Дисертації з теми "Palaeoclimate proxy"
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Saunders, Paul. "Can tufa Mg/Ca ratios be used as a palaeoclimate proxy?" Thesis, University of Hull, 2012. http://hydra.hull.ac.uk/resources/hull:6833.
Повний текст джерелаKearsey, Timothy. "Multi-proxy palaeoclimate reconstruction of the Permian-Triassic mass extinction event." Thesis, University of Plymouth, 2009. http://hdl.handle.net/10026.1/2096.
Повний текст джерелаManners, Hayley Rachael. "A multi-proxy study of the Palaeocene-Eocene Thermal Maximum in northern Spain." Thesis, University of Plymouth, 2014. http://hdl.handle.net/10026.1/2895.
Повний текст джерелаCampbell, Rochelle, Danny McCarroll, Iain Robertson, Neil J. Loader, Håkan Grudd, and Björn Gunnarson. "Blue Intensity In Pinus Sylvestris Tree Rings: A Manual For A New Palaeoclimate Proxy." Tree-Ring Society, 2011. http://hdl.handle.net/10150/622639.
Повний текст джерелаYoung, Abigail Lucy Frances. "Using Diatoms (Class Bacillariophyceae) as a biological proxy for environmental changes in the Canterbury high country, Lake Hawdon, New Zealand." Thesis, University of Canterbury. Geological Sciences, 2010. http://hdl.handle.net/10092/5074.
Повний текст джерелаBarrott, Julia Jayne. "Reconstructing North-West African palaeoclimate from speleothem geochemistry : past climate variability and implications for human history." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:9f59f1a2-591d-4b8b-8cda-b14bbfba01a3.
Повний текст джерелаFoster, Laura. "The potential of high resolution palaeoclimate reconstruction from 'Arctica islandica' /." Thesis, St Andrews, 2007. http://hdl.handle.net/10023/411.
Повний текст джерелаStott, Keziah Jane. "Assessing Arctica islandica as a proxy for Scottish marine climate change." Thesis, University of St Andrews, 2014. http://hdl.handle.net/10023/4817.
Повний текст джерелаLauterbach, Stefan. "Lateglacial to Holocene climatic and environmental changes in Europe : multi-proxy studies on lake sediments along a transect from northern Italy to northeastern Poland." Phd thesis, Universität Potsdam, 2011. http://opus.kobv.de/ubp/volltexte/2012/5815/.
Повний текст джерелаSedimente aus drei europäischen Seen wurden untersucht um die regionale Klimaentwicklung während des Spätglazials und Holozäns und die Reaktion der Ökosysteme auf Klimaschwankungen und menschlichen Einfluss zu rekonstruieren sowie die regionalen Besonderheiten der spätquartären Klimaveränderungen in einen überregionalen Kontext zu setzen. Die Sedimente des Jezioro Hańcza (Nordostpolen) wurden im Hinblick auf die frühholozäne Klimaentwicklung und die Identifikation möglicher Unterschiede gegenüber Westeuropa untersucht. Im Anschluss an die Erwärmung zu Beginn des Holozäns konnte eine weitere Verbesserung der Klimabedingungen zwischen 10 000 und 9000 Jahren vor heute nachgewiesen werden. Offensichtlich herrschten in Nordostpolen während der ersten 1500 Jahre des Holozäns noch relative kalte und trockene Klimabedingungen, höchstwahrscheinlich als Resultat besonderer regionaler atmosphärischer Zirkulationsverhältnisse. Eine antizyklonale Zirkulationszelle als Resultat eines Hochdruckgebiets über dem Rest des Skandinavischen Eisschilds verhinderte wahrscheinlich das Vordringen warmer und feuchter Luftmassen aus Westen und verursachte damit eine Abschwächung der frühholozänen Klimaverbesserung in dieser Region bis zum endgültigen Zerfall des Eisschilds, was grundsätzlich von der frühholozänen Klimaentwicklung in Westeuropa abweicht. Die spätglazialen Sedimente des Mondsees (Oberösterreich) wurden im Hinblick auf die regionale Klimaentwicklung und die Reaktion des Ökosystems auf abrupte