Carbon Isotope Composition Of CO2 Research Articles

CO2 in the atmosphere of Mars depleted in 13C

We present here vertically resolved measurements of the carbon isotopic composition of CO2 in the Martian atmosphere between the surface and 50 km of altitude. The results are based on data taken by the ExoMars Trace Gas Orbiter with the NOMAD instrument and have been aggregated to derive an average vertical profile of 13C/12C. We find no seasonal or spatial trends with variabilities beyond the sensitivity of the measurements. For the analysis, we developed a method that allows us to estimate whether the observed variability of isotopic measurements is beyond their intrinsic accuracy, by exploiting ab-initio spectroscopy and the radiometric noise of the instrument. Applying this method to our data, we find that atmospheric CO2 is depleted in 13C compared to the Earth standard by 30‰ to 45‰, in line with previous ground-based measurements values of the atmosphere and in contrast with the average value obtained by Curiosity at the surface (46 ± 4‰). These differences in isotopic signatures of CO2 as measured across the atmosphere and near-surface pose new questions when inferring the evolution and history of carbon on Mars, and suggest that processes such as a strong atmosphere-surface interactions may be fractionating the carbon reservoirs on the planet.

Raman spectral characteristics of 12CO2/13CO2 and quantitative measurements of carbon isotopic compositions from 50 to 450 °C and 50 to 400 bar

The carbon isotopic composition of CO2 is traced to its different origins and widely used in the fields of geology, biology, and chemistry. Raman spectroscopy can be performed in situ, is nondestructive, and requires no sample preparation; these characteristics enable Raman spectroscopy to be considered a new alternative method to measure the carbon isotopic composition of CO2. In this work, Raman spectra of high-purity 13CO2, 12CO2, and six 12CO2-13CO2 binary mixtures with known mixing ratios were collected using a High Pressure Optical Cell (HPOC) at 50–450 °C and 50–400 bar. The results showed that the characteristic peak positions of both 13CO2 and 12CO2 shift to lower wavenumbers with increasing temperature and decreasing pressure, but the peak positions of 13CO2 show a larger shift. The peak position difference of the corresponding characteristic peaks between 13CO2 and 12CO2 is greater than 15 cm−1 under the above temperatures and pressures, and the peaks can be distinguished. However, ν−13 overlays νH.B.12 near 1265 cm−1, ν+12 overlaps νH.B.13 near 1288 cm−1. The existence of 13CO2 can cause a change in the Fermi diad splitting of 12CO2 and affect the establishment of CO2 Raman densimeters. The positive correlation obtained between the peak intensity ratio and the content ratio is affected by temperature, pressure, and 13CO2 content. I+13/I+12 and I−13/I−12 were selected as the quantitative indices to establish Raman quantitative analysis models for the determination of the carbon isotopic composition of CO2, which can be applied to in-situ measurements of high-temperature and high-pressure systems.

Stable Isotope Evaluation of Geothermal Gases from the Kızıldere and Tekke Hamam Geothermal Fields, Western Anatolia, Turkey

