Tesi sul tema "Carbon isotope composition"
Segui questo link per vedere altri tipi di pubblicazioni sul tema: Carbon isotope composition.
Cita una fonte nei formati APA, MLA, Chicago, Harvard e in molti altri stili
Vedi i top-50 saggi (tesi di laurea o di dottorato) per l'attività di ricerca sul tema "Carbon isotope composition".
Accanto a ogni fonte nell'elenco di riferimenti c'è un pulsante "Aggiungi alla bibliografia". Premilo e genereremo automaticamente la citazione bibliografica dell'opera scelta nello stile citazionale di cui hai bisogno: APA, MLA, Harvard, Chicago, Vancouver ecc.
Puoi anche scaricare il testo completo della pubblicazione scientifica nel formato .pdf e leggere online l'abstract (il sommario) dell'opera se è presente nei metadati.
Vedi le tesi di molte aree scientifiche e compila una bibliografia corretta.
1
Barral, Cuesta Abel. "The carbon isotope composition of the fossil conifer Frenelopsis as a proxy for reconstructing Cretaceous atmospheric CO2". Thesis, Lyon, 2016. http://www.theses.fr/2016LYSE1148.
Abstract (sommario):
Le Crétacé a été une période d'instabilité climatique et du cycle du carbone, dont le CO2 atmosphérique a été désigné comme le driver majeur. Cependant, les reconstitutions du CO2 atmosphérique ne reflètent ni les dynamiques climatiques ni les grands évènements de perturbation du cycle du carbone décrits pour cette période. J'ai utilisé la composition isotopique de carbone de la plante fossile Frenelopsis (d13Cleaf) comme un nouvel proxy pour reconstituer le CO2 atmosphérique du Crétacé en termes de composition isotopique de carbone (d13CCO2) et de concentration (pCO2). La première courbe de d13CCO2 pour toute la durée du Crétacé a été construite à partir du d13C des carbonates marins. Sa comparaison avec des estimations de d13CCO2 à partir du d13Cleaf a révélé que les modèles développés jusqu'à maintenant ont une tendance à exagérer les valeurs de d13CCO2. Des estimations du fractionnement isotopique du carbone issu par des plantes (13Cleaf) obtenues à partir des nouvelles données d e d13Cleaf et d13CCO2 ont permis de reconstituer l'évolution à grande échelle de la pCO2. Ces résultats indiquent que le CO2 a probablement été une conséquence à long terme du changement climatique durant le Crétacé. Des cycles de d13CCO2 de ~1.2, ~2.1, ~5.4 et ~10.2 Ma ont été détectés, synchrones à ceux du niveau de la mer et à la cyclicité des paramètres de l'orbite terrestre décrits pour le Mésozoïque. Mes résultats fournissent une nouvelle perspective du système climatique et du cycle du carbone du Crétacé, dominés principalement par les paramètres orbitaux de la Terre et secondairement par des évènements catastrophiques de libération de CO2 d'origine volcanique dans l'atmosphèreThe Cretaceous was a period characterized by strongly marked climate change and major carbon cycle instability. Atmospheric CO2 has repeatedly been pointed out as a major agent involved in these changing conditions during the period. However, long-term trends in CO2 described for the Cretaceous are not consistent with those of temperature and the large disturbance events of the carbon cycle described for the period. This raises a double question of whether descriptions of the long-term evolution of atmospheric CO2 made so far are accurate or, if so, atmospheric CO2 was actually a major driver of carbon cycle and climate dynamics as usually stated. In this thesis the close relationship between the carbon isotope composition of plants and atmospheric CO2 is used to address this question. Based on its ecological significance, distribution, morphological features and its excellent preservation, the fossil conifer genus Frenelopsis is proposed as a new plant proxy for climate reconstructions during the Cretaceous. The capacity of carbon isotope compositions of Frenelopsis leaves (d13Cleaf) to reconstruct past atmospheric CO2, with regards to both carbon isotope composition (d13CCO2) and concentration (pCO2), is tested based on materials coming from twelve Cretaceous episodes. To provide a framework to test the capacity of d13Cleaf to reconstruct d13CCO2 and allowing for climate estimates from carbon isotope discrimination by plants (?13Cleaf), a new d13CCO2 curve for the Cretaceous based on carbon isotope compositions of marine carbonates has been constructed. Comparison with d13Cleaf-based d13CCO2 estimates reveals that although d13CCO2 and d13Cleaf values follow consistent trends, models developed so far to estimate d13CCO2 from d13Cleaf tend to exaggerate d13CCO2 trends because of assuming a linear relationship between both values. However, given the hyperbolic relationship between ?13Cleaf and pCO2, by considering an independently-estimated correction factor for pCO2 for a given episode, d13Cleaf values may be a valuable proxy for d13CCO2 reconstructions. ?13Cleaf estimates obtained from d13CCO2 and d13Cleaf values were used to reconstruct the long-term evolution of pCO2. The magnitude of estimated pCO2 values is in accordance with that of the most recent and relevant model- and proxy-based pCO2 reconstructions. However, these new results evidence long-term drawdowns of pCO2 for Cretaceous time intervals in which temperature maxima have been described
2
Gromov, Sergey S. [Verfasser]. "Stable isotope composition of atmospheric carbon monoxide : a modelling study / Sergey S. Gromov". Mainz : Universitätsbibliothek Mainz, 2014. http://d-nb.info/1051305497/34.
3
Czuba, Eva. "Development of a technique to study stable carbon isotope composition of NMHCs in ambient air". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape2/PQDD_0020/MQ56169.pdf.
4
Upsdell, Brynn. "The carbon and nitrogen composition of suspended particulate matter in Lake Erie, selected tributaries, and its outflow". Thesis, University of Waterloo, 2005. http://hdl.handle.net/10012/1219.
Abstract (sommario):
Since their introduction to Lake Erie, dreissenid mussels may have reengineered the cycling of nutrients in the lake so that the nearshore benthic community intercepts, retains, and recycles greater quantities of nutrients. This study traces particulate matter on a basin scale by characterizing the chemical composition (POC and PN concentrations, POC/PN mass ratios, δ13C and δ15N) of suspended particulate matter in Lake Erie, three tributary inflows, and the lake outflow between May and October, 2002. The data are used to 1) determine the relative contributions of allochthonous and autochthonous sources to suspended particulate matter, 2) identify possible sources of suspended particulate matter, and 3) compare suspended particulate matter in the eastern basin of Lake Erie with that in the central and western basins. Mean POC concentrations range from 175 to 4494 µg/L and mean PN concentrations range from 33 to 812 µg/L in this system. Mean POC/PN mass ratios are similar across all sampling locations, ranging between 4. 5 and 6. 9, and indicate that suspended particulate matter at these sites is mainly derived from autochthonous sources, particularly plankton. The ranges of δ13C (-34 to -22 ?) and δ15N (1 to 12 ?) identify terrestrial plants and soil matter, aquatic macrophytes, phytoplankton, and sewage as possible sources of suspended particulate matter at all sites. Plankton is probably the dominant source of suspended particulate matter at each site, with smaller contributions from allochthonous and other autochthonous sources. Significant differences in the concentration and isotope data between inflow and lake or outflow sites indicate that tributary inflows may receive greater contributions from terrestrial plants and soils and aquatic macrophytes than the lake and outflow. δ15N signatures also identify animal manure as a possible source of suspended particulate matter at the inflows. PN concentrations and δ15N signatures suggest that the shallowest nearshore sites close to Peacock Point in the eastern basin receive PN from a source that is not present at the other eastern basin sites or at the sites in the central and western basins. This source may be related to dreissenid mussels at these nearshore sites recycling nitrogen back into the water column.
5
Hamilton, Bryan T. "Small Mammals in portions of Great Basin National Park Susceptible to Groundwater Withdrawal: Diversity and Stable Isotope Perspectives". BYU ScholarsArchive, 2009. https://scholarsarchive.byu.edu/etd/1705.
Abstract (sommario):
To support population growth in Las Vegas, Nevada, large scale increases in groundwater pumping are planned across the state. This pumping could affect riparian areas in Great Basin National Park by lowering groundwater levels, reducing stream flows, and xerifying riparian vegetation. Great Basin National Park (GBNP) is mandated to manage its resources unimpaired for future generations. Loss of biodiversity is unacceptable under this mandate. If groundwater levels are reduced beyond a threshold, aquatic and riparian diversity would be lost, but the effects on small mammal communities are less clear. To provide baseline information and to consider the effects of groundwater withdrawal a priori, we sampled and compared small mammal communities in two watersheds susceptible to groundwater withdrawal and one non-susceptible watershed. We also used to stable isotopes of nitrogen, carbon, deuterium and oxygen to characterize small mammal communities. Evenness was higher in susceptible watersheds, which were distinct in species composition. Riparian and upland habitats in susceptible watersheds supported complementary small mammal communities, while communities in the non-susceptible watershed were more homogenous. Susceptible watersheds are located at the lowest elevations of GBNP where habitat heterogeneity due to the contrast between mesic riparian and xeric upland habitats is important in maintaining small mammal diversity. Partitioning was primarily seen in nitrogen and carbon isotopes which reflect feeding ecology (trophic level and primary production source), but was also seen in oxygen isotopes. Major differences in nitrogen and carbon isotopes were between taxonomic groups, while similarity was highest within these groups. Shrews and ermine were highest in nitrogen reflecting their high trophic positions. Harvest and piñon mice were intermediate in nitrogen suggesting omnivory, while chipmunks, voles, woodrats and pocket mice were apparently herbivorous. Carbon ratios were consistent with C3 based diets but were relatively enriched in Sigmodontinae species. Small mammal deuterium was similar to stream water suggesting that stream water is an important water source of water to small mammals. Oxygen enrichment relative to stream water and precipitation suggested that small mammals are sensitive to body water evaporation. Contrary to a previous study, oxygen isotopes were inversely related to water use efficiency. Increases in the rate of groundwater pumping adjacent to Great Basin National Park could lower water tables, reduce stream flows, and xerify riparian vegetation. We suggest that groundwater levels, streams flow and riparian vegetation, in addition to small mammal species composition will be important response variables in monitoring the effects of groundwater withdrawal. If predictions of groundwater withdrawal are realized, groundwater levels, stream flows, vegetation, microclimate, and invertebrates riparian dependent as well as small mammals will be negatively affected resulting in a decrease in diversity and loss of riparian species from affected areas.
6
Xia, Yang. "Impact of varying NH₄⁺˸NO₃⁻ ratios in nutrient solution on C-isotope composition of leaf- and root-respired CO₂ and putative respiratory substrates in C₃ plants". Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS222.
Abstract (sommario):
La composition isotopique (¹³C/¹²C) du CO₂ respiré par les feuilles et les racines dans l'obscurité et celle des substrats respiratoires putatifs, y compris les sucres solubles et les acides organiques (malate et citrate), l'activité de la PEPc ainsi que les échanges gazeux des feuilles ont été déterminés sur le haricot (Phaseolus vulgaris L.) et l’épinards (Spinacia oleracea L.) cultivés dans du sable avec différents rapports NH₄⁺: NO₃⁻ dans N fourni. Le CO₂ respiré par les feuilles était enrichi en ¹³C sous NO₃⁻ s’appauvrissant progressivement avec l’augmentation de la fraction de NH₄⁺ dans le N fourni, tandis que la composition isotopique du CO₂ issu de la respiration des racines restait inchangée quel que soit le rapport NH₄⁺: NO₃⁻. Nous avons suggéré qu'une plus grande quantité de pools enrichis en ¹³C fixés par la PEPc via la voie anaplérotique contribuait à la respiration foliaire sous NO₃⁻. Cependant, un effet similaire dans les racines attendu sous NH₄⁺ a été masqué en raison d'une refixation (par la PEPc) du CO₂ respiré (appauvrie en ¹³C). De manière inattendue, les modifications de la composition isotopique du C des métabolites individuels, leurs quantités, ainsi que l'activité de l’enzyme PEPc, présentaient des profils différents entre les deux espèces étudiées. Des expériences de double marquage (¹³C et ¹⁵N) sont nécessaires pour mieux comprendre l’impact de la plasticité métabolique du TCA sur l’écart isotopique entre le malate et le citrate et sur la composition isotopique du CO₂ respiré chez différentes espèces sous différentes formes d’azoteC-isotope composition of leaf- and root-respired CO₂ in the dark and that of putative respiratory substrates including soluble sugars and organic acids (malate and citrate), PEPc activity, as well as leaf gas exchanges were determined on bean (Phaseolus vulgaris L.) and spinach (Spinacia oleracea L.) plants grown in sand with varying ratios of NH₄⁺: NO₃⁻ in supplied N. Leaf-respired CO₂ was ¹³C enriched under NO₃⁻ nutrition and became progressively ¹³C depleted with increasing amount of NH₄⁺ in supplied N, while C-isotope composition of root-respired CO₂ remained unchanged across N-type gradient. We suggested that a higher amount of ¹³C enriched C-pools fixed by PEPc through anaplerotic pathway contributed to respired CO₂ in leaves under NO₃⁻ nutrition. However, a similar effect in roots expected under NH4+ nutrition was masked because of a rather ¹³C depleted C source (respired CO₂) refixation by PEPc. Unexpectedly, the changes in C-isotope composition of individual metabolites and their amounts as well as PEPc activity exhibited different patterns between the two species. Double labelling experiments (¹³C and ¹⁵N) are needed for better understanding the impact of metabolic plasticity of TCA on isotopic gap between malate and citrate and on C-isotope composition of respired CO₂ in different species under varying N-type nutrition
7
Yang, Chengfan. "Li isotope study of Yangtze River sediments : new constraints on climate, weathering and carbon cycle relationships". Electronic Thesis or Diss., Sorbonne université, 2020. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2020SORUS433.pdf.
