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Chevalier, Manuel. "Quantified Reconstructions of late Quaternary southern African Climate Change." Thesis, Montpellier, 2015. http://www.theses.fr/2015MONTS281.
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Pas de résumé en françaisSouthern African drylands are not suited for the application of climate reconstruction methods based on surface samples. Methods based on the co-existence approach, while still in their early days, are really promising, particularly those using probability density functions (pdfs) that have proven particularly valuable in certain cases as they can be applied to a wide range of plants assemblages. Most commonly applied to fossil pollen data, their performance can be limited by the taxonomic resolution of the pollen data, as many species may belong to a given pollen-type. Consequently, climate information associated with a taxon cannot always be precisely identified, resulting in less accurate reconstructions. This can become particularly problematic in regions of high biodiversity, such as southern African botanical hotspots. The first part of this PhD thesis presents the development of a novel pdf-based climate reconstruction method adapted to the southern African context. The method, which comes along with a dedicated software pack- age entitled CREST, sorts out this diversity issue by taking into account the different climatic requirements of each species constituting the broader pollen-type: pdfs are fitted in two successive steps, with parametric univariate pdfs fitted first for each species (pdfsp) followed by a combination of those individual species pdfs into a broader single pdf to represent the pollen-type as a unit (pdfpol). The curve resulting from the multiplication of the pdfpol describes the likelihood of different climate parameters based on the co-existence of a given set of taxa, each being weighted according to its normalized pollen percentage. Three majors properties were derived from this continental-scale statistical analysis: 1) the method saturates when the number of species composing a pollen type becomes larger than 30-40 species, 2) the per- formance decreases with distance to the core of the climatic space and 3) climate variables that have a direct impact of plant life cycles are better reconstructed.We revisited 13 pollen sequences (selection based on their length, continuity, chronology and pollen diversity) from southern African literature with the CREST method. To offset the limited individual potential of those sequences, we developed a Monte-Carlo framework to create interpolated curves integrating uncertainties associated with the reconstructions and age-depth models and then stack those curves together to extract regionally consistent patterns. This reanalysis allows for the quantified reconstruction of a range of distinct climatic variables from this critical region, and provides significant insight into the nature of long-term climate change. Temperature reconstructions show strong coherency among all sites considered, and parallel southwest Indian Ocean SSTs. Reconstructions of the amount of summer precipitation since mid-MIS 3 (Marine Isotope Stage 3) 45,000 years ago indicate a dichotomy in the precipitation pattern between interior and northeastern South African sites. At the glacial-interglacial timescale, precipitation in northeastern sites shows strong similarities with the Indian Ocean SST records as well as with records from the large East African lakes. Entering the Holocene, precessional forcing becomes more important and a north/south rainfall dipole appears, with a demarcation line located somewhere between Lakes Tanganyika and Malawi (3-9°S). Sites from the interior, while clearly following a similar dynamic, also appear to be sensitive to additional factors, including the position of the southern Westerlies, which may interact with tropical systems to create tropical-temperate troughs. Our results shed light on the complexity of the mechanisms driving South African rainfall, and clarify several key elements of the current debate, including limitations of models relying on direct insolation forcing to explain long-term climate dynamics
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余耀良 and Yiu-leung Yieu. "OSL dating of sediment and climate change of late quaternary." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hdl.handle.net/10722/192989.
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The objective of this project is to apply the Optical Stimulated Luminescence (OSL) technique to date the palaeo sediment from Mu Us Desert, part of the Inner Mongolia in northern China and reconstruct the palaeo environment. Five OSL samples were collected from Dagouwan, Salawusu River Valley at Inner Mongolia by Dr S. H. Li and his team in 2009. Extraction of 150μm to 180μm silt-size feldspar from collected dune sand, lacustrine facies and fluvial facies samples and running of luminescence dating therefore to obtain the age from 50ka to 90ka. Climate proxies - magnetic susceptibility, grain size, fossil vertebrates and fossil pollens have been analyzed and it is concluded that significant climate change occurred within this period, which change from domination of warm, humid and rainy summer monsoons (before 70ka) to cold, wind, windy strengthened dry winter wind and back to warm and humid again after 55ka.published_or_final_version
Applied Geosciences
Master
Master of Science
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Bostonalieva, Zhyldyz Kubatalievna [Verfasser]. "Late Quaternary Climate Change in Western Eurasia : A spatio-temporal review of climate proxies / Zhyldyz Kubatalievna Bostonalieva." Berlin : Freie Universität Berlin, 2015. http://d-nb.info/1068209399/34.
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Bergner, Andreas G. N. "Lake-level fluctuations and Late Quaternary climate change in the Central Kenya Rift." Phd thesis, Universität Potsdam, 2003. http://opus.kobv.de/ubp/volltexte/2005/107/.
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Diese Arbeit beschäftigt sich mit der Rekonstruktion von Klima in historischen Zeiten im tropischen Ostafrika. Nach einer Übersicht über die heutigen klimatischen Bedingungen der Tropen und den Besonderheiten des ostafrikanischen Klimas, werden die Möglichkeiten der Klimarekonstruktion anhand von Seesedimenten diskutiert. Es zeigt sich, dass die hoch gelegenen Seen des Zentralen Keniarifts, als Teil des Ostafrikanischen Grabensystems, besonders geeignete Klimaarchive darstellen, da sie sensibel auf klimatische Veränderungen reagieren. Veränderungen der Seechemie, wie sie in den Sedimenten aufgezeichnet werden, eignen sich um die natürlichen Schwankungen in der Quartären Klimageschichte Ostafrikas nachzuzeichnen. Basierend auf der guten 40Ar/39Ar- und 14C-Datierbarkeit der Seesedimente wird eine Chronologie der paläoökologischen Bedingungen anhand von Diatomeenvergesellschaftungen restauriert. Dabei zeigen sich für die Seen Nakuru, Elmenteita und Naivasha kurzfristige Transgression/ Regressions-Zyklen im Intervall von ca. 11.000 Jahren während des letzten (ca. 12.000 bis 6.000 J.v.H.) und vorletzten Interglazials (ca. 140.000 bis 60.000 J.v.H.). Zusätzlich kann ein allgemeiner, langfristiger Trend der Seeentwicklung von großen Frischwasserseen hin zu stärker salinen Gewässern innerhalb der letzen 1 Mio. Jahre festgestellt werden. Mittels Transferfunktionen und einem hydro-klimatischen Modellansatz können die restaurierten limnologischen Bedingungen als klimatische Schwankungen des Einzugsgebietes interpretiert werden. Wenngleich auch der zusätzliche Einfluss von tektonischen Veränderungen auf das Seeeinzugsgebiet und das Gewicht veränderter Grundwasserströme abgewogen werden, zeigt sich, dass allein geringfügig erhöhte Niederschlagswerte von ca. 30±10 % zu dramatischen Seespiegelanstiegen im Zentralen Keniarift führen. Aufgrund der etablierten hydrrologisch-klimatischen Wechselwirkungen werden Rückschlüsse auf die natürliche Variabilität des ostafrikanischen Klimas gezogen. Zudem wird die Sensitivität der Keniarift-Seen in Bezug auf die Stärke der äquatorialen Insolation und hinsichtilch variabler Oberflächenwassertemperaturen des Indischen Ozeans bewertet.In this work, an approach of paleoclimate reconstruction for tropical East Africa is presented. After giving a short summary of modern climate conditions in the tropics and the East African climate peculiarity, the potential of reconstructing climate from paleolake sediments is discussed. As demonstrated, the hydrologic sensitivity of high-elevated closed-basin lakes in the Central Kenya Rift yields valuable guaranties for the establishment of long-term climate records. Temporal fluctuations of the limnological characteristics saved in the lake sediments are used to define variations in the Quaternary climate history. Based on diatom analyses in radiocarbon- and 40Ar/39Ar-dated sediments, a chronology of paleoecologic fluctuations is developed for the Central Kenya Rift -lakes Nakuru, Elmenteita and Naivasha. At least during the penultimate interglacial (around 140 to 60 kyr BP) and during the last interglacial (around 12 to 4 kyr BP), these lakes experienced several transgression-regression cycles on time intervals of about 11,000 years. Additionally, a long-term trend of lake evolution is found suggesting the general succession from deep freshwater lakes towards more saline waters during the last million years. Using ecologic transfer functions and a simple lake-balance model, the observed paleohydrologic fluctuations are linked to potential precipitation-evaporation changes in the lake basins. Though also tectonic influences on the drainage pattern and the effect of varied seepage are investigated, it can be shown that already a small increase in precipitation of about 30±10 % may have affected the hydrologic budget of the intra-rift lakes within the reconstructed range. The findings of this study help to assess the natural climate variability of East Africa. They furthermore reflect the sensitivity of the Central Kenya Rift -lakes to fluctuations of large-scale climate parameters, such as solar radiation and sea-surface temperatures of the Indian Ocean.
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Kronborg, Pelle. "Identifying Quaternary Climate Change with XRF Analysis on Loess From South-Western England." Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-412179.
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Huge changes in climate occurred at the end of the last Quaternary glaciation. The end of this glaciation corresponds with the end of Pleistocene with its repeated glacial cycles and the start of the current geological epoch, the Holocene interglacial. The climate at this time was characterized by increasing temperatures and an increase in rainfall. This project focuses on understanding and examining these changes in climate using loess deposits from south-western England. Loess is an aeolian sediment and covers around 10 % of the Earth’s land surface and these deposits are excellent archives of past climate. Investigating loess can give understanding of past regional and local wind circulation patterns, atmospheric dustiness as well as weathering conditions. Studying paleoclimate is important since studying and understanding trends in past climate can increase our understanding of how the climate will change in the future. This study examined loess from two sites in south-western England, Porth Cressa and Lowland Point. These are relatively thin deposits; Lowland Point has a thickness of 180 cm and Porth Cressa has a thickness of 97 cm. England lacks the thick loess deposits that can be found in other parts of the world and thus the study of English loess has mostly been neglected. These deposits thus could contain unutilized information about paleoclimate. The elemental composition of the samples was examined using X-Ray Fluorescence (XRF). With the measured elemental composition, it’s possible to use weathering indices to see trends in postdepositional weathering. Low weathering intensities indicate a colder and drier climate, while higher weathering intensities indicate a warmer and more humid climate. The results from the weathering indices were plotted against depth at the two sites to identify changes in weathering and hence climate over time. Compared with the results from previous studies the results from some weathering indices seemed credible. Previous studies have indicated that the Chemical Proxy of Alteration (CPA) is the most appropriate weathering index for loess and the results from this study supports that theory. The results from the CPA show a trend with decreasing weathering intensities followed by a trend with increasing weathering intensities This implies that there was a period with decreasing temperatures/humidity followed by a period with increasing temperature humidity sometime at the end of the last glaciation. The geochemical data also showed support for a previous archaeological theory that there has been human reworking in the upper horizons at Lowland Point.Slutet av den sista kvartära glaciationen var en tid med stora klimatförändringar. Denna tid sammanfaller med slutet av Pleistocene och dess glaciära cyklar samt starten på den nuvarande geologiska epoken, Holocen. Klimatet vid den här tiden karaktäriserades av ökande temperaturer och ökande nederbörd. Det här projektet fokuserar på att granska och förstå dessa klimatförändringar med hjälp av lössjordar från sydvästra England. Löss bildas av vindburet sediment och täcker ungefär 10 % av jordens landyta, dessa avlagringar är utmärkta arkiv för historiskt klimat. Att undersöka lössjordar kan ge information om historiska regionala och lokala vindcirkulations-mönster, vittringsförhållanden samt mängden damm i atmosfären. Att undersöka paleoklimat är viktigt då förståelse för trender i tidigare klimat kan ge oss förståelse för hur klimatet kommer förändras i framtiden. Den här studien undersökte löss från två platser i sydvästra England, Lowland Point och Porth Cressa. Dessa avlagringar är relativt tunna; Lowland Point har en tjocklek på 180 cm och Porth Cressa har en tjocklek på 97 cm. England har inte de tjocka lössavlagringarna som går att hitta i andra delar av världen och därför har lite forskning utförts på brittiskt löss. Dessa avlagringar kan alltså innehålla oanvänd information om paleoklimat. Provernas grundämnessammansättning undersöktes med X-Ray Fluorescence (XRF). Med den uppmäta grundämnessammansättningen är det möjligt att använda vittringsindex för att se trender i vittring efter deposition. En låg vittringsintensitet indikerar ett kallare och torrare klimat medan en högre vittringsintensitet indikerar ett varmare och fuktigare klimat. Resultaten plottades mot djup för att visuellt identifiera förändringar i klimatet över tid. Vid jämförelse med tidigare studier verkade resultaten från vittringsindexen trovärdiga. Tidigare studier har föreslagit att CPA (Chemical Proxy of Alteration) är det mest lämpliga vittringsindexet för lössjordar och resultaten från denna studie stödjer den teorin. Resultaten från CPA visade på en trend med minskade vittringsintensitet följt av en trend med ökande vittrings intensitet. Detta antyder att det var en period med minskande temperatur/fuktighet följt av en period med ökande temperatur/fuktighet runt slutet av den senaste istiden. De geokemiska resultaten stödde också den tidigare arkeologiska teorin att mänsklig aktivitet har påverkat de övre horisonterna vid Lowland Point.