Volatiles transported from the Earth’s interior to the surface through permeable faults provide insights on the gas composition of deep reservoirs, mixing and migration processes, and can also be applied as gas-geothermometer. Here, we present carbon (δ13C), hydrogen (δ2H) and nitrogen (δ15N) isotopic data of CO2, CH4, and N2 from gas samples collected from the Kızıldere and Tekke Hamam geothermal fields, located along the eastern segment of the Büyük Menderes Graben, Turkey. The stable isotopic composition of carbon (δ13C) ranges from +0.30 to +0.99‰ (PDB) for CO2 from Kızıldere and is slightly more variable (−0.95 to +1.3‰) in samples from Tekke Hamam. Carbon isotope data in combination with CO2/3He data reveal that ~97% (Tekke Hamam) to ~99% (Kızıldere) of CO2 derives from limestone sources, with the residual CO2 being magmatic in origin with no evidence for CO2 from organic sources. The slightly higher contribution of limestone-derived CO2 in Kızıldere, compared to Tekke Hamam can be attributed to the higher temperatures of the Kızıldere reservoir and resulting amplified fluid–limestone interaction, as well as helium depletion during phase separation for Kızıldere samples. In contrast to the carbon isotopic composition of CO2, the δ13C values of methane from Kızıldere and Tekke Hamam are clearly distinct and vary between −23.6 and −20.8‰ for Kızıldere and −34.4 and −31.7‰ for Tekke Hamam, respectively. The δ2H-CH4 composition is also distinct, measured as −126.7‰ for Kızıldere and −143.3‰ for Tekke Hamam. CO2-CH4 carbon isotope geothermometry calculations based on the isotopic fractionation of δ13C between the dominant component CO2 and the minor component CH4 reveals temperatures 20–40 °C and 100–160 °C higher than the bottom–hole temperatures measured for Tekke Hamam and Kızıldere, respectively. Based on the CO2-CH4 carbon isotope disequilibrium, unusual high methane concentrations of ~0.3 to 0.4 vol.-% and CH4/3He-δ13C-CH4 relationships we suggest thermal decomposition of late (Tekke Hamam) to over-mature (Kızıldere) organic matter and, to some extent, also abiogenic processes as principal source of methane. The N2/36Ar ratios of most samples reveal the existence of a non–atmospheric nitrogen component within the gas mixture issuing from both fields, in addition to a constant contribution of atmospheric derived nitrogen accompanied into the system via the meteoric recharge of the geothermal system. Based on the δ15N isotopic ratios (varying between −4.44‰ and 4.54‰), the non–atmospheric component seems to be a mixture of both sedimentary (crustal organic) and mantle nitrogen. The thick Pliocene sedimentary sequence covering the metamorphic basement is the likely major source for the thermogenic content of CH4 and crustal N2 gas content in the samples.

Raman spectroscopic measurement guidelines for carbon isotopic composition of CO2

In principle, Raman spectroscopy can be applied to quantitatively measure the carbon isotopic composition (13CO2/12CO2) of CO2 in single fluid inclusion. Based on our recent work, it could be expressed as, 13CO2/12CO2 = (I13CO2/I12CO2)·(σ12CO2/σ13CO2), in which the ratio of cross section (σ12CO2/σ13CO2) is determined from Raman spectra of standard CO2 sample. In fact, before Raman spectroscopy can widely be utilized to quantitatively determine the carbon isotopic composition of CO2, it is necessary to improve the measurement accuracy and precision of 13CO2/12CO2. In this study, it is devoted to understand the factors which may affect the accuracy and precision of measured 13CO2/12CO2. Based on the discussion on error analysis, the Raman spectroscopic measurement guidelines are provided to ensure the accuracy and precision of measured 13CO2/12CO2. Additionally, this method is utilized to measure the 13CO2/12CO2 of analytical synthetic and natural CO2 samples in order to evaluate its reliability.

Mechanism of anomalous manifestations δ13C CO2 underground water on Tashkent geodynamic range

The results of long-term isotope and gas measurements of various groundwater sources in the Tashkent artesian basin are presented. In addition to areal studies, the results of regime observations of selected wells at the Tashkent geodynamic test site are also presented to identify prognostic features as a precursor to strong earthquakes. The first results were obtained related to the manifestation of the Nazarbek earthquake on December 11, 1980, with a magnitude of 5.3, a source depth of 10 km. On the basis of this earthquake, the behavior of isotopic and gas precursors at the Ulugbek well, Tashkent geodynamic test site, was analyzed. A quantitative analysis was made of the anomalous manifestation of the gas and isotopic composition of groundwater in the Ulugbek borehole during the preparation and execution of the Nazarbek earthquake. Determination of CO2 release from rock samples recovered from deep wells of the landfill made it possible to quantify the ratio of “background” CO2 mixing from carbonate decomposition to anomalous. Judging by the obtained ratio, the rocks during the preparation of the earthquake should emit 2 times more carbon dioxide than the background CO2. This was confirmed by observations of the CO2 content in the well, when an increase in its relative concentration of 250% was recorded. The analysis of the δ13C time series, obtained as a result of long-term regime observations of the carbon isotopic composition of CO2 in the groundwater of the Tashkent geodynamic test site, made it possible to identify significant anomalies in the carbon content.

