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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Nd-Isotope Mapping of the Grenville Province in Southern Labrador

Hewitson, Moumblow Rebecca 09 1900 (has links)
<p>New Nd isotopic data is presented, with previously published Nd model ages, to create a crustal formation age map that demonstrates the extent of crustal terranes of different ages within the Grenville Province in southeastern Labrador. An unpublished Nd data set from C. Gower was used for comparison with the data from this study. The previous UPb data has provided ages that define the geological history of southeast Labrador through four major orogenic events: the Makkovik orogeny (1860-1790 Ma), the Labradorian orogeny (1710-1600 Ma), the Pinwarian (1520-1460 Ma) and the Grenville orogeny (1085-985 Ma) (Gower, 2008). However, the high-grade metamorphism as a result of the Grenville orogeny has obscured the true age of the crustal material that formed the Grenville Province. The crustal formation ages detelmined through Nd analysis can distinguish boundaries between crustal terranes, even in areas with a complex geological history. <br />Previous Nd isotopic data included both the Grenville Province to the south, and the Paleoproterozoic Makkovik Province to the north, and demonstrated that older Nd values were located farther south than previously established but were unsuccessful in determining a crustal terrane boundary. <br />The data from this study provided depleted Mantle model (T DM) age ranges that overlapped from the Hawke River, Lake Melville and Mealy Mountains terranes which suggested that they are representative of one crustal block, which was renamed the Caliwright terrane. This terrane presented an age range of 1.87-1.94 Ga, which may reflect mixing between Pre-Labradorian and Labradorian magmatism. The data from Gower which included the Groswater Bay telTane, displayed a similar age range of 1.90 to 1.97 Ga, also indicating a single crustal source. In contrast, the Pinware terrane falls into two categories in which the northerly portion has Nd signatures similar to those of the Cartwright terrane, and the southern portion has ages indicating a juvenile Labradorian source. A mean Nd model age of 1.77 Ga was recorded for this data set as well as the data from Gower. Therefore the Pinware terrane was divided into north and south domains based on a proposed suture boundary between Gilbeli River and Red Bay. The data presented suggests that the original edge of the Makkovik continental margin passed just north of Red Bay and trends westwards into the interior of southern Labrador. I expect that relatively homogeneous Nd isotope signatures are located to the south of this boundary, whereas heterogeneous signatures are expected to the north.</p> / Master of Science (MS)
2

The Effects of Disconnected Entrapped Air on Hydraulic Conductivity in the Presence of Water Table Fluctuations

Marinas, Maricris 09 1900 (has links)
<p>The hydraulic conductivity of a groundwater system can possess high spatial and temporal variability in the presence of an entrapped air phase (quasi -saturated soils) which is a key factor in controlling hydraulic behaviour. Previous studies have provided evidence of reduced hydraulic conductivity caused by entrapped air; however, these did not address the dynamic behaviour of the entrapped gaseous phase. In this study, the hypothesis that the decreases in hydraulic conductivity caused by entrapped air are sensitive to fluctuations in the water table was tested using laboratory experiments. The effects of applying increasing confining pressures (water table elevation) on the nature of entrapped air and its effects on quasi-saturated hydraulic conductivity was investigated for a range of sands and for air entrapment by both upward water flow and ponded infiltration (downward flow). Laboratory experiments were conducted using the constant flux method on saturated/ quasi-saturated horizontally positioned sand columns using 1% bleach as the solution. Induced pressures ranged from 0 to 250 cm with changes in hydraulic conductivity calculated using collected timed-interval outflow discharge and the pressure gradient measured by a differential pressure transducer. The sand core was also instrumented to measure volumetric moisture (or air) content with time domain reflectometry (TDR) probes. Results show that a 250-cm increase in water pressure above atmospheric pressure induced changes in the volume of entrapped gas according to the ideal gas law indicating the primary and tertiary roles played by air phase compression and capillary pressure, respectively. The reduction in air content at the 250-cm pressure increased the quasi-saturated hydraulic conductivity by a factor of 1.20 to 1.64. The results were fitted to the van Genuchten (1980) and Faybishenko (1995) functions for unsaturated and quasi-saturated hydraulic conductivity, respectively. The changes in quasi-saturated hydraulic conductivity due to changes in air content are expected to ubiquitously occur in the presence of a fluctuating water table. Thus the understanding of this fundamental mechanism and its incorporation into cunent general models of flow and transport will aid in better understanding the unique role of entrapped air in groundwater systems.</p> / Master of Science (MS)
3

