Global ETD Search

1	Samband mellan vulkanutbrott och klimatförändringar : Analys och värdering av teorier om vulkanisk aska och gasers påverkan på det globala klimatet Johansson, Eva January 2015 (has links) This literature review analyses and discusses different theories and results regarding impact of volcanic eruptions on climate change in Earth's history. Present global warming has been attributed to anthropogenic emissions of greenhouse gases, mainly carbon dioxide, however changes in global temperatures have occurred before the onset of anthropogenic emissions. Certain prehistoric climate changes are thought to be caused by emissions of volcanic gases to the atmosphere. Many studies have investigated the connection between volcanic events and subsequent changes in global temperatures. A majority have concluded that volcanic sulfur dioxide is the main direct and indirect climate forcing gas influencing temperatures over time. Increased volcanic activity over the last 15 years is thought to be an inhibiting factor on present global warming. This is supported by evidence of past volcanic events preceding global cooling and warming periods during Holocene and prehistoric times. Further, there are indications that factors such as geographical position, season, gas composition, magnitude and duration of an eruption influences the extent of the climate forcing.Records of climate such as ice cores and tree growth rings and isotopic characterization have made it possible to identify volcano eruptions over time and determine the identity of the erupting volcano. Past and present data from these can be used to gain a better understanding of past climate changes as well as making predictions about future changes as a result volcanic eruptions. However, accuracy regarding temporal and spatial resolution of these records is of great importance for the validity of the results. sulfur dioxide volcanic gases climate forcing stratosphere volcanoes
2	Ecology of marine turtles under climate change Stokes, Kimberley Laura January 2014 (has links) Climate change threatens to disrupt biological systems around the globe, sparking debate over natural capacity for adaptation in a fragmented landscape. Marine turtles are evolutionarily ancient and have survived millions of years of prehistoric climate change, but are threatened by the rapidity of modern warming and a history of severe overexploitation that has left most populations depleted. This thesis explores a nesting aggregation of the green turtle (Chelonia mydas) in northern Cyprus, where a longitudinal programme of both intensive and extensive monitoring enables insight into individual and population level parameters and processes. Nesting on the two coastlines covered by this project is in the early stages of recovery, possibly in response to exhaustive nest protection efforts over the last twenty years. Saturation tagging at one key site allows us to confirm that recruitment of new breeders is an important driver of this trend, and that average clutch frequency has remained stable around three nests per female per year, validating nest-count derived abundance estimates at a regional scale. Concern has been raised, however, regarding recent changes in fishing practices which are impacting the local juvenile neritic phase, which may have a lagged effect on the recovery of this nesting population. A collaborative tracking effort including all other countries with major nesting in the Mediterranean allows us to identify major foraging grounds for this species, with two hotspots accounting for >50% of tracked individuals, as well as coastal and pelagic seasonal corridors of high use. Bycatch levels and mortality rates for turtles in these key areas are largely unknown and should be prioritised for investigation. Hatchling sex ratios from the main study beach are extremely female-biased (estimated 97% female for the twenty year period 1993-2012). A 1oC rise in average incubation temperatures threatens near complete hatchling feminisation on this beach, whilst a 2oC rise could reduce hatch success to less than 50%. Thermal effects on hatchling morphometrics are evident, with a 1oC rise in temperature reducing average length, width and weight by 1%, 2% and 3% respectively. More favourable incubation conditions were found early in the season, in deeper nests laid by larger females, and on beaches of lighter sand. In contrast, adult sex ratios at the main site are male-biased, posing questions regarding sex-specific survival rates and optimal hatchling sex ratios. A phenological shift towards earlier nesting is demonstrated for the first time in this species, and could potentially ameliorate warming effects. Carry-over climate forcing effects from the foraging ground influence the breeding frequency of individuals, driving population level responses in annual magnitude of nesting. This work emphasises the utility and necessity of long-term individual-based monitoring programmes in elucidating population trends and climate responses in iteroparous species with non-annual breeding. 597.92