Consistent weekly cycles of atmospheric NO2, CO, and CO2 in a North American megacity from ground-based, mountaintop, and satellite measurements

The weekday-weekend effect of anthropogenic emissions in cities, driven by the associated weekly changes in human activities, provides a unique opportunity to assess the sensitivity of observation networks (e.g., ground-based and space-borne instruments) on urban emissions. In this study, we focus on the weekly cycle amplitudes of nitrogen dioxide (NO2), carbon monoxide (CO), and carbon dioxide (CO2) in the Los Angeles (LA) megacity, where a significant weekly cycle of human activities exists. In addition, abundant observations are being produced continuously from existing ground-based, mountaintop, and satellite platforms to monitor carbon emissions and air quality in LA. From our analysis, significant agreement can be found in observations from different platforms. For NO2, a 30%–35% Sunday decline relative to mid-week mixing ratios can be observed from both ground-based and satellite observations. For CO, the Sunday drops from ground-based, mountain-top and satellite observations are 13%–20%. The TROPOMI instrument with its high spatial resolution provides detailed spatial information on the reduction of tropospheric NO2 and CO columns on Sundays. The spatial pattern is in good agreement with traffic density in LA. Impact due to the prevailing winds from the coast in the afternoon can also be observed. For anthropogenic CO2, we show that the weekly cycle of XCO2 enhancement above background from OCO-2 observations has a Sunday decline (15%–20%) consistent with ground-based observations and TCCON. This weekly pattern of CO2 in a megacity directly detected by OCO-2 is reported for the first time. In addition, we also investigate the weekly cycles in the stable carbon isotopic composition of CO2 (δ13C) from ground-based observations, which demonstrates the weekly variation in fossil fuel usage in LA. Finally, using the COVID-19 lockdown period as an example of a short-term perturbation on anthropogenic emissions, we found that the weekly cycle amplitude became larger during the lockdown period primarily because of the traffic volume changes in light-duty vehicles. This study highlights the consistencies and effectiveness of existing observing platforms in monitoring the anthropogenic emissions of the LA megacity.

Raman quantitative measurement for carbon isotopic composition of CO2: Theory and method

Raman spectroscopy is an efficient non-contact and non-destructive method. It is a potential approach to quantitatively measure the carbon isotopic composition (13CO2/12CO2) of CO2 in single fluid inclusion. Based on the theoretical analysis, Raman spectroscopy can reasonably be applied to measure the carbon isotopic composition of CO2. It can theoretically be expressed as, 13CO2/12CO2 = (I13CO2/I12CO2)·(σ12CO2/σ13CO2), in which the ratio of cross section (σ12CO2/σ13CO2) is determined from Raman spectra of standard CO2 sample. Therefore, Raman measurement process can be described as, from standard to analytical samples. In natural CO2 sample, the 13CO2 concentration is very low. Compared to 12CO2, Raman intensity of 13CO2 is much weaker. This greatly affects the accuracy and precision of Raman measurement on the 13CO2/12CO2. In this work, a method is provided in order to improve the accuracy and precision of measured 13CO2/12CO2.

Recycled crustal carbon in the depleted mantle source of El Hierro volcano, Canary Islands

