Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 62 for “"isotope fractionation"”.
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Hydrogen isotope fractionation in ammonia-oxidizing archaea
… years, the potential of the hydrogen stable isotope composition (δ2H) signature of isoprenoid glycerol dibiphytanyl glycerol tetraether (GDGT) membrane lipids of ammonia-oxidizing archaea (class Nitrososphaeria) as a novel palaeohydrological proxy has gained increasing attention. This PhD …
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Theory and Utility of the Three Isotope Fractionation Relationship
The field of isotope geochemistry began with the study of oxygen isotope geothermometry, most famously for carbonates. Traditionally oxygen isotope studies are only concerned with the relationship between one rare isotope, oxygen-18, and the common isotope, oxygen-16. In these cases, the abundance …
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Mass-independent sulfur isotope fractionation during photochemistry of sulfur dioxide
Mass-independent sulfur isotope signatures are observed in Archean and early Paleoproterozoic sedimentary sulfate and sulfide minerals, and provide the most robust constraints on early atmospheric oxygen levels. Smaller mass-independent sulfur isotope anomalies are observed in ice cores and …
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Physiology of multiple sulfur isotope fractionation during microbial sulfate reduction
… and produces sulfide that is depleted in heavy isotopes of sulfur relative to starting sulfate. The fractionation of S-isotopes is commonly used to trace the biogeochemical cycling of sulfur in nature, but a mechanistic understanding of factors that control the range of isotope fractionation is …
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Chromium and uranium isotopic exchange kinetics and isotope fractionation during oxidation of tetravalent uranium by dissolved oxygen
Chromium (Cr) and Uranium (U) isotopes (53Cr/52Cr and 238U/235U ratios) are very powerful new geochemical tools in environmental remediation and paleoredox reconstruction studies. Correctly interpreting Cr and U isotopic compositions in groundwater and sed- imentary rock samples requires thorough …
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A revised monod-type rate law predicting variable sulfur isotope fractionation factors as a function of microbial sulfate reduction rate
… is associated with characteristic sulfur isotope partitioning, which can serve as a proxy for the rate of this reactivity in a wide variety of reducing environments. We demonstrate a new model for this functional relationship through the use of a modified Monod-type rate expression …
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Oxygen and sulfur isotope fractionation by acidithiobacillus ferrooxidans during aerobic and anaerobic oxidation of copper sulfide minerals under simulated acid mine drainage conditions
Includes bibliographical references (pages 86-94).
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Investigating Controls on Variation in Isotopic Fractionation during Biodegradation of Chlorinated Ethenes and Ethanes
Kinetic isotope effects occur due to different reaction rates for light and heavy isotope-containing molecules, and are controlled by the bonds broken during degradation. For many primary pollutants, stable carbon, hydrogen, and chlorine isotope effects have been found to fit a Rayleigh model, …
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Selenium and Chromium Stable Isotopes and the Fate of Redox-Active Contaminants in the Environment
… of this study, I developed the chromium stable isotope system as a biogeochemical indicator and monitoring tool. After initial work designing the techniques, I measured chromium stable isotope fractionation in laboratory experiments and natural waters. I observed that the products of Cr(VI) …
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The production and fate of nitrogen species in deep-sea hydrothermal environments
… in concentrations. This thesis applies stable isotope approaches to further constrain the sources and fate of N-species in deep-sea vents across a variety of geological settings. First, I discuss isotope fractionation and reaction kinetics during abiotic reduction of nitrate (NO₃⁻) to ammonium …
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Using Silicon Isotopes to Trace the Biogenic Silica in the Southern Ocean
… silica (bSi) frustules. The use of stable isotopes and physicochemical factors (temperature, light, and trace metal) provides a promising method for understanding how Si and C fluxes will change in response to future climate change. The Si cycle in the Southern Ocean was investigated using …
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Using Silicon Isotopes to Trace the Biogenic Silica in the Southern Ocean
… silica (bSi) frustules. The use of stable isotopes and physicochemical factors (temperature, light, and trace metal) provides a promising method for understanding how Si and C fluxes will change in response to future climate change. The Si cycle in the Southern Ocean was investigated using …
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A heavy stable isotope approach to tracing mantle source and process
… part of this variability. Recently, heavy stable isotopes have been suggested as a new tool to complement existing tracers of mantle heterogeneity and lithology (e.g., major and trace elements, radiogenic isotopes), because mineral- and redox-specific equilibrium stable isotope fractionation …
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Isotope ratios in source determination of formaldehyde emissions
… It is possible to distinguish the 13C/12C isotope ratio of UF resins from the isotope ratio of plant biomass. Conditions during and after composite hot-pressing promote reactions that generate formaldehyde from wood and UF resin, and the kinetic isotope effect continuously lowers the …
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Exploring the contributions of liquid-phase sulfur chemistry to the mass-independent sulfur fractionation of the Archean rock record
Archean sulfur mass-independent fractionation (S-MIF) has been widely recognized as one of the strongest indicators for the rise of atmospheric oxygen in the Early Proterozoic. A decade after its discovery, the wide-ranging implications of Archean sulfur MIF have been discussed extensively and …
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The marine biogeochemistry of zinc isotopes
Zinc (Zn) stable isotopes can record information about important oceanographic processes. This thesis presents data on Zn isotopes in anthropogenic materials, hydrothermal fluids and minerals, cultured marine phytoplankton, natural plankton, and seawater. By measuring Zn isotopes in a diverse array …
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Modeling Departures From Abiotic Expectations During the Calcium Carbonate Precipitation Process
… influences on CaCO3 mineralization and isotope fractionation by: performing kinetic experiments directly within a modern carbonate spring; determining the carbon and oxygen isotopic composition of aragonite and coexisting spring water; and modeling these experimental results to establish …
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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
I present oxygen isotope data from modern diatom frustules that were collected from freshwater systems in the Jemez Mountains of northern 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 …
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The marine biogeochemistry of zinc isotopes
Zinc (Zn) stable isotopes can record information about important oceanographic processes. This thesis presents data on Zn isotopes in anthropogenic materials, hydrothermal fluids and minerals, cultured marine phytoplankton, natural plankton, and seawater. By measuring Zn isotopes in a diverse array …
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