Thesis (Ph.D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2010. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from student submitted PDF version of thesis. / Includes bibliographical references. / Anthropogenic activity is rapidly changing the global climate through the emission of carbon dioxide. Ocean carbon and sulfur cycles have the potential to impact global climate directly and through feedback loops. Numerical modeling, field and laboratory studies are used to improve our mechanistic understanding of the impact of natural variability on carbon and sulfur cycling. Variability in ocean physics, specifically changes in vertical mixing, is shown to significantly impact both cycles. The impact of interannual variability on the detection and attribution of anthropogenic carbon (Canthro) and the storage of Canthro in the Atlantic Ocean is analyzed using a three-dimensional global ocean model. Several regions are identified where empirical methods used to estimating Canthro are not able to correct for natural variability in the ocean carbon system. This variability is also shown to bias estimates of long term trends made from hydrographic observations. In addition, the storage of Canthro in North Atlantic mode waters is shown to be strongly influenced by water mass transformation during wintertime mixing events. The primary mechanisms responsible for seasonal variability in dimethylsulfoniopropionate (DMSP) degradation and dimethylsulfide (DMS) production in the oligotrophic North Atlantic are investigated using potential enzyme activity and gene expression and abundance data. Vertical mixing and UV radiative stress appear to be the dominant mechanisms behind seasonal variability in DMS production in the Sargasso Sea. This thesis demonstrates the importance of and dynamics of bacterial communities responsible for DMSP degradation and DMS production in oligotrophic surface waters. These findings suggest that modifications to current numerical models of the upper ocean sulfur cycle may be needed. Specifically, current static parameterizations of bacterial DMSP cycling should be replaced with a dynamic bacterial component including DMSP degradation and DMS production. / by Naomi Marcil Levine. / Ph.D.

Thermochemical water splitting cycles have been conceptualized and researched for over half a century, yet to this day none are commercially viable. The heavily studied Sulfur-Iodine cycle has been stalled in the early development stage due to a difficult HI-H₂O separation step and material compatibility issues. In an effort to avoid the azeotropic HI-H₂O mixture, an imidazolium-based ionic liquid was used as a reaction medium instead of water. Ionic liquids were selected based on their high solubility for SO₂, I₂, and tunable miscibility with water. The initial low temperature step of the Sulfur-Iodine cycle was successfully carried out in ionic liquid reaction medium. Kinetics of the reaction were investigated by I₂ colorimetry. The reaction also evolved H₂S gas, which led to the conceptual idea of a new Sulfur-Sulfur thermochemical cycle, shown below: / 4I₂(l)+4SO₂(l)+8H₂O(l)↔4H₂SO₄(l)+ 8HI(l) / 8HI(l)+H₂SO₄(l)↔ H₂S(g)+4H₂O(l)+4I₂(l) / 3H₂SO₄(g)↔ 3H₂O(g)+3SO₂(g)+1½O₂(g) / H₂S(g)+2H₂O(g)↔ SO₂(g)+3H₂(g) / The critical step in the Sulfur-Sulfur cycle is the steam reformation of H₂S. This highly endothermic step is shown to successfully occur at temperatures in excess of 800˚C in the presence of a molybdenum catalyst. A parametric study varying the H₂O:H₂S ratio, temperature, and residence time in a simple tubular quartz reactor was carried out and Arrhenius parameters were estimated. All reactive steps of the Sulfur-Sulfur cycle have been either demonstrated previously or demonstrated in this work. A theoretical heat-to-hydrogen thermal efficiency is estimated to be 55% at a hot temperature of 1100 K and 59% at 2000 K. As a highly efficient, all-fluid based thermochemical cycle, the Sulfur-Sulfur cycle has great potential for feasible process implementation for the transformation of high quality heat to chemical energy. / Graduation date: 2012

Underlying all applications of sulfur isotope analyses is our understanding of isotope systematics. This dissertation tests some fundamental assumptions and assertions, drawn from equilibrium theory and a diverse body of empirical work on biochemical kinetics, as applied to the multiple sulfur isotope systematics of microbial sulfate reduction. I take a reductionist approach, both in the questions addressed and experimental approaches employed. This allows for a mechanistic, physically consistent interpretation of geological and biological sulfur isotope records. The goal of my work here is to allow interpreters a more biologically, chemically and physically parsimonious framework to decipher the signals coded in modern and ancient sulfur isotope records. / Earth and Planetary Sciences

