En aquest treball s'estudia la convecció en una capa plana de fluid entre dues superfícies perfectament conductores sotmesa a un gradient advers de temperatura. Es considera el problema bidimensional amb periodicitat en la direcció longitudinal i s'incideix especialment en la generació espontània de vents. Les condicions de contorn que s'utilitzen a les superfícies (cas rígid) permeten esforços tallants no nuls, per això s'ha permés l'existència, no només d'un flux amb vent, sinó d'un flux de massa net. El problema es planteja en una caixa periòdica de longitud L i s'analitzen solucions d'aquesta longitud tant amb una parella de rotlles com amb més d'una. Aquests dos casos requereixen un estudi diferent, és per això que el treball es divideix en dues parts. La primera part consta de:(1) l'anàlisi d'estabilitat de solucions amb una sola parella de rotlles, que, gràcies a les simetries del sistema, factoritza en quatre problemes. Es presenten les corbes d'estabilitat pel número de Prandtl 10, destacant que és per valors de L petits on, via una bifurcació de Hopf, es genera vent amb un perfil antisimètric i que es troba una corba que presenta una bifurcació subcrítica estacionària amb vent antisimètric degut a la ressonància d'estats purs 1:2,(2) la dinàmica dels rotlles per a número de Prandtl 10, fixant alguns valors de L que són significatius de la dinàmica per aquest valor del número de Prandtl. En tots els casos, augmentant el número de Rayleigh, apareixen vents que bifurquen o no del flux bàsic i com a etapa final sempre es generen solucions amb un flux de massa net, solucions que han perdut qualsevol simetria, (3) un model d'equacions d'amplitud que justifica el caràcter de les bifurcacions secundàries i permet entendre el comportament no lineal de les solucions prop de la bifurcació. La segona part consta de:(4) l'anàlisi d'estabilitat de totes les solucions amb més d'una parella de rotlles enfront de qualsevol pertorbació periòdica que pugui cabre al contenidor. Utilitzant la teoria de Floquet es pot reduïr l'anàlisi a un domini de longitud la periodicitat bàsica de la solució. Això permet calcular quin és el rang de paràmetres on les parelles de rotlles són estables enfront de qualsevol pertorbació periòdica (es presenta el cas amb número de Prandtl 10). Els resultats ens diuen que les ressonàncies n-1:n amb n>1 dominen 'estabilitat de n parelles de rotlles,(5) el càlcul de totes les solucions estacionàries amb les mateixes simetries que els rotlles primaris. S'observa que ,el fet de que, fixant paràmetres, no hi hagi unicitat de solucions es deu a les ressonàncies 1:2n+1. / Thermal convection in a planar fluid layer with perfectly conducting surfaces and with an advers temperature gradient is studied. The bidimensional problem with periodicity in the longitudinal is considered. The spontaneous generation of winds is the main goal of this work. Rigid boundary conditions are used in the vertical, allowing the generation of a mean flow and a net mean mass flux. We set out the problem in a periodic container with lenght L and we analize solutions with this lenght containing one o more pairs of rolls. This two cases need a different study, is for this reasonthe work is divided into two parts. The firs part contains:(1) the stability analysis of solutions with one pair of rolls. This analysis , due to the symmetries of the system, factorize into four problems. The stability curves with Prandtl number 10 are calculated. We observe that for small values of $L$ a mean flow with an antisymmetric mean flow is generated via a Hopf bifurcation. We also detect a curve that presents a subcritical steady state bifurcation with an antisymmetric mean flow. This curve is due to the 1:2 resonance of pure mode states, (2) the nonlinear dynamics of rolls with Prandtl number 10 for some values of L, significant of the dynamics of this Prandtl number. In all cases, increasing the Rayleigh number, an spontaneos mean flow is generated. These mean flow can or cannot bifurcate from the basic convective regime but the final solutions present a net mean mass flux and no symmetries are present, (3) a model of amplitude equations that interprets the caracter of secundary bifurcations and nonlinear dynamics of them near the bifurcation. The second part contains:(4) the stability analysis of solutions with more than one pair of rolls with respect periodic perturbations. Using Floquet theory we reduce the analysis to a container with lenght the basic periodicity of solution. With this simplication we calculate the rang of parameters with stable pairs of rolls with respect any periodic instability (the case Prandtl number 10 is presented). The resultsclarify that the n-1:n resonances with n>1 dominate the stability of n pairs of rolls.(5) the research of all steady solutions with same symmetries that primary rolls. We observe that 1:2n+1 resonances produce the non-unicity of these solutions when some parameter values are fixed.

