Si la relation entre l’enregistrement géochimique au sein de ces travertins et les paramètres environnementaux semble admise, le détail des processus, notamment cinétique et dégazage, ainsi que leur poids respectifs dans les reconstitutions paléoenvironnementales ne sont clairement établis. Afin de mieux contraindre ces processus, un travail minutieux de reconnaissance des mécanismes de précipitation et d’enregistrement de la signature géochimique a été effectué sur les travertins –récents et fossiles- d’une source carbogazeuse située dans le Massif Central (France). Il couple expériences de laboratoire innovantes et travail sérié sur le terrain.Le taux de dégazage du CO2 dans les sources carbogazeuses est l’un des facteurs principaux conduisant aux conditions de précipitation via la modulation du taux de précipitation de la calcite et par conséquent, sa composition en 18O et 13C. Les tests en laboratoire ont été conduits en deux étapes : (1) caractérisation des mécanismes de dégazage seuls, et (2) des expériences combinant dégazage et précipitation pour mieux appréhender les processus cinétiques lors de la précipitation des travertins. En parallèle, un travail de terrain spécifique par pose de plaques de plexiglas le long de différents écoulement de la source, nous a permis de connaitre la résolution de précipitation des travertins et d’obtenir une meilleure estimation des facteurs de fractionnement.Les tests en laboratoire confirment que, lors d’un dégazage important, i.e. conduisant à la précipitation de travertins, la spéciation des espèces du carbone inorganique dissout (CID) et les flux entre ces espèces sont des paramètres primordiaux à considérer. Le facteur de fractionnementεDIC-CO2(g) qui dépend du pH suit alors une distillation de Rayleigh dans un système cinétique. Les évolutions des espèces carbonées en solution ont ainsi pu être modélisées à l’aide d’une équation de diffusion faisant intervenir les paramètres propres à l’expérience.Les résultats de terrain permettent de démontrer que les variations de conditions de précipitation sont principalement dues aux variations de conditions hydrodynamiques et, secondairement, aux variations de température, ce qui a pu être modélisé à l’aide de l’équation définie par Plummer en 1968 et qui a montré la variabilité des conditions de précipitation in-situ. Dans le cas des expériences de précipitation en laboratoire et par comparaison avec les données de terrain, le facteur de fractionnement εCID-calcite va dépendre des concentrations de chaque espèce de CID mais aussi de la partition du carbone entre phase gaz et phase solide. Pour l’oxygène 18, de 0°C à 10°C, les résultats acquis sur les travertins actuels nous ont permis d’utiliser la droite définie récemment par Coplen (2007) pour lier de façon fiable la température au moment de la précipitation et le facteur de fractionnement. Toutefois, pour des températures plus élevées, le facteur de fractionnement est plus important que ce qu’il devrait et confirmant ainsi la non-représentativité des droites de Coplen pour la détermination de la température de précipitation. Lors des expériences de précipitation la tendance est inverse à celle observée pour les travertins confirmant l’influence de la vitesse de dégazage et de l’indice de saturation sur le fractionnement isotopique. Nous avons également confirmé avec les expérimentations, l’impact de la vitesse de précipitation sur les teneurs isotopiques enregistrées dans les travertins.Ce travail a mis en lumière des mécanismes cinétiques complexes et qui ne sont pas complètement contraints par la seule utilisation des outils isotopiques. L’utilisation du partitionnement des éléments traces est un outil primordial pour appuyer l’étude de ces mécanismes. / The response of continental groundwater systems to recent climate fluctuations can be reconstructed via the continuous measurement of groundwater level, spring flow and climatic chronicles. When any data exist, recent reconstructions of groundwater dynamics may be reached through various recorders of environmental and hydrological conditions such as travertine. Although the relationship between geochemical records in travertine and environmental parameters seems to be accepted, the details of processes and their respective weight in the paleo-information are not clearly established.Rate of CO2 degassing in CO2-rich spring likely influences calcite precipitation rate and the related δ18O and δ13C composition. Isotopic equilibrium is rarely maintained during travertine deposition and the degassing rate is the main controlling factor of the disequilibrium. Due to the lack of knowledge, fractionation processes, either kinetic or equilibrium, occurring between CO2-rich water, gas and travertine required specific pH and temperature-controlled laboratory tests. These tests were conducted on synthetic water at different pH to focus only on the degassing processes. Other tests were conducted on trace elements partitioning during calcite precipitation, to identify the origin of isotopic signature variability, and to constraint the way of recording past conditions.All these tests confirmed that during a degassing leading to travertine precipitation, the speciation of dissolved inorganic carbon species is a major parameter to be tackled since a linear relationship between εDIC-CO2(g) and pH is observed. Indeed, we highlighted that for a high degassing rate, the isotopic equilibrium is not reached because the reaction greater involves light isotopes than heavy ones. There is thus different reaction rate between the species of dissolved inorganic carbon, the reactions occurring faster in the water than the one between water and gas, the latter being controlled by diffusion.

