This thesis makes several contributions to improve our understanding of the Neoproterozoic Paleobiology. In chapter 1, a comprehensive quantitative analysis of the Ediacara fossils indicates that the oldest Ediacara assemblage "the Avalon assemblage" already encompassed the full range of Ediacara morphospace. A comparable morphospace range was occupied by the subsequent White Sea and Nama assemblages, although it was populated differently. In contrast, taxonomic richness increased in the White Sea assemblage and declined in the Nama assemblage. The Avalon morphospace expansion mirrors the Cambrian explosion, and both may reflect similar underlying mechanisms. Chapter 2 describes problematic macrofossils collected from the Neoproterozoic slate of the upper Zhengmuguan Formation in North China and sandstone of the Zhoujieshan Formation in Chaidam. Some of these fossils were previously interpreted as animal traces. Our study of these fossils recognizes four genera and five species. None of these taxa can be interpreted as animal traces. Instead, they are problematic body fossils of unresolved phylogenetic affinities. Chapter 3 reports stable isotopes of the Zhamoketi cap dolostone atop the Tereeken diamictite in the Quruqtagh area, eastern Chinese Tianshan. Our new data indicate that carbonate associated sulfate (CAS) abundance decreases rapidly in the basal cap dolostone and δ34SCAS composition varies between +9â ° and +15â ° in the lower 2.5 m. In the overlying interval, CAS abundance remains low while δ34SCAS rises ~5â ° and varies more widely between +10â ° and +21â °. δ34Spy is typically greater than δ34SCAS measured from the same samples. We propose that CAS and pyrite were derived from two isotopically distinct reservoirs in a chemically stratified basin. Chapter 4 studies δ13C, δ18O, δ34SCAS, and δ34Spy of the Zhoujieshan cap carbonate that overlies the Ediacaran Hongtiegou glaciation. The Zhoujieshan cap dolostone shows positive δ13C values (0 â 1.7â °). δ34SCAS shows rapid stratigraphic variations from +13.9 to +24.1â °, probably due to relatively low oceanic sulfate concentrations. δ34Spy shows a steady stratigraphic trend. Thus, the δ34SCAS and δ34Spy trends are decoupled from each other. The decoupling of δ34SCAS and δ34Spy trends suggests that CAS and pyrite were derived from different sulfur pools, which were probably due to the postglacial basin stratification. / Ph. D.