The Canary Islands, in the eastern Atlantic, are among the most enigmatic Oceanic Island provinces on Earth, as the mantle source feeding its volcanism exhibits wide spatial heterogeneity and a multiplicity of sources. Multi-isotope whole-rock studies have long revealed the presence of a recycled oceanic crust/lithosphere component in the mantle source. However, noble gas systematics have been more challenging to interpret, and the available carbon isotope data is limited and cannot support/dismiss this interpretation. Here, we present the very first isotopic characterisation of CO2 and noble gases (He-Ne-Ar) in fluid inclusions (FI) in minerals hosted in mantle xenoliths from El Hierro, the youngest and westernmost island of the Canary volcanic archipelago. Six fresh xenoliths from El Julan cliff valley were analysed (3 spinel lherzolites and 3 spinel harzburgites). We find carbon isotopic compositions of CO2 in FI (δ13C) ranging from −2.38 to −1.23‰ in pyroxenes and from −0.19 to +0.96‰ in olivines. These unusually positive δ13C values, well above the typical mantle range (−8‰ < δ13C < −4‰), prove, for the first time, the presence of a recycled crustal carbon component in the local source mantle. We interpret this 13C-rich component as inherited from a mantle metasomatism event driven by fluids carrying carbon from C. In contrast, our El Hierro xenoliths identify a depleted mantle-like He signature, with an average Rc/Ra ratio (3He/4He normalised to air ratio and corrected for atmospheric contamination) of 7.45 ± 0.26 Ra. The involvement of depleted mantle-like fluids, variably admixed with air-derived components (possibly recycled via paleo-subduction event(s)), is corroborated by Ne-Ar isotopic compositions. The depleted mantle-like He signature suggests instead the involvement of a primordial He source in the local lithospheric mantle and indicates a marginal role played by past subduction events in modifying the local mantle He budget. When put in the context of previous 3He/4He measurements in FI and surface gases along the Canary archipelago, our results confirm an overall west-to-east decrease of Rc/Ra ratios, which may be interpreted as due to increasing contributions from the African sub-continental mantle, the addition of radiogenic 4He during magma migration in the oceanic crust (whose thickness increases eastward) and/or magma ageing.

New analytical approach to monitoring air quality in historical monuments through the isotopic ratio of CO2.

In this study, we evaluated indoor air quality to highlight the effects of environmental pollution in the field of cultural heritage. In particular, two important archeological places in the old part of the city of Salerno, Italy, were analyzed: Fruscione Palace and S. Pietro a Corte. The work focused on the influence of tourists on environmental pollution correlated to indoor air quality during some social and cultural events. Moreover, we focused on the possible use of the carbon isotopic composition of CO2 as a tool for environmental studies in the field of cultural heritage. The results showed a good relationship between the isotopic composition of CO2 and the variation of pollutants concentration in the air, demonstrating that it is a valid tool and non-invasive marker to monitor environmental pollution of museums and cultural heritage sites.

Origin of dissolved gas (CO2, O2, N2, alkanes) in pore waters of a clay formation in the critical zone (Tégulines Clay, France)

Understanding weathering processes in clay formations is an issue of primary importance for the preservation of our natural environment. Reactive-transport modeling used to simulate weathering of clay formations has indicated that reactive gases (CO2 and O2) are major parameters in controlling weathering processes.The Lower Cretaceous Tégulines marine-clay formation outcropping in the area of Brienne-le-Chateau (north-eastern France) has been investigated in the context of a sub-surface waste repository. We developed gas monitoring (CO2, O2, N2, alkanes) of core samples from two boreholes that entirely crosscut the Tégulines Clay formation, to define the consequences of weathering and oxidation processes on gases dissolved in pore waters. We discuss amounts of gas and the carbon isotopic composition of CO2 in terms of pore water chemistry including dissolved-inorganic carbon (DIC) and alkalinity, mineral reactivity, organic-matter degradation and oxygen diffusion. Degassing of samples conditioned under He atmosphere provided evidence of very high CO2 production in the soil (0–30 cm), and high CO2 degassing associated with a high oxygen level in the first 2–10 m of the clay. The CO2 degassing increase observed in weathered clay relative to preserved clay resulted from calcite dissolution due to pyrite oxidation and organic matter degradation. The δ13C of CO2 indicates that organic matter degradation was a major source of CO2 at shallow depths and down to 10–12 m, which is the maximum depth at which we observed fossil roots. Then the CO2 degassing decreased down to a constant value in preserved clay, where the carbonate system and the mineral assemblage control dissolved carbonates in pore waters. The profile of the δ13CCO2 also provides evidence of progressive CO2 diffusion of organic origin from the underlying Greensands aquifer in the lower part of Tégulines Clay up to ~40 m in the AUB230 borehole.As a first step toward understanding interactions between Tégulines Clay and near surface waters or water at the Greensands interface, we developed a reactive-transport model to simulate in one dimension weathering processes under ambient temperature, constrained by geochemical reactions in soil (organic matter degradation) and in the clay (pyrite oxidation and calcite dissolution), exchange, DIC and pore water chemistry. The simulation was carried out for 10 kyrs, assuming that weathering and soil formation began after the last glacial maximum. The DIC profile cannot be simulated without considering evaporation processes in agreement with the isotopic data. This type of approach combining a complete field dataset (reactive-gas concentrations, δ13C of CO2, major-ion concentrations, δ18O and δD of pore waters) and reactive-transport modeling is necessary for better understanding of chemical weathering processes in the critical zone.