The potato (Solanum tuberosum L.) crop serves as a staple food worldwide and is capable of reducing the world’s food shortages because unlike cereals and other agricultural crops, it is less affected by prices in the international markets. Research on alleviation of food crises suggested root and tuber crops such as potatoes to be the solution to the problem of food shortage. The crop is widely cultivated but is difficult to produce due to susceptibility to numerous pests and pathogenic organisms, as well as abiotic stresses. To control these pests and diseases, strategies to limit susceptibility to factors that interfere with the growth and development of plants, or breeding new varieties that are able to withstand stresses are being researched. Recent studies have shown that non essential nutrients such as Silicon (Si) are beneficial to plants in terms of yield, protection from fungal diseases and improved uptake of phosphorus. Since very little research has focused on the role of Si in improving potato production, three glasshouse pot trials were conducted at the Hatfield Experimental farm and Department of Plant Pathology glasshouses of the University of Pretoria to evaluate the effect of various soil amendments on potato yield and quality. The effect of these soil amendments on pH was also investigated as P-uptake and development of common scab in potatoes are pH dependent. The soil amendments consisted of different silicon sources and an agricultural lime. The Si sources were Calmasil slag (Middleburg) (30% Si- containing liming material), fly ash (50% Si nonliming material), and Si fume/ash (99% Si non-liming material). Agricultural lime (CaCO3) was included as a control. The purpose of the first two trials was to identify the most promising silicon-containing source for potato production, while the third trial evaluated the effect of this silicon source on soil pH and potato tuber yield. In all three trials, agricultural lime was used as a control. Due to the high demand for nutrients by the potato crop, other nutrient elements were added to the soil through fertigation every 7 to 14 days, depending on the growth stage of the plants. Plants were irrigated with distilled water when necessary to maintain an adequate moisture level i.e. moist but not too wet. Weekly observations on growth parameters were made. To select the most promising soil amendment, parameters such as leaf chlorophyll content, plant height, tuber number and mass (Fwt), fresh and dry weight (top growth) and change in soil pH were analyzed. Slag treated plants tended to produce tubers with higher mass and better appearance. In this study the highest increase in soil pH was observed in soil mixed with slag, compared to all the other silicon sources. Although there was no significant difference observed among treatments there was a distinct difference in plant growth between trials when soil was amended with lime and slag. Plants treated with slag tended to produce tubers that weigh more, whilst plants treated with lime grew taller and had the highest tuber number. There was a significant rise in soil pH from both lime and slag, which might have in turn influenced vegetative and tuber growth. / Dissertation (MInst(Agrar)--University of Pretoria, 2013. / gm2014 / Plant Production and Soil Science / unrestricted

Global carbon cycle dynamics and fluxes of CO2 between biosphere and atmosphere have been progressed through the use of Keeling Plots. Processes that control and effect the isotopic composition of soil-respired CO2, soil CO2, and equilibrated soil carbonate are specifically addressed in this study through the use of Keeling Plots. Replicate grassland soil profiles containing either C3 or C4 homogenized organic matter were constructed and maintained under controlled settings to encourage the production of soil-respired CO2 and the precipitation of pedogenic carbonate. Soil CO2 was sampled over five months and analyzed with IRMS. Keeling Plots illustrated source CO2 affected by mixing with atmospheric CO2 near the surface and equilibration with ¹³C-depleted CO2 at depth in the zone of likely carbonate precipitation. The δ13C Keeling Plot intercepts for the surface horizons (~ -24.7 per mil for C3 profiles and ~ -11.1 per mil for C4 profiles) follow the diffusion-production model when corrected with a constant 4.4 per mil diffusional fractionation, but the Keeling Plot intercepts for developing Bk horizons were curved towards depleted values (~ -36.2 per mil for C3 profiles and ~ -18.4 per mil for C4 profiles). This change in isotopic composition with depth deviates from the usual interpretations of Keeling Plots (steady-state, source to background diffusional mixing). δ13C Keeling Plot intercepts indicated evaporative enrichment in the surface horizons of C3 and C4 profiles). This study uses Keeling Plots as a measure of mixing to assess the efficacy of steady-state diffusion-production models of soil CO2 equilibration with soil carbonate.