Formaldehyde emissions from non-structural wood composites are regulated and the regulation target is urea-formaldehyde (UF) resin. UF resins are hydrolytically unstable and constantly emit formaldehyde as a function of temperature and relative humidity. When heated, wood also generates formaldehyde, but this was of little concern until 2010 when formaldehyde regulations became much more demanding. This regulation motivated the industry to account for all formaldehyde sources, synthetic as from resin, and biogenic as from wood. This effort represents first steps towards quantifying biogenic and synthetic contributions to formaldehyde emissions in non-structural wood composites. 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 product isotope ratios as a function of yield. If such isotope fractionation did not occur, it would be a simple matter to quantify contributions of wood and UF resin to formaldehyde emissions using static isotope ratios. Isotope fractionation, therefore, complicates the requirements for distinguishing biogenic and synthetic formaldehyde in wood composite emissions. Those requirements are 1) establish the reference carbon isotope ratios in wood and in UF resin (just the formaldehyde portion of UF), and 2) estimate the kinetic isotope effects in formaldehyde generation by wood and cured UF resin. The latter requirement fixes a range for the respective isotope ratios; the numerical ranges enable a simple model of the average isotope ratio for a mixture of biogenic and synthetic formaldehyde in wood composite emissions. Finally, the measured isotope ratio of captured emissions would be compared to the model. This work did not achieve all aspects of the requirements mentioned, but a solid foundation was established for future completion of the ultimate goals. In reference to requirement 1, the carbon isotope ratio of experimental Pinus taeda wood was accurately measured (including some isolated fractions) using isotope ratio mass spectroscopy (IRMS). IRMS of UF resin first requires removal of urea carbons- UF resin was subjected to acid hydrolysis and capture of the resin formaldehyde into aqueous ammonium hydroxide. This provided a nearly quantitative conversion (negligible isotope fractionation) of resin formaldehyde into hexamine for IRMS. Using this hexamine method, the formaldehyde carbon isotope ratios of two industrial UF resins were accurately measured, demonstrating basic feasibility for the project goal. Estimating the kinetic isotope effect (Requirement 2) required creation of a thermochemical reactor, where wood or cured UF resin was heated under N2 flow such that the emitted formaldehyde was easily captured. In this case, conversion of captured formaldehyde into hexamine was abandoned in favor of silica gel cartridges loaded with sodium bisulfite. Isolation and IRMS of the formaldehyde-bisulfite adduct were effective and considered easily transferable to industrial settings. This system was employed to measure fractionation in cured resin as a function of relative humidity, and in Pinus taeda wood as a function of relative humidity, temperature, and time. More information about isotope fractionation is required; but most notable was the fractionation behavior in wood where evidence was found for multiple formaldehyde generating reactions. Overall, this work established feasibility for the goals and laid the foundation for future efforts. / Master of Science / Home-interior products like cabinetry are often produced with wood composites adhesively bonded with urea-formaldehyde (UF) resin. UF resins are low cost and highly effective, but their chemical nature results in formaldehyde emission from the composite. High emissions are avoided, and the federal government has regulated and steadily reduced allowable emissions since 1985. The industry continuously improved UF technologies to meet regulations, as in 2010 when the most demanding regulations were implemented. At that time, many people were unaware that wood also generates formaldehyde; this occurs at very low levels but heating during composite manufacture causes a temporary burst of natural formaldehyde. Some wood types produce unusually high formaldehyde levels, making regulation compliance more difficult. This situation, and the desire to raise public awareness, created a major industrial goal: determine how much formaldehyde emission originates from the resin and how much originates from the wood. These formaldehyde sources can be distinguished by measuring the carbon isotope ratio, 13C/12C. This ratio changes and varies due to the kinetic isotope effect. Slight differences in 13C and 12C reactivity reveal the source as either petrochemical (synthetic formaldehyde) or plant-based (biogenic formaldehyde). This work demonstrates that achieving the industry goal is entirely feasible, and it provides the analytical foundation. The technical strategy is: 1) establish reference isotope ratios in wood and in UF resin, and 2) from the corresponding wood composite, capture formaldehyde emissions, measure the isotope ratio, and simply calculate the percentage contributions from the reference sources. However, a complication exists. When the reference sources generate formaldehyde, the respective isotope ratios change systematically in a process called isotope fractionation (another term for the kinetic isotope effect). Consequently, this effort developed methods to measure fractionation when cured UF resin and wood separately generate formaldehyde, with greater emphasis on wood. Isotope fractionation in wood revealed multiple fractionation mechanisms. This complexity presents intriguing possibilities for new perspectives on formaldehyde emission from wood and cured UF resin. In summary, this work demonstrated how source contributions to formaldehyde emissions can be determined; it established effective methods required to refine and perfect the approach, and it revealed that isotope fractionation could serve as an entirely novel tool in the materials science of wood composites.

No description available.

Algal/invertebratee ndosymbioseas re common in the marinee nvironmenta nd appeart o be nutritional in nature. The giant Tridacnid clams form a mutualistic extracellular endosymbiosis with dinoflagellate algae (zooxanthellae) of the species Symbiodiniunt microadriaticum. The large size of the Tridacnids is generally attributed to the nutritional role of their endosymbionts. This thesis examines the nature and mechanisms by which important biochemicals, such as lipids, are translocated from the symbionts to the host. Methodologies have been developed to enable the determination of the carbon isotope composition of individual saturated and polyunsaturated fatty acids to enable natural abundance isotopic variations in these compounds to be investigated in the Tridacnid-algal symbiosis. Compound specific isotope analysis of fatty acids in different species of Tridacnids, their zooxanthellae and non-symbiotic species reveal that several fatty acids are apparently directly translocated from algae to host. Evidence is presented for the synthesis of fatty acids from acetate by the clam. Carbon isotopic data also reveal that carbon limitation may play a role in lipid metabolsim in giant clams. Compound specific isotope analysis has also been used to investigate the contribution of translocated compounds during a diel cycle in clam haemolymph and reveals that concentrations of key metabolites vary over the diel cycle as a function of irradiance. The cyclic sugar alcohol scyllo-inositol was detected in clam haemolymph, which may be related to osmoregulation in the clam or to a signalling role in cell proliferation. Oxygen and carbon stable isotope compositions and strontium abundances of shell carbonate are examined in several clams subjected to varying degrees of phosphate and ammonium nutrient supplementation to investigate the relationship between growth rate and stable isotope compositions and strontium contents.

