Tesis sobre el tema "Changements récents"
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Hillcoat-Nalletamby, Sarah. "La dynamique des pratiques contraceptives à l'île Maurice : changements récents". Paris 5, 1995. http://www.theses.fr/1995PA05H050.
Texto completoDuring the past twenty years, changes in contraceptive practices have arisen in Mauritius : a drop in prevalence levels and in the number of regular users; an increase in contraceptive drop-out rates. Our objective has been two-fold : to analyse the degree and type change at the macro-level of the total population; furthermore, to study the socio-culture al factors influencing practices, as observed at the micro-level of the community. We conclude that the changes observed are not, as might be considered, the indication of a growing resistance to contraception. We suggest that both the continuity and forms of such practices are influenced by the "interference" between three types of factors : cycles of investment in population policy influencing the supply of services; the problems posed for access to family planning services by poor living conditions : the influence upon contraceptive practices of individual and group values and attitudes concerning birth control
Le, Breton Éric. "Réponses géomorphologiques et hydrologiques aux changements environnementaux récents au Sahel nigérien". Paris 1, 2012. http://www.theses.fr/2012PA010744.
Texto completoNguiffo-Boyom, Muriel. "Modèles à changements de régimes markoviens : Genèse, développement récents et utilisation pour l'analyse conjoncturelle". Paris 2, 2005. http://www.theses.fr/2005PA020041.
Texto completoTendelet, Jean-Ignace. "Les changements récents sur les marchés financiers internationaux et leur impact sur les liquidités internationales". Paris 2, 1993. http://www.theses.fr/1993PA020127.
Texto completoStrechie-Sliwinski, Claudia. "Enregistrement sédimentaire des changements environnementaux récents dans la zone Nord-Ouest de la Mer Noire". Paris 11, 2007. http://www.theses.fr/2007PA112178.
Texto completoThe purpose of this study is to investigate the processes and the recent environmental changes stored in the sediments from the North-Western part of the Black Sea in the last 30,000 years. We used sedimentary cores extracted from water depths ranging from 55 to 2100 m. In order to obtain information about the depositional environment and the chronology of the events, we used different methods: clay mineralogy analysis, sedimentology, environmental magnetism, organic matter characteristics and AMS radiocarbon chronology. Radiocarbon dating of the organic matter and fossil shells was used to obtain a precise chronology of the past events. It was difficult to correct the 14C data, because of the differences between the ages of organic matter and shells that varied significantly from one sample to another. This difficulty comes from the fact that the Black Sea basin contained in some periods oxygenated fresh water and in some periods stratified salty water. The correlation between the 14C data and the carbonate content allowed us to set up a chronology of the sediments. The clay mineralogy pointed out that the sediments containing smectite were carried into the basin mainly from the North and not from the South of the drainage basin, as previous studies indicated. The environmental magnetism study helped us to determine the significant variations in the oxygenation of the sediment and of the water column (i. E. , changes between oxygenated and anoxic conditions). The magnetism study together with the organic matter characteristics also indicates changes in the salinity of the water. Our study reveals the environmental changes that have occurred during the last 30,000 years
Pillet, Valentin. "Détection et attribution des changements morphologiques côtiers récents en milieu insulaire tropical (Polynésie française, Caraïbe)". Thesis, La Rochelle, 2020. http://www.theses.fr/2020LAROS019.
Texto completoLow-lying reef islands and coastal areas of tropical mountainous islands are highly vulnerable to the impacts of tropical cyclones and the expected effects of climate change. However, while the French metropolitan coasts have benefited from a significant effort to assess their long-term changes, French overseas islands are the least documented areas in French Territory. Based on this observation, this thesis examines the respective contribution of natural and anthropogenic drivers in the past evolution of reef islands (French Polynesia) and mountainous island beaches (Northern Lesser Antilles). This study relies on a combined approach between geomatic and fieldwork. From a multi-scalar (spatial and temporal) analysis, we detect and attribute the planimetric changes experienced by the sedimentary systems of the studied islands. Results on reef islands are comparable to those of previous studies which established that most of the islands have been stable or in expansion over the last decades. They allow to suggest conceptual models of long-term trajectories and examine the respective contribution of the drivers considered in this study. On mountainous island beaches, this study shows that local settings explain the high longitudinal variability detected in various climatic situations. In addition, this study contributes to the global samples of studied islands and to move forward on the understanding of past coastal changes in French overseas islands
Ropars, Pascale. "Réponse du bouleau glanduleux (Betula glandulosa Michx.) aux changements climatiques récents : implications pour l'écotone forêt boréale-toundra, Nunavik". Doctoral thesis, Université Laval, 2015. http://hdl.handle.net/20.500.11794/26225.
Texto completoAu cœur des changements environnementaux enregistrés dans les régions arctiques et subarctiques, la densification de la strate arbustive est probablement l’un des plus importants. Cette thèse propose d’en étudier la dynamique récente à l’écotone forêt boréale-toundra (Nunavik) afin de mieux en cerner les causes et d’en évaluer les conséquences. Dans un premier temps, la comparaison d’images aériennes (1957 et 2008) nous révèle une densification importante de la strate arbustive dans la région d’étude. Largement attribuée à Betula glandulosa, cette densification a été plus importante sur les terrasses que sur les sommets et hétérogène à l’échelle du paysage. Par la suite, je me suis attardée aux causes de l’hétérogénéité de la densification de la strate arbustive et ai trouvé que celle-ci était principalement attribuable à un ensemble de facteurs historiques et topographiques. De plus, j’ai pu montrer que la densification de la strate arbustive a une influence négative sur l’abondance des espèces arbustives non impliquées dans ce phénomène, mais qu’aucune relation n’a été décelée avec la diversité spécifique (richesse spécifique et indice de diversité de Shannon). Finalement, j’ai montré que la croissance radiale et axiale de B. glandulosa était fortement associée aux températures estivales chez les individus établis sur des sites bien drainés et aux précipitations hivernales chez ceux établis dans les combes à neige (milieu mal drainé où la neige persiste dans la saison de croissance). De surcroît, la forte augmentation de la croissance radiale de B. glandulosa entre 1990 et 2002 suggère que la densification de la strate arbustive observée dans la région d’étude est un phénomène récent. En somme, cette thèse a permis de mieux comprendre la dynamique de l’écotone forêt boréale-toundra au Québec subarctique dans un contexte de changements climatiques. Elle a aussi contribué à saisir toute l’importance d’une analyse à fine échelle de la croissance des espèces impliquées dans la densification de la strate arbustive ainsi qu’à approfondir nos connaissances sur une espèce structurante du Québec subarctique, B. glandulosa.
One of the major changes observed in northern terrestrial regions in response to climate change is arguably the recent shrub expansion. This thesis aims to study the recent dynamic of the shrub expansion at the forest tundra ecotone, northern Québec, in order to find its causes and evaluate its consequences on plant community. First, I compared two sets of aerial photographs (taken in 1957 and 2008) and found an increase in shrub cover that was mainly attributed to Betula glandulosa, a largely distributed erect shrub species. This increase was higher on terraces than on hilltops and strongly heterogeneous at the regional scale. Second, I found that the heterogeneity of the shrub expansion depended on both historical and topographic variables. Moreover, I showed that an increase in B. glandulosa cover had a negative influence on the abundance of other shrub species, but not on their diversity (species richness and Shannon diversity index). Finally, I found that B. glandulosa radial and axial growth were strongly associated with summer temperature when growing on well-drained sites, whereas they were mainly associated with winter precipitation when growing in snowbeds (well-watered sites where snow cover persist in the growing season). Dendrochronological analyses showed a sharp B. glandulosa growth increase between 1990 and 2002, therefore suggesting that the shrub expansion observed in the study region is quite recent. Overall, this thesis significantly improved our knowledge of the recent dynamic of the forest tundra ecotone in northern Québec. It also contributed to underline the importance of studying shrub expansion at the local scale and to improve our knowledge of B. glandulosa.
