Carbon Isotope Composition Of CO Research Articles

Determination of the triple oxygen and carbon isotopic composition of CO2 from atomic ion fragments formed in the ion source of the 253 Ultra high-resolution isotope ratio mass spectrometer.

RationaleDetermination of δ17O values directly from CO2 with traditional gas source isotope ratio mass spectrometry is not possible due to isobaric interference of 13C16O16O on 12C17O16O. The methods developed so far use either chemical conversion or isotope equilibration to determine the δ17O value of CO2. In addition, δ13C measurements require correction for the interference from 12C17O16O on 13C16O16O since it is not possible to resolve the two isotopologues.MethodsWe present a technique to determine the δ17O, δ18O and δ13C values of CO2 from the fragment ions that are formed upon electron ionization in the ion source of the Thermo Scientific 253 Ultra high‐resolution isotope ratio mass spectrometer (hereafter 253 Ultra). The new technique is compared with the CO2‐O2 exchange method and the 17O‐correction algorithm for δ17O and δ13C values, respectively.ResultsThe scale contractions for δ13C and δ18O values are slightly larger for fragment ion measurements than for molecular ion measurements. The δ17O and Δ17O values of CO2 can be measured on the 17O+ fragment with an internal error that is a factor 1–2 above the counting statistics limit. The ultimate precision depends on the signal intensity and on the total time that the 17O+ beam is monitored; a precision of 14 ppm (parts per million) (standard error of the mean) was achieved in 20 hours at the University of Göttingen. The Δ17O measurements with the O‐fragment method agree with the CO2‐O2 exchange method over a range of Δ17O values of −0.3 to +0.7‰.ConclusionsIsotope measurements on atom fragment ions of CO2 can be used as an alternative method to determine the carbon and oxygen isotopic composition of CO2 without chemical processing or corrections for mass interferences.

Temporal analysis of d13C CO2 and CO2 efflux in soil gas emissions at Mt. Etna: a new tool for volcano monitoring

We monitored the soil gas emission of CO 2 from selected sites of Mt. Etna volcano during the period February 2009 to December 2010 by measuring periodically the soil CO 2 efflux together with the associated stable carbon isotope composition of CO 2 from February 2009 to December 2010. Correlation between the two parameters showed distinct behaviors depending on the sites as a reflection of the different interactions between crustal and sub-crustal fluids. Where deep CO 2 interacted with shallow cold ground water and/or with shallow biogenic CO 2 , a positive correlation between soil CO 2 effluxes and carbon isotopes was evident and it depended strongly on the velocity of gas through the soil. In these cases, the highest CO 2 effluxes corresponded to d 13 C CO2 values similar to those of the deep magmatic CO 2 emitted from the crater and peri-crateric gas emissions at the summit. In areas where a shallow hydrothermal system was presumed, then a similar correlation was less evident or even absent, suggesting strong control on C isotopes arising from the interactions between CO 2 gas and dissolved HCO 3 - that occur in aquifers at T>120 °C. Marked temporal variations were observed in both parameters at all sites. No significant effect of meteorological parameters was found, so the observed changes were reasonably attributed to variations in volcanic activity of Mt. Etna. In particular, the variations were attributed to increased degassing of CO 2 from incoming new magma, possibly coupled with increased hydrothermal activity in at least some of the shallow aquifers of the volcano. The largest anomalies in the monitored parameters preceded the opening of the New Southeast crater in late 2009 and therefore they could represent a key to unveiling the dynamics of the volcano.

