isotopes by mass spectrometry. Our experimental results were grouped into four different batches, which were obtained during discrete time periods, while some adjustments to the experimental setup and protocols were implemented to improve the data quality. We discuss possible experimental errors among the four batches and conclude that Batch-4 provided the most reliable results. The average δ13C and δ18O values of the Batch-4 BaCO3 samples produced at 25 °C and pHNBS = 8.0 are −29.7 ± 0.7‰ (VPDB) and 18.8 ± 0.6‰ (VSMOW), respectively, which is strongly depleted relative to gaseous CO2 in the system (δ13CVPDB ≅ −10.7‰, δ18OVSMOW ≅ 37.9‰) . From the isotope data, we calculate our experimental 13KIF and 18KIF, which refer to the 13C/12C and 18O/16O fractionation between CO2(g) and BaCO3, where the δ13C and δ18O values of CO2(g) were calculated using known equilibrium fractionation factors. From the mean of Batch-4 results, we conclude 13KIF = 19.6 ± 0.8‰ and 18KIF = 18.8 ± 0.6‰ at 25 °C and pHNBS = 8.0. If full carbon KIF of ∼ 2.0‰ is assumed between CO2(g) and CO2(aq), then the mean 13KIF relative to CO2(aq) is 17.6 ± 0.8‰. Our KIFs are the largest values compared to previously reported experimental KIFs (except for one study), suggesting that our values are closest to the full isotope disequilibrium during CO2 hydration, as any partial re-equilibration tends to reduce observed KIFs.

Main controls on the stable carbon isotope composition of speleothems

The climatic controls on the stable carbon isotopic composition (δ13C) of speleothem carbonate are less often discussed in the scientific literature in contrast to the frequently used stable oxygen isotopes. Various local processes influence speleothem δ13C values and confident and detailed interpretations of this proxy are often complex. A better understanding of speleothem δ13C values is critical to improving the amount of information that can be gained from existing and future records. This contribution aims to disentangle the various processes governing speleothem δ13C values and assess their relative importance. Using a large data set of previously published records we examine the spatial imprint of climate-related processes in speleothem δ13C values deposited post-1900 CE, a period during which global temperature and climate data is readily available. Additionally, we investigate the causes for differences in average δ13C values and growth rate under identical climatic conditions by analysing pairs of contemporaneously deposited speleothems from the same caves. This approach allows to focus on carbonate dissolution and fractionation processes during carbonate precipitation, which we evaluate using existing geochemical models. Our analysis of a large global data set of records reveals evidence for a temperature control, likely driven by vegetation and soil processes, on δ13C values in recently deposited speleothems. Moreover, data-model intercomparison shows that calcite precipitation occurring along water flow paths prior to reaching the top of the speleothem can explain the wide δ13C range observed for concurrently deposited samples from the same cave. We demonstrate that using the combined information of contemporaneously growing speleothems is a powerful tool to decipher controls on δ13C values, which facilitates a more detailed discussion of speleothem δ13C values as a proxy for climate conditions and local soil-karst processes.

Carbon and Nitrogen Isotope Ratios of Food and Beverage in Brazil.

Several previous studies on targeted food items using carbon and nitrogen stable isotope ratios in Brazil have revealed that many of the items investigated are adulterated; mislabeled or even fraud. Here, we present the first Brazilian isotopic baseline assessment that can be used not only in future forensic cases involving food authenticity, but also in human forensic anthropology studies. The δ13C and δ15N were determined in 1245 food items and 374 beverages; most of them made in Brazil. The average δ13C and δ15N of C3 plants were −26.7 ± 1.5‰, and 3.9 ± 3.9‰, respectively, while the average δ13C and δ15N of C4 plants were −11.5 ± 0.8‰ and 4.6 ± 2.6‰, respectively. The δ13C and δ15N of plant-based processed foods were −21.8 ± 4.8‰ and 3.9 ± 2.7‰, respectively. The average δ13C and δ15N of meat, including beef, poultry, pork and lamb were -16.6 ± 4.7‰, and 5.2 ± 2.6‰, respectively, while the δ13C and δ15N of animal-based processed foods were −17.9 ± 3.3‰ and 3.3 ± 3.5‰, respectively. The average δ13C of beverages, including beer and wine was −22.5 ± 3.1‰. We verified that C-C4 constitutes a large proportion of fresh meat, dairy products, as well as animal and plant-based processed foods. The reasons behind this high proportion will be addressed in this study.