Barbraud, Christophe. "Forçage environnemental et prédateurs marins endothermes de l'Océan Austral: effets des changements climatiques récents et des pêcheries industrielles sur les populations". Habilitation à diriger des recherches, Université Paul Sabatier - Toulouse III, 2010. http://tel.archives-ouvertes.fr/tel-00770926.
Texto completoThabeet, Ali. "Réponse du pin sylvestre (Pinus sylvestris L) aux changements climatiques récents en région méditerranéenne française : spatialisation et quantification par la télédétection et la dendrochronologie". Aix-Marseille 3, 2008. http://www.theses.fr/2008AIX30074.
Texto completoThe objective of this thesis is a study of the consequences of recent climate change on the health and the growth of Pinus sylvestris by the quantification and spatialisation of their effects. The remote sensing was used to estimate the health status of P. Sylvestris via the Normalized Difference Vegetation Index (NDVI) at local and landscape scales. This analysis allowed an assessment of the relative importance of local attributes, e. G. Elevation, aspect and relative moisture index in the population decline observed due to a decrease of water availability as a result of a succession of dry years. Measures of shoot growth and the expression of sexuality of P. Sylvestris showed that the climate from years 2003 to 2005 was unfavourable to both growth and cone (female) production but was promoted the production of flowers (male). Radial growth has decreased at all sites, independent of local conditions. The decrease in radial growth indicates that the growing conditions of this species worsened prior to 2000. An analysis of the relationships between climate and ring widths allowed the identification of the main monthly climatic variables controlling tree-ring widths of this species. Amongst these, precipitation during April and May promotes growth at low altitude and May and June precipitation promotes growth at high altitude sites, together with February temperatures In contrast, June temperatures have a negatively effect on tree growth. The combined effects of a positive influence of precipitation with a negative influence of June temperatures underline the importance of water stress during the summer growth period. Using this information, a predictive model was constructed using response functions, to test the reaction of the P. Sylvestris to increases in the frequency of extremely unfavourable years, such as 2003. This analysis showed that year 2003 was not an isolated exceptional year, but forms a set of years with unfavourable climatic conditions, which began in 2000
Wardziak, Thomas. "Climat et biodiversité : application de récents développements méthodologiques à l'étude et la modélisation des pertes en eau par évaporation chez un amphibien". Thesis, Lyon 1, 2013. http://www.theses.fr/2013LYO10135/document.
Texto completoLn a context of climate change, it is critical to predict how organisms might be affected in their physical relations with environment. Amphibians are among the vertebrate groups the most affected by ecological changes, because of permanent transepidermal evaporative water loss (TEWL) through their skin. My thesis aims at setting up approaches to measure and model accurately the functional skin surface areas that contribute to TEWL, establishing laws of water transfer between an amphibian and its physical environment, and providing understanding on physiological responses to the skin pathogen Batrachochytrium dendrobatidis. We conducted experiments on adult males of the palmate newt (Lissotriton helveticus) during their terrestrial phase. Our results suggest that L. helveticus did not show any physiological adaptations to restrain TEWL. The ways to reduce TEWL result essentially in the expression of a stereotyped "$"-shaped water-conserving posture. We used a Magnetic Resonance lmaging-based 3D reconstruction method to generate 3D geometries of newt that is suitable for measuring skin surface areas, and for simulation purposes. We successfully performed 3D numerical analysis of TEWL, and proposed an original relationship to estimate TEWL rates in a large range of temperature and humidity. Finally, our results support the epidermal dysfunction hypothesis, which suggests that B. dendrobatidis compromises the ability of amphibians to rehydrate. My thesis would contribute to open new approaches to the science of amphibian water relations, and improve our knowledge of the effects of ecological changes on organisms
Mespoulet, Valérie. "Femmes et espace social : un état de la question à Taïwan : des structures sociales traditionnelles aux changements récents : quelle appropriation légitime de cet espace par les Taïwanaises contemporaines ?" Aix-Marseille 1, 2010. http://www.theses.fr/2010AIX10007.
Texto completoStrechie-Sliwinski, Claudia. "ENREGISTREMENT SEDIMENTAIRE DES CHANGEMENTS ENVIRONNEMENTAUX RECENTS DANS LA ZONE NORD-OUEST DE LA MER NOIRE". Phd thesis, Université Paris Sud - Paris XI, 2007. http://tel.archives-ouvertes.fr/tel-00399227.
Texto completoHimmich, Kenza. "Antarctic sea ice : a seasonal perspective". Electronic Thesis or Diss., Sorbonne université, 2024. http://www.theses.fr/2024SORUS105.
Texto completoAntarctic sea ice has undergone an abrupt reduction in 2016, following more than four decades of a slow increase. This could have wide-ranging consequences given the importance of Antarctic sea ice for climate, ocean, and local ecosystem. Yet, climate models fail to capture this observed evolution, leaving considerable uncertainty regarding its origin, impacts and future evolution. Models failure relates, but not only, to a poor understanding of fundamental Antarctic sea ice processes. In this thesis, we contribute to progress understanding of Antarctic sea ice, adopting a seasonal perspective. We investigate the drivers of seasonal sea ice edge advance and retreat, analyzing the roles of thermodynamic preconditioning, air-ice-sea heat fluxes and sea ice dynamics. We show that, in the mean state, timings of ice edge advance and retreat are largely controlled by thermodynamics, via preconditioning from mixed layer heat content and sea ice thickness, respectively. Variations in air-ice-sea heat fluxes and sea ice dynamics have a significant but secondary importance. This conclusion is supported by a simple thermodynamic model, observational analyses and the NEMO ice-ocean model. We also show that recent changes in sea ice seasonality are mainly driven by thermodynamics, similar to the mean state. The reduction in Antarctic sea ice following 2016 coincides with nearly circumpolar earlier retreat and later advance of the ice edge. Our analysis links these changes to thinner ice in winter, faster melt in spring and warmer upper ocean in summer, in line with ice-albedo feedback processes. Based on the circumpolar footprint of these changes, we argue that they likely have an oceanic origin
Omar, Haroun Suliman. "Climatologie du Soudan et hydrologie du système nilotique : évolution récente". Lyon 3, 1998. http://www.theses.fr/1998LYO31006.
Texto completoComte, Lise. "Changements globaux et distribution spatiale des espèces de poisson d'eau douce : observations récentes et prédictions futures". Toulouse 3, 2013. http://thesesups.ups-tlse.fr/2258/.
Texto completoDespite increasing recognition that recent climate changes are influencing biodiversity, the specific impacts of those changes are still largely unknown. This thesis highlights systematic stream fish species shifts towards higher elevation and upstream habitats, consistent with the geographic variation associated with climate change. The results demonstrated, however, that patterns in climate-driven range shifts were less marked than those attributed to non-climatic drivers, suggesting more severe longer-term effects of climate warming on stream fish and profound consequences on the ability of species to cope with future climate modifications. Nevertheless, the results also provide evidence that several mechanisms are linked to species' evolutionary history and some key biological and ecological traits, allowing species to persist in situ or to track their climatic niche through space. These research findings improve our ability to anticipate future climate change-induced impacts and will assist with initiating effective conservation and management strategies, which can no longer be effectively designed without taking into account climate change
Corre, Lola. "Évolution récente des océans tropicaux : le rôle de l'influence humaine". Toulouse 3, 2011. http://thesesups.ups-tlse.fr/1673/.
