In this dissertation, I use seismic imaging and waveform modeling methods to investigate melt migration processes and the structure of the magma plumbing system beneath the East Pacific Rise (EPR) and Endeavour segment of the Juan de Fuca Ridge, respectively. This work begins by studying shallow mantle reflections beneath the EPR. I find the amplitude versus offset and waveform characteristics of the reflections to be consistent with a sub-horizontal dunite channels located up to 20 km off-axis. The depth of the dunite channels correlate with patterns of mantle melt delivery and the predicted base of the thermal lithosphere, suggesting the channels are thermally controlled and may have formed in situ via dissolution by focused flow at the base of the lithosphere. This interpretation is consistent with field observations in ophiolites and numerical modeling of melt-focusing channels. The three-dimensional velocity structure of the Endeavour segment is then investigated to identify how patterns of mantle melt delivery influence the segment-scale distribution of crustal melt and crustal accretion. The results from this study indicate that the mantle magmatic system is skewed relative to the ridge-tracking crustal magmatic system and that this skew exerts primary control on magmatic, tectonic, and hydrothermal activity at the Endeavour segment. In regions where mantle melt delivery is axis-centered, mantle-derived melts are efficiently transported from the mantle to the crust, resulting in frequent crustal melt replenishment, associated seismogenic cracking, and enhanced crustal melt content that drives vigorous hydrothermal activity. Conversely, sites of off-axis melt delivery are characterized by less efficient vertical melt transport, resulting in infrequent crustal melt injection and hence, reduced crustal melt content and hydrothermal activity. Next, I focus on how along-axis variations in magma replenishment modulate crustal permeability and the intensity of hydrothermal circulation. Using full-waveform inversion, I show that sites of localized magma replenishment to the axial magma lens, along with induced seismogenic cracking, coincide with enhanced permeability. I conclude that the frequency of magma injection governs hydrothermal circulation patterns and heat flux at mid-ocean ridges. This dissertation includes previously published and unpublished coauthored material.

The biodiversity of two distinct marine environments was observed to describe the biogeocomplexity of these extreme ecological systems. A shallow-water hydrothermal vent in Papua New Guinea served as a study of a thermophilic ecosystem influenced by arsenic rich vent fluids while a 60 m deep offshore primarily anoxic karst sink served as a study of an anaerobic sulfur-influenced habitat. Both environments support unique biological communities that are influenced by the physical and chemical pressures imposed on them by the harsh conditions of these systems. In Tutum Bay, Ambitle Isle, Papua New Guinea, a transect was created from a shallow hydrothermal vent that extended 120 m away from the vent. Previous studies have shown that the geochemistry of the system is heavily influenced by arsenic which is toxic to most organisms. In this study, macro- and meiofauna were collected and scored and combined with bacterial sequence data collected along the length of the transect. It was found that near vent sites harbored biological communities more similar than sites further from the vent. Many species were found only at sites near the hydrothermal vent. Near-vent communities were less diverse than those away from the vent, and biodiversity generally increased as distance from the vent increased. Distinct correlations between thermophilic organisms and temperature were observed. The metabolic repertoire of the microbial communities suggests that many strategies are used to obtain energy and carbon. The relative abundance of bacteria containing genes to reduce arsenic was comparable to those able to reduce sulfur compounds. Primary production appeared to be a mix of chemo- and phototrophy. Food webs and association analysis suggest a complex interplay between macrofaunal, meiofaunal and bacterial communities. While the system is heavily influenced by arsenic, no specific correlation between the relative abundance of arsenic metabolizing organisms and the amount of arsenic in the system could be drawn. This is likely due to the fact that most of the arsenic produced by the system is readily adsorbed onto iron oxyhydroxides, reducing the arsenic's bioavailability. The anoxic conditions at Jewfish sink provide a different hurdle than the hot arsenic conditions found in Papua New Guinea. The anoxic conditions are shared by other pit features found in karst geography, but the metabolic processes between Jewfish sink and these other karst habitats are different. The blue holes and black holes of the Bahamas are some of the most well-studied of these karstic pits. In these features, which are large circular pits with diameters of over 300 m, light and sulfur are used as a means of energy acquisition. Jewfish sink, having an opening only 6 m in diameter, is light restricted compared to these systems. As a result, the strategy of organisms dwelling in the anoxic conditions of the sink is different than those found at the well-studied holes in the Bahamas. Geochemical measurements were recorded over two time periods spanning a combined total of 6 years. The anoxic bottom waters of Jewfish sink remain stable and contained high levels of sulfide throughout most of the seasons studies. Sequence analysis of prokaryotes within the sink showed that sulfur reducers had the highest relative abundance compared to other functional guilds. To monitor the changes of the microbial communities within the sink, bacterial communities were examined at 4 depths within the sink at 9 different intervals over a period of 685 days. Denaturing Gradient Gel Electrophoresis (DGGE) was used to fingerprint 16s rRNA bacterial communities and dissimilatory sulfite reducing communities by targeting the 16s rRNA bacterial gene and the dsr gene associated with dissimilatory sulfite reducing bacteria and archaea. The lowest depth studied within the sink (40 m) remained stable chemically and biologically until a turnover event occurred within the second winter of the study. This turnover event disrupted the biological communities at 40 m and led to a reestablished community comprised of different species that those found prior to the event. Upper waters within the sink show that clines establish themselves seasonally and partition zones that confine bacterial communities that are more similar to each other within these zones while excluding bacterial communities that are outside of these zones. Oxygenated water was shown to not contain prokaryotes containing the dsr gene. As the oxycline changed seasonally, dissimilatory sulfite reducing prokaryotes containing the dsr gene remained in the anoxic zone and required time to reestablish themselves whenever oxygenated water displaced them.