Persistence and Effectiveness of Hydroxypropyl-β-Cyclodextrin during Soil Remediation

Etherington, Jennifer 09 1900 (has links)
<p>Hydroxypropyl-β-cyclodextrin (HBβCD) is receiving increasing interest as an enhancing remediation agent used for soils contaminated with hydrophobic contaminants. While being used in remediation experiments, no previous study has investigated the fate of HBβCD under non-enhanced uncontrolled conditions in field soils. This study assesses the removal efficiency of DDT using 10%-HBβCD solutions within laboratory soil columns, and examines the persistence of HBβCD within uncontrolled un-enhanced field soil conditions. The bench scale soil column study was found to remove 19% and 20% of the initial DDT and DDE masses respectively after ten treatments of 10%- HBβCD solutions applied twice per day for one week. This definitively shows HBβCD does vertically mobilize DDT in the soil profile. Stable carbon isotopic measurements of technical grade HBβCD resulted in an expected 0 l3C value of -16%0. The expected stable carbon isotopic value (δl3C) of the initial untreated soils was -24.5%0. The soils treated with 10%-and 20%-HBβCD solutions both indicated an increase in carbon isotopic values during and after the experiment, indicating retention of HBβCD within the soil. Measurements of HBβCD in soils using liquid chromatograph mass spectrometry (LCMS) indicated a smaller persistence of HBβCD within the soils during and shortly after HBβCD applications. The carbon isotopic measurements and LCMS concentration of HBβCD reflected similar short and long-term trends for both increasing and decreasing concentrations. Evidence from both stable carbon isotope analysis and LCMS analysis indicated that HBβCD persisted in the soils six weeks after applications; however, there was no evidence of HBβCD in soils eleven months after the treatments ceased.</p> / Master of Science (MS)
4

Quantifying accuracy of measurements in the earth sciences by examination of residuals in statistically redundant observations

Hale, Richard Elliot. January 2006 (has links)
Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.
5

Paleoecology and taphonomy of vertebrate faunas from the Anza-Borrego Desert of California

Cassiliano, Michael Louis January 1994 (has links)
Sedimentary deposits in the Salton Trough of California record the infilling of the northern part of the Gulf of California. The final phase of deposition began about 4.0 Ma with development of the delta plain of the Colorado River and ended about 0.9/0.7 Ma after a period during which deposition was dominated by bedload streams. During the final phase of deposition, a diverse assemblage of mammals characteristic of the Blancan and Irvingtonian Mammal Ages inhabited the area. The Blancan-Irvingtonian boundary is placed in the Fish Creek-Vallecito Creek section at the lowest stratigraphic occurrence of Hammuthus at about 1.77 Ma. The Fish Creek-Vallecito Creek section contains superposed Blancan and Irvingtonian faunas separated by a newly recognized Blancan-Irvingtonian boundary in continuously deposited sediments correlated with the magnetic polarity time scale. It is proposed that the Fish Creek-Vallecito Creek section be recognized as the standard section in which to define the Blancan-Irvingtonian boundary. Taphonomic analysis indicates that skeletal elements accumulated in five major depositional environments: tidal flat, lacustrine, channel, channel "fill", and floodplain. Only the fluvial environments produced significant skeletal abundances and taxonomic diversity. Taphonomic analysis indicates that pre-transport taphonomic processes were more important than fluvial transport in modifying thanatacoenoses. Taphonomic analysis also suggests that taxonomic diversity and relative abundances of large and small mammals are reliably preserved so that assemblages can be used in realistic, but general, analyses of paleoecology and paleocommunity structure. Actualistic and cenogram methods were used to study the Fish Creek-Vallecito Creek paleocommunity. Both methods suggest a savannah-community. The cenogram analysis shows the structure of the paleocommunity based on body size distribution. The data are grouped into assemblages based on the following criteria: change in fluvial environment, change in taxonomic composition, and change in paleoclimate. Stable, discrete small- and large-sized components with homogeneous body-size distributions are separated by an unstable medium-sized component. Results are consistent regardless of how the data are grouped, suggesting confidence in the results, stability in the paleocommunity despite environmental change, and a reality to the existence of the paleocommunity.
6

TELESEISMIC STUDIES OF THE NORTH AMERICAN CORDILLERA: EVALUATING THE CHANGING STRUCTURE, COMPOSITION, AND FABRIC AFTER SUBDUCTION

