Differences In Carbon Isotope Composition Research Articles

Climate-growth relation and isotopic △13carbon responses of field-grown Pinus caribaea var. hondurensis and Pinus taeda to nutrient availability

This study aimed to characterize the development of Pinus caribaea var. hondurensis and Pinus taeda grown under two fertilization regimes (fertilized and control treatments) at field-grown condition. The growth, climate-growth relation, and intrinsic water use efficiency (WUEi) of the trees were assessed by a combined analysis of cross-sectional area (CSA) increment, water balance and carbon isotope discrimination (Δ13C ‰). The effect of fertilization on tree growth regime was assessed using inventory data collected yearly over 8 years. Additionally, monthly data of wood increments, monitored in nonfertilized stands over a period of 6 years, were utilized for correlations with meteorological variables (air temperature, rainfall, vapor pressure deficit, solar radiation and potential and actual evapotranspiration). The growth of Pinus caribaea and P. taeda was strongly influenced by multiple meteorological variables related to water availability and evapotranspiration. Differences in carbon isotope composition between treatments revealed that fertilized Pinus spp. displayed higher Δ13C values in some years, indicating improved water uptake efficiency due to increased nutrient availability. Pinus caribaea outperformed P. taeda in wood productivity and exhibited a heightened responsiveness to fertilization. In general, P. caribaea was shown to be more water-use efficient than P. taeda, as it is able to use smaller amounts of water for greater wood production.

The Validity of Protein in Australian Honey as an Internal Standard for C4 Sugar Adulteration

Recent media reports claimed that a large proportion of honey sold in Australian supermarkets was adulterated, although no specific details of the nature of the adulteration were made public. To investigate the basis of these claims, the current study was conducted with samples of Australian honey obtained from supermarkets or direct from beekeepers/small-scale producers. Without evidence to the contrary, it was assumed that the beekeeper honey would be unadulterated. Analysis of these samples using the official AOAC method (998.12) found that a proportion of both supermarket and beekeeper honeys had apparent C4 sugar contents greater than 7% and this proportion was similar to the failure rates reported by popular media. The AOAC test measures the difference in carbon isotopic composition between the honey (mostly sugar) and protein precipitated from the honey and relies on the assumption that nectar (the source of sugar) comes from the same plant species as pollen (the source of protein). Initial results found that most Australian honey failed the AOAC test because the protein was depleted in 13C with respect to the sugar although the sugar was in the normal range (δ13C more negative than – 24‰). A series of experiments investigated the nature of the precipitate obtained from Australian honey and found the weight of precipitate was greater than the amount of protein measured in the honey and the precipitate contained non-protein material. Based on these findings, a modification to the AOAC method is proposed whereby samples, after addition of sodium tungstate and acid, are left unheated for 48 h for a floc to form. This procedure produced a precipitate that was mostly comprised of protein. It is also recommended that the acceptance criteria for Australian honey are increased from 1 to 2‰ difference between the carbon isotopic composition of the honey and the precipitate. Using the modified method and acceptance criteria, the failure rate for Australian honey was no more than 8%, compared to 37% using the official method.

13C/12C Carbon Isotope Fractionation between Atmospheric Carbon Dioxide and Photosynthesis Products in Plant Leaves As Affected by the Spectral Composition of Lighting Environment

We investigate the effects that the spectral composition of radiation that plants are exposed to during their development has on the fractionation of carbon isotopes between atmospheric carbon dioxide and the primary products of photosynthesis in plant tissues. The difference in carbon isotope composition between carbon in air near the leaves and carbon in the leaves varies in the range of 7 to 19 depending on the spectral composition of incident light, with an increase in the red component resulting in enrichment of the leaves with the light isotope 12C. This differences are (i) the measure of isotope fractionation during the vital activity of plants and (ii) the rate of carbon assimilation due to photosynthetic reactions.

