Extr. de: Diss.--Physique--Stuttgart (Allemagne)--Université de Stuttgart, 2001. / Thèse rédigée en anglais avec un résumé en allemand. Bibliogr. p. 183-188.

Dissertation--Faculty of science--University of Oulu, 2002. / Notes bibliogr.

Thesis (Ph. D.)--University of Washington, 1989. / Vita. Includes bibliographical references (leaves [145]-152).

Thesis (Ph. D.)--University of Hawaii at Manoa, 2004. / Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 2005. / Vita. Includes bibliographical references (leaves 159-190).

Hydrothermal activity is one of the dominant processes affecting the chemical and thermal evolution of oceanic crust at the mid-ocean ridge (MOR), but little is known about the sub-surface portions of ridge hydrothermal systems. These systems can be investigated using numerical modeling techniques, and models of two-dimensional cross-sections are utilized in this study to investigate the behavior of MOR hydrothermal systems. The influence of magma chamber geometry is explored by modeling two extremes of proposed geometry. Seismological evidence supports a dike-like 2 km half-width chamber, and models of this chamber indicate that: (1) complete crystallization of the magma requires 30,000 years, (2) hydrothermal upflow and hot springs are concentrated in a narrow band within 1.5 km of the ridge axis for the lifetime of the system, (3) a large hydrothermal cell forms and remains centered above the distal tip of the intrusion for the lifetime of the system, (4) effective hydrothermal activity ends by 70,000 yrs. Petrological evidence supports a wide sill-like chamber 15 km in half-width, and models of this chamber indicate that: (1) complete crystallization of the magma requires 100,000 yrs, (2) hydrothermal vents are present at the ridge axis, but most of the vents are located 5-10 km away from the axis, (3) a large hydrothermal cell develops at the distal tip of the magma chamber, while a series of small but vigorous cells develops directly above the intrusion, both features migrate toward the ridge axis as the magma solidifies, (4) effective hydrothermal activity ends by 170,000 yrs. Substantially different hydrothermal systems develop around these two chamber geometries and comparison of the models shows this is because different patterns of near-critical P-T conditions developed around them. The fundamental influence on the nature and pattern of hydrothermal circulation at MOR is the distribution of near-critical conditions.

Reproduction de : Thèse de doctorat : Génie électrique : Toulouse, INPT : 2007. / Titre provenant de l'écran-titre. Bibliogr. 63 réf.

Symbioses between prokaryotes and eukaryotes are ubiquitous in our biosphere, nevertheless, the effects of such associations on the partners' ecology and evolution are poorly understood. At hydrothermal vents, dominant invertebrate species typically host bacterial symbionts, which use chemical energy to fix carbon to nourish their hosts and themselves. In this dissertation, I present evidence that symbiont metabolism plays a substantive, if not major, role in habitat use by vent symbioses. A study of nearly 300 individuals of the symbiotic snail Alviniconcha sp. showed specificity between three host species and three specific symbiont phylotypes, as well as a novel lineage of Oceanospirillales. Additionally, this study revealed a structured distribution of each Alviniconcha-symbiont combination across ~300 km of hydrothermal vents that exhibited a gradient in geochemical composition, which is consistent with the physiological tendencies of the specific symbiont phylotypes. I also present a comparison of the in situ gene expression of the symbionts of Alviniconcha across that same geochemical gradient, which further implicates symbiont energy and nitrogen metabolism in governing the habitat partitioning of Alviniconcha. Finally, I present data that allies productivity and sulfur metabolism in three coexisting vent symbioses, demonstrating specific interaction with the environment. Three symbioses, namely the snails Alviniconcha and Ifremeria, and the mussel Bathymodiolus, are found around vents with differing concentrations of sulfide, thiosulfate and polysulfide. Using high-pressure, flow-through incubations and stable isotopic tracers, I quantified symbiont productivity via sulfide and thiosulfate oxidation, and provided the first demonstration of thiosulfate-dependent autotrophy in intact hydrothermal vent symbioses. I further demonstrated that vent symbioses can excrete thiosulfate and/or polysulfides, implicating them in substantively influencing the sulfur chemistry of their habitats. In summary, this dissertation demonstrates the importance of symbiont physiology to the ecology of prokaryote-eukaryote symbioses by revealing that symbiont activity may be critically important to the distribution of symbioses among specific niches, as well as can alter the geochemical environment through uptake and excretion of chemicals.

No description available.

Graduation date: 1999