Дисертації з теми "Oxygen isotopes, atmospheric effects"

The Antarctic continent has traditionally been a successful searching ground for meteoritic material due to its cold and dry climate. Meteorites, and their microscopic analogues micrometeorites, were originally sampled from Antarctic ice and snow. Recently, however, a large collection of micrometeorites was discovered in sedimentary traps and moraine deposits from the Transantarctic Mountains, where extraterrestrial dust particles have accumulated for a prolonged time span (ca. 3–4 Ma). Micrometeorites (or ‘cosmic dust’) show unique chemical and isotopic signatures, which originate from a large and diverse amount of asteroidal and cometary bodies within the Solar System. In addition, they document major events such as the origin and evolution of the Solar System, and provide insight into the source region of their precursor bodies. These sedimentary deposits consequently represent a valuable archive that documents the flux of extraterrestrial material to Earth and ancient meteoritic events over Antarctica.Yet, much of this information is lost during the atmospheric entry stage, where cosmic dust is subjected to frictional heating and is partially or completely molten down. This may significantly alter the original physicochemical and isotopic properties of extraterrestrial dust particles. A thorough understanding of these physicochemical processes is thus required to reconstruct the atmospheric entry of cosmic dust (but also larger objects) and interpret their chemical and isotopic data. During the course of this PhD research, multiple sedimentary deposits from the Sør Rondane Mountains (Dronning Maud Land, East Antarctica) were petrographically examined and chemically-isotopically characterized using state-of-the-art instruments. Furthermore, various experiments and numerical models were constructed to replicate the atmospheric entry stage of both small- and large-sized meteoritic material. This study has demonstrated that the Sør Rondane Mountains sedimentary deposits contain a rich and pristine variety of extraterrestrial- and impact-related materials, including micrometeorites, microtektites and meteoritic condensation spherules. Statistical analysis suggests that the Sør Rondane Mountains micrometeorite collection is representative of the contemporary flux of cosmic dust to Earth. Extraterrestrial material is subjected to a complex interplay of redox and volatilization processes during atmospheric entry heating, which allow to explain the chemical trends observed in cosmic dust. Isotopic studies also suggest that at least a minor fraction of the micrometeorite population has sampled new, unknown types of asteroidal and/or cometary bodies. Microtektites and meteoritic condensation spherules have been linked to major meteoritic events on Earth ca. 790 ka and ca. 430 ka ago, respectively, and underline the importance of the Earth’s atmosphere during their formation. The results of this PhD research emphasize the scientific value of Antarctic sedimentary deposits and provide more insight into the processes taking place during the atmospheric entry of extraterrestrial material.<br>Le continent antarctique a traditionnellement été un terrain de recherche fructueux pour le matériel extraterrestre en raison de son climat froid et sec. Les météorites et leurs analogues microscopiques, les micrométéorites, ont été à l'origine échantillonnés dans la glace et la neige de l'Antarctique. Plus récemment, une grande collection de micrométéorites a été découverte dans des pièges sédimentaires et des dépôts de moraine des montagnes transantarctiques, où des particules de poussière extraterrestres se sont accumulées pendant une période prolongée (environ 3-4 Ma). Les micrométéorites (ou « poussière cosmique ») présentent des signatures chimiques et isotopiques uniques, qui proviennent d'une quantité importante et diversifiée de corps astéroïdes et cométaires au sein du système solaire. En outre, elles documentent des événements majeurs tels que l'origine et l'évolution du système solaire et donnent un aperçu de la région source de leurs corps parents. Ces dépôts sédimentaires représentent par conséquent une archive précieuse qui documente le flux de matière extraterrestre vers la Terre et les événements météoritiques anciens au-dessus de l'Antarctique.Pourtant, une grande partie de cette information est perdue au cours de l'étape d'entrée dans l'atmosphère, où la poussière cosmique est soumise à un chauffage par friction et est partiellement ou complètement fondue. Cela peut altérer considérablement les propriétés physico-chimiques et isotopiques d'origine des particules de poussière extraterrestres. Une compréhension approfondie de ces processus physico-chimiques est donc nécessaire pour reconstituer l'entrée atmosphérique des poussières cosmiques (mais aussi des objets plus gros) et interpréter leurs données chimiques et isotopiques. Au cours de cette recherche de doctorat, plusieurs dépôts sédimentaires des montagnes Sør Rondane (Dronning Maud Land, Antarctique de l'Est) ont été examinés pétrographiquement et caractérisés chimiquement et isotopiquement. En outre, diverses expériences et modèles numériques ont été construits pour reproduire l'étape d'entrée dans l'atmosphère de matériaux météoritiques de petite et de grande taille.Cette étude a démontré que les dépôts sédimentaires des montagnes Sør Rondane contiennent une variété riche et peu altérée de matériaux extraterrestres et de cratères d’impacts, notamment des micrométéorites, des microtektites et des sphérules de condensation météoritique. L'analyse statistique suggère que la collection de micrométéorites des montagnes Sør Rondane est représentative du flux contemporain de poussière cosmique vers la Terre. La matière extraterrestre est soumise à une interaction complexe de processus d'oxydo-réduction et de volatilisation lors de l'entrée dans l'atmosphère, ce qui permet d'expliquer les tendances chimiques observées dans la poussière cosmique. Des études isotopiques suggèrent également qu'au moins une fraction mineure de la population de micrométéorites a échantillonné de nouveaux types inconnus d’astéroïdes et/ou de comètes. Les microtektites et les sphérules de condensation météoritiques ont été liées à des événements météoritiques majeurs sur Terre il y a ~790 ka et ~430 ka, respectivement, et soulignent l'importance de l'atmosphère terrestre lors de leur formation. Les résultats de cette recherche doctorale soulignent la valeur scientifique des dépôts sédimentaires de l'Antarctique et donnent un meilleur aperçu des processus qui se déroulent lors de l'entrée dans l'atmosphère de matière extraterrestre<br>Doctorat en Sciences<br>info:eu-repo/semantics/nonPublished