Zircon U-Pb dating and stable isotopic compositions for constraining the genesis of the Chagangnuoer magnetite deposit in western Tianshan, NW China

The Chagangnuoer magnetite deposit in western Tianshan (NW China) is hosted by submarine volcanic rocks and marble lens, with a resource of >220 Mt Fe at 38 wt%. Two major orebodies FeI and FeII are current in production. Pervasive garnet skarn, magnetite, actinolite–epidote, and marble zones are developed at Chagangnuoer. Paragenetic sequences are divided into garnet–pyroxene (I), magnetite–pyrite ± chalcopyrite (II), actinolite–epidote–K-feldspar (III), garnet ± tremolite ± scapolite (IV), magnetite ± hematite (V), actinolite–epidote (VI), and sulfide–calcite–quartz (VII) stages. A diorite beneath the FeII and a granodiorite with skarn alteration have zircon U-Pb ages of 329 ± 2 and 317 ± 4 Ma, respectively. These intrusions have high potassic to shoshonitic, metaluminous affinities, and significant Nb, Ta, Ti and Sr anomalies. Stage II magnetite has δ18OV-SMOW compositions of 1.9–3.5‰, higher than Stage V magnetite (0.5–2.1‰), indicating a hydrothermal fluid source of magmatic origin. The δ18O values of garnet, actinolite, epidote and quartz range from 4.1 to 12.2‰. Stage VII calcite has δ13CV-PDB of −2.0 to −0.8‰ and δ18O of 8.9 to 9.9‰, lower than for the marble (average δ13C + 2.3‰, δ18O 12.8‰). δ34SV-CDT compositions for pyrite and chalcopyrite from Stages II and VII vary between 0.8 and 13.1‰. The isotopic compositions imply that minor non-magmatic sources (e.g., marine carbonate, seawater, and meteoric water) have been circulated into hydrothermal fluids producing the skarn alterations and associated iron mineralization. The early-stage skarn alteration and main Fe mineralization relate to the emplacement of diorite stock at depth, whereas the late-stage skarn-magnetite assemblages are intimately associated with the granodiorite. The Chagangnuoer deposit is concluded to be magnetite skarns formed by magmatic-hydrothermal fluids that emanated from the dioritic and granodioritic magmas intruding above a sub-arc mantle wedge and that metasomatized intensely with the Carboniferous andesitic-rhyolitic volcanic rocks and carbonate.

Formula omitted]C signatures of organic aerosols: Measurement method evaluation and application in a source study

