Organic reactions are systematically examined experimentally and theoretically to determine the role dynamics plays in the outcome of the reaction. It is shown that trajectory studies are of vital importance in understanding reactions influenced by dynamical motion. This dissertation discusses how a combination of kinetic isotope effects, theoretical calculations, and quasiclassical dynamics trajectories aid in the understanding of the solvolysis of p-tolyldiazonium cation in water, the cycloadditions of cyclopentadiene with diphenylketene and dichloroketene, and the cycloaddition of 2- methyl-2-butene with dichloroketene. In the solvolysis of p-tolyldiazonium cation, significant 13C kinetic isotope effects are qualitatively consistent with a transition state leading to formation of an aryl cation, but on a quantitative basis, the isotope effects are not adequately accounted for by simple SN1 heterolysis to the aryl cation. The best predictions of the 13C isotope effects for the heterolytic process arise from transition structures solvated by clusters of water molecules. Dynamic trajectories starting from these transition structures afford products very slowly. The nucleophilic displacement process for aryldiazonium ions in water is determined to be at the boundary of the SN2Ar and SN1 mechanisms. The reaction of cyclopentadiene with diphenylketene affords both [4 + 2] and [2 + 2] cycloadducts directly. This is surprising. There is only one low-energy transition structure for adduct formation. Investigation of this reaction indicates that quasiclassical trajectories started from a single transition structure afford both [4 + 2] and [2 + 2] products. Overall, an understanding of the products, rates, selectivities, isotope effects, and mechanism in these reactions requires the explicit consideration of dynamic trajectories.

Thesis (Ph.D.) -- Macquarie University, School of Earth Sciences, 1996. / "September, 1995" Bibliography: leaves 171-183.

This study investigates the isotopic signatures of human skeletal remains that were recovered from several sites along the coast and inland in the north-central Patagonian region of Argentina. Human skeletal remains, dating from 2500 BP through the early historic period, are examined to determine the relative significance of terrestrial and aquatic food resources and subsequently, the extent to which coastal food resources were exploited by indigenous Argentinians. Carbon and nitrogen isotopes contained within human bone collagen and apatite are measured quantitatively to determine the relative significance of marine and terrestrial foods. This study, one of the first isotopic studies of indigenous diet on the Atlantic coast of Argentina, is significant because it provides initial results to be used for the reconstruction of aboriginal subsistence patterns prior to and after European contact.

During the Medieval period of Denmark, economic and trade relations grew inter-regionally, with culture, ideas, and products being transferred on a more regular basis through the 11th to 13th centuries. Beginning around 1050 AD and lasting until AD 1536, the country faced drastic climatic changes, shifting economic and agricultural practices, and disease outbreaks (most notably the bubonic plague). The current study seeks to investigate mobility during this period from two medieval cemeteries around Horsens, Denmark: the rural site of Sejet and the urban site of Ole Wormsgade, both used throughout the 12th to 16th centuries. A previous isotopic analysis using oxygen indicated that some movement was seen at these sites, with three individuals identified as potential migrants from other Scandinavian regions. This study compares the existing oxygen isotopic data with variations in 87Sr/86Sr ratios from these samples. Such ratios represent local bedrock baselines of strontium, which are slightly different between eastern and western Denmark. ICP-MS was used to measure 87Sr/86Sr ratios, and results are interpreted in the context of climatic changes and shifting socioeconomic practices. The results suggest that longer-distance movements into Denmark were seen during the Early Medieval Period. The potential migrant identified in this research points to movement towards the rural population at Sejet, and could possibly connect this migration with marriage rules influencing immigration at the time. This research demonstrates that movement during the medieval period of Denmark was a complex, dynamic, and multilinear process during a time of increasing urbanization. / October 2015