Texto completoDue to its high heat capacity, the ocean integrates the surface fluxes, producing high signal-to-noise ratio at decadal and longer timescales. On the contrary, long-term changes in atmospheric variables are difficult to measure due to the atmosphere high variability on short timescales. Looking at oceanic variables is thus interesting in order to successfully detect a response to the anthropogenic climate change. This manuscript further examines recent upper ocean temperature and surface ocean salinity changes. As 80% of the excess heat caused by increasing greenhouse gas concentrations, over the last decades, has accumulated in the ocean, the rate of ocean warming is one of the best indicators of the Earth's energy imbalance. Surface ocean salinity provides Nature's largest possible rain gauge and can be efficiently used as an indicator of the changing marine water cycle. Detection methods are applied to assess whether a human influence can be detected in the recent observed changes
Fourt, Maïa. "Histoire de la pêche des éponges en Méditerranée et son adaptation récente au changement régional". Thesis, Aix-Marseille, 2019. http://theses.univ-amu.fr.lama.univ-amu.fr/191217_FOURT_178pyka634dl637hqgt642gcc_TH.pdf.
Texto completoIn the Mediterranean Sea, small scale fisheries are firmly anchored in the culture of this maritime area. Sponge fishing has been practiced in the Mediterranean since antiquity. Although contributing to an important exportation market until the mid-20th century, it has recently shown signs of weakness, leading to the collapse of the overall production. This study proposed an interdisciplinary approach applied to over two centuries of sponge fishing history. The first part of this study presents a spatial analysis of the fishery at the Mediterranean scale, considering several key periods in order to identify geographical areas where important changes have occurred. The second part analyses the sponge production and the fishing effort variations in the Aegean area and in Tunisia. The last part of this work is dedicated to an analysis of the fishermen’s adaptive choices faced to the sponge fishing activity upheavals. The study shows that up to the 1970s the factors that influenced this fishery were mainly the societal demand, the fragile economic situation of the fishing communities, changes in uses, as well as the socio-political and economic relationships between Mediterranean countries. Since 1986, frequent epizootic events related to changes in thermal regimes have weakened the sponge stocks. Remaining fishermen have mainly adapted to the irregular availability of the resource by targeting other species, or by relying more on other already existing fishing activities
Serrurier, Carol. "Chronique d'une impossible transition : transformation et résistance au changement dans les romans récents de Nadine Gordimer (1980 à 1995)". Nancy 2, 2000. http://www.theses.fr/2000NAN21019.
Texto completoThe years between 1980 and 1995 delineate one of the most fascinating transition periods of the end of the Twentieth Century. This thesis examines the political and social changes and their effects on the individual and on the group through four of the novels by one of that country's foremost writers, Nobel Prize winner in literature (1991), Nadine Grodimer. In addition to the reciprocal influences operating between text and context, this transversal study analyses transformation and resistance to change in such postcolonial areas as identity, place and sense of belonging, as well as the more universal concerns of belief systems and interpersonal relationships. Gordimer's writing, with its narratological density and its wealth of imagery and intertextual references, provides fertile ground for the study of the subject chosen
Tabel, Jalal. "Impacts des changements environnementaux passés durant le Quaternaire récent sur la dynamique forestière du Moyen Atlas marocain". Thesis, Montpellier, 2015. http://www.theses.fr/2015MONTS184/document.
Texto completoThis thesis discusses the paleoenvironmental and paleoclimatic changes that have affected the ecosystems of the Moroccan Middle Atlas since the last glacial period, and focuses around 25000 cal BP. The three sedimentary sequences that have been studied in this thesis were taken along a North-South transect in the Middle Atlas. This study is based on a multi-bio-indicators approach, including palynology, geochemical elements and particle size, in order to better understand the dynamic of previous ecosystems and to highlight the human activities on these ecosystems and on their catchment areas.The results obtained show that during the last glacial period, and until the beginning of the Holocene, steppe vegetation was predominant in the Middle Atlas, in reaction to cold and arid climate conditions. However, populations of cedars, oaks and pine trees remained in micro-refugia. Although the beginning of the Holocene reveals an expansion of oaks and pines trees (the main components of Mediterranean forests ecosystems), the steppe (which is composed of Artemisia, Chenopodiaceae and grasses) persisted till 6.5 ka cal BP. These drought-tolerant ecosystems reflect a warm beginning of the Holocene, with an amount of precipitation that was low enough to allow the expansion of forests similar to those we can observe in Europe and other areas of the Mediterranean. It’s only since 6.5 ka cal BP that cedars forests have started to grow at the altitudes of the sites we studied (around 1600m), and that aquatic plants have proliferated in the marshes where we took our samples. We can then observe a sharp decline of tree cover, including deciduous oaks, starting 4.5 ka cal BP and an expansion of herbaceous taxa. These are the consequences of a tendency to conditions that were more arid, attesting the installation of the Mediterranean climate as we know it today. The first environmental changes linked to human impact have only been recorded, through palynology and biochemical data, from ca. 1500 cal BP. The results obtained in this thesis are in line with those obtained in other paleoenvironmental studies conducted in the Mediterranean area, for the glacial period as well as for the beginning of arid conditions starting 5.5 ka cal BP
Tremblay, Julie. "Analyse dendroécologique du changement récent dans le régime d'enneigement insulaire au réservoir Robert-Bourassa, Québec nordique". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0006/MQ44978.pdf.
Texto completoChen, Quan. "Signatures détritiques des changements paléoenvironnementaux du Quaternaire récent dans le bassin nord de la mer de Chine du Sud". Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS492/document.
Texto completoThe aim of this study is to reconstruct late Quaternary environmental changes in the northern South China Sea by applying multi-disciplinary proxies of land-sea interaction, East Asian monsoon, and oceanic circulation. Investigations of clay and magnetic mineralogy, major element composition, and grain size were performed on marine sediment Core MD12-3432 retrieved from the continental slope of the northern South China Sea. The core covers the last 400 ka with a sedimentation rate varying between 4.5 and 24 cm/ka. We examined the accuracy of existing calibration methods on major element composition obtained by XRF core-scanning, because downcore variations in interstitial water content should strongly affect scanned element contents. We proposed a quadratic polynomial correction to account for this effect and implemented it in the calibration methods. Data from Core MD12-3432 show that the improved calibration process now correctly converts XRF core-scanning data into major element concentrations. Our results on high-resolution major element composition, clay and magnetic mineralogy, and grain size data indicate that low-latitude climate changes influence various terrigenous fractions in different ways. In bulk sediment, K₂O/Al₂O₃ ratio mainly reflects the relative contribution of detrital supply from Taiwan, and its variation exhibits eccentricity cycles. The ratio increases during interglacials, showing that strong precipitation and denudation are induced by enhanced East Asian summer monsoon. In clay fractions, smectite/(illite+chlorite) ratio presents both eccentricity and precession periodicities, in phase with the northern hemisphere summer insolation changes and therefore with the East Asian summer monsoon evolution. Based on the knowledge of sediment provenances, these results suggest that high smectite/(illite+chlorite) ratios illustrate contemporaneous chemical weathering intensity in Luzon. It supports the understanding that East Asian summer monsoon is enhanced during interglacial periods and when the boreal summer insolation is strong. Therefore, these two ratios are appropriate sedimentary tracers for East Asian summer monsoon evolution in the South China Sea. The magnetic fraction yields complementary information about environmental changes in the South China Sea. The magnetic mineral assemblage of Core MD12-3432 is mainly composed of magnetite, sulphide, and hematite, and the relative contributions of all these magnetic mineral contents change with time. Variations on precessional band related to the low latitude East Asian monsoon are observed in magnetic properties and grain size values. High magnetic inputs with high hematite proportion, which is part of fine-grain sediment, are observed during the precession minima. These events occurring during arid periods may illustrate enhanced eolian inputs caused by changes in intensity and/or winds pathway of winds, probably related to enhanced winter monsoon. Besides the low-latitude climate changes, global climate and tectonic activity also influence the terrigenous composition at the studied site at different timescales. A long-term increase in pyrrhotite content with respect to magnetite and hematite and in illite/chlorite contents indicates an increasing contribution of fine grained sediments from Taiwan. This is most likely related to the intensification of Taiwanese orogeny over the last 400 ka. On glacial-interglacial scale, coeval increases observed in sedimentation rate, magnetite/pyrrhotite content, kaolinite content, and grain size during glacial periods are attributed to sea-level changes. Low sea-level during glacial periods exposes the vast shelf and allows the Pearl River to deliver more and coarser terrigenous sediments to our site
Gardelle, Julie. "Evolution récente des glaciers du Pamir-Karakoram-Himalaya : apport de l'imagerie satellite". Phd thesis, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-00864042.
