Carbon isotopes, studies

Concerns over atmospheric methane as a greenhouse gas and the large contribution of biomethanogenesis as a source of this gas make it important to determine the relative significance of various components of this activity. A recent paper (8) summarized estimates (28-30) of source fluxes of atmospheric methane based on several carbon isotopic studies and presented new data on natural sources and biomass burning. These data (Table III) show that of a total flux of 594 million tons (Tg) per year, 83% is produced via biomethanogenesis from a combination of natural (42%) and anthropogenic (41%) sources. 

Stable carbon isotope studies of Swartkrans fossils. In C.K. Brian, ed., Swartkrans, A... 

Marbles occur in many regional and contact metamorphic terrains in the world and isotopic studies of marbles have been carried out and report by many authors. Carbon isotope studies of marbles can be useful, in many cases, to reveal the origin of carbonates because differences in carbon isotope ratios of marbles can reflect different origins. 

Mechanisms by Carbon Isotope Studies, in Isotopic and Cosmic Chemistry, North Holland, Amsterdam, 1964. 

Rodelli et al. (198 ) recently reported the first stable carbon isotope study of a mangrove community. They obtained good separation of the primary producers, with... 

Palmer, S. M., D. Hope, M. F. Billet, J. J. C. Dawson, and C. L. Bryant. 2001. Sources of organic and inorganic carbon in a headwater stream Evidence from carbon isotopic studies. Biogeochemistry 52 321—338. 

Rounick, J. S., M. J. Winterbourn, and G. L. Lyon. 1982. Differential utilization of allochthonous and autochthonous inputs by aquatic invertebrates in some New Zealand streams A stable carbon isotope study. Oikos 39 191—198. 

Cachier, H., Buat-Menard, P., Fontugne, M. and Chesselet, R. (1986) Long range transport of continentally derived carbon in the marine atmosphere evidence from stable carbon isotope studies. Tellus, 38,161-177. 

Unfortunately, equations (3.19) and (3.20), although the best currently available for the data, can only be considered tentative. The weakness lies in the temperature dependence. As mentioned earlier, it is not known whether the results reflect a temperature dependence or a change in the proportion of aragonite to calcite. Another shortcoming in this relationship is that the temperature range of the experiments, 20° to 63°C (if Baertschi s data are included), is well above the temperature at which many organisms secrete carbonate. Because benthic foraminifera have proved very useful in carbon isotopic studies, it is important to have carbon isotopic equilibrium defined over their temperature range. 

Regional aquifers consist, in certain cases, of a recharged outcrop of a conductive rock layer that dips below other rocks and is thus partially confined (section 2.8). Occasionally, wells tap only the confined section of such an aquifer, but in other cases wells also exist in the recharge area. In such systems carbon isotope studies are relevant for... 

Pearson D. G., Davies G. R., Nixon P. H., and Mattey D. P. (1991b) A carbon isotope study of diamond facies pyroxenites and associated rocks from the Beni Bousera peridotite, north Morocco. In Orogenic Lherzolites and Mantle Processes, Spec. Vol. J. Petrol, (eds. M. A. Menzies, C. Dupuy, and A. Nicolas). Oxford University Press, Oxford, UK, pp. 175-189. 

Carbon isotopic studies alone are not able to resolve the source of such carbon isotopic variability and the relative importance of these competing models. Thus, current approaches are to combine carbon isotopic studies with nitrogen abundance, aggregation, isotopic composition and even age determinations on the same diamonds (e.g., Hauri et al, 1999, 2002). 

Magaritz M. and Taylor H. P., Jr. (1976) Oxygen, hydrogen, and carbon isotope studies of the Franciscan Formation Coast Ranges, California. Geochim. Cosmochim. Acta 40, 215-234. 

Baud A., Magaritz M., and Holser W. T. (1989) Permian-Triassic of the Tethys, carbon isotope studies. Geol. Rundsch. 78, 649-677. 

Sackett W. M. (1989) Stable carbon isotope studies on organic matter in the marine environment. In Handbook of Environmental Isotope Geochemistry (eds. P. Fritz and J. C. Fontes). Elsevier, Heidelberg, vol. 3, pp. 139-169. 

Hartgers W. A., Sinninghe Damste J. S., Requejo A. G., Allan J., Hayes J. M., Ling Y., Tiang-Min X., Primack J., and de Leeuw J. W. (1993) A molecular and carbon isotopic study towards the origin and diagenetic fate of diaromatic carotenoids. Org. Geochem. 22, 703-725. 

Oehler, D.Z., Schopf, J.W. and Kvendolden, K.A., 1972. Carbon isotopic studies of orgemic matter in Precambrian rocks. Science, 175 1246—1248. 

The techniques used in carbon isotope studies by Abell and Yong were described by Abell et al. (1985). Carbonates (around 120 samples) were analysed by conventional reaction with phosphoric acid. Kerogen (around 250 samples) was extracted with concentrated HCl, rinsed with deionized water and a 5 2 mixture of concentrated HF-HCl (Yong, unpubl. data). 

Although the bulk of cations are derived by carbonate dissolution in soil and epikarst, carbon isotope studies indicate that the bulk of carbon is derived from organic sources dripwaters and modem speleothems typically have 80-95% modem carbon (Genty et al., 2001a). In Drake s (1983) coincident system (open system of section 7.4.2), most dead carbon from aquifer dissolution diffuses out of the soil as C02 into the atmosphere. 

R. Benner, M.L. Fogel, E.K. Sprague, R.E. Hudson (1987) Depletion of C in lignin and its implications for stable carbon isotope studies. Nature 329, 708-710... 

In 1996, Mojzsis et al. reported a new carbon isotope study of the Isua rocks. Instead... 

Schouten S., Schoell M., Rijpstra W.I.C., Sinninghe Damste J.S., de Leeuw J.W. (1997) A molecular stable carbon isotope study of organic matter in immature Miocene Monterey sediments, Pismo basin. Geochim. Cosmochim.Acta... 

Mazeas, L, Budzinski H (2002) Stable carbon isotopic study (12C/13C) of the fate of petrogenic PAHs (methylphenanthrenes) during an in-situ oil spill simulation experiment. Org Geochem 33, 1253-1258. 

Melchiorre EB, Criss RE, Rose TP (1999) Oxygen and carbon isotope study of natural and synthetic malachite. Econ Geol 94 245-259... 

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