Cette thèse exploite les données de haute fréquence, plus proches des « vrais » processus de prix, mais qui engendrent un certain nombre de problèmes techniques qui nous permettent de réexaminer certains modèles d'évaluation des actifs financiers et la gestion des risques financiers. Nous commençons par explorer un phénomène dénommé « Rose des vents » découvert par Crack et Ledoit (1996) caractérisant les échanges à très haute fréquence. Cette question a déjà fait l'objet de plusieurs études qui n'ont pu complètement caractériser les conditions de cette structure sur quelques titres du marché français. Nous montrons dans un deuxième essai que la précision d'une mesure de risque efficiente, appelée Valeur-en-risque, est améliorée lorsqu'on utilise des données de haute fréquence. Nous exploitons une Analyse en Composants Indépendantes pour extraire les facteurs de risques, et nous montrons qu'elle donne des résultats plus robustes, hors échantillon, qu'une extraction par composantes principales. Nous généralisons ensuite les modèles traditionnels d'évaluation des prix des actifs aux moments d'ordres supérieurs « réalisés ». Nous montrons que cette généralisation améliore sensiblement les estimations. Nous terminons cette thèse par une extension sur l'extraction d'un temps d'échanges implicite qui permet de retrouver une distribution Gaussienne des rendements. Nous obtenons, à partir d'une méthode d'optimisation directe, un temps implicite sur plusieurs titres du marché français des actions.

La théorie de la Relativité d'échelle peut être utilisée pour contraindre des modèles dynamiques précis de systèmes gravitationnels. Dans un premier temps, l'objet de ce travail est d'explorer les possibilités théoriques liées aux diverses solutions de l'équation de Schrödinger généralisée (qui n'est autre que la forme prise par l'équation du mouvement dans un espace-temps fractal). Ces solutions théoriques sont alors utilisées pour modéliser la dynamique de plusieurs systèmes gravitationnels stationnaires. Nous analysons en détail : (i) la morphogenèse des vents stellaires, (ii) la dynamique du Groupe Local de galaxies et (iii) la dynamique des paires de galaxies dans l'univers proche. Une attention particulière a été portée sur l'élaboration d'un catalogue de paires de galaxies à partir d'un ensemble représentatif de sous-catalogues existant. L'ensemble des résultats montre l'existence de structures dans l'espace des phases en accord avec les diverses prédictions permises par la Relativité d'échelle. Nous concluons que l'utilisation des principes de la Relativité d'échelle permet de dévoiler et ainsi de mieux comprendre la dynamique des systèmes gravitationnels.