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Walker, Angela Jane. "Rhyolite volcanism at Öræfajökull volcano, S.E. Iceland : a window on Quaternary climate change." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/rhyolite-volcanism-at-oraefajokull-volcano-se-iceland--a-window-on-quaternary-climate-change(c00888e4-53a6-4fd0-ad54-110be2a42952).html.
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Öræfajökull is an ice-capped stratovolcano situated in the south east of Iceland which has developed throughout the mid to late Quaternary. It has erupted basaltic and rhyolitic lavas during interglacial and glacial periods, many of which display strong physical evidence of volcano-ice interaction. This makes Öræfajökull an ideal location to reconstruct terrestrial palaeo-environments. The area of Goðafjall and Hrútsfjall is one of a small number of rhyolitic depositional centres situated on the south west flanks of the volcano and is the first rhyolitic area of Öræfajökull to be mapped in detail.The relatively high K content of the rhyolitic units make them good candidates for 40Ar/39Ar dating, yielding eruption ages that provide a temporal constraint on the development of the stratovolcano. 40Ar/39Ar dating of young rocks (<1 My) is challenging and many of the samples were found to contain both excess and atmospheric argon. A small number exhibited a fractionated argon source with a sub-atmospheric 40Ar/36Ar ratio that could not be explained by a single episode of mass fractionation. Soret thermal diffusion has been suggested as a possible mechanism for fractionation, although further investigation is required.Two dominant rhyolite eruptions have been identified by detailed field mapping supported by the geochemical application of chemostratigraphy. The stratigraphically lower group of lavas outcrop between 100 to 380 m.a.s.l. and were erupted subaerially into a relatively ice-free environment at the base of the edifice. A 40Ar/39Ar age of 202 ± 9 ka implies that eruption occurred during the interglacial MIS 7. Conversely the upper group of lavas show strong evidence of volcano-ice interaction, suggesting that they were erupted subglacially and confined by ice with a minimum ice surface elevation of at least 800 m.a.s.l. These lavas yield a 40Ar/39Ar age of 116 ± 14 ka, which implies that eruption occurred during the transitional period between the MIS5e interglacial and colder sub-stages prior to MIS 4.At least two further glacial advances have occurred since the emplacement of the subglacial rhyolite unit. In addition, an ice confined trachydacite flow from the Vatnafjall ridge situated 20 km north east of Goðafjall has also been dated yielding a 40Ar/39Ar age of 95 ± 7 k. This lava was emplaced at an elevation of over 700 m in the presence of an adjacent valley fill glacier was at least 700 m thick.Ice thickness has varied dramatically throughout the evolution of Öræfajökull and glacial erosion has played an important role in its topographic development.
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McGarry, Siobhan Frances. "Multi-proxy Quaternary palaeoenvironmental records from speleothem pollen and organic acid fluorescence." Thesis, University of Exeter, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341161.
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Higginson, Matthew James. "Chlorin pigment stratigraphy as a new and rapid palaeoceanographic proxy in the quaternary." Thesis, University of Bristol, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310592.
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DeJong, Benjamin D. "Effects of Quaternary Climate Change on Tributary Sedimentation and Geomorphology in Eastern Grand Canyon." DigitalCommons@USU, 2007. https://digitalcommons.usu.edu/etd/6752.
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Climate variability has had a dramatic impact on eastern Grand Canyon tributaries over the past -100 ky. This is readily observed in the Lava Chuar and Comanche catchments, which host well preserved colluvial remnants and river terraces that resulted from several climate-induced cycles of aggradation and incision. This study investigates these climate responses using surveying, sedimentology, and luminescence geochronology methods to investigate the mechanisms and timing of their deposition. The survey data demonstrate that the concavity of terrace treads is lower than modern drainages. The sedimentology suggests the prevalence of stream-flow reworking of debris flow deposits and portrays an expected down-stream fining of deposits. Results of geochronology indicate that Lava Chuar Creek aggraded from -100-90 ka (S4), 61-55 ka (S3o), 50-35 ka (S3y), and 14-7 ka (S2). Comanche Creek similarly aggraded twice during the time period from 77-35 ka (S3) and also from 26-22 ka (S2). The response of eastern Grand Canyon tributaries to glacial-interglacial climate cycling appears to be more complicated than formerly thought. Previous conceptual models assumed that stream aggradation in arid settings occurred as a response to one specific set of climatic and biologic conditions, but new field data and luminescence dates on terrace materials reveal that there are at least two sets of conditions that were conducive to aggradation along local streams. First, streams aggraded during cooler, wetter climates, which is inferred to be due to increased sediment supply (e.g. S4 and S3y in Lava Chuar). With the transition to warmer interglacial climates came higher intensity storms and decreased vegetation density in catchments, based on previous paleoclimate studies. These conditions caused remobilization and redeposition of older sediment and resulted in a second set of stream aggradation phases (e.g. S3o and S2 in Lava Chuar). Meanwhile, the Colorado River aggraded only once per climate cycle during glacial advances and subsequent climate transitions. Thus, tributaries have responded more frequently and more sensitively to changing local conditions compared to the relatively insensitive Colorado River. This is supported by tighter correlation of tributary records to trends in regional paleoclimate records than to global ice records.
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Candy, Ian. "Quaternary climate change and landform development in southeast Spain : U-series dating of calcretes." Thesis, University of Reading, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.414519.
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Pugh, Jeremy Mark. "The late Quaternary environmental history of the Lake Heron basin, Mid Canterbury, New Zealand." Thesis, University of Canterbury. Geological Sciences, 2008. http://hdl.handle.net/10092/1766.
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The Lake Heron basin is an intermontane basin located approximately 30 kms west of Mount Hutt. Sediments within the basin are derived from a glacier that passed through the Lake Stream Valley from the upper Rakaia Valley. The lack of major drainage in the south part of the basin has increased the preservation potential of glacial phenomena. The area provides opportunities for detailed glacial geomorphology, sedimentology and micropaleontogical work, from which a very high-resolution study on climate change spanning the Last Glacial Maximum (LGM) through to the present was able to be reconstructed. The geomorphology reveals a complex glacial history spanning multiple glaciations. The Pyramid and Dogs Hill Advance are undated but possibly relate to the Waimaungan and Waimean glaciations. The Emily Formation (EM), previously thought to be MIS 4 (Mabin, 1984), was dated using Be10 to c. 25 ka B.P. The EM was largest advance of the Last Glacial Maximum (LGM). Ice during the LGM was at least 150m thicker than previously thought, as indicated by relatively young ages of high elevation moraines. Numerous moraine ridges and kame terraces show a continuous recession from LGM limits, and, supported by decreasing Be10 ages for other LGM moraines, it seems ice retreat was punctuated by minor glacial readvances and still-stands. These may be associated with decadal-scale climate variations, such as the PDO or early ENSO-like systems. There are relatively little sedimentological exposures in the area other than those on the shores of Lake Heron. The sediment at this location demonstrates the nature of glacial and paraglacial sedimentation during the later stages of ice retreat. They show that ice fronts oscillated across several hundred metres before retreating into Lake Heron proper. Vegetation change at Staces Tarn (1200m asl) indicates climate amelioration in the early Holocene. The late glacial vegetation cover of herb and small shrubs was replaced by a low, montane forest about 7,000 yrs B.P, approximately at the time of the regional thermal maxima. From 7,000 and 1,400 yrs B.P, temperatures slowly declined, and grasses slowly moved back onto the site, although the montane forest was still the dominant vegetation. Fires were frequent in the area extending back at least 6,000 years B.P. The largest fire, about 5,300 yrs B.P, caused major forest disruption. But full recovered occurred within about 500 years. Beech forest appears at the site about 3,300 yrs B.P and becomes the dominant forest cover about 1,400 yrs B.P. Cooler, cloudier winters and disturbance by fire promoted the expansion of beech forest at the expense of the previous low, montane forest. Both the increased frequency of fire events and late Holocene beech spread may be linked to ENSO-related variations in rainfall. The youngest zone is characterised by both a dramatic decline in beech forest and an increase in grasses, possibly representing human activity in the area.
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O'Connor, Peter W. "Aeolian activity and environmental change in the Central Mega Kalahari : implications for the timing, nature and causes of late Quaternary aridity." Thesis, University of Sheffield, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284355.
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Sbrocco, Elizabeth Jones. "A seascape genetics approach to exploring the phylogeographic response of marine fishes to late Quaternary climate change." Thesis, Boston University, 2012. https://hdl.handle.net/2144/32056.
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Thesis (Ph.D.)--Boston UniversityPLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you.
Whether a species will flourish or face extinction under a new climate regime is largely determined by its dispersal ability, its adaptive capacity or some combination of these processes. These processes have also played important roles in the evolutionary histories of species, ultimately shaping their contemporary distributions. In terrestrial studies, a landscape genetics approach is often used to explain how geographic, ecological and evolutionary processes interact to structure spatial genetic variation across populations, but these approaches have only begun to be used in marine ecosystems. This dissertation fills an emerging niche in marine ecology by taking an interdisciplinary seascape genetics approach to investigating the interplay of climate, dispersal and adaptation as shallow-water marine fishes respond to environmental heterogeneity over space and climatological shifts over time. [TRUNCATED]
2031-01-02
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Ivory, Sarah Jean. "Vegetation and Climate of the African Tropics for the Last 500,000 Years." Diss., The University of Arizona, 2013. http://hdl.handle.net/10150/293752.
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In the last few decades, we have been witness to unprecedented changes in precipitation and temperature. Such alterations to our climate system have important implications for terrestrial ecosystems that billions of people depend on for their livelihood. The situation is especially tenuous for those living directly off the landscape via resources from natural ecosystems or subsistence agriculture as in much of tropical Africa. Studies of past climates provide potential analogues and help validate models essential for elucidating mechanisms that link changes in climate mean and variability and how they may affect ecosystem distribution and productivity. However, despite the importance of the paleo-record for insight into the future, tropical proxy records are rare, low resolution, and too short to capture important intervals that may act as analogs, such as the Last Interglacial (MIS 5e; ~130-115ka).Long, high-resolution drill cores from Lake Malawi, southeast Africa, provide a record of tropical climate and vegetation that extends back ~1.2mya, comprising many continuous glacial-interglacial cycles. My primary research involves conducting pollen analyses on these cores. First, I analyzed a high-resolution interval of the shortest Malawi core in order to better understand abrupt vegetation transitions during the Last Deglaciation. Further analysis was conducted on the longest Malawi core, beginning with an interval covering all of the Penultimate Glacial through the Last Interglacial. The resultant pollen data has shown that abrupt, large-scale landscape transitions from forest to desert follow local insolation and lake levels at the site, with a strong dependence of forest/woodland vegetation types on mean rainfall as well as rainfall seasonality. The interpretation of paleodata requires a good understanding of modern processes, thus another project has focused on using model simulations of the Last Interglacial and modern satellite NDVI time series to highlight dynamical and statistical relationships between vegetation and climate change. This work suggests that despite suggested links between monsoon intensity and SSTs in the southern African tropics, insolation controls on atmospheric circulation are the primary drivers of vegetation reorganization. In addition, this work highlights the importance of rainfall seasonality and dry season length in addition to precipitation controls on vegetation.
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Dabat, Pivotto Isabelle. "Etude comparative des octocoralliaires méditerranéens : de la phylogéographie aux processus adaptatifs." Thesis, Aix-Marseille, 2014. http://www.theses.fr/2014AIXM4082.