This dissertation presents a design concept for shape-morphing structures that have two stable configurations. The design concept defines the methodology of transforming a planar structural shape into spatial structural shape using bistable compliant mechanisms. Bistable complaint mechanisms are used to achieve structural stable configurations. The dissertation incorporating geometrical relationships for the mechanisms that form the primary structure described in step-by-step process. This dissertation implements the design layouts for designer to creating shape-morphing structures including origami. The novel contribution of the work is classified in three models. The first model presents a methodology to induce bistability behavior into an origami reverse fold and partially spherical compliant mechanism. The second model presents the design and development of a bistable triangle-shaped compliant mechanism with motion limits and dwell behavior at the two stable configurations. This mechanism can be arrayed to create shape-morphing structures. The third model presents a design and development for a collapsible bistable compliant mechanism used for a shape morphing lamina-emergent frustum. Finally, physical prototypes of all models are presented as proof of concept.

This project tests the hypothesis that the Langobard migration into the Roman/Byzantine Veneto (northeastern Italy) resulted in significant dietary changes from Late Antiquity (4-5th centuries AD) to the Early Medieval period (6-8th centuries AD). At the end of the Great Germanic Migrations in AD 568, Langobards from Pannonia entered and occupied two-thirds of the Italian peninsula. It is unclear how large these migrations were, as historical documents exaggerate mass movements; however, conservative estimates suggest they made up 8% of the areas they occupied. The degree to which the Langobards influenced economic change and subsistence in this area is poorly understood. Therefore, the goal of this research is to use stable isotope analyses on human remains in conjunction with historical and archaeological data to understand how the migration of the Langobards influenced the population structure and political economy (diet) in the Veneto. A total of 149 individual bone samples from seven sites spanning the 4-8th centuries AD from the Veneto underwent stable carbon and nitrogen isotope analysis. In addition, 60 premolars were sampled for stable carbon, nitrogen, and oxygen isotope analysis to assess migration and dietary changes. Previous paleodietary analyses suggest that the traditional Roman diet consisted of C3 terrestrial plants, such as wheat and barley, and domesticated animals with some contributions from fish. The Langobards consumed a mix of C3 and C4 (millet and sorghum) terrestrial plants and animals. C4 plants such as millet were often considered a low socioeconomic status food source during the Roman Empire. The results indicate that migrating Langobards are not present in the cemetery samples; however, migrating Roman/Byzantines are. This suggests a migration inland from the Byzantine occupied coast for better economic prospects. Byzantine occupied areas in Italy experienced heavy taxations, while the Langobards reduced this burden on the location populations. The dietary analyses show significant differences in diet between local and non-local individuals, with non-local individuals consuming more C3 energy sources (wheat) earlier in life. In terms of overall diet in the Veneto, there appears to be an increase in millet consumption from Late Antiquity to the Early Medieval period. There are no significant differences in socioeconomic status or sex, suggesting that millet became standardized in the Veneto, reflecting a sociocultural change in dietary practices. This research is significant because it fills a geographical and chronological gap in Italian history, during a period of significant migration and economic change.