Terrestrial diet in prehistoric human groups from southern Poland based on human, faunal and botanical stable isotope evidence

We present stable carbon and nitrogen isotope analyses of animal and human bones from south-eastern Poland, dated to the Neolithic and the Bronze Ages. The analyses are discussed against the background of archaeobotanical data from the studied sites from Miechów and Mozgawa. The mean values of δ13C and δ15N obtained from wheat grains from south-eastern Poland were used to model human palaeodiet. Our results show high levels of plant proteins in the diet, taking into account crop grain enriched in heavy nitrogen instead of the δ15N values for plants estimated from herbivore collagen. Dental abrasion analyses suggests the contribution of a highly abrasive food component in the diet (e.g. from plants). As the number of samples was limited and there were no statistically significant differences between chronological and gender groups, we conclude that despite some small differences in carbon isotopic composition between genders, Miechów site societies were egalitarian in this respect. Despite the presence of millet in the studied area in the Bronze Age no evidence of C4 plant consumption was noted in the δ13C of human and animal bones.

Comparison of Sustained Deficit and Pre- and Postveraison Regulated Deficit Irrigation on Malbec and Syrah Grapevines

The objective of this study was to compare the effect of sustained deficit irrigation and regulated deficit irrigation strategies on the yield components and berry composition of two winegrape cultivars (Vitis vinifera L.) that differ in their hydraulic behavior. Malbec and Syrah grapevines were grown in southern Idaho under arid conditions and were drip-irrigated weekly from fruit set until harvest to supply 35 or 70% of estimated vine water demand that was delivered either as a sustained amount (35, 70) or the amount was altered at veraison (3570, 7035). In both cultivars, the 7035 and 35 treatments produced fruit with a greater concentration of anthocyanins and phenolics than the 3570 and 70 treatments. In both cultivars, the yield of the 7035 treatment was ~30% greater than the 35 treatment and ~15% lower than the 70 treatment. The 7035 treatment was provided ~58% more water than the 35 treatment and ~20% less water than the 70 treatment. In both cultivars, the 3570 and 7035 treatments had a similar ratio of yield reduction to water savings, similar carbon isotope composition, and similar seasonal average weekly midday leaf water potential. The 3570 and 35 treatments had greater bud injury (low pruning weight and low cluster number per vine) and slower recovery from injury than the 7035 and 70 treatments after exposure to an extreme cold weather event. Despite inherent differences in carbon isotope composition, the 70 and 7035 treatments offer the best potential in both cultivars for sustained productivity under challenging climatic conditions.

Influence of retained bitumen in oil-prone shales on the chemical and carbon isotopic compositions of natural gases: Implications from pyrolysis experiments

Abstract Retained bitumen in oil-prone source rocks has a significant impact on late gas generation but such influence is still poorly quantified because it is quite difficult to restore the bitumen content retained in a mature source rock. In this study, a suite of artificially-matured samples were prepared from a moderate maturity shale sample to represent shales with different amount of retained bitumen. These samples were then pyrolyzed in sealed gold tubes to investigate how the amount of retained bitumen affects the changes in chemical and carbon isotopic compositions of generated gases, and the uncertainty of the evaluation of gas maturity and source identification. The results indicate that the decrease in yields of hydrocarbon gases is proportional to the reduction of retained bitumen content, however, a progressive enrichment in heavier carbon isotope (13C) of gaseous hydrocarbons occurs while less amount of bitumen is retained in shales. This experimental observation partly explains the heterogeneity of methane carbon isotopes for shale gases that have identical thermal maturity levels. Although the amount of retained bitumen can significantly change the carbon isotopic ratios of individual gas (δ13C1, δ13C2, and δ13C3), the difference in carbon isotopic composition between gaseous components such as ethane and methane (δ13C2 ‒δ13C1) or propane and ethane (δ13C3 ‒δ13C2) are not significantly affected, and therefore these differential values can be potentially used as maturity indicators for overmature natural gases exhibiting no carbon isotopic reversals. Geochemical and carbon isotopic diagrams that are widely used for the identification of oil- and kerogen-cracking gases are also found to be affected by the retained bitumen content. These results illustrate that it is necessary to take into account the retained bitumen content of shales when thermal maturity and genetic origin of natural gases derived from oil-prone source rocks are being evaluated.