Abstract (sommario):
Au cours de ce travail, j’ai réalisé une série d'études dans le bassin du Changjiang (Yangtze), afin de mieux comprendre l'influence de ces effets.Tout d'abord, l'exploitation du barrage des Trois Gorges (TGD) a modifié la composition géochimique des sédiments en aval. Depuis 2003, les sédiments venant des hauts bassins ont été en grande partie retenus en amont, tandis que les sédiments précédemment déposés dans le bassin moyen-inférieur ont été progressivement remis en suspension. Ces processus expliquent l’évolution géochimique des sédiments exportés vers la mer de Chine. En deuxième partie, une étude systématique démontre que les compositions isotopiques en lithium des phases dissoutes et particulaires se comportent de façon conservative dans la zone de mélange de l'estuaire du Changjiang. Cependant, les phases échangeables ne représentent qu'une faible quantité de Li, ce qui explique son impact négligeable dans cette zone. Troisièmement, Cette étude confirme que dans les grands bassins versants, l'altération chimique peut réagir rapidement à de grandes amplitudes climatiques. Ceci est particulièrement bien illustré, dans la carotte CM97, par la période du Younger Dryas. Depuis 2 000 ans, les δ7Li des argiles s’accentuent clairement par rapport à la période précédente, à cause de l'érosion des sols de plaines induite par l'homme. En résumé, ces résultats apportent de nouveaux éclairages sur l'interprétation des proxys et sur la réponse de l'altération chimique aux variations climatiques, ce qui est essentiel pour mieux quantifier l’impact du l’altération continentale sur les climats passés et futurs de notre planèteIn order to better understand the weathering-climate feedback, a series of studies was carried out in the Changjiang (Yangtze) Basin. First, the operation of the Three Gorges Dam (TGD) changed downstream sediment geochemical compositions. Before 2003, large amounts of upstream-derived sediments deposited and experienced further weathering in the mid-lower basin. Since 2003, strong riverbed sediment resuspension changed the roles of the mid-lower reaches from important sinks to major sources of sediments delivered to the sea. As a consequence, an intensified weathering intensity of downstream sediment was observed.Second, dissolved δ7Li exhibit a conservative behavior in the Changjiang Estuary. During the process of SPM transported offshore, weathering product flocculated and deposited, while primary minerals resuspended. The combined effect resulted in the UCC-like SPM δ7Li values. There is a Li isotope fractionation between the dissolved load and exchangeable phase. However, this process shows negligible impact on δ7Li of dissolved load and particulates. Third, weathering response to climate is complex in large river basins. During the Younger Dryas, the positive excursion of clay δ7Li is consistent with enhanced incongruent weathering, in response to temperature cooling. The minor variation of clay δ7Li at 11 – 2 ka likely indicate stable weathering and mile climate variation. Over the last 2 kyr, the fluctuation of clay δ7Li is mostly caused by intensification of human activities. In summary, this thesis sheds new lights on the weathering-climate feedback over geologic past, and provides perspectives on how human activities affect natural processes
8
Allan, Wendy Lynne. "Variation in the stable carbon isotope composition of needle and annual rings in Pseudotsuga menziesii (Mirb.) Franco and its relation to water use needle nitrogen content and productivity". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1996. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/mq21902.pdf.
9
Rabarijaona, Arivoara. "L'efficience intrinsèque d'utilisation de l'eau (WUEi) du chêne sessile conditionne-t-elle sa résilience à la sécheresse ?" Electronic Thesis or Diss., Paris, AgroParisTech, 2023. http://www.theses.fr/2023AGPT0016.
Abstract (sommario):
La migration assistée constitue une solution pour adapter les peuplements forestiers face à l'augmentation en intensité et fréquence des sécheresse. Elle nécessite néanmoins l'identification des populations les plus résilientes à la sécheresse, et la caractérisation de leur diversité. L'efficience d'utilisation de l'eau (WUE) est un trait pertinent à évaluer pour ce choix car elle traduit un compromis entre l'assimilation carbonée et la perte d'eau par transpiration. En combinant dendrochronologie et isotopie, cette thèse évalue le rôle de WUE sur les performances de croissance et la résilience à la sécheresse du chêne sessile (Quercus petraea).D'abord, WUE a été comparé entre 16 populations dont les individus, issus de graines provenant de sites répartis sur un large gradient pédoclimatique, ont grandi dans la plantation comparative de Sillegny. Des différences significatives de WUE ont été trouvées entre les populations, mais elles n'étaient pas corrélées avec les conditions pédoclimatiques des sites d'origine. Cependant, les populations de provenance à sols sableux montraient de plus fortes augmentations de WUE en réponse à la sécheresse de 2003 par rapport à 2000, comparées aux populations des provenances sur sols limoneux. Par ailleurs, les arbres ayant une forte WUE avaient eu une croissance élevée lors des années humides uniquement. Quoique ces résultats suggèrent une adaptation du chêne sessile, reflétée par la plasticité de WUE à la sécheresse, les variabilités de WUE intra-populations étaient plus importantes que celles entre populations.Ensuite, la variabilité phénotypique de WUE a été étudiée à l'intérieur de deux populations à conditions pédoclimatiques contrastées, à Blois (humide) et La Harth (sec), où tous les arbres de la placette d'étude ont été échantillonnés. Le lien entre WUE et croissance radiale a été particulièrement examiné. Alors que le contrôle stomatique semblait être le facteur clé dans les variations interannuelles de WUE, ses variations inter-individuelles (intra-annuelle) étaient plutôt pilotées par l'assimilation nette de CO2, fortement impactée par le statut social. Ainsi, les relations intra-annuelles entre WUE et croissance apparaissent plus significatives quand la pression de compétition devient plus forte au sein du peuplement (au stade mature), et quand la lumière devient plus limitante que l'eau (dans un site humide, à Blois).Enfin, l'effet de WUE au stade jeune sur la trajectoire de croissance des arbres a été évalué pour les mêmes sites de Blois et la Harth. À la Harth, les arbres avec un WUE plus élevé au stade jeune sont les plus dominants en 2021, suggérant une sélection en faveur d'un fort WUE dans ce milieu. En revanche, ce n'est pas le cas à Blois, où l'effet de WUE au stade jeune sur le statut social des arbres s'arrête après 60 ans. La réponse des arbres à la sécheresse n'était pas affectée par WUE au stade jeune à Blois et seulement durant les premières décennies à La Harth. Par ailleurs, la plasticité de la WUE à la sécheresse semble moins impliquée dans le processus de sélection, à mesure que les arbres vieillissent et sont exposés à des variations environnementales.WUE est un trait complexe influencé par divers facteurs, notamment la génétique, les conditions micro-environnementales et l'âge des arbres. Étant donné que les variations intra-populations sont plus marquées que les différences entre populations, et que le lien entre WUE et la résilience à la sécheresse est relativement faible, le choix des populations de chêne sessile plus adaptées à la sécheresse ne peut se faire sur la base de WUE uniquementAssisted migration constitute a possibility to adapt forest ecosystems face to the increase in drought intensity and frequency. However, this strategy requires identification of drought-resistant populations and characterization of the diversity within them. Water use efficiency (WUE) is a key trait to assess for this choice, as it reflects a trade-off between carbon assimilation and water loss through transpiration. By combining dendrochronology and stable isotope analysis, this thesis investigates the effect of WUE on the growth performance and resilience to drought of sessile oak (Quercus petraea).Firstly, WUE was compared among 16 populations whose individuals, from seeds originating from sites along a wide range of pedoclimate gradient, had grown in the common garden Sillegny. Significant differences in WUE were found among these populations, but these differences were not correlated with the pedoclimatic conditions of the sites of origin. However, populations from provenances with sandy soils showed a larger increase in WUE in response to the drought of 2003 (compared to the wet year of 2000) than populations from provenances with silty soils. In addition, trees with higher WUE showed larger radial growth only in wet years. Although these results suggest an adaptation of the sessile oak, reflected by the plasticity of WUE to drought, the variability of WUE within populations was higher compared to the differences among populations.Then, the phenotypic variability of WUE was studied within two populations with contrasting soil and climate conditions, at the Blois (wet) and the Harth (dry) sites. All the trees within each plot were sampled, with a particular focus on the relationship between WUE and radial growth. While stomatal control appeared to be the key factor in inter-annual variations in WUE, the inter-individual (intra-annual) variability in WUE was driven more by net CO2 assimilation, which is strongly affected by tree social status. The intra-annual relationships between WUE and growth appeared more significant as the competition among trees within the stand intensified (particularly when trees become mature), and when light availability became a limiting factor rather than water (in a humid site, at Blois).Finally, the effect of WUE expressed by trees at a young age on growth trajectory was assessed within the Blois and the Harth stands. At the Harth site, trees with higher WUE during their young age were the most dominant in 2021, suggesting selection for higher WUE in dry environment. In contrast, at the Blois site, the effect of WUE at the young age on the social status of the trees ceased after 60 years. The response of trees to drought was not significantly affected by WUE at the young age at the Blois site and only during the first decades at the Harth site. Moreover, the plasticity of WUE to drought might play a diminishing role in the selection process as trees age and were exposed to changing environmental conditions.WUE is a complex trait influenced by multiple factors, including genetics, microenvironmental conditions, and tree age. Given that intra-population variations were more pronounced than differences among populations, and that the relationship between WUE and resilience to drought was tenuous, the selection of drought-adapted sessile oak populations cannot be only based on WUE
10
Fichtler, Esther [Verfasser], Martin [Akademischer Betreuer] Worbes e Rupert [Akademischer Betreuer] Wimmer. "Ecological information of ring width, stable carbon isotope composition and wood anatomical variables in tropical tree rings - A contribution to dendrochronology in the tropics / Esther Fichtler. Gutachter: Martin Worbes ; Rupert Wimmer. Betreuer: Martin Worbes". Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2012. http://d-nb.info/1042262241/34.
11
Triolo, Roberta. "Hierarchy of factors impacting grape berry mass at different scales and its direct and indirect effects on grape and wine composition". Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0336/document.
Abstract (sommario):
La masse de la baie est le résultat de l’effet intégré de plusieurs facteurs. La recherche a été dessinée afin d’étudier l’effet simultané des facteurs majeurs influençant la masse et la composition de la baie, de les hiérarchiser selon leur degré d’impact à des échelles différentes, de séparer leur effet direct et indirect sur la composition du raisin et de comparer le profil de vins élaborés à partir de petites et grosses baies. L’étude a été conduite sur deux sites expérimentaux, localisés dans les régions de Saint-Emilion (France) et Alcamo (Italie), pendant les années 2014 et 2015. Sur le premier site, les vignes sont plantées sur deux types de sols, tandis que sur le deuxième, deux traitements hydriques étaient appliqués. A l’échelle intra-parcellaire, l’état hydrique de la vigne représente le facteur le plus important, tandis que l’effet du nombre de pépins par baie n’est pas significatif. Des résultats opposés sont obtenus lorsque les relations sont étudiées à l’échelle de la grappe et de la plante. A large échelle, les facteurs impactent directement et indirectement la composition du raisin et les petites baies produisent des moûts et des vins plus concentrés. A l’inverse, à l’échelle de la grappe et de la plante, la masse de la baie n’influence pas la composition du raisin. Seule la concentration en anthocyanes est significativement liée à la masse à toutes les échelles. Cette relation est particulièrement évidente sous conditions hydriques limitantes. Un déficit hydrique augmente le ratio pellicule/pulpe, indépendamment de la masse de la baie. Petites et grosses baies d’une parcelle ayant une condition hydrique homogène, tendent à avoir un profil similaireFinal berry mass is the result of the integrated effect of several factors. They also influence berry composition. The present work was designed to study the simultaneous effect of major factors influencing berry mass and composition, to hierarchize their impact at different scales, to distinguish their direct and indirect effect on berry composition and to compare the profile of wines made from large and small berries. The study was carried out simultaneously on two vineyards located in the Saint Emil ion (France) and Alcamo (Sicily) areas, during 2014 and 2015. On the first site, vines were planted on two soil types, while on the second site two different irrigation treatments were applied. Depending on the scale, some factors homogeneously impacted the berry mass and composition. At the intra-parcel scale, vine water status represented the most impacting factor, while berry seed number did not have significant effect. Opposite results were obtained when the investigation was carried out at the intra-bunch and intra-plant scales. At large scale, factors impacted directly and indirectly berry compounds and grape juices and wines produced from smaller berries were more concentrated. Neither at intra-bunch, nor at intra-plant scales, berry size effect on juice composition was significant. Only anthocyanin concentration was related to berry size at all scales. This fact was particularly obvious in berries produced under limited water conditions. Water deficit increased the skin to flesh ratio, independently of berry size. This means that small and large berries, produced from a single parcel with homogenous water uptake conditions, tend to have similar enological profiles
12
Denis, Marie. "Mécanismes de solubilisation et transfert de matières organiques dissoutes à l'échelle d'un bassin versant agricole : apport de l'étude de la composition moléculaire". Thesis, Rennes 1, 2017. http://www.theses.fr/2017REN1S045/document.
Abstract (sommario):
Les matières organiques dissoutes (MOD), en tant que sources de nutriments ou potentiels vecteurs de pollution, sont impliquées dans de nombreuses problématiques environnementales. Bien qu'elles fassent l'objet de nombreuses études depuis plusieurs décennies, les mécanismes gouvernant leur solubilisation et leur transfert depuis les sols vers les systèmes aquatiques demeurent sujets à discussion. En s'appuyant sur l'étude de la composition moléculaire des MOD par hydrolyse et méthylation assistée par température et couplée à la chromatographie en phase gazeuse et à la spectrométrie de masse (HMT-CPG-SM), cette thèse a pour objectif d'apporter une meilleure compréhension de leurs mécanismes de solubilisation et de transfert à l'échelle d'un bassin versant agricole. Ce travail s'est appuyé sur le bassin versant expérimental de Kervidy-Naizin (Morbihan, Observatoire de Recherche en Environnement AgrHys) afin d'observer les processus mis en jeux à deux échelles temporelles différentes. A l'échelle de la crue, ce travail a permis de préciser l'impact des conditions hydrologiques spécifiques sur la dynamique des MOD. A l'échelle annuelle, l'utilisation conjointe de la signature isotopique du carbone (δ13C) et de la composition moléculaire des MOD a permis de préciser les mécanismes de transfert de MOD impliqués à l'échelle du versant. L'utilisation de la HMT-CPG-SM s'est avéré un outil adéquat pour l'étude de la dynamique des MOD. L'ensemble des résultats ainsi obtenus ont permis de souligner l'importance des conditions hydrologiques et en particulier de la dynamique de nappe dans les processus de solubilisation et de transfert des MODDissolved organic matter (DOM), as sources of nutrient or pollutant dissemination pathway are implied in numerous environmental issues. Although DOM have been the subject of numerous studies for several decades, the mechanisms implied for their solubilization and their transport from soils to aquatic systems are still a matter of discussion. Based on DOM molecular composition determined using thermally assisted hydrolysis and methylation –gas chromatography – mass spectrometry (THM-GC-MS), this thesis aims to provide a better understanding of their solubilization and transfer mechanisms at the scale of an agricultural headwater catchment. This work was conducted on the experimental headwater catchment of Kervidy-Naizin (France, Environmental Research Observatory AgrHys) in order to determine the processes implied at two temporal scales. At the scale of a rain event, this work has clarified the impact of hydrological conditions on the DOM dynamics. At annual scale, the use of carbon isotope signature (δ13C) and DOM molecular composition allowed to clarify the DOM transfer mechanisms at the slope scale. The use of THM-GC-MS appears to be a suitable tool for the study of DOM dynamics. The results thus obtained allowed to highlight the role of hydrological conditions and in particular the water-table level in the solubilization and transfer of DOM
13
Nel, Jacques A. "Vegetation and microbial determinants of soil carbon isotopic composition". Master's thesis, University of Cape Town, 2018. http://hdl.handle.net/11427/28072.