Frassetto, Andrew Michael January 2009 (has links)
The cessation of wide-scale subduction and orogenic compression during the early to mid-Cenozoic radically altered the North American Cordillera. This dissertation summarizes the results of three seismic studies, conducted in different regions of western North America, aimed at understanding how the structure and character of the crust and upper mantle relate to regions of post-subduction magmatism and persisting high elevations. Across the southern Basin and Range and Colorado Plateau teleseismic receiver functions show that only the Colorado Plateau contains thick crust commensurate with its high elevation. In contrast the southern Basin and Range has a relatively uniform crustal thickness of ~30 km, which is inadequate to support the high elevations of some of its metamorphic core complexes. We conclude that local variations in the density of the crust or upper mantle may support at least some high elevations in the southern Basin and Range. A large dataset of receiver functions collected across the Sierra Nevada show a complicated crust-mantle boundary which varies geographically, transitioning from thin crust beneath the eastern Sierra to thick crust underlying the western foothills. The thicker crust coincides with xenoliths sampling a remnant mafic-ultramafic residue produced during arc magmatism in the late Cretaceous. Modeling of receiver functions suggests that recent volcanism throughout the elevated eastern Sierra and nearby Basin and Range results from continued foundering of this dense material and its replacement with asthenosphere at relatively shallow depths in the upper mantle. In the Canadian Cordillera, regional observations of shear-wave splitting constrain the orientation and magnitude of seismic anisotropy. A pronounced and unusual trend of shear-wave splitting across the central British Columbia suggests that eastward directed flow of mantle asthenosphere fuels recent, widespread and geochemically distinct post-subduction volcanism within the northern slab window. These observations show how local and dynamic processes contribute to the support of lingering high elevations across western North America and that regions formerly associated with subduction may experience renewed magmatism due to inflow and subsequent melting of asthenospheric mantle.
7

Seismic Coupling and Hydrological Responses

Rashid, Shahid January 2006 (has links)
In seismology, the capability of an earthquake to induce other seismic events has been widely accepted for decades. For example, the term aftershock involves a strong relation of such a seismic event with the incidence of a main shock. Moreover, hydrological changes (water level in wells and streams, geyser eruption and remote seismicity) in response to remote earthquakes have been reported for many years. A matter of current debate concerns the spatiotemporal scale of interaction among seismic events. However, there appears to be no clear image of what is the exact method of transmission of the triggering energy for the phenomena listed above. It appears that the P-wave and the S-wave are inadequate in terms of ground strain magnitudes at teleseismic distances, while the amplitude of the surface waves generally decreases exponentially with depth in the Earth and could not be responsible for triggering deeper earthquakes or deep-seated fluid flow fluxes in 3-5 km deep reservoirs. This leaves some other wave as a possible triggering energy sources. <br /><br /> This thesis is based on a diffusion-dynamic theory that predicts a low velocity displacement wave, called a soliton wave, propagating in liquid-saturated porous media with velocity ~100-300 m/s, analogous to a tsunami that travels with the loss of little energy. This is hypothesized to be the mechanism for energy transfer that could be sufficient to promote changes in local pore pressure and therefore to alter the ambient effective stresses. It is also hypothesized that a soliton wave packet is emitted by a primary seismic event and may trigger sympathetic secondary earthquakes at a remote distance, fluid level fluctuation in wells, changes in geyser eruption behaviour, and changes in microseismic frequency, amplitude and patterns in appropriate places (e. g. under water reservoirs, in areas of active hydrothermalism, in tectonically active areas, and so on). <br /><br /> This thesis undertakes a review of some of these phenomena, and finds that the evidence as to what is the triggering mechanism is not clear. Also, it appears that the soliton hypothesis is not at all disproved by the data, and there may be some evidence of its existence. <br /><br /> To reveal the evidence of this kind of wave (soliton) in nature, real sequence and K-Q cases velocity data bases of earthquake interactions in the year of 2003 have been constructed by using information from Incorporated Seismological Research Institute (IRIS). The qualitative and quantitative analysis demonstrates that interactions between seismological and hydrological systems due to soliton waves are a definite possibility. However, the growth of fluid fluxes, geysers eruption and remote seismicity are controlled by both the principal stresses and the pore pressure. Hence, this interaction depends on the hydromechanical properties of rock such as permeability, compressibilities, and viscosities of fluids, saturations, and porosity. Perhaps the strongest argument in favour of a low-velocity soliton trigger is that the other seismic waves seem to be inadequate, and there is no evidence for their actions as a trigger. <br /><br /> The practice of detection and analysis of a soliton is not undertaken in this work. Because current devices are incapable to measure such a wave as they are on the surface and insensitive to liquid-solid coupling, sensitive and precise sensors in the low frequency range must be installed within the liquid saturated zone, preferably under the water table, to advance further work.
8