3	Du plateau au fond de vallée : apport de l'étude de trois sites archéologiques à la compréhension des dynamiques géomorphologiques holocènes en Normandie / From the plateau to the valley : contribution of three geoarchaeological studies to the comprehension of geomorphological dynamics during the Holocene in Normandy Gonnet, Adrien 27 October 2017 (has links) Depuis la fin du Pléistocène, l’évolution des conditions environnementales et les pratiques anthropiques ont influencé les dynamiques morpho-sédimentaires des bassins versants du Nord-Ouest européen. Les petits hydrosystèmes sont particulièrement sensibles à ces évolutions qui s’expriment dans les archives sédimentaires. La démarche adoptée confronte les données des géosciences, de l’archéologie et de la géomorphologie, pour appréhender les interrelations Homme/climat/environnement durant l’Holocène en Normandie. En étudiant les archives pédo-sédimentaires de trois sites archéologiques des plateaux aux fonds de vallée, l’objectif est de discriminer les forçages climato-anthropiques pour chaque épisode d’érosion/sédimentation. L’étude des plateaux normands à Villers-Ecalles dévoile une intense troncature érosive des luvisols holocènes à la fin de La Tène. Les colluvions stockées en fond de vallon soulignent la continuité des dépôts et l’intensification de l’érosion à l’époque moderne. Les archives sédimentaires de Brionne, en pied de versant, ont révélé la séquence Tardiglaciaire et la diagenèse tufacée du début de l’Holocène. La séquence holocène d’une vallée littorale, la Scie, permet de reconstituer son évolution diachronique, les dynamiques morpho-sédimentaires et l’évolution du couvert végétal. L’étude des sites met en évidence la synchronicité de certains événements, malgré des épisodes parfois locaux. Les schémas d’évolution s’inscrivent dans le contexte bien documenté du Bassin parisien. La comparaison des séquences témoigne de la complexité des réponses aux interactions Homme/milieu et d’une mosaïque de pression anthropique différentielle pendant l’Holocène. / Since the end of the Pleistocene, the variations of environmental and anthropic conditions influenced the morpho-sedimentary dynamics of North-Western european catchments. The small hydrosystem are very sensitive to these evolutions, recorded in sedimentary archives. Our approach confronts geoscience, archaeology and geomorphological data, in order to apprehend the interrelationships between Human activity, climate and environment during the Holocene in Normandy. By studying the sedimentary archives from three settlements, from the plateau to the valleys, our aim is to discriminate climato-anthropic forcing for each episode of erosion and sedimentation. The three sites, located in small catchments, give pedo-sedimentary references for each geosystemic unit. The study a loessic plateau shows an intense erosion of Holocene luvisol since the end of La Tene period. The colluvial deposits, accumulated in a dry valley show the continuity of detrital sedimentation, and the intensification of erosional processes during modern times. At the bottom of a slope, the study of Brionne’s sedimentary archives reveals the Late Glacial sequence and the tufa diagenesis at the early Holocene. The Holocene sequence on a small coastal valley, la Scie, allows to reconstruct its diachronical evolution, the morphosedimentary dynamics and the landcape evolution. The diachronical evolution of these three sites shows the synchronicity of events, even if some ones appear to be local. These data enter in the well-documented context of the Paris Basin. Comparing those sequences has revealed the spatial and chronological complexity of the landscape responses to the human and climate forcing. Géoarchéologie Normandie Holocène Forçages anthropiques Forçages climatiques Dynamiques morpho-sédimentaires Bassin parisien Nord-Ouest européen Geoarchaeology Normandy Holocene Human and climate forcing Morphosedimentary dynamics Paris Basin North-Western Europe 910.02