Hydrothermal systems at oceanic spreading centers play an important role in the composition of seawater, the formation of ore deposits, the support of microbial and macrofaunal ecosystems, and even for the development of life on early earth. These circulation systems are driven by heat transport from the underlying magma chamber, where latent heat of crystallization and sensible heat from cooling are transferred by vigorous, high Rayleigh number convection through a thin conductive boundary layer. The traditional study of magmatic-hydrothermal systems is primarily based on the time-series observation, which takes the form of repeat visits, continuous offline monitoring by autonomous instruments, or continuous online monitoring by instruments with satellite or cable links to shore. Although a number of studies have deployed autonomous monitoring instruments at vents and around mid-ocean ridges to investigate geophysical and hydrothermal processes, the data are still rather limited and a comprehensive understanding of magma-hydrothermal processes at oceanic spreading centers is lacking. Numerical modeling needs to be employed to elucidate the dynamic behavior of magmatic hydrothermal systems and for testing completing hypotheses in these complex, data-poor environments. In this dissertation, I develop a mathematical framework for investigating heat transport from a vigorously convecting, crystallizing, cooling, and replenished magma chamber to an overlying hydrothermal system at an oceanic spreading center. The resulting equations are solved numerically using MATLAB. The simulations proceed step-by-step to investigate several different aspects of the system. First, I consider a hydrothermal system driven by convection, cooling and crystallization in a ~ 100 m thick basaltic magma sill representing an axial magma chamber (AMC) at an oceanic spreading center. I investigate two different crystallization scenarios, crystal-suspended and crystal-settling, and consider both un-replenished and replenished AMCs. In cases without magma replenishment, the simulation results for crystals-suspended models show that heat output and the hydrothermal temperature decrease rapidly and crystallinity reaches 60% in less than ten years. In crystals-settling models, magma convection may last for decades, but decreasing heat output and hydrothermal temperatures still occur on decadal timescales. When magma replenishment is included, the magmatic heat flux approaches steady state on decadal timescales, while the magma body grows to double its original size. The rate of magma replenishment needed ranges between 5 x 10⁵ and 5 x 10⁶ m³/yr, which is somewhat faster than required for seafloor spreading, but less than fluxes to some terrestrial and subseafloor volcanoes on similar timescales. The heat output from a convecting, crystallizing, replenished magma body that is needed to drive observed high-temperature hydrothermal systems is consistent, with gabbro glacier models of crustal production at mid-ocean ridges. Secondly, I study the heat transfer model from a parametric perspective and examine the effects of both initial magma chamber thickness and magma replenishment rate on the hydrothermal heat output. The initial rate of convective heat transfer is independent of the initial sill thickness; but without magma replenishment, the rate of decay of the heat output varies linearly with thickness, resulting in short convective lifetimes and decaying hydrothermal temperatures for sills up to ~ 100m thick. When magma replenishment is included in crystals settling scenarios at constant or exponentially decreasing rates of ~ 10⁻⁸ m/s to the base of the sill, growth of the sill results in stabilized heat output and hydrothermal temperature on decadal timescales and a relatively constant to increasing thickness of the liquid layer. Sills initially ~ 10 m thick can grow, in principal, to ~ 10 times their initial size with stable heat output and a final melt thickness less than 100m. Seismic data provides evidence of AMC thickness, but it can not discriminate whether it denotes initial magma thickness or is a result of replenishment. These results suggest that magma replenishment might not be seismically detectable on decadal time scales. Periodic replenishment may also result in quasi-stable heat output, but the magnitude of the heat output may vary considerably in crystals suspended models at low frequencies; compared to crystals settling models. In these models the direct coupling between magmatic and hydrothermal heat output suggests that heat output fluctuations might be recorded in hydrothermal vents; but if damping effects of the basal conductive boundary layer and the upflow zone are taken into account, it seems unlikely that heat output fluctuations on a time scale of years would be recorded in hydrothermal vent temperatures or heat output. Thirdly, I extend the work to the binary system motivated by the fact that the real magmas are multi-component fluids. I focus on the extensively studied binary system, diopside-anorthite (Di-An), and investigate the effects of convection of a two-component magma system on the hydrothermal circulation system through the dynamic modeling of both temperature and heat output. I model the melt temperature and viscosity as a function of Di concentration, and incorporate these relations in the modeling of the heat flux. Simulations comparing the effects of different initial Di concentrations indicate that magmas with higher initial Di concentrations convect more vigorously, which results in faster heat transfer, more rapid removal of Di from the melt and growth of crystals on the floor. With magma replenishment, I assume that the magma chamber grows either horizontally or vertically. In either case magma replenishment at a constant rate of ~ 10⁻⁸ m³/a can maintain relatively stable heat output of 10⁷-10⁹ Watts and reasonable hydrothermal vent temperatures for decades. The final stabilized heat flux increases with increasing Di content of the added magma. Periodic replenishment with a 10 year period results in temperature perturbations within the magma that also increase as a function of increasing Di. With the simple magma model used here, one can not discern conclusively whether the decrease in magma temperature between the 1991/1992 and the 2005/2006 eruptions at EPR 9°50'N involved replenishment with more or less evolved magmas. Fourthly, I investigate a high-silica magma chamber as the hydrothermal circulation driver. I construct viscosity models for andesite and dacite melts as a function of temperature and water content and incorporate these expressions into a numerical model of thermal convective heat transport from a high Rayleigh number, well-mixed, crystallizing and replenished magma sill beneath a hydrothermal circulation system. Simulations comparing the time dependent heat flux from basalt, 0.1wt.% andesite, 3wt.% andesite, and 4wt.% dacite, indicate that higher viscosity magmas convect less vigorously, which results not only in lower heat transport and hydrothermal vent temperatures, but also in a lower decay rate of the vent temperature. Though somewhat colder, hydrothermal systems driven by unreplenished high-silica melts tend to have a longer lifetime than those driven by basalts, assuming a heat output cutoff of 10⁷ Watts. As in the basaltic case, magma replenishment at a rate of ~ 3 x 10⁵ - 3 x 10⁶ m³/a can maintain relatively stable heat output of 10⁷-10⁹ Watts and hydrothermal vent temperatures for decades. Idealized models of porous flow through the lower crust suggest such replenishment rates are not likely to occur, especially for high-viscosity magmas such as andesite and dacite. Long term stability of hydrothermal systems driven by these magmas requires an alternate means of magma replenishment. Finally, the dissertation concludes by discussing some avenues for future work. Most important of these are to: (1) couple magma convection with more realistic hydrothermal models and (2) link magma chamber processes to better physical models of replenishment and eruption.