Carbon isotopic characterization of cider CO2 by isotope ratio mass spectrometry: a tool for quality and authenticity assessment

The cider market is an important sector of the food industry in certain regions. Adulteration of cider can happen in several ways: for example, by the addition of sugar, or of exogenous CO(2) to certain types of cider. Because such practices are not allowed by either Spanish legislation or the legislation of other countries, it is essential to study possible methods to detect these unauthorized practices. For this purpose a procedure was required to study the stable carbon isotopic composition of CO(2) in cider. A liquid sample of cider was transferred to a vial and CO(2) from the headspace of the vial was analyzed using a peripheral device interfaced to an isotope ratio mass spectrometer. Separation of the CO(2) from water and ethanol was achieved using a gas chromatography column located in the peripheral device. The values for repeatability and reproducibility obtained indicated the robustness of the method, which is required for routine analysis. Ninety cider samples from various origins were analyzed, most of which showed a (13)C content consistent with the declared origin. The δ(13)C ranged from -24.80‰ to -20.89‰ for ciders with endogenous carbon dioxide (-22.74 ± 0.79‰) and -37.13‰ to -26.00‰ if industrial CO(2) was added. Several samples were also suspected of C4 sugar addition prior to the fermentation. A fast, accurate and simple method for cider adulteration detection was developed. The addition of exogenous CO(2) as well as C4 sugar addition prior to fermentation could be detected. The method showed advantages over existing methods in term of simplicity (no sample preparation and very long-term stability of the sample), speed (less than 10 min/sample) and precision ((r ≤0.32 and R ≤0.42).

Environmental and physiological controls on the carbon isotope composition of CO2 respired by leaves and roots of a C3 woody legume (Prosopis velutina) and a C4 perennial grass (Sporobolus wrightii)

Accurate estimates of the δ(13) C value of CO(2) respired from roots (δ(13) C(R_root) ) and leaves (δ(13) C(R_leaf) ) are important for tracing and understanding changes in C fluxes at the ecosystem scale. Yet the mechanisms underlying temporal variation in these isotopic signals are not fully resolved. We measured δ(13) C(R_leaf) , δ(13) C(R_root) , and the δ(13) C values and concentrations of glucose and sucrose in leaves and roots in the C(4) grass Sporobolus wrightii and the C(3) tree Prosopis velutina in a savanna ecosystem in southeastern Arizona, USA. Night-time variation in δ(13) C(R_leaf) of up to 4.6 ± 0.6‰ in S. wrightii and 3.0 ± 0.6‰ in P. velutina were correlated with shifts in leaf sucrose concentration, but not with changes in δ(13) C values of these respiratory substrates. Strong positive correlations between δ(13) C(R_root) and root glucose δ(13) C values in P. velutina suggest large diel changes in δ(13) C(R_root) (were up to 3.9‰) influenced by short-term changes in δ(13) C of leaf-derived phloem C. No diel variation in δ(13) C(R_root) was observed in S. wrightii. Our findings show that short-term changes in δ(13) C(R_leaf) and δ(13) C(R_root) were both related to substrate isotope composition and concentration. Changes in substrate limitation or demand for biosynthesis may largely control short-term variation in the δ(13) C of respired CO(2) in these species.

Short‐term dynamics of the carbon isotope composition of CO2 emitted from a wheat agroecosystem – physiological and environmental controls

Understanding environmental and physiological controls of the variations in δ(13) C of CO(2) respired (δ(13) C(R)) from different compartments of an ecosystem is important for separation of CO(2) fluxes and to assess coupling between assimilation and respiration. In a wheat field, over 3 days we characterised the temporal dynamics of δ(13) C(R) from shoots and roots, from the soil and from the whole agroecosystem. To evaluate the basis of potential variations in δ(13) C(R), we also measured δ(13) C in different organic matter pools, as well as meteorological and gas exchange parameters. We observed strong diel variations up to ca. 6% in shoot, root and soil δ(13) C(R), but not in δ(13) C of the putative organic substrates for respiration, which varied by not more than ca. 1% within 24 h. Whole ecosystem-respired CO(2) was least depleted in (13) C in the afternoon and most negative in the early morning. We assume that temporally variable respiratory carbon isotope fractionation and changes in fluxes through metabolic pathways, rather than photosynthetic carbon isotope fractionation, governs the δ(13) C of respired CO(2) at the diel scale, and thus provides insights into the metabolic processes related to respiration under field conditions.