Klimaschwankungen untersucht. Während die Erwärmung zu Beginn des Holozäns von einer zeitgleichen Reaktion des Ökosystems begleitet wurde, war die Reaktion des Ökosystems auf die Erwärmung zu Beginn des Spätglazials deutlich verzögert. Insbesondere die Ausbreitung von Nadelwäldern und die Reduktion des klastischen Eintrags folgten der spätglazialen Erwärmung erst mit einer Verzögerung von ca. 500–750 Jahren. Die Abkühlung zu Beginn der Jüngeren Dryas war durch eine deutliche Synchronizität zwischen Temperatur- und Vegetationsänderung gekennzeichnet, wohingegen der Anstieg des klastischen Eintrags erst 150–300 Jahre verzögert folgte. Eine komplexe Reaktion des Ökosystems zeigt sich auch während kurzfristiger spätglazialer Klimaschwankungen. Zusammenfassend lässt sich sagen, dass abrupte Klimaveränderungen durch komplexe und zeitlich variable Reaktionsmuster des Ökosystems gekennzeichnet sind, die hauptsächlich von dessen Klimasensitivität und den ökologischen Ausgangsbedingungen abhängen. Eine zweite Studie an den Sedimenten des Mondsees konzentrierte sich auf zwei Klimaschwankungen vor ca. 8200 und 9100 Jahren, für die Schmelzwassereintrag in den Nordatlantik und ein damit verbundenes Zusammenbrechen der thermohalinen Zirkulation als Ursache angesehen wird. Durch Warvenzählungen und 14C-Datierungen konnten sowohl die Dauer (ca. 150 Jahre) als auch das absolute Alter der Kältephase vor ca. 8200 Jahren zuverlässig bestimmt werden, welche in guter Übereinstimmung mit Resultaten aus anderen Paläoklimaarchiven stehen. Darüber hinaus wurde eine kurze Warmphase direkt im Anschluss an das Abkühlungsereignis identifiziert, die auch in anderen Klimaarchiven im nordatlantischen Raum nachweisbar ist. Diese wurde wahrscheinlich durch ein Wiedererstarken der thermohalinen Zirkulation verursacht, welches darüber hinaus eine Verschiebung ozeanischer und atmosphärischer Frontsysteme zur Folge hatte. Obwohl andere Klimaarchive auch nach dem Abkühlungsereignis vor ca. 9100 Jahren auf ein Wiedererstarken der thermohalinen Zirkulation hindeuten, finden sich in den Sedimenten des Mondsees keine Anzeichen für eine solche Wärmeperiode, was die Komplexität des globalen Klimasystems verdeutlicht. Die holozänen Sedimente des Lago d’Iseo (Norditalien) wurden im Hinblick auf die regionale Erdbebenaktivität und den Einfluss von Klima und Mensch auf Erosionsprozesse im Einzugsgebiet und den klastischen Eintrag in den See untersucht. Zahlreiche kleinere detritische Lagen in den Sedimenten spiegeln Eintrag durch extreme Oberflächenabflussereignisse wieder. Während des Früh- und Mittelholozäns zeigt sich eine deutliche Übereinstimmung zwischen erhöhtem klastischen Eintrag und kühleren und feuchteren Klimaverhältnissen, was auf einen dominanten Einfluss der natürlichen Klimavariabilität hindeutet. Im Gegensatz dazu zeigen Phasen erhöhten klastischen Eintrags während des Spätholozäns teilweise auch eine Korrelation mit erhöhter Siedlungsaktivität, was die Komplexität der Einflüsse auf Erosionsprozesse im Einzugsgebiet verdeutlicht. Darüber hinaus konnten auch fünf größere Ereignislagen nachgewiesen werden, welche durch Rutschmassen und Turbidite gekennzeichnet sind und für die lokale Erdbeben als Ursache vermutet werden. Die jüngste Ereignislage kann mit einem historisch dokumentierten proximalen Erdbeben im Jahr AD 1222 korreliert werden. Für die anderen vier Ereignislagen werden bisher undokumentierte prähistorische Erdbeben als Ursache angenommen.
Barral, Cuesta Abel. "The carbon isotope composition of the fossil conifer Frenelopsis as a proxy for reconstructing Cretaceous atmospheric CO2." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSE1148.