Microbes, including Bacteria, are globally important mediators of elemental transformations in the marine water column, but not until recently has their biomass been suggested to contribute significantly to carbon export flux. Here I characterize lipid and carbon isotopic signatures in marine particulate organic matter (POM) explicitly at microbial size scales, and I quantitatively explore how these signatures are transferred down the water column. In the North Pacific Subtropical Gyre (NPSG) an isotopically-enriched pool of submicron POM appears to dominate export to mesopelagic depths, supporting recent observations that bacterioplankton communities contribute to export flux in proportion to their biological abundance. In the Eastern Tropical North Pacific (ETNP) complex pathways emerge for the flux of POM to the deep ocean. I use the largest data set to date for natural \(^{13}C\) signatures of individual water column lipids to reveal that submicron and larger-size suspended POM size classes are isotopically distinct. Results point to de novo production of lipids above and within the oxygen minimum zone. I develop quantitative models to deconvolve the signatures of sinking and in situ sources of these lipids. Results converge on a best-fit model for downward flux in the ETNP that includes both surface-derived and sub-photic zone lipids. Overall results from the modern ocean suggest that approximately half of total suspended POM is submicron in size, much of it is bacterial in origin, and despite the small size of this material, it participates dynamically in water column export flux. These results also suggest some revised interpretations of organic matter signatures in the geologic record. I formulate a quantitative model of marine microbial production and degradation, and reproduce "inverse" isotopic signatures found in lipids and organic matter preserved in Proterozoic sedimentary rocks. Results suggest that the disappearance of this inverse \(^{13}C\) pattern was a consequence of the shift from Bacteria to Eukarya as dominant producers of marine autotrophic biomass. Together, results of this thesis reveal that heterogeneity in the isotopic signatures of marine suspended POM is associated with particle size, and by extension, must be a function of the composition of the total planktonic community. / Earth and Planetary Sciences

The Waimakariri-Avon River system is an important component of the Christchurch aquifer system and has been identified as one of, if not the, primary groundwater flow path. The Waimakariri-Avon River system is ideally suited to geochemical tracing of surface water- groundwater interaction and while many past studies have been undertaken to characterise this system, in terms of its geochemistry and physical hydrogeological components, there is still a large amount of uncertainty as to how long it takes for groundwater to flow from the Waimakariri River, through the Waimakariri-Avon River groundwater system, to the springs that feed the Avon River. The primary goals of this thesis were to; 1) Constrain the residence time of groundwater connecting the Waimakariri-Avon River groundwater system using stable oxygen and hydrogen isotopes and analysis of anionic concentrations of: chloride, fluoride, nitrate, nitrite, bromide and sulfate, 2) Provide additional evidence of a hydrological connection between the Waimakariri River and the Avon River systems, 3) Present observations of the stable isotopic and anionic response of surface water to rainfall events, 4) Identify stable isotopic and anionic surface water variation along the Waimakariri-Avon River system, and establish the reasons for these. This study presents the use of natural isotopic and anionic tracers to characterise the residence time of the groundwater that flows between the Waimakariri and Avon Rivers, by sampling surface water and meteoric water at sites that are part of the Waimakariri-Avon River system. 375 samples were collected from 10 surface water and 4 rainwater sites distributed across the Waimakariri-Avon River surface water-groundwater flow path between March 5th and August, 2014. Additionally the study provides further stable isotopic evidence of the connection between the Waimakariri and Avon Rivers, as well as presents the variability of surface water chemistry in response to rainfall events. Identification of isotopic and anionic variation along the Waimakariri-Avon River system, by surface water sampling, was also conducted to establish the probable causes of observed variations. This study found that the use of large rainfall events, as natural tracers, was not conclusive in establishing the groundwater residence time of the Waimakariri-Avon River system within the 4.5 month sampling period available. Surface water sampling provided further evidence in support of past studies that have determined an isotopic connection between the Waimakariri River and the Avon River with mean stable isotopic values for the Waimakariri River (-8.85‰ δ18O and-60.65 δD) and Avon River (-8.53‰ δ18O and -58.72 δD) being more similar than those of locally derived meteoric water (-5.48‰ δ18O and -35.13 δD). Observations of surface water chemistry variations thorough time determined and identified clear responses to rainfall events as deviations from baseline values, coinciding with rainfall events. Isotopic variation along the Waimakariri-Avon River system was shown to reflect Waimakariri River derived shallow groundwater with the contributions from rainwater increasing with increased proximity to the Avon River mouth. Anionic profiling of the Waimakariri-Avon River system identified increasing concentrations of chloride, nitrate, sulfate, nitrite and bromide, relative to the Waimakariri River, with increased proximity to the Avon River mouth. Fluoride concentrations were identified in lower concentration, relative to the Waimakariri River, with increased proximity to the Avon River mouth. Fluoride and nitrite concentrations were attributed predominantly, if not entirely, to an atmospheric source as mean concentrations were greater in meteoric waters by a factor of at least 2, compared to surface water samples. Chloride and bromide have been attributed to possible salt water mixing as a result of the interaction of upwelling deeper groundwater with the marine and estuarine sands beneath the upper unconfined aquifer, that act as a confining layer within the Christchurch aquifer system. Nitrate and sulfate concentrations have been attributed to potential fertilizer usage and past land-use impacts. A significant step-change increase in chloride, bromide, nitrate and sulfate concentrations was observed between the surface water sample sites at Avonhead Park and the University of Canterbury. The step-change coincides with the boundary of the upper confining layer within the Christchurch aquifer system, and explains the increases in chloride and bromide concentrations. It also suggests a widely distributed source area as concentrations do not become diluted at the Avon River site, at Hagley Park, , which would be expected from the addition of other tributaries, if they did not have similarly high chloride and bromide concentrations. The area between these two sites has also been identified by Environment Canterbury as potentially impacted by past agricultural land-use practices and may explain the increases in nitrate and sulfate concentrations.