Dimethylsulphoniopropionate (DMSP) and dimethylsulphoxide (DMSO) (collectively DMSP/O) are produced by marine algae, including symbiotic algae within corals. These sulphur compounds are important not only in sulphur cycle dynamics but also in potentially mediating atmospheric conditions, alleviating the effects of climate change and contributing to reef health. Most research has focused on the production of DMSP and its major degradation product, the climatically active gas, dimethylsulphide (DMS) by Acropora corals in the Great Barrier Reef. However, mechanisms for the production and release of DMSP/O by different reef taxa is poorly understood. Recently the importance of mesophotic reefs as refugia for shallow water corals has been postulated, however their role in the marine sulphur cycle is unknown. This research aimed to improve our understanding of the contemporary and climate change induced seawater and tissue production of DMSP/O in a range of reef environments and taxa. This was achieved through a combination of laboratory and field - based studies, using modern and established techniques. An effect of both elevated temperature and OA on increased tissue and seawater concentrations of DMSP/O production is reported in field and laboratory studies. Contrasting effects of benthic cover on tissue DMSP/O distributions and seawater DMSP are also noted. The importance of the physical and hydrodynamic environment on biogeochemical connectivity both within a reef and between neighbouring reefs is also focussed on. Crucially, however, the novel tissue and seawater data from mesophotic sites suggests that deeper reefs could affect the biogeochemistry of their shallow water counterparts. The key finding from this work is that climate change will result in increased seawater DMSP concentrations via two mechanisms; through the increase of cellular production of DMSP/O in all reef taxa, and by increasing the biomass of prolific DMSP producers as reefs transition to a fleshy/macroalgal assemblage. Whilst this could potentially mediate the effects of climate change, it will probably also worsen overall reef health, lead to a restructuring of reef communities from the microbial level upwards and will have possibly permanent and deleterious effects on overall ecosystem function.

