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Evaluation de l'archive naturelle cernes d'arbre comme traceur du climat passé au nord de la Patagonie / Evaluation of tree-ring archive as paleoclimatic tracer in northern PatagoniaLavergne, Aliénor 08 January 2016 (has links)
L’Hémisphère Sud, et plus précisément le sud de l’Amérique du Sud, sont très sous-représentés dans les reconstitutions climatiques globales du fait d’un manque de données paléoclimatiques robustes. Mes travaux de thèse ont donc porté sur l’évaluation de l’archive naturelle cernes d’arbre, abondante le long de la Cordillère des Andes, comme traceur paléoclimatique. Je me suis ainsi appliquée à étudier la réponse régionale de deux espèces d’arbre (Fitzroya cupressoides et Nothofagus pumilio) natives du nord de la Patagonie (41°S, Argentine) aux forçages climatiques externes en analysant leurs différents paramètres physiques. Pour cela, j’ai commencé par déterminer l’influence du climat local et de grande échelle sur leur croissance en étudiant les variations temporelles de leurs largeurs de cerne, puis j’ai essayé d’extraire le signal climatique enregistré dans la composition isotopique de l’oxygène et du carbone de la cellulose de ces cernes. Deux résultats majeurs de ma thèse ont émergé: j’ai mis en évidence (1) des réponses non-linéaires de la croissance au cours du temps liées aux changements de régimes climatiques et, (2) le fort potentiel du delta18O et delta13C de la cellulose pour enregistrer les variations de température d’été-automne sur une large région aux latitudes moyennes de l’Amérique du Sud (35°-55°S). Du fait des relations fortes qui les lient aux températures, les outils isotopiques peuvent être utilisés pour reconstituer des chronologies de température mais aussi des modes climatiques tels que l’Oscillation Antarctique. / The Southern Hemisphere, and particularly southern South America, are very under-represented in global climate reconstructions due to a lack of robust paleoclimatic data. My thesis was therefore focused on the evaluation of the tree-ring archive, which is widespread along the Andes, as a paleoclimatic tracer. I studied the regional response to external climate forcing of two native species (Fitzroya cupressoides and Nothofagus pumilio) in northern Patagonia (41°S, Argentina), by analysing their different physical tree-ring parameters. In this perspective, I analysed the temporal variations of the width and of the oxygen and carbon isotopic compositions of the cellulose of their rings and related them to local and large-scale climate variations. Two major results of my thesis have emerged: I highlighted (1) non-linear growth responses over time related to shifts in climate regimes and, (2) the potential of cellulose delta18O and delta13C to record summer-autumn temperature variations over a large area in the mid latitudes of South America (35°-55°S). As their variations are strongly linked to temperature the isotopic tools can be used to reconstruct chronologies of temperature but also of climate modes such as the Southern Annular Mode.
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Climate and Vegetation Change in Late Pleistocene Central Appalachia: Evidence fromStalagmites and Lake CoresBaxstrom, Kelli W. 04 June 2019 (has links)
No description available.
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Testing Spillover of Nocturnal Predators in Agroecosystems: The Influence of Ditch Type and Prey AvailabilityWoloschuk, John Robert 26 November 2019 (has links)
No description available.
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Holocene Climate Change in the Subtropical Eastern North Atlantic: Integrating High-resolution Sclerochronology and Shell Midden Archaeology in the Canary Islands, SpainParker, Wesley G. 02 June 2020 (has links)
No description available.
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Geochemistry of soils from the Shackleton Glacier region, Antarctica, and implications for glacial history, salt dynamics, and biogeographyDiaz, Melisa A. January 2020 (has links)
No description available.
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The Influence of Diet and Foraging Behavior on Carotenoid Ornaments in the Brown Booby (<i>Sula leucogaster</i>)Michael, Nathan January 2020 (has links)
No description available.
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Investigating surface spring snow : Changes in the isotopic composition and conductivity along an orographic precipitation gradient in northern Fennoscandia / Undersökning av ytsnö på våren : Förändringar av isotopsammansättning och konduktivitet längs en nederbördsgradient i norra FennoskandiaAndersson, Sara January 2023 (has links)
Stable isotopes of oxygen (O18) and hydrogen (H2) are used as proxies of past climates when ice preserved in the polar icecaps. The main assumption when doing paleoclimatic reconstructions using these isotopes is that the isotopic composition of the snow that turned into ice reflect the present temperature of the planet during deposition. In this study, I investigate to what extent the composition of O18 and H2 varies as a function of precipitation. I tested the following hypotheses: i) δO18 and δH2 decreases due to fractionation during orographic fallout, and ii) the electric conductivity in the snow decreases with distance from sea due to fading marine inputs. The hypotheses were tested with field samples gathered along a precipitation gradient from the Norwegian coast to Kiruna, Northern Sweden. To support my first hypothesis, I found a decrease from -9.32% δO18 (-54.85% δH2) to -25.48% δO18 (-109.54 % δH2) due to orographic deposition over the Scandes with a drastic drop in Abisko caused by a rain shadow. Similarly, I found a considerable variation and decreasing trend of conductivity along the precipitation gradient. My study raises awareness that δO18 in snow is in fact dependent on precipitation regimes rather than temperature regimes in this area, which should be considered when interpreting environmental records of δO18 in a paleoclimatic context. Lastly, I suggest further studies targeting the effects of post-depositional processes (melting, sublimation, and anthropogenic influence) on the isotopic composition and conductivity, especially with a changing climate.