Isotopic analyses of bone phosphate oxygen from a modern alligator, ostrich, and elephant have provided a means for examining diagenesis and thermoregulatory strategy within the dinosaur Acrocanthosaurus atokensis. The Acrocanthosaurus specimen is assumed to retain an original isotopic signature, based on a lack of linear correlation between δ18Ophosphate and structural δ18Ocarbonate, equal standard deviations between δ18Ophosphate values for spongy and compact bone, and a significant difference between δ18Ophosphate and cement δ18Ocarbonate. Interbone and intrabone temperature variation patterns suggest that Acrocanthosaurus followed a homeothermic pattern of heat distribution (i.e. maintenance of a 4°C temperature range). Comparison with the modern animals yields a closer resemblance to the ostrich and elephant versus the alligator, thereby suggesting Acrocanthosaurus was endothermic. The Acrocanthosaurus sacral spines and palatal bones show evidence of use as heat shedding structures and the braincase yields a significantly higher calculated temperature than the body.

Nitrate is a common groundwater contaminant. Due to adverse health effects, waters above the Maximum Contaminant Level (MCL) of 10 mg NO3-N/L or 0.71 mmols/L, are banned from domestic consumption by the EPA. Studies have measured elevated nitrate concentrations in arid land soils and groundwater around the world. These elevated concentrations could be detrimental to the environment and to human health. Thus, it is important to consider the different sources and processes affecting nitrate concentrations Here, a novel triple isotope system approach was employed, coupling δ17O with δ18O and δ15N of nitrate to determine the sources (atmospheric, terrestrial, fertilizer, wastewater) and removal processes influencing nitrate concentrations in the Tucson basin groundwater system. Results show low groundwater nitrate concentrations (0.2 mmols/L) where wastewater was not a predominant source of water, versus high concentrations (1 mmols/L) above the MCL in groundwaters where wastewater was the dominant water source. Furthermore, groundwater up to 1.6 Km away from the wastewater stream was contaminated with effluent recharge waters. In addition, denitrification was inferred from δ18O and δ15N data with this inference reinforced by δ17O data and δ15N enrichments up to 26. Finally, low atmospheric nitrate was measured in groundwater, representing up to 6% of total nitrate. The triple isotope approach studied here is ideal for determining the proportion of atmospheric nitrate versus other terrestrial nitrate sources and the significance of nitrate removal processes.

Groundwater and surface water samples were taken at 14 locations at a lowland rainforest site (La Selva Biological Station) in Costa Rica for the analysis of DIC, DOC, 14C, 13C, 36Cl, 18O, and other geochemical parameters. The data are consistent with the mixing of two endmember groundwaters. One is a local water having low Cl concentrations (<0.07 mM), low DIC (<3.0 mM), high 14C (>100 pmc), δ13C between -22? and -26?, and highly variable 36Cl/Cl ratios. This chemistry is consistent with locally recharged shallow groundwaters having short residence times in which the DIC originates from plant root respiration and atmospheric deposition is the only source of Cl. The other endmember is bedrock groundwater, representing interbasin groundwater flow (IGF) into La Selva and having relatively high Cl concentration (>0.9 mM), high DIC (about 14 mM), low 14C (<8 pmc), high δ13C (-3? to -5?), and a low and more consistent 36Cl/Cl ratio. This chemistry is consistent with the expectations for bedrock groundwater recharged on the flanks of Volcan Barva to the north of La Selva, with a majority of the DIC and Cl derived from magmatic degassing and dissolution of the volcanic rocks that make up the aquifer. A 14C age of 750 ? 4650 years before present was estimated for the bedrock groundwater endmember using NETPATH geochemical mass-balance modeling software, suggesting an average linear velocity of 3-20 m/yr for this groundwater; the actual age is probably closer to the upper limit, and velocity closer to the lower limit. The results of this study are consistent with prior work using major ion, 18O, and physical hydrologic data, suggesting that the conclusions about IGF and groundwater mixing at this site are correct. Also, new DIC data for bedrock groundwater and previous hydrologic data on bedrock groundwater inputs to the Arboleda watershed at La Selva suggest that IGF of bedrock groundwater is responsible for a large inorganic carbon flux into lowland watersheds (about 740 grams of carbon per m2 of watershed each year for the Arboleda).