Texto completoAmraoui, Laïla. "Variabilités climatiques régionales et changement global : cas de l'évolution climatique récente au Maroc, en Mauritanie et sur leur proche océan". Thesis, Lyon 3, 2013. http://www.theses.fr/2013LYO30069/document.
Texto completoIn the context of global contemporary climate change, regional climate analyses are of major interest as they allow accounting for spatial heterogeneity of climate change. Our study provides for an analysis of recent climate changes in Morocco and Mauritania and their nearby Ocean. It focuses on the evolution in the lower layers of the atmosphere, taking into account the thermal conditions (air temperature at 2m), the coastal climate dynamics (sst and upwelling), and atmosphere dynamics made of atmospheric pressures and surface winds. For all the studied meteorological parameters, the variability and inter-annual evolution are analyzed on monthly and annual / seasonal scales.Statistical analyzes based primarily on linear regressions and Hubert's segmentation helped show that the Moroccan-Mauritanian zone has experienced over the past six decades (1950-2008), contrasting climate changes both at the spatial and seasonal scales. The most significant results are hereunder summarized :•A contrasted thermal evolution with a more pronounced warming in Morocco and the Sahara than in Mauritania,•Increase the intensity of the upwelling on the Moroccan coast and decrease on the Mauritanian,•A strong and dominant upward trend in atmospheric pressure, resulting, in particular, in a Mediterrano-Saharan AA strengthening and lower Saharan thermal pressure during summer,•A general downward trend in wind speed, in parallel with a rotation of the compass rose from north to northeast for marine trade winds, and from north to east for the continental trade winds.Hubert’ Segmentation confirmed that the major climatic fluctuations in the Moroccan-Mauritanian area and their nearby ocean occurred during the 1970s. This is true at the level of air temperatures, the upwelling, and SLP, while the disruption that affected the wind speed and the frequency of the main directions of the trade winds occurred between 1960 and 1970. A second period of disruption has been demonstrated by Hubert’s segmentation. It relates to the 1990s in air temperature chronological series and SLP
Sarr, Mamadou Adama. "Évolution récente du climat et de la végétation au Sénégal : cas du Bassin versant du Ferlo". Lyon 3, 2009. http://www.theses.fr/2009LYO31058.
Texto completoUnderstand the evolution and the recent variability of the climate in the arid and semi-arid regions is a necessity in order to anticipate what could be the consequences on the environments and on the societies of those regions, and thus define the strategic politics of sustainable development. To reach that goal, we have organised our research in three parts. The first part treats of the geographical plan through a detailed description of the physical environment and of the different systems of the ground occupation. This description put in evidence a fragile ecosystem under high pressure due to the activities which are employed here. The description summarizes also the middle climate frame by accentuating on the general mechanisms of the general circulation of West Africa which is part of the study zone. The analysis constitutes a recall of the dynamic average global conditions of the climatic tropical field which, in relation with local and regional factors, determines the average components of time in the study field and its margins. The second part concerns the analysis of the spatiotemporal variability on the period going from 1951 until 2005 by putting the accent more on the recorded rainfall than on other climatic parameters such as temperature, evaporation, relative humidity and insulation. But it underlines first the physical and methodological constraints which are compulsory for the statistic analysis of the parameters and justify also the models retained for the use of the database. The analysis of the recorded rainfall results show a high variability, but also a quasi stationarity from the end of the years 1970 and that until the middle of the 1980’s, and since an increase of the annual precipitation volumes on the totality of the study field. Compared to the evolution of other parameters (insulation, temperatures, evaporation and relative humidity), the middle of the 1980’s and the beginning of the years 1990’s appear like a period of trend “break up” justifying the questioning on the persistence or not of the dry trend of the Sahel climate in its totality. The third part starts by the analysis of the evolution of the vegetal production different time scale on the basis of a serie of synthesis images NDVI (Normalized Differential Vegetation Index) of NOAA-AVHRR on the period going from 1981 until 2005. The evaluation of the inter-annual and intra-annual evolution of the vegetal production in relation with the precipitations in the study field demonstrates a good correlation. On the other hand, the anthropic actions, within the framework of execution of the politics of planning disturb this close relation. This situation is put in evidence by the results obtained in the analysis of the cartography of the ground occupation changes between 1990 and 2002. The study conceived on the treatment of the images TM (Thematic Mapper) and ETM+ (Enhanced Thematic Mapper Plus) of Landsat in support of the statements of grounds; confirms the human action in the expansion from the bush savannah to arborous. After defining the characteristics, the follow up tool of the vegetation of the sensor SEVIRI of the satellite MSG is proposed. The corroboration of this new product is done on the basis of a comparative study with those of SPOT-VEGETATION and NOAA-AVHRR, frequently used in the scientific field. After a recall of the essential results of the research, the general conclusion insists on the exploration of solutions for water problems, important for a performing agriculture and a reduced mobility of the pastoral activity. And that passes through the multiplication of studies on the climatic variability, mostly on local scale. The general conclusion shows also the necessity of an approach of multi-sensors for the vegetation follow up. Finally, in order to bring more precisions for the comprehension of the thesis, you will find in the appendix elements concerning the characteristics of satellites as well as the sensors used and a study of cross validation on the techniques of spatial interpolation
Boulain, Nicolas. "Effet des facteurs climatiques et anthropiques dans l'évolution récente des écosystèmes tropicaux : modélisation spatialisée du bilan hydrique d'un petit bassin versant sahélien". Paris 6, 2004. http://www.theses.fr/2004PA066016.
Texto completoMondolfo, Philip. "Transformations récentes dans le champ du travail social : l'exemple de l'assistance sociale polyvalente : les conditions de diffusion et d'adaptation au changement". Paris 10, 1995. http://www.theses.fr/1995PA100088.
