Ocean-continent convergence and subsequent continental collision are responsible for continental growth, mountain building, and severe tectonic events including volcanic eruptions and earthquake activity. They are also key driving forces behind the extensive thermal and compositional heterogeneities at crustal and mantle depths. Active subduction along the Calabrian Arc in southern Italy and the Hellenic Arc are examples of such collisional tectonics. The first part of this thesis examines the subduction related deformations within the crust beneath the southern Apennines. By modeling regional surface wave recordings of the largest temporary deployment in the southern Apennines, a lower-crustal/upper-mantle low-velocity volume extending down to 50 km beneath the mountain chain is identified. The magnitude (~ 0.4 km/s slower) and anisotropic nature (~ 10%) of the anomaly suggest the presence of hot and partially molten emplacement that may extend into the upper-crust towards Mt. Vulture, a once active volcano. Since the Apulian basement units are deformed during the compressional and consequent extensional events, our observations favor the ``thick-skin'' tectonic growth model for the region. In the deeper mantle, active processes are thermodynamically imprinted on the depth and strength of the phase transitions. This thesis examines more than 15000 SS precursors and provides the present-day reflectivity structure and topography associated with these phase transitions. Through case studies I present ample evidence for both slab penetration into the lower mantle (beneath the Hellenic Arc, Kurile Island and South America) and slab stagnation at the bottom of the Mantle Transition Zone (beneath the Tyrrhenian Sea and eastern China). Key findings include (1) thermal anomalies (~ 200 K) at the base of the MTZ, which represent the deep source for Cenozoic European Rift Zone, Mount Etna and Mount Cameroon volcanism, (2) significant depressions (by 20-40 km) at the bottom of the Mantle Transition Zone beneath subducting slabs, (3) a strong 520-km reflector near subducting slabs, (4) a weak and elevated (15-25 km) 410-km reflector within active deformation zones, (5) strong lower mantle reflectors (~ 900 km) while slabs penetrate into the lower mantle, and (6) consistency between the topography of a 300-km reflector and an exothermic phase transformation. / Geophysics

<p>This dissertation identifies and quantifies the impact of processes driving two biogeochemical phenomena of interest by considering them in the context of the large-scale circulation in which they occur. Both processes occur in the North Pacific transition zone (NPTZ), a basin-wide region near the subpolar-subtropical gyre boundary. </p><p>First, this work investigates the physical forcing behind the large seasonal variability in the location of the Transition zone chlorophyll front (TZCF). The TZCF is a persistent gradient in sea surface color that separates high chlorophyll waters to the north from low chlorophyll waters to the south. The chlorophyll front shifts seasonally by about 1000 km, oscillating between its southernmost winter latitude and its northernmost summer latitude. The forcing behind this seasonal signal is of interest because a number of migratory marine animals, both commercial and endangered, appear to track it.</p><p>This first study finds that vertical processes, traditionally viewed as controlling the dynamical supply of nutrients to surface waters, are insufficient to explain seasonal variations in nutrient supply to the transition zone. Instead, the wind-driven horizontal Ekman transport of nutrients, moving southward from the subpolar gyre into the northern reaches of the subtropical gyre, drives the southward migration of the TZCF. Such lateral transport of nitrate supports up to 40% of new primary productivity in the region annually, and nearly all of new primary productivity in the winter. </p><p>Second, this work investigates why the North Pacific transition zone waters are a notably strong sink for atmospheric carbon dioxide (CO2) on a mean annual basis, while seasonally they vary from a sink in the winter to a neutral to weak source in the summer. As the partial pressure of carbon dioxide (pCO2) in the surface mixed layer exerts primary control on the direction and magnitude of air-sea carbon exchange, this study quantifies the impact of processes regulating seawater pCO2: temperature, salinity, advection of dissolved inorganic carbon (DIC) and alkalinity (ALK), mixing of DIC and ALK, biology, and air-sea carbon flux.</p><p>Seasonal controls on pCO2 in the North Pacific transition zone differ from annual controls. Temperature effects dominate the seasonal signal, but are partially countered throughout the year by opposing processes. In spring and summer, biological drawdown partially offsets the increase in pCO2 due to warming waters; in fall and winter, the vertical entrainment of carbon moderates the decrease in pCO2 due to cooling waters. On a mean annual basis, air-sea carbon flux, biology, mixing, and advection all have a net impact on seawater pCO2. Though important seasonally, temperature has a small impact on pCO2 and air-sea carbon flux annually, accounting for only about 15-20% of oceanic carbon uptake through temperature-driven solubility changes.</p><p>This second study again finds an important role for lateral processes to play in regulating biogeochemical phenomena in the North Pacific transition zone. The ability of the region to uptake atmospheric carbon year after year is maintained by those processes exporting carbon from its surface waters: the vertical export of organic carbon to depth, and the lateral geostrophic advection of carbon out of the region. This lateral advection alone determines the location of the sink region: of the processes impacting seawater pCO2 on a mean annual basis, only the geostrophic divergence of DIC disproportionately lowers pCO2 in the transition zone latitudes, supporting greater atmospheric CO2 uptake here than in surrounding regions.</p><p>This dissertation identifies and quantifies processes driving biogeochemical features in the North Pacific transition zone, finding the large-scale circulation in the region plays a significant role in regulating these processes. The unique physical oceanographic characteristics of the NPTZ, and in particular the lateral transport, support biological and chemical attributes notably distinct from adjacent waters.</p> / Dissertation