L’Internet des Objets représente un défi technique pour la communication 5G à cause de son hétérogénéité caractéristique : la bande 2.4 GHz ISM, par exemple, est partagée entre différents types de technologies, comme Wifi, Bluetooth et Zigbee. En plus de la perte de qualité de communication, des études récentes montrent que l’interférence augmente de façon significative la consommation d’énergie. Donc, traiter l’interférence devient une tâche importante pour assurer la réussite de la transmission de données. Cette thèse approche deux aspects différents des réseaux hétérogènes. La première partie présente une étude expérimentale sur la nature de l’interférence entre dispositifs IEEE 802.11 et 802.15.4, ses impacts dans la fiabilité de la communication et propose une description statistique. La conclusion principale est que, dans ce contexte, l’interférence présente un comportement non-Gaussien, plus précisément, impulsif. Des travaux théoriques récents alliés avec ces résultats expérimentaux montrent que la distribution α-stable est plus convenable pour représenter bruits impulsives. Cela signifie que, une fois optimal, les architectures de communication classiques basé sur assomption Gaussienne, particulièrement la méthode des moindres carrés et le récepteur linéaire, ne sont plus optimales et présentent une perte de performance significative. La deuxième partie présente une architecture MIMO basé sur codage Alamouti, estimation de canal supervisée basé sur méthode Least Absolute Deviation et récepteur p-norme avec une estimation de p. L’architecture proposée présente une performance supérieure au méthode classique. / Internet of Things represents a technical challenge for 5G communications due to is characteristic heterogeneity: the 2.4 GHz ISM band, for example, is shared between different kind of technologies, such Wifi, Bluetooth and Zigbee. In addition to the loss of quality of communication, recent studies show that interference increases significantly the energy consumption. So, dealing with interference becomes an important task to ensure successfull data transmission. The present thesis approaches two aspects of heterogeneous networks. The first part presents an experimental study on the nature of interference between IEEE 802.11 and IEEE 802.15.4 devices, its impacts on the communication reliability and proposes an statistical description of it. The main conclusion of this part is that, on this context, the interference may present a non-Gaussian behavior, more precisely, an impulsive behavior. Recent theoretical works allied with these experimental results show that the α-stable distribution is more adequate to represent impulsive noises. It means that the, once optimal, classical communication architectures based on the Gaussian assumption, particularly the Least Squares based channel estimation and linear receiver, are not optimal anymore present a significant loss of performance. The second part presents a robust MIMO architecutre based on Alamouti coding, supervised channel estimation based on Least Absolute Deviation and p-norm receiver with an estimator for p. The proposed approach outperforms the classical method.

Calcium stable isotope ratios are a relatively new tool that biogeochemists can use to investigate the biogeochemical cycle of calcium in terrestrial ecosystems, having seen widespread application only in the past 15 years. To advance the application of calcium isotopes in biogeoscience research, I conducted three investigations focused on interpreting calcium isotope ratios in streamwater and in the cation exchange pool of forest soils. In the first study, we observe a shift toward lower 44Ca/40Ca ratios in streamwater draining a New Hampshire watershed after an experimental clearcutting event. Isotope ratio measurements of ecosystem calcium pools indicate that enhanced leaching of the soil exchangeable pool produced the observed shift in 44Ca/40Ca ratios. A trend towards decreased 44Ca/40Ca ratios in soils in the years following the harvesting indicates that calcium leached from the soil exchangeable reservoir was likely replaced by calcium released by the decay of belowground biomass, maintaining pre-harvest levels of exchangeable calcium even in the face of a significant ecosystem disturbance. In a second study, we observed significant differences in the 44Ca/40Ca of the soil exchange pool between two neighboring tropical watersheds, although 44Ca/40Ca of calcium inputs (bedrock and atmospheric deposition) at the two sites were indistinguishable. Further, both sites had higher 44Ca/40Ca ratios compared with external inputs, a relatively rare observation globally. We propose that hurricane disturbance best explains the high 44Ca/40Ca at each site, and that the difference in 44Ca/40Ca between the two sites can be accounted for by the magnitude of disturbance at each site. Finally, a synthesis of our new data with previously published results shows that globally, soil exchangeable 44Ca/40Ca ratios can be higher, lower or equal to external inputs. Modeling work indicates that in addition to isotopic fractionation, the balance in fluxes between vegetation and soil is critical in determining how soil exchangeable 44Ca/40Ca ratios vary relative to external inputs. When plant uptake and return to the soil are equal, soil and external inputs 44Ca/40Ca are equal, while high soil 44Ca/40Ca ratios develop when uptake exceeds return. Soil develops low 44Ca/40Ca when biomass obtains calcium from sources other than the exchangeable reservoir.