Analysis of growth and form in Aerothyris kerguelenensis (rhynchonelliform brachiopod) - Shell spiral deviations, microstructure, trace element contents and stable isotope ratios

Brachiopods are usually attached benthic marine invertebrates with a shell (exoskeleton) that archives modifications of the environment via chemical proxies. Growth lines regularly occurring (i.e. excluding random ones) at the shell's surface reflect phenotypically controlled interruptions or changes in secretion (Williams et al., 1997). Modifications in the secretion rate and reorientation of shell elements within the thickness of the shell induce marked changes in shell morphology providing elements for estimating age throughout ontogeny for specimens of Aerothyris kerguelenensis (Davidson 1880, formerly known as Waldheimia kerguelensis Davidson, 1978), from the Southern Indian Ocean. Maxima and minima of deviations from underlying shell spiral growth (SSD), plus maps (SEM-EDS) and Electron Microprobe (WDS) of Mg, S, Ca, Mn, Fe that are components of shells along with Scanning Electron Microscopy (SEM) all show evidence of rhythms at different time scales, including annual ones. Growth rates differ in young and adult forms as well as between dorsal and ventral valves; additionally the amplitudes of Mg peaks are higher early in ontogeny and in the primary shell layer, progressively decreasing with sporadic peaks. Anterior regions of shells are more informative regarding external growth (i.e. major growth marks) and mainly record later events in the life of the individual. Posterior regions are informative for internal morphology (cumulative growth) and reveal Mg bands and related concentrations that are consistent with the main extrema (maxima and minima) observed when using SSD and WDS analyses. Mg/Ca ratios indicate fluctuations in temperature and food supply during the growth period. Seawater temperatures calculated from the oxygen isotope compositions of the secondary layer of calcite in shells of A. kerguelenensis are close to those measured in situ in the environment in which they live. However, the difference in carbon isotope composition between the two studied shells reveal that these specimens record isotopic compositions most likely resulting from a combination of kinetic ‘vital’ isotope effects that may, sometimes, mimic equilibrium values.

Variability in the carbon isotope composition of individual amino acids in plant proteins from different sources: 1 Leaves

The natural carbon isotope composition of individual amino acids from plant leaf proteins has been measured to establish potential sources of variability. The plant leaves studied, taken from a range of plant groups (forbs, trees, grasses, and freshwater aquatic plants), showed no significant influence of either season or environment (water and light availability) on their Δδ13C values. Plant groups did, however, differ in carbon isotope composition, although no consistent differences were identified at the species level. A discriminant analysis model was constructed which allowed leaves from (1) nettles, (2) Pooideae, (3) other Poales, (4) trees and (5) freshwater higher plants to be distinguished from each other on the basis of their natural abundance 13C/12C ratios of individual amino acids. Differences in carbon isotope composition are known to be retained, to some extent, in the tissues of their consumers, and hence an understanding of compound-specific variation in 13C/12C fractional abundance in plants has the potential to provide dietary insights of value in archaeological and ecological studies.

Elemental and stable isotopic study of sweeteners and edible oils: Constraints on food authentication

Elemental concentrations and stable isotopic compositions of 41 sweeteners (syrups, honeys, and sugars) and 43 edible oils were determined to evaluate their potential as parameters for food authentication. The addition of as little as 10% of corn syrup to pure maple syrup can be detected using molar ratios of Na/(Na+K) and Na/(Na+Ca) for maple syrups. The detection of more than 15% adulterant in maple syrup and honey is also possible due to the 13‰ difference in carbon isotopic composition of C3 plants for authentic honeys and maple syrups (25.1±1.1‰) relative to the carbon isotopic composition of C4 plants for corn syrups and cane sugars (−11.4±0.8‰) as major adulterant agents. Nearly constant net oxygen (1.028±0.002) as well as hydrogen (0.974±0.005) isotope fractionation factors between honeys and average local meteoric waters from two areas, Kingston and Costa Rica, suggests that these isotope ratios of honeys are good candidates to authenticate their geographic locations. The net oxygen (1.03±0.001) as well as hydrogen (0.894±0.003) isotope fractionation factors between olive oils and local meteoric waters from different parts of Italy suggests that these isotope ratios are independent of the oil processing method and therefore can be used to trace geographic locations.