Les processus d'éjection de masse des étoiles sont un phénomène largement répandu. Les vents, les jets stellaires ou les jets extra-galactiques sont caractérisés par une forte accélération du plasma éjecté et une morphologie plus ou moins bipolaire, plus ou moins focalisée le long de l'axe de rotation de la source. Nous avons effectué différentes analyses des rôles de la pression, du champ magnétique et de la rotation du plasma dans les processus de formation et d'accélération des jets et sur leur stabilité. Les travaux exposés montrent, en particulier, le rôle essentiel du couplage magnétocentrifuge et du gradient de densité aussi bien dans la formation que dans la stabilisation des jets. L'étude des écoulements de vents de disques et de couronnes, nous a amené à étudier en détails le rôle des surfaces critiques et leur lien essentiel avec les conditions limites. Nous avons montré l'analogie des écoulements MHD avec la métrique des trous noirs : les surfaces critiques sont l'analogue des horizons. Il existe aussi des ergosphères MHD, distinctes des horizons, qui n'ont pas nécessairement le rôle prédominant qu'on leur a parfois accordé. Les modèles autosimilaires de vents de couronne nous ont permis d'établir des critères originaux sur la collimation des vents en jets et de relier la focalisation la distribution d'énergie sur la source. Par ailleurs, nous avons introduit la notion de rotateurs magnétiques efficaces et inefficaces pour distinguer entre les sources de jets confinés thermiquement et celles de jets confinés magnétiquement. L'application de ces modèles au vent solaire (données de la sonde Ulysse) et aux jets d'étoiles jeunes (jets de classes 2), nous a permis de valider les critères de collimation. Nous avons proposé un scénario pour l'évolution des jets en vents au cours de l'évolution stellaire, tout en proposant une autre origine pour la formation des jets protostellaires de classe 0. Par ailleurs, ces mêmes critères nous ont permis d'avancer une nouvelle interprétation de la classification des jets extragalactiques. Pour ces jets, une extension relativiste des modèles, sur laquelle nous travaillons, est cependant nécessaire.

This thesis is an investigation into biogenic sulfide oxidation and sulfate reduction associated with hydrothermal systems at oceanic spreading centers. First, the production of sulfur floc and 'snowblower' events due to sulfide oxidizing bacteria is investigated. The effects of sulfur floc on the pososity is shown to be negligible. 'Snowblower' events are shown to be sulfur floc that is stored over long periods of time mixed with a component of sulfur floc being created in a bloom event. Secondly, biogenic sulfate reduction in hydrothermal recharge zones is investigated and the effects on the concentration profiles is considered.

Seafloor hydrothermal systems play a key role in Earth fs energy and geochemical budgets. They also support the existence and development of complex chemosynthetic biological ecosystems that use the mineral-laden fluids as a source of energy and nutrients. This dissertation focuses on two inter-related topics: (1) heat output and geochemical fluxes at mid-ocean ridges, and (2) structural deformation of oceanic lithosphere related to subsurface serpentinization in submarine settings. The determination of heat output is important for several reasons. It provides important constraints on the physics of seafloor hydrothermal processes, on the nature of the heat sources at mid-ocean ridges, and on nutrient transport to biological ecosystems. Despite its importance, measurements of hydrothermal heat outputs are still scarce and cover less than 5% of active hydrothermal vent sites. In this work, we report development of two new devices designed to measure fluid flow velocities from the submersible at temperatures of up to 450 C and depths 5,000 m. By using these instruments on 24 Alvin dives, new measurements of hydrothermal heat output have been conducted at the Juan de Fuca Ridge, including first measurements from the High Rise and Mothra hydrothermal fields. The collected data suggest that the high-temperature heat output at the Main Endeavour Field (MEF) may be declining since the 1999 eruption. The flow measurement results, coupled with in-situ geochemical measurements, yielded the first estimates of geochemical fluxes of volatile compounds at MEF and Mothra. Our findings indicate that geochemical flux from diffuse flows may constitute approximately half of the net geochemical flux from Juan de Fuca Ridge. It has recently been recognized that serpentinization of mantle peridotites, due to its exothermic nature, may be a mechanism contributing to the heat output at mid-ocean ridges. The tectonic response of the crust to serpentinization of extensively distributed peridotites at mid-ocean ridges and subduction zones could provide a means of characterizing serpentinized regions in the oceanic lithosphere. These regions are often associated with surface topographic anomalies that may result from the volume expansion caused by the serpentinization reactions. Although there is a clear correlation between tectonics and serpentinization, the link is complex and still not understood. In this dissertation, we calculated the transformation strain and surface uplift associated with subsurface serpentinization of variously shaped ultramafic inclusions. Application of the results to explain the anomalous topographic salient at the TAG hydrothermal field (Mid-Atlantic Ridge) suggests that this feature may result from a serpentinized body beneath the footwall of a detachment fault. Because the depth of the potential serpentinized region appears to be more than 1.5 times the size of the inclusion, the uplift profile is relatively insensitive to the exact location or shape of the serpentinized domain. The rate of exothermic heat release needed to produce the serpentinized volume may contribute to the ongoing diffuse flow. Application of the results to an uplift feature associated with the Kyushu ]Palau subduction zone in the western Pacific, shows that approximately 3% transformational strain in an inclined serpentinized region of the mantle wedge near the subducted Kyushu ]Palau Ridge may result in the observed uplift on the Miyazaki Plain. Using the uplift data may help to constrain the level of the subsurface serpentinization.