Stable isotope analyses are powerful tools for reconstructing ancient ecologies and ecosystems, as they are independent of morphology and directly reflect dietary ecology. The application of stable isotope analyses, however, is not without limitations, as determination of food web dynamics using these methods often relies on poorly tested assumptions. The guiding thread of this thesis is the testing of foundational cornerstones on which these methods rely, in order to validate the suitability of applying these techniques to different mammalian clades, and to more reliably and confidently interpret the isotopic signals preserved in extinct organisms. The first chapter of this thesis tests the validity of an important assumption behind the interpretation of stable carbon isotope analyses for understanding diet in terrestrial mammalian herbivores: if, as assumed for almost two decades, mammalian bioapatite δ¹³C is enriched by 14‰ relative to dietary δ¹³C. By analyzing new isotopic data from a never before assessed herbivorous group spanning a broad range of body masses—sloths (Xenarthra, Mammalia)— and other mammals with experimentally controlled or observationally known diets, I discovered considerable variation in diet–bioapatite δ¹³C enrichment among mammals. Statistical tests (ordinary least squares, quantile, robust regressions, Akaike information criterion model tests) documented independence from phylogeny, and a previously unrecognized strong and significant correlation of δ¹³C enrichment with body mass for all mammalian herbivores. A single-factor body mass model outperformed all other single-factor or more complex combinatorial models evaluated, including for physiological variables (metabolic rate and body temperature proxies), and indicated that body mass alone predicts δ¹³C enrichment. These analyses, spanning more than 5 orders of magnitude of body sizes, yield a size-dependent prediction of isotopic enrichment across Mammalia and for distinct digestive physiologies, permitting reconstruction of foregut versus hindgut fermentation physiologies for fossils and refined mean annual paleoprecipitation estimates based on δ¹³C of mammalian bioapatite. Second, I sought to evaluate the existing paradigm governing identification of closed canopy rainforests in the fossil record using mammalian δ¹³C data: the presence of mammals with dietary δ¹³C <-31‰, which has only been observed in closed canopy rainforests in Equatorial Africa, the only other tropical ecosystem sampled extensively. This chapter provides a characterization of δ¹³Cbioapatite, δ¹³Chair and δ¹⁵Nhair of a modern mammalian community in western Amazonia, in Peru, to test if the isotopic structure of mammals in this Neotropical ecosystem is similar to those in African tropical rainforests. The results indicate that despite their marked geographical and taxonomic differences, median δ¹³Cdiet values from closed canopy rainforests in Amazonia (-27.4‰) and equatorial Africa (-26.9‰) are not significantly different. Amazonian mammals, however, seem to exploit a narrower spectrum of dietary resources than equatorial African mammals, as depicted by the absence of highly negative δ¹³Cdiet values previously proposed as indicative of rainforests (<-31‰). I hypothesize that differential effects of late Pleistocene extinction may be responsible for the ecological disparities among the two rainforests, by significantly reducing evolutionary time and dietary breadth reflected in the modern Amazonian mammalian community. Finally, the third chapter of this dissertation evaluates assumptions behind δ¹⁵N amino acid compound specific analyses in order to test the controversial hypothesis of carnivory and consumption of proteins of animal origin in fossil sloths. This analytical technique relies on three main assumptions. First, that the offset between the δ¹⁵N of glutamic acid (δ¹⁵NGlx) and phenylalanine (d15NPhe) in the organism under study will increase with increasing trophic level. Second, that the offset between δ¹⁵NGlx and δ¹⁵NPhe at the base of the food chain is relatively constant and has a value of -8.4‰ for C3 ecosystems. Third, that the trophic discrimination factor in all ecosystems (the difference in δ¹⁵NGlx relative to δ¹⁵NPhe with increasing trophic level) is 7.6‰. The results of my experiments conducted on extant xenarthrans (sloths and anteaters) with controlled diets document that only the first assumption holds true. Rather than relying on an equation with constants introducing uncertainties and that are not applicable to organisms feeding on a combination of items of different origin (e.g., C3 + C4 plants), δ¹⁵NGlx and δ¹⁵NPhe values by themselves can accurately reconstruct the trophic position of organisms. Indeed, the results on δ¹⁵NGlx and δ¹⁵NPhe herein obtained for five xenarthran species in controlled feeding experiments, combined with mammalian data available from the literature, show strong and significant correlations between these two AAs and with trophic positions. Both the TP equation and the regression analyses of δ¹⁵NGlx and δ¹⁵NPhe suggest that the Pleistocene fossil ground sloths 𝘔𝘺𝘭𝘰𝘥𝘰𝘯 𝘥𝘢𝘳𝘸𝘪𝘯𝘪𝘪 and 𝘕𝘰𝘵𝘩𝘳𝘰𝘵𝘩𝘦𝘳𝘪𝘰𝘱𝘴 𝘴𝘩𝘢𝘴𝘵𝘦𝘯𝘴𝘪𝘴 were not pure herbivores as commonly presumed, but rather that they were both mixed feeders/omnivores, incorporating items of animal origin in their diets.