Analysis of the stable carbon isotope 13C in organic carbon (OC) can give insight into sources and atmospheric processing of carbonaceous aerosols, provided the 13C source signatures are known. However, only few data on 13C signatures of OC emitted by common sources of carbonaceous aerosol are available in Europe. We present and evaluate an improved version of a measurement method to obtain δ13C signatures on organic aerosols desorbed from filter samples at three different desorption temperatures (200 °C, 350 °C and 650 °C) and apply it in a source study.With our calibration approach, the reproducibility of a L-Valine reference material desorbed at a single temperature step of 650 °C shows a standard deviation of 0.19‰ over a period of more than one year. The average δ13C value for this reference material over 248 measurements is −24.10‰, which shows only a slight bias to the nominal value of −24.03‰. Repeated analysis of ambient filter samples desorbed at three temperature steps show typical standard deviations of about 0.3‰ for all temperature steps (200 °C, 350 °C and 650 °C). Isotopic fractionation due to partial thermal desorption during the individual temperature steps was tested on single compound reference materials. It showed significant isotopic fractionation only at temperature steps, in which a very minor fraction of the compound was desorbed. Possible isotope effects caused by charring of organic material were investigated and found to be not significant.The thermal desorption method was applied to various source filter samples from the region of Naples, Italy. We analyzed two different biomass burning sources, exhaust from a city bus and traffic emissions collected in a tunnel and compared these to ambient filter samples from the same region. δ13C signatures of the total OC show values in a narrow range of about −28‰ to −26‰ for all sources, which does not allow a source apportionment only based on 13C. Nevertheless, the results add information to a source inventory of δ13C, where information of 13C in organic aerosol from specific emission sources are rare. City bus emissions show little variation of δ13C over the temperature steps, whereas biomass burning aerosol is enriched in 13C for OC desorbed at 650 °C. For PM10 samples in the urban tunnel an enrichment in δ13C at the 650 °C temperature steps was observed, which is likely caused by the contribution of carbonate carbon to the carbonaceous material desorbed at this temperature step.

Palynofloral, palynofacies and carbon isotope of Permian coal deposits from the Godavari Valley Coalfield, South India: Insights into the age, palaeovegetation and palaeoclimate

Palynological studies of the present Permian sediments play a vital role in biostratigraphic and palaeoecological interpretations. Additionally, the palynofacies analysis, Total Organic Carbon (TOC) content and δ13C value in the present study focus largely for the palaeoenvironmental and palaeoclimatic reconstruction and also provides information about processes responsible for sedimentary deposits along with their lithological counter parts. The palynological investigation of 306 m deep borehole (MSM-25) from the Somavaram area of the Godavari Valley Coalfield has led to infer five distinct palynofloral assemblages. The Artinskian (Palynofloral assemblage-I and II), Guadalupian (Palynofloral assemblage-III and IV), and Lopingian (Palynofloral assemblage-V) ages have been assigned to the palynofloral assemblages based on the palynofloral evidence. The distinct stable carbon isotope ratios also comprehend these ages with extreme climatic events. The Artinskian age (−22.4‰) is characterized by relatively higher average δ13C values, whereas lowest average δ13C values are observed at the Lopingian age (−24.0‰) with intermediate average δ13C value (−23.2‰) during Guadalupian age. In the present study, the Permian-Triassic (P-T) transition is marked by the distinct negative carbon-isotope excursion followed by a distinct recovery during the early Triassic time period. The relative variability of palynofacies components, such as palynomorphs, structured terrestrial phytoclasts, opaque phytoclasts, degraded organic matter (OM) and amorphous OM, is related to hydrodynamic perturbations during the deposition time. Based on the dominance and sub-dominance of the palynofacies, three distinct depositional phases have been identified, representing differential environmental settings. The palynomorphs and structured terrestrial phytoclasts dominate the Palynofacies assemblage A suggesting forest swamp environment, while in the Palynofacies assemblage B the dominance of degraded OM and amorphous OM characterize Reed marshes/lakeshore setting and the abundance of opaque phytoclasts in the Palynofacies assemblage C indicate oxidized swamp environment.

Contrasting patterns of tree species mixture effects on wood δ13C along an environmental gradient