Source Apportionment of Particulate Matter Based on Carbon Isotope Mass Balance Model

In the process of source apportionment for particulate matter by mass balance model, the colinearity between various source profiles leads to the different analyzing results. For this reason, carbon isotopic apportionment based on the difference in carbon isotopic composition of particulate from different sources was put forward in this study. On the basis of chemical mass balance model, carbon isotope mass balance model is built to discriminate the sources including soil dust, coal dust and vehicle exhaust dust. This improved method has been used in the source apportionment of particulate in Taiyuan, and the results showed that the contributions of vehicle exhaust dust, coal dust and soil dust to air particulate in Taiyuan are 45%,13% and 18% respectively in heating season, while 23%,21% and16% in non-heating season. Therefore, the control of ash fly from burning coal is a long-term and arduous task.

D-depleted organic matter and graphite in the Abee enstatite chondrite

A combination of NanoSIMS and High resolution transmission electron microscopy (HRTEM) imaging along with Raman spectroscopy was used to characterize the carbonaceous phases in HF/HCl residue of the Abee enstatite chondrite. This acid residue hosts a very D-depleted component (δD=−480‰). This residue is a mixture of graphite and highly disordered insoluble organic matter. The latter exhibits a significant mesoporosity (i.e., 200–500nm scale), and also shows concentric and elongated stacks of polyaromatic layers. Insoluble organic matter is shown to be the most D-depleted component in Abee. We also determined, by using NanoSIMS, carbon isotopic composition of graphite and insoluble organic matter in the acid residue (δ13C=−11.3±2.9‰ and −28.4±2.2‰, respectively).We identified graphite in metal-rich clasts and in the matrix of Abee, associated with enstatite, sulfide and metal, but we could not localize highly disordered organic matter in our section. Regardless, given the vulnerability of organic matter to thermal degradation, we suggest that it was added to Abee parent body during the latest stage of its formation, after any thermal metamorphism or partial melting of Abee parent body.A genetic link between organic matter and graphite in Abee is excluded based on our HRTEM and carbon isotopic data. The differences in carbon isotopic compositions between these phases are consistent with previous data obtained by stepwise heating experiments and indicate that graphite is not derived from a pure thermal solid-state graphitization of the organic matter. Rather, we suggest that graphite precipitated from a melt rich in C during the partial melting of the Abee parent body. Insoluble organic matter in Abee has the lowest D/H ratio among the extraterrestrial organics. Organics in most carbonaceous and ordinary chondrites are believed to have been subjected to irradiations in low temperature environments, resulting in a dramatic isotopic fractionation through exchange and reaction with gaseous molecular hydrogen during their synthesis. In contrast, Abee organic matter was likely synthesized in a neutral (i.e., not ionized) environment where thermodynamic processes at equilibrium most likely controlled its isotopic composition.This organic matter could have been accreted in a minor component of Abee like the dark inclusions without (or prior to) exposure to the radiation responsible for D enrichments in other meteoritic organics. During the last brecciation events that have affected the Abee parent body, these inclusions could have been mixed with other Abee components. The properties of this organic matter can be interpreted as an indication that thermodynamic processes acted in the synthesis of organic matter in the protosolar disk, in addition to ion/molecule and gas/grains reaction witnessed by the D-rich insoluble organic matter contained in carbonaceous chondrites.

