Carbon Isotope Ratio Of CO2 Research Articles

Carbon and hydrogen isotopic variations in gold tube gas pyrolysates from an Athabasca oil sand

Closed system gold tube pyrolysis experiments were conducted on an oil sand bitumen from the Athabasca region in western Canada to investigate gas isotope variation with heating temperatures. Experiments were carried out at 350–650 °C and a pressure of 50 MPa, with heating rates of 2 °C/h and 20 °C/h. The progressive cracking of bitumen and liquid oil lead to continuous release of methane with increasing pyrolysis temperatures, while the yields of wet gas components increase initially at the lower temperature range and then decrease drastically at high temperatures. A general trend of 13C- and 2H-enrichment in the gas products is seen with increasing pyrolysis temperatures due to thermal cracking of various hydrocarbon and non-hydrocarbon components. Isotopic variations can be quite extensive, commonly occurring for both hydrocarbon gases and CO2 as pyrolysis progresses. A carbon isotopic rollover (isotope of gas component shifting from 13C enrichment to 12C-enrichment with increasing temperature) occurs for bulk hydrocarbon gas components at low temperature (< 450 °C), while rollover only occurs for ethane and propane at high temperature (> 550 °C), where partial reversal (lower carbon numbered gas component becomes more 13C-enriched relative to higher carbon numbered ones) also exists. The isotopic values of CO2 show a wide range of variation with the highest δ13C value seen at the lowest temperature while the lowest δ13C value occurs at 500 °C and 550 °C for 2 °C/h and 20 °C/h, respectively. Relative 13C-enrichment occurs only in the high temperature range. The unusual carbon isotope ratios of CO2 in pyrolysates is likely related to biodegradation influence on the precursors, but further investigation is still called for. Hydrogen isotopic values of hydrocarbon gases show even more dramatic variation than that seen for carbon. While methane is progressively 2H-enriched to 650 °C, ethane and propane are relatively 2H-enriched when the pyrolysis temperature is < 500 °C, while the trend is inverted at higher temperatures. Data presented here clearly deviate from the trajectories expected by simple equilibrium or Rayleigh-type kinetic cracking models. Dynamic generation, destruction and mixing processes govern the final isotopic signature in an associated gas product. Isotopic rollover and reversal seem to be a common phenomenon during thermal evolution where heterogeneous precursors are available. While the reaction system of pyrolysis at high temperature differs completely from source rock evolution at low temperature and some artifacts are inevitably involved, the isotope behavior observed here may provide some insights into the complexity in natural cases and help our understanding of the mechanisms of isotopic evolution during thermal maturation.

Monitoring the movement of artificially injected CO2 at a shallow experimental site in Korea using carbon isotopes

The greenhouse effect is closely related to elevated atmospheric CO2 concentrations and therefore, carbon capture and storage (CCS) has attracted attention worldwide as a method for preventing the release of CO2 into the atmosphere, which highlights the importance of monitoring CO2 released from subsurface deposits. In this study, CO2 gas with a δ13C value of −30‰ was injected into soil through pipes installed at a depth of 2.5 m, and samples of CO2 gas released from the soil surface and three soil depths were collected from September 2015 to March 2016 to estimate subsurface CO2 movement. Before and after CO2 injection, the δ13C values of CO2 released from the soil surface ranged from −24.5 to −13.4‰ (average −20.2 ± 2.1‰, n = 25) and from −31.6 to −11.9‰ (average −23.2 ± 4.3‰, n = 49), respectively. The results indicated that the leakage of injected CO2 was successfully detected at the surface. The δ13C values were visualized using an interpolation map to estimate the subsurface CO2 distribution, which confirmed that diffusion of the injected CO2 gas extended to the soil zone where CO2 was not injected. Additionally, variation in δ13C for soil CO2 was detected at the three soil depths (15, 30, and 60 cm), where the values were −16.1, −20.0, and −22.1‰, respectively. Different δ13C values horizontally and vertically indicated that soil heterogeneity led to different CO2 migration pathways and rates. We suggest that the carbon isotope ratio of CO2 is an effective tool for concurrently monitoring CO2 leakage on and under surface in a soil zone if a thorough baseline study is carried out in the field.

Development of a Stable Carbon Isotopes Analysis Instrument Based on Tunable Diode Laser Absorption Spectroscopy

A compact laser spectrometry instrument was developed for high precision measurements of isotope ratio of CO2 by tunable diode laser absorption spectroscopy in the mid-infrared at 2.7 μm. The experimental spectrum of carbon isotopologues in the gas phase near 3641 cm−1 is very suitable for real-time analysis of these isotopologues. Simultaneous measurements of the mixing ratio and the corresponding δ13C values of CO2 in the atmosphere were performed. The achieved standard deviation (1σ) of δ13C was 1.8‰. The Allan analysis of the time series of the mixing ratio of CO2 shows a measurement precision of 0.2‰ for δ13C with an optimum integration time of about 130 s. The spectrometer is capable of real-time measurements of stable carbon isotope ratios of CO2 under ambient conditions.