Hydrogeological control on carbon dioxide input into the atmosphere of the Chauvet-Pont d'Arc cave.

Carbon dioxide (CO2) concentration (CDC) is an essential parameter of underground atmospheres for safety and cave heritage preservation. In the Chauvet cave (South France), a world heritage site hosting unique paintings dated 36,000years BP, a high-sensitivity monitoring, ongoing since 1997, revealed: 1) two compartments with a spatially uniform CDC, a large volume (A) (40,000 to 80,000m3) with a mean value of 2.20±0.01% vol. in 2016, and a smaller remote room (B) (2000m3), with a higher mean value of 3.42±0.01%; 2) large CDC annual variations with peak-to-peak amplitude of 2% and 1.6% in A and B, respectively; 3) long-term changes, with an increase of CDC and of its annual amplitude since 1997, then faster since 2013, reaching a maximum of 4.4% in B in 2017, decreasing afterwards. While a large effect of seasonal ventilation is ruled out, monitoring of seepage at two dripping points indicated that the main control of CDC seasonal reduction was transient infiltration. During periods of water deficit, calculated from surface temperature and rainfall, CDC systematically increased. The carbon isotopic composition of CO2, correlated with water excess, is consistent with a time-varying component of CO2 seeping from above. The CO2 flux, which is the primary driver of CDC in A and B, inferred using box modelling, was found to confirm the relationship between water excess and reduced CO2 flux into A, compatible with a more constant flux into B. A buoyancy-driven horizontal CO2 flow model in the vadose zone, hindered by water infiltration, is proposed. Similarly, pluri-annual and long-term CDC changes can likely be attributed to variations of water excess, but also to increasing vegetation density above the cave. As CDC controls the carbonate geochemistry, an increased variability of CDC raises concern for the preservation of the Chauvet cave paintings.

Arctic soil carbon turnover controlled by experimental snow addition, summer warming and shrub removal

Northern latitude tundra heaths have accumulated large amounts of organic carbon (C) in the soil. Changes in climatic conditions such as temperature and winter precipitation might affect the C balance and potentially change these tundra ecosystems from being C sinks to sources of CO2 emitted to the atmosphere. However, studies on C fluxes with single and combined winter snow and summer warming effects are scarce. This study investigates gross ecosystem production (GEP), ecosystem respiration (ER), net ecosystem production (NEP) and carbon isotopic composition of CO2 emitted from a dry heath in arctic Greenland one and two years following field manipulations of summer temperature, shrub abundance and winter snow depth. Our aims were to quantify climatic change effects on CO2 fluxes and the growing season carbon balance of the ecosystem and to investigate shifts in δ13C of emitted CO2 potentially due changes in emission from old soil C versus recently fixed carbon. Ecosystem CO2 fluxes and δ13C-CO2 were measured using closed chambers, and soil CO2 concentrations and δ13C were measured depth-specifically using gas probes.We found a significant increase of CO2 emissions in all treatments during both years. Growing season NEP increased by 38 and 73% with 1 m enhanced winter snow depth, by 113 and 144% with summer warming and by 61 and 320% with total shrub removal in 2013 and 2014, respectively. The snow effect can be explained by the delay in the onset of growth as indicated by early season reduced vegetation greenness. The effect of warming was a result of an increase of ER by 39 and 32%, and the effect of shrub removal was mainly due to a reduction in GEP by 34 and 48%, in 2013 and 2014, respectively. Furthermore, the δ13C of the carbon source of CO2 emitted from warmed plots increased significantly two years after the experiment was initiated. This might indicate increased decomposition of 13C enriched soil organic matter and hence increased mineralization of the old carbon stock in the soil under warmed conditions. The increase of NEP, the additive response of all treatments, and the indications of increased emission of carbon from old stocks due to warming (or warming-induced drying), demonstrate the risk of a relatively fast feedback to climate warming during the snow-free season.