The 13C/12C isotopic signal of day‐respired CO2 in variegated leaves of Pelargonium × hortorum

In leaves, although it is accepted that CO(2) evolved by dark respiration after illumination is naturally (13) C-enriched compared to organic matter or substrate sucrose, much uncertainty remains on whether day respiration produces (13) C-depleted or (13) C-enriched CO(2). Here, we applied equations described previously for mesocosm CO(2) exchange to investigate the carbon isotope composition of CO(2) respired by autotrophic and heterotrophic tissues of Pelargonium × hortorum leaves, taking advantage of leaf variegation. Day-respired CO(2) was slightly (13) C-depleted compared to organic matter both under 21% O(2) and 2% O(2). Furthermore, most, if not all CO(2) molecules evolved in the light came from carbon atoms that had been fixed previously before the experiments, in both variegated and green leaves. We conclude that the usual definition of day respiratory fractionation, that assumes carbon fixed by current net photosynthesis is the respiratory substrate, is not valid in Pelargonium leaves under our conditions. In variegated leaves, total organic matter was slightly (13) C-depleted in white areas and so were most primary metabolites. This small isotopic difference between white and green areas probably came from the small contribution of photosynthetic CO(2) refixation and the specific nitrogen metabolism in white leaf areas.

A new method to measure carbon isotope composition of CO2 respired by trees: stem CO2 equilibration

Summary 1. Applying Keeling plot techniques to derive δ13C of respiratory input in a closed non‐equilibrated chamber can lead to large errors because steady‐state diffusion rules are violated in a non‐steady‐state environment. To avoid these errors, respiratory δ13C can be derived using equilibrated closed chambers. 2. We introduce a new method to obtain stem respired CO2δ13C (δst‐r) with closed equilibrated stem chambers (E‐SC). We present a theoretical model describing the equilibration process, test the model against field data and find excellent agreement. The method is further tested by comparing it with closed non‐equilibrated stem chambers (NE‐SC); we found no difference between these methods. 3. Our theoretical model to describe CO2 diffusion from the respiratory pool into the chamber and the equation to derive the δ13C of the efflux are general. They could be applied to other ecosystem components (e.g. soils). 4. Our method is easy to implement, cost effective, minimizes sources of error and allows for rigorous leak detection. One major limitation is its inability to detect rapid change; the equilibration process requires 15 ± 2 h. A second limitation is that it cannot be used for species that produce abundant pitch at sites of stem wounding (e.g. Pseudotsuga menziesii). 5. Investigating δ13C of CO2 respired by different ecosystem components is necessary to interpret δ13C of ecosystem respiration. This parameter has major implications with respect to global carbon cycle science.

On the metabolic origin of the carbon isotope composition of CO2 evolved from darkened light‐acclimated leaves in Ricinus communis

The (13)C isotopic signature (delta(13)C) of CO(2) respired from plants is widely used to assess carbon fluxes and ecosystem functioning. There is, however, a lack of knowledge of the metabolic basis of the delta(13)C value of respired CO(2). To elucidate the physiological mechanisms driving (12)C/(13)C fractionation during respiration, the delta(13)C of respired CO(2) from dark-acclimated leaves during the night, from darkened leaves during the light period, and from stems and roots of Ricinus communis was analysed. The delta(13)C of potential respiratory substrates, the respiratory quotient and the activities of phosphoenolpyruvatecarboxylase (PEPc) and key respiratory enzymes were also measured. It is shown here that the CO(2) evolved from darkened light-acclimated leaves during the light period is (13)C-enriched, and that this correlates with malate accumulation in the light and rapid malate decarboxylation just after the onset of darkness. Whilst CO(2) evolved from leaves was generally (13)C-enriched (but to a lesser extent during the night), CO(2) evolved from stems and roots was depleted compared with the putative respiratory substrates; the difference was mainly caused by intensive PEPc-catalysed CO(2) refixation in stems and roots. These results provide a physiological explanation for short-term variations of delta(13)C in CO(2), illustrating the effects of variations of metabolic fluxes through different biochemical pathways.