Shallow-water hydrothermal vents occur world-wide in regions of volcanic activity. The vents located at Tutum Bay, Ambitle Island, Papua New Guinea are unique in that the vent fluids and surrounding sediments contain some of the highest concentrations of arsenic in a natural system. This study addresses the effects of the vent system on the benthic communities, focusing on the eukaryotes, macrofauna, meiofauna and bacteria. Samples were collected in November 2003 and May/June 2005. Analysis of the 2003 macrofaunal samples indicated that pH, rather than arsenic was influencing the benthic community, and that the hydrothermal influence occurred at a greater distance than expected. Results of more intensive sampling carried out in 2005 are the primary focus of this dissertation. The pore water and sediment characteristics revealed distinct physical habitats corresponding with distance from the vent. There was a trend of decreasing temperature and arsenic concentration and increasing salinity and pH with distance from the vent. The vent sediment was poorly sorted volcanic gravel, while sediments along the transect showed a gradient from fine, well sorted volcanic sands to coarser carbonate sands farther away. The macrofauna showed a trend of increasing diversity with distance from the vent and similar taxa were present in both the 2003 and 2005 samples. The vent community was dominated by the polychaete Capitella cf. capitata. The inner transect from 30 m to 140 m had low diversity. Dominant taxa included thalassinid shrimp and the amphipod Platyischnopus sp.A. The 180 m to 300 m sites had significantly higher diversity. The Danlum Bay reference site had relatively higher diversity than the nearshore transect sites and was dominated by deposit feeding polychaetes. Macrofaunal community structure was influenced by the sediment characteristics, notably by CaCO3 content, sorting and median grain size. The meiofaunal community also showed changes with distance from the vent. Chromadorid nematodes were dominant at the vent site and were a major component of the meiofauna at most sites, along with copepods. The meiofaunal community at the reference site showed greater similarity to the vent community and both sites had low abundances. Nematodes were more abundant than copepods near the vent, but copepods were more abundant farther offshore and at the reference site. Meiofaunal community structure was influenced primarily by the pore water temperature and salinity. Biological interactions with the macrofaunal community through physical disturbance and predation may also influence the meiofaunal community.  The molecular analysis of eukaryotic and bacterial diversity also revealed changes with distance from the vent. The 0 m and reference sites grouped together due to the presence of fungal sequences and the 140 m and 300 m sites grouped together due to a common molluscan sequence. Metazoans and fungi dominated the eukaryote sequences. The most abundant eukaryotic OTUs included fungi matching Paecilomyces sp. and Cladosporium cladosporioides and metazoans matching Viscosia viscosa (Nematoda) and Astarte castanea represented by 24 phyla and was dominated by Actinobacteria and γ-Proteobacteria. More bacterial phyla were present near the vent, while more overall OTUs were found at the intermediate sites along the transect. The most distant site had much lower diversity dominated by Firmicutes. The macrofaunal community had the strongest correlation with environmental variables. Comparison between the meiofauna and the metazoan sequences showed the proportion of nematodes found in both datasets were comparable, but the meiofauna analysis found a higher proportion of arthropods, while the molecular results were disproportionally high for platyhelminthes. Overall, the vents increased the complexity of the system by creating unique habitats. The extreme environment created by the hydrothermal activity maintained the surrounding habitat at an early successional stage colonized by a few opportunistic species. There was a gradation in the benthic communities away from the vent towards a more carbonate based climax community. The low pH environment had an effect on the sediment composition, which in turn influenced the benthic community. These findings can serve as a model for studying the potential effects of ocean acidification and climate change on benthic communities and marine biocomplexity.