4	Multispectral imaging of Sphagnum canopies: measuring the spectral response of three indicator species to a fluctuating water table at Burns Bog Elves, Andrew 02 May 2022 (has links) Northern Canadian peatlands contain vast deposits of carbon. It is with growing urgency that we seek a better understanding of their assimilative capacity. Assimilative capacity and peat accumulation in raised bogs are linked to primary productivity of resident Sphagnum species. Understanding moisture-mediated photosynthesis of Sphagnum spp. is central to understanding peat production rates. The relationship between depth to water table fluctuation and spectral reflectance of Sphagnum moss was investigated using multispectral imaging at a recovering raised bog on the southwest coast of British Columbia, Canada. Burns Bog is a temperate oceanic ombrotrophic bog. Three ecohydrological indicator species of moss were chosen for monitoring: S. capillifolium, S. papillosum, and S. cuspidatum. Three spectral vegetation indices (SVIs) were used to characterize Sphagnum productivity: the normalized difference vegetation index 660, the chlorophyll index, and the photochemical reflectance index. In terms of spectral sensitivity and the appropriateness of SVIs to species and field setting, we found better performance for the normalized difference vegetation index 660 in the discrimination of moisture mediated species-specific reflectance signals. The role that spatiotemporal scale and spectral mixing can have on reflectance signal fidelity was tested. We were specifically interested in the relationship between changes in the local water table and Sphagnum reflectance response, and whether shifting between close spatial scales can affect the statistical strength of this relationship. We found a loss of statistical significance when shifting from the species-specific cm2 scale to the spectrally mixed dm2 scale. This spatiospectral uncoupling of the moisture mediated reflectance signal has implications for the accuracy and reliability of upscaling from plot based measurements. In terms of species-specific moisture mediated reflectance signals, we were able to effectively discriminate between the three indicator species of Sphagnum along the hummock-to-hollow gradient. We were also able to confirm Sphagnum productivity and growth outside of the vascular growing season, establishing clear patterns of reflectance correlated with changes in the local moisture regime. The strongest relationships for moisture mediated Sphagnum productivity were found in the hummock forming species S. capillifolium. Each indicator Sphagnum spp. of peat has distinct functional traits adapted to its preferred position along the ecohydrological gradient. We also discovered moisture mediated and species-specific reflectance phenologies. These phenospectral characteristics of Sphagnum can inform future monitoring work, including the creation of a regionally specific phenospectral library. It’s recommended that further close scale multispectral monitoring be carried out incorporating more species of moss, as well as invasive and upland species of concern. Pervasive vascular reflectance bias in remote sensing products has implications for the reliability of peatland modelling. Avoiding vascular bias, targeted spectral monitoring of Sphagnum indicator species provides a more reliable measure for the modelling of peatland productivity and carbon assimilation estimates. / Graduate peatland peatland restoration peatland monitoring peatland modelling peat peat moss multispectral multispectral imaging multicamera array multitemporal multiple linear regression linear mixed effects Sphagnum sphagna Sphagnum capillifolium Sphagnum papillosum Sphagnum cuspidatum spatiospectral uncoupling near-sensing remote sensing phenospectral phenology phenologies phenospectral bias phenospectral libraries carbon assimilation carbon dioxide carbon dynamics carbon emissions carbon geographies carbon mineralization carbon sequestration carbon source carbon sink carbon storage irrecoverable carbon climate forcing methane Ecological Restoration restoration ecology ecohydrology ecohydrological restoration hydrology ecohydrological gradients ecological integrity reflectance nature based solutions ombrotrophic moss raised peatland mires mires photochemical reflectance index normalized difference vegetation index chlorophyll index climate change climate forcing climate envelope climatope nonvascular vascular bias plant functional type plant functional types structure equation models spectral vegetation indices hummock hollow acrotelm catotelm diplotelmic biocrusts organic soil periodicity moisture deficit senescence rejuvenescence productivity photosynthesis light use efficiency photosynthetic function photosynthetically active radiation water table hydrology rewetting depth to water table landscape change landscape degradation peat subsidence Burns Bog

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