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Ma thèse s'inscrit dans le cadre de l'étude de l'impact des changements environnementaux sur la biodiversité marine, à une échelle intra-spécifique et inter-spécifique. Les modèles choisis sont des Octocoralliaires méditerranéens (corail rouge; Corallium rubrum, et gorgones Paramuricea clavata et Eunicella cavolini). Mieux comprendre les conséquences génétiques des fluctuations passées sur les organismes permet d'appréhender les conséquences génétiques à venir des changements environnementaux en cours. Durant ma thèse, nous avons donc étudié par une approche de phylogéographie comparée l'évolution de ces espèces : plusieurs marqueurs de séquences ont été utilisés afin de tenter de détecter des changements démographiques passés et de reconstituer l'histoire évolutive de ces espèces. L'étude du complexe d'espèces du genre Eunicella a mis en évidence que des limites d'espèces floues entre E. cavolini et E. singularis liés à de possibles flux de gènes entre elles. Par ailleurs, l'impact du changement climatique en cours a été étudié en conditions expérimentales. En aquarium, les résultats obtenus sur E. cavolini ont permis de détecter des phénomènes d'adaptation en présence de flux de gènes. En complément, l'étude de la phénologie de deux espèces, P. clavata et E. cavolini, a été initiée et suggère la possibilité de maintien de niveaux comparables d'effort reproducteur entre différents régimes thermiques. A travers diverses collaborations, cette thèse a permis à la fois de développer de nouveaux modèles mais aussi de réaliser une approche intégrative de l'étude de l'adaptation des Octocoralliaires de Méditerranée face au changement climatique passé et en coursMy PhD thesis is in the context of the study of the impact of environmental changes on marine biodiversity, with an intra-specific and inter-specific level. Selected models are Mediterranean octocorals (red coral Corallium rubrum and gorgonians Paramuricea clavata and Eunicella cavolini). Better understanding the genetic consequences of these past fluctuations on organisms will help us understanding the potential future consequences of current climate change. During my PhD, we studied the evolution of these species through comparative phylogeography: several nuclear loci were used to try to detect past demographic changes and to reconstruct the evolutionary history of these species. The study of the Eunicella spp. species complex showed that genetic boundaries between E. cavolini and E. singularis were not clear with potential gene flow between them. Moreover, the impact of ongoing climate change has been studied in experimental conditions. In aquariums, the results obtained on E. cavolini have revealed adaptive processes in the presence of gene flow. Through various collaborations, this thesis has allowed both to develop new models but also to achieve an integrative approach of the study of the adaptation of Mediterranean octocorals facing past and ongoing climate change
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Heroy, David Carlson. "Sand- and Clay-Size Mineralogy of the Ganges and Brahmaputra Rivers: Records of River Switching and Late-Quaternary Climate Change." W&M ScholarWorks, 2000. https://scholarworks.wm.edu/etd/1539617766.
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Burge, Philip Ian. "A Record of Environmental and Climatic Change from the West Coast, South Island, New Zealand, using Beetle Fossils." Thesis, University of Canterbury. Geological Sciences, 2007. http://hdl.handle.net/10092/1381.
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Fossil beetle based palaeoclimatic and palaeoenvironmental reconstructions are presented from the Westport region, West Coast, South Island, New Zealand for the last glacial cycle. They include the longest continuous fossil beetle record from New Zealand, covering 16,000 years over the OIS 3/OIS 2 transition. Early last glacial (OIS 4) and mid- Holocene (OIS 1) reconstructions are also presented. The assumptions underlying fossil beetle research in New Zealand are tested indicating beetles are suitable proxies for reconstructing palaeotemperature and palaeoprecipitation. This thesis provides the first quantitative estimates of temperature and precipitation from the Westport region for the last glacial. Reconstructed temperatures indicate stadial cooling was seasonal. Maximum cooling was ca. 5℃ in winter and ca. 2-3℃ in summer. Winter cooling is consistent with previous quantitative estimates from New Zealand. Mean annual precipitation decreased a maximum 35-40% during stadials. Temperatures and precipitation varied during OIS 3/2 indicating multiple possible drivers for glaciation. A glacial advance ca. 34-28ka BP correlates with ca. 5℃ winter cooling and ca. 40% less precipitation, which supports temperature driven glaciation whereas a glacial advance ca. 24-22ka BP correlates with ca. 3℃ winter cooling and precipitation similar to present, which supports precipitation forced glaciation. Palaeoenvironmental reconstructions of stadial vegetation from the Westport region indicate lowland Nothofagus fusca-type forest during OIS 4 and a forest-grassland mosaic during OIS 3/2. These records contrast with pollen-based reconstructions of a treeless landscape in Westport during stadials but are consistent with quantitative estimates of stadial cooling. A shift of reproductive strategy in arboreal vegetation may explain the lack of tree pollen in stadial pollen records. This is significant for our understanding of glacial palaeoecology and palaeoclimatology as pollen records may not accurately represent stadial vegetation.
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Piva, Andrea <1978>. "High-resolution stratigraphy of Central and Southern Adriatic Quaternary deposits of sub-Milankovian climate change on Mediterranean circulation." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2007. http://amsdottorato.unibo.it/456/.
Full textAbstract:
This volume is a collection of the work done in a three years-lasting PhD, focused in the analysis of Central and Southern Adriatic marine sediments, deriving from the collection of a borehole and many cores, achieved thanks to the good seismic-stratigraphic knowledge of the study area.
The work was made out within European projects EC-EURODELTA (coordinated by Fabio Trincardi, ISMAR-CNR), EC-EUROSTRATAFORM (coordinated by Phil P. E. Weaver, NOC, UK), and PROMESS1 (coordinated by Serge Bernè, IFREMER, France). The analysed sedimentary successions presented highly expanded stratigraphic intervals, particularly for the last 400 kyr, 60 kyr and 6 kyr BP. These three different time-intervals resulted in a tri-partition of the PhD thesis. The study consisted of the analysis of planktic and benthic foraminifers’ assemblages (more than 560 samples analysed), as well as in preparing the material for oxygen and carbon stable isotope analyses, and interpreting and discussing the obtained dataset. The chronologic framework of the last 400 kyr was achieved for borehole PRAD1-2 (within the work-package WP6 of PROMESS1 project), collected in 186.5 m water depth. The proposed chronology derives from a multi-disciplinary approach, consisting of the integration of numerous and independent proxies, some of which analysed by other specialists within the project. The final
framework based on: micropaleontology (calcareous nannofossils and foraminifers’ bioevents), climatic cyclicity (foraminifers’ assemblages), geochemistry (oxygen stable isotope, made out on planktic and benthic records), paleomagnetism, radiometric ages (14C AMS), teprhochronology, identification of sapropel-equivalent levels (Se). It’s worth to note the good consistency between
the oxygen stable isotope curve obtained for borehole PRAD1-2 and other deeper Mediterranean records. The studied proxies allowed the recognition of all the isotopic intervals from MIS10 to MIS1 in PRAD1-2 record, and the base of the borehole has been ascribed to the early MIS11.
Glacial and interglacial intervals identified in the Central Adriatic record have been analysed in detail for the paleo-environmental reconstruction, as well. For instance, glacial stages MIS6, MIS8 and MIS10 present peculiar foraminifers’ assemblages, composed by benthic species typical of polar regions and no longer living in the Central Adriatic nowadays. Moreover, a deepening trend in the paleo-bathymetry during glacial intervals was observed, from MIS10 (inner-shelf environment) to MIS4 (mid-shelf environment).Ten sapropel-equivalent levels have been recognised in PRAD1-2 Central Adriatic record. They showed different planktic foraminifers’ assemblages, which allowed the first distinction of events occurred during warm-climate (Se5, Se7), cold-climate (Se4, Se6 and Se8) and temperate-intermediate-climate (Se1, Se3, Se9, Se’, Se10) conditions, consistently with literature. Cold-climate
sapropel equivalents are characterised by the absence of an oligotrophic phase, whereas warm-temeprate-climate sapropel equivalents present both the oligotrophic and the eutrophic
phases (except for Se1). Sea floor conditions vary, according to benthic foraminifers’ assemblages, from relatively well oxygenated (Se1, Se3), to dysoxic (Se9, Se’, Se10), to highly dysoxic (Se4, Se6, Se8) to events during which benthic foraminifers are absent (Se5, Se7). These two latter levels are also characterised by the lamination of the sediment, feature never observed in literature in such
shallow records. The enhanced stratification of the water column during the events Se8, Se7, Se6, Se5, Se4, and the concurring strong dilution of shallow water, pointed out by the isotope record, lead to the hypothesis of a period of intense precipitation in the Central Adriatic region, possibly due to a northward shift of the African Monsoon. Finally, the expression of Central Adriatic PRAD1-2 Se5 equivalent was compared with the same event, as registered in other Eastern Mediterranean areas. The sequence of substantially the same planktic foraminifers’ bioevents has
been consistently recognised, indicating a similar evolution of the water column all over the Eastern Mediterranean; yet, the synchronism of these events cannot be demonstrated. A high resolution analysis of late Holocene (last 6000 years BP) climate change was carried out for the Adriatic area, through the recognition of planktic and benthic foraminifers’ bioevents. In particular, peaks of planktic Globigerinoides sacculifer (four during the last 5500 years BP in the most expanded core) have been interpreted, based on the ecological requirements of this species, as warm-climate, arid intervals, correspondent to periods of relative climatic optimum, such as, for instance, the Medieval Warm Period, the Roman Age, the Late Bronze Age and the Copper Age. Consequently, the minima in the abundance of this biomarker could correspond to relatively cooler and more rainy periods. These conclusions are in good agreement with the isotopic and the pollen data. The Last Occurrence (LO) of G. sacculifer has been dated in this work at an average age of 550 years BP, and it is the best bioevent approximating the base of the Little Ice Age in the Adriatic. Recent literature reports the same bioevent in the Levantine Basin, showing a rather consistent age. Therefore, the LO of G. sacculifer has the potential to be extended to all the Eastern Mediterranean. Within the Little Ice Age, benthic foraminifer V. complanata shows two distinct peaks in the shallower Adriatic cores analysed, collected hundred kilometres apart, inside the mud belt environment. Based on the ecological requirements of this species, these two peaks
have been interpreted as the more intense (cold and rainy) oscillations inside the LIA. The chronologic framework of the analysed cores is robust, being based on several range-finding 14C AMS ages, on estimates of the secular variation of the magnetic field, on geochemical estimates
of the activity depth of 210Pb short-lived radionuclide (for the core-top ages), and is in good agreement with tephrochronologic, pollen and foraminiferal data. The intra-holocenic climate oscillations find out in the Adriatic have been compared with those pointed out in literature from other records of the Northern Hemisphere, and the chronologic constraint seems quite good. Finally, the sedimentary successions analysed allowed the review and the update of the foraminifers’ ecobiostratigraphy available from literature for the Adriatic region, thanks to the
achievement of 16 ecobiozones for the last 60 kyr BP. Some bioevents are restricted to the Central Adriatic (for instance the LO of benthic Hyalinea balthica , approximating the MIS3/MIS2 boundary), others occur all over the Adriatic basin (for instance the LO of planktic Globorotalia inflata during MIS3, individuating Dansgaard-Oeschger cycle 8 (Denekamp)).
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Hughes, Matthew William. "Late Quaternary Landscape Evolution and Environmental Change in Charwell Basin, South Island, New Zealand." Phd thesis, Lincoln University. Agriculture and Life Sciences Division, 2008. http://theses.lincoln.ac.nz/public/adt-NZLIU20080214.132530/.
Full textAbstract:
Charwell Basin is a 6 km-wide structural depression situated at the boundary between the axial ranges and faulted and folded Marlborough Fault Zone of north-eastern South Island, New Zealand. The basin contains the piedmont reach of the Charwell River, and a series of late Quaternary loess-mantled alluvial terraces and terrace remnants that have been uplifted and translocated from their sediment source due to strike-slip motion along the Hope Fault which bounds the basin to its immediate north. The aim of this study was to provide an interdisciplinary, integrated and holistic analysis of late Quaternary landscape evolution and environmental change in Charwell Basin using terrain analysis, loess stratigraphy, soil chemistry and paleoecological data. The study contributes new understanding of New Zealand landscape and ecosystem responses to regional and global climatic change extending to Marine Isotope Stage (MIS) 6, and shows that climatically-forced shifts in biogeomorphic processes play a significant role in lowland landscape evolution.
Morphometric analysis of alluvial terraces and terrace remnants of increasing age demonstrated geomorphic evolution through time, with a decrease in extent of original planar terrace tread morphology and an increase in frequency of steeper slopes and convexo-concave land elements. Paleotopographic analysis of a >150 ka terrace mantled by up to three loess sheets revealed multiple episodes of alluvial aggradation and degradation and, subsequent to river abandonment, gully incision prior to and coeval with loess accumulation. Spatial heterogeneity in loess sheet preservation showed a complex history of loess accumulation and erosion. A critical profile curvature range of -0.005 to -0.014 (d2z/dx2, m-1) for loess erosion derived from a model parameterised in different ways successfully predicted loess occurrence on adjacent slope elements, but incorrectly predicted loess occurrence on an older terrace remnant from which all loess has been eroded. Future analyses incorporating planform curvature, regolith erosivity and other landform parameters may improve identification of thresholds controlling loess occurrence in Charwell Basin and in other South Island landscapes.