The scarcity of carbonate on Mars has been difficult to reconcile with the morphologic evidence for a wet epoch in Martian history, and has weakened early interpretations of a water-rich Noachian. Limited soil carbonate from pre-Silurian Earth has created a similar conundrum, and in both instances this paradox has likely led to overreaching interpretations about past climates. To better understand the formation of carbonate on Mars, early Earth, and in present day hyperarid climates, we examined the distribution of carbonate in the Atacama Desert—a region that spans multiple climate regimes and allows us to isolate the effects of precipitation and plant cover on soil mineralogy. To better quantify the influences of vegetation on carbonate we utilized a simple one-dimensional precipitation model and simulated carbonate formation with or without plant cover under a range of relevant climatic conditions and soil morphologies. In the Atacama we found two distinct zones with only trace (<5%) carbonate: the "absolute desert" with precipitation too low to sustain plant life, and the high Andes where precipitation was significantly higher, but where the low mean annual temperature (MAT) inhibits plants. The fog-supported, low-elevation coastal "lomas" below approximately 800 meters above sea level (masl) and the higher elevations between approximately 2500-4500 masl are variably vegetated and contain abundant carbonate within the soils. Plants increase total evapotranspiration and its distribution with depth, weathering rates, and total pCO₂. Our model results show that all of these factors increase the formation of pedogenic soil carbonate. Without the influence of vegetation the diminished carbonate that is produced is flushed through the shallow soil, where it eventually precipitates in the deep vadose zone or is entrained by groundwater.

No description available.

Water and gas samples were collected from coalbed methane wells and surface coal mines in the Powder River Basin and analyzed for solute chemistry, isotopes, and gas composition to determine timing and source of recharge, nutrient influxes, extent of methanogenesis, and redox conditions. Delta18O-H2O values and hydraulic gradients show recharge to coal beds is principally from the southern basin margin with inputs from the western and eastern margins. Detectable 14C in coal waters indicates they were recharged <50,000 BP. Correlation of deltaD-CH4 and deltaD-H2O values suggests that methane has accumulated since the Late Pleistocene. Nutrient concentrations were low and did not correlate to groundwater recharge sources. Coal gases from the northwestern basin are isotopically-depleted suggesting 'early stage' methanogenesis, whereas coal gases from the central southeastern basin are isotopically-enriched suggesting 'late stage' methanogenesis. Several wells have elevated SO4 and oxygen, which may be due to recent hydrologic changes from groundwater pumping.

In surface hydrology, much attention is paid to the effects of changing water fluxes, however there is less of a focus on the effects of changing energy fluxes. These energy fluxes are an important driver of many hydrological processes such as evapotranspiration and snow sublimation/ablation. The hypothesis that varying energy fluxes are important to the hydrological features of a catchment is tested by an experiment that involves calculating mean transit times for a number of catchments that drain different aspects of a large dome located in the Valles Caldera, New Mexico, called Redondo Peak. These catchments have different orientations and therefore receive different amounts of solar radiation. There is a general correlation between mean transit times, as determined by lumped-parameter convolution, and aspect, suggesting that in the Valles Caldera, transit times might be affected by a variety of features that are influenced by exposure to solar radiation, such as slope steepness, vegetation patterns, and soil depth. To put these transit times into context, I also used a distributed physically-based model to simulate a number of factors simultaneously to determine how hydrological features are influenced by aspect. This modeling excercise has illuminated the aspect-dependence of hydrological features such as the timing and intensity of snowmelt and soil moisture patterns, and it has quantified differences in energy and water fluxes on different aspects. These factors affect both water storage and water fluxes, and are therefore tied to transit times.