Chemostratigraphy of the Late Mesoproterozoic Atar Group, Taoudeni Basin, Mauritania: Muted isotopic variability, facies correlation, and global isotopic trends

Sedimentary strata of the Atar/El Mreiti groups, Taoudeni Basin, Mauritania, are characterized by carbon isotope values that fall largely between −2.5‰ and +4.0‰, and contain stratigraphic trends that are strikingly similar to those recorded worldwide in strata with depositional ages from ∼1.2Ga to 1.1Ga. Chemostratigraphic results are consistent with recent Re–Os dates of ∼1.1Ga for Atar/El Mreiti group strata (Rooney et al., 2010) and support an emerging dataset that identifies the Late Mesoproterozoic as an isotopically distinctive interval in Earth history. The relatively low-amplitude carbon isotope variability limits the use of chemostratigraphy in detailed correlation during this time interval. In this study, we combine chemostratigraphic data with key chronostratigraphic horizons and detailed analysis of depositional facies to construct a rigorous and testable model for the intrabasinal correlation of Atar and el Mreiti group strata. Data support a depositional model that results in broadly uniform stratigraphic thicknesses across the West African craton, with predominantly stromatolitic facies of the Atar Group (Mauritania) and the Hank and Dar Cheikh groups (Algeria) representing deposition on shallow-water craton margins, and clayey-carbonate and shale facies of the El Mreiti Group (Mauritania) representing deposition on a broad, shallow-water, epicratonic platform. Within this stratigraphic framework, regional differences in carbon isotope composition are interpreted to reflect spatial differences in water chemistry likely associated with local carbon cycle dynamics in cratonic environments that have limited exchange with the open ocean. Similarly, distinct differences in trace element composition recorded in multilayered marine cements within deeper-water stromatolitic reef facies are interpreted to reflect vertical differences in water chemistry associated with redox-gradients in the water column.We use this multifaceted approach to test a recent hypothesis that suggests correlation of Atar/el Mreiti group strata with glaciogenic strata of the Vazante Group, São Francisco craton. Critically, preservation of shallow-water carbonate and evaporite strata across more than 1200km of the predominantly epicratonic Taoudeni Basin—with minimal evidence for high-amplitude sea level change—is consistent with inferences of late Mesoproterozoic highstand conditions in a global greenhouse climate. Such characteristics are inconsistent with suggestions of a time-equivalency with glaciogenic strata of the Vazante Group, São Francisco craton, despite broad similarities in Re–Os geochronology and carbon isotope composition. Together, these results emphasize both the utility and limitations of carbon isotope stratigraphy to inform hypotheses regarding global correlation and biospheric evolution.

Carbon isotopes in surface-sediment carbonates of modern Lake Qinghai (Qinghai–Tibet Plateau): Implications for lake evolution in arid areas

To further investigate the significance of carbon isotopes of lake carbonates in arid areas, we examined the carbon isotopic composition of ostracods, bulk carbonate, fine-grained carbonates, and associated water DIC (dissolved inorganic carbon) from Lake Qinghai and several small lakes and ponds surrounding Lake Qinghai. We obtained three major results. 1) The carbon isotopic compositions of ostracods, bulk carbonate, and fine-grained carbonates in the lakes and ponds are clearly correlated with water δ13CDIC values, which vary with water salinity in the Lake Qinghai area. 2) The variation in the δ13CDIC values of lake water is mainly controlled by CO2 exchanges between the atmosphere and lake waters in the Lake Qinghai area. 3) Ostracods, bulk carbonate and fine-grained carbonates show consistent trends of isotopic composition in the study area, and the differences in carbon isotopic composition between authigenic carbonates and ostracods may be explained by the differences in carbon isotopic composition between the DIC of surface water and that of the water near to the sediment–water interface as well as the ‘vital offsets’ of ostracods.Our results suggest that variations in the δ13C values of carbonates in Lake Qinghai and other lakes in this arid, high-altitude area are primarily controlled by the carbon-isotope ratios of the lake water DIC, which in turn are related to water salinity. Therefore, changes in carbonate δ13C values may be used to indirectly indicate changes in water salinity in the Lake Qinghai area.