A loess chronostratigraphic framework was developed for, and pedogenic phases identified in, the three loess sheets mantling the >150 ka terrace. Except for one age, infrared-stimulated luminescence dates from both an upbuilding interfluve loess exposure and colluvial gully infill underestimated loess age with respect to the widespread Kawakawa/Oruanui Tephra (KOT; 27,097 ± 957 cal. yr BP), highlighting the need for improvements in the methodology. Onset of loess sheet 1 accumulation started at ca. 50 ka, with a break at ca. 27 ka corresponding to the extended Last Glacial Maximum (eLGM) interstadial identified elsewhere in New Zealand. Loess accumulation through MIS 3 indicates a regional loess flux, and that glaciation was not a necessary condition for loess generation in South Island. Loess accumulation and local alluvial aggradation are decoupled: the youngest aggradation event only covers ~12 kyr of the period of loess sheet 1 accumulation. Older local aggradation episodes could not be the source because their associated terraces are mantled by loess sheet 1. In the absence of numerical ages, the timing of L2 and L3 accumulation is inferred on the basis of an offshore clastic sediment record. The upbuilding phase of loess sheet 2 occurred in late MIS 5a/MIS 4, and loess sheet 3 accumulated in two phases in MIS 5b and late MIS 6.
Biogenic silica data were used to reconstruct broad shifts in vegetation and changes in gully soil saturation status. During interglacial/interstadial periods (MIS 1, early MIS 3, MIS 5) Nothofagus¬-dominated forest covered the area in association with Microlaena spp grasses. Lowering of treeline altitude during glacial/stadial periods (MIS 2, MIS 3, MIS 5b, late MIS 6) led to reduction in forest cover and a mosaic of shrubs and Chionochloa spp, Festuca spp and Poa spp tussock grasses. Comparison of interfluve and gully records showed spatial heterogeneity in vegetation cover possibly related to environmental gradients of exposure or soil moisture. A post-KOT peak in gully tree phytoliths corresponds to the eLGM interstadial, and a shift to grass-dominated vegetation occurred during the LGM sensu stricto. Diatoms indicated the site became considerably wetter from ca. 36 ka, with peak wetness at ca. 30, 25 and 21 ka, possibly due to reduced evapotranspiration and/or increased precipitation from a combination of strengthened westerly winds and increased cloudiness, or strengthened southerly flow and increased precipitation. Human influence after ca. 750 yr BP led to re-establishment of grassland in the area, which deposited phytoliths mixed to 30 cm depth in the soil.
A coupled gully colluvial infilling/vegetation record showed that sediment flux during the late Pleistocene was ~0.0019 m3 m-1 yr-1 under a shrubland/grassland mosaic, and Holocene sediment flux was ~0.0034 m3 m-1 yr-1 under forest. This increase of 60% through the last glacial-interglacial transition resulted from increased bioturbation and down-slope soil transport via root growth and treethrow, which formed a biomantle as evidenced by slope redistribution of the KOT. These results contrast with sediment transport rates and processes hypothesised to occur contemporaneously in adjacent mountain catchments. This suggests that intraregional biogeomorphic processes can differ significantly depending on topography and geological substrate, with different landscapes responding in unique ways to the same climate shifts. Analysis of Quaternary terrestrial landscape evolution in non-glaciated mountainous and lowland areas must therefore consider spatial and temporal heterogeneity in sediment fluxes and underlying transport processes.
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Thompson, Warren. "Late Quaternary fluvial system response to climatic change over the past 200ka on Mallorca, Illes Balears." Thesis, University of Derby, 2017. http://hdl.handle.net/10545/622714.
Full textAbstract:
Outcrops of late Quaternary deposits along the north–east coast of Mallorca were examined, and a high resolution chronological framework established using optically stimulated luminescence of quartz and feldspar grains. Coastal sections at Es Barrancar and Cala Mata record a complex succession of alluvial fan deposition with a minor aeolian component, mainly deposited during the last two glacial cycles. For the last ~200ka different orbital configurations appear to have produced a series of subtly different climatic scenarios that resulted in great variations in the regional availability of moisture. In turn, each of these climatic scenarios set in motion a distinct set of sedimentary processes, which imprinted themselves upon the character of fluvial system response recorded in the alluvial archives on Mallorca. Within the resulting complex of sediments were units of fluvially reworked aeolianite which, although truncated in places, were traceable laterally along wide sections of the sea front outcrops of both fan systems. These archives yielded 47 new OSL and pIRIR290 ages which suggest a number of previously unrecognised periods of enhanced fluvial activity. Luminescence ages identify significant ephemeral fluvial activity taking place during MIS 6, MIS 5 sub-stages d/c, b/a, and across the MIS 5/4 boundary. Another major phase of reworking corresponds with the middle part of MIS 3, and continued sporadically into the Last Glacial Maximum. These fluvial reworking events have been interpreted as having taken place during cold arid climatic intervals, when vegetation was at a minimum, precipitation was low and displayed a much higher degree of seasonality, enhancing the effects of runoff.
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Enayat, Misha. "20,000 14C Years of Climate and Environmental Change in Europe : A Coleopteran-based Reconstruction with an Anthropocenic Focus." Thesis, Umeå universitet, Miljöarkeologiska laboratoriet, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-106655.
Full textAbstract:
This thesis builds on the work of previous coleopteran-based climatic reconstructions to recreate the environment and climate of the last 20,000 14C years of northwest Europe using the data and methods available within the Bugs Coleopteran Ecology Package, and aims to assess the ability of the BugsCEP results to provide information regarding events and anthropogenic changes on environment during the Anthropocene. Samples and data from 134 sites across northwest Europe and the British Isles were included in this study. The Mutual Climatic Range method and the BugStats module based on habitat code classifications were used to create the climatic and environmental reconstructions respectively, the results of which are provided in eight isotherm maps for 14.5-9 14C years BP and 2 EcoFigure graphs for 20,000 14C to present. While the results of some isotherm maps align with the changes described in previous studies, other climate trends are muted within these results. Likewise, some previously recognized environmental shifts in Europe are visible, whereas other major events are not distinguishable within the environmental record. An assessment of the environmental reconstruction results finds that though there is not sufficient material to support any proposed Anthropocene start dates, effects of anthropogenic influence upon the environment may be visible starting within the last 2,000 14C years; the results also show some support for the Vera Hypothesis.
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Kouns, Carolina, and Yael Margulis. "Rock-magnetic and Soil Organic Carbon Proxies of Climate Change from Loess – Aeolian Sediments of Brittany, France." Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-445688.
Full textAbstract:
The aeolian sediment loess, which consists of mineral dust, is one of the most detailed terrestrial record of both global and regional climate changes. As climate changes in the past cover a much wider range of climate variability than humans have directly recorded, the soil memory of loess is vital for understanding the Earth’s climate system. By examining past climate records and analyzing past climate changes and factors that have instigated changes, inferences regarding future climate can be made. Therefore, the aim of this research was to define the specific depositional and post-depositional conditions of a loess sequence in Primel-Tr gastel, Brittany, north-western France. This was done by examining the magnetic susceptibility (MS), and loss on ignition (LOI) of 63 samples from the Primel-Tr gastel sequence. The result suggests that the lower part was formed during a relatively long, cold and dry period, with significant temperature oscillations, resulting in several periglacial phases. The data also shows an increase in the MS signal for the middle units, which then gradually decreases simultaneously as there is a sharp rise in the proportion of organic matter (OM). This is followed by a steep drop and finally an overall increase in OM, which suggests that this period has been characterized by both stadial and interstadial phases. The upper part displays a general increase in MS values, as well as increased organic matter, which implies a milder climate with increased temperatures. The study provides the first comprehensive estimate of the regional climate variability and provides a base towards a more comprehensive and overarching understanding of our climate system.
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Hughes, Matthew W. "Late Quaternary landscape evolution and environmental change in Charwell Basin, South Island, New Zealand." Lincoln University, 2008. http://hdl.handle.net/10182/305.
Full textAbstract:
Charwell Basin is a 6 km-wide structural depression situated at the boundary between the axial ranges and faulted and folded Marlborough Fault Zone of north-eastern South Island, New Zealand. The basin contains the piedmont reach of the Charwell River, and a series of late Quaternary loess-mantled alluvial terraces and terrace remnants that have been uplifted and translocated from their sediment source due to strike-slip motion along the Hope Fault which bounds the basin to its immediate north. The aim of this study was to provide an interdisciplinary, integrated and holistic analysis of late Quaternary landscape evolution and environmental change in Charwell Basin using terrain analysis, loess stratigraphy, soil chemistry and paleoecological data. The study contributes new understanding of New Zealand landscape and ecosystem responses to regional and global climatic change extending to Marine Isotope Stage (MIS) 6, and shows that climatically-forced shifts in biogeomorphic processes play a significant role in lowland landscape evolution. Morphometric analysis of alluvial terraces and terrace remnants of increasing age demonstrated geomorphic evolution through time, with a decrease in extent of original planar terrace tread morphology and an increase in frequency of steeper slopes and convexo-concave land elements. Paleotopographic analysis of a >150 ka terrace mantled by up to three loess sheets revealed multiple episodes of alluvial aggradation and degradation and, subsequent to river abandonment, gully incision prior to and coeval with loess accumulation. Spatial heterogeneity in loess sheet preservation showed a complex history of loess accumulation and erosion. A critical profile curvature range of -0.005 to -0.014 (d²z/dx², m⁻¹) for loess erosion derived from a model parameterised in different ways successfully predicted loess occurrence on adjacent slope elements, but incorrectly predicted loess occurrence on an older terrace remnant from which all loess has been eroded. Future analyses incorporating planform curvature, regolith erosivity and other landform parameters may improve identification of thresholds controlling loess occurrence in Charwell Basin and in other South Island landscapes. A loess chronostratigraphic framework was developed for, and pedogenic phases identified in, the three loess sheets mantling the >150 ka terrace. Except for one age, infrared-stimulated luminescence dates from both an upbuilding interfluve loess exposure and colluvial gully infill underestimated loess age with respect to the widespread Kawakawa/Oruanui Tephra (KOT; 27,097 ± 957 cal. yr BP), highlighting the need for improvements in the methodology. Onset of loess sheet 1 accumulation started at ca. 50 ka, with a break at ca. 27 ka corresponding to the extended Last Glacial Maximum (eLGM) interstadial identified elsewhere in New Zealand. Loess accumulation through MIS 3 indicates a regional loess flux, and that glaciation was not a necessary condition for loess generation in South Island. Loess accumulation and local alluvial aggradation are decoupled: the youngest aggradation event only covers ~12 kyr of the period of loess sheet 1 accumulation. Older local aggradation episodes could not be the source because their associated terraces are mantled by loess sheet 1. In the absence of numerical ages, the timing of L2 and L3 accumulation is inferred on the basis of an offshore clastic sediment record. The upbuilding phase of loess sheet 2 occurred in late MIS 5a/MIS 4, and loess sheet 3 accumulated in two phases in MIS 5b and late MIS 6. Biogenic silica data were used to reconstruct broad shifts in vegetation and changes in gully soil saturation status. During interglacial/interstadial periods (MIS 1, early MIS 3, MIS 5) Nothofagus-dominated forest covered the area in association with Microlaena spp grasses. Lowering of treeline altitude during glacial/stadial periods (MIS 2, MIS 3, MIS 5b, late MIS 6) led to reduction in forest cover and a mosaic of shrubs and Chionochloa spp, Festuca spp and Poa spp tussock grasses. Comparison of interfluve and gully records showed spatial heterogeneity in vegetation cover possibly related to environmental gradients of exposure or soil moisture. A post-KOT peak in gully tree phytoliths corresponds to the eLGM interstadial, and a shift to grass-dominated vegetation occurred during the LGM sensu stricto. Diatoms indicated the site became considerably wetter from ca. 36 ka, with peak wetness at ca. 30, 25 and 21 ka, possibly due to reduced evapotranspiration and/or increased precipitation from a combination of strengthened westerly winds and increased cloudiness, or strengthened southerly flow and increased precipitation. Human influence after ca. 750 yr BP led to re-establishment of grassland in the area, which deposited phytoliths mixed to 30 cm depth in the soil. A coupled gully colluvial infilling/vegetation record showed that sediment flux during the late Pleistocene was ~0.0019 m³ m⁻¹ yr⁻¹ under a shrubland/grassland mosaic, and Holocene sediment flux was ~0.0034 m³ m⁻¹ yr⁻¹ under forest. This increase of 60% through the last glacial-interglacial transition resulted from increased bioturbation and down-slope soil transport via root growth and treethrow, which formed a biomantle as evidenced by slope redistribution of the KOT. These results contrast with sediment transport rates and processes hypothesised to occur contemporaneously in adjacent mountain catchments. This suggests that intraregional biogeomorphic processes can differ significantly depending on topography and geological substrate, with different landscapes responding in unique ways to the same climate shifts. Analysis of Quaternary terrestrial landscape evolution in non-glaciated mountainous and lowland areas must therefore consider spatial and temporal heterogeneity in sediment fluxes and underlying transport processes.