La formation du gypse (CaSO4.2H2O) dans les bassins marginaux méditerranéens au cours du Messinien est contrôlée par la restriction des bassins et par le cycle hydrologique local. La compétition entre l’évaporation et l’apport d’eau douce par les rivières, en association avec des échanges limites avec la Méditerranée, ont permis la mise en place de conditions chimiques favorables à la formation du gypse. La restriction des bassins entraine, de plus, l’augmentation de la consommation de l’oxygène par les microorganismes, l’anoxie, et la mise en place d’un cycle biogéochimique actif du soufre. Au cours de cette étude, j’utilise la composition isotopique stable du gypse en tant que traceur des cycles de l’eau et du soufre dans les bassins marginaux. Le but est de mieux comprendre les conditions hydrologiques et géochimiques qui ont mené à la précipitation du gypse. Ce problème se place dans un débat actuel de la communauté scientifique, particulièrement depuis que de récents travaux proposent qu’une partie du gypse dans les bassins marginaux aurait pu précipiter à partir d’une colonne d’eau à faible salinité (£ 35 PSU) - hypothèse qui peut sembler peu réaliste d’un point de vue géochimique. J’ai mené une analyse isotopique à haute-résolution des couches de gypse qui composent les alternances cycliques gypse-marnes dans les bassins messiniens de Caltanissetta (BC, Sicile) et du Piémont (BP, nord-ouest de l’Italie). Ces alternances gypse-marnes correspondraient à l’expression sédimentaire des cycles astronomiques de précession (~20 ka), pendant lesquels les bassins marginaux ont subi une alternance de conditions climatiques arides et humides. Le cycle hydrologique a été trace grâce aux mesures des compositions isotopiques de l’oxygène et de l’hydrogène de l’eau de cristallisation des gypses ; le cycle biogéochimique du soufre a quant à lui été trace en mesurent les compositions isotopiques du soufre et de l’oxygène des ions sulfates des gypses. J’ai pu observer que : (1) les isotopes de l’eau piégée dans les gypses sont nettement plus légers que ceux théoriquement attendus pour des gypses ayant précipite uniquement à partir d’une eau de mer, et (2) l’eau du BC est caractérisée par un plus fort déficit en deutérium - compare à sa teneur en 18O - que l’eau du BP. Combine a un modèle hydrologique numérique, ces observations impliquent que (1) la précipitation des gypses est réalisée sous l’influence d’un apport d’eau douce fluviatile important, particulièrement au nord du BP, et est donc caractérisée par de très faibles salinités (27-50 psu pour le BC et 10-42 psu dans le BP) ; (2) le contraste de déficit en deutérium entre les deux bassins résultant de la différence de teneur en deutérium des flux évaporais respectifs, est contrôlée par a une différence d’humidité atmosphérique : cela implique que l’atmosphère au-dessus du BC était plus sèche que celle au-dessus du BP. Nous pouvons alors proposer qu’un gradient latitudinal d’humidité relative similaire à l’actuel existait au Messinien, apportant la preuve d’un climat de type méditerranéen dans la région il y a 5.97 Ma. La composition isotopique des ions sulfate suggère globalement une formation de gypse sous influence marine. Cependant, des divergences observées avec la signature marine messinienne mettent en évidence un cycle biogéochimique du soufre actif, contrôlé par la réduction des sulfates et l’oxydation des sulfures. En particulier : (1) les sulfates du BP enrichis en 18O et 34S sont indicateurs d’une sulfato-reduction dans un système géochimique ouvert ou la perte de 32S est liée a la formation de minéraux soufres sédimentaires ; (2) l’enrichissement (BC) ou l’appauvrissement (BP) significatifs en 18O dans les échantillons alors que la teneur en 34S est la même que celle de l’eau de mer indique une reoxydation de sulfure dans un système géochimique ferme d’un bassin marginal soit évaporait (BC) soit dilue (BP). / The formation of gypsum (CaSO4.2H2O) in Messinian Mediterranean marginal basins is controlled by basin restriction and the local hydrological cycle. Acting together, evaporation, river input and restricted water exchange with the Mediterranean basin bring about the chemical conditions for gypsum formation. Basin restriction also leads to enhanced microbial oxygen consumption, anoxia, and the triggering of active biogeochemical sulfur cycling. In this work I use the stable isotopic composition of gypsum as a proxy of water and sulphur cycling in the marginal basins. The goal is to better understand the hydrological and geochemical conditions that lead to gypsum precipitation. This is an open question, especially since recent work has proposed that part of the gypsum in marginal basins precipitated from a low-salinity (£ 35 PSU) water column - a hypothesis that seems unrealistic based on simple geochemical considerations. I carried out a high-resolution isotopic study of gypsum layers composing gypsum-marl cycles in the Messinian Caltanissetta (Sicily) and Piedmont (north-western Italy) marginal basins (CB and PB, respectively). These gypsum-marl cycles are thought to be the sedimentary expression of astronomical precession cycles (~20 kyr), during which the marginal basins experienced a succession of arid and wet conditions. The hydrological cycle was tracked by measuring the oxygen and hydrogen isotope composition of the gypsum-bound water molecule; the biogeochemical sulfur cycle was tracked by measuring the sulfur and oxygen isotope composition of the gypsum sulfate ion. I observed that: (1) the isotopes of gypsum-bound water are considerably lighter than those expected for gypsum precipitated via evaporation of seawater, and (2) water in the Caltanissetta basin was characterized by a higher deuterium deficit - compared to its 18O content - than water in the Piedmont basin. In conjunction with a hydrological box-model, these observations imply that (1) gypsum precipitation takes place under the influence of large riverine freshwater fluxes, particularly in the North Piedmont basin, that result in very low salinities (27-50 psu in CB and 10-42 psu in PB) and (2) the contrast in deuterium deficit results from atmospheric humidity-drived difference in the deuterieum content of the evaporative flux, implying that the atmosphere over the CB was drier than that over the PB. Thus, a latitudinal relative humidity gradient similar to the modern one existed in the Messinian, providing evidence for a Mediterranean-like climate in the region 5.97 million years ago. The isotopic composition of the gypsum sulfate ion suggests that it originates from coeval sea water. Deviation from the Messinian marine signature, however, highlights an active biogeochemical sulfur cycle driven by sulfate reduction and sulfide oxidation. In particular, (1) 18O- and 34S-rich sulfate in the Piedmont basin indicates sulfate-reduction in a geochemically open system where 32S is lost to sedimentary sulfide minerals, and (2) significant 18O-enrichment (CB) or 18O-depletion (PB), in samples where the 34S concent is that of seawater, indicates re-oxidation of sulphide in a geochemically closed system of an evaporative (CB) or dilution (PB) marginal basin. A strong relation between the hydrological cycle and the biogeochemical cycle is thus highlighted in marginal Messinian basins