Повний текст джерелаThe Cretaceous was a period characterized by strongly marked climate change and major carbon cycle instability. Atmospheric CO2 has repeatedly been pointed out as a major agent involved in these changing conditions during the period. However, long-term trends in CO2 described for the Cretaceous are not consistent with those of temperature and the large disturbance events of the carbon cycle described for the period. This raises a double question of whether descriptions of the long-term evolution of atmospheric CO2 made so far are accurate or, if so, atmospheric CO2 was actually a major driver of carbon cycle and climate dynamics as usually stated. In this thesis the close relationship between the carbon isotope composition of plants and atmospheric CO2 is used to address this question. Based on its ecological significance, distribution, morphological features and its excellent preservation, the fossil conifer genus Frenelopsis is proposed as a new plant proxy for climate reconstructions during the Cretaceous. The capacity of carbon isotope compositions of Frenelopsis leaves (d13Cleaf) to reconstruct past atmospheric CO2, with regards to both carbon isotope composition (d13CCO2) and concentration (pCO2), is tested based on materials coming from twelve Cretaceous episodes. To provide a framework to test the capacity of d13Cleaf to reconstruct d13CCO2 and allowing for climate estimates from carbon isotope discrimination by plants (?13Cleaf), a new d13CCO2 curve for the Cretaceous based on carbon isotope compositions of marine carbonates has been constructed. Comparison with d13Cleaf-based d13CCO2 estimates reveals that although d13CCO2 and d13Cleaf values follow consistent trends, models developed so far to estimate d13CCO2 from d13Cleaf tend to exaggerate d13CCO2 trends because of assuming a linear relationship between both values. However, given the hyperbolic relationship between ?13Cleaf and pCO2, by considering an independently-estimated correction factor for pCO2 for a given episode, d13Cleaf values may be a valuable proxy for d13CCO2 reconstructions. ?13Cleaf estimates obtained from d13CCO2 and d13Cleaf values were used to reconstruct the long-term evolution of pCO2. The magnitude of estimated pCO2 values is in accordance with that of the most recent and relevant model- and proxy-based pCO2 reconstructions. However, these new results evidence long-term drawdowns of pCO2 for Cretaceous time intervals in which temperature maxima have been described
Rice, Emma May. "Testing the late-Holocene climate signal from ombrotrophic bogs in southernmost Chile and the Falkland Islands : a multi-proxy, multi-profile and multi-site approach." Thesis, University of Plymouth, 2017. http://hdl.handle.net/10026.1/9666.
Повний текст джерелаLabuhn, Inga. "Climate Variability in Southwest France During the Last 2000 Years : Proxy Calibration and Reconstruction of Drought Periods Based on Stable Isotope Records from Speleothems and Tree Rings." Phd thesis, Université Paris Sud - Paris XI, 2014. http://tel.archives-ouvertes.fr/tel-01063541.
Повний текст джерелаGranger, Robyn. "Palaeoenvironmental reconstruction of late Holocene climate dynamics in Southwest Africa using a multi-proxy characterization of Namaqualand mudbelt sediments." Master's thesis, University of Cape Town, 2016. http://hdl.handle.net/11427/20528.
Повний текст джерелаCabedo, Sanz Patricia. "Identification of variability in sub-Arctic sea ice conditions during the Younger Dryas and Holocene." Thesis, University of Plymouth, 2013. http://hdl.handle.net/10026.1/2858.
Повний текст джерелаXia, Qikai. "High precision TIMS U-Th disequilibrium dating and C, O, Sr isotope-based multi-proxy palaeoclimatic study of Speleothems in Australia /." [St. Lucia, Qld.], 2004. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe18421.pdf.
Повний текст джерелаKock, Simone. "Tree-growth rings as a palaeoclimate proxy for the Karoo basin." Thesis, 2018. https://hdl.handle.net/10539/25875.