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Zhang, Jingran [Verfasser]. "Responses of late Quaternary sediments to climate change : Luminescence dating of coastal, lacustrine and aeolian deposits from northern China and Germany / Jingran Zhang." Berlin : Freie Universität Berlin, 2016. http://d-nb.info/110219705X/34.
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Winer, Emily R. "Interpretation and Climatic Significance of Late Quaternary Valley-fill Deposits in Wadi Hasa, West-Central Jordan." Miami University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=miami1272313345.
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Zhang, Jingran [Verfasser]. "Responses of regional sedimentary archives to Late Quaternary climate change : Luminescence dating of coastal, lacustrine and aeolian deposits from northern China and Germany / Jingran Zhang." Berlin : Freie Universität Berlin, 2016. http://d-nb.info/1112476091/34.
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Murad, Waheed [Verfasser], Frank [Akademischer Betreuer] Schlütz, Hermann [Akademischer Betreuer] Behling, and Markus [Akademischer Betreuer] Hauck. "Late Quaternary Vegetation History And Climate Change In The Gobi Desert, South Mongolia / Waheed Murad. Gutachter: Hermann Behling ; Markus Hauck ; Frank Schlütz. Betreuer: Frank Schlütz." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2012. http://d-nb.info/1043029214/34.
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Norström, Elin. "Late Quaternary climate and environmental change in the summer rainfall region of South Africa : a study using trees and wetland peat cores as natural archives /." Stockholm : Department of Physical Geography and Quaternary Geology, Stockholm university, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-7375.
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Balch, Deborah P. "Quaternary Ostracode Paleoecology and Its Link to Climate Change in the Bonneville Basin: A Detailed Study of the Glad800 Core GSL00-4, Great Salt Lake, Utah." Thesis, The University of Arizona, 2003. http://hdl.handle.net/10150/249251.
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We report the results of a detailed paleoecological study of the Bonneville Basin covering the last ~240,000 years. Our study used fossil ostracodes and a sedimentological record obtained from the August 2000 GLAD800 drilling operation at the Great Salt Lake. We analyzed 125 samples, taken at ~1 meter intervals from core GSL00-4, for ostracodes and other paleoecologic and sedimentological indicators of environmental change. Multivariate analyses applied to the ostracode data indicate an alternation between three major environments at the core site over the cored interval. The environments fluctuated most often between shallow saline, open -water lake conditions (when the lake was high enough to inundate the core site) and salt or freshwater, spring -fed marsh (when the water level was at or lower than the core site). But occasionally, the core site was submerged by deep fresh water. Immediately following deep lake phases, crashes in lake level from rapid desiccation resulted in the deposition of thick evaporite units. These environmental changes are consistent with shoreline studies of regional lake level fluctuations, but provide considerable new detail on both the timing and environmental conditions associated with the various lake phases. Our age model (using dates obtained from ¹⁴C, U- series, tephra and biostratigraphic chronologies) allowed us to associate the core's record of regional paleohydrology to the marine oxygen isotope stages record of global climate change. The core contains high resolution, continuous records for the last three glacial/interglacial sequences. In each case we found that fresh open-water conditions (i.e. lake highstands) correspond with maximum glacial advances, except for the smaller, less intense OIS 4 glaciation, when the lake remained saline. Salt and freshwater marshes were dominant environments for most of the interglacials. However, throughout most of the Quaternary, this basin has contained a shallow, saline open-water lake.
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Koutsouris, Alexander. "Data resolution effects onwater resource planning andmanagement : The Kisumu – Lake Victoria region study." Thesis, Stockholm University, Department of Physical Geography and Quaternary Geology, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-36565.
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In the Kisumu District, Kenya, unreliable rainfall pattern has been identified as one of the main causes for poverty in rural areas. The negative effects of such unreliable patterns could be mitigated through improved water resource management and planning. However, estimates of current (and future) water availability will likely differ depending on whether managers draw upon data gathered at a local-scale or regional-scale. This is particularly important in developing regions where, due to lack of data availability, managers are often limited in their choice of data resolution. This study investigates the potential effect of spatial resolution of data on water management and planning by comparing hydro-climatic trends in local-scale data with trends in regional-scale data. The influence of adopting local-scale versus regional-scale data is further demonstrated by estimate the storage requirements of proposed irrigation ponds for farmers in the Orongo village of the Kisumu District located in Kenya, Africa. Results indicate a low correlation between local and regional hydro-climatic trends. Data spatial scale directly influences water resources management leading to a 300% difference in estimated storage requirement for the average farmer.
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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.
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RésuméUne série de sondages continentaux (FZ4, FZ5, et SZY) ont été collectés dans la plaine de Fuzhou et dans la montagne de Ningde. Les trois enregistrements ont permis de reconstituer et ainsi de comprendre l'évolution de la végétation ainsi que d'évaluer l'impact de la mousson est-asiatique et les changements du niveau marin sur les environnements du quaternaire récent. Ma thèse donne un aperçu de la végétation passée et des changements paléoclimatiques au cours des 50000 dernières années. Pour les derniers millénaires je me suis aussi intéressé aux activités humaines préhistoriques et leur relation avec les changements de l'environnement local durant l'Holocène. Dans cette thèse, j'ai utilisé une approche multidisciplinaire incluant principalement la palynologie, la sédimentologie, le paléomagnétisme et la micropaléontologie pour reconstituer les environnements passés.L'enregistrement palynologique SZY issu d'une tourbière subalpine couvre les 50000 dernières années en continu. Les diversité de la flore et des changements forestiers au cours des 50 dernières millénaires permettent de reconstituer l'évolution de la mousson régionale dans le sud-est de la Chine. Les changements climatiques estimés par un indice de mousson saisonnier, la température et les précipitations mensuelles ont été quantitativement reconstruits.Les assemblages polliniques pendant la période entre ca. 50 et 30,4 ka cal BP, correspondant au stade isotopique marin (MIS) 3, sont caractérisés par une forte abondance de pollen arboricole, principalement subtropicaux Quercus, Castanopsis/Lithocarpus avec des taxons tempérés de montagne à feuillage caduque tels que Fagus et Alnus et accompagné de quelques conifères mésiques de montagne telles que les Taxodiaceae et Tsuga. Une telle composition de l'écosystème suggère que le MIS 3 était plutôt humide avec une forte mousson d'été. L'insolation d'été élevée peut avoir entraîné une intensification de la mousson au cours de cette période et a donc contribué au maintien d'un tel écosystème subtropical. Une expansion progressive des taxons arborés feuillus, qui a remplacé les taxons subtropicaux à feuillage persistant pendant la période du dernier maximum glaciaire (LGM) (de ca. 30,4 à 11,8 environ cal ka BP), indique que le climat est devenu beaucoup plus frais que lors du MIS 3. Cet intervalle froid se produit entre ca. 21 et 17 cal ka BP lorsque la savane arbustive a augmenté et la forêt de feuillus a diminué rapidement. Cet événement est également marqué par la concentration de pollen qui montre des valeurs faibles au cours du dernier maximum glaciaire. Ceci est probablement lié à un paysage ouvert ou semi-ouvert sous un climat plus sec et plus froid que durant le MIS 3. En comparaison avec les études des isotopes de l'oxygène (δ18O/δ16O) issues de spéléothèmes et ses carottes de glace du Groenland, plusieurs événements climatiques rapides pourraient être reconnues tels que le Dryas récent et l'interstade Bølling-Allerød qui ont marqué la fin de la dernière période glaciaire. Au cours de l'Holocène, la forêt sempervirente est restaurée rapidement. Le groupe arboré à feuillage persistant est devenu plus élevé que celui à feuilles caduques à environ 8000 cal BP. Ceci reflète un renforcement de la mousson d'été. Deux événements rapides semble être enregistré à ca. 8,2 cal ka BP et 5 cal ka BP, probablement causé par des événements de refroidissement au cours de l'Holocène. Dans le tronçon inférieur de la rivière Min, l'étude interdisciplinaire de deux enregistrements révèlent que l'environnement sédimentaire dans la plaine de Fuzhou a connu des cycles de sédimentation à plusieurs reprises au cours de l'Holocène. La première transgression marine dans a eu lieu aux alentours de ca. 9000 cal yr BP, et a atteint son plus haut niveau entre ca. 7000 et 4000 cal yr BP. La granulométrie et l'analyse des diatomées ainsi que les datations 14C AMS permettent de décrire la transgression marine etAbstractA 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
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Marden, Christopher J. "Late Quaternary glacial history of the South Patagonian icefield at Torres del Paine, Chile." Thesis, University of Aberdeen, 1993. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=128187.
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The principal aim of the thesis is to determine the Late Quaternary glacial history of the South Patagonian Icefield at Torres del Paine (51°S, 73°W), Chile. The secondary aim is to compare this glacial history with palaeoclimatic records from elsewhere to test the theory that climate change over the last glacial-interglacial cycle was synchronous between the two polar hemispheres. Synchronous climate change cannot be explained as an atmospheric response to insolation changes unless fundamental ocean-atmosphere reorganisations occurred (Broecker and Denton, 1990). Empirical glacial-geologic data from southern South America is therefore used to test recent models of global climate change. The global pattern of climate change over the last glacial-interglacial cycle is assessed by reviewing proxy palaeoclimate records including isotope records from polar ice cores and deep sea sediment cores, and glacial geologic records from the southern Andes. Conclusions from this review form the basis for hypotheses about what 'should' have happened at Torres del Paine. To test these hypotheses glacial geologic investigations were undertaken on site. Geomorphological evidence is used to define eight icesheet, deglaciation and valley glacier stages; ice extended ca.50km east of the modern South Patagonian Icefield margin during the last glaciation. Basal dates from peat bogs provide dating control for some glacial stages. Pumice fragments associated with glacial deposits were derived from an eruption of Volcan Reclus ca.12,000 yr BP and therefore constrain the Lateglacial depositional sequence. Models of the glacial history are constructed. Evidence that climate change at Torres del Paine was synchronous with other sites is equivocal. However, significant results are: (a) evidence of a Late-Lateglacial ('Younger Dryas') advance - the first such site in Patagonia; (b) evidence that deglaciation occurred slowly; and (c) evidence that the greatest extent of ice did not necessarily coincide with the coldest part of the last glaciation.
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Rich, Julie. "Landscape response to late Quaternary climatic change on the Southern High Plains, USA." Thesis, University of Oxford, 2003. http://ora.ox.ac.uk/objects/uuid:bb12bdee-0ab1-4a02-8847-aa7b1cbc8c69.
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Long-term palaeo-climatic conditions have primarily been interpreted from ocean marine sediments and ice cores. Few middle and low latitude continental records exist that provide insight into continental response to climate change over time. This research offers new chronologies on a variety of low latitude continental deposits from the Southern High Plains, and demonstrates their importance as palaeo-environmental archives. These chronologies extend the existing Southern High Plains palaeo-environmental record from the historic period to the late-middle Pleistocene, and provide an important basis from which to examine landscape response to late Quaternary climate change. This study demonstrates the applicability of optical dating procedures to well-bleached sedimentary features, such as lunettes, lacustrine material, tufa, and coversands. The precision and accuracy of the technique permits the detection of historic depositional events, whilst the range of the dating technique extended the chronology to the middle-late Pleistocene. The physical isolation of the Southern High Plains from its surrounding areas for the last 1.6 Ma has preserved a record of past climatic fluctuations within the aeolian and fluvio-lacustrine sediments. This research has demonstrated that the Southern High Plains landscape is sensitive to periods of less effective moisture, causing reactivation during historic drought periods (e.g. 1930s "Dust Bowl" event). Coversands and small playa lunettes were active during glacial and interglacials. This suggests that these features are sensitive to smaller scale climatic fluctuations that result in reduced effective moisture for the region during both glacial and interglacial periods. Large lake lunettes were inactive during the Wisconsin glacial. During this same period, active lacustrine and tufa deposition occurred; this offers evidence of greater effective moisture for the Southern High Plains, which resulted in regional recharge. The record of climate change preserved in the lunettes, lacustrine material, tufa, and coversands has provided insight into the response of this dynamic landscape to climatic fluctuations and has been employed for the reconstruction of the palaeo- environmental history of the Southern High Plains. An understanding of landscape response is important in light of the future of the Southern High Plains environment as global temperatures increase, and is critical to a complete evaluation of continental response to climatic change.