Abstract (sommario):
Typically, soil δ¹³C and δ¹⁵N values tend to increase with depth across a wide range of ecosystems. Changes in δ¹³C with depth have been attributed to vegetation changes (i.e. C₃/C₄ shifts), but the similarity in δ¹³C and δ¹⁵N profiles suggest that microbial decomposition may play an important role. The determinants of soil δ¹³C and δ¹⁵N, however, are complex and microbial decomposition and vegetation shifts are not the only mechanisms that drive the fractionation of the isotopes with depth. We explored the utility of using δ¹³C as a proxy for vegetation change by considering alternative mechanisms for the changes in soil δ¹³C with depth. These alternate mechanisms may weaken the interpretation of soil δ¹³C as an indicator of vegetation change if the measured δ¹³C changes are small. We hypothesized that: (1) if soil-related processes such as mineralization and dark CO₂-fixation by microbes and roots contribute significantly to the δ¹³C signature of bulk soil at depth, one cannot simply determine whether the δ¹³C value of the soil at depth is indicative of a past vegetation assemblies (i.e. C₃/C₄ transitions); (2) changes in soil δ¹³C and δ¹⁵N values are linked through common microbially mediated decomposition-related processes; (3) anaplerotic CO₂ fixation by microbes and roots may contribute significantly to soil δ¹³C values, while N₂-fixation may contribute to soil δ¹⁵N values with depth. Microbial processing of SOM during decomposition leads to ¹³C-enrichement of SOM with depth and has been modelled using a Rayleigh distillation process. Anaplerotic fixation of soil CO₂ is, however, known to occur in microbes and roots and we suggest that this has a role in determining soil SOM δ¹³C values through cumulative incorporation of bulk atmosphere CO₂ into SOM. These processes vary greatly between soils and environments. The correspondence between soil δ¹³C and δ¹⁵N was assessed by compiling data from soil depth profiles from widely distributed sites and conducting an analysis of global δ¹³C and δ¹⁵N variations in surface soils in order to determine relationships between soil isotopes and with climate and soil properties. Strong positive correlations between δ¹³C and δ¹⁵N values through soil profiles were found at a number of sites and were found to be independent of vegetation type. Globally, soil δ¹³C and δ¹⁵N values were also found to be significantly positively correlated across a wide range of climates and biomes. The global correspondences between δ¹³C and δ¹⁵N values may suggest a mechanistic link between δ¹³C and δ¹⁵N through the process of SOM decomposition and microbial processing. Anaplerotic CO₂ fixation by soil microbes and roots was assessed using soils from 10 sites across South Africa differing in soil properties and incubated in the dark for 3 d under continuous exposure to ¹³CO₂- and ¹⁵N₂-enriched atmospheres with varying soil moisture (10, 50 and 100% of field capacity) and temperature (4, 25, 40°C). There was no evidence of significant N₂ fixation in any treatment. Significant soil anaplerotic CO₂ fixation, however, occurred in all soils. Highest rates of anaplerotic CO₂ fixation occurred in soils at 50% field capacity and 25°C, suggesting a link with microbial biotic activity. Soils with low C and N concentrations and low C:N ratios exhibited the highest rates of CO₂ fixation in soils, indicating a link between anaplerotic CO₂ fixation rates and soil nutrient status. The higher rates of CO₂ fixation in soils with low nutrients may indicate that soil microbes rely increasingly on anaplerotic fixation as SOM-N declines, forcing greater reliance on de novo amino acid synthesis, and thus anaplerotic CO₂ fixation. The ubiquitous occurrence of anaplerotic ¹³CO₂ fixation in these soils indicates that anaplerotic fixation is likely important in contributing to determining soil δ¹³C values. Diffusion of low δ¹³C bulk atmospheric CO₂ (ca. -10‰) into the soil atmosphere (<< -10‰) will drive soil CO₂ δ¹³C towards ca. -10‰, and constant anaplerotic CO₂ fixation will result in SOM δ¹³C also tending towards 10‰ in more highly processed SOM deeper in the soil. The consequences of decomposition and the linked anaplerotic activity for soil δ¹³C values may be erroneously interpreted as evidence for C₄ vegetation being invaded by C₃ vegetation, potentially leading to incorrect conservation decisions. We argue that δ¹³C should only be used as a proxy for vegetation change where decomposition rates and anaplerotic CO₂ fixation are low and/or their effect on soil δ¹³C values can be accounted for.
14
Shelkov, Denis Alexander. "N and C isotropic composition of different varieties of terrestrial diamonds and carbonado". Thesis, Open University, 1997. http://oro.open.ac.uk/54608/.
Abstract (sommario):
During the course of this research an instrument utilising combustion as a means of gas extraction capable of N, e, Ar and He analysis has been developed and the entire analytical procedure has been automated. N and e isotopic analysis has been performed on eclogitic and peridotitic diamonds (mainly from Yakutian kimberlites and the Roberts Victor kimberlite pipe). Diamonds with unusual (light and heavy relative to the peak of ol3e distribution of mantle diamonds) carbon isotopic signatures were considered for the research so that diamonds in the range of δ¹³C from -30‰ to + 2.8‰ were characterised for δ¹⁵N. The results together with data obtained previously by the others define fields for eclogitic and peridotitic diamonds on a plot of δ¹⁵N vs. δ¹³C. The model of mantle nitrogen and carbon evolution is discussed. A comprehensive comparison between carbonado and other known forms of microcrystalline diamond (framesites and shock diamonds) has been made for a number of parameters: N and e isotopic composition and N content; 4He content; morphology of the inner structure of diamond aggregates. It can be concluded that carbonado is generally similar to frame sites and all facts known about carbonado can be explained on the grounds of common mantle origin involving subducted carbon and nitrogen. Since extremely high 4He concentrations are encountered in carbonado this parameter is considered to be the most singular feature of this diamond variety and the radial distribution of 4He in single diamond crystals has been studied. A 4He content comparable with that in carbonado was found in the 30 J.lm skin of diamond crystals (up to 1.4 x 10⁻²) suggesting that carbonado could acquire high 4He concentration in the same geological processes as single diamond crystals and making carbonado indistinguishable from mantle diamonds in terms of He content. An additional result of the investigation is that the maximum of 4He diffusion coefficient for diamond at mantle P,T conditions can be estimated (≈4x10⁻²¹ ) from the 4He zoning identified in the interior of a diamond crystal from the Finsch kimberlite. A number of diamonds of impact origin from Popigai crater and Ebeliakh river placer deposits were studied for N, C and Ar isotopic compositions. It was concluded that diamonds from these two localities have resulted from separate impact events and that diamond aggregates studied are most probably consist of a mixture of different Ar and N carriers (e.g. two types of diamond grains).
15
Burke, Roger Allen Jr. "Stable Hydrogen and Carbon Isotopic Compositions of Biogenic Methanes". Scholar Commons, 1985. https://scholarcommons.usf.edu/etd/7658.
Abstract (sommario):
Stable hydrogen and carbon isotopic compositions of biogenic methanes collected from the sediments of several deep-sea, nearshore marine-estuarine, and freshwater environments were determined. The isotopic compositions of methane samples from eight different DSDP Sites (mean σD-CH4 = -1850>/∞, std. dev. = 70>/∞, n = 75; mean σ13C-CH4 = -71.30/∞, std. dev. = 6.30/∞, n = 44) are generally typical of methane formed via C02 reduction in deep-sea sediments.
Methane collected from several freshwater environments was D-depleted (mean σD-CH4 = -3000>/∞ , std. dev. = 260/∞, n = 20) and 13C-enriched (mean σ13C-CH4 = -60.10/∞, std. dev. = 6.10/∞, n = 20) compared to the deep-sea methane. Normally, acetate dissimilation is thought to account for about 60 to 70% of the total methane production in freshwater sediments.
Nearshore marine-estuarine methanes appear to be isotopically intermediate (mean σD-CH4 = -2580>/∞ , std. dev. = 230/∞, n = 46; σ13C-CH4 = -61.80/∞, std. dev. = 3.10/∞, n = 46) between deep-sea and freshwater methanes. Variation in the relative importance of the two main methanogenic pathways, acetate dissimilation and C02 reduction, is probably the single most important factor responsible for the differences in methane isotopic compositions among these three different types of environments. Other factors that probably contribute to the methane isotopic differences are temperature, sedimentation rate, organic matter type and amount, concentration of alternate electron acceptors, rate of methane formation and possibly postgenerative isotopic equilibration.
Shallow aquatic sediments are thought to be an important source of methane to the atmosphere; the methane produced in these systems, including the ones sampled in this study, is generally substantially more 13C-depleted than expected based on the σ13C of atmospheric methane and the isotopic fractionation associated with the atmospheric sink process. Too few oD data are available to allow evaluation of the role of shallow aquatic sediments in determining atmospheric σD-CH4.
16
Buckingham, Sarah. "Dissolved Organic Carbon In Topsoils : Concentration,Flux and Isotopic Composition". Thesis, Lancaster University, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.531683.
17
Yates, Paul David. "The content and stable isotopic composition of carbon in spherical micrometeorites". Thesis, Open University, 1992. http://oro.open.ac.uk/54849/.
Abstract (sommario):
Micrometeorites are extraterrestrial bodies that have survived atmospheric entry to be found on Earth as grains <1mm in diameter. Of the annual flux of extraterrestrial material to the Earth ca.99% is supplied by the micrometeorites. The lifetime of the micrometeroids in the interplanetary medium in extremely ephemeral, but their population is maintained largely by ejection of particles from cometary nuclei and from collisional debris from the asteroid belt. As such, the micrometeorites are of fundemental importance to cosmogony, because they may provide the only means, at present, to directly study cometary material, and sample a far less biased cross section of the asteroid belt than conventional meteorites. A static gas source mass spectrometer for carbon isotope measurements built in the Planetary Sciences Unit has been tested and shown capable of routinely analysing ca.1 nanogram of carbon (as carbon dioxide) to precisions of ca.±1%o. To enable this gain in sensitivity to be exploited, a sample preparation and carbon dioxide extraction system has been devised that typically imparts a total of less than 20 nanograms of extraneous carbon contamination to the samples. An advantage of the mass spectrometer is its ability to make accurate isotopic abundance measurements of the blank contribution for the purpose of making corrections to the analytical data. The instrument and inlet system has been applied to studies of micrometeorites > 200∝m in diameter. A procedure has been developed involving three analytical techniques (chemical/petrographic, X-ray diffraction and stable carbon isotope). Carbon isotopic analyses of multiple-sample aliquots of deep-sea, and individual Greenland and Antarctic micrometeorites has enabled the identification of components that are similar to those within the stony chondritic meteorites. More specifically, components have been revealed that may indicate a generic connection to primitive chondrites. Carbon isotopic characterisation of acid-resistant residues prepared from micrometeorite-rich Greenland cryoconite suggested that the micrometeorites contain pre-solar dust grains of silicon carbide, graphite and diamond. which provides an additional indication of the primitive nature of some micrometeorites. Experiments to produce micrometeorite analogues by pulse-heating microgram-sized samples of whole-rock meteorites showed that indigenous carbonaceous species can survive pulse-heating above their normal combustion temperatures. The overall conclusion of the investigation is that the flux of > 200∝m micrometeorites is dominated by a steroidal material and that the atmospheric entry heating process is poorly understood.
18
Launois, Thomas. "Modélisation de la composition isotopique des cernes d'arbres (13C et 18O) et des transferts de COS entre l'atmosphère et la biosphère continentale pour quantifier les flux bruts de carbone". Thesis, Versailles-St Quentin en Yvelines, 2014. http://www.theses.fr/2014VERS0039/document.
Abstract (sommario):
Dans un contexte de changement climatique, le fonctionnement de la biosphère continentale peut être durablement affecté par l’augmentation d’extrêmes climatiques, diminuant l’assimilation photosynthétique du carbone ou augmentant la respiration de l’écosystème. Quantifier le stockage de carbone par les écosystèmes et prédire leur sensibilité aux changements climatiques repose donc fortement sur notre capacité à diagnostiquer séparément les flux de photosynthèse et de respiration à différentes échelles. La productivité primaire brute (GPP) n’est cependant pas directement mesurable. Des approches indirectes ont été proposées pour estimer les flux bruts biosphériques (GPP et respiration), combinant différents traceurs et notamment les isotopologues stables du CO2 (13C et 18O), et, plus récemment, la mesure de l’oxysulfure de carbone dans l’atmosphère (COS). Dans ce contexte, mes travaux de thèse ont exploré deux approches. La première visant à utiliser les mesures isotopiques des cernes d’arbres et leur largeur, toutes liées aux variations de l’activité photosynthétique. Les variations interannuelles du flux de photosynthèse modélisées par un modèle de biosphère continentale ont ainsi pu être évaluées et comparées aux mesures in situ. La seconde visant utiliser les mesures atmosphériques de COS pour contraindre les estimations de GPP des modèles actuels de biosphère, en (1) établissant un nouveau bilan global des sources et puits de ce gaz, (2) optimisant les différents termes de sources et puits de COS et (3) estimant le potentiel de ce nouveau traceur pour valider/invalider les flux bruts de photosynthèse (GPP) simulés par les modèles actuels de biosphère continentaleIn the context of global climate change, the behavior of the terrestrial biosphere can be durably affected by the increased frequency and intensity of extreme climatic events, which can decrease the photosynthetic assimilation of carbon and/or increase the respiration rate of the ecosystems. Therefore, quantifying the carbon storage capacity of the ecosystems and predicting their sensitivity to climate changes strongly rely on our capacity to separately estimate the photosynthesis and respiration rates at different scales. The gross primary productivity (GPP) is however not directly measurable. Indirect approaches have been proposed to estimate the biospheric gross fluxes (GPP and respiration), combining for instance stable isotopologues of CO2 (13C and 18O), and, more recently, the measure of carbonyl sulfide (COS) concentrations in the atmosphere. In this context, my PhD work followed two complementary approaches. In the first approach, isotopic measurements and tree-ring widths were used, because both of them are linked to the photosynthetic activity. The inter-annual variations of the photosynthetic fluxes simulated with the ORCHIDEE continental biosphere model were evaluated and compared with in situ measurements. The second approach consisted in using atmospheric measurements of OCS concentrations and in exploring their potential to constrain the current estimates of the GPP in dynamic global vegetation models (DGVM), by (1) establishing a new global budget of sources and sinks of this gas, (2) optimizing the source and sink terms of this cycle and (3) estimating the potential of this new tracer to validate/invalidate the simulated GPP when using current DGVMs
19
Lockheart, Matthew James. "Isotope compositions and distributions of individual compounds as indicators for environmental conditions : comparisons between contemporary and Clarkia fossil leaves". Thesis, University of Bristol, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389098.