Hydro-biogeochemical impacts of fugitive methane on a shallow unconfined aquifer

Oil and gas development can result in natural gas migration into shallow groundwater. Methane (CH4), the primary component of natural gas, can subsequently react with solutes and minerals in the aquifer to create byproducts that affect groundwater chemistry. Hydro-biogeochemical processes induced by fugitive gas from leaky oil and gas wells are currently not well understood. We monitored the hydro-biogeochemical responses of a controlled natural gas release into a well-studied Pleistocene beach sand aquifer (Canadian Forces Base Borden, Ontario, Canada). Groundwater samples were collected before, during, and up to 700 days after gas injection and analyzed for pH, major and minor ions, alkalinity, dissolved gases, stable carbon isotope ratios of CO2 and CH4, and microbial community composition. Gas injection resulted in a dispersed plume of free and dissolved phase natural gas, affecting groundwater chemistry in two distinct temporal phases. Initially (i.e. during and immediately after gas injection), pH declined and major ions and trace elements fluctuated; at times increasing above baseline concentrations. Changes in the short-term were due to invasion of deep groundwater with elevated total dissolved solids entrained with the upward migration of free phase gas and, reactions that were instigated through the introduction of constituents other than CH4 present in the injected gas (e.g. CO2). At later times, more pronounced aerobic and anaerobic CH4 oxidation led to subtle increases in major ions (e.g. Ca2+, H4SiO4) and trace elements (e.g. As, Cr). Microbial community profiling indicated a persistent perturbation to community composition with a conspicuous ingrowth of taxa implicated in aerobic CH4 oxidation as well anaerobic S, N and Fe species metabolism.

Biogeochemical protocols and diagnostics for the CMIP6 Ocean Model Intercomparison Project (OMIP)

Abstract. The Ocean Model Intercomparison Project (OMIP) focuses on the physics and biogeochemistry of the ocean component of Earth system models participating in the sixth phase of the Coupled Model Intercomparison Project (CMIP6). OMIP aims to provide standard protocols and diagnostics for ocean models, while offering a forum to promote their common assessment and improvement. It also offers to compare solutions of the same ocean models when forced with reanalysis data (OMIP simulations) vs. when integrated within fully coupled Earth system models (CMIP6). Here we detail simulation protocols and diagnostics for OMIP's biogeochemical and inert chemical tracers. These passive-tracer simulations will be coupled to ocean circulation models, initialized with observational data or output from a model spin-up, and forced by repeating the 1948–2009 surface fluxes of heat, fresh water, and momentum. These so-called OMIP-BGC simulations include three inert chemical tracers (CFC-11, CFC-12, SF6) and biogeochemical tracers (e.g., dissolved inorganic carbon, carbon isotopes, alkalinity, nutrients, and oxygen). Modelers will use their preferred prognostic BGC model but should follow common guidelines for gas exchange and carbonate chemistry. Simulations include both natural and total carbon tracers. The required forced simulation (omip1) will be initialized with gridded observational climatologies. An optional forced simulation (omip1-spunup) will be initialized instead with BGC fields from a long model spin-up, preferably for 2000 years or more, and forced by repeating the same 62-year meteorological forcing. That optional run will also include abiotic tracers of total dissolved inorganic carbon and radiocarbon, CTabio and 14CTabio, to assess deep-ocean ventilation and distinguish the role of physics vs. biology. These simulations will be forced by observed atmospheric histories of the three inert gases and CO2 as well as carbon isotope ratios of CO2. OMIP-BGC simulation protocols are founded on those from previous phases of the Ocean Carbon-Cycle Model Intercomparison Project. They have been merged and updated to reflect improvements concerning gas exchange, carbonate chemistry, and new data for initial conditions and atmospheric gas histories. Code is provided to facilitate their implementation.

Continuous measurements of stable carbon isotopes in CO2 with a near-IR laser absorption spectrometer

A near-IR laser absorption spectrometer using a technique of wavelength modulation spectroscopy is used to measure stable carbon isotope ratios of ambient CO2 (δ13C) via the absorption lines 12CO2 R(17) (2ν1+ν12−ν12+ν3) at 4978.205cm−1 and 13CO2 P(16) (ν1+2ν2+ν3) at 4978.023cm−1. The isotope ratios are measured with a reproducibility of 0.02‰ (1σ) in a 130-s integration time over a 12-h period. The humidity effect on δ13C values has been evaluated in laboratory experiments. The δ13C values of CO2 in ambient air were measured continuously over 8days and agreed well with those from isotope ratio mass spectrometry of canister samples. The spectrometer is thus capable of real-time, in situ measurements of stable carbon isotope ratios of CO2 under ambient conditions.