Microbiomes in Soils Exposed to Naturally High Concentrations of CO2 (Bossoleto Mofette Tuscany, Italy).

Direct and indirect effects of extremely high geogenic CO2 levels, commonly occurring in volcanic and hydrothermal environments, on biogeochemical processes in soil are poorly understood. This study investigated a sinkhole in Italy where long-term emissions of thermometamorphic-derived CO2 are associated with accumulation of carbon in the topsoil and removal of inorganic carbon in low pH environments at the bottom of the sinkhole. The comparison between interstitial soil gasses and those collected in an adjacent bubbling pool and the analysis of the carbon isotopic composition of CO2 and CH4 clearly indicated the occurrence of CH4 oxidation and negligible methanogenesis in soils at the bottom of the sinkhole. Extremely high CO2 concentrations resulted in higher microbial abundance (up to 4 × 109 cell g–1 DW) and a lower microbial diversity by favoring bacteria already reported to be involved in acetogenesis in mofette soils (i.e., Firmicutes, Chloroflexi, and Acidobacteria). Laboratory incubations to test the acetogenic and methanogenic potential clearly showed that all the mofette soil supplied with hydrogen gas displayed a remarkable CO2 fixation potential, primarily due to the activity of acetogenic microorganisms. By contrast, negligible production of acetate occurred in control tests incubated with the same soils, under identical conditions, without the addition of hydrogen. In this study, we report how changes in diversity and functions of the soil microbial community – induced by high CO2 concentration – create peculiar biogeochemical profile. CO2 emission affects carbon cycling through: (i) inhibition of the decomposition of the organic carbon and (ii) promotion of CO2-fixation via the acetyl-CoA pathway. Sites naturally exposed to extremely high CO2 levels could potentially represent an untapped source of microorganisms with unique capabilities to catalytically convert CO2 into valuable organic chemicals and fuels.

Magmatic Signature in Submarine Hydrothermal Fluids Vented Offshore Ventotene and Zannone Islands (Pontine Archipelago, Central Italy)

Geochemical investigations carried out on submarine hydrothermal fluids vented offshore the Pontine Islands (Tyrrhenian Sea) revealed the existence of gas vents to the W of Zannone Island and SW of Ventotene Island. The geochemical features of the CO2-rich gas samples show a clear mantle-derived signature with3He/4He of 3.72-3.75 Ra and 1.33 Ra at Zannone and Ventotene, respectively. Gas geochemistry denotes how CO2-rich gases undergo fractionation processes due to CO2dissolution to a variable extent favoring enrichment in the less soluble gas species, i.e., CH4, N2, and He. The carbon isotope composition of CO2, expressed asδ13C vs. V-PDB, ranges from -0.71 and -6.16‰ at Zannone to 1.93‰ at Ventotene. Preliminary geothermometric and geobarometric estimations indicate equilibrium temperatures in the range of 150-200°C at Zannone and &gt;200°C at Ventotene besides H2O pressures in the range of 5 bar and 20 bar at Zannone and Ventotene, respectively. Although the latest volcanic activity at the Pontine Archipelago is dated Middle Pleistocene, the combination of the new geochemical information along with geothermometric estimations indicates that cooling magmas are likely releasing enough thermal energy to form an efficient hydrothermal system.