Thin cylindrical shell structures may provide an interesting breakthrough for deployable structures for small satellites. Its bi-stable behaviour allows two different stable configurations: coiled and deployed. Several projects worldwide are using tape springs for satellites and for the SEAM project, at KTH, 1 meter long tape springs will be used for booms. This thesis investigates the energy stored inside the tape spring according to its layup configuration and the different fiber orientations. With a thickness around 0.3 mm and a length of one meter, the booms will deploy sensors with a quite low deployment speed in order to minimize the shick load during the deployment phase. A Matlab code is written to compare the stored strain energy. Another aim is to find an adequate layout all along the tape spring, it means change the fiber orientation to decrease the energy released, but also generating main manufacturing issue.

Given its crucial role in atmospheric chemistry and its global warming potential, methane(CH4) deserves to be accurately budgeted. However, the recent renewed rise in atmosphericCH4 growth rates from 2007 on, after a few years of slow-down, attests that sources are notcompensated anymore by sinks, and calls for a better assessment of the processes contributingto the global CH4 budget. Among natural sources, oceanic emissions are still subject tomany uncertainties, due to the lack of sampling. This is particularly relevant in polar regions,where the role of sea ice on CH4 sea-air fluxes is largely unknown.In an effort to contribute to a better characterisation of CH4 dynamics in oceanic environments,we investigated very contrasted settings during a journey from temperate to polarregions and applied the concentration and stable isotope approach.We start by evaluating the performance of a commercially available in situ CH4 sensor(CONTROS HydroC® CH4 from Kongsberg Contros) in controlled and natural environments,with the hope of using it in the framework of our various field campaigns. Although thissensor has the potential to significantly increase the spatial and temporal resolution comparedto discrete sampling, the long response time prevents from using its measurements as absolutevalues in dynamic natural environments and calls for progress in the field of technologies forcontinuous in situ dissolved CH4 measurements. However, the sensor turns out to be veryuseful during cruises to observe relative changes in dissolved CH4 concentrations and guidethe discrete sampling episodes.Our journey starts in the Scheldt estuary, at the transition between land and sea. Stableisotope analyses reveal that the unusual enrichment of dissolved CH4 in 13C and D in theupper estuary could result from intense microbial oxidation or an unknown source upstream.In the lower part of the estuary, this enriched CH4 mixes with depleted CH4 produced bymethanogenesis in the sediments, before entering the North Sea.In the shallow coastal Wadden Sea, we highlight the dominant contribution of coastal areasto oceanic CH4 emissions. The progressive increase in dissolved CH4 concentrations coincidedwith a 2°C warming of seawater. Submarine groundwater discharge, controlled by thespring-neap tide cycle, and tidal pumping might also have contributed to temporal variationsin dissolved CH4 concentrations and isotopic composition.In the Barents Sea, sailing towards polar latitudes, we find that the fractional sea-ice coverdid not induce a significant change in CH4 concentration nor isotopic composition at theocean-atmosphere interface. Local CH4 seepages at the seafloor might be a relict of gashydrate dissociation after the retreat of the Scandinavian Ice Sheet from the continental shelfafter the Last Glacial Maximum.Trapped in landfast sea ice at Barrow (Arctic) and Cape Evans (Antarctic), we find thatthe processes governing CH4 dynamics in sea ice happen to be dependent on the season andthe regional setting, and can be unravelled thanks to stable isotope analyses. At Barrow,the range of delta-13C values points towards in-ice microbial oxidation of CH4 produced bymethanogenesis in the underlying sediments. At Cape Evans, the much higher delta-13C valuessuggest a hydrothermal origin of CH4 trapped in sea ice and/or aerobic production withinsea ice.The journey ends in the Ross Sea, where the high variability and supersaturation observed indissolved CH4 concentrations, as well as carbon isotope signatures typical of a thermogenicorigin, suggest that gas seepages on the continental shelf might be the main source of CH4 tothe water column.This unique dataset of CH4 concentration and stable isotope composition in seawater, in seaice and in the atmosphere, highlights the spatial and temporal variability of the processesgoverning CH4 dynamics across the various oceanic environments investigated. This thesisprovides an example of how the isotopic approach can be successfully applied to disentanglethe biogeochemical cycle of CH4. To better constrain oceanic emissions, we recommend theimplementation of an extensive monitoring network to measure dissolved CH4 continuously,particularly in shallow coastal regions, which contribute the most. Eventually, further studiesshould focus on the Southern Ocean, which has yet to reveal its secrets with regard to CH4dynamics. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished