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The carbon isotope fractionation in the coccolithophore Emiliania huxleyi constitutes the basis for the paleo-pCO₂ barometry. Under the premise that the carbon isotope fractionation is dependent on the availability of dissolved CO₂, measurements of the carbon isotope ratio of sedimentary alkenones can potentially produce a proxy record of ancient atmospheric CO₂ levels. However, recent studies, including this thesis have suggested that other factors than CO₂ may influence the carbon isotope fractionation in Emiliania huxleyi and hence the validity of the proxy. In this thesis work the effects of irradiance on carbon isotope fractionation were studied in batch cultures of non-calcifying Emiliania huxleyi. It was found that the biomass becomes more ¹³C depleted as the light intensity decreases. This is in agreement with utilization of CO₂ via passive diffusion where fractionation is a function of the rate of diffusion of CO₂ into the cell relative to the rate of carbon utilization. However, results reported in the literature for a calcifying strain show the opposite trend with a ¹³C enrichment of the biomass. These results suggest that the carbon utilization of the calcifying strain of Emiliania huxleyi differ from that of the non-calcifying strain. This is supported by observations in the literature, which indicates a connection between the process of calcification and the supply of carbon for photosynthesis. A mechanism for the effect of calcification on carbon isotope fractionation in light limited cells is presented here. The mechanism is based on the fact that the calcification and photosynthesis respond differently to light limitation. This difference leads to an imbalance in the rate of calcification to the rate of photosynthesis ratio (C/P), which ultimately affects the availability of CO₂ inside the cell. Apart from light, the availability of nutrients has also been shown to affect calcification. Nutrient starved cells will enhance calcification to the degree that the C/P ratio changes, thus affecting the internal concentration of CO₂. To study the effect of these environmental parameters on carbon isotope fractionation, C₃₇:₂-alkenones were extracted from samples of marine particulate organic matter. The particulate organic matter was collected together with information of the environmental conditions during three cruises in the North-East Pacific and during a Pacific transect from Victoria B.C. to Guam. Results from the NE Pacific show a lower carbon isotope fractionation in samples collected at the bottom of the euphotic zone compared to samples collected in the mixed layer. This may be an expression of the effect of light limitation. In this work carbon isotope fractionation shows no correlation with dissolved CO₂. Instead, a correlation with the ratio of phosphate concentration to concentration of dissolved CO₂ ([PO3/4⁻/[CO₂]aq.) was observed. Nitrate availability appears to play an important role in maintaining this relationship as in the absence of nitrate the carbon isotope fractionation is lower than can be predicted from the relationship relating carbon isotope fractionation to [PO3/4⁻/[CO₂]aq. The C₃₇:₂-alkenone based results from the Pacific transect shows a strong correlation between carbon isotope fractionation and phosphate. This correlation is independent of the concentration of dissolved CO₂, implying a nutrient dominated control of isotope fractionation. However, this control may not be typical as the transect passed through waters with very low nutrient levels. Therefore, the results seen here may be a consequence of extreme nutrient conditions. In conclusion, the results presented in this thesis challenge the classical belief that the carbon isotope fractionation in Emiliania huxleyi is a direct function of the availability of dissolved CO₂ by suggesting that the observed isotope fractionation is a result of a complex interaction between environmental factors such as irradiance and the availability of nutrients. In particular, a correlation between phosphate concentration and carbon isotope fractionation has been found. / Graduate

No description available.