Texto completoThe first goal of this research is to verify, thanks to a socio-historical approach comparing organizational principles and work patterns before and after the introduction of "RMI" (supplementary benefit for people in severe distress) and local decentralization, whether there has been a dramatic change in multi-purpose social relief. With this perspective, the new occupational model currently developing in this sector can be delineated, showing its breaking points and boundaries. The ensuing study of the way this model is actually implemented gives evidence to an uneven propagation according to location. It has been envisaged to explain the phenomenon thanks to the theory of two-step flow. But this theory has shown its limits in a semi-professional context. The combined effect of such parameters as organization, command, skills, group dynamics and environment has been brought to light, so that the resulting interactions and tensions make room for varying degrees of convergence of the factors, the structuring thereof being implemented by mediating cadres. As a conclusion, it may be said that fild effects and the rules which govern the organization of each space have to be taken into account in a sociology of dissemination
Yue, Yuanfu. "Végétation, climat et changement du niveau marin durant le quaternaire récent dans la province de Fuzhuo, sud-est de la Chine". Thesis, Montpellier 2, 2012. http://www.theses.fr/2012MON20185.
Texto completoAbstractA series of sediment cores (FZ4, FZ5, and SZY) were collected in Fuzhou plain and Ningde mountain area. The three cores, located respectively in the near coast basins and mountains, are well suited for understanding the evolution of vegetation and the impact of the East Asian monsoon and sea level changes on the Quaternary environments. My thesis provides insight into regional palaeovegetation and palaeoclimatic changes over the last 50000 years, as well as an investigation of the prehistoric human activities and their relationship with local environmental change during the Holocene. In this thesis, I have used a multidisciplinary approach including palynology, sedimentology, paleomagnetism and micropaleontology to reconstruct the past environments. The SZY pollen record from a subalpine peat bog covers the past 50,000 years continuously. The diverse flora and forest changes during the last 50 ka indicate regional monsoon evolution in subtropical southeastern China. The climate proxies such as seasonal monsoon index, monthly temperature and precipitation were quantitatively reconstructed.The pollen assemblage during the period ca. 50-30.4 cal ka BP, roughly corresponding to Marine Isotope Stage (MIS) 3, was characterized by high abundance of arboreal pollen, mainly subtropical evergreen Quercus, Castanopsis/Lithocarpus mixed with temperate mountain deciduous broad-leaved trees such as Fagus, Alnus and accompanied with some mountain mesic conifers such as Taxodiaceae and Tsuga. Such ecosystem composition suggests that MIS 3 was rather wet with strong summer monsoon. The high summer insolation may have caused an intensification of the summer monsoon during this period and thus helped maintaining such subtropical ecosystem.A gradual expansion of deciduous broad-leaved taxa which replaced the subtropical evergreen ones during the Last Glacial Maximum (LGM) period (ca. 30.4-11.8 cal ka BP), indicates that climate became much cooler than during MIS 3. The coldest interval occurs during the interval ca. 21-17 cal ka BP, when the shrubby savanna increased and the broadleaved forest rapidly declined. This event is marked also in the pollen concentration which show low values during the LGM. This is probably related to an open or semi-open landscape under a colder and dryer climate than during MIS 3. In comparison with regional oxygen isotope data (δ18O/δ16O) from speleothems and Greenland ice cores, several rapid climate events could be recognized, for instance the Younger Dryas and the Bølling-Allerød interstadial that marked the final stages of the last glacial period. During the Holocene, the evergreen forest restored rapidly. The evergreen pollen group became higher than the deciduous one at around 8000 cal yr BP, reflecting the strengthening of the Summer Monsoon. Two sharp events occurred at ca. 8.2 cal ka BP and ca. 5 cal ka BP, probably caused by cooling events during the Holocene.In the lower reach of Min River, the interdisciplinary study of two cores reveal that the sedimentary environment in Fuzhou Plain experienced several sedimentation cycles during the Holocene. The marine transgression into Fuzhou basin took place in around ca. 9000 cal BP, and reached its highest sea level at 7000-4000 cal BP. Grain-size and diatom analysis and AMS dating allow to depict the marine transgression and reconstruct its timing. Pollen analyses support the warm subtropical climate during the Mid-Holocene with dense forest dominated with evergreen broadleaved taxa. The optimal climate and the formation of marine estuary during the high-stand of the sea level were in favor of the development of the Neolithic culture (mainly Tanshishan Culture between ca. 6800-4500 cal yr BP) where the fishing and hunting were the main economic lifestyles.The sedimentological results show that the retreat of the coastline took place during the late Holocene. This is indicated by a layer of tidal peat dated around ca.1900 cal yr
Bodin, Xavier. "Géodynamique du pergélisol alpin : fonctionnement, distribution et évolution récente. L'exemple du massif du Combeynot (Hautes Alpes)". Phd thesis, Université Paris-Diderot - Paris VII, 2007. http://tel.archives-ouvertes.fr/tel-00203233.
Texto completoBertrand, Olivia. "Enregistrement molécularie de changements d'usage des sols et de pressions anthropiques : l'exemple d'un étang piscicole (Lansquenet, Lorraine)". Thesis, Université de Lorraine, 2012. http://www.theses.fr/2012LORR0352/document.
Texto completoThe sedimentary series, collected in terrestrial and aquatic ecosystems, constitute records or archives of the state of a system at a given moment of the past and relate its evolution in relation to natural disturbances and anthropogenic pressure. In the following manuscript, the sedimentary record of a fish pond has been studied using a multidisciplinary approach. In particular, the characterization at the molecular and macromolecular scale of the organic matter in sediments of the pond Lansquenet allowed to reconstruct the history of its watershed. On the basis of biomarkers and molecular ratios (terrestrial to aquatic ratio: TAR(HC), C29/C27(ST), aquatic/macrophyte proxy: Paq, perylene, syringyl/vanillyl, cinnamyl/vanillyl, acid/aldehyde of syringyl and vanillyl units), this work has enabled us to understand, at the scale of a watershed, the changes in organic matter origins (terrestrial and/or aquatic, natural and/or anthropogenic) over a period of several centuries. Moreover, the results unraveled the depositional conditions as well as preservation conditions in the sedimentary profile, directly influenced by land use and human activities. The confrontation of organic geochemical data with sedimentological, mineralogical and palynological data was a real benefit and validated the use of a series of organic compounds as relevant and sensitive biomarkers regarding environmental and paleoenvironmental modifications. This study highlighted thus the succession of use of the Lansquenet site from a swampy area to the settlement of a fish pond punctuated by drier periods
Charru, Marie. "LA PRODUCTIVITÉ FORESTIÈRE DANS UN ENVIRONNEMENT CHANGEANT : CARACTÉRISATION MULTI-ÉCHELLE DE SES VARIATIONS RÉCENTES À PARTIR DES DONNÉES DE L’INVENTAIRE FORESTIER NATIONAL (IFN) ET INTERPRÉTATION ENVIRONNEMENTALE". Thesis, Paris, AgroParisTech, 2012. http://www.theses.fr/2012AGPT0027/document.
