Carbon dioxide isotopic composition

An alcohol of normal composition is equilibrated in one tube with carbon dioxide of known composition fi (usually tank carbon dioxide) and another with labeled carbon dioxide of known composition n . After equilibration, the measured atom fractions of in the COg are % and 2, respectively. If a sample of the same alcohol of unknown isotopic composition, d, is then analyzed under the same conditions, using tank carbon dioxide (of composition n,), it can be shown that... 

The interstitial air trapped during this process preserves a largely unaltered record of the composition of past atmospheres on time scales as short as decades and as long as several hundred thousand years. Such records have provided critical information about past variations in carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), carbon monoxide (CO), and the isotopic composition of some of these trace species. In addition, studies of the major elements of air nitrogen, oxygen, and argon, and their isotopic composition, have contributed... 

The radiocarbon ratio also evolves very rapidly from its initial value of -50 to an average value of about -8 per mil. This evolution is not a consequence of evaporative concentration but, instead, of an approach to equilibrium with atmospheric carbon dioxide. Average surface seawater contains significantly less radiocarbon than does the atmosphere because its isotopic composition is affected by exchange with the deep ocean as... 

Let us first introduce some important definitions with the help of some simple mathematical concepts. Critical aspects of the evolution of a geological system, e.g., the mantle, the ocean, the Phanerozoic clastic sediments,..., can often be adequately described with a limited set of geochemical variables. These variables, which are typically concentrations, concentration ratios and isotope compositions, evolve in response to change in some parameters, such as the volume of continental crust or the release of carbon dioxide in the atmosphere. We assume that one such variable, which we label/ is a function of time and other geochemical parameters. The rate of change in / per unit time can be written... 

Ordinarily electrical amplification is used to compensate for differences in isotope abundances in the gas being measured. Thus, for carbon dioxide all three Faraday collectors are used with relative signal amplification at m/z = 44, 45, and 46 of 1 91 500 (since the normal abundance ratios 12C/13C 91, and 160/180 500). The amplified signals from all three detectors are thus comparable in intensity. Because of this feature, however, IRMS should only be used on gases with isotope composition close to natural abundance. Enriched material should not be used without careful recalibration since there is no guarantee of a linear response of electric signal to ion current for widely different isotope ratios. 

Carbon and oxygen isotope compositions of sixteen marbles from epidote amphibolites of the Sambagawa metamorphic belt and of three diamondbearing marbles from the Kumdy-Kol area of Kokchetav Massif were measured. Powdered calcite from the marbles was decomposed by 100 percent phosphoric acid at 60°C to obtain carbon dioxide gas for isotopic analyses. Isotopic measurements were carried out using a triple-collector mass spectrometer (Finnigan MAT Delta E). All data are given in terms of a conventional expression in... 

Barhng J, Arnold GL, Anbar AD (2001) Natural mass-dependent variations in the isotopic composition of molybdenum. Earth Planet Sci Lett 193 447 57 Barnes I, Irwin WP, White DE (1978) Global distribution of carbon dioxide discharges and major zones of seismicity. US Geological Survey, Water-Resources Investigation 78-39, Open File Report... 

DeNiro MJ, Epstein S (1979) Relationship between the oxygen isotope ratios of terrestrial plant cellulose, carbon dioxide and water. Science 204 51-53 DeNiro MJ, Epstein S (1981) Isotopic composition of cellulose from aquatic organisms. Geochim Cosmochim Acta 45 1885-1894... 

Gerlach TM, Taylor BE (1990) Carbon isotope constraints on degassing of carbon dioxide from Kilauea volcano. Geochim Cosmochim Acta 54 2051-2058 Gerlach TM, Thomas DM (1986) Carbon and sulphur isotopic composition of Kilauea parental magma. Nature 319 480-483... 

Isotopic Compositions of Carbon Monoxide, Carbon Dioxide, and Formaldehyde (Pearson100) ... 

Prior to 1991, numerous isotopic measurements of stratospheric carbon dioxide were made, though only for 5 0. A mass-independent isotopic composition was later observed in samples from 26 km to 35.5 km, with a deviation from the expected isotopic composition (Thiemens et al., 1991). It has been established that the mass independence arises from isotopic exchange between electronically excited atomic oxygen, 0( D), and CO2 ... 

Andres R. J., Marland G., Boden T., and Bischof S. (2000) Carbon dioxide emissions from fossil fuel consumption and cement manufacture, I75I-I99I, and an estimate of their isotopic composition and latitudinal distribution. In The Carbon Cycle (eds. T. M. E. Wigley and D. S. Schimel). Cambridge University Press, pp. 53-62. 

Cerhng T. E., Solomon D. K., Quade J., and Bowman J. R. (1991) On the isotopic composition of carbon in soil carbon-dioxides. Geochim. Cosrnochim. Acta 55(11), 3403-3405. 

Horibe Y., Shigehara K., and Takakuwa Y. (1973) Isotope separation factors of carbon dioxide-water system and isotopic composition of atmospheric oxygen. J. Geophys. Res. 78, 2625-2629. 

Hypothesis 2. Diffusion of DOC and sulfate from confining bed pore waters provides sources of electron donor (organic carbon) and electron acceptor (sulfate). Carbon dioxide produced by this reaction drives shell material dissolution/ calcite cement precipitation which can explain the major ion and carbon isotope composition of Black Creek aquifer water. 

Mora C. I., Driese S. G., and Seager P. G. (1991) Carbon dioxide in the Paleozoic atmosphere evidence from carbon-isotope compositions of pedogenic carbonate. Geology 19, 1017-1020. 

Homibrook E. R. C., Longstaffe F. J., and Fyfe W. S. (2000) Evolution of stable carbon isotope compositions for methane and carbon dioxide in freshwater wetlands and other anaerobic environments. Geochim. Cosmochim. Acta 64, 1013-1027. 

Figure 6 The Holocene ice-core record of the variability of methane, carbon dioxide, and S C02- (a) The methane record from ice cores in Greenland and Antarctica, showing significant variability including variability in the interpolar gradient (Chappellaz et al., 1997). (b) The results of a three-box model used to infer the latitudinal distribution sources of methane at four different time spans during the Holocene Epoch (Chappellaz et al., 1997). (c, d) The carbon dioxide concentration and its isotopic composition from Taylor Dome, Antarctica (Indermuhle et al., 1999). Note the dissimilarities among the trends in this figure (Raynaud et al. (2000) reproduced by permission of Elsevier from Quat. Set. Rev., 2000, 19, 9-17 (figure 1)).

---