Graduation date: 1998

Thesis (Ph. D.)--University of Washington, 1999. / Vita. Includes bibliographical references (leaves 98-114).

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Les vents galactiques jouent un rôle important dans l'évolution des galaxies et du milieu intergalactique. Les supernovae se produisant peu de temps après un sursaut de formation d'étoiles dans une galaxie créent un vent cohérent enrichi en métaux. Ce projet de maîtrise visait à créer, en collaboration avec mon superviseur Hugo Martel et son chercheur postdoctoral Matthew Pieri, une simulation semi-analytique de type Monte Carlo dans laquelle les vents galactiques anisotropes seraient représentés par deux cônes sphériques voyageant dans des directions opposées. Cette simulation suit la formation de ~ 20 000 galaxies à l'intérieur d'un volume cubique comobile de (12h ^pc) 3 , dans un univers ACDM. Les vents produits par ces galaxies pourront soit souffler le gaz d'un halo en processus d'effondrement avoisinant, empêchant ainsi sa formation, soit déposer des métaux dans le milieu intergalactique, contribuant ainsi à la formation plus rapide de nouvelles galaxies. Les vents galactiques anisotropes suivent la direction de moindre résistance et, par conséquent, voyagent de préférence dans les régions de faible densité, loin des structures cosmologiques dans lesquelles les galaxies se forment. Les vents galactiques anisotropes peuvent enrichir en métaux plus efficacement les régions de faible densité. À l'opposé, dans les milieux de haute densité, il y a moins de croisements entre les vents anisotropes provenant d'une même structure cosmologique. L'enrichissement de cette structure est donc grandement réduit. Les vents hautement anisotropes peuvent traverser les vides cosmologiques et déposer des métaux dans d'autres structures cosmologiques. / Galactic outflows play an important role in the evolution of galaxies and the intergalactic medium. Supernovae following a starburst in a galaxy create a coherent metal-enriched outflow. The aim of tins master project was to create, in collaboration with my supervisor Hugo Martel and his postdoctoral researcher Matthew Pieri, a semi-analytical Monte Carlo simulation in which galactic outflows are represented as two spherical cones travelling in opposite directions. This simulation tracks the formation of ~ 20 000 galaxies in a comoving cubic volume of size (12h 1Mpc)3 , in a ACDM universe. Outflows produced by those galaxies could either blow away the gas of a halo in process of collapsing, thus preventing its formation, or deposit metals in the intergalactic medium, and so contribute to a faster formation of new galaxies. Anisotropic outflows follow the path of least resistance and thus travel preferentially into low-density regions, away from cosmological structures where galaxies form. Anisotropic outflows can significantly enrich low-density Systems with metals. Conversely, in the high-density regions, there is less crossing between anisotropic outflows located in a common cosmological structure, so the enrichment in this structure is significantly reduced. Highly anisotropic outflows can travel across cosmological voids and deposit metals in other, unrelated cosmological structures.

Natural vents in the Gulf of Mexico are actively expelling water and hydrocarbons. They are ubiquitous along continental margins, and I characterize a single vent in the Ursa Basin at leaseblocks MC852/853. Seismic data reveal that the vent is elevated ~75 meters above the seafloor and is roughly circular with a ~1.2 km diameter. A transparent zone centered underneath the vent extends to ~1500 meters below seafloor; this zone is commonly interpreted to record the presence of gas. There is a strong negative polarity seismic reflection that rises rapidly at the vent’s boundaries and is horizontal within a few meters of the seafloor beneath the vent edifice. I interpret that this reflection records a negative impedance contrast, marking the boundary between hydrate and water above and free gas and water below: it is the bottom-simulating reflector. Salinities beneath the vent increase from seawater concentrations to >4x seawater salinity one meter below seafloor. Temperature gradients within the vent are ~15x the background geothermal gradient. I model the coexistence of high salinity fluids, elevated temperature gradients, and an uplifted bottom-simulating reflector with two approaches. First, I assume that high salinity fluids are generated by dissolution of salt bodies at depth and that these hot, saline fluids are expelled vertically. Second, I model the solidification of gas hydrate during upward flow of gas and water. In this model, free gas combines with water to form hydrate: salt is excluded and heat is released, resulting in the generation of a warm, saline brine. The two models result in predictable differences of salinity and temperature. A better understanding of the hydrogeological processes at vent zones is important for quantifying the fluxes of heat and mass from submarine vents and is important for understanding the conditions under which deep-sea biological vent communities exist. / text

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Abstract The ubiquity of the Calvin-Benson-Bassham cycle (CBB) amongst autotrophic organisms suggests that it provides an advantage over a wide range of environmental conditions. However, in some habitats, such as hydrothermal vents, the reductive citric acid cycle (rCAC) is an equally predominant carbon fixation pathway. It has been suggested that the CBB cycle poses a disadvantage under certain circumstances due to being more energetically demanding compared to other carbon fixation pathways. The purpose of this study was to compare the relative metabolic cost of cell biosynthesis by an autotrophic cell using either the CBB cycle or the rCAC. For both pathways, the energy, in ATP, required to synthesize the macromolecules (DNA, RNA, protein, and cell envelope) for one gram of biomass was calculated, beginning with CO2. Two sulfur-oxidizing chemolithoautotrophic proteobacteria, Thiomicrospira crunogena XCL-2, and Sulfurimonas autotrophica were used to model the CBB cycle and rCAC, respectively while Escherichia coli was used to model both pathways because it has had its cell composition extremely well-characterized. Since these organisms have had their genomes sequenced, it was possible to reconstruct the biochemical pathways necessary for intermediate and macromolecule synthesis. Prior estimates, based solely on the ATP cost of pyruvate biosynthesis, suggested that the cellular energetic expense for biosynthesis from the CBB cycle was more than that from the rCAC. The results of this study support this conclusion; however the difference in expense between the two pathways may not be as extreme as suggested by pyruvate synthesis. Other factors, such as oxygen sensitivity, may act in concert with energetic expense in contributing to the selective advantages between different autotrophic carbon fixation pathways.