Establishing mixed-species stands is frequently proposed as a strategy to adapt forests to the increasing risk of water scarcity, yet contrasted results have been reported regarding mixing effects on tree drought exposure. To investigate the drivers behind the spatial and temporal variation in water-related mixing effects, we analysed the δ13C variation in 22-year tree ring chronologies for beech and pine trees sampled from 17 pure and mixed pine–beech stands across a large gradient of environmental conditions throughout Europe. In the pure stands, average δ13C values were lower for beech (−27.9‰ to −22.2‰) than for pine (−26.0‰ to −21.1‰), irrespective of site conditions. Decreasing SPEI values (calculated over June to September) were associated with an increase in δ13C for both species, but their effect was influenced by stand basal area for pine and site water availability for beech. Mixing did not change the temporal constancy of δ13C nor the tree reaction to a drought event, for any of the species. While the mixing effect (Δ δ13C = δ13C pure stands − δ13C mixed stands) was on average positive for beech and non-significant for pine across the whole gradient, this effect strongly differed between sites. For both species, mixing was not significant at extremely dry sites and positive at dry sites; on moderately wet sites, mixing was positive for beech and negative for pine; at sites with permanent water supply, no general patterns emerge for any of the species. The pattern of mixing effect along the gradient of water availability was not linear but showed threshold points, highlighting the need to investigate such relation for other combinations of tree species.

Geochemical, stable isotopic, palynological characterization of surface dry soils and atmospheric particles over Jodhpur city (Thar Desert, Rajasthan) during peak summer of 2013

Atmospheric dust originating from the Thar Desert (India) acts as the local source of mineral dust in South Asia, spreading over an area of 0.32 × 106 km2. Regional studies conducted during peak boreal summer are required to characterize this mineral dust that blows in form of episodic dust storms towards Indo-Gangetic Plains (IGP), using a multi-tracer approach. To achieve this goal, atmospheric PM10 particles were collected along with surface dry soils between 3 and 11 June, 2013, from in and around the Jodhpur city (26.2389°N, 73.0243°E) to glean elemental composition, stable isotopic and palynological (pollen types) database. Typical crustal elemental ratios, e.g. Si/Al, Ca/Al, Fe/Al, K/Al, Mg/Al, Ti/Al, varied in narrow ranges 8.1 ± 1.21, 1.02 ± 1.53, 0.50 ± 0.14, 0.34 ± 0.06, 0.19 ± 0.06 and 0.06 ± 0.02, respectively. Average Sr/Al, Rb/Al and Zr/Al ratios were found to be 39.70 ± 12.24, 18.00 ± 2.0 and 70.83 ± 13.11 (μg gm−1/wt%), respectively. Average δ13C, δ15N, δ34S values of surface soils were − 10.5‰ ± 4.0, 11.4‰ ± 1.6 and 3.6‰ ± 2.1, while δ13C and δ15N of atmospheric PM10 particles varied in ranges − 25.6‰ ± 0.67 and 9.9‰ ± 1.7, respectively. Observed palynoassemblage indicated the open nature of vegetation that usually grows under warm-humid conditions with traces of few allergens and pathogens. Generated chemical-isotopic-pollen database could be utilized for deciphering origin of dust storms in IGP. Detailed multi-proxy characterization of mineral dust from the Thar Desert can further help to determine its role in influencing air quality and human health.

Production of long-chain n-alkyl lipids by heterotrophic microbes: New evidence from Antarctic lakes

Long-chain n-alkyl lipids are traditionally ascribed to an origin from terrestrial vascular plants because these compounds are major constituents of higher plant leaf waxes. Over the past half century, numerous studies have taken advantage of these sedimentary biomarkers and their isotopic ratios to reconstruct paleo-environmental and paleo-climatological changes at a variety of time scales. However, it is uncertain and extremely difficult to determine if these compounds can also derive from microbes because of the prevalence of higher plants in most environments around the globe. Here we show, for the first time from natural sediment samples, that long-chain n-alkyl lipids can predominantly originate from aquatic microbial sources at three high-latitude (>69°S latitude) Antarctic lakes, where no vascular plants are present in the surrounding land mass. The high carbon isotopic values (up to –12‰) of these long-chain n-alkyl lipids exclude the possibility that these compounds are transported by wind from adjacent vegetated land masses. Instead, these isotope values are similar to lipids produced by aquatic microbial mats with an average bulk δ13C value of –14.2 ± 1.7‰, indicating heterotrophic microbes are the likely source of these long-chain n-alkyl lipids. For comparison, we also show that when even small amount of vascular plants and mosses are present in the study region, for instance at Long Lake (∼62°S latitude) in the Antarctic Peninsula, the carbon isotopic values of sedimentary long-chain n-alkyl lipids decline dramatically, suggesting a rapid proportional increase in the relative contribution of leaf wax sources to total long-chain n-alkyl lipid inventory in lake sediments.