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Removal of CO2 directly from anthropogenic sources (capture) and its disposal in geological formations can take place for medium-term time periods (storage), or it can be permanent (sequestration), with the CO2 eventually becoming dissolved in the aqueous phase. The latter is the main subject of this dissertation. Carbon dioxide sequestration covers a wide range of strategies and alternatives. The main objective of CO2 sequestration alternatives is secure disposal of carbon in large amounts and for a lengthy time scale (typically 1000 years). Injection of CO2 into subsurface formations is generally considered as the main option for CO2 sequestration. Geological sequestration through injection covers a broad variety of target formations: disposal in depleted oil and gas reservoirs, trapping in oil reservoirs, replacing CH4 in coal bed methane recovery processes, trapping in deep aquifers, and salt cavern placement are the major CCS alternatives in geologic formations. In this thesis, hydrogeologic interaction between the injectant (CO2) and the host fluid (saline water) during injection is the main subject of the project. Because of the density and viscosity contrast of displacing and displaced fluids, the pattern of saturation progression is complicated. A set of semi-analytical solutions is developed for quick estimation of the position of isosats (contours of saturation) during primary injection in homogenous cases with simple geometry. All of the mathematical solutions are developed based on two assumptions; incompressible fluids and rocks and vertical equilibrium (capillary-gravity condition) for geometries with large aspect ratio (L >> H). First, a series of analytical solutions for primary drainage for a set of linear relative permeability functions is developed. The first analytical solution is based on the assumption of locally linearized Leverett-J functions, and by using the method of characteristics, a formulation for the isosats’ geometry is obtained. A semi-analytical solution is then proposed for calculation of the position of isosats with linearized relative permeability functions and arbitrary capillary-saturation correlation. The analytical solution is extended to incorporate a specific form of nonlinearity of the relative permeability function. Nonlinear relative permeability functions are also incorporated in another semi-analytical solution, and the positions of the isosats for any arbitrary Leverett-J function and relative permeability functions are developed. Sequential gas-saline injection is also modeled in that chapter. For approximate verification of the analytical solutions, a FEM numerical model is developed and the results of the analytical solutions are compared with the numerical solutions. These new analytical solutions provide powerful tools for prediction of saturation distribution during injection in vertical and horizontal wells, as well as for carrying out stochastic assessments (Monte Carlo simulations) and parametric weight assessment. The domain of applications of the new solutions go far beyond the limited question of CO2 sequestration: they can be used for injection of any less viscous fluid into a reservoir, whether the fluid is lighter or denser than the host fluid (gas injection, water-alternating gas injection, water injection into viscous oil reservoirs, solvent injection).

Submitted by Geandra Rodrigues (geandrar@gmail.com) on 2018-01-11T14:03:02Z No. of bitstreams: 1 anacristinajunqueiraribeiro.pdf: 2351237 bytes, checksum: 7ebcb12130e80eb708ce7b21695b6c0c (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2018-01-23T13:36:51Z (GMT) No. of bitstreams: 1 anacristinajunqueiraribeiro.pdf: 2351237 bytes, checksum: 7ebcb12130e80eb708ce7b21695b6c0c (MD5) / Made available in DSpace on 2018-01-23T13:36:51Z (GMT). No. of bitstreams: 1 anacristinajunqueiraribeiro.pdf: 2351237 bytes, checksum: 7ebcb12130e80eb708ce7b21695b6c0c (MD5) Previous issue date: 2017-12-27 / A diferença entre ambiente urbano e rural é percebida claramente pela população. Entretanto, zonas intermediárias, tidas como zonas de transição, preocupam os profissionais da área de transportes, pela necessidade eminente de melhoria na segurança viária. A ocupação populacional nas zonas de transição passa despercebida pelo poder público, carecendo de infraestrutura e segurança. O objetivo principal desta pesquisa é a conceituação das zonas de transição como elemento de proposta de segurança viária. A delimitação da pesquisa se faz no âmbito da rodovia BR 116 devido à sua importância, ligando o nordeste ao sul do país. O foco no trecho de Leopoldina à Caratinga se faz pela importância socioeconômica para a região sendo, ainda, meio de circulação urbana dos municípios cortados por ela. Primeiramente foi feita uma revisão bibliográfica de temas como zona urbana, zona rural, rodovias e segurança, e uma observação dos ambientes rodoviários a fim de visualizar a segurança viária nas áreas de transição. O desenvolvimento tem como base metodológica a análise qualitativa da zona de transição a partir de parâmetros pré-definidos. Como resultado, tem-se a verificação de trechos caracterizados como zonas de transição. Conclui-se sobre a conceituação do termo a partir de parâmetros pré-estabelecidos e a necessidade de tratamento da área quanto às questões de segurança viária. / The difference between urban and rural environment is clearly seen by the population. However, intermediate zones, considered as transition zones, cause some concern among transport professionals and academics, due to the imminent need for improvement in road safety. Population occupation in transition zones is unnoticed by the public power, lacking infrastructure and road safety. The main objective of this research is the conceptualization of transition zones as an element of road safety proposal. The delimitation of the research is done under the BR 116 highway due to its importance, linking the northeast to the South of the country. The focus in the section of Leopoldina to Caratinga is made by the socioeconomic importance for the region, being an area of passage for the daily urban displacements. The method used is based primarily on the literature review of themes such as urban areas, rural areas, highways and security, and the observation of road environments in order to visualize road safety in transition areas. The development has as methodological basis the qualitative analysis of the transition zone from pre-defined parameters. As a result, there is the verification of stretches characterized as transition zones. It concludes on the conceptualization of the term from pre-established parameters, and the need of treatment of the area regarding road safety issues.

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