As lower microwave frequency bands become saturated with users, there is a motivation for the research of applications that utilize higher frequencies, especially the 60 GHz band. This band is plagued with high atmospheric absorption due to atmospheric oxygen, but has a lot of bandwidth, which makes it desirable for multi-media applications. Recently, research of wideband digital links within the 60 GHz band gained the interest of the wireless communication industry when the FCC announced that a license is not required for a wideband digital signal in this band. Previous research on 60 GHz signals focused on how much attenuation due to atmospheric oxygen exists in the link. But a look at the physical properties of atmospheric oxygen reveals both the reason why atmospheric oxygen absorbs electromagnetic waves and how pressure affects atmospheric oxygen. Atmospheric oxygen resonates at 60 GHz due to transitions between its three closely spaced rotational states. These transitions, combined with the magnetic dipole moment of atmospheric oxygen, cause attenuation and phase dispersion in electromagnetic waves. At lower pressures, the individual resonance lines of atmospheric oxygen appear in the attenuation and the phase dispersion plots. As pressure increases, the resonance lines broaden and contribute to neighboring resonant lines. The effect of attenuation and phase dispersion in a wideband signal becomes greater at lower atmospheric pressures, which results in signal distortion. The signal distortion leads to more bit errors and results in the presence of inter-symbol interference (ISI) in the received signal. This thesis aims to analyze the effects of atmospheric oxygen on a wideband digital link, especially at lower pressures and higher data rates. In order to simulate the effects of atmospheric oxygen in the atmosphere, an empirical atmospheric model was used, which characterizes the behavior of oxygen under various atmospheric pressures. A wideband communication system was simulated with the absorption and dispersion due to atmospheric oxygen represented as a transfer function and placed in the link part of the system. Eye diagrams were used to view the impact of the atmospheric oxygen attenuation and phase dispersion in the signal. Also bit error rate plots were computed in order to determine the extra margin needed.<br>Master of Science

The geochemical analysis of bioapatite in vertebrate skeletal tissues is an important tool used to obtain ecological information from fossil animals. An important consideration when conducting stable isotope and trace element analyses is obtaining biogenic information that has been unaffected by diagenetic processes. A two-step pretreatment procedure is commonly used remove diagenetically altered material by removing organic material, via an oxidation reaction with H2O2 or NaOCl, and secondary carbonate, via dissolution in dilute acetic acid, from bioapatite. While much work has been done to determine the efficacy of the pretreatment process, little research has been conducted to determine the potential effects of this process on the oxygen isotope composition of enamel bioapatite. A comparison between δ18O values of fossil enamel treated with 18O-depleted (δ18O = -10.0 / V-SMOW) and 18O-enriched solutions (δ18O = +16.4 / V-SMOW). On average, samples treated with 18O-enriched solutions had δ18O values at least 0.4 / V-PDB more positive than samples treated with 18O-depleted solutions. These results suggest that the isotopic composition of solutions used in the pretreatment process can significantly affect the δ18O values of fossil enamel prior to isotopic analysis. Diagenetic alteration can potentially be assessed using the linear relationship between δ18O values of the carbonate and phosphate components of bioapatite, as any deviation from a slope of 1 suggests alteration. Comparing the relationship between δ18Op and δ18Oc for fossil mammals from the Hadar Formation suggests that this method is successful at identifying samples that are significantly different from the remaining samples due to diagenetic alteration. The relationship between δ18Oc and δ18Op for the majority of sampled fossils from the Hadar Formation has a slope very close to 1 with an average offset, and apparent fractionation factor, between δ18Oc and δ18Op consistent with modern mammals. Therefore, it is likely that many of the fossil mammals sampled from the Hadar Formation retain in vivo δ18O values relating to the δ18O value of the water they consumed. The reliability of paleodietary reconstructions using trace element ratios (notably Sr/Ca and Ba/Ca) is strongly dependent on the preservation of biogenic trace element concentrations. Although most trace element ratio research relies on bone bioapatite, enamel has a better preservation potential and may successfully preserve biogenic trace element relationships. An analysis of Sr/Ca, Ba/Ca, and Zn/Ca ratios indicates that, despite rare earth element concentrations greater than the 1ppm observed in modern enamel, mammals from the Hadar and Busidima formations potentially reflect feeding strategies observed in modern counterparts, i.e. grazers have higher Sr/Ca and Ba/Ca ratios than browsers and omnivores