Application of a stable carbon isotope for identifying Broussonetia papyrifera pollen.

The objective of this study was to investigate whether δ13C values can be used to identify pollen specie in the atmosphere. A Burkard 7-day recording volumetric spore trap was used to collected pollens in the atmosphere in Tainan City, Taiwan, from January 2 to December 28, 2006, and a light microscope was used to identify the pollen species and concentrations. A Burkard cyclone sampler was used to collect particulate matter and an elemental analyzer with an isotope ratio mass spectrometer was used to analyze the δ13C values. Our data showed that the predominate pollen specie in the atmosphere was Broussonetia papyrifera pollen and that the annual average concentration was 27 grains/m3 (pollen season, 36; nonpollen season, 9 grains/m3). The average δ13C value was - 26.19‰ for particulate matter in the atmosphere (pollen season, - 26.00‰; nonpollen season, - 26.28‰). No significant association was observed between δ13C values and Broussonetia papyrifera pollen concentrations. However, the δ13C value in the atmosphere was associated with the levels of Broussonetia papyrifera pollen among the samples with a diameter of particulate matter smaller than 10μm at a level lower than 40μg/m3. In addition, the relative contribution of Broussonetia papyrifera pollen to the carbon in the atmosphere using a two end-member mixing models was found to be associated with the Broussonetia papyrifera pollen concentration. In summary, our study suggested that δ13C values can be applied in the assessment of Broussonetia papyrifera pollen specie under specific conditions in the atmosphere.

Thermal Imaging Reliability for Estimating Grain Yield and Carbon Isotope Discrimination in Wheat Genotypes: Importance of the Environmental Conditions.

Canopy temperature (Tc) by thermal imaging is a useful tool to study plant water status and estimate other crop traits. This work seeks to estimate grain yield (GY) and carbon discrimination (Δ13C) from stress degree day (SDD = Tc − air temperature, Ta), considering the effect of a number of environmental variables such as the averages of the maximum vapor pressure deficit (VPDmax) and the ambient temperature (Tmax), and the soil water content (SWC). For this, a set of 384 and a subset of 16 genotypes of spring bread wheat were evaluated in two Mediterranean-climate sites under water stress (WS) and full irrigation (FI) conditions, in 2011 and 2012, and 2014 and 2015, respectively. The relationship between the GY of the 384 wheat genotypes and SDD was negative and highly significant in 2011 (r2 = 0.52 to 0.68), but not significant in 2012 (r2 = 0.03 to 0.12). Under WS, the average GY, Δ13C, and SDD of wheat genotypes growing in ten environments were more associated with changes in VPDmax and Tmax than with the SWC. Therefore, the amount of water available to the plant is not enough information to assume that a particular genotype is experiencing a stress condition.

Evaluating the Extent of North Atlantic Deep Water and the Mean Atlantic δ13C From Statistical Reconstructions

