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 60 for “"Oxygen isotopes"”.
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Oxygen Isotopes as a Tracer of DOM Processes in River-Estuary Systems
… organic matter (DOM) in natural waters, stable isotopes are used to provide insight into both the sources of DOM and the processes affecting its alteration. Through the research presented here, oxygen isotopes are incorporated into the study of DOM through the adaptation of a pyrolysis elemental …
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Constructing a High-Resolution Record of Silurian Paleoclimate Using Carbonate Oxygen Isotopes
The collection of δ¹⁸O data from carbonates provides insight into the temperature of Earth millions of years ago. Paleozoic δ¹⁸O records are currently compiled from brachiopod fossils because of their resistance to diagenetic alteration, but this data is relatively sparse and not well …
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Oxygen isotopes as a tracer of biospheric CO2 gross fluxes : a local feasibility study
Quantitative knowledge of gross biospheric CO2 fluxes is crucial in atmospheric carbon cycle budgeting, especially in view of unknown biospheric feedback mechanisms to an increasing atmospheric CO2 mixing ratio or to temperature changes. The 18O/16O ratio of CO2 has the potential to separate …
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Assessment of oxygen sources and sinks in the northern Gulf of Mexico using stable oxygen isotopes
… biological and physical processes that control oxygen dynamics. Yet, based on oxygen concentration measurements alone, it is difficult to separate the effects of biological factors from physical factors. To address this problem, I used a dual budget approach to assess the importance of oxygen …
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Triple oxygen isotopes and oxygen/argon ratio measurements to enhance coastal and open ocean production/respiration comparisons
… study presents in situ measurements of gross oxygen production (G) derived from triple oxygen isotope analysis and of net community oxygen production (N) derived from O2/Ar ratios at station L4, which is part of the Western English Channel Observatory (WECO) and a latitudinal transect through …
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Interpreting Early Triassic (Smithian) sea-level change and climate using sequence stratigraphy and oxygen isotopes of conodont apatite
… was likely eustatic. Samples were collected for oxygen isotopic analyses of conodont apatite from the two field locations (in Utah) in a sequence stratigraphic framework to better understand the Smithian paleoclimate. Due to an up to ~1.5 ° disparity of values between the two locations, …
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Ecosystem metabolism in salt marsh tidal creeks and ponds : applying triple oxygen isotopes and other gas tracers to novel environments
… thesis describes new methods to apply the triple oxygen isotope tracer of photosynthetic production in a salt marsh. Additionally, noble gases are applied to constrain air-water exchange processes which affect metabolism tracers. These stable, natural abundance tracers complement traditional …
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New evidence for complex mosasaur paleobiology: oxygen isotopes in enamel reveal habitat variation of clidastes from the Mooreville Chalk, Alabama
… temporal resolution. By analyzing the oxygen isotope composition of enamel phosphate in eight consecutive, fully erupted teeth, I reconstruct the ecological niche of a Clidastes propython individual from the Mooreville Chalk in Pickens County, Alabama. The isotopic record is then …
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Sulfur, carbon, and oxygen isotopes of coexisting sulfides and carbonates in gas and oil seeps from the Gulf of Mexico
… and isotope measurements of carbon and oxygen by isotope ratio mass spectrometry (IRMS) in coexisting carbonates from 5 sites (GC-140, GC-185, GC-272, MC-929, and GB-382) in the GOM. Pyrite grains (FeS₂) yield variable δ³⁴S values and are considerably more ³⁴S-depleted in seeps with …
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Ecosystem metabolism in salt marsh tidal creeks and ponds : applying triple oxygen isotopes and other gas tracers to novel environments
… thesis describes new methods to apply the triple oxygen isotope tracer of photosynthetic production in a salt marsh. Additionally, noble gases are applied to constrain air-water exchange processes which affect metabolism tracers. These stable, natural abundance tracers complement traditional …
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Investigating evidence of high frequency glacial eustacy in the Lower Mississippian (Tournasian) Lodgepole Formation of southwest Montana : insights from conodont oxygen isotopes
… of southwest Montana. We combined conodont-oxygen isotopes (δ18Oapatite¬) and carbonate-carbon isotopes (δ13Ccarb) with cyclostratigraphy of Woodhurst cycles to test the hypothesis that the cycles developed in response to glacial eustasy, evaluate the timing and initiation of the Late …
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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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Geology and isotope geochemistry of the Beaver-Temiskaming Silver Mine, Cobalt, Ontario
… Depositional temperatures were about 210-240°C (oxygen isotopes in silicates), 211-258°C (arsenopyrite composition) and 130-227°C (coexisting sulphides). Carbonate isotopic data were reset by meteoric water. Connate waters, interpreted from fluid inclusion data, equilibrated with Archean …
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Analysis of calcite-filled faults in carbonate strata, balcones trend near Waco, Texas.
… dips across the stronger strata. Carbon stable isotopes in 174 samples indicate that the water from which the calcite precipitated is formation water and not meteoric water, while oxygen isotopes indicate that precipitation of secondary calcite in the fault cores occurred between 48° and 110°C. …
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Climate and habitat reconstruction of hominid sites in northern China with paleosol stable isotopes
… geochemistry of paleosols, including carbon isotopes of soil organic matter and pedogenic carbonates, and oxygen isotopes of pedogenic carbonates, can provide evidences for tree:grass ratios, air surface temperature and soil moisture conditions. These data can also help resolve disagreements …
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Rates of natural climate change : a study of speleothems
… caves. The start of growth, growth rate, oxygen isotopes, carbon isotopes and luminescence intensity in two speleothems from southern Ireland provide high-resolution records of rapid palaeoclimate changes in that region during the Late Glacial. Several of these palaeoclimate proxies appear …
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Investigation of the Oxygen Isotope Exchange Between Carbon Dioxide and O3 via O(1D)
… shows an increasing enrichment in the heavy oxygen isotopes with altitude which preferential enrichment for 17O according to d17O =1.7 d18O. This is contrary to tropospheric CO2 where d17O ~ 0.5d18O. These isotope enrichments are transferred from O3 into CO2, but details of the mechanism are …
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Integrated approach to solving reservoir problems and evaluations using sequence stratigraphy, geological structures and diagenesis in Orange Basin, South Africa
… spectroscopy (EDS), and stable carbon and oxygen isotopes geochemistry to determine the diagenetic alteration at deposition and post deposition in the basin. The shale samples were subjected to Rock-Eval pyrolysis and accelerated solvent extraction (ASE) prior to gas chromatographic (GC) …
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Deciphering isotopic signals of monsoon-induced upwelling in foraminifera from the Western Arabian sea sediment trap
… measured for shape, and analyzed for carbon and oxygen isotopes to document how each species responded to phases of the upwelling system, and to determine the utility of these planktonic foraminifera as upwelling indicators. The oxygen isotopic composition of the two thermocline dwellers remained …
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