Thesis: Ph. D., Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2017.<br>Cataloged from PDF version of thesis. Page 216 blank.<br>Includes bibliographical references (pages 179-215).<br>Salt marshes are physically, chemically, and biologically dynamic environments found globally at temperate latitudes. Tidal creeks and marshtop ponds may expand at the expense of productive grass-covered marsh platform. It is therefore important to understand the present magnitude and drivers of production and respiration in these submerged environments in order to evaluate the future role of salt marshes as a carbon sink. This thesis describes new methods to apply the triple oxygen isotope tracer of photosynthetic production in a salt marsh. Additionally, noble gases are applied to constrain air-water exchange processes which affect metabolism tracers. These stable, natural abundance tracers complement traditional techniques for measuring metabolism. In particular, they highlight the potential importance of daytime oxygen sinks besides aerobic respiration, such as rising bubbles. In tidal creeks, increasing nutrients may increase both production and respiration, without any apparent change in the net metabolism. In ponds, daytime production and respiration are also tightly coupled, but there is high background respiration regardless of changes in daytime production. Both tidal creeks and ponds have higher respiration rates and lower production rates than the marsh platform, suggesting that expansion of these submerged environments could limit the ability of salt marshes to sequester carbon.<br>by Evan M. Howard.<br>Ph. D.

Numerous studies have analyzed isotopic variation of meteoric and dripwater in karst environments for paleoclimate reconstructions or aquifer recharge capacity. What is poorly understood is how the isotopic signal of δ18O and δ2H is transferred through the hydrologic cycle based upon storm type, frequency, intensity, and teleconnection activity in the tropical karst areas. At Harrison’s Cave, Barbados, a Hobo Onset event data logger was attached to a tipping bucket rain gauge to count the tips and record the total rainfall every 10 minutes. In the cave a Hobo data logger was used to record relative humidity and temperature at 10-minute intervals. Rainwater, dripwater, and stream water samples were collected at a weekly resolution and refrigerated before sample analysis. The study period was from July, 2012 to October, 2013, with data from the data loggers only until June, 2013 due to inability to reach the study site. The samples were analyzed using the Picarro Cavity Ring Down Spectroscopy Unit-Water L1102-I through laboratories at the University of Kentucky and the University of Utah. The samples were reported in per mil and calibrated. The teleconnection (NAO, AMO, and ENSO) and other atmospheric data were obtained from the Climate Prediction Center or the NOAA Earth System Research Laboratory-Physical Sciences Division. The weekly isotope signatures were linearly regressed against total rainfall for Harrison’s Cave and surface temperature with no statistically significant correlation, indicating the amount effect was not present at a weekly resolution. The amountweighted precipitation δ18O values were calculated on a monthly basis and compared to TRMM monthly rainfall and island-wide monthly rainfall, and a statistically significant negative correlation was found between both datasets. This confirmed that the amount effect dominates the island’s rainfall isotopic signature at a monthly resolution, and that specific atmospheric influences represented in weekly rainfall were less influential on a weekly basis. It is hypothesized that the variation in weekly rainfall is due to quick initiating, rain-out, and dissipation of convective storm systems over the island. In terms of evaporative influences, the samples do not deviate much from the Global Meteoric Water Line (GMWL), indicating minimal evaporation, which is typical for tropical locations. When the d-excess parameters were calculated, there were distinct variations with minimal evaporation occurring in the 2013 calendar year. This is attributed to coastal storm formation in the tropics.

Les oxydes d'azote atmosphériques (NOx=NO+NO2) sont des composés clefs en chimie de l'environnement, jouant un rôle central pour la capacité oxydante de l'atmosphère et le cycle de l'azote. La composition isotopique du nitrate atmosphérique (NO?3 particulaire et HNO3 gazeux), constituant leur puits ultime, renseigne sur leur bilan chimique. Le rapport 15N/14N donne une indication de leurs sources, alors que l'anomalie isotopique en oxygène (?17O=d17O-0.52×d18O) révèle la nature de leurs mécanismes d'oxydation. Des études couplées de d15N et ?17O d'échantillons de nitrate atmosphérique collectés dans l'Arctique, en Antarctique et dans l'atmosphère marine au dessus de l'Océan Atlantique, où le bilan des NOx est souvent mal connu ont été effectuées. À ces fins, le défi que constitue la mesure simultanée des trois rapports isotopiques du nitrate (17O/16O, 18O/16O et 15N/14N) dans le même échantillon représentant moins d'une micromole a été relevé. La solution adoptée tire avantage des propriétés d'une bactérie dénitrifiante, utilisée pour convertir le nitrate en N2O, dont la composition isotopique totale a été mesurée en utilisant un système automatisé de chromatographie en phase gazeuse et spectrométrie de masse de rapport isotopique. Les principaux résultats obtenus via les isotopes de l'oxygène permettent l'identification claire de transitions saisonnières entre voies d'oxydation des NOx, y compris le rôle majeur des composés halogénés réactifs au printemps polaire en régions côtières. Les isotopes de l'azote ont quant à eux permis d'apporter de nouvelles contraintes sur le cycle de l'azote dans les régions polaires, grâce au fractionnement significatif induit par les phénomènes de remobilisation post-dépôt affectant le nitrate dans le manteau neigeux, et l'émission de NOx qui en découle