An atomic beam type of apparatus designed to produce a polarized He³ beam with an intensity of approximately one microampere and 90% polarization is described. He³ is a monatomic gas consisting of atoms with zero electronic magnetic moment and nuclear spin of ½. As no initial molecular dissociation is required, an intense, supersonic neutral beam can be produced with a miniature Laval nozzle cooled to liquid He⁴ temperatures. The velocity distribution of the particles in the Laval beam and the trajectories of these particles in a radially symmetric hexapole magnet have been computed. Sufficient separation of the two beams, consisting of particles in the two possible nuclear spin states, is achieved with a magnet in which the diameter of the gap between the pole pieces increases from 3mms at the entrance to 6mm in 15 cms and is then constant for 35cms. After ionization the nuclear polarization of the singly ionized particles depends upon the magnetic field strength at the position of the ion. Theoretical calculations show that field strengths of 6000 gauss at both the ionizer and target (in reaction studies) are sufficient to give 90% nuclear polarization. For an input gas temperature and pressure of 2.2°K and 15 mm.Hg. the Laval nozzle (throat diameter, 0.2 mm) has been designed to produce a supersonic beam of Mach number 4 with an intensity of 6.5x10¹⁵ particles/sec at the magnet entrance. Assuming 40% transmission through the magnet (one half of the beam being removed by the polarization process) and an ionization efficiency of 0.25%, the resulting ion beam intensity is 6.5x10¹² ions per second or approximately one microampere. The low temperature atomic beam source has been tested at liquid nitrogen temperature with a He⁴ beam. The measured beam intensity of 9x10¹³ particles/cm²/sec at the magnet exit, 76 cms from the nozzle, agrees favourably with the calculated intensity of 1.2x10¹⁴ atoms/ cm² sec under these operating conditions. The measured field gradient of 70,000 gauss/cm. near the pole tips of the hexapole splitting magnet is more than required for separating the atoms in the two nuclear spin states. A pulsed nuclear magnetic resonance method for measuring the nuclear polarization of the neutral He^ beam prior to ionization is described. The angular distribution and polarization of the protons produced by the D(He³,p)He⁴ reaction with an incident, polarized He³ beam of 150 Kev bombarding energy has been calculated, This angular distribution is isotropic. In the plane of the reaction, the proton polarization, which may be measured by a second scattering experiment, is -2/3 the incident He³ polarization. The angular distribution and polarization of the protons from this reaction has been calculated for the case of polarized and unpolarized He³ beams incident on a polarized deuteron target. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The cross section for the photodisintegration of a three body nucleus, helium-3, has been accurately measured for the first time. The He³( ɣ,p)D reaction cross section has been measured at gamma ray energies of 6.14, 6.97 and 7.08 Mev and found to be 0.104 ± .007, 0.298 ± .050 and 0.308±.024 milli-barns respectively. The photodisintegration cross section agrees with that calculated from the D(p,ɣ)He³ reaction using the principle of detailed balance to within the experimental errors. This is an accurate verification of this principle as applied to a direct nuclear-photon interaction. The photodisintegration reaction was observed in a cylindrical gridded ionization chamber using a helium-3, methane, and argon gas mixture. The F¹⁹(p, αɣ)016 reactions at proton bombarding energies of 873.5 kev and 935 kev were used as the source of gamma rays of well defined energy. The energy resolution of the chamber was adequately good to give a reasonable separation of the 642 kev photodisintegration reaction product peak from the electron background and the 765 kev peak from the He³(n,p)T reaction. It was necessary to reduce the tritium contamination in the helium-3 gas in order to reduce the background arising from the beta decay of the tritium; purification to less than 1 part tritium in 10¹⁰ parts helium was achieved. Proposed measurements of the photodisintegration cross section at higher gamma ray energies using ionization chambers and other types of detectors are discussed. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Ratio recording methods in mass spectrometry have hitherto been successfully used in analyses involving only a few of the lighter elements. In all these cases a great improvement in precision has resulted. This thesis describes a means whereby grid ratio recording can be extended to the precise measurement of complex spectra in the high mass range. In particular, lead isotope studies in geophysics provide a great and continuing need for increased analytical precision. The project has involved the construction of a complete mass spectrometer which incorporates two main features which have not been used before in mass spectrometry. The first of these is a scanning mechanism which moves the collector across the stationary ion beams. It is this innovation which has made possible the development of grid ratio recording. Since the total ion beam is stationary, variations in its intensity during the scanning process can be monitored accurately. A servo-divider system is arranged to make the measuring system Insensitive to variations in the total ion beam by recording the individual ion beam currents as fraction of the total Ion beam. The ratio system will effectively reduce large variations in the total Ion beam due to changes in source conditions by a factor of fifteen. Smaller variations are reduced to below the noise level existing in the recording system itself. The second principle which is believed to be new to mass spectrometry is the method by which the results of an analysis are presented by the instrument. An expanded scale system of recording has been developed whereby the amplitude of an ion current is presented as a digit on a counting tube, with the remainder displayed as a peak on a chart recorder. It is demonstrated that the expanded scale arrangement will record a known signal with a standard deviation of less than 0.02%. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