Earth’s climate can exist in many stable states that are vastly different from the modern climate state. Understanding modern and future climate requires a thorough understanding of the full range of possible climate states and the processes that trigger transitions between states. Quantitative reconstructions of past climate variables provide constrains on the magnitude, mechanisms and feedbacks involved in producing stable climate states. As such, they provide insights into past climate states unobservable today. This thesis focuses on quantifying three metrics of past climate systems: (a) quantitative rainfall amount, which provides means for assessing how the spatial distribution of rainfall changed in the past, (b) the isotopic composition of past rainwater (δP ), which provides means for understand- ing how atmospheric circulation changed in the past, and (c) relative humidity, which provides estimates of evaporative processes and hydrospheric fluxes. The regions studied are in the two far reaches of the Asian continent. In eastern Asia, changes in rainfall amount and δP over the past 125 ka were studied using geomorphological evidence from a closed basin lake in Inner Mongolia, China and compound-specific δDwax and δ13Cwax from organic molecules in lake sediments. In western Asia, the research focused on processes that govern modern δP and modern δDwax and δ13Cwax in soils. In addition the hydrological regime of the Eastern Mediterranean and the Levant during the Last Glacial Maximum were studied using evidence from speleothem δ18Oc and foraminifera δ18O. These records provide empirical and quantitative information about rainfall amount, δP and relative humidity at singular locations, and as such provide the building blocks for producing coherent large-scale reconstruction of the migration of rain-belts in the past.

This thesis investigates stable isotope signals (i.e. δ18O and δ2H) in various information carriers such as lake water and lacustrine sediments, aiming to develop and refine the use of isotope tracers in hydrology and paleohydrology studies. Located at the confluence of the Peace and Athabasca Rivers at the western end of Lake Athabasca, the PAD is a key node in the Mackenzie River Drainage system, the single large freshwater source discharging into the Arctic Ocean from continental Northern America. The delta is one of the world’s largest freshwater deltas, has hundreds of shallow lakes and wetlands, and has been regularly monitored for isotopic composition in surface water bodies over a 7-year period. Because of the hydrological significance of the delta, as well as the availability of a wealth of ancillary information collected by previous studies, the PAD serves as a natural laboratory to develop and refine the application of stable isotopes in understanding landscape hydrological conditions in present and past. The outcomes also provide critical information for the development of scientifically informed management strategies for water resources in the delta. In the study of modern processes, a novel coupled isotope tracer method was developed to characterize the isotopic composition of input water to lakes. The method is based on coupling the well-known Craig-Gordon model, which describes the evaporative enrichment process for both isotopes, with the Local Meteoric Water Line to constrain the isotopic composition of input water to lakes. The application of this method in two sampling campaigns (2000 and 2005) demonstrated significant temporal changes in source water to PAD lakes at landscape scale. The results also revealed the previously underestimated role of snowmelt to the northern part of the delta. In a laboratory culture experiment, effort was undertaken to understand the constant fractionation between aquatic cellulose and environmental water, which is routinely observed in field studies. This led to the development of a new conceptual characterization of the apparent cellulose-water relation that reconciles discrepancies among previous observations. This new interpretation supports the notion that oxygen in cellulose is fully inherited from CO₂during photosynthesis, but that aquarium studies may incorporate an unintended artefact from CO₂that has not undergone complete biochemically mediated exchange with water. The variable slope of the cellulose-water δ18O relation observed in culture experiments is attributed to varying degree of exchange, related to the residence time of CO₂in the water. This is in contrast to natural systems where long residence time of CO₂is likely to ensure full exchange, thus supporting the application of a constant apparent cellulose-water oxygen isotope fractionation in paleoenvironmental studies. Insights gained from these studies were applied in a multiproxy paleolimnological investigation of a shallow lake in the central part of the delta near the shoreline of Lake Athabasca. The Craig-Gordon modelling approach was applied to quantitative interpretation of a cellulose d18O record from lake sediments. Constraints provided by interpretation of other proxies allowed the development of a semi-quantitative assessment of changes in lake water balance over the past one thousand years. The inferred hydrological history indicated significant shifts in the source of water to the lake, including persistent influence from Lake Athabasca during the Little Ice Age (~ AD 1540-1880), as well as rapid change during the last century that is unprecedented in the last millennium. Overall, the thesis demonstrates our improved understanding of hydrological conditions based on various isotopic archives such as lake water and aquatic cellulose. New information acquired from these studies concerning the range and rate of hydrological variability in the present and past provides a fundamental baseline for evaluating the potential impacts of future climate change and human disturbance in the Peace-Athabasca Delta.