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Persistence in a Changing World: Bison and Horse Dietary Niche, Body Size, and Relative Abundance in Late Pleistocene BeringiaKelly, Abigail 14 July 2022 (has links)
No description available.
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Transport of Deuterium-Labeled Tocopherols During PregnancyAcuff, Robert V., Dunworth, Robert G., Webb, Lisa W., Lane, Jonathan R. 01 January 1998 (has links)
With use of deuterium-labeled isotopes of RRR-and all-rac-α-tocopheryl acetate, the transport of vitamin E in pregnancy was evaluated to determine whether the placenta discriminates between these compounds. Fifteen pregnant subjects were recruited 5 d before delivery to receive 15, 30, 75, 150, or 300 mg vitamin E/d in capsules containing d3-RRR-α-tocopheryl acetate and d6-all-rac-α-tocopheryl acetate (1:1, by wt). Maternal blood was obtained before dosing, at hospital admission, and at parturition. Cord blood samples were obtained at parturition. Deuterium-labeled and unlabeled tocopherol contents were determined by gas chromatography-mass spectrometry in plasma and lipoproteins (chylomicrons, VLDL, LDL, and HDL). Maternal plasma and lipoproteins obtained at delivery had higher concentrations of d3-RRR-α- tocopherol than d6-all-rac-α-tocopherol regardless of the vitamin E dose administered (P < 0.05). Cord plasma at delivery also had higher concentrations of d3-RRR-α-tocopherol than d6-all-rac-α-tocopherol in plasma irrespective of the dose administered (P < 0.05). In lipoproteins isolated from cord blood, tocopherol concentrations were greatest in the HDL fraction (P < 0.05), whereas in maternal blood they were greatest in the LDL fraction (P < 0.05). We conclude that the placental-fetal unit, the fetal liver, or both further discriminate between RRR- and all-rac-α-tocopherol.
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The Nature and Origin of Pebble Dikes and Associated Alteration: Tintic Mining District (Ag-Pb-Zn), UtahJohnson, Douglas M 01 November 2014 (has links) (PDF)
In many ore deposits throughout the world, brecciation often accompanies or occurs in association with mineralization (Sillitoe, 1985). Such is the case in the Tintic Mining District (Ag-Pb-Zn) of north-central Utah, where unique breccia features called pebble dikes occur alongside significant mineralization. Pebble dikes are tabular bodies of breccia, which consist of angular to rounded clasts of quartzite, shale, carbonate, and minor igneous rock cemented in a fine-grained clastic matrix. All clasts now lie above or adjacent to corresponding source rocks. Dikes are thin, typically less than 0.3 m wide to as much as 1 m, and can exceed 100 m in length. The average of the largest clast sizes is less than 3 cm but correlates positively with pebble dike width. Contacts are sharp and an envelope of fine breccia surrounds roughly half of the dikes. Pebble dikes are mostly hosted in an Eocene rhyolite lava flow, which displays argillic to silicic alteration when in contact with a pebble dike, but are also hosted in an assortment of folded Paleozoic sedimentary rocks. The dikes show a strong northeast trend in orientation, following a regional fabric of northeast-trending strike-slip and oblique-slip faults.The formation of pebble dikes has been historically attributed to the intrusion of the Silver City Stock, the Tintic District's main productive intrusion (Morris and Lovering, 1979; Hildreth and Hannah, 1996; Kim, 1997; Krahulec and Briggs, 2006). However, pebble dikes are spatially associated with a previously unrecognized porphyritic unit, informally named the porphyry of North Lily, which is texturally, mineralogically, and chemically distinct from the Silver City Stock, and like pebble dikes, is emplaced in northeast-trending plugs and dikes. Pebble dikes show a strong spatial correlation to outcrops of the porphyry of North Lily. Additionally, clasts of the porphyry of North Lily have been found in pebble dikes, while pebble dike quartzite clasts have been found as xenoliths in the porphyry of North Lily. These similarities and interactions suggest simultaneous formation. Low-grade alteration associated with pebble dikes indicates that they formed at elevated temperatures (<150°C). Stable isotope characteristics of rhyolite altered during the emplacement of pebble dikes suggests that the dikes formed in the presence of heated groundwater, with little to no magmatic water association. The overall physical, spatial, and chemical characteristics of pebble dikes of the Tintic Mining District suggest that they formed by the mobilization of breccia in the explosive escape of groundwater that had been heated by the porphyry of North Lily. This escape occurred along pre-existing northeast-trending faults and fractures. Pebble dikes then became pathways for later ore fluids, easing the creation of the district's abundant mineral resources.
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