Deciphering atmospheric CO2 change

Carbon Cycle Many different processes and carbon sources can affect the concentration of atmospheric carbon dioxide (CO2), so to understand past, present, and likely future variability of CO2, those mechanisms and reservoirs must be identified. Bauska et al. present a record of the stable carbon isotopic composition of CO2 over the interval between 50,000 and 35,000 years ago, which reveals that the primary source of atmospheric carbon during millennial-duration events probably was organic carbon residing in the deep ocean, whereas more abrupt events occurring over centennial time scales were associated both with hydrological change in the tropics and rapid increases in Northern Hemisphere temperature. Geophys. Res. Lett. 45 , 7731 (2018).

Impact of decade-long warming, nutrient addition and shading on emission and carbon isotopic composition of CO2 from two subarctic dwarf shrub heaths

This study investigated ecosystem respiration, soil respiration and carbon isotopic composition in CO2 emitted from two subarctic shrub heaths with contrasting moisture regimes. The reported measurements were conducted 22 years (mesic heath) and 12 years (wet heath) upon initiation of in situ climate change related manipulations of temperature, nutrient availability and light.The aim was to quantify expected climatic change effects on soil and ecosystem respiration, and to investigate whether the emitted CO2 originates from old carbon stores in the soil or from newly fixed carbon. Ecosystem and soil respiration was measured using closed chambers and CO2 in the soil profile was sampled with gas probes installed at different depths.At the mesic heath ecosystem respiration was increased 46% by warming while soil respiration increased 133% by nutrient addition. At the wet heath, warming increased ecosystem respiration by 99% and soil respiration by 58%. Litter addition, short time warming and shading generally did not change ecosystem- and soil respiration.The carbon isotope compositions of the sources to CO2 were not significantly altered by any of the treatments at the two heaths across the growing season. However, there was a tendency across growing season towards an increased δ13C source value after 22 years of warming in the mesic shrub heath, and the effect was statistically significant in June, indicating increased decomposition of 13C enriched material. Hence, although more of the old carbon stock in the soil was possibly mineralized under warmed conditions, indicating a risk of long lasting positive feedback on climate warming, the effect was only periodically strong enough to gain statistical significance, despite strong warming-induced effect on ecosystem respiration, and may be counteracted by increased C gain by higher primary production.

Effects of climate factors and vegetation on the CO2fluxes and δ13C from re-established grassland

The relationship between stable carbon isotope composition (δ13 C -CO2 ) of soil CO2 flux, vegetation cover and weather conditions was investigated in a short-term campaign at a temperate re-established grassland in Germany. During August-September 2016, we measured surface CO2 flux with a closed-chamber method at high and low soil moisture content (‘wet’, ‘dry’), with and without above ground vegetation (‘planted’, ‘clear-cut’) and estimated the effects of treatments on respective δ13 C -CO2 values. The concentration and stable carbon isotope composition of CO2 were determined using the gas chromatography and mass spectrometry analyses. The δ13 C -CO2 of the soil fluxes decreased over sampling time for the ‘dry-warm’ conditions and canopy manipulation. The ecosystem-derived δ13 C -CO2 values (corrected for the atmospheric δ13 C -CO2 ) which included predominately soil-and rhizosphere respiration were –26.2 ± 0.8‰ for the ‘dry-warm’ conditions and decreased down to –28.1 ± 1.4‰ over a period of 28 days from late August to the end of September. The decrease coincided with the lowering of CO2 flux and could be attributed to changes in plant physiological processes at the end of the vegetation season. Though the removal of shoots did not significantly affect the δ13 C -CO2 values as compared with the control, the pattern of further δ13 C -CO2 decrease (down to –28.8 ± 0.8‰) supported the role of living vegetation in a contribution of 13 C-enriched CO2 to the ecosystem respiration.