20
Bonne, Jean-Louis. "Observations continues de la composition atmosphérique au sud Groenland". Electronic Thesis or Diss., Versailles-St Quentin en Yvelines, 2015. http://www.theses.fr/2015VERS008V.
Abstract (sommario):
Le but de ma thèse est de conduire et d’utiliser les premières observations atmosphériquesde surface du CO2, de l’O2, du CH4 et de la composition isotopique de la vapeur d’eau et desprécipitations dans la région peu instrumentée du sud du Groenland. Quelles informations cesobservations locales peuvent-elles nous apporter à la fois concernant les processus atmosphériqueslocaux et concernant le transport atmosphérique à grande échelle ? Peut-on en extrairedes informations sur les échanges entre la surface et l’atmosphère, qui constituent une part crucialedes cycles biogéochimiques du carbone et de l’eau ? L’interprétation paléoclimatique desenregistrements de carottes de glace au Groenland peut-elle bénéficier de ces observations ?Après une validation des observations menées à Ivittuut, sur la côte sud-ouest du Groenland,en regard de normes internationales de qualité, confirmant leur représentativité des variationsatmosphériques, j’ai commencé par interpréter ces observations en analysant leur variabilité àdifférentes échelles de temps et découlant de processus spécifiques. Ceci m’a permis de montrerque le site de mesure était très peu influencé par des phénomènes locaux : peu de sources localesde gaz à effet de serre, et de processus locaux agissant sur la composition isotopique de la vapeurd’eau. Cette caractéristique facilite l’attribution des variations observées à des changements detransport atmosphérique de grande échelle en lien avec des sources distantes.Pour comprendre les variations observées, je les ai mises en relation avec des observationsissues d’autres sites ainsi qu’avec des sorties de modèles atmosphériques de grande échelle. D’unepart, j’ai constaté que de nombreuses variations de la composition atmosphérique à l’échelle synoptiquepouvaient être expliquées par des modifications du transport atmosphérique de grandeéchelle. J’ai aussi pu identifier la représentativité spatiale de nos observations, et contribuerà l’évaluation de modèles atmosphériques de grande échelle. Enfin, un cas d’étude durant lavague de chaleur ayant affecté la totalité du Groenland durant l’été 2012 m’a permis de suivrele transport atmosphérique de masses d’air et d’observer en plusieurs points ses impacts sur lacomposition isotopique de la vapeur d’eau, notamment sur la conservation du signal d’excès endeutérium, qui n’avait jamais été observée auparavant.Enfin, la combinaison des observations et de la modélisation atmosphérique m’a permis demettre en évidence les contributions de l’observation atmosphérique en terme de documentationdes échanges entre la surface et l’atmosphère : par une attribution des valeurs observées auxsources potentielles identifiées par modélisation des masses d’air affectant la station pour le CH4et la composition isotopique de la vapeur d’eau, et par la comparaison des observations à dessimulations de transport direct de sources connues issues d’inventaires pour le CH4 ou modéliséespour le CO2 et l’O2 océaniqueSouth Greenland is a key region placed under Arctic and Northern Atlantic influences, whichis poorly documented in terms of atmospheric monitoring. The aim of my thesis is to conductand use the first regional atmospheric observations of CO2, O2, CH4 and isotopic compositionof water vapour and precipitation performed in Ivittuut, a coastal site in south-west Greenland.Which information can we infer from these atmospheric observations, in terms of localatmospheric processes and large scale atmospheric transport variations? Can we use these observationsto document the surface-air exchanges of these compounds, which represent an importantpart of the water and carbon biogeochemical cycles?After validating the observations regarding international precision recommandations, I havebeen able to analyse the variabilities at different time scales, resulting from different specificprocesses. This highlighted the fact the atmospheric composition of our site is weakly influencedby local processes, either for local greenhouse gases sources or small scale atmosphericvariations affecting water vapour isotopic composition. This facilitates the interpretation of ourobservations in terms of large scale atmospheric transport signals.To better understand the observed variations, I related our data series with other observationsoriginating from different sites, and with outputs from different atmospheric models. Ihave first witnessed the links between variations of atmospheric composition and large synopticscale atmospheric transport changes. Then, I have identified the spatial representativity of ourobservations and contributed to the evaluation of atmospheric models. The case study of astrong heat wave covering Greenland during summer 2012 allowed me to study the transport ofwater vapour within an air mass between different stations. It allowed me to provide the firstexperimental observation of deuterium excess conservation during atmospheric transport.Finally, combining observations and atmospheric simulations, I have documented surfaceairexchanges of the observed compounds: first by the attribution of observed values of CH4and water vapour isotopic composition to their simulated potential origins, secondly by thecomparison of observed variations with the direct simulation of atmospheric transport of eitherCH4 sources estimated from inventories or simulated CO2 and O2 air-sea fluxes from an oceanmodel
21
Kanpanon, Nicha. "La composition isotopique en carbone est-elle un indicateur écophysiologie pertinent de l’efficience d’utilisation de l’eau de l’hévéa ?" Thesis, Université de Lorraine, 2015. http://www.theses.fr/2015LORR0240/document.
Abstract (sommario):
Les plantations d’hévéa (Hevea brasiliensis) s’étendent vers des zones non traditionnelles de production en Thaïlande où des conditions plus sèches ont pu conduire à une diminution de la croissance des arbres et de la production de latex. Des paramètres physiologiques utiles pour sélectionner des génotypes adaptés sont nécessaires, comme l’efficience d’utilisation de l’eau (WUE). La discrimination isotopique du carbone est largement utilisée comme proxy pour WUE et peut être aisément utilisée dans des programmes de sélection pour la tolérance à la sécheresse. δ13C des feuilles et les échanges gazeux foliaires ont été mesurés sur de jeunes plants de dix clones d’hévéa cultivés en pot dans une pépinière. La gamme de δ13C des feuilles entre ces dix clones était restreinte et la corrélation entre δ13C et WUEi était significative que sous fort déficit de pression de vapeur saturante, ce qui signifie que la prédiction de WUE par δ13C serait peu précise. Il y avait une large gamme de δ13C entre les génotypes dans une collection de 49 génotypes sauvages d’hévéa cultivés dans le nord-est de la Thaïlande en saison sèche et en saison des pluies. δ13C était relativement stable avec une bonne corrélation entre les saisons. Cette étude montre que la variabilité génétique de δ13C est prometteuse pour des futurs programmes de sélections si une bonne corrélation entre δ13C et WUE peut être établie. L’absence de corrélation entre de δ13C du latex (δ13C-L) et des composés solubles extraits des feuilles (δ13C-S) prélevées sur des arbres saignés et non saignés âgés de 20 ans suggère que photosynthétats récemment produits se mélangent à un stock important d’hydrate de carbone impliqués dans la régénération du latex après la saignée. Donc, δ13C du latex n’est pas un indicateur pertinent de WUEThe rubber (Hevea brasiliensis) plantations extend to non-traditional area in Thailand where dryer conditions has been reported to impair the growth of rubber trees and latex production. Physiological parameters helpful for breeding adapted genotypes are required, such as water use efficiency (WUE). Carbon isotope discrimination is widely used as a proxy for WUE that can easily be used for selection and breeding programs for drought tolerance. Leaf δ13C and leaf gas exchange were measured on young saplings of 10 rubber clones growing in pot in a common garden. The range of leaf δ13C among 10 clones was narrow and the correlation between δ13C and WUEi was significant under high vapour pressure deficit only, which means the prediction of WUE by δ13C would have low precision. There were large δ13C variations among the genotypes at all seasons in a collection of 49 wild genotypes of rubber in Northeastern Thailand. δ13C was rather stable with a good correlation between rainy and dry season. The genetic variability of δ13C is promising for breeding if a good correlation between δ13C of leaf and WUE can be established. The lack of correlation between δ13C of latex (δ13C-L) and of leaf soluble compounds (δ13C-S) collected from tapped and untapped 20 year-old rubber trees suggests that recent photosynthates are mixed in the large pool of stored carbohydrates that are involved in latex regeneration after tapping. Thus δ13C of latex is not a relevant indicator of WUE of rubber trees
22
Murray, Andrew P. "Factors controlling the abundance and carbon isotopic composition of land-plant derived compounds in crude oils". Thesis, Curtin University, 1998. http://hdl.handle.net/20.500.11937/1100.
Abstract (sommario):
This thesis describes a study in petroleum geochemistry and specifically of the application of Land-plant derived hydrocarbons to elucidating source matter type, depositional environment and thermal maturity of crude oils. Large volumes of petroleum have been generated from land-plant organic matter in many parts of the world, but especially in the Tertiary deltaic provinces of the USA, Canada, Africa, Southeast Asia, Australia and New Zealand. Compared to oils from other regions, these oils have a relatively complex pattern of biomarkers or molecular fossils, a feature reflecting the diversity of deltaic depositional environments and the advanced state of plant evolution during late Mesozoic and Tertiary time. The molecular and carbon isotopic composition of these oils is useful in identifying the character of their source beds and also in understanding the conditions that give rise to oil-prone sediments generally.Despite their widespread occurrence in oils and sediments, land-plant biomarkers have been used less frequently than compounds of algal origin as markers for source, depositional environment and thermal maturity. The present work sets out to extend the range of land-plant biomarker and isotope tools available to the petroleum geochemist and to provide a firmer foundation for some of the existing tools. A systematic study of the biomarker and n-alkane carbon-isotope composition of a set of late Mesozoic/Tertiary-age oils was carried out as a preamble to more focussed investigations. A comparison of the biomarker and n-alkane isotope data showed that parameters such as the oleanane/hopane ratio overestimate the higher plant contribution to marine deltaic oils. The abundance of bicadinane isomers was found to be much more variable than that of the oleananes, probably because of their close association with the highly resinous, dipterocarp hardwoods of Southeast Asia. However, small amounts of bicadinanes were found in an oil from outside the paleogeographic range of the dipterocarp family, indicating a more general source. Retention indices based on the regular hopane series were calculated for the main bicadinane and methyl bicadinane isomers and for a group of oleanoid triterpanes.Source rock depositional setting proved to be the primary control on the shape of the n-alkane isotope profile, with negatively sloping curves being characteristic of fluvio-deltaic and marginal lacustrine oils and flat or positively sloping curves typical of marine oils. The difference is probably related to the bacterial reworking of higher plant matter in the fluvio-deltaic environment. A slight isotopic anomaly at n-C(subscript)17 correlates with the abundance of algal-derived steranes and may indicate a minor marine contribution to the source of an fluvio-deltaic oil. A study of sediments from the South Sumatra Basin and New Zealand showed that the n-alkane isotope profile is determined mainly by source matter type and is little influenced by thermal maturity or depositional environment.Based on the results of the work described above, three aspects were chosen for further examination. These were: a) the factors controlling the carbon isotopic composition of n-alkanes and of resin-derived compounds in terrigenous oils; b) the influence of source, maturity and biodegradation on the abundance of bicadinanes, especially the effect of maturity on the isomer distribution, and c) the factors controlling the abundance of oleananes and rearranged oleananes in oils and Ancient sediments, especially the role of depositional environment.A preliminary study using sediments, from the Visayan Basin (Philippines) showed the bicadinane isomeric distribution to be sensitive to maturity. This suggested new maturity parameters which would be resistant to even severe biodegradation and largely immune to interference from diagenetic effects. A more detailed study of a marine-fluvio-deltaic depositional sequence from the South Sumatra Basin confirmed that the maturity indices based on bicadinanes and aromatic analogs were less subject to non-maturity influences than those based on the steranes and aromatic hydrocarbons. The values obtained for the bicadinane indices were compared with the maturity required for oil generation as estimated by kinetic modelling and with conventional maturity indicators such as sterane epimerisation and the methyl phenanthrene index. Values for several of the indices were also measured for 17 Tertiary-age oils from Southeast Asia, Papua New Guinea, New Zealand and Australia. The main bicadinane maturity indicator (BMI-1) continues to change into the oil window and hence is useful in ranking the relative maturity of oils as well as sediments. Values of BMI-1 for two oils having unusually low sterane maturities were found to be normal and, in the light of this observation, the conventional explanation for low sterane epimerisation of many Tertiary-age oils was critically evaluated.The oleananes, as markers for the angiosperms, provide valuable source and age information when present in an oil. Nevertheless, their abundance is not quantitatively related to the land plant input and indeed their presence results from a small "leak" in diagenetic processes leading primarily to aromatic oleanoids. Evidence is presented that contact of plant matter with seawater during early diagenesis enhances the expression of oleananes in a mature sediment or oil. Oleananes are absent or present at very low concentrations in samples from the base of an Eocene coal seam affected by post-depositional seawater intrusion. However, their abundance increases toward the top of the seam in correlation with % organic sulphur, dibenzothiophene/phenanthrene and the homohopane index. Similarly, in deltaic sediments from the South Sumatra Basin, oleanane/hopane is strongly correlated with indicators of marine influence such as C[subscript 27]/C[subscript 29] steranes and of oxic/anoxic conditions such as the homohopane index. In each case, increasing oleanane abundance is accompanied by a reduction in the extent of aromatisation and, for the South Sumatra Basin, the proportion of A-ring contracted oleananes. An angiosperm-derived Miocene coal from the Philippines, deposited under freshwater conditions, shows abundant aromatic oleanoids but no oleananes. These results show that oleananes need to be used with caution as age and source markers in fluvio- deltaic and lacustrine petroleum systems. On the other hand, their sensitivity to early diagenetic conditions may make them useful in locating effective source rocks in such systems.Compounds derived from plant resins are major components of some terrigenous oils. Although recent studies have elucidated the molecular structure of resinites, very little information was available on the carbon isotope composition of resinites prior to the present study. No carbon isotope studies of resin-derived compounds in oils had been performed. Hence, carbon stable isotope analyses were carried out on a set of modern and fossil resins of diverse origins and compound specific isotope analysis was used to characterise individual hydrocarbons in resin pyrolysates and oils derived from resinitic source matter. The results showed that "Class V' resinites derived from gymnosperms are enriched in the heavy carbon isotope compared with the angiosperm-derived "Class W' resinites. Furthermore, both the fossil resinites themselves and individual hydrocarbons derived from them are isotopically heavy compared with modern plant resins. The reasons for these differences and their implications for petroleum geochemical studies are discussed.