乾燥再湿潤による土壌有機物分解CO2の 放出率･炭素同位体比の変化

乾燥再湿潤による土壌有機物分解CO2の 放出率･炭素同位体比の変化

Genotypes of Brassica rapa respond differently to plant-induced variation in air CO2 concentration in growth chambers with standard and enhanced venting

Growth chambers allow measurement of phenotypic differences among genotypes under controlled environment conditions. However, unintended variation in growth chamber air CO2 concentration ([CO2]) may affect the expression of diverse phenotypic traits, and genotypes may differ in their response to variation in [CO2]. We monitored [CO2] and quantified phenotypic responses of 22 Brassica rapa genotypes in growth chambers with either standard or enhanced venting. [CO2] in chambers with standard venting dropped to 280 micromol mol(-1) during the period of maximum canopy development, approximately 80 micromol mol(-1) lower than in chambers with enhanced venting. The stable carbon isotope ratio of CO2 in chamber air (delta13C(air)) was negatively correlated with [CO2], suggesting that photosynthesis caused observed [CO2] decreases. Significant genotype x chamber-venting interactions were detected for 12 of 20 traits, likely due to differences in the extent to which [CO2] changed in relation to genotypes' phenology or differential sensitivity of genotypes to low [CO2]. One trait, 13C discrimination (delta13C), was particularly influenced by unaccounted-for fluctuations in delta13C(air) and [CO2]. Observed responses to [CO2] suggest that genetic variance components estimated in poorly vented growth chambers may be influenced by the expression of genes involved in CO2 stress responses; genotypic values estimated in these chambers may likewise be misleading such that some mapped quantitative trait loci may regulate responses to CO2 stress rather than a response to the environmental factor of interest. These results underscore the importance of monitoring, and where possible, controlling [CO2].

Understanding the Stable Isotope Composition of Biosphere‐Atmosphere CO2 Exchange

Stable isotopes of atmospheric carbon dioxide (CO2) contain a wealth of information regarding biosphere‐atmosphere interactions. The carbon isotope ratio of CO2 (δ13C) reflects the terrestrial carbon cycle including processes of photosynthesis, respiration, and decomposition. The oxygen isotope ratio (δ18O) reflects terrestrial carbon and water coupling due to CO2‐H2O oxygen exchange. Isotopic CO2 measurements, in combination with ecosystem‐isotopic exchange models, allow for the quantification of patterns and mechanisms regulating terrestrial carbon and water cycles, as well as for hypothesis development, data interpretation, and forecasting. Isotopic measurements and models have evolved significantly over the past two decades, resulting in organizations that promote model‐measurement networks, e.g., the U.S. National Science Foundation's Biosphere‐Atmosphere Stable Isotope Network, the European Stable Isotopes in Biosphere‐Atmosphere Exchange Network, and the U.S. National Environmental Observatory Network.

断層帯の物質科学と地震の発生過程 カルサイトの炭素・酸素同位体比から見た野島断層浅部破砕帯のシール過程の解明

The Nojima fault appeared on the surface in the northern part of Awaji Island, central Japan as a result of the Hyogo-ken Nanbu earthquake (1995, M = 7.2). Active fault drilling was performed by the Disaster Prevention Research Institute (DPRI), Kyoto University, and core samples were retrieved from 1410 to 1710 m, which were composed of intact and fractured granodiorites. We obtained calcite samples and gas samples from the vein in marginal fracture and non-fracture zones. We analyzed the carbon and oxygen isotope ratios of calcite and carbon dioxide to investigate the characteristic isotope ratios of fluids in the active fault zone, to estimate the origins of fluids, and to determine the sealing process of fractures. The analyzed values of carbon and oxygen isotope ratios of calcite were -10.3 to -7.2‰, 18 to 23/00, respectively, and carbon isotope ratios of CO2 were -21 to -17‰. If carbon isotope ratios of calcite were at equilibrium with those of CO2, the precipitation temperature of calcite is calculated to be 30 to 50°C. This temperature is consistent with the present temperature of the depth where drilling cores were retrieved. Oxygen isotope ratios of H2O that, precipitated calcite were calculated to be -1.8 to -5.5‰. These values indicate calcite were precipitated from mixed fluids of sea water and meteoric water. Therefore, the marginal fracture zone of the Nojima fault was sealed with calcite, which was generated from mixing of sea water and meteoric water in situ.