Physicochemical parameters and age of the Vasil’kovskoe gold deposit (northern Kazakhstan)

A superlarge gold-ore stockwork of the Vasil’kovskoe deposit (with gold resources of more than 380 tons) is located at the contact of porphyroblastic granodiorites and diorites in northern Kazakhstan. The specifics of the Vasil’kovskoe deposit is a wide occurrence of gray (so-called ore) gold-bearing quartz, which, together with white quartz, composes quartz-sulfide veins and veinlets in the stockwork. Based on thermobarogeochemical and isotope-geochemical data, we have established that gray quartz and arsenopyrite of the deposit formed with the participation of K-Na-Mg-Cl-containing aqueous CO2-hydrocarbon fluids at 250-550 °C, 0.1-2.5 kbar, and salinity of 7.0-22.5 wt.% NaCl equiv. (seldom, >30-40 wt.% NaCl equiv.). The cyclic recurrence of parameter fluctuations was accompanied by the deposition of gold, which led to the formation of gold-rich veinlet ores in the stockwork core. White quartz formed at lower temperatures, 120-310 °C, and 0.2-1.0 kbar, with the participation of Ca-Na-Cl-containing fluids with salinity of 2.0-11.0 wt.% NaCl equiv. In addition to H2O and CO2, hydrocarbons and their derivates (paraffins, olefins, arenes, alcohols, ethers, aldehydes, ketones, and carboxylic acids) as well as nitrogen-containing (C2H3N, C3H9N, C7H5N, and C8H5NO2) and sulfur-containing (CS2, COS, SO2, C2H6S2, etc.) compounds (indicators of reducing conditions) were involved in the ore formation. The sulfur isotope composition of sulfides (534S = +5.7 to + 11.8%c) and the carbon isotope composition of CO2 in fluid inclusions in gray (513C = -2.1 to -4.6%c) and white (513C = -11.0 to -21.4%c) quartz as well as its positive and negative anomalies of Eu point to the crustal source of the fluids. The gray color of quartz is due to abundant CO2-hydrocarbon-containing inclusions, carbon particles, and sulfides. Crystallization of ore-hosting granodiorites happened in the period from 490.0 ± 4.4 to 443.5 ± 4.1 Ma. The age of the areal K-feldspathization of granodiorites, preceding the ore formation, is 375.2 ± 3.7 Ma. Formation of gold-including parageneses took place in the period from 311.7 ± 6.4 to 279.2 ± 2.5 Ma, i.e., lasted no less than 30 Myr.

Quantitative analysis and measurement of carbon isotopic compositions in individual fluid inclusions by micro-laser Raman spectrometry

Micro-laser Raman spectroscopy is a non-destructive technique to quantitatively determine the carbon isotopic compositions of CO2 in individual fluid inclusions.

Different carbon reservoirs of auriferous fluids in African Archean and Proterozoic gold deposits? Constraints from stable carbon isotopic compositions of quartz-hosted CO2-rich fluid inclusions

Stable carbon (and when present, nitrogen) isotope ratios of fluid inclusions in quartz from selected gold deposits in Ghana and Zimbabwe have been analyzed using a crushing device interfaced to an isotopic ratio mass spectrometer (IRMS) in order to constrain possible sources of the auriferous fluids. The study revealed a striking difference in stable carbon isotopic compositions of CO2 in quartz-hosted fluid inclusions from Archean and Paleoproterozoic orogenic gold deposits and points to diverse sources of CO2 in the studied deposits. Whether this finding can be generalized for other Archean and Proterozoic orogenic gold deposits worldwide remains open. However, a significant CO2 contribution by mantle degassing can be ruled out for every deposit studied. Devolatilization of greenstone belt rocks is the most likely source for CO2 in some Archean Au deposits in Zimbabwe, whereas CO2 in Proterozoic vein-type Au deposits in the West African Craton is most likely derived from Corg-bearing metasedimentary rocks. The δ13CCO2 values of high-density CO2-rich, water-poor inclusions hosted in quartz pebbles from the world-class Au-bearing conglomerate deposits at Tarkwa (Ghana) differ considerably from the δ13CCO2 values of similar high-density CO2-rich inclusions in vein quartz from the giant Ashanti deposit (Ghana) and disprove the idea of derivation of the Tarkwaian quartz (and gold?) from an older equivalent to the Ashanti vein-type gold deposit.