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2016.<br>Ph. D. Joint Program in Oceanography (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2012<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 179-192).<br>Since the Last Glacial Maximum (LGM, ~ 20,000 years ago) air temperatures warmed, sea level rose roughly 130 meters, and atmospheric concentrations of carbon dioxide increased. This thesis combines global models and paleoceanographic observations to constrain the ocean's role in storing and transporting heat, salt, and other tracers during this time, with implications for understanding how the modem ocean works and how it might change in the future. -- By combining a kinematic ocean model with "upstream" and "downstream" deglacial oxygen isotope time series from benthic and planktonic foraminifera, I show that the data are in agreement with the modem circulation, quantify their power to infer circulation changes, and propose new data locations. -- An ocean general circulation model (the MITgcm) constrained to fit LGM sea surface temperature proxy observations reveals colder ocean temperatures, greater sea ice extent, and changes in ocean mixed layer depth, and suggests that some features in the data are not robust. -- A sensitivity analysis in the MITgcm demonstrates that changes in winds or in ocean turbulent transport can explain the hypothesis that the boundary between deep Atlantic waters originating from Northern and Southern Hemispheres was shallower at the LGM than it is today.<br>by Daniel Edward Amrhein.<br>Ph. D.

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.<br>Earth and Planetary Sciences

Thesis (Ph. D.)--Georgia State University, 2008.<br>Title from file title page. Eirik J. Krogstad, committee chair; Andrey Bekker, committee co-chair; W. Crawford Elliott, Timothy E. LaTour, committee members. Description based on contents viewed Aug. 27, 2009. Includes bibliographical references (p. 207-219).

L'ozone (O3) possède une anomalie isotopique en oxygène qui est unique et caractéristique, offrant ainsi un précieux traceur des processus oxydatifs à l'œuvre dans l'atmosphère moderne mais aussi ceux ayant eu lieu dans le passé. Cette signature isotopique, dénotée Δ17O, se propage au sein du cycle atmosphérique de l'azote réactif (NOx = NO + NO2) et est préservée lors du dépôt du nitrate (NO3-) présent dans l'aérosol, par exemple. L'anomalie isotopique en oxygène portée par le nitrate, Δ17O(NO3-), représente ainsi un traceur de l'importance relative de l'ozone ainsi que celle d'autres oxydants dans le cycle des NOx. Ces dernières années, de nombreux travaux de recherche ont été dédiés à l'interprétation des mesures de Δ17O(NO3-). Pourtant, les processus atmosphériques responsables du transfert de l'anomalie isotopique de l'ozone vers le nitrate ainsi que leur influence globale sur la composition isotopique du nitrate à différentes échelles spatiales et temporelles sont encore mal compris. De plus, la magnitude absolue ainsi que la variabilité spatio-temporelle de Δ17O(O3) sont peu contraintes, car il est difficile d'extraire de l'ozone de l'air ambiant. Cet obstacle technique contrecarre l'interprétation des mesures de Δ17O depuis plus d'une décennie. Les questions scientifiques posées au cours de ce travail de thèse ont été choisies dans le but de combler ces lacunes. Le principal outil d'analyse utilisé dans ce travail est la " méthode bactérienne " associée à la spectrométrie de masse en flux continu (CF-IRMS), une combinaison de techniques qui permet l'analyse de la composition isotopique totale du nitrate (c'est-à-dire, la mesure de δ15N, δ18O et Δ17O). Cette méthode a été employée pour l'analyse isotopique d'échantillons de nitrate obtenus pour deux cas d'études : (i) une étude des variations spatiales de la composition isotopique du nitrate atmosphérique sur la côte californienne à l'échelle journalière; et (ii) une étude du transfert du nitrate et de sa composition isotopique à l'interface entre l'air et la neige à l'échelle saisonnière sur le plateau Antarctique. En outre, cette méthode a été adaptée à la caractérisation isotopique de l'ozone via la conversion chimique de ses atomes d'oxygène terminaux en nitrate. Au cours de cette thèse, un important jeu de données rassemblant de nombreuses mesures troposphériques de Δ17O(O3) a été obtenu, incluant une année entière de mesures à Grenoble, France (45 °N) ainsi qu'un transect latitudinal de collecte dans la couche limite au-dessus de l'océan Atlantique, entre 50 °S to 50 °N. Ces observations ont permis de doubler le nombre de mesures troposphériques de Δ17O(O3) existantes avant cette thèse et d'accroître de manière conséquente notre représentation globale de cette variable isotopique essentielle. Enfin, les deux cas étudiés et présentés dans ce document révèlent des aspects nouveaux et inattendus de la dynamique isotopique du nitrate atmosphérique, avec d'importantes conséquences potentielles pour la modélisation de la qualité de l'air et l'interprétation de l'information isotopique contenue dans les carottes de glace prélevées aux pôles.