Retroflection from Slanted Coastline Modeling Rings Injection into the South Atlantic during Glacials/Interglacials

Unknown Date (has links)
Recent proxies analysis suggest that, at the end of the last glacial, there was a significant increase in the injection of Agulhas rings into the South Atlantic (SA). This brought about a dramatic increase in the salt-influx (from the Indian Ocean) into the SA helping re-start the then-collapsed meridional overturning cell (MOC), leading to the glacial termination. Here, we propose a mechanism through which large variations in ring production take place. To gain a preliminary understanding of the processes in question, we develop a nonlinear analytical model of retroflection from a slanted non-zonal coastline. In is known that the balance of long-shore momentum flux requires that the solution of retroflecting currents involves ring shedding on the western side. An important aspect of the ring dynamics is the ring intensity α (analogous to the Rossby number), which reaches its maximum value of unity when the upstream potential vorticity (PV) is zero. Friction leads to a slow-down and a decrease in α. The main difficulty is that the solution of the system of equations for conservation of mass and momentum of zonal currents leads to the conclusion that the ratio (Φ) of the mass flux going into the rings and the total incoming mass flux is approximately 4α/(1+2α) . This yields the "vorticity paradox"-- only relatively weak rings (α ¬ >1/2 ) could satisfy the necessary condition Φ ¬ >1. Physically, this means, for example, that the momentum-flux of zero PV currents upstream is so high that, no matter how many rings are produced and no matter what size they are, they cannot compensate for it. We show here that when the slant of coastline (γ) exceeds merely 15°, Φ does not reach unity regardless of the value of α. Namely, the paradox disappears even for small slants. Our slowly varying nonlinear solution does not only let us circumvent the paradox. It also gives a detailed description of the rings growth rate and the mass flux going into the rings as a function of time. Interestingly, for significant slants (γ ¬1/2 ) could satisfy the necessary condition Φ ¬ >1. Physically, this means, for example, that the momentum-flux of zero PV currents upstream is so high that, no matter how many rings are produced and no matter what size they are, they cannot compensate for it. We show here that when the slant of coastline (γ) exceeds merely 15°, Φ does not reach unity regardless of the value of α. Namely, the paradox disappears even for small slants. Our slowly varying nonlinear solution does not only let us circumvent the paradox. It also gives a detailed description of the rings growth rate and the mass flux going into the rings as a function of time. Interestingly, for significant slants (γ ¬1. Physically, this means, for example, that the momentum-flux of zero PV currents upstream is so high that, no matter how many rings are produced and no matter what size they are, they cannot compensate for it. We show here that when the slant of coastline (γ) exceeds merely 15°, Φ does not reach unity regardless of the value of α. Namely, the paradox disappears even for small slants. Our slowly varying nonlinear solution does not only let us circumvent the paradox. It also gives a detailed description of the rings growth rate and the mass flux going into the rings as a function of time. Interestingly, for significant slants (γ ¬°) , the rings reach a terminal size corresponding to a balance between the β -force and both the upstream and downstream momentum fluxes. This terminal size is unrelated to the ultimate detachment and westward drift due to β. The developed model enables us to obtain the nonlinear analytical solutions for eddy shedding, including the theoretical ranges of detached eddies radii, their propagation speeds, and their periods of detachment, as well as the average amount of mass flux going into the rings. Using the dependence of these aspects on the coastline slant, we show that there are restricted possibilities for ring detachment when the coast is oriented in the north –south direction. We define a critical coastline angle below which there is rings shedding and above which there is almost no shedding. In the case of the Agulhas region, the particular shape of the African continent implies that rings can be produced only when the retroflection occurs beyond a specific latitude where the angle is critical. During glaciation, the wind stress curl (WSC) vanished at a latitude lower than that of the critical angle, which prohibited the retroflection from producing rings. When the latitude at which the WSC vanishes migrated poleward towards its present day position, the corresponding coastline angle decreased below the critical angle and allowed for a vigorous production of rings. Simple process-oriented numerical simulations (using the Bleck and Boudra model) are in good agreement with our results and enable us to affirm that, during the glacials, the behavior of the Agulhas Current (AC) was similar to that of the modern East Australian Current (EAC), for which the coastline slant is supercritical. / A Dissertation submitted to the Geophysical Fluid Dynamics Institute in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Degree Awarded: Spring Semester, 2008. / Date of Defense: December 14, 2007. / Plant of the Coastline, Agulhas Current, Glacial periods, Rings injection, Retroflection, Eddies / Includes bibliographical references. / Doron Nof, Professor Directing Dissertation; Joel Kostka, Outside Committee Member; Carol Anne Clayson, Committee Member; Georges Weatherly, Committee Member.
9