An evaluation of the potential of using Raman spectroscopy to determine the carbon isotope composition of CO 2 inclusions

An evaluation of the potential of using Raman spectroscopy to determine the carbon isotope composition of CO 2 inclusions

The carbon isotope composition of CO2 respired by trunks: comparison of four sampling methods

The (13)C natural abundance of CO(2) respired by plants has been used in the laboratory to examine the discrimination processes that occur during respiration. Currently, field measurements are being expanded to interpret the respiration delta(13)C signature measured at ecosystem and global levels. In this context, forests are particularly important to consider as they represent 80% of the continental biomass. The objective of this investigation was to compare four methods of sampling the CO(2) respired by trunks for the determination of its carbon isotope composition: three in situ methods using chambers placed on the trunk, and one destructive method using cores of woody tissues. The in situ methods were based either on a Keeling plot approach applied at the tissue level or on an initial flush of the chamber with nitrogen or with CO(2)-free air. In parallel, we investigated the possibility of an apparent discrimination during tissue respiration by comparing the delta(13)C signature of the respired CO(2) and that of the organic matter. The study was performed on six tree species widely distributed in temperate and mediterranean areas. The four methods were not significantly different when overall means were considered. However, considering the individual data, the Keeling plot approach and the nitrogen flush methods gave fairly homogeneous results, whereas the CO(2)-free air method produced more variable results. The core method was not correlated with any of the chamber methods. Regardless of the methodology, the respired CO(2) generally was enriched in (13)C relative to the total organic matter. This apparent enrichment during respiration was variable, reaching as much as 3-5 per thousand. This study showed that, on the whole, the different sampling techniques gave similar results, but one should be aware of the variability associated with each method.

Carbon isotope systematics and CO 2 sources in The Geysers-Clear Lake region, northern California, USA

Carbon isotope analyses of calcite veins, organic carbon, CO 2 and CH 4 from 96 rock and 46 gas samples show that metamorphic calcite veins and disseminated, organically-derived carbon from Franciscan Complex and Great Valley Sequence rocks have provided a primary carbon source for geothermal fluids during past and present hydrothermal activity across The Geysers-Clear Lake region. The stable isotope compositions of calcite veins vary widely on a regional scale, but overall they document the presence of 13C-poor fluids in early subduction-related vein-precipitating events. δ 13C values of calcite veins from the SB-15-D corehole within The Geysers steam field indicate that carbon-bearing fluids in the recent geothermal system have caused the original diverse δ 13C values of the veins to be reset. Across The Geysers-Clear Lake region the carbon isotope composition of CO 2 gas associated with individual geothermal reservoirs shows a general increasing trend in δ 13C values from west to east. In contrast, δ 13C values of CH 4 do not exhibit any spatial trends. The results from this study indicate that regional variations in δ 13C–CO 2 values result from differences in the underlying lithologies. Regional CO 2 contains significant amounts of carbon related to degradation of organic carbon and dissolution of calcite veins and is not related to equilibrium reactions involving CH 4. CO 2 from degassing of underlying magma chambers is not recognizable in this region.

Chemical and isotopical characterisation of fluid manifestations of Ischia Island (Italy)

Between 1994 and 1995, gas samples from fumaroles and thermal waters were collected on Ischia Island. The chemical composition of the shallow and deep natural hydrothermal fluids discharged is related to the main hydrological and lithological characteristics of the rock formations present in the reservoir. A biphase reservoir (liquid+gas) is identified, where the dominant liquid has a temperature of about 280°C. On the basis of δ 13C TDC values it was possible to hypothesize a deep source characterised by carbon isotopic values varying from 0 to −3 δ‰. These values are noticeably more positive with respect to those attributed to magmatic CO 2 (δ 13 C CO 2 ranging from −5 to −8 δ‰), thus suggesting a magmatic source modified by crustal contamination. This hypothesis is supported by the carbon isotopic composition of CO 2 in sampled gases, which varied from 0 to −5 δ‰. The inferred isotopic value of carbon of magmatic CO 2 would then be about −2 δ‰. The observed differences in C isotopic composition between fumarolic and magmatic gases would be caused by kinetic and/or equilibrium fractionation processes. These processes would cause a fractionation of δ 13C of deep CO 2 towards more negative values (down to −5‰). Actually, CO 2 removal or addition processes caused by the interaction between deep gases and shallow hydrothermal waters are likely to be responsible for the different chemical and isotopic compositions of gaseous emissions. For these reasons, and on the basis of the homogeneity of geothermometric values, the existence of a single, large reservoir that feeds all of the fluids discharged at Ischia Island can be hypothesised. Based on acquired data, a new geochemical model of the geothermal system of Ischia Island is proposed.

