Academic literature on the topic 'Proxy paléoenvironnemental'
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Journal articles on the topic "Proxy paléoenvironnemental":
Aguiar, Antônia Elisangela Ximenes, Heloísa Helena Gomes Coe, Marco Madella, and Maria Lucia Brito da Cruz. "O USO DO BIOINDICADOR FITÓLITO EM ESTUDOS AMBIENTAIS E ARQUEOLÓGICOS NO BRASIL (UTILISATION DU BIOINDICATEUR PHYTOLITE DANS DES ÉTUDES ENVIRONNEMENTALES ET ARCHÉOLOGIQUES AU BRÉSIL)." Revista GeoNordeste, no. 1 (July 5, 2019): 80–104. http://dx.doi.org/10.33360/rgn.2318-2695.2019.i1p80-104.
Dissertations / Theses on the topic "Proxy paléoenvironnemental":
Guida, Manrique Leydy Carolina. "Mécanismes contrôlant la séquestration du gadolinium, du rhénium et du sélénium dans des conditions de faible teneur en oxygène." Electronic Thesis or Diss., Université Grenoble Alpes, 2024. http://www.theses.fr/2024GRALU015.
Trace elements, despite their scarcity (less than 100 parts per million) on Earth, serve diverse purposes: some act as micronutrients, while others, known as critical metals, possess unique industrial and medical applications. In oxygen-deprived natural aquatic systems electron transfers involve biogeochemical reactions catalyzed by iron, sulfur and trace elements. Understanding their reactivity in these environments remains a challenge. My Ph.D. research focus on filling this knowledge gap concerning three specific elements (rhenium (Re), selenium (Se), and gadolinium (Gd)). They exist in various chemical aqueous species in water: monovalent anion (perrhenate, ReO4—), divalent anion (selenate, SeO42—and selenite, SeO32—) or cation (Gadolinium, Gd3+). Rhenium is a critical metal, while selenium is a bioessential element at low levels, and becomes toxic in higher concentrations. Gadolinium is a rare earth element and a critical metal as well, due to its wide use as a contrast agent in magnetic resonance imaging (MRI).These elements are most concentrated in marine sediments formed in oxygen-deprived environments. Common mineral phases include pyrite (FeS2) and magnetite (Fe3O4) depending on sulfide content in those environments, and origin (autogenic vs. detritic, e.g., from volcanic rocks) of the particles. My research, presented across four chapters, investigates surface reduction (Re(VII), Se(VI) and Se(IV)) and the sorption (Gd(III)) processes on/into magnetite and pyrite particles. Employing various analytical methods such as XAFS spectroscopy, STEM-EELS spectro microscopie and MC-ICP-MS, our study reveals distinct reactive pathways. Re(VII) reacts with sulfidic water to form Re(III, IV, V)2S7 nanoparticles, while at lower concentrations Re is reduced and incorporated into particles, in different pathways characterized by less isotopic fractionation with pyrite than with magnetite. We also show that pyrite nanoparticles reduce Se(VI) and Se(IV), down to surface Se(0) or structure Se(-I) depending on whether adsorption or co-precipitation occurs. Lastly, Gd substitutes for Fe(III) in magnetite nanoparticles up to 5% Fe substitution by Gd. We attempt to unify the affinity behaviour of these and other trace elements with anoxic Fe-bearing sediments in the light of the hard and soft acids and bases principle.The study provides new insights into the mechanisms that govern the sequestration of metals and metalloids in sedimentary settings. The significance of this research lies in its relevance to contemporary scientific and technological endeavours, particularly in understanding how processes in Fe and sulfidic systems work like trace elements, Fe and S mobility, mass balance in the global sedimentary cycles to the exploration, mining and recycling of potential repositories of metals. Furthermore, it enhances our current understanding of the use of palaeoenvironmental proxies to reconstruct the Earth's formation. Finally, this study also has implications for the treatment of nuclear waste and pollution, particularly in the management of selenium (Se) and gadolinium (Gd) contamination
Beaudoin, Anne. "Reconstitution paléoenvironnementale de la région du lac Nettilling, (Nunavut) : une analyse multi-proxy." Thesis, Université Laval, 2014. http://www.theses.ulaval.ca/2014/30317/30317.pdf.
Servera-Vives, Gabriel. "Dynamique holocène du paysage et mobilités des pratiques territoriales au mont Lozère (Massif central, France) : Approche paléoenvironnementale multi-indicateurs à haute résolution spatio-temporelle." Thesis, Limoges, 2014. http://www.theses.fr/2014LIMO0031/document.