AbstractBenthic δ13C is often used to infer past changes in ocean circulation, though the interpretation of this proxy is difficult due to data scarcity and uncertainties. We present two methods for reconstructing the δ13C signal of North Atlantic Deep Water (NADW) and Antarctic Bottom Water and calculating the average oceanic δ13C values for the Atlantic Ocean based on δ13C from benthic foraminifera. The two simple statistical models are described and tested for the Holocene and the Last Glacial Maximum. The first statistical model consists of regressions of the δ13C data, which vary quadratically with depth and linearly with latitude. It differentiates between two regions, one for NADW and another for Antarctic Bottom Water. The second method consists of a hyperbolic tangent regression, which is bound asymptotically by the water mass source region averages (end‐members). To test the robustness of the statistical models, two isotope‐enabled climate models, the UVic ESCM and LOVECLIM, are sampled randomly, generating “pseudoproxies.” These are then used for testing the accuracy of the statistical models against the complete climate model δ13C outputs. We quantitatively compare the average δ13C and NADW depth against the original climate model outputs. We find that both statistical approaches are robust, regardless of the spatial distribution of the pseudoproxies, with the quadratic approach better able to capture the shape of NADW δ13C signal. Hence, this method can potentially be applied to different δ13C data sets to evaluate past changes in NADW.

Assimilation of Allochthonous Matter by Estuarine Consumers During the 2015 El Niño Event

The El Nino phenomenon refers to a warming of the tropical Pacific basin whose meteorological effects influence the dynamics of aquatic ecosystems around the world. Prior studies have shown that strong El Nino events are highly correlated with high rainfall episodes and high freshwater discharge into subtropical estuaries, with subsequent changes in species composition, abundance, and diversity of their biota. In this work, we evaluated the hypothesis that riverine allochthonous matter associated with the strong 2015 El Nino event is assimilated by decapod crustaceans and fishes of a southwestern Atlantic estuary. We analyzed carbon (δ13C) and nitrogen (δ15N) stable isotope ratios of primary food sources and consumers in the estuary and of riverine allochthonous matter. Our findings revealed that higher water surplus and lower salinity associated with the 2015 El Nino coincided with an increase in the number of freshwater fish species and a decrease in the number of marine- and estuarine-dependent fishes inside the estuary. In addition, most estuarine consumers had lower average δ13C values during the wet period associated with the 2015 El Nino. This seemed to reflect the assimilation of 13C-depleted riverine matter, which according to Bayesian isotope mixing models ranged from 11% (adult resident decapod crustaceans) to 60% (adult resident fishes) during the wet season. Further studies are needed to evaluate the role of El Nino events on structuring food web organization in estuaries under the influence of this climatic phenomenon, which may become more frequent and intense in a global warming scenario.

Determination of the stable carbon isotopic compositions of 2-methyltetrols for four forest areas in Southwest China: The implications for the δ13C values of atmospheric isoprene and C3/C4 vegetation distribution

Isoprene is the most abundant non-methane hydrocarbons (NMHCs) in the troposphere and is released predominantly by vegetation. The δ13C values of atmospheric isoprene vary with different plant types (e.g. C3 and C4 plants). In this work, aerosol samples were collected in four forest areas in Sichuan Province, China, i.e., the Baima Spring Scenic Area (BM), the Panzhihua Cycas Nature Reserve (PZ), the Gongga Mountain National Nature Reserve (GG) and the Wolong National Nature Reserve (WL) during the summers of 2010–2012. The stable carbon isotopic compositions of 2-methyltetrols, the stable products of isoprene oxidation by OH, were measured using a GC/C/IRMS (gas chromatography/combustion/isotopic ratio mass spectrometry) with methylboronic acid derivatization. The stable carbon isotopic fractionation coefficient of isoprene oxidized by OH (OHεi) was derived in laboratory. With the δ13C values of 2-methyltetrols, OHεi and meteorological parameters, the δ13C values of atmospheric isoprene were calculated. The results show that forests can remarkably change the δ13C values of isoprene in the regional scales, making significant contributions to isoprene emissions. Moreover, C3/C4 proportions of shrubs and grasses depend on altitudes. The average δ13C values of atmospheric isoprene are −24.18 ± 1.72‰, −25.81 ± 1.36‰, −24.96 ± 0.94‰, −25.89 ± 1.35‰ for BM, PZ, GG and WL, respectively. The average δ13C value of atmospheric isoprene in SW China and the surrounding areas was −25.23 ± 1.44‰. C4 plants emitted 26.9 ± 10.3% of isoprene in the research atmosphere.