A l’échelle des cycles glaciaires-interglaciaires (G/IG) du Quaternaire, la concentration atmosphérique en CO₂ (p CO₂) est associée à d’importantes variations, notamment pendant les transitions entre périodes glaciaires et interglaciaires, aussi appelées terminaisons, qui enregistrent des augmentations de pCO₂ de l’ordre de 100 ppm en quelques milliers d’années. Alors que les rôles de la circulation océanique et de l’étendue de la couverture de glace sur le pCO₂ sont étudiés depuis plusieurs années, peu de travaux s’intéressent à l’impact de la productivité biologique. L’objectif de cette thèse est de reconstruire les changements de productivité biologique et d’estimer leur contribution sur les variations de pCO₂ atmosphérique au cours des derniers 800 000 ans (ka), en portant une attention particulière à la Terminaison V (~425 ka) et au stade isotopique (MIS) 11, l’interglaciaire enregistré vers 400 ka. Pour cela, deux approches ont été combinées pour remonter aux variations globales et locales de la productivité biologique. Des mesures de Δ¹⁷O de O₂ effectuées dans les bulles d’air piégé dans la carotte de glace EPICA Dome C (Antarctique) entre 400 et 800 ka, ont permis de compléter les mesures préexistantes et remonter aux variations de la productivité biosphérique globale exprimée en flux d’oxygène au cours des derniers 800 ka. Des analyses micropaléontologiques (coccolithes, foraminifères) et géochimiques (COT, CaCO₃, XRF) ont été effectuées sur une carotte sédimentaire du secteur Indien de l’Océan Austral (MD04-2718) pour remonter aux variations d’efficacité de la pompe biologique au cours des derniers 800 ka. Les résultats obtenus durant cette thèse ont permis de montrer qu’à l’échelle des cycles G/IG, la productivité biosphérique globale et la productivité carbonatée dans l’Océan Austral sont plus importantes pendant les interglaciaires comparées aux glaciaires, ce qui minimise l’impact de la productivité organique marine sur la pCO₂ atmosphérique. La Terminaison V et MIS 11 enregistrent la plus forte productivité biosphérique des derniers 800 ka et la plus importante production carbonatée marine des 9 derniers interglaciaires dans l’Océan Austral. Alors que la forte productivité carbonatée est une source de CO₂ pour l’atmosphère, l’augmentation de la productivité de la biosphère permettrait de contrebalancer l’augmentation de pCO₂ via la photosynthèse<br>During glacial-interglacial cycles of the Quaternary, the atmospheric CO₂ (pCO₂) concentration is associated with important variations, in particular during transitions between glacial and interglacial periods, also called terminations, with increases of up to 100 ppm of pCO₂ in a few thousand years. While the roles of oceanic circulation and sea-ice cover on pCO₂ are studied for several years now, little is known on the impact of biological productivity. The goal of this thesis is to reconstruct the past changes in biological productivity and to estimate their contributions on atmospheric pCO₂ variations over the last 800 000 years (ka), with particular attention to Termination V (~425 ka) and Marine Isotope Stage (MIS) 11, the interglacial period around 400 ka. Two different approaches were combined to reconstruct global and local variations of biological productivity. Measurements of Δ¹⁷O of O₂ in the air trapped in the Antarctic EPICA Dome C ice core between 400 and 800 ka allowed to complete the pre-existing record and trace back variations of global biosphere productivity expressed in oxygen fluxes over the past 800 ka. Micropaleontological (coccoliths, foraminifera) and geochemical (TOC, CaCO₃, XRF) analyses were performed on a sediment core of the Indian sector of the Southern Ocean (MD04-2718) to reconstruct the changes in biological pump efficiency over the past 800 ka. The results obtained during this thesis showed that, at the scale of glacial-interglacial cycles, global biospheric productivity and Southern Ocean carbonate production are more important during interglacial periods compared to glacial periods, minimizing the impact of marine organic productivity on atmospheric pCO₂. Termination V and MIS 11 register the strongest biosphere productivity of the past 800 ka and the highest marine carbonate production of the past 9 interglacial periods in the Southern Ocean. While the important carbonate production is a source of CO₂ for the atmosphere, the rise in biosphere productivity would counterbalance the increase in pCO₂ through photosynthesis