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Oliveira, Paulo Eduardo De. "A palynological record of Late Quaternary vegetational and climatic change in southeastern Brazil /." The Ohio State University, 1992. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487779914825271.
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Campos, Marília de Carvalho. "Variabilidade milenar da Corrente do Brasil e do clima da América do Sul durante o último período glacial." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/100/100136/tde-27072016-113954/.
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A Corrente do Brasil (CB) representa o ramo sul da bifurcação da Corrente Sul Equatorial que interage com a margem continental sudeste do Brasil. A temperatura da superfície do mar na região da CB exerce um importante papel no controle da intensidade e posição da Zona de Convergência do Atlântico Sul, um dos principais componentes do Sistema de Monção da América do Sul (SMAS). Tal sistema atmosférico é responsável pela precipitação de verão em grande parte do continente sul-americano, sendo, portanto, uma feição natural de grande importância para o contexto político-econômico nacional e internacional. Além disto, a CB é marcantemente influenciada pela Atlantic Meridional Overturnig Circulation (AMOC), cujas oscilações pretéritas foram responsáveis por mudanças abruptas no clima global. Atualmente, os poucos registros paleoceanográficos disponíveis no sudoeste do Atlântico Sul não permitem uma reconstituição detalhada das mudanças ocorridas na CB durante o último período glacial. Esta Dissertação de Mestrado visou reconstituir a variabilidade da CB ao redor de 32°S durante os eventos Heinrich Stadial (HS) 3 e 2, bem como seus impactos no clima da porção sudeste da América do Sul. Para tanto, foi investigado um testemunho sedimentar marinho coletado na margem continental sul do Brasil sob a influência da CB. Para este testemunho foram produzidos modelo de idades baseado em datações 14C, análises de isótopos estáveis de carbono e oxigênio, bem como análises de Mg/Ca, ambas em testas de foraminíferos planctônicos e análises de fluorescência de raios-X em amostras de sedimento total. Os resultados mostram que durante os eventos HS (notadamente durante o HS2) ocorreu marcante aumento na taxa de sedimentação bem como nas razões ln(Ti/Ca) e ln(Fe/Ca), e diminuição na composição dos isótopos estáveis de carbono bem como na temperatura e salinidade da superfície do mar. Tais alterações foram relacionadas à desintensificação da AMOC, à intensificação da ressurgência do Oceano Austral e ao fortalecimento do SMAS. A ocorrência de uma estrutura em w nos registros dos HSs apresentados aqui, bem como em registros do Atlântico Norte e da América do Sul, sugere que esta estrutura é uma característica do HS2, e possivelmente também do HS3The Brazil Current (BC) represents the southern branch of the bifurcation of the South Equatorial Current that interacts with the southeastern Brazilian continental margin. Sea surface temperature at BC region plays an important role in controlling the intensity and position of the South Atlantic Convergence Zone, which represents one of the main componets of the South American Monsoon System (SAMS). This atmospheric system is responsible for summer precipitation in a large sector of South America, and, therefore, it is a natural feature of great importance for the national and international political-economic context. Moreover, the BC is markedly influenced by the Atlantic Meridional Overturning Circulation (AMOC) whose past oscillations generated marked global abrupt climatic changes. Presently, the few paleoceanographic records available from the western South Atlantic do not allow a detailed reconstruction of the changes that happened in the BC during the last glacial cycle. This MSc. dissertation aimed at reconstructing the variability of the BC around 32°S during the events Heinrich Stadial (HS) 3 and 2, as well as its impacts on the climate of southeastern South America. Therefore, we investigated one marine sediment core collected in the southern Brazilian continental margin, under the influence of the BC. For this core we produced an age model based on 14C ages, downcore records of carbon and oxygen stable isotopes and Mg/Ca, both in tests of planktonic foraminifera, and X-ray fluorescence in bulk sediment samples. During HSs (notably during HS2), the records show marked increases in sedimentation rate as well as in ln(Ti/Ca) and ln(Fe/Ca), and decrease in the stable carbon isotopic composition as well as sea surface temperature and salinity. Such changes were releted to the weakening of the AMOC, the intensification of the Southern Ocean upwelling, and the strengthening of the SAMS. The occurrence a w-structure in our HS records as well as in North Atlantic and South American records, suggest that such structure is a pervasive feature of HS2, and possibly also HS3
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Al-Omari, Saʹad. "A speleothem-based investigation of Late Quaternary climatic and environmental change in the central Zagros Mountains (Iran)." Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.614922.
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Thorpe, Joanna Lucy. "Records of late Quaternary climatic change from Tswaing crater lake, South Africa, and the Central Kenyan Rift." Thesis, University College London (University of London), 2006. http://discovery.ucl.ac.uk/1445898/.
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The relative influence of precessionally-driven changes in direct insolation and changes in boundary conditions associated with glacial-interglacial cycles on climatic conditions at low latitudes remains uncertain. This thesis presents records of late Quaternary climatic change from Tswaing crater lake in South Africa and from the Naivasha and Nakuru-Elmenteita basins in the Central Kenya Rift, with the aim of increasing our understanding of the nature and causes of climatic change at low latitudes in Africa. The sedimentary sequence from Tswaing crater lake provides some of the longest terrestrial records of palaeoclimatic change in southern Africa, but the confidence associated with these records is limited by chronological uncertainty. This thesis presents five new 230Th/234U dates from the lower, previously undated section of the sequence, which are used to construct a new age-depth model for the sediments. When viewed in light of this chronology, new sedimentological, geochemical, and diatom assemblage records from the sequence indicate that boundary conditions associated with glacial-interglacial cycles determined climatic conditions at the site over the last -150 kyr, and that the obliquity of the earth's axis may have affected conditions between -150 and -350 kyr B.P. Diatomite beds deposited in the Naivasha and Nakuru-Elmenteita basins at the time of the last interglacial document a period in which deep, dilute lakes existed in the Central Kenya Rift. 518Odiatom records from these 40Ar/39Ar-dated beds are used to reconstruct palaeohydrological conditions during this lake-level highstand. The records indicate that lake levels in both basins responded to increases in precipitation driven by peaks in March and September insolation on the equator, and by increased tropical sea-surface temperatures. It is therefore concluded that precipitation in the Central Kenya Rift was influenced by both precessionally-driven changes in insolation and global boundary conditions during this period.
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Bookhagen, Bodo. "Late quaternary climate changes and landscape evolution in the Northwest Himalaya geomorphologic processes in the Indian summer monsoon domain /." Phd thesis, [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=974115487.
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Meckler, Anna Nele. "Late quaternary changes in nitrogen fixation and climate variability recorded by sediments from the Gulf of Mexico and the Caribbean Sea /." Zürich : ETH, 2006. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=16811.
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Yamamoto, Masaya. "Evolutionary history and conservation genetics of Primula sect. Reinii (Primulaceae), an endangered endemic primrose group in Japan." Kyoto University, 2018. http://hdl.handle.net/2433/232378.
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Kyoto University (京都大学)0048
新制・課程博士
博士(人間・環境学)
甲第21177号
人博第849号
新制||人||203(附属図書館)
29||人博||849(吉田南総合図書館)
京都大学大学院人間・環境学研究科相関環境学専攻
(主査)教授 瀬戸口 浩彰, 教授 加藤 眞, 教授 市岡 孝朗
学位規則第4条第1項該当
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Duhamel, Maxence. "Restitution des changements de l’hydrologie des masses d’eaux intermédiaires et profondes de la Méditerranée au cours des derniers 145 ka à partir de la mesure de la composition isotopique du Nd de foraminifères Variations in eastern Mediterranean hydrology during the last climatic cycle as inferred from neodymium isotopes in foraminifera Changes in the intermediate water masses of the Mediterranean Sea during the last climatic cycle - new constraints from neodymium isotopes in foraminifera." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASS120.
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Cette thèse vise à faire progresser notre connaissance de l’hydrologie des masses d’eaux intermédiaires et profondes de la Méditerranée au cours du dernier cycle climatique (derniers 145 ka), et de contraindre les modèles de circulation océanique ayant permis les dépôts de niveaux riches en matière organique (ORL et sapropèles). La composition isotopique en Nd (εNd) d’échantillons de foraminifères de carottes localisées à des bathymétries intermédiaires et profondes de la mer Tyrrhénienne, de l’Adriatique, de la mer Ionienne et du bassin Levantin ont été analysées. Ce travail a permis de mettre en évidence que les eaux intermédiaires et profondes de la Méditerranée Orientale sont systématiquement plus radiogéniques durant les périodes glaciaires que durant les interglaciaires. Nous avons démontré que ces changements ne peuvent pas être attribuée entièrement aux variations des apports éoliens et fluviatiles du Nord de l’Afrique mais à d’importantes modifications dans la quantité d’eau Atlantique (AW) pénétrant en Méditerranéen. Les périodes de bas niveaux marins glaciaire sont associées à une réduction des flux d’eau Atlantique à travers les détroits de Gibraltar et Siculo-tunisien en induisant des masses d’eau profonde plus radiogéniques en Méditerranée orientale. Surimposées à ces fluctuations glaciaires-interglaciaires, les périodes humides Africaines et de dépôts de sapropèles sont systématiquement caractérisées par des valeurs εNd plus radiogéniques. Cela a été attribué à l’arrêt de la convection profonde des eaux moins radiogéniques de surface associée à une augmentation du temps de contact des masses d’eaux profondes avec les sédiments radiogéniques des marges continentales du bassin Levantin. Nos résultats mettent en évidence durant les terminaisons I et II une augmentation de la contribution d’eau moins salées d’origine Nord Atlantique (MAW) d’environ 55 % pouvant avoir pré-conditionné la Méditerranée orientale plusieurs milliers d’année avant le dépôt des sapropels S1 et S5.La comparaison des enregistrements d’εNd obtenus dans les bassins Orientale et Occidentale sur le dernier cycle climatique montre un gradient d’εNd plus fort entre les deux bassins aux profondeurs intermédiaires et profondes durant les stades glaciaires. Cela est cohérent avec un échange d’eau plus faible de part et d’autre du détroit Siculo-tunisien durant les périodes de bas niveau marin glaciaire. Durant les hauts niveaux marins des périodes les interglaciaires les échanges d’eau sont au contraires plus forts entre les deux bassins induisant un transfert à la mer Tyrrhénienne des variations de la composition isotopique en Nd observée en Méditerranée orientale. Ainsi, les périodes humides africaines induisant une stratification des masses d’eaux et les dépôts de sapropèles à l’est, sont associées à des signatures d’eaux plus radiogéniques qui sont alors transportées par la LIW en Mer Tyrrhénienne. Surimposé à ces variations orbitales, des variations rapides de l’εNd ont pu être mises en évidence dans le chenal de Corse. Chaque événements froids des hautes latitudes de l’hémisphère Nord (Younger Dryas et événements de Heinrich) se caractérisent par une LIW plus radiogénique dans la mer Tyrrhénienne impliquant une réduction de la formation d’eau intermédiaire dans le Golfe du Lion (lié à de plus forts apports d’eaux douces depuis l’Atlantique lors des événements de Heinrich) et/ou une production plus importante de LIW en Méditerranée orientale (lié à un refroidissement de la surface du Nord de la Méditerranée lors des événements de Heinrich)This thesis aims to advance our knowledge of the hydrology of the intermediate and deep water masses of the Mediterranean during the last climatic cycle (last 145 ka), and to constrain the ocean circulation models that allowed the deposition of organic matter-rich sediments (ENT and sapropels). The Nd isotopic composition (εNd) of foraminifera samples in cores located at intermediate and deep bathymetries of the Tyrrhenian Sea, the Adriatic Sea, the Ionian Sea and the Levantine Basin were analyzed. This work allowed to highlight that the intermediate and deep waters of the Eastern Mediterranean are systematically more radiogenic during the glacial stadiums than during the interglacials. We have shown that these changes cannot be entirely attributed to variations in dust and river inputs from northern Africa but to significant changes in the amount of Atlantic (AW) water entering the Mediterranean. Periods of low sea ice levels are associated with a reduction in Atlantic water flows through the straits of Gibraltar and Siculo-Tunisia by inducing more radiogenic deep-water masses in the eastern Mediterranean. Superimposed on these glacial-interglacial fluctuations, African humid periods and sapropel deposits are systematically characterized by more radiogenic εNd values. This has been attributed to the cessation of deep convection of less radiogenic surface water associated with an increase in the contact time of deep-water bodies with radiogenic sediments from the continental margins of the Levantine basin. Our results highlight during terminations I and II an increase in the contribution of less salty water of North Atlantic origin (MAW) of around 55% which may have pre-conditioned the eastern Mediterranean several thousand years before the deposit S1 and S5 sapropels. A comparison of the εNd recordings obtained in the Eastern and Western basins over the last climate cycle shows a stronger gradient of εNd between the two basins at intermediate and deep depths during the glacial stadiums. This is consistent with a weaker water exchange across the Siculo-Tunisian Strait during periods of low sea ice. On the contrary, during the high sea levels of the interglacial periods, water exchanges are stronger between the two basins, inducing a transfer to the Tyrrhenian Sea of variations in the isotopic composition of Nd observed in the eastern Mediterranean. Thus, the African wet periods inducing a stratification of the water masses and the deposits of sapropels in the east, are associated with signatures of more radiogenic waters which are then transported by the LIW in the Tyrrhenian Sea. Superimposed on these orbital variations, rapid variations in εNd could be highlighted in the Corsica channel. Each cold event in the high latitudes of the Northern Hemisphere (Younger Dryas and Heinrich events) is characterized by a more radiogenic LIW in the Tyrrhenian Sea involving a reduction in the formation of intermediate water in the Gulf of Lion (linked to more strong freshwater inflows from the Atlantic during the Heinrich events) and / or a greater production of LIW in the eastern Mediterranean (linked to a cooling of the northern Mediterranean surface during the Heinrich events)
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Cañellas, Boltà Núria. "Dinàmica de la vegetació en relació amb els canvis climàtics, els processos geològics i l'impacte humà a l'illa de Pasqua des del Glacial tardà. Estudi paleoecològic dels sediments del llac Rano Raraku." Doctoral thesis, Universitat de Barcelona, 2014. http://hdl.handle.net/10803/145926.