23
Rieley, Gareth. "Molecular and isotropic studies of natural environments : distributions and stable carbon isotopic compositions of individual lipids". Thesis, University of Bristol, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385652.
24
Launois, Thomas. "Modélisation de la composition isotopique des cernes d'arbres (13C et 18O) et des transferts de COS entre l'atmosphère et la biosphère continentale pour quantifier les flux bruts de carbone". Electronic Thesis or Diss., Versailles-St Quentin en Yvelines, 2014. http://www.theses.fr/2014VERS0039.
Abstract (sommario):
Dans un contexte de changement climatique, le fonctionnement de la biosphère continentale peut être durablement affecté par l’augmentation d’extrêmes climatiques, diminuant l’assimilation photosynthétique du carbone ou augmentant la respiration de l’écosystème. Quantifier le stockage de carbone par les écosystèmes et prédire leur sensibilité aux changements climatiques repose donc fortement sur notre capacité à diagnostiquer séparément les flux de photosynthèse et de respiration à différentes échelles. La productivité primaire brute (GPP) n’est cependant pas directement mesurable. Des approches indirectes ont été proposées pour estimer les flux bruts biosphériques (GPP et respiration), combinant différents traceurs et notamment les isotopologues stables du CO2 (13C et 18O), et, plus récemment, la mesure de l’oxysulfure de carbone dans l’atmosphère (COS). Dans ce contexte, mes travaux de thèse ont exploré deux approches. La première visant à utiliser les mesures isotopiques des cernes d’arbres et leur largeur, toutes liées aux variations de l’activité photosynthétique. Les variations interannuelles du flux de photosynthèse modélisées par un modèle de biosphère continentale ont ainsi pu être évaluées et comparées aux mesures in situ. La seconde visant utiliser les mesures atmosphériques de COS pour contraindre les estimations de GPP des modèles actuels de biosphère, en (1) établissant un nouveau bilan global des sources et puits de ce gaz, (2) optimisant les différents termes de sources et puits de COS et (3) estimant le potentiel de ce nouveau traceur pour valider/invalider les flux bruts de photosynthèse (GPP) simulés par les modèles actuels de biosphère continentaleIn the context of global climate change, the behavior of the terrestrial biosphere can be durably affected by the increased frequency and intensity of extreme climatic events, which can decrease the photosynthetic assimilation of carbon and/or increase the respiration rate of the ecosystems. Therefore, quantifying the carbon storage capacity of the ecosystems and predicting their sensitivity to climate changes strongly rely on our capacity to separately estimate the photosynthesis and respiration rates at different scales. The gross primary productivity (GPP) is however not directly measurable. Indirect approaches have been proposed to estimate the biospheric gross fluxes (GPP and respiration), combining for instance stable isotopologues of CO2 (13C and 18O), and, more recently, the measure of carbonyl sulfide (COS) concentrations in the atmosphere. In this context, my PhD work followed two complementary approaches. In the first approach, isotopic measurements and tree-ring widths were used, because both of them are linked to the photosynthetic activity. The inter-annual variations of the photosynthetic fluxes simulated with the ORCHIDEE continental biosphere model were evaluated and compared with in situ measurements. The second approach consisted in using atmospheric measurements of OCS concentrations and in exploring their potential to constrain the current estimates of the GPP in dynamic global vegetation models (DGVM), by (1) establishing a new global budget of sources and sinks of this gas, (2) optimizing the source and sink terms of this cycle and (3) estimating the potential of this new tracer to validate/invalidate the simulated GPP when using current DGVMs
25
Bonne, Jean-Louis. "Observations continues de la composition atmosphérique au sud Groenland". Thesis, Versailles-St Quentin en Yvelines, 2015. http://www.theses.fr/2015VERS008V/document.
Abstract (sommario):
Le but de ma thèse est de conduire et d’utiliser les premières observations atmosphériquesde surface du CO2, de l’O2, du CH4 et de la composition isotopique de la vapeur d’eau et desprécipitations dans la région peu instrumentée du sud du Groenland. Quelles informations cesobservations locales peuvent-elles nous apporter à la fois concernant les processus atmosphériqueslocaux et concernant le transport atmosphérique à grande échelle ? Peut-on en extrairedes informations sur les échanges entre la surface et l’atmosphère, qui constituent une part crucialedes cycles biogéochimiques du carbone et de l’eau ? L’interprétation paléoclimatique desenregistrements de carottes de glace au Groenland peut-elle bénéficier de ces observations ?Après une validation des observations menées à Ivittuut, sur la côte sud-ouest du Groenland,en regard de normes internationales de qualité, confirmant leur représentativité des variationsatmosphériques, j’ai commencé par interpréter ces observations en analysant leur variabilité àdifférentes échelles de temps et découlant de processus spécifiques. Ceci m’a permis de montrerque le site de mesure était très peu influencé par des phénomènes locaux : peu de sources localesde gaz à effet de serre, et de processus locaux agissant sur la composition isotopique de la vapeurd’eau. Cette caractéristique facilite l’attribution des variations observées à des changements detransport atmosphérique de grande échelle en lien avec des sources distantes.Pour comprendre les variations observées, je les ai mises en relation avec des observationsissues d’autres sites ainsi qu’avec des sorties de modèles atmosphériques de grande échelle. D’unepart, j’ai constaté que de nombreuses variations de la composition atmosphérique à l’échelle synoptiquepouvaient être expliquées par des modifications du transport atmosphérique de grandeéchelle. J’ai aussi pu identifier la représentativité spatiale de nos observations, et contribuerà l’évaluation de modèles atmosphériques de grande échelle. Enfin, un cas d’étude durant lavague de chaleur ayant affecté la totalité du Groenland durant l’été 2012 m’a permis de suivrele transport atmosphérique de masses d’air et d’observer en plusieurs points ses impacts sur lacomposition isotopique de la vapeur d’eau, notamment sur la conservation du signal d’excès endeutérium, qui n’avait jamais été observée auparavant.Enfin, la combinaison des observations et de la modélisation atmosphérique m’a permis demettre en évidence les contributions de l’observation atmosphérique en terme de documentationdes échanges entre la surface et l’atmosphère : par une attribution des valeurs observées auxsources potentielles identifiées par modélisation des masses d’air affectant la station pour le CH4et la composition isotopique de la vapeur d’eau, et par la comparaison des observations à dessimulations de transport direct de sources connues issues d’inventaires pour le CH4 ou modéliséespour le CO2 et l’O2 océaniqueSouth Greenland is a key region placed under Arctic and Northern Atlantic influences, whichis poorly documented in terms of atmospheric monitoring. The aim of my thesis is to conductand use the first regional atmospheric observations of CO2, O2, CH4 and isotopic compositionof water vapour and precipitation performed in Ivittuut, a coastal site in south-west Greenland.Which information can we infer from these atmospheric observations, in terms of localatmospheric processes and large scale atmospheric transport variations? Can we use these observationsto document the surface-air exchanges of these compounds, which represent an importantpart of the water and carbon biogeochemical cycles?After validating the observations regarding international precision recommandations, I havebeen able to analyse the variabilities at different time scales, resulting from different specificprocesses. This highlighted the fact the atmospheric composition of our site is weakly influencedby local processes, either for local greenhouse gases sources or small scale atmosphericvariations affecting water vapour isotopic composition. This facilitates the interpretation of ourobservations in terms of large scale atmospheric transport signals.To better understand the observed variations, I related our data series with other observationsoriginating from different sites, and with outputs from different atmospheric models. Ihave first witnessed the links between variations of atmospheric composition and large synopticscale atmospheric transport changes. Then, I have identified the spatial representativity of ourobservations and contributed to the evaluation of atmospheric models. The case study of astrong heat wave covering Greenland during summer 2012 allowed me to study the transport ofwater vapour within an air mass between different stations. It allowed me to provide the firstexperimental observation of deuterium excess conservation during atmospheric transport.Finally, combining observations and atmospheric simulations, I have documented surfaceairexchanges of the observed compounds: first by the attribution of observed values of CH4and water vapour isotopic composition to their simulated potential origins, secondly by thecomparison of observed variations with the direct simulation of atmospheric transport of eitherCH4 sources estimated from inventories or simulated CO2 and O2 air-sea fluxes from an oceanmodel
26
Murray, Andrew P. "Factors controlling the abundance and carbon isotopic composition of land-plant derived compounds in crude oils". Curtin University of Technology, Centre for Petroleum and Environmental Organic Geochemistry, 1998. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=10771.
Abstract (sommario):
This thesis describes a study in petroleum geochemistry and specifically of the application of Land-plant derived hydrocarbons to elucidating source matter type, depositional environment and thermal maturity of crude oils. Large volumes of petroleum have been generated from land-plant organic matter in many parts of the world, but especially in the Tertiary deltaic provinces of the USA, Canada, Africa, Southeast Asia, Australia and New Zealand. Compared to oils from other regions, these oils have a relatively complex pattern of biomarkers or molecular fossils, a feature reflecting the diversity of deltaic depositional environments and the advanced state of plant evolution during late Mesozoic and Tertiary time. The molecular and carbon isotopic composition of these oils is useful in identifying the character of their source beds and also in understanding the conditions that give rise to oil-prone sediments generally.Despite their widespread occurrence in oils and sediments, land-plant biomarkers have been used less frequently than compounds of algal origin as markers for source, depositional environment and thermal maturity. The present work sets out to extend the range of land-plant biomarker and isotope tools available to the petroleum geochemist and to provide a firmer foundation for some of the existing tools. A systematic study of the biomarker and n-alkane carbon-isotope composition of a set of late Mesozoic/Tertiary-age oils was carried out as a preamble to more focussed investigations. A comparison of the biomarker and n-alkane isotope data showed that parameters such as the oleanane/hopane ratio overestimate the higher plant contribution to marine deltaic oils. The abundance of bicadinane isomers was found to be much more variable than that of the oleananes, probably because of their close association with the highly resinous, dipterocarp hardwoods of ++Southeast Asia. However, small amounts of bicadinanes were found in an oil from outside the paleogeographic range of the dipterocarp family, indicating a more general source. Retention indices based on the regular hopane series were calculated for the main bicadinane and methyl bicadinane isomers and for a group of oleanoid triterpanes.Source rock depositional setting proved to be the primary control on the shape of the n-alkane isotope profile, with negatively sloping curves being characteristic of fluvio-deltaic and marginal lacustrine oils and flat or positively sloping curves typical of marine oils. The difference is probably related to the bacterial reworking of higher plant matter in the fluvio-deltaic environment. A slight isotopic anomaly at n-C(subscript)17 correlates with the abundance of algal-derived steranes and may indicate a minor marine contribution to the source of an fluvio-deltaic oil. A study of sediments from the South Sumatra Basin and New Zealand showed that the n-alkane isotope profile is determined mainly by source matter type and is little influenced by thermal maturity or depositional environment.Based on the results of the work described above, three aspects were chosen for further examination. These were: a) the factors controlling the carbon isotopic composition of n-alkanes and of resin-derived compounds in terrigenous oils; b) the influence of source, maturity and biodegradation on the abundance of bicadinanes, especially the effect of maturity on the isomer distribution, and c) the factors controlling the abundance of oleananes and rearranged oleananes in oils and Ancient sediments, especially the role of depositional environment.A preliminary study using sediments, from the Visayan Basin (Philippines) showed the bicadinane isomeric distribution to be sensitive to maturity. This suggested new maturity parameters which would be ++
resistant to even severe biodegradation and largely immune to interference from diagenetic effects. A more detailed study of a marine-fluvio-deltaic depositional sequence from the South Sumatra Basin confirmed that the maturity indices based on bicadinanes and aromatic analogs were less subject to non-maturity influences than those based on the steranes and aromatic hydrocarbons. The values obtained for the bicadinane indices were compared with the maturity required for oil generation as estimated by kinetic modelling and with conventional maturity indicators such as sterane epimerisation and the methyl phenanthrene index. Values for several of the indices were also measured for 17 Tertiary-age oils from Southeast Asia, Papua New Guinea, New Zealand and Australia. The main bicadinane maturity indicator (BMI-1) continues to change into the oil window and hence is useful in ranking the relative maturity of oils as well as sediments. Values of BMI-1 for two oils having unusually low sterane maturities were found to be normal and, in the light of this observation, the conventional explanation for low sterane epimerisation of many Tertiary-age oils was critically evaluated.The oleananes, as markers for the angiosperms, provide valuable source and age information when present in an oil. Nevertheless, their abundance is not quantitatively related to the land plant input and indeed their presence results from a small "leak" in diagenetic processes leading primarily to aromatic oleanoids. Evidence is presented that contact of plant matter with seawater during early diagenesis enhances the expression of oleananes in a mature sediment or oil. Oleananes are absent or present at very low concentrations in samples from the base of an Eocene coal seam affected by post-depositional seawater intrusion. However, their abundance increases toward the top of the seam in correlation with ++
% organic sulphur, dibenzothiophene/phenanthrene and the homohopane index. Similarly, in deltaic sediments from the South Sumatra Basin, oleanane/hopane is strongly correlated with indicators of marine influence such as C[subscript 27]/C[subscript 29] steranes and of oxic/anoxic conditions such as the homohopane index. In each case, increasing oleanane abundance is accompanied by a reduction in the extent of aromatisation and, for the South Sumatra Basin, the proportion of A-ring contracted oleananes. An angiosperm-derived Miocene coal from the Philippines, deposited under freshwater conditions, shows abundant aromatic oleanoids but no oleananes. These results show that oleananes need to be used with caution as age and source markers in fluvio- deltaic and lacustrine petroleum systems. On the other hand, their sensitivity to early diagenetic conditions may make them useful in locating effective source rocks in such systems.Compounds derived from plant resins are major components of some terrigenous oils. Although recent studies have elucidated the molecular structure of resinites, very little information was available on the carbon isotope composition of resinites prior to the present study. No carbon isotope studies of resin-derived compounds in oils had been performed. Hence, carbon stable isotope analyses were carried out on a set of modern and fossil resins of diverse origins and compound specific isotope analysis was used to characterise individual hydrocarbons in resin pyrolysates and oils derived from resinitic source matter. The results showed that "Class V' resinites derived from gymnosperms are enriched in the heavy carbon isotope compared with the angiosperm-derived "Class W' resinites. Furthermore, both the fossil resinites themselves and individual hydrocarbons derived from them are isotopically heavy compared with modern plant resins. The reasons for ++
these differences and their implications for petroleum geochemical studies are discussed.