Carbon isotopic compositions of pore and matrix carbonates in carbonate nodules, and origin of carbonate formation

Carbon isotopes of pedogenic carbonate are often used to study paleoenvironments, but the existence of detrital carbonate changes the carbon isotopic composition. To develop an experimental method to determine existence of detrital carbonate in carbonate nodules, and to avoid it during isotope analysis, 23 pedogenic carbonate nodules in Miocene loess from the Loess Plateau of China were studied through micromorphology and carbon isotope analysis. The difference in carbon isotopic composition between matrix carbonate (B) and pore carbonate (A) (delta C-13((B-A))) ranges from 0.27aEuro degrees to 0.44aEuro degrees in nodules containing detrital carbonate and -0.16aEuro degrees to 0.13aEuro degrees in nodules where detrital carbonate is absent. The latter is within measurement error, but the former is beyond it. Here we propose an isotopic approach to determine if nodules contain detrital carbonate: if delta C-13((B-A)) is within the measurement error, the nodules do not contain detrital carbonate, and vice versa. We suggest that it is better to analyze pore carbonate instead of matrix carbonate when using carbon isotope of carbonate nodules to reconstruct paleoenvironments.

Carbon nutrition of mature green orchid Serapias strictiflora and its mycorrhizal fungus Epulorhiza sp.

We studied the nutritional modes of the orchid Serapias strictiflora and its mycorrhizal fungus Epulorhiza sp. using the differences in carbon isotopic composition (δ13C) of C3 orchid and C4 maize tissues. We found that if cultivated in substrate lacking any organic compounds, the mycorrhizal extraradical mycelia (δ13C = -26.3 ± 0.2 ‰) developed well, despite being fully dependent on nutrition from orchid roots (δ13C = -28.6 ± 0.1 ‰). If the mycorrhizal fungus had additional access to and colonized decaying maize roots (δ13C = -14.6 ± 0.1 ‰), its isotopic composition (δ13C = -21.6 ± 0.4 ‰) reflected a mixture of biotrophy and saprotrophy. No statistically significant differences in δ13C of new storage tubers were found between Epulorhiza-associated orchids with (δ13C = -28.2 ± 0.1 ‰) and without access to maize roots (δ13C = -28.6 ± 0.2 ‰). We conclude that autotrophy is the predominant nutritional mode of mature S. strictiflora plants and that they supply their mycorrhizal fungus with substantial amount of carbon (69 ± 3 % of the fungus demand), even if the fungus feeds saprotrophically.

Past century changes in Araucaria angustifolia (Bertol.) Kuntze water use efficiency and growth in forest and grassland ecosystems of southern Brazil: implications for forest expansion

Abstract Araucaria angustifolia (Bertol.) Kuntze is an indigenous conifer tree restricted to the southern region of South America that plays a key role in the dynamics of regional ecosystems where forest expansion over grasslands has been observed. Here, we evaluate the changes in intrinsic water use efficiency (iWUE) and basal area increment (BAI) of this species in response to atmospheric CO2, temperature and precipitation over the last century. Our investigation is based on tree‐rings taken from trees located in forest and grassland sites in southern Brazil. Differences in carbon isotopic composition (δ13C), 13CO2 discrimination (Δ13C) and intracellular carbon concentration (Ci) are also reported. Our results indicate an age effect on Δ13C in forest trees during the first decades of growth. This age effect is not linked to an initial BAI suppression, suggesting the previous existence of nonforested vegetation in the forest sites. After maturity all trees show similar temporal trends in carbon isotope‐derived variables and increasing iWUE, however, absolute values are significantly different between forest and grassland sites. The iWUE is higher in forest trees, indicating greater water competition or nutritional availability, relative to grassland, or both. BAI is also higher in forest trees, but it is not linked with iWUE or atmospheric CO2. Nevertheless, in both forest and grassland sites A. angustifolia has had growth limitations corresponding to low precipitation and high temperatures observed in the 1940s.