Variation of Leaf Carbon Isotope in Plants in Different Lithological Habitats in a Karst Area

Drought is the major factor that limits vegetation recovery in rocky desertification areas. The leaf carbon isotope (δ13C) value is related to plant water-use efficiency (WUE) and is of great significance in revealing the WUE characteristics of species in karst areas. Measurements of the δ13C value in plant leaves and the nutrient and water contents of lithologic soils were obtained for six woody species (cypress, Cupressus funebris Endl.; mansur shrub, Coriaria nepalensis Wall.; camphor, Cinnamomum bodinieri Levl.; birch, Betula luminifera H. Winkl.; alder, Alnus cremastogyne Burk. and dyetree, Platycarya longipes Wu.) planted in three different lithologic soil types (dolomite, dolomite sandstone, limestone) in the karst area of Guizhou Province. The results showed that C. funebris in the dolomite sandstone soil had the highest δ13C value (−27.19‰), whereas C. bodinieri in the limestone soil had the lowest δ13C value (−31.50‰). In terms of lithology, the average leaf δ13C values were −28.66‰ (dolomitic sandstone), −28.83‰ (dolomite), and −29.46‰ (limestone). The δ13C values of C. funebris and A. cremastogyne were significantly lower in the limestone soil than in the dolomite and dolomite sandstone soil, indicating that the WUE of some tree species is affected by soil conditions under different lithological development processes. Moreover, the relationship between the δ13C value in the leaves and the comprehensive soil conditions varied among the species, and the δ13C value was negatively correlated with the soil water content in all three soil types. Our study provides basic data on the composition characteristics of the δ13C value of tree species, which is beneficial for the selection of tree species for vegetation restoration and afforestation in karst areas.

Carbon isotope and rare earth element composition of Late Quaternary sediment gravity flow deposits on the mid shelf of East China Sea: Implications for provenance and origin of hybrid event beds

AbstractThe East China Sea Shelf has an unusually wide and low gradient shelf, supplied from sediment‐charged rivers and large river delta systems, with bottom currents sweeping the sea floor and located in the path of strong typhoons. Sediment gravity flow deposits, including four hybrid event beds and a high density turbidite, are identified in a core from the mid‐shelf of the East China Sea. The hybrid event beds typically comprise three or two internal divisions from the base to the top: (i) H1, H3 and H5; or (ii) H3 and H5. Radiocarbon ages of the hybrid event beds were in the range of 3821 to 8526 yr bp. Based on correlation with surrounding cores, the hybrid events may have happened at any time between 1930 yr bp and 3890 yr bp. The δ13C values in hybrid event beds together with bathymetry data suggest local erosion on the shelf. The average δ13C value for the H1 division is similar to the H3 division in the hybrid event beds, implying that the organic matter in the H1 and H3 divisions may come from the same source area. Cross‐plots of upper continental crust normalized rare earth elements in the five units reveal that the sediment source of the four hybrid event beds and the turbidite was ultimately primarily from Korean rivers. Partial transformation from a moderate‐strength debris flow with the additional role of erosional bulking can explain occurrences of hybrid event beds on the East China Sea Shelf. The data indicate that hybrid sediment gravity flow deposits were sourced from intra‐shelf failures and subsequently transformed and deposited as hybrid event beds. The study shows that hybrid sediment gravity flows and turbidity currents may not necessarily indicate proximity to a major fluvial or deltaic system and that intra‐shelf sedimentation can be a sediment source. It is unlikely that the debris flows and turbidity currents were triggered by a hyperpycnal flow or tsunami, because both can carry continental and/or coastal signals which have not been recognized in the core. Typhoons are the probable triggering mechanism.