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Aquesta tesi doctoral es centra en la paleoecologia de l’Illa de Pasqua (Rapa Nui) (27ºS 109ºW). El present treball ha caracteritzat la vegetació a la conca del llac i la seva dinàmica com a resposta als canvis ambientals durant els darrers 34000 anys a partir d’indicadors ambientals (macrorestes vegetals, diatomees, registre palinològic, geoquímic i fàcies sedimentari) analitzats en sediments de testimonis de sondeig del llac Raraku. Els resultats han evidenciat variacions significatives en la composició de la vegetació en relació a canvis climàtics a llarg termini, modificacions de la morfologia de la conca per rebliment sedimentari i, en els últims tres mil•lennis, les activitats humanes. El llac Raraku i els seus entorns han experimentat grans canvis transformant-se d’un llac profund amb forts pendents envoltat per un palmerar obert a un llac somer amb vegetació dominada per palmeres, desprès a una torbera amb una successió de plantes dominants, el retorn a condicions de llac, i finalment el reemplaçament dels palmerars de l’entorn per vegetació herbàcia. A més a més, s’han observat fluctuacions menors en la vegetació durant el període glacial i la desglaciació, que podrien ser conseqüència de canvis climàtics ràpids com el Younger Dryas i esdeveniments Heinrich (H1-H3), donant suport a la hipòtesi de l’ocurrència d’aquests fenòmens a la regió del Pacífic Sud. En el treball s’ha dut a terme l’anàlisi de la successió sedimentaria més contínua fins el moment pels darrers 3,7 cal ka BP. L’estudi ha caracteritzat el reemplaçament de la vegetació dominada per palmeres per prats, iniciat el c. 2,4 cal ka BP, com un procés llarg i gradual-esglaonat en contrast amb el patró sobtat d’estudis anteriors. La presència i expansió de la planta ruderal d’origen americà Verbena litoralis, juntament amb la correlació significativa del seu augment amb increments en el registre de carbó, suggereixen la implicació de les activitats humanes en aquest procés de reemplaçament. L’identificació de hiatus sedimentaris suggereixen la contribució del clima als canvis de vegetació. Aquests resultats indiquen el probable establiment de l’home a l’illa 1500 anys abans de la data actualment acceptada, i el possible paper de poblacions provinents d’Amèrica. La magnitud i rapidesa dels canvis de vegetació a causa de les variacions climàtiques i del rebliment del llac des del final de l’últim glacial són similars als ocorreguts durant la presència humana. D’altra banda s’han identificat restes macrofòssils com a possibles indicadors de condicions ambientals i s’ha reconegut per primera vegada la presència d’una nova planta nativa a l’illa actualment extirpada: Dianella cf. intermedia/adenanthera.This dissertation focuses on the paleoecology of Easter Island (Rapa Nui) (27°S 109°W). The study has characterised vegetation of the lake’s basin and its dynamics in response to environmental changes during the past 34000 years from several environmental indicators (macroremains plants, diatoms, palynological, geochemical and sedimentary facies records) analized in lacustrine sediment cores of lake Raraku. The results show significant changes in the composition of the vegetation in relation to long-term climatic changes, variations on the lake basin morphology due to sedimentary infilling and human activities in the last three millennia. Lake Raraku and its surroundings have undergone significant changes, such as the transformation of the deep lake surrounded by open palm grove into a shallow lake with palm-dominant vegetation around, the hydrosere succession into a mire with a plant succession, the return to lake conditions, and finally the replacement of palm vegetation by herbs. Moreover, small fluctuations in vegetation during the glacial period and deglatiation have been observed and could be the result of rapid climate changes such as the Younger Dryas and Heinrich events H1-H3. This supports a wide occurrence of these events, including the Pacific South region. The multiproxy analysis of the most continuous sequence to date for the last 3.7 ka BP has characterised the replacement of palm-dominated vegetation by grasslands as a long and gradual process, starting at c.2.4 ka BP, in contrast with the abrupt pattern from previous studies. The presence of the weed of American origin Verbena litoralis, together with significant correlation with charcoal increases, suggest the involvement of human activities in the replacement process. Sedimentary gaps observed in the sequence suggest the contribution of climatic effects as well. These results indicate that human settlement occurred likely 1500 years before the date currently accepted, and a possible role of people coming from America. The study shows that vegetation changes due to climate and lake basin morphological variations are similar in rate and magnitude to those occurred during human presence. On the other hand, several macrofossil remains have been identified as potential indicators of environmental conditions and the presence of a new plant native to the island, now extirpated, Dianella cf. Intermediate/adenanthera, has been recognized for the first time.
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Melo, Warita Alves de. "Filogeografia e estrutura genética de uma árvore de floresta estacional neotropical Tabebuia roseoalba (RIDL.) Sandwith (Bignnoniaceae)." Universidade Federal de Goiás, 2014. http://repositorio.bc.ufg.br/tede/handle/tede/5594.
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Tabebuia roseoalba (RIDL.) Sandwith (Bignoniaceae) is widely distributed in Neotropical seasonally dry forests, occurring mainly from Northeast towards the Central West and Southeast Brazil, and also in Paraguay, Bolivia and Peru. The phylogeography of this species may help us to understand how historical events influenced its genetic diversity and in the current geographic distribution of seasonally dry forests. The results were based on the sequencing of three chloroplast intergenic spacers (psbA-trnH, trnC-ycf6 and trnStrnG2S) and the nuclear ribosomal region (nrDNA) (ITS1 + 5.8S + ITS2). We sampled 18 populations (235 individuals) in North, Central West and Southeast. The three chloroplast regions generated a fragment of 1,519 base pairs and 37 haplotypes. We found high haplotype diversity (h = 0.839) and low nucleotide diversity (π = 0.00610 SD = 0.00311) and were found. A fragment of 506 base pairs was generated for nrDNA and 14 haplotypes were identified. The haplotype diversity (h = 0.336) was lower than chloroplast diversity but nucleotide diversity (π = 0.01669 SD = 0.00857) was higher. Populations of Tabebuia rosealba are highly differentiated (FST = 0. 684; p = 0.001) with low gene flow (Nm < 1.0) among all population pairs. Our results also showed significant population reduction followed by expansion (Mismatch Distribution SSD = 0.20746; p = 0.0002, Tajima D = - 1.766; p = 0.008, Fs = - 23.702; p = 0.001), and the Extended Bayesian Skyline Plot (EBSP) also showed population reduction. Coalescent dated tree showed an ancient time to most recent ancestor (TMRCA) dated from ~4.9 Ma (CI 95% 1.9 Ma) in the Pliocene. Both the median-joining network and the coalescent tree showed evidences of incomplete lineage sorting. Our data show that the current pattern of diversity found so far is in consonance with a wide distribution of this species in the past, strongly suggesting that the climate changes of the Quaternary Period had strongly influenced the genetic diversity pattern and the geographical distribution of the species.
Tabebuia roseoalba (RIDL.) Sandwith (Bignoniaceae) é amplamente distribuída em florestas estacionais semideciduais e deciduais neotropicais, do Nordeste para o Centro- Oeste e Sudeste do Brasil, sendo também encontrada no Paraguai, Bolívia e Peru. Conhecer o padrão filogeográfico desta espécie nos ajuda a entender quais eventos históricos influenciaram na atual distribuição geográfica das florestas estacionais. Sendo assim, estamos interessados em compreender os efeitos das mudanças climáticas do período quaternário sobre os atuais padrões de diversidade genética e distribuição geográfica da espécie T. roseoalba e das florestas estacionais. Os nossos resultados foram baseados em três regiões intergênicas cloroplastidiais (psbA-trnH, trnC-ycf6 e trnStrnG2S) e uma região ribossômica nuclear (nrDNA) (ITS1 + 5.8S + ITS2). Foram amostrados 235 indivíduos distribuídos em 18 populações coletadas nas regiões Norte, Centro-Oeste e Sudeste. As três regiões cloroplastidiais concatenadas geraram um fragmento de 1519 pares de bases, a diversidade haplotípica foi alta (h = 0,839) e a diversidade nucleotídica foi baixa (π = 0,00610 +/- 0,00311) e foram encontrados 37 haplótipos. Obteve-se um fragmento de 506 pares de bases para a região nuclear, uma diversidade haplotípica menor (h = 0,336) uma diversidade nucleotídica maior (π = 0,01669+/-0,00857) e 14 haplótipos foram identificados. Encontrou-se uma alta diferenciação entre as populações (FST = 0,684; p = 0,001), demonstrando insignificativo fluxo gênico. Foi encontrado sinal de retração seguido de expansão populacional (Distribuição de diferenças par a par SSD = 0,20746, p = 0,0002; D de Tajima D = -1,766, p = 0,008; teste de Fu FS = -23,706, p = 0,001), a análise de Extended Bayesian Skyline Plot (EBSP) também foi significativa, porém o índice de Raggedness não foi significativo (r = 0,029; p = 0,999). O ancestral comum mais recente entre as linhagens foi datado a cerca de ~4,9 ± 1,9 Ma (Ma) antes do presente no Plioceno. As redes de haplótipos e a árvore de coalescência mostraram não haver relação filogenética das linhagens e o espaço geográfico, evidenciando possivelmente arranjo incompleto de linhagem. Os nossos dados mostram que o atual padrão de diversidade encontrado é condizente com uma ampla distribuição desta espécie no passado, sugerindo que as oscilações climáticas do período Quaternário teriam influenciado grandemente o padrão da diversidade genética encontrada, a distribuição geográfica da espécie e das florestas estacionais neotropicais.
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Furini, Paulo Roberto. "Modelagem preditiva de distribuição passada e futura de Ficus adhatodifolia Schott., Ficus insipida Willd. e Ficus citrifolia Mil. (Moraceae)." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/59/59139/tde-26052015-143536/.