Spatial and Temporal Trends of Mercury Concentrations in Young-of-the-Year Spottail Shiners (Notropis hudsonius) in the St. Lawrence River at Cornwall, ON

The St. Lawrence River at Cornwall, Ontario is an "Area of Concern" because of mercury (Hg) biomagnification from bottom sediments. To assess the spatial and temporal distribution of Hg in the food web, young-of-the-year (YOY) spottail shiners (Notropis hudsonius) were collected in August 2005 from five sites along the Cornwall waterfront within a Hg-contaminated zone and two reference zones. The results were compared to analyses made between 1979 and 2000 by the Ontario Ministry of the Environment. Total Hg concentrations in spottail shiners from the contaminated zone were significantly higher than in reference zones, confirming previous observations. Within the contaminated zone, there were significant differences in Hg concentrations among three sites spaced about 500 m apart, consistent with a high degree of site fidelity of YOY fish and suggesting a possible internal source of Hg. Hg concentrations in spottail shiners are decreasing regionally, although year-to-year variability was high, particularly in the contaminated zone. Stable isotope analyses of spottail shiners did not reveal any differences in nitrogen isotope composition among zones that would indicate differences in food-web structure and Hg biomagnification. However, carbon sources at an upstream reference zone were not the same as within the Area of Concern. Differences in carbon isotope composition at two sites within the contaminated zone corresponded to differences in Hg concentrations, consistent with a unique internal source of Hg. The variation in Hg contamination of YOY spottail shiners over fine spatial and temporal scales provide important insights about the potential release of Hg from contaminated sediments and the role of climate in regional trends. Sessile YOY fish provide a precise indicator for demonstrating these differences and for assessing their cause.

Bone mineral density of spine and femur in healthy Taiwan adolescents

A combination of NanoSIMS and High resolution transmission electron microscopy (HRTEM) imaging along with Raman spectroscopy was used to characterize the carbonaceous phases in HF/HCl residue of the Abee enstatite chondrite. This acid residue hosts a very D-depleted component (δD = −480‰). This residue is a mixture of graphite and highly disordered insoluble organic matter. The latter exhibits a significant mesoporosity (i.e., 200–500 nm scale), and also shows concentric and elongated stacks of polyaromatic layers. Insoluble organic matter is shown to be the most D-depleted component in Abee. We also determined, by using NanoSIMS, carbon isotopic composition of graphite and insoluble organic matter in the acid residue (δ13C = −11.3 ± 2.9‰ and −28.4 ± 2.2‰, respectively).We identified graphite in metal-rich clasts and in the matrix of Abee, associated with enstatite, sulfide and metal, but we could not localize highly disordered organic matter in our section. Regardless, given the vulnerability of organic matter to thermal degradation, we suggest that it was added to Abee parent body during the latest stage of its formation, after any thermal metamorphism or partial melting of Abee parent body.A genetic link between organic matter and graphite in Abee is excluded based on our HRTEM and carbon isotopic data. The differences in carbon isotopic compositions between these phases are consistent with previous data obtained by stepwise heating experiments and indicate that graphite is not derived from a pure thermal solid-state graphitization of the organic matter. Rather, we suggest that graphite precipitated from a melt rich in C during the partial melting of the Abee parent body. Insoluble organic matter in Abee has the lowest D/H ratio among the extraterrestrial organics. Organics in most carbonaceous and ordinary chondrites are believed to have been subjected to irradiations in low temperature environments, resulting in a dramatic isotopic fractionation through exchange and reaction with gaseous molecular hydrogen during their synthesis. In contrast, Abee organic matter was likely synthesized in a neutral (i.e., not ionized) environment where thermodynamic processes at equilibrium most likely controlled its isotopic composition.This organic matter could have been accreted in a minor component of Abee like the dark inclusions without (or prior to) exposure to the radiation responsible for D enrichments in other meteoritic organics. During the last brecciation events that have affected the Abee parent body, these inclusions could have been mixed with other Abee components. The properties of this organic matter can be interpreted as an indication that thermodynamic processes acted in the synthesis of organic matter in the protosolar disk, in addition to ion/molecule and gas/grains reaction witnessed by the D-rich insoluble organic matter contained in carbonaceous chondrites.