Using δ13C to reveal the importance of different water transport pathways in two nested karst basins, Southwest China

This study used carbon (C) isotope sourcing to determine transport processes of dissolved inorganic carbon (DIC) from the land surface to river catchments in Southwest China. Both nested karst watersheds investigated (Chenqi and Houzhai) are representative of typical karst landform environments (e.g., primary forest, secondary forest, and farmland). We measured DIC concentrations and the δ13C values of rainfall, river water, groundwater, soil, and plants. To do so, we used IsoSource (a Visual Basic program) to determine source partitioning over time (seasonal) and across the two nested watersheds. In 2017, the mean DIC concentration was 0.06 ± 0.03 mmol L−1 and the rainfall δ13CDIC value was −14.4‰ ±1.9‰. We found similar DIC concentrations in the surface and groundwater of both watersheds, ranging from 0.20 to 0.71 mmol L−1 (seasonal) and from −3.7‰ to −9.4‰ (δ13CDIC) in the Chenqi catchment and from 0.33 to 0.60 mmol L−1 (seasonal) and from −10.3‰ to −6‰ (δ13CDIC) in the Houzhai watershed. The average δ13C values of soil and local plants were −24.6 ± 1.4‰ and −28.9 ± 1.2‰ in the Chenqi catchment and −25.8 ± 0.9‰ and −27.2 ± 1.8‰ in Houzhai watershed, respectively. In addition, carbonate bedrock and groundwater were the main sources of surface water in the Chenqi and Houzhai nested watersheds, both being greater than 30%. Source percentages were ∼20% from atmospheric deposition and ∼10% from soil. Furthermore, HCO3− was the predominant form of DIC (pH values > 8), and the contribution rates of dissolved carbonate minerals (HCO3−) were approximately 10.4% and 19.6% in the Chenqi catchment and the Houzhai watershed, respectively.

Mineralogical, compositional and isotope characterization of human kidney stones (urolithiasis) in a Sri Lankan population.

In order to understand the processes of stone formation, compositional, spectroscopic, mineralogical and crystallographic characteristics of human urinary stones collected from patients in Sri Lanka were investigated in detail. The data showed that the majority of urinary calculi were calcium oxalate, either whewellite or weddellite. Other solid phases of stones were composed of struvite, uricite and hydroxylapatite. However, mixed compositions were common except for whewellite stones which occur frequently in pure form. Scanning electron microscope observations and associated energy-dispersive X-ray analyses revealed that whewellite or weddellite was well crystalized compared to other stones types, while phosphate stones were mostly cryptocrystalline. The average δ13C and δ18O of stones were - 32.2‰ (- 37.3 to - 17.4‰) and - 24.2‰ (- 26.7‰ to - 8.9‰), respectively. The δ13C values were highly depleted compared to North American and European urinary stones. This may be due to food habits of Asians who consume rice as the staple food.

Variations in δ13C of water–soluble leaf and phloem organic matter of Platycladus orientalis: influences of photosynthetic and post–photosynthetic fractionation

ABSTRACTAnalysis of variations in water–soluble organic matter (WSOM) δ13C of leaves and phloem can efficiently describe the δ13C distributions within plants and identify the temporal variation of δ13C. In this study, WSOM δ13C values of both leaves and phloem (twig, stem, and root) of Platycladus orientalis were measured during seven sunny days, including 2–hour interval measurements at three days for diel pattern analysis and 6–hour interval measurements at the remaining four days for day–to–day variation analysis. Analysis of WSOM δ13C in different plant organs showed that 13C was generally depleted from leaves to twigs, then enriched in stems and subsequently depleted in roots. Stems were significantly 13C–enriched compared to twigs (p < 0.05), while δ13C differences between stems and other organs and among leaves, twigs and roots were not significant (p > 0.05). No clear diel patterns in δ13C of leaves and phloem were found. Daily average δ13C values indicated that all plant organs had more positive values on sunny days during the dry season than during the wet season. Both photosynthetic and post–photosynthetic fractionation influence variations in WSOM δ13C. These results have implications for research on plant physiology and plant water use.