Повний текст джерелаThe almost complete stratigraphic and fossil records of the Karoo Basin have made it one of the main focal points for Gondwanan palaeoenvironmental studies. The majority of Karoo palaeoenvironmental studies use vertebrate, invertebrate, macroflora and microflora fossils as proxies. Very few studies have been done on the Karoo fossil woods and their significance as palaeoenvironmental, and more specifically palaeoclimate, proxies. In this preliminary study, thirty-one Agathoxylon wood samples from the Ecca-Beaufort contact and five of the Beaufort Group’s (Karoo Basin) formations have been analysed to reconstruct the palaeoclimate for the Karoo Basin during the Beaufort times. The growth rings of each sample underwent a detailed growth ring analysis where six palaeoclimate significant anatomical features were chosen and used to obtain palaeoclimate information. The growth rings are generally wide and reflect a seasonal climate with warm/moderate temperatures and sufficient rainfall. The presence of false rings in some of the growth rings suggests that some years experienced water-stressed/semi-arid conditions. The intra-ring variation and CSDM curves of the growth rings indicate that the fossil wood samples generally reflect ‘complacent’ trees with deciduous habits. The majority of growth rings contain shear zones (i.e. S-type growth rings), which indicate a seasonal climate but can also be seen as indicators of zones with weakened wood cells (due to disease or post-depositional compression). Although this study only represents a small sample size (thirty-one specimens with very few growth rings each), the growth ring analysis illustrates the palaeoclimate potential of the Karoo fossil woods and how they could aid in improving Karoo Basin palaeoenvironmental interpretations. However, a wider geographic range and more fossil woods from other stratigraphic positions/time periods are required for the basin-wide palaeoclimate reconstruction that would make these improved palaeoenvironmental interpretations possible.
MT 2018
Sachse, Dirk [Verfasser]. "Compound-specific hydrogen isotope ratios of sedimentary n-alkanes : a new palaeoclimate proxy / von Dirk Sachse." 2005. http://d-nb.info/976737396/34.
Повний текст джерелаBelli, Romina. "Replicate palaeoclimate multi-proxy data series from different speleothems from N. Italy: reproducibility of the data and new methodologies." Thesis, 2013. http://hdl.handle.net/1959.13/1037787.
Повний текст джерелаChanges in geochemical and physical properties of speleothems are considered to be accurate proxies of climate variability. However, the climate signal is modified by the internal dynamics of the whole karst system. The aim of the research was to obtain reproducible data extracted by established and non-conventional techniques from two coeval speleothems removed at Grotta Savi cave (Italy), to gain information about regional climate responses across the Last Glacial Maximum to Holocene transition. Different past hydrological regimes for the two stalagmites’ drips were reconstructed on the basis of stalagmites’ physical characteristics and this helped to disentangle the global from the local phenomena. This non-conventional approach, was applied here for the first time on fossil sample, resulting in a benchmark for interpreting the chemical proxies, and enabling assessment of calcite formation environment, hitherto not possible. The interpretation of δ18O values as reflecting past hydrology was then validated by using the Hydrology Index. The Index, developed in this study, considers two independent proxies: the Mg concentrations and the fraction of Sr uptake that is not dictated by growth rates. The method allowed recognition of a non-hydrological component encapsulated in δ18O values, then interpreted as changes of air mass provenance and rainfall seasonality. The δ13C was chiefly driven by temperature-dependent soil respiration rate. However, a hydrological component was also detected in the δ13C by using dead carbon proportion (dcp) and 87Sr/86Sr ratios. Increases of 87Sr/86Sr ratios suggest increases of aeolian dust deflated from proximal subalpine periglacial regions facilitated by vegetation-cover reduction, soil destabilisation and windier conditions, which in turn enhanced drier conditions. Although, the dcp trend was likely related to a local, faster, soil organic matter turnover, enhanced by warmer conditions, episodes of high dcp values were possibly hydrologically induced, as a result of wetter conditions. Furthermore, the Hydrology Index and δ13C signal allowed reconstructing that wet conditions occurred during climate cooling, an improvement relative to the state of the art of δ13C interpretation, where more commonly wet conditions occurs during warming. The comparison of δ13C trend of Savi with another stalagmite with similar physical characteristics, but from a cave (Sofular) located in Turkey, revealed a common trend despite the impact of the last glaciation having been drastic at Savi (no speleothem growth). Such δ13C similarity could be related to global phenomena and point to an intriguing possibility, which needs future testing, that speleothems may encode information of the C cycle, similar to soil carbonates. The palaeoclimate interpretation extracted from the Savi records between 15 to 9 ka indicates that the Younger Dryas (YD) was a dramatic climate reversal. In the northern Adriatic, the YD is characterised by high hydrological variability, strong winds and a cooling, which resulted in a decrease of vegetation cover and increase of soil erosion. The wind regime was possibly orographically induced, with the Alps acting as a barrier, deviating westerly winds and causing increased windiness in the northern Adriatic region. The Savi records reveal a significant Early Holocene anomaly (10.4 ka), whose drier and colder conditions were probably amplified by a local synoptic framework.