Thèse de doctorat : Sciences de l'Univers et de l'environnement : Paris 12 : 2007. / Thèse uniquement consultable au sein de l'Université Paris 12 (Intranet). Titre provenant de l'écran-titre. Bibliogr. : 97 réf.

The most universal abiotic influence is temperature, and thus, thermotolerance, adaptations and response to thermal variation, is a fundamental factor shaping evolution. Prokaryotic life may have an upper thermal limit near \(150^{\circ}C\); however, eukaryotic survival is limited to \(50^{\circ}C\) – the thermal maximum for sustained biosynthesis and homeostasis. My research focuses on understanding the physiological and biochemical factors that limit eukaryotic thermotolerance, by studying an organism near the upper limit of all eukaryotes: Paralvinella sulfincola. P. sulfincola, a hydrothermal vent polychaete, has the broadest known thermal range of any metazoan: \((5-48^{\circ}C)\). This species, along with the mesotolerant congener with Paralvinella palmiformis, is found at vents along the Juan de Fuca Ridge, Washington, USA. Making an ideal study system, both species are found in similar habitats, genetically comparable, and amenable to recovery and shipboard experimentation. Here, I present data from a series of high pressure in vivo experiments that investigate stress response to variations in temperature, pH, sulfide concentration, and duration. Field work was coupled with a suite of biomolecular techniques including pyrosequencing, comparative proteomics, enzyme assays, and quantitative PCR. From this research, the first to quantify global protein and antioxidant responses to temperature in an extremely thermotolerant eukaryote, three primary conclusions can be reached. 1) Pronounced thermal tolerance in P. sulfincola is likely enabled by its constitutive expression of heat shock proteins and limited by its ability to quickly and appropriately respond to the commensurate increase in oxidative stress. 2) Thermal tolerance limits are likely negatively affected by synergistic multistress effects. 3) Antioxidant gene expression response differs significantly between chronically and acutely stressed treatments, supporting the theory that oxidative stress is limiting in this system.

At hydrothermal vents, thermal and chemical gradients generated by the mixing of hydrothermal fluids with seawater provide diverse niches for prokaryotic communities. To date, our knowledge of environmental factors that shape bacterial and archaeal community composition and metabolic activities across these gradients within the active sulfide structures is limited. While many studies have laid the foundation for our understanding of the extent of diversity in relation to varying hydrothermal settings, few studies exists regarding the detailed spatial relationships between vent geochemistry and the abundance, distribution, and metabolic characteristics of the endolithic hosted communities. Even fewer data have been generated on the magnitude of metabolic rates and factors controlling the kinetics of these reactions have not been well constrained.

Thesis (Ph. D.)--Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2007. / Title from Web page (viewed on Mar. 24, 2008). "September 2007." Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 2008. / Vita. Includes bibliographical references (leaves 131-141).

Thesis (M.S.)--University of California, San Diego, 1990. / Includes bibliographical references (leaves 71-72).

Thesis (M.S.)--Joint Program in Oceanography/ Applied Ocean Science and Engineering, Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution, 2005. / Bibliography: p.63-65.

Thesis (M. S.)--Earth and Atmospheric Sciences, Georgia Institute of Technology, 2008. / Lowell, Robert, Committee Chair ; Newman, Andrew, Committee Member ; Peng, Zhigang, Committee Member.