Texto completoGrowth trends have been reported in many regions of Europe over the twentieth century. However, an integrated assessment of productivity changes, including focus on a wide geographical scale, analysis of spatial heterogeneity, and the inter-specific diversity of growth responses is still lacking. The aim of this Ph.D work was to assess recent changes in forest productivity on a national, regional and local scale in France, and to investigate their potential environmental causes, based on statistical modeling approaches of stand basal area increment (BAI), and environmental indicators. We used the French NFI data for 8 species of contrasted ecological niches and distributions (Fagus sylvatica, Quercus robur, Quercus petraea, Quercus pubescens, Picea abies, Abies alba, Pinus sylvestris and Pinus halepensis), taken in pure and even-aged stands. We identified the main factors influencing tree species productivity on a national scale, and produced productivity maps suggesting that species distribution ranges are not always limited by environmental conditions. Between 1980 and 2005, the productivity trends reported were positive, modal or non-significant for all species, except the two Mediterranean species for which productivity decreased, highlighting inter-specific differences in these changes. We observed strong variations of productivity changes, both in intensity and sign, on a regional and intra-regional scale. These results question the relevance of wide-scale average assessments and highlight their context-dependence. The role of recent climatic warming in featuring the BAI trends was highlighted. This work provides an enriched scale- and species-dependent assessment of tree species reaction to a changing environment. We emphasized the species- and context dependence of productivity changes, due to differences in species autecology and spatial variations in the limiting factors. Further focus on the effect of environmental factors and their complex interactions is needed for the prediction of species future productivity
Blouin, Sébastien. "Impact de la variabilité climatique récente (1970-2002) sur le débit des rivières alimentant en eau la grande région de Québec". Thesis, Université Laval, 2006. http://www.theses.ulaval.ca/2006/23854/23854.pdf.
Texto completoAubert, Cyril. "Changements environnementaux et climatiques dans l'ouest iranien durant les 15000 dernières années : apport des assemblages fossiles de chironomes (insectes, diptères) des séquences lacustres dans les provinces de Fars (SO Iran) et d'Ardabil (NO Iran)". Thesis, Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0400.
Texto completoSeveral questions are still to be addressed in the palaeoenvironmental studies of SW Asia including: (i) the 4500 yr long delay in post-glacial expansion of the deciduous forest of Zagros, (ii) the hydroclimatic changes during the early neolithization and domestication, and (iii) the role of climate versus anthropogenic forcings in ecosystem and societal changes. Palaeoenvironmental studies in Iran can help to address the above questions because of the strategic geographical position of this country in SW Asia. According to our results, chironomids (insects - diptera), as paleohydrological bioindicators, are a promising tool to investigate climate and human impacts on ecosystems. They have proved to be very good proxies of hydrological conditions of wetlands and also to reveal anthropogenic water management interventions in the past. The comparison with other palaeoecological indicators confirmed suitability of subfossil chironomids for palaeohydrological reconstructions
Chaverot, Sylvain. "Impact des variations récentes des conditions météo-marines sur les littoraux meubles du Nord-Pas-de-Calais". Littoral, 2006. http://www.theses.fr/2006DUNK0146.
Texto completoThe aim of this doctoral dissertation is to analyse the response of low-lying sandy coasts of Nord-Pas-de-Calais to high energy events at various spatial and temporal scales. First, the evolution of the shoreline was determined by comparison of geometrically rectified aerial photographs from the second half of the XXth century. This was followed by an analysis of meteorological and tide-gauge data from three stations along the Côte d'Opale (Boulogne-sur-Mer, Calais, Dunkirk). This analysis focuses on high magnitude events (in terms of wind velocity and surge height), which likely have the most significant impacts on shorelines. To assess the potential impact of high water levels during high energy periods, on sandy shorelines at a short time-scale (event) and at a medium time-scale (several years) on macrotidal environments, meteorological and geomorphologic data have been integrated into a storm erosion susceptibility index using different parameters (water level above dune toe, event duration, height of the waves). Finally, this study includes an evaluation of the possible impacts of climate change on the evolution of unconsolidated shorelines. Some of the expected consequences on coasts include sea-level rise and an increase in storm intensity and frequency. Such scenarios would result in an acceleration of coastal erosion and more frequent flooding of low-lying sandy coastlines, which are highly vulnerable. Zones at risk of marine flooding in a vulnerable area of the Côte d'Opale are mapped
Goursaud, Sentia. "Variabilité climatique récente de l'Antarctique : apports des enregistrements issus de carottes de névé". Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAU037/document.
Texto completoDocumenting recent Antarctic climate variability is needed in order to understand the mechanisms at play, associated with the role of Antarctic mass balance for global sea level rise. Proxy records from Antarctic shallow firn cores are precious data, which complement instrumental and remote sensing observations to continuously cover the whole continent. Within these ice cores, water stable isotopes are commonly used to quantify past changes in local temperature.This PhD thesis was initiated within the French Agence Nationale de la Recherche “Improving the Accurancy of SUrface Mass balance of Antarctica” (ASUMA) project, which aims to reconstruct and to identify the processes controlling the spatio-temporal variability of the surface mass balance (SMB) in Adélie Land. I used water stable isotopes records from recently drilled shallow firn cores, as well as atmospheric simulations performed with the high resolution atmospheric general circulation model ECHAM5-wiso model, equipped with water stable isotopes, atmospheric reanalyses and back-trajectories, instrumental and remote sensing climate observations.In a first part, I assessed the skills of the ECHAM5-wiso with respect to Antarctic temperature, SMB, δ18O and deuterium excess (hereafter d-excess), as a prerequisite for the exploitation of the model to interpret isotope compositions. I developed Antarctic-wide diagnostics of the δ18O-temperature and d-excess- δ18O relationships, showing differences in the spatial, seasonal and interannual δ18O-temperature slopes. Within the international working group of PAGES (Past Global Changes) Antarctica 2k, I used the calibrations inferred from ECHAM5-wiso to reconstruct temperatures over 7 Antarctic regions from a synthesis of ice core δ18O records spanning the past 2,000 years.In a second part, new water stable isotope records from two firn core drilled in Adélie Land, the S1C1 and the TA192A, were investigated, covering the periods 1947-2007 and 1998-2014 respectively. The reconstructed SMB display a high spatial variability (74.1 ± 14.1 cm w.e. y-1 and 21.8 ± 6.9 cm w.e. y-1 for the TA192A and S1C1 respectively), consistent with Adélie Land stake data. Using an updated database of Antarctic water stable isotope datasets, I showed that the mean isotopic values (δ18O and d-excess) in Adélie Land are in line with the range of Antarctic coastal values. Statistical analyses show no relationship between our records and local surface air temperature, at the inter-annual scale, but significant relationships with atmospheric back-trajectories and isotopic simulations, suggesting that water stable isotopes in Adélie Land provide fingerprints of the variability of atmospheric dynamics and moisture transport, at the seasonal and inter-annual scales.The analyses performed during this PhD thesis have been limited by the few available Adélie Land water stable isotope records, and by the lack of understanding of deposition and post-deposition processes. Further work is thus needed to exploit the new firn cores drilled within the ASUMA project, and to monitor continuously Adélie Land water stable isotopes in precipitation, surface water vapour and surface snow, in combination with tools of atmospheric simulations such as back-trajectory simulations provided with moisture sources diagnostics, as well as water stable isotopes-enabled atmospheric general and regional circulation models
Chesnoiu, Gabriel. "Environnement solaire et pollutions atmosphériques particulaires en région Hauts-de-France : évolution récente et scénarios futurs". Electronic Thesis or Diss., Université de Lille (2022-....), 2023. http://www.theses.fr/2023ULILR061.