Gayler, Lucyna Maria. "A palaeoenvironmental history of the Paroo and Warrego Regions, Australia: a multi-proxy, multi-site approach." Thesis, 2008. http://hdl.handle.net/1959.13/33470.
Повний текст джерелаThe records of environmental change in Australia’s arid zone can be greatly enriched by employing a multi-proxy approach and landscape-scale analysis. This research uses these tools to construct a palaeoenvironmental history of the Paroo/Warrego Region. While the Region’s flow regimes and water balances are characterised by medium-term (decadal) variability (Young, 1999), its hydrological records are inadequately brief. Subsequently, land and water management decisions are based on short term data, risking irreversible damage, desertification or loss of diversity. A better understanding of this highly dynamic landscape can thus improve the land and resource management outcomes. While dating was constrained by a lack of funds, the Paroo/Warrego history reconstructed from fluvial and aeolian deposits correlated well with events recorded from other inland regions of the Australian continent. In summary, this new research provided evidence of high lake water levels prior to the Last Glacial. The extreme aridity at the onset of Last Glacial caused long term drying of the lakes and mobilisation of the red sand dunes. In latter stages of the glacial phase the aridity gave way to periodic fluctuations between flood and drought events that probably lasted until 16 000 - 14 000 BP. The new climatic regime resulted in formation of gypsum lunettes and later, following reduction in gypsum supply, clay lunettes. The orientation of red sand dunes and lunettes indicates a more northerly extent of the westerlies than in modern times. Around the late Pleistocene-early Holocene boundary the climate became more stable and wetter, but still somewhat drier than during the pre-Last Glacial lacustrine phase. As a result, the region’s lakes reverted to a permanent and semi-permanent status. A strong aridity signal, comparable to the semi-regular droughts of the Last Glacial, was recorded in the Paroo/Warrego lakes during the late 1890s-1940s period of below average rainfall. It was followed by 50 years of wetter conditions with two extremely wet phases in the 1950s and the 1970s. Finally, the most recent records suggest a new drying trend. The semi-arid vegetation appears to have adapted to climate variability, with herbs and grasses expanding with the onset of wet conditions before being replaced by Chenopodiaceae as the landscape started to dry. The fresher lake basins and water courses were likely to provide refuge during prolonged arid phases and dispersal foci during intervening wetter periods, thus enabling greater flexibility in response to changes and enhancing resilience. The European land use interfered with the natural cycles and balances, leading to decrease in ground cover, suppression of fire, increase in runoff and catchment erosion, acceleration of sediment accumulation rates in wetlands, resulting in decline of their water holding capacity, and expansion of woody vegetation. The research improved the processing protocols, reference databases, and transfer of methods to enable greater sample processing efficiency and improve results. The use of multiple proxies (including biotic and abiotic components) and sites, as well as different depositional features, provided access to a broader picture of environmental change than was previously possible. It also facilitated multi-scale resolution, allowing discrimination between localised responses of individual lakes and regional trends. The full value of this research will come from informing natural resource managers, whose actions will shape the future landscapes of the Paroo and Warrego Region.
Gayler, Lucyna Maria. "A palaeoenvironmental history of the Paroo and Warrego Regions, Australia: a multi-proxy, multi-site approach." 2008. http://hdl.handle.net/1959.13/33470.