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As glaciações do Quaternário moldaram os padrões filogeográficos das espécies em geral. Em algumas regiões da América do Sul, (e.g. Cerrado e Caatinga) a mudança estrutural foi mais acentuada, havendo o predomino de savanas, ao passo que em outras regiões (e.g. Amazônica e Mata Atlântica) as mudanças foram menores, formando áreas de refúgios florestais. A Modelagem Preditiva de Distribuição de espécies usa associações entre variáveis ambientais e registros de ocorrência da espécie para estimar modelos que representam as condições ambientais favoráveis à espécie. Neste trabalho foram estudadas três espécies de figueiras Neotropicais com características ecológicas distintas, representando duas linhagens filogenéticas independentes, i.e., seções Americana (Ficus citrifolia) e Pharmacosycea (Ficus adhatodifolia e Ficus insipida). Foram gerados modelos para os cenários passados (Interglacial 140.000 e Glacial 21.000 anos atrás), presente e futuro (2050 e 2070, nos cenários otimistas e pessimistas) para as três espécies estudadas usando o programa Maxent 3.3.3k. Os resultados obtidos mostram que para F. adhatodifolia as variáveis mais importantes nos modelos foram temperatura mínima do mês mais frio e precipitação do mês mais seco. Para F. insipida as variáveis mais importantes nos modelos foram temperatura mínima do mês mais frio e precipitação anual. Para F. citrifolia as variáveis mais importantes nos modelos foram temperatura mínima do mês mais frio e precipitação do mês mais chuvoso. Os modelos projetados no cenário interglacial, para as três espécies estudadas, apresentaram áreas de adequabilidade ambiental próximas ao cenário atual. Durante o período glacial F. adhatodifolia mostrou uma mudança considerável em sua área de ocorrência, ocorrendo em regiões consideradas refúgios para algumas espécies. Ficus insipida apresentou uma retração na sua adequabilidade ambiental, porém mantendo-se na região amazônica, enquanto que F. citrifolia teve um aumento na sua área de adequabilidade. Nos cenários futuros (2050 e 2070) F.adhatodifolia apresentou uma diminuição em sua área de ocorrência em ambos os cenários otimista e pessimista, F. insipida apresentou um aumento em sua área de adequabilidade ambiental e F.citrifolia apresentou uma diminuição e fragmentação na região Amazônica nos cenários otimista e pessimista de 2050 e otimista de 2070. As exigências ambientais e os possíveis padrões filogeográficos das três espécies são discutidos no contexto dos modelos preditivos gerados.The Quaternary glaciations shaped the phylogeographic patterns of species in general. In some regions of South America (e.g.Cerrado and Caatinga) structural change was more pronounced and savannas predominated, whereas in other regions (e.g. Amazon and Atlantic Forest) changes were minor, forming areas of forest refuges. Species distribution Predictive Modeling uses associations between environmental variables and species occurrence records to estimate models that represent the environmental conditions favorable to the species. In the present study we chose three species of Neotropical Ficus with different ecological characteristics, representing two independent phylogenetic lineages, i.e., sections Americana (Ficus citrifolia) and Pharmacosycea (F.adhatodifolia and F.insipida). We generated models for the past (interglacial 140,000 years ago and Glacial 21,000 years ago), present and future scenarios (2050 and 2070 in optimistic and pessimistic scenarios) for the three study species using Maxent 3.3.3k program. Our results showed thatfor F. adhatodifolia the most important variables in the models were minimum temperature in the coldest month and precipitation in the driest month. For F.insipida the most important variables in the models were minimum temperature in the coldest month and annual precipitation. For F. citrifolia the most important variables in the models were minimum temperature in the coldest month and precipitation in the wettest month. The models designed for the interglacial stage showed areas of environmental suitability similar to the current scenario of the three species. During the glacial period F. adhatodifolia showed a considerable change in its range, occurring in regions considered refuges for some species. Ficus insipida had its environmental suitability decreased, but remained in the Amazon region, while F. citrifolia increased its area of suitability. In the future models (2050 and 2070) F.adhatodifolia showed a decrease in its range on both optimistic and pessimistic scenarios, F.insipida showed an increase in its area of environmental suitability and F.citrifolia has been decreasing and fragmentation in the Amazon region in the optimistic and pessimistic scenarios 2050 and optimistic 2070. The environmental requirements and the potential phylogeographic patterns of the study species are discussed in the context of the generated predictive models.
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Kirby, Benjamin Thomas. "Surface Exposure Dating of Stream Terraces in the Chinese Pamir: Glacial Chronology and Paleoclimatic Implications." Columbus, Ohio : Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1211900394.
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Abreu, Tatianne Piza Ferrari. "Estudo filogeográfico de Micrurus lemniscatus (LINNAEUS, 1758) (SERPENTES: ELAPIDAE)." Universidade Federal de Goiás, 2014. http://repositorio.bc.ufg.br/tede/handle/tede/7706.
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Micrurus lemniscatus is a South American coral snake species, popularly known as “coral verdadeira”. It is widely distributed in Seasonally Dry Forests (SDF), Gallery Forests and Rainforests. The Tertiary events and the climatic oscillations of the Quaternary affected the distribution of these ecosystems altering, in turn, the distribution of animals associated to these habitats. We hypothesize that the forest expansion and contraction cycles caused by climate fluctuations may have influenced the current distribution and genetic structure of M. lemniscatus. This study aimed to study the evolutionary relationships and patterns of divergence among M. lemniscatus lineages and infer the historical biogeographic events that influenced the distribution and genetic variation. Twenty-nine individuals of M. lemniscatus were sampled from 16 localities in the states of Tocantins, Bahia, Goiás, Alagoas, Mato Grosso, Maranhão, Pará and Amazônia. Three mitochondrial regions (COI, 16S and ND4L) were sequenced, and together generated a fragment of 1595 bp and 23 different haplotypes. The analyses showed a very ancient lineage divergence ~ 4.5 Myr and high genetic differentiation among localities (FST=0.932; p<0.01), suggesting a limited gene flow among geographical regions. The demographic analyzes and neutrality tests indicated that there is no sign of expansion and that populations have constant size (Tajima’s D = 0.521; p = 0.763 and Mismatch distribution = 0.009; p= 0.779). In the analysis of the evolutionary relationship between haplotypes (by median-joining network method), no relationship between lineage and geographical space was found, suggesting incomplete lineage sorting. The results corroborate and give evidence that populations of M. lemniscatus were distributed in a more continuous region in the past, and the current distribution of this species may be the result of the reduction and separation of the geographical scope of their distribution, rather than having itself been an expansion event. This may be the result of cycles expansion of SDF and retraction of the rainforests during the cool and dry phases of the Quaternary.
Micrurus lemniscatus é uma espécie de cobra coral verdadeira sul-americana. Essa espécie possui uma ampla distribuição, ocorrendo em vários tipos de hábitats, incluindo Floresta Estacional Decidual e Semidecidual (FED), Matas de Galeria e Florestas Úmidas. No passado, os eventos do Terciário e as oscilações climáticas no Quaternário provavelmente influenciaram o padrão de distribuição dessas florestas, alterando a distribuição dos organismos associados à esses habitats. Hipotetiza-se que, os ciclos de expansão e retração florestal causados pelas flutuações climáticas podem ter influenciado a atual distribuição e estruturação genética de M. lemniscatus. Este trabalho teve por objetivo avaliar os padrões e relações evolutivas das linhagens genéticas de M. lemniscatus e compreender quais foram os eventos históricos biogeográficos que influenciaram a distribuição e a variação genética atual. Foram utilizados 29 amostras de indivíduos de M. lemniscatus de 16 localidades dos Estados de Tocantins, Bahia, Goiás, Alagoas, Mato Grosso, Maranhão, Pará, e Amazônia. Três regiões mitocondriais (COI, 16S e ND4L) foram sequenciadas, e juntas geraram um fragmento de 1595 pb e 23 diferentes haplótipos. As análises evidenciaram uma divergência bem antiga de linhagens, ~4,5 milhões de anos atrás e uma alta diferenciação genética entre as localidades (FST=0,932; p<0,01), o que sugere um fluxo gênico limitado entre essas regiões. As análises demográficas e testes de neutralidade indicaram que não há sinal de expansão e que as populações possuem tamanho constante (D de Tajima= 0,521; p= 0,763 e Distribuição de Mismatch= 0,009; p= 0,779). Na análise de relação evolutiva entre os haplótipos (pelo método median-joining network), não foi encontrada relação entre as linhagens e o espaço geográfico, sugerindo arranjo incompleto de linhagens. Os resultados corroboram e dão evidências de que as populações de M. lemniscatus eram distribuídas em uma região mais contínua no passado, e a atual distribuição desta espécie pode ser o resultado da redução e separação da abrangência geográfica de sua distribuição, ao invés de ter ocorrido propriamente um evento de expansão. Isso pode ser resultado dos ciclos de expansão das FED e retração das florestas úmidas durante as fases mais frias e secas do Quaternário.
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Mauffrey, Marie-Aline. "Impact des variations du climat et du niveau marin sur les canyons sous-marins du Golfe du Lion (France) et de la marge de l'Ebre (Catalogne) au cours du Plio-Quaternaire." Thesis, Perpignan, 2015. http://www.theses.fr/2015PERP0047/document.
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Les fluctuations du climat et du niveau marin, de plus ou moins grande amplitude, influencent le taux d’érosion sur le continent, le transport de sédiment vers l’océan et sa distribution vers le bassin profond. Les canyons sous-marins, structures érosives de premier abord, sont les zones de transfert privilégiées entre le plateau continental et le bassin profond. Peu d’études se sont concentrées sur la relation entre le remplissage des canyons, l’acheminement des sédiments et les variations du niveau marin. La chronologie de leur mise en place et de leur évolution aux échelles de temps géologiques restent également largement spéculatifs. Ce travail est consacré à la genèse des canyons sous-marins au Plio-Quaternaire sur les marges de l’Ebre et du Golfe du Lion, en Méditerranée occidentale. Cette genèse intervient après la crise de salinité messinienne, qui a conduit au démantèlement par érosion continentale des marges méditerranéennes. Après une initiation par érosion régressive au Pliocène, les canyons sous-marins connaissent un développement majeur lors de la mise en place des cycles climatiques de 100 ka au Quaternaire, en lien avec l’amplification des oscillations du niveau marin pouvant atteindre 150 m. L’utilisation et la comparaison de données sismiques (2D et 3D) de résolution et pénétration différentes, couplées à des calages chrono-stratigraphiques par forages, permettent de mettre en évidence le lien important entre les cycles climatiques de Milankovitch (principalement 100 et 41 ka) et l’architecture des têtes de canyons. Les changements rapides du climat et du niveau marin (cycles de Bond) ont également une influence importante sur le flux sédimentaire et les processus de transport, ainsi que sur la connexion/déconnexion avec les systèmes fluviatilesClimate and sea-level changes with various magnitudes control continental erosion, sediment transport and its delivery to the deep basin. Submarine canyons, that are erosional features at a first glance, are conduits for sediment transport from the continental shelf to the deep sea. Little studies focused on the relationship between canyon infill, sediment delivery and sea-level variations. The chronology of canyon development and evolution through geological time remains speculative. This thesis is dedicated to the understanding of the genesis of submarine canyons in the western Mediterranean Sea during the Plio-Quaternary. This period occurred after the major erosion of Mediterranean continental margins during the Messinian Salinity Crisis. Canyons were initiated by retrogressive erosion during the Pliocene. They further developed in relation with the amplification of sea-level changes during the Quaternary (up to 150 m). The results are based on a large range of 2D and 3D seismic data resolution and chrono-stratigraphic constraints. The stratigraphic signature of Milankovitch (mainly 100 and 40 ka) is revealed within canyon heads. Rapid climate and sea-level changes (Bond Cycles) have also a distinct signature by controlling the type and amount of sediment delivered in canyon heads, and the connection/disconnection with fluvial systems
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Hillenbrand, Claus-Dieter. "Glazialmarine Sedimentationsentwicklung am westantarktischen Kontinentalrand im Amundsen- und Bellingshausenmeer : Hinweise auf Paläoumweltveränderungen während der quartären Klimazyklen = Glaciomarine sedimentation on the continental margins of the Amundsen and Bellingshausen Seas, West Antarctica : indications for paleoenvironmental changes during the Quaternary climatic cycles /." Bremerhaven : Alfred-Wegener-Inst. für Polar- und Meeresforschung, 2000. http://www.gbv.de/dms/bs/toc/309875390.pdf.
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Murad, Waheed. "Late Quaternary Vegetation History And Climate Change In The Gobi Desert, South Mongolia." Doctoral thesis, 2011. http://hdl.handle.net/11858/00-1735-0000-000D-EF60-5.
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Gu, Fang. "Late Quaternary vegetation, climate and ocean dynamics inferred from marine sediment cores off southeastern South America." Doctoral thesis, 2018. http://hdl.handle.net/11858/00-1735-0000-002E-E49A-9.
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