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Showing 1 to 20 of 20 for “"Fractionation factors"”.
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Oxygen and Hydrogen Isotopic Fractionation Factors Determined in Experimental Clay-Water Systems
Made available in DSpace on 2014-12-14T07:10:54Z (GMT). No. of bitstreams: 1 7915378.pdf: 3168865 bytes, checksum: d709693b3b9b193a5b4f3eac2831364a (MD5) Previous issue date: 1979
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A revised monod-type rate law predicting variable sulfur isotope fractionation factors as a function of microbial sulfate reduction rate
… minimum ( 1 = 0.998) and maximum ( 2 = 0.930) fractionation factors and (2) a rate-controlling electron donor factor (DF). These parameters constrain a model which produced realistic predicted shifts in the apparent fractionation factor ( obs) as a function of reduction rate in an electron …
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Dominant substrates used by methanogens in hypersaline environments
… at all of the Guerrero Negro sites. Apparent fractionation factors were calculated to determine if they could be used to predict dominant substrates of hypersaline methanogenesis. Because TMA and MeOH were used, apparent fractionation factors were expected to be high and in the range of 1.04 …
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Selenium Stable Isotope Ratios in Wetlands: Insights Into Biogeochemical Cycling and How a Diffusive Barrier Affects the Measured Fractionation Factor
… reduction, sorption, and assimilation. Isotope fractionation studies can potentially distinguish reduction from other removal processes, and possibly quantify the amount of reduction, assuming that the correct isotope fractionation factor, alpha, is applied. Typically, alpha is determined under …
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Application of Hydrogen and Oxygen Isotope Ratios of Water to the Study of Evaporation, Palaeoclimate, and Ancient Marine Conditions
… is achieved by experimentally determining the fractionation factors between amorphous Mg-silicate and the water from which it precipitates. This is followed by calculating the fractionation factors as these precipitates undergo synthetic metamorphism to true talc. Isotopic measurements from …
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The geochemistry of methane isotopologues
… from knowledge of 13C/12C and D/H isotope fractionation factors alone.
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Uranium isotopic fractionation induced by U(VI) adsorption onto common aquifer minerals
… and field studies finding a ~1‰ isotopic fractionation with the U(IV) product enriched in 238U. However, the isotopic fractionation produced by adsorption may complicate the use of 238U/235U to trace microbial reduction. A previous study found that adsorption of U(VI) onto Mn oxides …
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The geochemistry of methane isotopologues
… from knowledge of ¹³C/¹²C and D/H isotope fractionation factors alone.
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The Biogeochemistry of Carbon Isotopes in Local Lakes
… of DIC would require precise knowledge of fractionation factors associated with algal species and other biological and physicochemical factors, such as pH, temperature, and cell growth rate.
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Trace Elements and Sulfur Isotope Variations in Endowed and Non-Endowed Porphyry Systems of the Dawson Range Mineral Belt, Yukon Territory
… the endowment criteria of mineral deposits, as fractionation factors are subject to changing conditions throughout the ore system's geological history. Understanding the regional zonation of δ34S can be a useful complementary tool in refining exploration findings, particularly when combined with …
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Isotopic fractionation of chromium and uranium during abiotic and microbial Cr(VI) reduction and microbial U(VI) reduction
… a redox-indicator. The magnitude of the isotopic fractionation must be determined to connect observed Cr isotope ratios to the extent of reduction. This study determines the Cr isotopic fractionation factors for Cr(VI) reduction by Fe(II) phases (Fe(II-doped goethite, FeS, green rust, siderite and …
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Isotope Systematics of Gypsum and its Hydration Water
… the calculation of the gypsum-water isotope fractionation factors, and the application of the method to constrain the palaeohydrologic conditions in two temporally and geographically disparate sites. Measurement of the isotopic composition of gypsum hydration water is used to examine the …
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The dynamics of ¹³C in several New Zealand lakes
… enough to affect. photosynthetic carbon isotopic fractionation, and hence plankton 𝜹¹³C values. The enrichment of ¹³C in the dissolved inorganic carbon (DIC) pool during periods of high photosynthetic productivity also affects plankton 𝜹¹³C values. Analysis of diurnal changes in 𝜹¹³C and DIC …
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Spatially controlled Fe isotope variations at Torres Del Paine
… Likewise, experimentally determined equilibrium fractionation factors argue against fractional crystallization producing the isotopically heavy granites. Loss of a magnetite equilibrated Fe-bearing fluid would enrich the high silica granites in isotopically heavy Fe; however, the need for …
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Oxygen isotopes in diatom silica : a new understanding of silica-water oxygen isotope fractionation in diatom frustules and an application of diatom d180 values as a record of paleohydrologic variability in a middle-Pleistocene lacrustine core from the Valles Caldera, New Mexico
… The frustules display a constant silica-water fractionation over the measured temperature range (5.1 to 37.8°C) regardless of species. This relationship is in close agreement with other published silica-water fractionation factors for laboratory cultured diatom samples; however, it is as much …
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Petrology and geochemistry of Sangeang Api and recent volcanism in the Sumbawa-Flores sector of the Sunda Arc: the response of along-arc geochemistry to subduction processes.
… = 0.109‰ ±0.066). Using published fractionation factors, it is shown that whilst magnetite mineral separates records equilibrium compositions (mean δ⁵⁷Fe = 0.142‰ ±0.072), Fe-Mg silicate mineral separates display significant disequilibrium in their compositions (mean δ⁵⁷Feoliv = …
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Theory and Utility of the Three Isotope Fractionation Relationship
… scales with the 18O-16O relationship through a fractionation processes and is thought to not provide any new information. However, the discovery of large “mass independent” isotope effects for ozone chemistry has driven a multitude of uses for triple isotope relationships. Triple stable isotope …
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Dynamics of soil processes under extreme meteorological boundary conditions - response of below-ground carbon, sulfur, and iron cycling in fen soils
… peat to responsible for this observation. These factors could support a local depletion of alternative electron acceptors and methanogenesis could thus occur in locally distinct micro-environments. The analysis of the isotopic composition of the dissolved CO2 and the methane produced suggested …
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Emerging stable isotope techniques in hydrothermal research: new methods applied to carbonates and hydrous minerals in ore deposits and geothermal fields
… (Chapter 4). Intramineral oxygen isotope fractionation values in kaolinite and muscovite, determined by comparison of δ18OOH measured by TD-OA-ICOS with δ18Osilicate measured by fluorination, are similar to existing constraints. Refinement of this approach should be carried out to test the …
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A geochemical and stable isotope study of some rocks from the Bandelierkop formation, southern marginal zone of the Limpopo Belt, South Africa( vol.1 Text)
… a similarity in mineral-mineral stable isotope fractionation factors is observed for all the pelitic rocks, including the orthoamphibole gneisses found immediately south of the orthopyroxene isograd. These features preclude the presence of pervasive fluid infiltration after peak metamorphism. …