Stable isotope measurements of carbon fractions (OC/EC) in airborne particulate: A new dimension for source characterization and apportionment

A method to measure 13C/ 12C ratios of individual carbon fractions of airborne particular matter (PM) from filter samples using a stepwise thermal desorption/combustion OC/EC analyzer (via thermal optical transmission, (TOT) coupled with gas chromatography separation, followed by isotopic ratio mass spectrometer (GC-IRMS) analysis has been developed. In the TOT instrument, carbon fractions are released at different temperature ranges and different redox conditions. Organic carbon fraction (OC) was released at a relatively low temperature ( T = 550 °C), whereas, elemental carbon or black carbon fraction (EC or BC) was released at a high temperature ( T>800 °C) via combustion. A temperature step of 870 °C without oxygen was chosen to remove the impact of carbonate carbon (CC) and possible cross-impact from OC and EC. All the fractions were collected cryogenically and subject to carbon isotope measurements via GC-IRMS. To evaluate the precision, accuracy and linearity range of the measurements, the different types of blanks and standards were investigated, including OC (i.e. glucose, sucrose, n-Alkanes and polycyclic aromatic hydrocarbons (PAHs), CC (i.e. carbonates) and EC (i.e. carbon black and graphite). The overall precision and the accuracy of the method is ∼0.3‰. The method was applied to Pacific2001 aerosol samples from the Greater Vancouver area in Canada. The results show that good baseline separations in thermographs can be achieved for individual carbon fractions (i.e. OC and EC) using optimized temperature plateau and retention times; relative small difference in carbon isotopic composition between OC and EC ( Δ 13 C OC – EC = δ 13 C OC – δ 13 C EC ) were found in tunnel samples, whereas, the largest Δ 13C OC–EC were obtained in forest air samples; the Δ 13C OC–EC in ambient PM is likely dependant upon the dominant sources present in the vicinity of the sampling sites; the distribution of 13C/ 12C ratios of OC/EC can provide useful information for source characterization and apportionment of ambient particulate matter.

Stable Isotope Composition of Organic Compounds Transported in the Phloem of European Beech ‐ Evaluation of Different Methods of Phloem Sap Collection and Assessment of Gradients in Carbon Isotope Composition during Leaf‐to‐Stem Transport

The analysis of stable isotope composition (delta13C, delta15N, delta18O) of phloem-transported organic matter is a useful tool for assessing short-term carbon and water balance of trees. A major constraint of the general application of this method to trees at natural field sites is that the collection of phloem sap with the "phloem bleeding" technique is restricted to particular species and plant parts. To overcome this restriction, we compared the contents (amino compounds and sugars) and isotope signatures (delta13C, delta15N, delta18O) of phloem sap directly obtained from incisions in the bark (bleeding technique) with phloem exudates where bark pieces were incubated in aqueous solutions (phloem exudation technique with and without chelating agents [EDTA, polyphosphate] in the initial sampling solution, which prevent blocking of sieve tubes). A comparable spectrum of amino compounds and sugars was detected using the different techniques. O, C, or N compounds in the initial sampling solution originating from the chelating agents always decreased precision of determination of the respective isotopic signatures, as indicated by higher standard deviation, and/or led to a significant difference of mean delta as compared to the phloem bleeding technique. Hence, depending on the element from which the ratio of heavy to light isotope is determined, compounds lacking C, N, and/or O should be used as chelating agents in the exudation solution. In applying the different techniques, delta13C of organic compounds transported in the phloem of the twig (exudation technique with polyphosphate as chelating agent) were compared with those in the phloem of the main stem (phloem bleeding technique) in order to assess possible differences in carbon isotope composition of phloem carbohydrates along the tree axis. In July, organic compounds in the stem phloem were significantly enriched in 13C by > 1.3 per thousand as compared to the twig phloem, whereas this effect was not observed in September. Correlation analysis between delta13C and stomatal conductance (Gs) revealed the gradient from the twigs to the stem observed in July may be attributed to temporal differences rather than to spatial differences in carbon isotope composition of sugars. As various authors have produced conflicting results regarding the enrichment/depletion of 13C in organic compounds in the leaf-to-stem transition, the different techniques presented in this paper can be used to provide further insight into fractionation processes associated with transport of C compounds from leaves to branches and down the main stem.