In March of 2000, March of 2001, and April of 2002, multibeam bathymetry and backscatter data were collected, which revealed several low-temperature hydrothermal submarine springs in the Mudhole Submarine Springs (MHSS) area that were investigated by SCUBA divers. High-resolution multibeam sonar provides a precise way of defining the geomorphology of the seafloor. The bathymetry data were used to understand (1) vent geomorphology and how it varied from vent to vent; (2) spatial patterns of active vents compared to extinct vents and known land springs identified by Kohout (1977) and Breland (1980); and (3) potential correlations between geochemical and geomorphological characteristics of the vents in the study area. SCUBA observations show that MHSS, Spring #3, New Spring, Northern Rusty, Rusty, and Near Rusty are active springs, while Dormant Spring and Sinister Spring were extinct or inactive at the time of the March 2001 cruise.During the April 2002 cruise the locations of Rusty Spring, New Spring and MHSS were confirmed. Two submarine springs, Creature Hole and Sparky Lee were also confirmed. Spring #3 is the deepest spring and Dormant Spring is the shallowest. There appears to be a rough spatial correlation between vents located on land and the vents on the seafloor, in which all known vents are either to the west or north of Lake Okeechobee. Vent distribution in the MHSS study area appears to correlate with the structural pattern of the local seafloor. Backscatter data and SCUBA observations show that fine to medium grain siliciclastic sediment bands overlie limestone hardbottom in a NE-SW orientation. Although vent geomorphologies are generally distinctive, vent activities generally correlate with the steepness of vent depressions.Most active vents had slopes of 6 degrees or greater, with the exception of Rusty Spring and Near Rusty Spring whose slopes ranged from 2.5 degrees and 6 degrees; whereas all the inactive vents had slopes of 5 degrees or less. Most active vents have "V"-shaped profiles versus the "U"-shaped profiles of most of the inactive vents. The inactive springs have shallower maximum depths and shallower ambient seafloor depths than the active vents.

<p>Genetic diversity, population structure, and connectivity influence interactions among communities and populations. At hydrothermal vents in the western pacific, population structure in vent-associated species could occur at spatial scales ranging from vent sites separated by a few hundred meters to oceanic basins separated by more than 3000 kilometers. The spatial scale of population structure has important conservation implications; species that are well-connected across large geographic regions are more resilient to natural and anthropogenic disturbance. This dissertation examines the genetic diversity, population structure, and connectivity of 3 vent-associated species in the western Pacific. It first presents results from the development of microsatellite primers for Ifremeria nautilei, a deep-sea vent associated snail, then uses mitochondrial COI sequences and a suite of microsatellite markers to examine the broader connectivity of three vent-associated species, Ifremeria nautilei, Chorocaris sp. 2, and Olgasolaris tollmanni, across three back-arc basins in the western Pacific. </p><p>Within Manus Basin, no significant genetic differentiation was detected in populations of Ifremeria nautilei (based on COI and microsatellite), Chorocaris sp. 2 (based on COI and microsatellite), or Olgasolaris tollmanni (based on COI). A previously documented low-abundance cryptic species, Chorocaris sp. 1, was detected from a single site, South Su (based on COI). The population of I. nautilei in Manus Basin was found to be significantly differentiated from a second population that appeared to be panmictic across North Fiji and Lau Basin (based on COI and microsatellites). Chorocaris sp. 2 was also found to be significantly differentiated between Manus and North Fiji Basin (based on COI). Both I. nautilei and Chorocaris sp. 2 showed signs of potential low-level migration between Manus and other southwestern Pacific basins. O. tollmanni was undifferentiated between Manus and Lau Basin (based on COI). It is likely that a variable impedance filter exists that limits the realized dispersal of some, but not all species between Manus Basin and other western Pacific back-arc basins. The presence of a variable filter has implications for the conservation and management of hydrothermal vents in Manus Basin, as it is unclear what effects sustained anthropogenic disturbance will have on isolated populations of I. nautilei and Chorocaris sp. 2.</p> / Dissertation