Carbon isotope composition of Antarctic plants

Carbon isotope compositions of Antarctic land plants are first reported. The most interesting feature is the isotope specificity of the species. For example Usnea antarctica from different locations shows relatively narrow range of the δ 13C-values from −22.44 to −21.29‰ (7 samples), Drepanocladus sp. from −24.86 to −23.49‰ (8 samples), and Andreaea depressincrvis from −23.87 to −23.23‰ (3 samples) etc. Usually, in inhabited lands and parts of the world with rich flora and developed soil, isotopic specificity of species is masked by variations of carbon isotope composition of CO 2. In Antarctic conditions influence of local sources of CO 2 on the isotope composition of CO 2 is appeared to be minimal. Therefore the δ 13C-variations inherent to individual plant physiology and biochemistry can be distinguished on the background of the stable level of the atmospheric CO 2 δ 13C-value. The latter is best to reflect the global state of the carbon cycle.

Origin of trace gases in submarine hydrothermal vents of the Kolbeinsey Ridge, north Iceland

Two hydrothermal fields of the Kolbeinsey Ridge area, north of Iceland, show vent gas characteristics which can be related to the subsurface conditions. Helium isotopes ( R/R air = 9.8, 10.9) indicate a mantle-derived origin and can be considered as a mixture of MORB helium and a deep-mantle plume helium component. The carbon isotope composition of CO 2 ranges between −2.4 and −7.8‰. The less negative δ 13C-CO 2 values were found at Grimsey. The data from Grimsey are very similar to those previously published and regarded as being characteristic for the Icelandic magmatic source. However, small amounts of biogenic CO 2 and/or subsurface calcite precipitation are responsible for the lighter isotope values of CO 2 from Kolbeinsey. CH 4/ 3He ratios which are higher than in MORB indicate an additional (sedimentary) methane source for Kolbeinsey and Grimsey hydrothermal gases. The presence of higher hydrocarbons up to butane, together with the carbon isotope values of methane (δ 13C = −26.1 to −39.8‰) suggest a probably high-mature organic source within thick sediments of the Tjörnes Fracture Zone and smaller depressions on the west side of the Kolbeinsey Ridge crest. Geochemical characteristics of hydrocarbons present in KR hydrothermal fluids are, however, typical for a mixed (thermogenic and high-temperature hydrothermal, e.g. EPR-type) origin. Moreover, it is likely that secondary processes such as bacterial oxidation and thermal cracking determined the geochemical characteristics of the gases.