Surface Heating and Restratification of the Ocean after a Tropical Cyclone

Unknown Date (has links)
Ocean transport of heat is a substantial component of the climate system but its characteristics and dynamic causes are still somewhat unknown. Prior research has shown that global observations from the ocean and atmosphere indicate that the ocean and atmosphere transport about 6 PW of energy from the equatorial regions towards the poles. Studies have shown that approximately 2 PW of that transport are carried by the ocean. It has been proposed that global tropical cyclone activity could account for a large amount of the mixing needed to explain the thermohaline circulation driving this transport. However, there remain insufficient observations to conclusively prove this hypothesis. After a tropical cyclone moves across the ocean it leaves behind a wake of colder temperatures in the upper ocean. The cold wake is primarily caused by mixing, upwelling and an enthalpy flux into the atmosphere. This study makes use of the JASON-1, and TOPEX/POSEIDON satellite altimeters to investigate the amount of heating of the ocean required to re-stratify the ocean to pre storm conditions. Argo floats are also used to validate results found from the sea surface height anomalies from satellite. In order to attain the necessary spatial and temporal resolution, the Climate System Forecast Reanalysis (CFSR) model is used. Given that CFSR is a coupled atmospheric and ocean model, it enabled this study to compare the modeled storms and then the impact of storms on the ocean. After the storm passed through the area, surface heating fluxes could be determined over the duration of the storm thus providing a direct comparison of heat loss and net heat gain over the entire duration of the storm. It was found that during the time period of the cold wake, the surface heating imbalance was high enough to account for all of the rewarming of the cold wake. Therefore it is possible that global cyclone activity could account for the large amount of mixing required to explain the thermohaline circulation. / A Thesis submitted to the Department of Earth, Ocean, and Atmospheric Sciences in partial fulfillment of the requirements for the degree of Master of Science. / Degree Awarded: Spring Semester, 2011. / Date of Defense: April 30, 2011. / Cold Wake, Argos Floats, Sea Surface Height Anomaly, Ocean Restratification / Includes bibliographical references. / Carol Anne Clayson, Professor Directing Thesis; Robert Hart, Committee Member; Paul Ruscher, Committee Member.
10

Determining the Error Characteristics of H*WIND

Unknown Date (has links)
The HRD Real-time Hurricane Wind Analysis System (H*Wind) is a software application used by NOAA's Hurricane Research Division to create a gridded tropical cyclone wind analysis based on a wide range of observations. One application of H*Wind fields is calibration of scatterometers for high wind speed environments. Unfortunately, the accuracy of the H*Wind product has not been studied extensively, and therefore the accuracy of scatterometer calibrations in these environments is also unknown. This investigation seeks to determine the uncertainty in the H*Wind product and estimate the contributions of several potential error sources. These error sources include random observation errors, relative bias between different data types, temporal drift resulting from combining non-simultaneous measurements, and smoothing and interpolation errors in the H*Wind software. The effects of relative bias between different data types and random observation errors are determined by performing statistical calculations on the observed wind speeds. We show that in the absence of large biases, the total contribution of all error sources results in an uncertainty of approximately 7% near the storm center, which increases to nearly 15% near the tropical storm force wind radius. The H*Wind analysis algorithm is found to introduce a positive bias to the wind speeds near the storm center, where the analyzed wind speeds are enhanced to match the highest observations. In addition, spectral analyses are performed to ensure that the filter wavelength of the final analysis product matches user specifications. With increased knowledge of these error sources and their effects, researchers will have a better understanding of the uncertainty in the H*Wind product, and can then judge the suitability of H*Wind for various research applications / A Thesis submitted to the Department of Earth, Ocean, and Atmospheric Science in partial fulfillment of the requirements for the degree of Master of Science. / Degree Awarded: Fall Semester, 2010. / Date of Defense: October 8, 2010. / Hurricane, Tropical Cyclones, Wind Analysis, Uncertainty / Includes bibliographical references. / Mark Bourassa, Professor Directing Thesis; Mark Powell, Committee Member; Robert Hart, Committee Member; Guosheng Liu, Committee Member.

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