Five sedimentary sequences have been studied in the Mont Lozère with the aim to reconstruct the landscape dynamics and the land-use through the longue durée. The use of a multi-proxy analysis has allowed us both to identify distinct rhythms of human-induced landscape shift and to establish the local/regional extent of these changes. The use of high spatial, chronological and analytical resolution has enabled a correct integration of the results of this research with those supplied by the PCR-Mont Lozère project. As a result, a series of land-uses in a mountain environment from the Neolithic to present time has been proposed. A long history of socio-environmental interactions in Mont-Lozère is evidenced. A first shepherding phase in Early Neolithic (4550-4400 cal BC) has been evidenced. During Late Neolithic pastoral practices and related slash-and-burn strategies attain its highest activity. In the Iron Age Period a noticeable deforestation of both foothills and higher environments takes place as a consequence of the overall increase farming and metallurgical activities. Forest clearances increase even more during High-Medieval times, at the same time that farming activities reinforce. During the Middle Ages a more complex and diversified land-use system, including farming, metallurgy, mining and charcoal production, is recorded. The development of farming activities in the Late Medieval resulted in a more evident forest clearance of the Massif. This area remained unchanged until the 19th century, when the decay of agriculture and shepherding occurs and forest replanting in Mont Lozère is recorded. The history of highland herb communities of Nardus stricta correctly matches the main phases of land-use and underlines the key-role of farming in the genesis and evolution of this cultural landscape
Se han estudiado cinco secuencias sedimentarias en el Mont Lozère con el objetivo de reconstruir la dinámica paisajística y los usos del suelo en la longue durée. La utilización de un análisis multiproxy ha permitido determinar los principales ritmos de antropización y establecer su carácter regional y/o local. La alta resolución espacial, cronológica y analítica hapermitido la integración de resultados con aquellos obtenidos en el marco del PCR-Mont Lozère y proponer los usos de la montaña que han modelado el paisaje cultural desde el Neolítico hasta la actualidad. Se ha evidenciado una larga historia de las interacciones socioambientales en el Mont Lozère, con una primera fase de carácter agropastoral en el Neolítico Antiguo, en ca. 4550-4400 cal BC. El Neolítico Final es una fase de marcado impacto agropastoral en la que se generalizan las quemas para abrir claros en el bosque. En la Edad del Hierro se inicia una marcada deforestación en el piedemonte y los espacios de altitud, coincidiendo con un desarrollo agropastoral y metalúrgico. En el periodo altomedieval se amplifican las deforestaciones coincidiendo con un marcado incremento de las actividades agropastorales. En la Plena Edad Media se evidencia un sistema diversificado que implica metalurgia, agricultura, pastoreo, minería y carboneo. El desarrollo agropastoral de la Baja Edad Media supone una marcada deforestación en el macizo que se extiende hasta mitad del s. XIX, momento en que se inicia el declive del agropastoralismo y empiezan las reforestaciones en el Mont Lozère. La historia de las formaciones herbosas con Nardus stricta de los espacios somitales sigue estas principales fases de antropización y revela el papel clave del agropastoralismo en la génesis y evolución de este paisaje cultural
Darfeuil, Sophie. "Vers une meilleure compréhension des paléothermomètres moléculaires Uk'37 et TEX86 : apports d'une double approche données-modèles appliquée à la marge ibérique." Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4363/document.
My PhD project aims at better understanding the functioning of both organic proxies of sea surface temperature (SST), Uk’37 and TEX86, especially in terms of season and depth of alkenone and tetraether production, over the last 160 000 years on the Iberian Margin. The originality of this project lies in its double approach: on the one hand, with the acquisition of Uk’37 and TEX86 sedimentary records from the Iberian Margin, and on the other hand with the use of a coupled physics-biogeochemistry regional model to simulate these temperature proxies for 3 climate modes: at present, during the last glacial maximum, and during Heinrich Stadials. The comparison of biomarker results with those from modeling tests of production scenarios provided the following conclusions. Uk’37 does record annual mean SSTs, whereas TEX86 shows a priori too high temperature for this area. The formulation of a regional calibration for TEX86 index enables to obtain coherent past annual mean SSTs. The best location to apply both paleothermometers on the Iberian Margin is the Shackleton site. After refined analysis of multiproxy signal timings, TEX86 production seems to take place at intermediate depth, potentially by archaean communities coming from the Mediterranean Sea. Latitudinal thermal gradient variations are quantified, and glacial/interglacial surface and intermediate water masses reorganizations during 'Heinrich like' events are considered
Servera, Vives Gabriel. "Evolución del paisaje holoceno y movilidad de las prácticas humanas en el Mont Lozère (Macizo Central, Francia): estudio paleoambiental multi-proxy a alta resolución espaciotemporal = Dynamique holocène du paysage et mobilités des pratiques territoriales au mont Lozère (Massif central, France) : approche paléoenvironnementale multi-indicateurs à haute résolution spatio-temporelle." Doctoral thesis, Universitat de Barcelona, 2014. http://hdl.handle.net/10803/671884.
Five sedimentary sequences have been studied in the Mont Lozère with the aim to reconstruct the landscape dynamics and the land-use through the longue durée. The use of a multi-proxy analysis has allowed us both to identify distinct rhythms of human-induced landscape shift and to establish the local/regional extent of these changes. The use of high spatial, chronological and analytical resolution has enabled a correct integration of the results of this research with those supplied by the PCR-Mont Lozère project. As a result, a series of land-uses in a mountain environment from the Neolithic to present time has been proposed. A long history of socio-environmental interactions in Mont-Lozère is evidenced. A first shepherding phase in Early Neolithic (4550-4400 cal BC) has been evidenced. During Late Neolithic pastoral practices and related slash-and-burn strategies attain its highest activity. In the Iron Age Period a noticeable deforestation of both foothills and higher environments takes place as a consequence of the overall increase farming and metallurgical activities. Forest clearances increase even more during High-Medieval times, at the same time that farming activities reinforce. During the Middle Ages a more complex and diversified land-use system, including farming, metallurgy, mining and charcoal production, is recorded. The development of farming activities in the Late Medieval resulted in a more evident forest clearance of the Massif. This area remained unchanged until the 19th century, when the decay of agriculture and shepherding occurs and forest replanting in Mont Lozère is recorded. The history of highland herb communities of Nardus stricta correctly matches the main phases of land-use and underlines the key-role of farming in the genesis and evolution of this cultural landscape.