Texto completoThe solar radiation incident at the surface, primary source of energy for life on Earth and for photovoltaic resources, exhibits strong spatiotemporal variabilities, mainly due to the influence of atmospheric properties.The main objective of this thesis is to analyze the recent variability and future evolution of the solar environment in the Hauts-de-France region (HdF), which is characterized by a strong influence of cloudy conditions and significant levels of particulate pollution.We first use continuous coincident measurements of aerosol optical properties and incident solar radiation at the surface conducted in Lille between 2010 and 2022. The development of a classification of sunshine conditions into three categories (clear sky, cloudy sky with visible or non-visible sun) allows us to obtain solar environment climatologies for the different situations. Furthermore, the use of a multivariate decomposition based on radiative transfer simulations allows us to analyze the influence of cloud and atmospheric aerosol variability on the measured solar environment in Lille. Spring and summer, two key seasons in terms of solar resource, are marked by less cloudy conditions and high aerosol concentrations. In spring, the aerosol direct radiative effect is maximum, with an average reduction of the incident global irradiance of about -9 W/m² (-23 W/m² in the absence of clouds in the direction of the Sun). Aerosols significantly alter the partition between direct and diffuse solar radiation, increasing the proportion of diffuse irradiance by a factor of 2 on average under clear skies. In Lille, our analysis also highlights a trend over the study period of increasing global and direct solar flux (approximately +4 W/m²/year) for these two seasons, in connection with a decrease in the frequency of cloudy conditions.To spatially extend the study conducted in Lille to the entire HdF region and its surroundings, we use climate simulations from the ALADIN-Climat regional model, which includes the TACTIC aerosol scheme. Analysis of a first set of HINDCAST simulations for the period 2010-2020 shows satisfactory comparisons with flux and aerosol measurements from several sites in our study area. This approach also highlights maximum sunshine and global flux in spring and summer, especially in the southern part of the study region, the English Channel, and the North Sea, as well as particularly high levels of aerosols over the Benelux and the HdF region. Furthermore, the recent increasing trend of the global irradiance measured in Lille due to the decrease in the frequency of cloudy conditions is confirmed by ALADIN-Climat over a large part of the region. Finally, using three additional sets of ALADIN-Climat simulations in climate mode, we analyze the possible future evolution, in spring and summer, of the solar environment in 2050 and 2100 compared to the period 2005-2014 for two contrasting CMIP6 climate scenarios. For the relatively optimistic SSP1-1.9 scenario, ALADIN-Climat projects an increase in global flux in spring and summer in 2100, especially over England and the eastern part of the study area, in connection with a coincident decrease in cloud cover and aerosols. For the more pessimistic SSP3-7.0 scenario, ALADIN-Climat simulates, on the contrary, a significant decrease in global flux across the entire region for both seasons, in connection with an increase in aerosols and water vapor. In summer, ALADIN-Climat simulates a decrease in cloud cover that compensates for these initial effects, more so in 2050 than in 2100. In spring, the simulations project an increase in cloud cover, which amplifies the decrease in global flux as early as 2050
Maciejewski, Lise. "Reconnaissance et dynamique récente des habitats forestiers dans le contexte de la Directive Habitats-Faune-Flore". Electronic Thesis or Diss., Paris, AgroParisTech, 2021. http://www.theses.fr/2021AGPT0001.
Texto completoIn 1992, European natural habitats became items to be conserved in the same way as species were, thanks to the Habitats Directive. This enlarged the scope of action of nature protection public policies to a new level of biodiversity organisation. But the late recognition of the conservation value of habitats and the gaps in their definitions partly explain the absence of time series data at the national scale. This limits our capacity to monitor and assess their conservation status and to adapt conservation measures at the national and local levels. The present thesis work first investigates rapid, formalised approaches for identifying forest habitats. Then, these approaches are used to study the recent dynamics of forest habitats in relation to two substantial changes that occurred in the past decades, i.e., climate warming and the creation of the Natura 2000 network.We first studied the uncertainties linked to the identification of forest habitats when assigning floristic surveys to habitat types by comparing five expert’s judgements with three automatic classification programs. We highlighted high variability among expert judgements, and comparable efficiency between automatic classification programs and expert judgements. We also demonstrated that a limited number of species was sufficient to identify forest habitats, and that surveys carried out in winter could be used too. We thus created time series of standardised data on forest habitats based on different floristic survey sources, whether assigned to a habitat type or not.Secondly, we created 5,701 pairs of historical (before 1987) and recent (after 1997) floristic surveys, and highlighted that 11% of the pairs located in highlands had shifted towards forest habitats characteristic of warmer climate conditions. The increased dominance of these habitats led us to conclude that thermophilisation was underway in highlands. However, no significant shift was observed in lowlands, hence a substantial difference between the thermal requirements of plant communities and current temperatures: a climatic debt is developing. In the face of these different impacts, we proposed that nature protection public policies could be more efficient if they were implemented and prioritised differently in highlands vs. lowlands.Finally, we studied 155 Natura 2000 sites distributed across mainland temperate and mountainous France, and showed that the number of very large trees in the plots where they were observed had increased significantly more inside the network than outside it since its implementation. We thus evidenced that the conservation measures implemented in Natura 2000 forests, which are managed and exploited, have already had positive effects on very large trees – considered as a characteristic of old-growth forests and also used as biodiversity and conservation status indicators of forest habitats.This thesis work was necessary to complement the numerous studies already available at the species and plant community scales, for it is indispensable to aim for the simultaneous conservation of all the levels of organisation of biodiversity to be efficient. Knowing the scope of validity of the tools used to identify forest habitats, but also understanding the recent dynamics of forest habitats and its influencing factors provide useful data to implement surveillance and adapt public policies and management actions, and thereby reach greater efficiency
Herlédan, Maïwenn. "Biodiversité des amibes à thèque et environnements de l'archipel de Kerguelen : caractérisation actuelle et évolution récente sous contrainte climatique". Electronic Thesis or Diss., Université de Lille (2022-....), 2023. http://www.theses.fr/2023ULILR002.
Texto completoThe objective of this PhD is to describe the current diversity of testate amoebae on the Kerguelen archipelago depending on climate and environmental context and to understand the recent evolution of the last 260 years by a paleoenvironmental approach combining microscopic observations, sedimentology and geochemistry. Located at the polar front in the sub-Antarctic zone, the Kerguelen archipelago is subject to extreme wind and precipitation conditions while being preserved from direct anthropic impacts. This makes it an ideal natural environment to study the impact of global climate change on the environment.Two scientific campaigns on the Kerguelen archipelago in 2019 and 2021 have allowed us to collect samples of current plants (mainly bryophytes and azorelles), underlying soils and soil cores. The samples studied were selected to reflect the geographical and geological diversity of the archipelago, in terms of rainfall (west-east contrast), sedimentary nature (organic soil, alluvial sediments, etc.. ) and petrographic context (basalts - phonolites). Optical observations of the testate amoebae communities growing in the plant samples (101 samples) have allowed us to build a new database of testate amoebae in the archipelago. Sedimentological and geochemical analyses (water content, elemental and isotopic analyses, mineralogy) were carried out in parallel on 485 soil samples in order to characterize the environmental parameters.This work has allowed to update and complete the 1981 database of 50 species with the description of 107 species of testate amoebae. Sedimentological analyses of soils revealed significant differences in terms of weathering between the western and eastern parts of the archipelago, reflecting contrasting rainfall patterns. This trend is also reflected in the testate amoebae assemblages whose diversity, variable according to the type of environment, is much greater in the west. The coupling of these different observations has made it possible to highlight the ecological affinities of certain species with specific environments, which depend mainly on the water content of the sediment, the type of environment and the vegetation, thus allowing the definition of indicator species. The use of this approach to reconstruct recent paleoenvironments from the different soil cores has allowed us to highlight local changes in the environment, which could be attributable to recent climate change. This study demonstrates the relevance of testate amoebae not only as an environmental indicator but also for tracing the recent evolution of paleoenvironmental conditions under climatic constraints
Massuel, Sylvain. "Evolution récente de la ressource en eau consécutive aux changements climatiques et environnementaux du sud-ouest Niger. Modélisation des eaux de surface et souterraines du bassin du kori de Dantiandou sur la période 1992-2003". Phd thesis, Université Montpellier II - Sciences et Techniques du Languedoc, 2005. http://tel.archives-ouvertes.fr/tel-00011097.