This thesis investigates stable isotope signals (i.e. δ18O and δ2H) in various information carriers such as lake water and lacustrine sediments, aiming to develop and refine the use of isotope tracers in hydrology and paleohydrology studies. Located at the confluence of the Peace and Athabasca Rivers at the western end of Lake Athabasca, the PAD is a key node in the Mackenzie River Drainage system, the single large freshwater source discharging into the Arctic Ocean from continental Northern America. The delta is one of the world’s largest freshwater deltas, has hundreds of shallow lakes and wetlands, and has been regularly monitored for isotopic composition in surface water bodies over a 7-year period. Because of the hydrological significance of the delta, as well as the availability of a wealth of ancillary information collected by previous studies, the PAD serves as a natural laboratory to develop and refine the application of stable isotopes in understanding landscape hydrological conditions in present and past. The outcomes also provide critical information for the development of scientifically informed management strategies for water resources in the delta. In the study of modern processes, a novel coupled isotope tracer method was developed to characterize the isotopic composition of input water to lakes. The method is based on coupling the well-known Craig-Gordon model, which describes the evaporative enrichment process for both isotopes, with the Local Meteoric Water Line to constrain the isotopic composition of input water to lakes. The application of this method in two sampling campaigns (2000 and 2005) demonstrated significant temporal changes in source water to PAD lakes at landscape scale. The results also revealed the previously underestimated role of snowmelt to the northern part of the delta. In a laboratory culture experiment, effort was undertaken to understand the constant fractionation between aquatic cellulose and environmental water, which is routinely observed in field studies. This led to the development of a new conceptual characterization of the apparent cellulose-water relation that reconciles discrepancies among previous observations. This new interpretation supports the notion that oxygen in cellulose is fully inherited from CO₂during photosynthesis, but that aquarium studies may incorporate an unintended artefact from CO₂that has not undergone complete biochemically mediated exchange with water. The variable slope of the cellulose-water δ18O relation observed in culture experiments is attributed to varying degree of exchange, related to the residence time of CO₂in the water. This is in contrast to natural systems where long residence time of CO₂is likely to ensure full exchange, thus supporting the application of a constant apparent cellulose-water oxygen isotope fractionation in paleoenvironmental studies. Insights gained from these studies were applied in a multiproxy paleolimnological investigation of a shallow lake in the central part of the delta near the shoreline of Lake Athabasca. The Craig-Gordon modelling approach was applied to quantitative interpretation of a cellulose d18O record from lake sediments. Constraints provided by interpretation of other proxies allowed the development of a semi-quantitative assessment of changes in lake water balance over the past one thousand years. The inferred hydrological history indicated significant shifts in the source of water to the lake, including persistent influence from Lake Athabasca during the Little Ice Age (~ AD 1540-1880), as well as rapid change during the last century that is unprecedented in the last millennium. Overall, the thesis demonstrates our improved understanding of hydrological conditions based on various isotopic archives such as lake water and aquatic cellulose. New information acquired from these studies concerning the range and rate of hydrological variability in the present and past provides a fundamental baseline for evaluating the potential impacts of future climate change and human disturbance in the Peace-Athabasca Delta.