27
Perga, Marie-Elodie. "Origines et flux de carbone en lacs : étude par analyse de la composition en isotopes stables du carbone et de l'azote du zooplancton et des poissons". Chambéry, 2004. http://www.theses.fr/2004CHAMS031.
Abstract (sommario):
Les communautés piscicoles sont situées au sommet des chaînes trophiques. Cette position dans le réseau trophique lacustre leur confère, de ce fait, un rôle potentiel d'intégrateurs des processus sous- jacents, à l'échelle de l'écosystème. De plus, la composition en isotopes stables d'un organisme dépend des voies qui transfèrent le carbone jusqu'à cet organisme. Notre hypothèse de base était donc que la composition en isotopes stables des poissons pourrait donc constituer un indicateur relatif de fonctionnement trophique des lacs. Pour valider cette hypothèse, nous avons employé, dans un premier temps, le corégone, Coregomus lavaretus, un salmoniforme zooplanctonophage commun dans les lacs alpins, comme modèle biologique. Une étude préalable avait révélée que la composition en isotopes stables du carbone des corégones était très variable au sein des lacs alpins. Selon notre hypothèse, cette variabilité serait le reflet de différences dans les voies de transferts du carbone dans les réseaux trophiques de ces lacs. Les facteurs explicatifs de cette variabilité inter-lacs ont donc, dans un premier temps, été étudiés. Au terme de cette première partie, la composition isotopique du corégone s'est montrée être effectivement un indicateur du fonctionnement trophique des lacs. Les perturbations peuvent modifier les flux de carbone au sein des systèmes et devraient, de fait, conduire à des changements dans les compositions isotopiques des communautés de poissons. L'effet de deux perturbations d'origine anthropique sur la composition isotopique des poissons a, par la suite, été analysé: la première est relative à l'eutrophisation -restauration de deux lacs alpins, la seconde concerne le marnage dans deux réservoirs africains. Les résultats de ces deux études indiquent que des modifications majeures, engendrées par ces perturbations, dans l'origine et les flux de carbone dans les réseaux trophiques, sont enregistrées dans l'histoire isotopique des communautés piscicolesFish communities occupy the top of food chains. How fish obtain their constitutive carbon depends consequently of all the carbon pathways at the downer levels of the food web. This trophic position confers to fish a potential role of integrators of the underlying processes, at the ecosystem scale. Moreover, stable isotopes composition of an organism depends on all the pathways that transfer carbon up to this organism. Consequently, we wondered in what extent the stable isotopes composition of fish could be a proxy of the trophic functioning of lakes. To address this assumption, whitefish, Coregonus lavaretus, a zooplanktivorous salmonid common in alpine lake, was, in a first time, used as biological model. A preliminary study had revealed the stable isotope composition of whitefish was quite variable among alpine lakes. According to our idea, this variability mirrors differences in the carbon pathways of the food web of these lakes. To understand what was reflected by this variability, we studied initially in what extent it resulted from intrinsic factors (such as lake size or trophic status). This study has then lead us to deepen the role played by the zooplankton compartment in carbon pathways up to Whitefish. In the final stage of this first part, the isotopic composition of whitefish appeared as a proxy for lake trophic functioning. Changes in environmental factors can alter carbon pathways in food webs. If fish are efficient integrators of carbon pathways, impacts of perturbations should be mirrored on their isotopic compositions. Impacts of two anthropogenic perturbations of stable isotope composition of fish were then evaluated : the first one relates to eutrophication - restoration of two alpine lakes, the second one to water levels changes in two Malian reservoirs. Results from these two studies reveal that major changes, ensuing from these perturbation, in carbon origins and fluxes within lake food webs are recorded in the isotopic history of fish communities
28
Berry, Stephanie C. Carleton University Dissertation Biology. "The influence of vegetation and soil carbon dioxide exchange on the concentration and isotopic composition of atmospheric carbon dioxide within plant canopies". Ottawa, 1994.
29
Coleman, Joanna Michelle. "Controls on the distribution and carbon isotopic composition of archaeal biomarkers in organic-rich and methanogenic marine sediments". Thesis, University of Bristol, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.416770.
30
Wan, Zhenzhu. "Stable Carbon and Nitrogen Isotopic Studies of Devonian Land Plants -- An Indicator of Paleoclimate and Paleoenvironmental Changes". University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1343068259.
31
Westgate, Timothy David. "Compositional and carbon isotopic characteristics of abiogenically derived hydrocarbons at the Kidd Creek Mine, Timmins, Ontario". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0013/MQ40763.pdf.
32
Tarits, Corinne. "Etude des variations de composition isotopique du carbone et de l'oxygène dans le domaine de la précipitation spontanée homogène du carbonate de calcium : modélisation du comportement isotopique du carbone dans ce domaine". Paris 5, 1990. http://www.theses.fr/1990PA05P617.
33
Carvajal-Ortiz, Humberto. "Carbon isotopic composition of plant-derived organic matter in tropical sedimentary sequences as a recorder of Late Cretaceous-Early Paleogene changes in the carbon cycle". [Ames, Iowa : Iowa State University], 2007.
34
Pearce, Andrew M. "Carbon and oxygen isotopic compositions of some late Proterozoic and early Cambrian carbonates in the southern Adelaide geosyncline /". Title page, contents and abstract only, 1992. http://web4.library.adelaide.edu.au/theses/09S.B/09s.bp359.pdf.
Abstract (sommario):
Thesis (B. Sc.(Hons.))--University of Adelaide, Dept. of Geology and Geophysics, 1993."National grid reference: Noarlunga SI (54-4) 6627 IV Cassini SI (53-16) 6326 I Stokes Bay SI (53-16) 6326 IV." Includes bibliographical references.
35
Zakharova, Anna. "Soil organic matter dynamics: influence of soil disturbance on labile pools". Thesis, University of Canterbury. School of Biological Sciences, 2014. http://hdl.handle.net/10092/9944.
Abstract (sommario):
Soils are the largest pool of carbon (C) in terrestrial ecosystems and store 1500 Gt of C in their soil organic matter (SOM). SOM is a dynamic, complex and heterogeneous mixture, which influences soil quality through a wide range of soil properties. Labile SOM comprises a small fraction of total SOM (approximately 5%), but due to its rapid turnover has been suggested to be most vulnerable to loss following soil disturbance. This research was undertaken to examine the consequences of soil disturbance on labile SOM, its availability and protection in soils using the isotopic analysis of soil-respired CO₂ (δ¹³CO₂).
A range of soils were incubated in both the short- (minutes) and long-term (months) to assess changes in labile SOM. Shifts in soil-respired δ¹³CO₂ over the course of soil incubations were found to reflect changes in labile substrate utilisation. There was a rapid depletion of δ¹³CO₂ (from a starting range between -22.5 and -23.9‰, to between -25.8 and -27.5‰) immediately after soil sampling. These initial changes in δ¹³CO₂ indicated an increased availability of labile SOM following the disturbance of coring the soil and starting the incubations. Subsequently δ¹³CO₂ reverted back to the initial, relatively enriched starting values, but this took several months and was due to labile SOM pools becoming exhausted.
A subsequent study was undertaken to test if soil-respired δ¹³CO₂ values are a direct function of the amount of labile SOM and soil physical conditions. A range of pasture soils were incubated in the short-term (300 minutes), and changes in soil-respired δ¹³CO₂ were measured along with physical and chemical soil properties. Equilibrium soil-respired δ¹³CO₂, observed after the initial rapid depletion and stabilisation, was a function of the amount of labile SOM (measured as hot water extractable C, HWEC), total soil C and soil protection capacity (measured as specific soil surface area, SSA). An independent experimental approach to assess the effect of SSA, where labile SOM was immobilised onto allophane – a clay mineral with large, active surface area – indicated limited availability of labile SOM through more enriched δ¹³CO₂ (in a range between -20.5 and -20.6 ‰) and a significant (up to three times) reduction in HWEC.
In the third study, isotopic measurements were coupled with CO₂ evolution rates to directly test whether equilibrium soil-respired δ¹³CO₂ can reflect labile SOM vulnerability to loss. Soils were sampled from an experimental tillage trial with different management treatments (chemical fallow, arable cropping and permanent pasture) with a range of C inputs and soil disturbance regimes. Soils were incubated in the short- (300 minutes) and long-term (600 days) and changes in δ¹³CO₂ and respiration rates measured. Physical and chemical fractionation methods were used to quantify the amount of labile SOM. Pasture soils were characterised by higher labile SOM estimates (HWEC; sand-sized C; labile C respired during long-term incubations) than the other soils. Long-term absence of plant inputs in fallow soils resulted in a significant depletion of labile SOM (close to 50% based on sand-sized C and HWEC estimates) compared with pasture soils. The values of δ¹³CO₂ became more depleted in 13C from fallow to pasture soils (from -26.3 ‰ to -28.1 ‰) and, when standardised (against the isotopic composition of the solid soil material), Δ¹³CO₂ values also showed a decrease from fallow to pasture soils (from -0.3 ‰ to -1.1 ‰). Moreover, these patterns in isotopic measures were in strong agreement with the amount of labile SOM and its availability across the soils, and were best explained by the isotopic values of the labile HWEC fraction.
Collectively, these results confirm that labile SOM availability and utilisation change immediately after soil disturbance. Moreover, isotopic analysis of soil-respired CO₂ is a powerful technique, which enables us to probe mechanisms and examine the consequences of soil disturbance on labile SOM by reflecting its availability and the degree of SOM protection.
36
Zymela, Steve. "Carbon, oxygen and strontium isotopic composition of diagenetic calcite and siderite from the Upper Cretaceous Cardium formation of western Alberta". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/NQ30184.pdf.
37
Zymela, Steve. "Carbon, oxygen and strontium isotopic composition of diagenetic calcite and siderite from the Upper Cretaceous Cardium Formation of Western Alberta /". *McMaster only, 1996.
38
Gangloff, Sophie. "Evaluation of the mechanisms of trace elements transport (Pb, Rare Earth Elements,... ) and the elemental and isotopic fractionation (Ca and Sr) at the interface water-soil-plant". Thesis, Strasbourg, 2016. http://www.theses.fr/2016STRAH002/document.
Abstract (sommario):
Ce travail est axé sur l’étude d’un profil de sol et des solutions de sol prélevés sur une parcelle expérimentale couvertes d’épicéas. Tous ces échantillons proviennent du Bassin Versant du Strengbach (Observatoire HydroGéochimique de l’Environnement – OHGE), ont été échantillonnés à différentes profondeurs (5, 10, 30 et 60 cm) et durant la période comprise entre 2009 et 2013.Les caractérisations des extraits des sols par spectroscopie Infra-Rouge ont permis de mettre en évidence les modifications des groupements fonctionnels organiques avec la profondeur et que ces modifications ont une forte incidence sur le comportement des cations (majeurs et traces) dans le sol. Des expérimentations d’ultra-filtration ont permis d’identifier les flux colloïdaux et dissous du carbone organique ainsi que ceux des éléments majeurs et traces présents dans les solutions de sol. L’utilisation conjointe des traceurs isotopiques (87Sr/86Sr et δ44/40Ca) et chimiques (Terres Rares) ont mis en évidence des processus ayant lieu aux interfaces eau-sol-plante, comme le prélèvement racinaire ou l’altération des solsThis work is focused on the study of a profile of soil and soil solutions collected on an experimental plot covered with spruce. All these samples come from the watershed of the Strengbach (environment - OHGE Hydrogeochimique Observatory), were sampled at different depths (5, 10, 30 and 60 cm) and during the period between 2009 and 2013. Characterizations of soil extracts by infrared spectroscopy allowed to highlight changes in the organic functional groups with depth and that these changes have a significant impact on the behaviour of the cations (major and trace) in the soil. Ultrafiltration experiments helped to identify flows of colloidal and dissolved organic carbon as well as those of the major and trace-element present in soil solutions. The joint use of isotope tracers (87Sr / 86Sr and δ44 / 40 Ca) and chemical (Rare Earth Elements) have highlighted processes taking place at the water-soil-plant interface, as the uptake by root or soil alteration
39
Grice, Kliti. "Distributions and stable carbon isotopic compositions of individual biological markers from the Permian Kupferschiefer (Lower Rhine Basin, N.W. Germany)". Thesis, University of Bristol, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.283943.
40
Jansen, Kirstin. "Stable Isotopes and Metabolite Profiles as Physiological Markers for the Drought Stress Sensitivity in Douglas-Fir Provenances (Pseudotsuga menziesii (MIRB.) FRANCO)". Doctoral thesis, Humboldt-Universität zu Berlin, 2018. http://dx.doi.org/10.18452/19617.