Li Chak Ming = 18O氧同位素效應對La0.67Ca0.33MnO3薄膜之影響 / 李澤銘.<br>Thesis (M.Phil.)--Chinese University of Hong Kong, 2005.<br>Includes bibliographical references.<br>Text in English; abstracts in English and Chinese.<br>Li Chak Ming = 18O yang tong wei su xiao ying dui La0.67Ca0.33MnO3 bo mo zhi ying xiang / Li Zeming.<br>Acknowledgement --- p.i<br>Abstract --- p.ii<br>論文摘要 --- p.iii<br>Table of Contents --- p.iv<br>List of Figures --- p.viii<br>List of Tables --- p.xi<br>Chapter Chapter 1 --- Introduction<br>Chapter 1.1 --- Magnetoresistance (MR) 1 - --- p.1<br>Chapter 1.1.1 --- Magnetoresistance (MR) 1 - --- p.1<br>Chapter 1.1.2 --- Giant Magnetoresistance (GMR) 1 - --- p.1<br>Chapter 1.1.3 --- Anisotropy Magnetoresistance (AMR) 1 - --- p.2<br>Chapter 1.1.4 --- Colossal Magnetoresistance (CMR) --- p.1-4<br>Chapter 1.1.5 --- Double exchange mechanism 1 - --- p.6<br>Chapter 1.1.6 --- Jahn-Teller effect --- p.1-6<br>Chapter 1.1.7 --- Tolerance factor 1 - --- p.7<br>Chapter 1.1.8 --- The effect of doping --- p.1-10<br>Chapter 1.2 --- Possible origin of oxygen isotope effect --- p.1-12<br>Chapter 1.3 --- Our approach --- p.1-14<br>Chapter 1.4 --- Scope of this thesis work --- p.1-14<br>Chapter Chapter 2 --- Experimental methods<br>Chapter 2.1 --- Thin film deposition --- p.2-1<br>Chapter 2.1.1 --- Facing Target Sputering (FTS) --- p.2-1<br>Chapter 2.1.2 --- Vacuum system --- p.2-4<br>Chapter 2.2 --- Annealing systems --- p.2-6<br>Chapter 2.2.1 --- Oxygen annealing system --- p.2-6<br>Chapter 2.2.2 --- Oxygen exchange system --- p.2-8<br>Chapter 2.2.3 --- Vacuum annealing system --- p.2-10<br>Chapter 2.3 --- Characterization --- p.2-12<br>Chapter 2.3.1 --- a -step profilometer --- p.2-12<br>Chapter 2.3.2 --- X-ray diffraction (XRD) --- p.2-12<br>Chapter 2.3.3 --- Resistance measurement --- p.2-15<br>Chapter Chapter 3 --- Epitaxial growth of LCMO single layer thin film<br>Chapter 3.1 --- Fabrications and characterization of La0.67Ca0.33MnO3 target --- p.3-1<br>Chapter 3.2 --- Substrate materials --- p.3-6<br>Chapter 3.3 --- Preparation of LCMO thin film --- p.3-8<br>Chapter 3.3.1 --- Deposition conditions --- p.3-8<br>Chapter 3.3.2 --- Deposition procedure --- p.3-10<br>Chapter 3.3.3 --- Post-annealing effect --- p.3-13<br>Chapter Chapter 4 --- Oxygen in LCMO thin film<br>Chapter 4.1 --- Introduction --- p.4-1<br>Chapter 4.2 --- High Pressure Oxygenation --- p.4-2<br>Chapter 4.3 --- Characterization --- p.4-7<br>Chapter 4.3.1 --- Determination of oxygen content --- p.4-9<br>Chapter 4.3.2 --- "Tolerance factor, t" --- p.4-12<br>Chapter Chapter 5 --- Oxygen isotope effect in LCMO thin film<br>Chapter 5.1 --- Introduction --- p.5-1<br>Chapter 5.2 --- Identification on successiveness of oxygen exchange --- p.5-4<br>Chapter 5.2.1 --- Sample preparation --- p.5-4<br>Chapter 5.2.2 --- Oxygen annealing treatment --- p.5-4<br>Chapter 5.2.3 --- Identification of 18O by SIMS --- p.5-4<br>Chapter 5.3 --- Investigation of isotope effect on LCMO thin film --- p.5-7<br>Chapter 5.3.1 --- Sample preparation --- p.5-7<br>Chapter 5.3.2 --- Oxygen exchange --- p.5-7<br>Chapter 5.3.3 --- Vacuum annealing --- p.5-9<br>Chapter 5.3.4 --- Isotope effect --- p.5-9<br>Chapter 5.4 --- Conclusions --- p.5-19<br>Chapter Chapter 6 --- Isotope effect on the hopping activation energy<br>Chapter 6.1 --- Introduction --- p.6-1<br>Chapter 6.1.1 --- Variable range hopping --- p.6-2<br>Chapter 6.1.2 --- Small polaron models --- p.6-2<br>Chapter 6.2 --- Activation energy --- p.6-4<br>Chapter 6.3 --- Discussions --- p.6-9<br>Chapter Chapter 7 --- Conclusions --- p.7-1

Cellulose-inferred lake water oxygen-isotope records were obtained from five throughflow lakes situated along a north-south transect across Fennoscandia to help develop a better picture of Holocene changes in atmospheric circulation in the region. This research addresses prior evidence for the existence of non-temperature-dependent shifts in d18O of precipitation in the early Holocene attributed to changes in atmospheric circulation. The validity of this hypothesis is tested through the development of oxygen-isotope records from lake sediments and their interpretation in the context of independent reconstructions of temperature and precipitation from pollen and chironomid head-capsules collected from the same or nearby sites, and well-documented changes in vegetation composition. Records of carbon and nitrogen elemental content and isotopic composition and magnetic susceptibility are included in this multi-proxy investigation. Extensive modern isotope hydrology datasets spanning several years at four of the five sites also help to inform interpretations of the cellulose d18O records. Key results from this research are: 1) Elevated d18O in relation to prevailing temperature occurred during the early Holocene (c. 10,000-6000 cal. BP) for sites in northern Fennoscandia (Lake Tibetanus, Lake Spåime), in harmony with previous interpretations suggesting that strong zonal atmospheric circulation led to deepening of the precipitation and isotope shadows in the lee of the Scandes Mountains. 2) Evidence from a southern site (Arbovatten) reveals a previously unrecognized negative offset in the d18O-temperature relation during the early Holocene, apparently transferred directly from the North Atlantic without the orographic effects associated with a topographic barrier. 3) The modern d18O-temperature relation appears to have been established throughout Fennoscandia by c. 6000-4000 cal. BP, probably due to generally weaker circumpolar atmospheric circulation in response to lower summer insolation. 4) Comparison of two sites (Lake Spåime, Svartkälstjärn) in a west-east transect across central Fennoscandia reveals higher-frequency variability in atmospheric circulation at submillennial scales throughout the Holocene, which appears to be analogous to contemporary variability in the North Atlantic Oscillation (NAO) at seasonal-to-decadal time-scales. Evidence of such NAO-like variability also exists at two northern sites (Lake Keitjoru, Oikojärvi) during the Holocene, likely reflecting variations in summer and winter atmospheric circulation. 5) Complex lake-specific changes in productivity occurred in response to Holocene climate change, as revealed by carbon and nitrogen elemental and isotopic data in lake sediments. A major shift in atmospheric circulation pattern occurring at c. 4000 cal. BP probably led to a reduction in soil-derived 13C-depleted nutrients in five lakes (Lake Keitjoru, Oikojärvi, Lake Spåime, Svartkälstjärn, Arbovatten) associated with changes in terrestrial vegetation. Changes in sediment nitrogen isotope composition also occurred in these lakes at c. 4000 cal. BP, possibly reflecting changing nutrient supply dynamics because of enhanced nitrogen losses during spring snowmelt.

This thesis describes a method for calculating lake evaporation as a proportion of water inputs (E/I) for large surface water bodies, using stable isotope ratios of oxygen (18O/16O) and hydrogen (2H/1H) in water. Evaporation as a proportion of inflow (E/I) is calculated for each Laurentian Great Lake using a new dataset of 516 analyses of δ18O and δ2H in waters sampled from 75 offshore stations during spring and summer of 2007. This work builds on previous approaches by accounting for lake effects on the overlying atmosphere and assuming conservation of both mass and isotopes (18O and 2H) to better constrain evaporation outputs. Results show that E/I ratios are greatest for headwater Lakes Superior and Michigan and lowest for Lakes Erie and Ontario, controlled largely by the magnitude of hydrologic inputs from upstream chain lakes. For Lake Superior, stable isotopes incorporate evaporation over the past century, providing long-term insights to the lake’s hydrology that may be compared to potential changes under a future – expectedly warmer – climate. Uncertainties in isotopically derived E/I are comparable to conventional energy and mass balance uncertainties. Isotope-derived E/I values are lower than conventional energy and mass balance estimates for Lakes Superior and Michigan. The difference between conventional and isotope estimates may be explained by moisture recycling effects. The isotope-based estimates include only evaporated moisture that is also advected from the lake surface, thereby discounting moisture that evaporates and subsequently reprecipitates on the lake surface downwind as recycled precipitation. This shows an advantage of applying an isotope approach in conjunction with conventional evaporation estimates to quantify both moisture recycling and net losses by evaporation. Depth profiles of 18O/16O and 2H/1H in the Great Lakes show a lack of isotopic stratification in summer months despite an established thermocline. These results are indicative of very low over-lake evaporation during warm summer months, with the bulk of evaporation occurring during the fall and winter. This seasonality in evaporation losses is supported by energy balance studies. For Lakes Michigan and Huron, the isotope mass balance approach provides a new perspective into water exchange and evaporation from these lakes. This isotope investigation shows that Lake Michigan and Lake Huron waters are distinct, despite sharing a common lake level. This finding advocates for the separate consideration of Lake Michigan and Lake Huron in future hydrologic studies.

碩士<br>明志科技大學<br>材料工程系碩士班<br>105<br>AgxO thin films were deposited by reactive co-sputtering with various oxygen flow rates.The films' structural and mechanical properties were examined. Then, the samples were tested for their antibacterial behaviors against Escherichia coli. It was first found that the dissolution of Ag ion was varied depending on oxygen contents. The Ag ion concentration would reach a maximum value with the increase of oxygen contents, then level off. The antibacterial efficiency of TaOxNy-Ag films against Escherichia coli could be much improved, comparing with that of TaN-Ag films, i.e. the higher oxygen content, the better antibacterial efficiency. The reasons for this were found to be due to smaller metal particles for TaOxNy-Ag, and, more importantly, the existence of silver oxide. This result was proved with ICP-OES by measuring the solubility of metal ions. The annealed TaN-Ag thin films were then treated in either wet (immersed) environments by APPJ. It is found, after activation, the dissolution rate of Ag ions could be increased significantly. Hence the antibacterial efficiency was increased tremendously.