Les cheminées et sédiments hydrothermaux actifs du Bassin de Guaymas (Mexique) hébergent diverses communautés microbiennes présentant différents métabolismes, y compris ceux impliqués dans les cycles biogéochimiques du soufre et du fer. Il est établi, que, dans ces écosystèmes dynamiques, les micro-organismes qui dépendent pour leur croissance des substrats présents dans leur environnement pourraient à leur tour, affecter localement la composition du fluide hydrothermal et la minéralogie des cheminées, la composition des sédiments, en favorisant la dissolution et/ou la précipitation de certaines phases minérales. Pour étudier ces interactions procaryotes-biotopes, et établir des liens entre la structure, l’activité et les signatures isotopiques des communautés microbiennes et les caractéristiques physico-chimiques des systèmes hydrothermaux du Bassin de Guaymas, une approche pluridisciplinaire mettant en oeuvre des techniques de microbiologie, de géochimie et d’isotopie, lors des cultures d’enrichissements en bioréacteur et des études de colonisation de substrats basaltiques a été réalisée. Ces travaux ont permis : 1) de caractériser la diversité des micro-organismes de différents compartiments de l’écosystème hydrothermal (cheminée et sédiments) du Bassin de Guaymas par des approches culturales et moléculaires ; 2) de décrypter le fonctionnement des cycles biogéochimiques du soufre et du fer en mettant en évidence la présence simultanée, à haute température et en anaérobiose, de micro-organismes sulfo-réducteurs, sulfato-réducteurs, sulfo-oxydants mais également ferri-réducteurs et ferro-oxydants ; et 3) de mieux comprendre les interactions procaryotes-minéraux-fluide en soulignant le rôle des microorganismes dans la modification des conditions environnementales, la formation de minéraux ainsi que leur rôle direct ou indirect dans les fractionnements des isotopes du Fer et Soufre. Ces études ont donc permis de montrer l’importance des interactions croisées entre les différents composantes : communautés microbiennes, le fluide (fluide hydrothermal, eaux interstitielles des sédiments, eau de mer) et les structures minérales des écosystèmes hydrothermaux. / Active hydrothermal chimney and sediments of the Guaymas Basin (Mexico) host various microbial communities with different metabolisms, including those involved in biogeochemical cycles of sulfur and iron. It is established that, in these dynamic ecosystems, microbial activity depends on the availability of substrates in their environment and that prokaryotes could, in return locally affect the composition of the hydrothermal fluid and mineralogical composition of the chimney or sediment, by mediating the dissolution and / or precipitation of some mineral phases. In order to study these prokaryotes-biotope interactions, and establish links between the structure, the activity and the isotopic signatures of microbial communities with the physico-chemical characteristics of hydrothermal systems of Guaymas Basin, a multidisciplinary approach based on the implementation of microbiology, geochemistry and isotope technics was performed using enrichment cultures in bioreactors and the study of the colonization of basaltic substrates. This work led to: 1) characterize the diversity of microorganisms in different hydrothermal compartments (chimney and sediments) of the Guaymas Basin using both cultural and molecular approaches; 2) to decrypt the functioning of sulfur and iron biogeochemical cycles, by highlighting the occurrence, at high temperature and anaerobic condition, of sulfur-reducing, sulfate-reducing, sulfur-oxidizing and also iron-reducing and iron-oxidizing prokaryotes ; and 3) to better understand the prokaryote-mineral-fluid interactions by pointing out the role of microorganisms in environmental condition changes, mineral precipitation and their direct or indirect role in iron and sulfur isotope fractionation. Thus these studies have demonstrated the importance of the cross-interactions between the different hydrothermal components: microbial communities, fluids (hydrothermal fluid, sediment pore water, sea water) and mineral structures.

Cette étude se situe dans le cadre des recherches menées par le CEAEA sur la production massive d'hydrogène, sans émission de gaz à effet de serre, via un cycle thermo-chimique de décomposition de l'eau couplé à une source de chaleur à haute température d'origine nucléaire. Dans le cas particulier du cycle dit« Iode-Soufre», on doit extraire H2 à partir d'un mélange H2/HI/H20 très corrosif, opération pour laquelle des procédés membranaires ont été proposés. L'objectif de ce travail est le développement de membranes zéolithiques de type MFI susceptibles d'être utilisées dans ce contexte. Nous présentons les différents matériaux utilisés, la méthodologie de synthèse de couches minces de Silicalite-1 et de ZSM-5 synthétisée sans structurant organique, les techniques de caractérisation des membranes. Une étude cinétique nous a permis d'optimiser et de contrôler les conditions d'obtention de ces couches minces déposées sur des substrats tubulaires en Ti02 et plans en Al2O3-α. De nombreuses expériences de perméation ont été réalisées, pour des gaz simples (H2, He, Ar, N 2, C02, SF6) et des mélanges gazeux (H2/H20/Ar) et (H2/H20/HI/Ar). Les effets de la température, de la pression amont, de l'épaisseur et de la longueur de la couche mince ainsi que du gaz vecteur ont été étudiés en détail. Il apparaît que la présence de molécules d'H20 dans le système joue un rôle prépondérant sur la perméation des autres molécules. / In the general context of massive and "carbon free" hydrogen production studies, the aim of this work was the development of zeolitic MFI membranes for hydrogen extraction and separation. The methodology of synthesis, the membranes characterization techniques as well as the permeation experimental setup are presented. Optimization and control of the elaboration of Ti02 supported Silicalite-1 and template free ZSM-5 membranes have been reached. Details of the full kinetic study that we performed are given. Numerous permeation experiments, involving pure gas (H2, He, Ar, N2, C02, SF6) and mixtures (H2/H20/Ar) and (H2/H 20/HI/Ar) have been carried on. The effects of temperature, feed pressure, thickness and length of the membranes, as well as the role of the sweeping gas have been emphasized. In the case of gas mixtures, the presence of H20 molecules appears to be a predominant factor.

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