Повний текст джерелаThe records of environmental change in Australia’s arid zone can be greatly enriched by employing a multi-proxy approach and landscape-scale analysis. This research uses these tools to construct a palaeoenvironmental history of the Paroo/Warrego Region. While the Region’s flow regimes and water balances are characterised by medium-term (decadal) variability (Young, 1999), its hydrological records are inadequately brief. Subsequently, land and water management decisions are based on short term data, risking irreversible damage, desertification or loss of diversity. A better understanding of this highly dynamic landscape can thus improve the land and resource management outcomes. While dating was constrained by a lack of funds, the Paroo/Warrego history reconstructed from fluvial and aeolian deposits correlated well with events recorded from other inland regions of the Australian continent. In summary, this new research provided evidence of high lake water levels prior to the Last Glacial. The extreme aridity at the onset of Last Glacial caused long term drying of the lakes and mobilisation of the red sand dunes. In latter stages of the glacial phase the aridity gave way to periodic fluctuations between flood and drought events that probably lasted until 16 000 - 14 000 BP. The new climatic regime resulted in formation of gypsum lunettes and later, following reduction in gypsum supply, clay lunettes. The orientation of red sand dunes and lunettes indicates a more northerly extent of the westerlies than in modern times. Around the late Pleistocene-early Holocene boundary the climate became more stable and wetter, but still somewhat drier than during the pre-Last Glacial lacustrine phase. As a result, the region’s lakes reverted to a permanent and semi-permanent status. A strong aridity signal, comparable to the semi-regular droughts of the Last Glacial, was recorded in the Paroo/Warrego lakes during the late 1890s-1940s period of below average rainfall. It was followed by 50 years of wetter conditions with two extremely wet phases in the 1950s and the 1970s. Finally, the most recent records suggest a new drying trend. The semi-arid vegetation appears to have adapted to climate variability, with herbs and grasses expanding with the onset of wet conditions before being replaced by Chenopodiaceae as the landscape started to dry. The fresher lake basins and water courses were likely to provide refuge during prolonged arid phases and dispersal foci during intervening wetter periods, thus enabling greater flexibility in response to changes and enhancing resilience. The European land use interfered with the natural cycles and balances, leading to decrease in ground cover, suppression of fire, increase in runoff and catchment erosion, acceleration of sediment accumulation rates in wetlands, resulting in decline of their water holding capacity, and expansion of woody vegetation. The research improved the processing protocols, reference databases, and transfer of methods to enable greater sample processing efficiency and improve results. The use of multiple proxies (including biotic and abiotic components) and sites, as well as different depositional features, provided access to a broader picture of environmental change than was previously possible. It also facilitated multi-scale resolution, allowing discrimination between localised responses of individual lakes and regional trends. The full value of this research will come from informing natural resource managers, whose actions will shape the future landscapes of the Paroo and Warrego Region.
Strandberg, Gustav. "Modelling regional climate-vegetation interactions in Europe : A palaeo perspective." Doctoral thesis, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-140536.
Повний текст джерелаStudiet av paleoklimat är viktigt för att det ger kunskap om hur klimatsystemet fungerar samt för att det sätter nuvarande klimatförändring i ett nödvändigt perspektiv. Genom att studera (för)historiska perioder ökar vi vår kunskap om dessa perioder, men också om vilka processer som har betydelse för klimatets variationer. Denna avhandling behandlar framförallt interaktionen mellan klimat och växtlighet. Förändringar i växtligheten kan påverka klimatet på flera olika sätt. Dessa kan delas in i två huvudgrupper: biogeokemiska och biogeofysikaliska processer. Denna avhandling studerar de biogeofysikaliska effekterna på klimatet i klimatmodeller. Klimatmodeller är ett nödvändigt verktyg för att studera hur klimatet svarar på förändringar i klimatsystemet, samt för att göra förutsägelser om framtidens klimat. De biogeofysikaliska processerna är förknippade med markytans egenskaper. Förändrad växtlighet förändrar markytans albedo (förmågan att reflektera inkommande soltrålning), skrovlighet och förmågan att transportera vatten från marken till atmosfären genom evapotranspiration (summan av avdunstning och transpiration), vilket i sin tur påverkar energiflödena mellan markytan