On the basis of data published prior to 1960, two basic lead isotope models - the isochron model and the primary lead model - were postulated to fit those crustal leads that have had the simplest history. The present writer's analyses of samples from Southern Finland, and the results of other research workers, now indicate that the primary lead model more adequately describes these leads, and that primary "isochrons" are either very short, or else non-existent. Lead in conformable deposits and in ultrabasic sulfides were postulated by R.L. Stanton to be examples of primary lead. Analyses of samples from several massive lead-zinc conformable deposits have indicated that the leads of many of these deposits possess primary lead characteristics. The present thesis describes a technique devised to prepare tetramethyllead from the conformable chalcopyrite deposits and ultrabasic sulfides and describes some initial results. This is a free radical technique, involving the reaction of methyl radicals with a lead mirror evaporated out of a sulfide. It appears to be capable of preparing tetramethyllead from samples containing one to two orders of magnitude less lead than previously reported for such a technique. Unfortunately, the full extent of the method cannot be utilized with present gas source mass spectrometer facilities, and only fair precision (0.4%) is possible at 10 ppm. lead. Samples from the conformable chalcopyrite deposits of Mt. Isa were analysed. The lead isotope ratios were found to be significantly different from those of the massive lead-zinc deposits. The results, interpreted with other lead and sulfur isotope data, suggest that these deposits could be the result of metal-bearing solutions entering a partially enclosed bay. Initial results for two ultrabasic deposits suggest that the lead in the sulfides is not necessarily primary; for example, that in two Stillwater ultrabasic complex samples appears to be the result of three stages of development. Hence, both the present lead isotope analyses, and those reported earlier by Ostic (1963) indicate that Stanton's geological criteria, while good, are not completely adequate for identifying primary leads. It is here suggested that sulfur isotope analyses might indicate which of these samples have been contaminated by crustal leads. During the investigation of the gas source mass spectrometric analyses of small tetramethyllead samples, lead isotope fractionation was observed. This occured with molecular flow into the mass spectrometer. Lead isotope fractionation has not been reported previously, and has some interesting geophysical implications. A preliminary study suggests that such fractionation in nature is likely to be rare, except possibly in biological processes in the sea. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

This study focuses on a mid-sized watershed of upper Ogilvie River (~4,500 km2 at the western extent of the 77,000 km2 Peel River basin) located at the northern extent of the discontinuous permafrost in central Yukon. Annual hydrograph is analyzed by characterizing the river flow components using geochemical tracers (anions, cations, and dissolved organic and inorganic carbon), stable isotopes (δ2H, δ18O, and δ13C) and radioactive isotopes (14C and 3H). The 2014 and 2015 flows are characterized by high weathering solute concentrations (Ca2+, Mg2+, SO42-, and DIC) in the winter that spike just prior to freshet, diluted to the lowest concentrations at the peak of freshet, and slowly recover throughout the summer and fall responding to overall flow fluctuations. Biogenic solutes (K+ and DOC) are lowest in the winter time and spike at the start of freshet. Two groundwater components, shallow and deep, were identified with corresponding tritium-based residence times of less than a year and three years, respectively. The local meteoric water line, developed based on the local precipitation samples δ2H=6.77·δ18O-24.54 (R2=0.98), was used to determine the recharge mix of the groundwaters: 65% rain and 35% snowmelt. The recharge waters interact greatly with soil (open system weathering) and carbonate bedrock (closed system weathering) as evident via the δ13C and F14C signatures of the active layer waters, shallow groundwater and deep groundwater. Radiocarbon of DIC proved to be an important tool to differentiate the weathering conditions by demonstrating F14C carbonate dilution resulting in groundwater F14C as low as 0.57. Based on the δ18O based hydrograph separation, deep groundwater comprised almost half of the annual discharge. The groundwater discharge reached its maximum flow of 129 m3/s during freshet when it contributed 44% to the flow. The potential groundwater recharge pathways include thermal contraction cracks in permafrost and bedrock fractures. The recharge is thought to occur over vegetated areas. In the summer, likely only large precipitation events result in recharge. In comparison to discharge, the annual DIC exports from the study catchment (5.6 gC/m2/yr) were disproportionally high in the winter time and the DOC exports (2.1 gC/m2/yr) varied proportionally with discharge.