Effect of Phytoplankton Cell Geometry on Carbon Isotopic Fractionation

The carbon isotopic compositions of the marine diatom Porosira glacialis and the marine cyanobacterium Synechococcus sp. were measured over a series of growth rates (μ) in a continuous culture system in which the concentration and carbon isotopic composition of CO 2(aq) were determined. These data were compared with previously published isotopic results of growth rate experiments using the marine diatom Phaeodactylum tricornutum and the marine haptophyte Emiliania huxleyi. Systematic relationships were found to exist between μ/[CO 2(aq)] and carbon isotopic fractionation (ϵ P) for each species. Maximum isotopic fractionation (ϵ f) for P. glacialis, E. huxleyi, and P. tricornutum was ∼25‰, suggesting that this value may be typical for maximum fractionation associated with Rubisco and β-carboxylases for marine eukaryotic algae. By contrast, ϵ f determined for Synechococcus clone CCMP838 was ∼7‰ lower. The slopes of the lines describing the relationship between ϵ P and μ/[CO 2(aq)] for eukaryotic algal species were different by a factor of more than 20. This result can be accounted for by differences in the surface area and cellular carbon content of the cells. Comparison of chemostat experimental results with calculated results using a diffusion based model imply that the algae in the experiments were actively transporting inorganic carbon across the cell membrane. Our results suggest that accurate estimates of paleo-[CO 2(aq)] from ϵ P measured in sediments will require knowledge of growth rate as well as cell surface area and either cell carbon quota or cell volume. Given growth rate estimates, our empirical relationship permits reliable calculations of paleo-[CO 2(aq)] using compound-specific isotopic analyses of C 37 alkadienones (select haptophytes) or fossilized frustules (diatoms).

Extraction and carbon isotope analysis of CO 2 from scapolite in deep crustal granulites and xenoliths

Carbon isotope compositions of scapolite from granulite facies gneisses and lower crustal xenoliths document the composition and constrain the source of carbon in scapolite from the lower crust. CO 2 is extracted from scapolite without fractionating carbon isotopes by reaction with phosphoric acid at 25 or 75°C. Thus, partial yields of CO 2 from scapolite are sufficient for accurate carbon isotopic analysis. Isotopic compositions of coexisting scapolite and calcite in high-grade calc-silicate gneisses and marbles, and consideration of the crystal chemical environment of CO 3 in the scapolite structure, indicate little fractionation of 13C 12C between scapolite and calcite (0.1 ± 1.2%.) at equilibrium conditions of 650–800°C. The carbon isotope composition of CO 2 extracted from scapolite in twenty-nine samples of regional granulite facies gneisses, amphibolites, calc-silicate gneisses, and crustal xenoliths yield values of δ 13C that range from −10 to −1%. (PDB). High-grade marbles and graphitic paragneisses are precluded as major sources of carbon for scapolite in the high grade rocks analyzed in this study, as the former are isotopically enriched, and the latter isotopically depleted in 13C 12C relative to the range of isotopic compositions determined here. The δ 13C values for mafic granulites and amphibolites in granulite terranes composed of supracrustal sequences (−10.1 to −4.0%.) may reflect the isotopic composition of diagenetic carbonate present in their basaltic protoliths. The values of δ 13C for scapolite in mafic xenoliths and some granulite facies orthogneisses (−8.2 to −1.2%.) are consistent with crystallization of the scapolite from a mafic melt or derivation of CO 2 from mafic melts emplaced in the lower crust or upper mantle. The values of δ 13C for scapolites from calc-silicate gneisses and calc-silicate xenoliths (−10.0 to −2.9%.) may result from depletion of 13C 12C as a result of decarbonation of calcite-bearing protoliths during prograde metamorphism.

13C/ 12C partitioning and kinetics of CO 2 absorption by hydroxide buffer solutions

Absorption of CO 2 gas into a borate buffer solution is a linear function of time. The measured absorption rate log r = −10.33(mol cm −2 s −1) compares well to a value calculated from the diffusion constant of CO 2(aq) and the rate constant for the reaction of CO 2(aq) with OH −. The stable carbon-isotope composition of the dissolved carbonate is constant as function of time, and is depleted in 13C by 19.5‰ with respect to the gas phase. The kinetic fractionation due to diffusion is [( 13D/ 12D) 0.5 − 1] × 10 3 = − 0.7/% , while that caused by the chemical reaction is [( 13k/ 12k) 0.5 − 1] × 10 3 = − 18.8/% . These values have to be taken into account if a borate buffer is used for sample concentration techniques in order to deduce the carbon-isotope composition of CO 2(g). Absorption of CO 2 into a Ba(OH) 2 solution is a linear function of time, too. But the absorption rate varies with the experimental boundary conditions. The precipitated BaCO 3 is depleted in 13C with respect to the gas phase. However, δ 13C values are not constant and decrease as a function of time.