Abstract (sommario):
In Mitteleuropa werden zukünftig häufigere Trocken- und Hitzeperioden mit wirtschaftlichen Einbußen in der Waldwirtschaft erwartet. Die Douglasie (Pseudotsuga menziesii (Mirb.) Franco) wird als Alternative für die wirtschaftlich bedeutsame, jedoch trockenheitsempfindliche Fichte diskutiert (Picea abies (L.) H.Karst.). Zwei Unterarten, die Küsten- (FDC) und die Inlandsdouglasie (FDI), sind im ausgedehnten natürlichen Verbreitungsgebiet in Nordamerika beheimatet, welches ein großes Potenzial für die Auswahl produktiver und trockenresistenter Herkünfte bietet. Unser Ziel war, die Trockenreaktion verschiedener Douglasienherkünfte unter Verknüpfung morphologischer und physiologischer Parameter und die der Trockenheitsresistenz bzw. -empfindlichkeit zugrundeliegenden Mechanismen zu erforschen. Ein Herkunftsversuch in Südwestdeutschland ermöglichte die Untersuchung 50-jähriger Douglasien verschiedener Herkünfte entlang eines Höhengradienten. Unter kontrollierten Bedingungen simulierten wir die Effekte einer Hitzewelle auf Jungbäume zweier Provenienzen. Wir analysierten die Kohlenstoff- und Sauerstoff-Stabilisotopenzusammensetzung, den Gaswechsel der Blätter, Veränderungen im Stoffwechsel und das Baumwachstum.
Unsere Ergebnisse zeigen bei FDC aus humiden Regionen hohe Wachstumseinbußen unter Trockenheit und moderat bis stark verringerte stomatäre Leitfähigkeit, unterstützt durch Photoprotektion. FDC aus Regionen mit starker Sommertrockenheit reagierten kaum mit Stomataschluss und Wachstumseinbußen auf Trockenheit, jedoch mit starker Osmoregulation und Monoterpen-Emissionen, welche zur Trockenresistenz beitragen könnten. FDI aus einer ariden Region zeigten hohe An, geringes Wachstum und stark antioxidative und photoprotektive Mechanismen.
Die Herkünfte unterscheiden sich stark in ihrer Trockenreaktion und ihren Schutzmechanismen. Der Anbau trockenresistenter Herkünfte wird an Standorten von Vorteil sein, für die eine Häufung von ariden Sommerperioden vorhergesagt wird.In Central Europe, more frequent periods of dry and hot weather are expected in the future with economic losses in the forestry sector. Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) is discussed as a timber species alternative to the economically important but drought-sensitive spruce (Picea abies (L.) H. Karst.). Two subspecies, the coastal (FDC) and the interior Douglas-fir (FDI), are native to an extensive natural range in North America, offering a great potential for the selection of productive and drought tolerant provenances. Our goal was to investigate the drought response of different Douglas-fir provenances on the morphological and physiological level, as well as the mechanisms underlying drought resistance or susceptibility. A provenance trial in southwestern Germany established in 1958 allowed the study of 50-year-old Douglas-fir trees of diverse provenances along a height gradient. Under controlled conditions, we simulated the effects of a heat wave on young trees of two provenances. We analyzed carbon and oxygen stable isotopic composition, leaf gas exchange, changes in metabolism and tree growth. FDC from humid regions responded to drought with strong growth decline and a medium to strong stomatal closure, supported by enhanced instantaneous photoprotection. FDC from regions with very dry summer conditions showed a small growth decline and anisohydric regulation of stomatal conductance under drought, supported by high levels of osmotic adjustment. High monoterpene emissions might contribute to the drought resistance. FDI from an arid region showed high assimilation rates, low growth potential and a high antioxidant, photoprotective, drought and heat protective potential. The provenances differ greatly in their dry reaction and their protective mechanisms. The cultivation of drought resistant crops will be beneficial at sites predicted to accumulate arid summer periods.
41
Bouyer, Laure. "Impact de la disponibilité en nutriments sur le fonctionnement hydrique et carboné de peupliers dans des contextes de sécheresse variés". Thesis, Orléans, 2019. http://www.theses.fr/2019ORLE3100.
Abstract (sommario):
La disponibilité en eau et en nutriments sont deux facteurs limitant la croissance et la productivité des forêts. Malgré un historique important de travaux sur le rôle physiologique des principaux éléments minéraux, l’impact du statut nutritif des arbres sur leur capacité de réponse à la sécheresse demeure très largement inconnu. Cette thèse visait à évaluer le rôle de la disponibilité en nutriments sur des caractères clés indicateurs du fonctionnement hydrique et carboné comme la croissance et ses déterminants architecturaux, l’efficience d’utilisation de l’eau (WUE), la vulnérabilité à la cavitation ou encore les teneurs en glucides non structuraux, en réponse à des sécheresses d’intensités variées chez le peuplier. Deux dispositifs expérimentaux complémentaires ont été support des expériences, l’un en serre et l’autre en pépinière, et les travaux se sont concentrés sur un maximum de quatre génotypes sélectionnés pour leur comportement contrasté en termes de croissance et de régulation stomatique. Les résultats majeurs sont les suivants : 1) une disponibilité en nutriments plus importante augmente la croissance et WUE en conditions hydriques limitantes, 2) une disponibilité en nutriments plus importante n’augmente pas nécessairement les risques de dysfonctionnements hydrauliques, 3) l’épuisement des réserves carbonées, notamment de l’amidon, coïncide avec l’embolie massive du xylème à mortalité en cas de sécheresse sévère, et 4) une plus grande disponibilité en azote diminue la mise en réserve glucidique, notamment en condition de sécheresse modérée. Cette étude illustre pour la première fois de façon explicite la covariance au cours du temps entre les dysfonctionnements hydrauliques et l’épuisement des réserves chez une essence à croissance rapide très vulnérable à la sécheresse, et donne un exemple de la façon dont ces relations sont modulées par la disponibilité en nutrimentsThe availability of water and nutrients are two main factors limiting tree growth and forest productivity. Despite the strong legacy of research on forest nutrition, the role of nutrients in modulating tree drought responses remains largely unknown. This thesis aimed to evaluate the role of nutrient availability on key traits related to water and carbon relations such as growth and its determinants, water-use efficiency (WUE), vulnerability to cavitation, or non-structural carbohydrate (NSC) contents, in poplars under contrasting drought intensities. Research experiments relied on two complementary experimental designs, one in a greenhouse and the other in an outdoor common garden, and considered a maximum of four genotypes primarily selected for their contrasting growth and stomatal regulation. The main findings are as follows: 1) a higher nutrient availability increases growth and WUE under moderate drought, 2) a higher nutrient availability does not necessarily increase the risk of xylem hydraulic failure, 3) NSC depletion, in particular starch, co-occurs with massive xylem embolism under lethal drought, and 4) a higher nutrient availability reduces NSC storage, especially under moderate drought. This study shows for the first time the temporal covariance between the dynamics of xylem hydraulic failure and carbon starvation in a fast-growing but highly vulnerable tree species, and gives an example of how these relationships are modulated by nutrient availability
42
Melo, Antonio Willian Flores de. "Avaliação do estoque e composição isotópica do carbono do solo no Acre". Universidade de São Paulo, 2004. http://www.teses.usp.br/teses/disponiveis/91/91131/tde-29072004-160525/.
Abstract (sommario):
O estado do Acre está localizado no extremo oeste do Brasil, ocupando uma região que teve grande influência geológica da cordilheira dos Andes. Os solos apresentam características pedológicas bem distintas das encontradas no restante da Amazônia brasileira, predominando Cambissolos, Luvissolos e Argissolos, geralmente eutróficos, jovens e pouco intemperizados. Pouco se sabe sobre o impacto do uso da terra sobre a matéria orgânica nestas condições de solo. Os objetivos deste trabalho foram: Estimar o estoque de carbono das principais classes de solos do Estado do Acre e comparar com estudos feitos para região amazônica. Avaliar o efeito da mudança no uso e cobertura da terra sobre o estoque de carbono e composição isotópica da matéria orgânica em duas condições de solo no Acre. Para alcançar os objetivos o trabalho foi executado em duas escalas, regional e local. No primeiro caso, foram estimados os estoques de carbono até um metro de profundidade, utilizando um mapa de solos na escala 1:1.000.000 e dados analíticos de perfis de levantamentos pedológicos realizados na região. No segundo caso foram determinados a concentração de carbono, d13C e densidade do solo de amostras coletadas em pastagens de 12-15 anos, 20 anos e floresta, nas profundidades de 0-5, 5-10, 10-20, 20-30, 30-40, 50-60, 70-80 e 90-100 cm, em Argissolo (bem drenado) e Luvissolo (mal drenado). Os solos do Acre armazenam em torno de 1 Pg (1 Pg = 1015 g) de carbono no primeiro metro de profundidade, cerca de 75 % deste valor concentra-se nos primeiros 30 cm. Os solos do Acre apresentam menor concentração de carbono (média 6,5 kg m-2) quando comparados com a média dos solos da Amazônia, embora apresentem melhor fertilidade. A principal razão para este resultado é a maior taxa de decomposição da matéria orgânica nestes solos devido aos constantes ciclos de seca e umedecimento. Estes ciclos estão associados a interação entre o regime pluviométrico e as características físicas (principalmente estrutura) incipientes destes solos, que fazem com que ocorra um lençol freático suspenso que oscila no perfil do solo, podendo chegar até a superfície do mesmo. A mudança no uso da terra alterou de maneira distinta os estoques e a dinâmica da matéria orgânica em Argissolos (bem drenados) e Luvissolos (mal drenados). As pastagens sobre Luvissolos apresentaram maior estoque de carbono (média de 8,4 kg m-2 até 1 m de profundidade), entretanto, os dados isotópicos mostraram que a maior parte deste carbono era remanescente da floresta e uma pequena proporção foi introduzida pela pastagem (< 40 % na camada 0-5 cm da pastagem de 20 anos). O inverso ocorreu com pastagens sobre Argissolos que apresentaram menor estoque (média de 6,4 kg m-2 até 1 m de profundidade) e grande proporção de carbono da pastagem (> 70 % na camada 0-5 cm da pastagem de 20 anos). Os resultados acima sugerem que: 1) A taxa de decomposição do carbono em Luvissolos é menor que em Argissolos, e o tempo de residência da meteria orgânica maior. Os Argissolos tendem a perder muito mais carbono com a mudança no uso e cobertura da terra. 2) A produtividade da pastagem é baixa sobre Luvissolos, indicando que alem da fertilidade do solo outras características, como estrutura, devem ser consideradas para definição das praticas de manejo que objetivam a obtenção de melhor desempenho da gramínea.The State of Acre is located in the extreme west of Brazil, occupying an area that had great geological influence from the mountain chain of Andes. The soils present pedologic characteristics very different from the ones found in the remaining of Brazilian Amazon, prevailing Inceptisols, Alfisols, and Ultisols, generally eutrophic, young and little weathered. Not much is known about the impact of the use of the earth on the organic matter in these soil conditions. This work had as objectives to estimate the stock of carbon of the main classes of soils of the State of Acre and to compare with studies carried out for the Amazon area. To evaluate the effect of the change in the use and covering of the earth on the stock of carbon and isotopic composition of the organic matter in two soil conditions in Acre. To reach the objectives the work was performed in two scales, local and regional. The first case estimated the stocks of carbon up to one meter deep, using a map of soils in the scale 1:1.000.000 and analytic data of pedologic profiles accomplished in the area. The second case determined the concentration of carbon, d13C and density of the soil of samples collected at 12-15, 20 year-old pasture lands, and forest in the depths 0-5, 5-10, 10-20, 20-30, 30-40, 50-60, 70-80 e 90-100 cm, in Ultisols (well drained) and Alfisols (poorly drained). The soils of Acre store around 1 Pg of carbon in the first meter of depth, around 75% of this value is concentrated on the first 30 cm. The soils of Acre present smaller concentration of carbon (6.5 kg m-2, average) when compared with the average of the soils of the Amazon, although they present better fertility. The main reason for this result is the large rate of incident decomposition on these soils due to the constant drought cycles and moistening. These cycles are associated with the physical characteristics (mainly structure) incipient of these soils that impede the percolation of the pluvial waters saturating very quickly and favoring superficial flow off. As the water concentrates on the surface of the soil, it tends to evaporate easily. The effect of the change in the covering and land use on stock and dynamics of the organic matter of the soils happens differently in Ultisols (well drained) and Alfisols (poorly drained). In the two conditions of soils there was a tendency to decrease the total stock of carbon and increase carbon of C4 origin, however, in Ultisols it was very stressed. Pasture lands on Alfisols presented larger stock of carbon (average of 8.4 kg m-2 to 1 m), however, the data of d13C showed that most of carbon was remaining of the forest and a small proportion was introduced by the pasture land (< 40 % to 0-5 cm in 20 yr old pasture). The inverse fact occurred with pasture lands on Ultisols that presented smaller stock (average of 6.4 kg m-2 to 1 m) and great proportion of carbon of the pasture land (> 70 % to 0-5 cm in 20 yr old pasture). This result suggests two conclusions. 1) the rate of carbon decomposition in Alfisols is smaller than in Ultisols, and the time of residence of the organic matter is larger. Ultisols tend to lose carbon more readily with the change in the land use and covering of the land. 2) pasture productivity is low on Alfisols, indicating that besides soil fertility other characteristics, as structure, should be considered in order to establish the management practice to obtain the best output from the grass.
43
Brandon, Margaux. "Les changements majeurs de la productivité biologique au cours du Quaternaire et leurs impacts sur les cycles du carbone et de l’oxygène". Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASJ010.
Abstract (sommario):
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 photosynthèseDuring 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
44
劉, 衛., Wei LIU, 純. 森泉, Jun MORIIZUMI, 弘実 山澤, Hiromi YAMAZAWA, 孝夫 飯田 e Takao IIDA. "Depth Profiles of Radiocarbon and Carbon Isotopic Compositions of Organic Matter and CO_2 in a Japanese Forest Area((2)Summaries of Research Using AMS)". 名古屋大学年代測定資料研究センター, 2006. http://hdl.handle.net/2237/13664.
45
Licari, Laetitia. "Ecological preferences of Benthic Foraminifera in the Eastern South Atlantic : distribution patterns, stable carbon isotopic composition, and paleoceanographic implications = Ökologische Ansprüche benthischer Foraminiferen im östlichen Südatlantik /". Bremerhaven : Alfred-Wegener-Inst. für Polar- und Meeresforschung, 2006. http://www.gbv.de/dms/bs/toc/514912308.pdf.