Detailed mechanistic studies were conducted on several organic reactions that exhibit product selectivity (regio-, peri-, or enantioselectivity). The organic reactions studied were electrophilic aromatic substitutions, Diels-Alder cycloadditions of 1,3- dienes with cyclopentadieneone, Lewis acid catalyzed ene reactions with olefins, chlorinations of alkynes, and the enantioselective intramolecular Stetter reaction. Analyses of these systems were conducted by measurement of kinetic isotope effects, standard theoretical calculations, and in some cases dynamic trajectories. Mechanistic studies of electrophilic aromatic substitution, Lewis acid catalyzed ene reaction with olefins, the chlorination of alkynes, and the Diels-Alder cycloadditions of 1,3-dienes with cyclopentadienones, suggest that the origin of selectivity is not always a result of selectivity result from a kinetic competition between two closely related pathways to form distinct products. All of these systems involve one transition state on a potential energy surface that bifurcates and leads to two distinct products. In these systems, experimental kinetic isotope effects measured using natural abundance methodology, theoretical modeling of the potential energy surfaces, and trajectory analyses suggests that selectivites (regio- and periselectivities) are a result of influences by momenta and steepest-descent paths on the energy surface. The work here has shown that in order to understand selectivity on bifurcating surfaces, transition state theory is not applicable. In place of transition state energetics, the guiding principles must be those of Newtonian dynamics. In the mechanistic studies for the enantioselective intramolecular Stetter reaction, the origin of selectivity is a result of multiple transition states and their relative energies. Experimental H/D kinetic isotopes effects had lead to the conclusion that two different mechanisms were operating for reactions where carbenes were generated in situ versus reactions using free carbenes. However, 13C kinetic isotope effects and theoretical modeling of the reaction profile provide evidence for one mechanism operating in both cases.

In light of recent studies that show oxygen isotope fractionation in carbonate minerals to be a function of HCO3 2-; and CO3 2- concentrations, the oxygen isotope fractionation and exchange between water and components of the carbonic acid system (HCO3 2-, CO3 2-, and CO2(aq)) were investigated at 15, 25, and 40 (degrees)C. To investigate oxygen isotope exchange between HCO3 2-, CO3 -2, and H2O, NaHCO3 solutions were prepared and the pH was adjusted over a range of 2 to 12 by the addition of small amounts of HCl or NaOH. After thermal, chemical, and isotopic equilibrium was attained, BaCl2 was added to the NaHCO3 solutions. This resulted in immediate BaCO3 precipitation; thus, recording the isotopic composition of the dissolved inorganic carbon. Data from experiments at 15, 25, and 40 (degrees)C (1 atm) show that the oxygen isotope fractionation between HCO3 2-; and H2O as a function of temperature is governed by the equation: 1000 ;HCO3--H2O = 2.66 + 0.05(106T-2) + 1.18 + 0.52. where is the fractionation factor and T is in kelvins. The temperature dependence of oxygen isotope fractionation between CO32 and H2O is 1000 CO32--H2O = 2.28 + 0.03(106T-2) - 1.50 + 0.29. The oxygen isotope fractionation between CO2(aq) and H2O was investigated by acid stripping CO2(aq) from low pH solutions; these data yield the following equation: 1000 CO2(aq)-H2O = 2.52 + 0.03(106T-2) + 12.12 + 0.33. The kinetics of oxygen isotope exchange were also investigated. The half-times for exchange between HCO3- and H2O were 3.6, 1.4, and 0.25 h at 15, 25, and 40 (degrees)C, respectively. The half-times for exchange between CO2 and H2O were 1200, 170, and 41 h at 15, 25, and 40 (degrees) C, respectively. These results show that the 18O of the total dissolved inorganic carbon species can vary as much as 17 at a constant temperature. This could result in temperature independent variations in the 18O of precipitated carbonate minerals, especially in systems that are not chemically buffered.

Thesis (M.Sc.)--College of William and Mary. / Vita. Includes bibliographical references.