Texto completoDans cet objectif, une régionalisation du modèle de fine échelle abc-rwf a été réalisée à partir d'un jeu simulé de 50 bassins endoréiques, pour lesquels des relations entres les descripteurs physiographiques et le ruissellement calculé sont apparues significatives. La formulation d'une fonction représentant fidèlement le ruissellement simulé d'un bassin, peut être étendue à un ensemble de bassins par l'adjonction de fonctions prédictives non linéaires paramétrées sur la base de seulement 5 descripteurs physiographiques des bassins. Le modèle de méso-échelle Zarbhy permet ainsi un calcul simplifié du ruissellement des 377 bassins endoréiques identifiés sur les 5000 km² du bassin tout en limitant l'imprécision supplémentaire par rapport au modèle abc rwf.
La réalisation du couplage surface-souterrain soulève une insuffisance de la recharge forcée par le ruissellement calculé sur certaines années pour permettre la simulation de la hausse de la nappe dans des gammes de paramétrisation admissibles. Bien que l'extrême variabilité des processus hydrologiques disparaisse en partie à l'échelle régionale, la variabilité intersaisonnière demeure encore difficile à reproduire.
Le schéma de la recharge ponctuelle spatialement distribuée est compatible avec la modélisation hydrodynamique réalisée, qui dans son état actuel ne permet cependant pas de quantifier avec précision l'influence de la recharge indirecte sur la dynamique de hausse de la nappe.
Face à l'insuffisance de la recharge calculée, une étude combinant géophysique électrique, géochimie et modélisation hydrologique a été entreprise. Elle suggère le lessivage d'une bande minéralisée entre 5 et 10 m de profondeur à l'aplomb des multiples chenaux sableux de la zone d'épandage de Wankama. Cette expérimentation prometteuse ouvre la voie à de nouvelles investigations vers la caractérisation des processus de recharge. L'existence d'une infiltration profonde (>25 m) au moins épisodique, sous les zones d'épandage sableuses peut être envisagée.
Massuel, Sylvain. "Évolution récente de la ressource en eau consécutive aux changements climatiques et environnementaux du sud-ouest du Niger : modélisation des eaux de surface et souterraines du bassin du kori de Dantiandou sur la période 1992-2003". Montpellier 2, 2005. http://www.theses.fr/2005MON20093.
Texto completoCartapanis, Olivier. "Variabilité de la zone de minimum d’oxygène du Pacifique Est équatorial au cours du Quaternaire récent". Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4365/document.
Texto completoThis thesis aims at documenting the spatiotemporal variations of the Oxygen Minimum Zone (OMZ) of the northeastern Pacific, and identifying the mechanisms that caused theses variations. The study is based on the geochemical analyses of major, minor, and trace elements of sediments from the northeastern Pacific, by combining ICP-MS and XRF scans measurements. These measurements allowed distinguishing the effect of biologic productivity and oceanic ventilation on sediment oxygenation. I was able to highlight the predominant impact of the productivity off the Baja California Margin (23°N), which varied in phase with the high northern Atlantic temperature across the past 120,000 years. Moreover, oceanic ventilation did play an important role off the Papagayo Gulf (12°N), because of the advection of water mass coming from the high northern and southern latitudes. OMS intensity in the northeastern Pacific could thus be influenced by changes in the atmospheric and oceanic circulation, in relation to high northern and southern latitudes climates
Jebri, Beyrem. "Attribution et reconstruction du rôle de la variabilité interne et des forçages externes sur le climat passé récent et du dernier millénaire". Electronic Thesis or Diss., Sorbonne université, 2020. http://www.theses.fr/2020SORUS162.
Texto completoUsing large ensembles of IPSLCM5A model simulations, we first investigate the roles of internal variability (and in particular the IPO) and external forcing in driving recent Peru-Chile regional cooling. The simulations reproduce the relative cooling, in response to an externally-forced southerly wind anomaly, which strengthens the upwelling off Chile in recent decades. This southerly wind anomaly results from the expansion of the Southern Hemisphere Hadley Cell in response to increasing greenhouse gases and stratospheric ozone depletion since ~1980. An oceanic heat budget confirms that the wind-forced upwelling dominates the cooling near the coast while a wind-forced deepening of the mixed layer drives the offshore cooling, irrespectively of the IPO phase, hence indicating the preeminent role of external forcing. Constraining the climate sensitivity from observations remains however fraught with uncertainties due to the limited instrumental window of observation. In a second part, a data assimilation method is developed to reconstruct past natural variability relying on a particles filter using CMIP-class climate models. Such method is confronted with a problem of degeneracy associated with the resolution of a large problem with a limited number of particles. This issue has been resolved using a statistical emulator of the IPSL model (LIM) as an integration model in a particle filter with resampling. The validation of this new method, called SIR-LIM, allows the reconstruction of the climate variability of the past centuries by assimilating observations and proxy records into a CMIP-class coupled model while preserving the physical coherence along the simulation
Chouinard, Christian. "Reconstitutions des températures de surface au Canada : des températures basales du glacier laurentidien aux changements récents du climat arctique". Thèse, 2008. http://www.archipel.uqam.ca/876/1/D1648.pdf.
Texto completoGenovesi, Linda. "Indices micropaléontologiques et géochimiques de changements récents de l'oxygénation et la température des eaux profondes du Golfe du St-Laurent". Mémoire, 2009. http://www.archipel.uqam.ca/2363/1/M11005.pdf.
Texto completoMujica, Marialejandra. "Reconstitution des taux récents d’accumulation de carbone et des conditions paléoécologiques de la tourbière boréale Degerö Stormyr, Suède". Thèse, 2016. http://hdl.handle.net/1866/18725.
Texto completoIn the event that the important carbon reservoir sequestered in peatlands were to be destabilized, the impacts on global climate could be major. However, the factors influencing carbon accumulation rates at decadal and centennial scale in peatlands have not yet been clearly identified and past and contemporary carbon accumulation dynamics of the same study site have rarely been compared. This project aimed to (1) reconstruct fine scale (cm) carbon accumulation rates for the Degerö Stormyr peatland (Sweden), (2) identify the key factors influencing accumulation rates and (3) compare the reconstructed rates to modern carbon fluxes measured at the site. Two complementary methodological approaches were used: paleoecological reconstructions and modelling. The main conclusions of this thesis are that: (1) Apparent rates of carbon accumulation are mainly related to hydroclimatic conditions in the acrotelm, but are influenced by the vegetation composition of the peat in the catotelm. (2) True rates of carbon accumulation for the recent period (≈ last 130 years) are similar to the net ecosystem carbon balance measured on site. (3) The comparison between recent and long-term carbon accumulation dynamics suggests that Degerö Stormyr has sequestered more carbon over the past decades. The results of this thesis highlight the importance of studying factors influencing carbon accumulation rates at different time scales and suggest that emphasis should be placed on decadal and centennial scales.
Aguiar, Lazar Augustin A. "Impact de la variabilité climatique récente sur les écosystèmes des Niayes du Sénégal entre 1950 et 2004". Thèse, 2009. http://www.archipel.uqam.ca/2222/1/D1774.pdf.
Texto completoLoisel, Julie. "Reconstitution paléoécologique de deux tourbières boréales à l'holocène récent dans le bassin versant de la Rivière Eastmain, Baie James, Québec". Mémoire, 2009. http://www.archipel.uqam.ca/2291/1/M10987.pdf.
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