46
Chiapini, Mariane. "Genesis and organic matter chemistry of sombric horizons in subtropical soils (Paraná State, Brazil)". Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/11/11140/tde-18052017-184016/.
Abstract (sommario):
Soil organic matter (SOM) plays an important role in the global carbon cycle. Therefore, it is important to understand the stability of SOM, which is related to several processes. Its intrinsic properties may be related to its stability, for example black carbon is considered to be relatively resistant to degradation. In most soils, the dark horizons coincide with the superficial layers or horizons due to the greater accumulation of organic matter, but in the southern states of Brazil, the presence of soils with dark subsurface horizons is frequently observed. The dark subsurface horizon of these soils are similar to a sombric horizon. Aspects about its origin, formation and preservation have not yet been fully elucidated. The objective of this work is to understand the formation of \'sombric\' horizons in soils of the region from Tijucas do Sul (Paraná, Brazil). Five soil profiles were described and collected, from which three originate from a toposequence and contained a \'sombric\' horizon (P1-P3), a reference soil that is representative of the area (P5) and an intermediate soil (P4) that showed morphology between the reference soil and the soils with a \'sombric\' horizon. To this end SOM is studied for its molecular composition by the pyrolysis technique coupled to gas chromatography and mass spectrometry (pyrolysis-GC-MS). In addition, 13C isotopic composition (δ13C) and phytolytic composition were studied in order to understand paleoclimatic conditions. These results will be related to past environmental conditions using 14C dating techniques, and supported by classical soil analysis. The samples of the horizons were submitted to the SOM chemical fractionation, generating two fractions: extractable fraction with NaOH (EXT) and residue (RES). The morphology of the profiles showed an intense biological activity in A horizons and a wide distribution of microfragments of charcoals. The lateral continuity of \'sombric\' horizons in toposequence soils was also observed, which differentiated them (P1-P3) from buried A horizons. The distribution of SOM in the fractions studied was the same for the five profiles studied: EXT> RES. Products related to wildfires such as polyaromatics (PAHs; BC) were found in all profiles, but in greater relative abundance in the \'sombric\' horizons, indicating a higher incidence of fire during the formation of these horizons and these compounds can be related to the maintenance of dark color of the \'sombric\' horizons. In relation to the paleoclimatic conditions it was observed that the dark subsurface horizons were developed during the Mid-Holocene under vegetation composed mainly by C4 grasses with shrubs, evidencing a drier climate corresponding to a higher fire incidence.A matéria orgânica do solo (MOS) desempenha um papel importante no ciclo global do carbono. Portanto, é importante entender a estabilidade da MOS, que está relacionada a vários processos. As suas propriedades intrínsecas podem estar relacionadas com a sua estabilidade, por exemplo, o \"black carbon\" é considerado relativamente resistente à degradação. Na maioria dos solos, os horizontes escuros coincidem com as camadas ou horizontes superficiais devido ao maior acúmulo de matéria orgânica, mas nos estados do sul do Brasil, a presença de solos com horizontes subsuperficiais escurecidos é frequentemente observada. O horizonte subsuperficial escurecido destes solos assemelha-se a um horizonte sômbrico. Aspectos sobre sua origem, formação e preservação ainda não foram totalmente elucidados. O objetivo deste trabalho é compreender a formação de horizontes \'sômbricos\' em solos da região de Tijucas do Sul (Paraná, Brasil). Foram descritos e coletados cinco perfis de solo, dos quais três estão localizados em uma topossequência e continham um horizonte similar ao sômbrico (P1-P3), um solo de referência representativo da área (P5) e um solo intermediário (P4) que apresentou uma morfologia entre o solo de referência e os solos com horizonte \'sômbrico\'. Para este fim, a MOS foi estudada pela sua composição molecular através da técnica de pirólise acoplada à cromatografia gasosa e espectrometria de massa (pirólise-GC-MS). Além disso, estudou-se a composição isotópica 13C (δ 13C) e a composição fitolítica, a fim de compreender as condições paleoclimáticas que foram relacionados com as condições ambientais passadas usando técnicas de datação com 14C, e suportados pelas análises clássicas de solo. As amostras dos horizontes foram submetidas ao fracionamento químico MOS, gerando duas frações: fração extraível com NaOH (EXT) e resíduo (RES). A morfologia dos perfis mostrou uma intensa atividade biológica nos horizontes A e uma ampla distribuição de microfragmentos de carvão. Observouse também a continuidade lateral de horizontes \'sômbricos\' em solos da topossequência (P1-P3), diferenciando-os dos horizontes A enterrados. A distribuição da MOS nas frações estudadas pela pirólise foi a mesma para os cinco perfis: EXT> RES. Os produtos relacionados a incêndios florestais como os poliaromáticos (PAHs, BC) foram encontrados em todos os perfis, mas em maior abundância relativa nos horizontes sômbricos, indicando uma maior incidência de incêndio durante a formação destes horizontes. Os PAHs podem estar relacionados com a manutenção da cor escura dos horizontes \'sômbricos\'. Em relação às condições paleoclimáticas observou-se que os horizontes subsuperficiais escurecidos foram desenvolvidos durante o Holoceno Médio sob vegetação composta principalmente por gramíneas C4 com arbustos, evidenciando um clima mais seco correspondente a maior incidência de incêndio.
47
Kallel, Nejib. "Variation de la composition isotopique de l'oxygène et du carbone des foraminifères : traceur de la circulation océanique pendant le dernier maximum glaciaire et lors de la dernière déglaciation". Paris 11, 1988. http://www.theses.fr/1988PA112124.
Abstract (sommario):
Les compositions isotopiques de l'oxygène et du carbone des foraminifères benthiques provenant de sédiments prélevés dans l'océan ont été utilisées pour reconstituer le mode de circulation océanique intermédiaire et profonde lors du dernier maximum glaciaire (≈18. 000 ans BP) dans l'océan Indien et l'océan Pacifique. Cette étude a permis de montrer que, lors du dernier maximum glaciaire, la circulation océanique était complètement différente de celle d'aujourd'hui. Un front hydrologique sépare les eaux intermédiaires de l'océan Indien et de l'océan Pacifique Equatorial des eaux profondes sous-jacentes. Alors que les eaux intermédiaires bien ventilées étaient sensiblement aux mêmes températures qu'aujourd'hui, l'eau profonde était plus froide qu'aujourd'hui de quelques degrés. Dans l'océan Pacifique, l'eau profonde était plus ventilée que celle de l'océan Indien Sud, indiquant soit la présence d'une source d'eau profonde relativement riche en oxygène dans le Sud de l'océan Pacifique, soit l’intensification de la formation de l'Eau Intermédiaire Nord Pacifique. Pendant la déglaciation, le passage du mode de circulation glaciaire à celui de l'Holocène s'amorce vers 12. 500 ans BP avec la diminution de l'influence de l'Eau Intermédiaire Nord Pacifique. La reprise de la formation active de l'Eau Profonde Nord Atlantique apparaît vers 9. 000 ans BP et les conditions holocènes franches sont atteintes vers 8. 000 ans BP dans tous les océans et à toutes les profondeursOxygen and carbon isotopic composition of benthic foraminifera from different oceanic sediment cores have been used to reconstruct the pattern of intermediate and deep ocean circulation during last glacial maximum (18,000 years BP) in the Indian and Pacifie oceans. Results show that the glacial oceanic circulation was significantly different from the modern one. A deep hydrological front separated intermediate water of the Indian and Equatorial Pacifie from underlying deep water. Glacial intermediate water was weil ventilated and has approximately the same temperatures than today. By contrast, glacial deep water was cooler by severa!degrees than modern one. In the Pacifie ocean, deep water was more ventilated than that in the Southern Indian ocean indicating the formation of relatively ventilated deep water in the South Pacifie or the increase of the influence of the North Pacifie Intermediate Water. As late as 12,500 yr BP deep oceanic circulation was similar to the glacial one. The decrease of the influence of the North Pacific Intermediate Water has appeared at about 12,500 yr BP and the onset of the active formation of the North Atlantic Deep Water has appeared at about 9,000 yr BP. Holocene conditions have been reached at about 8,000 yr BP in ali oceans and at ali water depths
48
Tarantola, Alexandre. "Les mécanismes rédox contrôlant la chimie du carbone dans les fluides de l'anchi-métamorphisme : composition des paléofluides, géochimie isotopique, cristallochimie des minéraux phylliteux dans la partie externe des alpes centrales (Suisse)". Nancy 1, 2005. http://www.theses.fr/2005NAN10163.
Abstract (sommario):
Ce travail caractérise les mécanismes auxquels se déroule la transition entre les zones à CH4 et à H2O dans les séries anchi-métamorphiques de la partie Externe des Alpes Centrales, Suisse. Les inclusions fluides piégées dans des quartz fibreux enregistrent l'augmentation des conditions métamorphiques au sein de la roche durant l'orogène Alpin. La fin de la zone à CH4 montre une augmentation de la teneur en CO2 à 270 ± 5°C. La diminution de CH4 et CO2 dans la zone à H2O coïncide avec la présence de calcite remplissant les fentes Alpines. Le fractionnement isotopique (delta13C) entre le méthane et la calcite est en accord avec les températures d'homogénéisation des inclusions fluides. DeltaD(H2O) et delta13C(CO2) des inclusions fluides à la fin de la zone à CH4 caractérisent l'oxydation du méthane. En accord avec les analyses par spectroscopie Mössbauer et EELS, la néoformation de chlorite et muscovite à partir de biotite détritique est considérée comme le moteur de la réaction d'oxydation du CH4This works characterizes the mechanisms at which occurs the transition between CH4- and H2O- dominated fluid zone in the anchi-metamorphic rocks of the External part of Central Alps, Switzerland. Fluid inclusion trapped in fibre quartz during crack-and-seal mechanism record increasing metamorphic conditions during Alpine orogene. The end of the CH4-zone is characterized by a marked increase of CO2 at 270 ± 5°C. The decrease of CH4 and CO2 in the H2O-zone is contemporaneous with presence of calcite, totally filling Alpine fissures. Isotopic fractionation (delta13C) between methane and calcite is in agreement with homogenisation temperatures of fluid inclusion. DeltaD(H2O) and delta13C(CO2) values of fluid inclusions at the end of the CH4-zone characterise methane oxidation. In agreement with Mössbauer spectroscopy and EELS analyses, neoformation of chlorite and muscovite from detrital biotite is considered as the Fe-reduction driving force of the oxidation of fluid
49
Aboglila, Salem Abdulghni-O. "Organic and isotopic geochemistry of source-rocks and crude oils from the East Sirte Basin (Libya)". Thesis, Curtin University, 2010. http://hdl.handle.net/20.500.11937/2118.
Abstract (sommario):
The Sirte Basin is a major oil producing area in Libya, but the understanding of the processes that have led to the petroleum accumulation is still limited. Exploration studies of this area have shown that the oils are mixtures of several charges and may be from different source rocks. The main aims of this thesis are to improve our understanding of the petroleum accumulation history in the East Sirte Basin.Biomarker ratios, together with stable carbon (δ[superscript]1[superscript]3C) and hydrogen (δD) isotopic compositions of individual hydrocarbons have been applied to 24 crude oils from the East Sirte Basin to delineate their sources and respective thermal maturities. The crude oil samples are divided into two main families (A and B) based on differences in source inputs and thermal maturity. Using source-specific biomarker parameters based on pristane/phytane (Pr/Ph), hopane/sterane ratios, dibenzothiophene (DBT) / phenanthrene (P), Pr/n-C[subscript]1[subscript]7, Ph/n-C[subscript]l[subscript]8 and the distribution of tricyclic and tetracyclic terpanes, family B oils are ascribed a marine source rock deposited under sub-oxic conditions, whereas family A oils have a more terrestrial source affinity. This source classification is supported by the stable carbon isotopic compositions (δ[superscript]1[superscript]3C) of the n-alkanes. Family A oils were found to be more mature based on differences between the stable hydrogen isotopic compositions (δD) of Pr and Ph and the n-alkanes, as well as the δ[superscript]1[superscript]3C values of n-alkanes.Within a complex geological setting several potential source rocks have been recognised, ranging in age from Precambrian to Eocene. Biomarker ratios, together with δ[superscript]1[superscript]3C and δD of individual hydrocarbons have been applied to 21 source rock extracts from the East Sirte Basin to establish their respective thermal maturity and palaeoenvironmental conditions of deposition. Rock Eval pyrolysis data obtained from the source rocks of the Sirte, Tagrifet, Rakb, Rachmat, Bahi and Nubian Formations show that the organic matter (OM) is mainly dominated by a Type II/III kerogen. Vitrinite reflectance (% R[subscript]o range: 0.46 – 1.38) data support variations in thermal maturity and indicate mature to post mature rocks of Sirte and Rachmat Formations and early to mid stage maturities for the rest of the formations. The Sirte Formation in the studied area was found to be relatively more thermally mature than the Tagrifet, Rakb, Rachmat, Bahi, and Nubian Formations, reflected by δD of Pr and Ph (less depleted in D).Various unusual steroid biomarkers in the oils and East Sirte source-rocks were identified by gas chromatography- mass spectrometry (GC-MS) and GC- metastable reaction monitoring (MRM) mass spectrometry. These included 24-norcholestanes, dinosteranes, 4α-methyl-24-ethylcholestanes and triaromatic steroids. Diatoms, dinoflagellates and/or their direct ancestors are the proposed sources of these components. These biomarker parameters have been used to establish a Mesozoic oil-source correlation of the East Sirte Basin. This is consistent with the presence of dinoflagellate cysts in the Nubian Formation of Lower Cretaceous age.
50
Sun, Shuwen [Verfasser], Gesine [Akademischer Betreuer] Mollenhauer, Gesine [Gutachter] Mollenhauer e Tommaso [Gutachter] Tesi. "Characterization of terrestrial organic carbon in the Amazon System : insights from biomarkers and their isotopic composition (Delta-C-13 and Delta 14C) / Shuwen Sun ; Gutachter: Gesine Mollenhauer, Tommaso Tesi ; Betreuer: Gesine Mollenhauer". Bremen : Staats- und Universitätsbibliothek Bremen, 2018. http://d-nb.info/1163012912/34.