och atmosfären. Dessa förändringar påverkar sedermera klimatet. Det är emellertid inte självklart på vilket sätt; tätare växtlighet (t.ex. skog i stället för äng) ger minskat albedo vilket ger högre temperatur, men också ökad evapotranspiration vilket däremot ger lägre temperatur. Växtlighetsförändringars påverkan på klimatet studeras i denna avhandling i fyra olika (för)historiska perioder: två väldigt kalla perioder utan mänsklig påverkan (ca 44 000 och 21 000 år sedan), en varm period med liten mänsklig påverkan (ca 6 000 år sedan) och en kall period med avsevärd mänsklig påverkan (ca 200 år sedan). I tillägg till det studeras också dagens klimat. Resultaten visar att förändringar i växtlighet lokalt kan ha en signifikant effekt på klimatet. Kombinationen av dessa perioder ger en uppskattning av effekten av både naturlig och antropogen växtlighet i olika klimatsammanhang. Förändrad växtlighet kan ändra temperaturen med 1-3 °C beroende på årstid och område. Responsen är inte densamma överallt utan beror på lokala egenskaper hos markytan. Under vinterhalvåret är oftast albedoeffekten viktigast eftersom skillnaden i albedo mellan skog och öppet landskap då är mycket stor. Under sommarhalvåret är evapotranspirationen oftast viktigast eftersom skillnaden i albedo mellan olika växtlighetstyper då oftast är små. En förutsättning för det är att det finns tillräckligt med vatten tillgängligt för evapotranspiration. I torra områden förändras evapotranspirationen inte särskilt mycket när växtligheten förändras, vilket gör att albedoeffekten dominerar även på sommaren. Slutsatsen av dessa studier blir att förändrad växtlighet kan ha en betydande effekt på klimatet, jämförbar med den effekt som ökade halter av växthusgaser har i scenarier för framtida klimat. Alltså är det viktigt att ha en korrekt beskrivning av växtligheten i studier av (för)historiskt, nutida och framtida klimat. Det betyder att växtligheten har potentialen att fungera som en återkopplingsmekanism till naturliga klimatvariationer, men också att människan kan påverka klimatet genom att förändra växtligheten. Det betyder också att mänskligheten kan ha påverkat klimatet innan vi började använda fossilt bränsle. Följaktligen kan växtlighetsförändringar användas som ett sätt att lokalt begränsa klimatförändringar.
At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.
Swindles, Graeme T., G. Plunkett, and H. M. Roe. "A Delayed Climatic Response to Solar Forcing at 2800 cal. BP: Multi-Proxy Evidence from Three Irish Peatlands." 2007. http://hdl.handle.net/10454/2699.
Повний текст джерелаMultiproxy palaeohydrological records from three raised bogs in Northern Ireland indicate that a major shift to wetter/cooler climatic conditions postdated the rapid decrease in solar activity at 2800 cal. BP by ~100 years. This event is bracketed by two wiggle-match radiocarbon-dated cryptotephra layers in each profile, enabling a high degree of chronological precision. These replicated data corroborate previous findings based on Irish peat humification profiles, and may indicate spatial complexity in the climatic response to solar activity between oceanic and continental areas.
Bunney, E. "Leaf wax n-alkane variation in Dodonaea viscosa along an environmental gradient." Thesis, 2015. http://hdl.handle.net/2440/117963.
Повний текст джерелаThe variation in distribution and abundance of leaf wax n-alkanes has been proposed as a proxy for palaeoclimate. Understanding environmental controls on the variation in distribution and abundance of leaf wax n-alkanes is therefore necessary to determine if this is a robust tool for extracting climatic information from palaeo archives. Results of previous work to create a modern baseline for this proxy have, in some cases, been confounded by differences in species or plant type between sites or along gradients. This study investigates leaf wax n-alkane variation within a species of Australian shrub, Dodonaea viscosa, which inhabits a wide range of climatic conditions. Leaf wax n-alkane data from 43 individuals of D. viscosa were analysed from a climatic gradient ranging from central Australia to Kangaroo Island, with a mean annual temperature range of 13.9—22.7 °C and precipitation range of 164—808 mm/yr. Concentration of n-alkanes increase with increasing temperature along the gradient. Annual mean aridity index has the strongest relationship with the average chain length (ACL) of leaf wax n-alkanes and suggests that water availability is a strong driver of variation in ACL. In addition to n-alkane data, carbon isotope ratio (δ13C) and specific leaf area (SLA) data were measured to determine if this species shows predictable responses to these established and climatically sensitive leaf traits. Predicted responses in δ13C and SLA are observed in this species. Only weak effects of subspecies on leaf trait relationships with climate are found in this study. Scanning electron microscopy was used to qualitatively assess differences in leaf wax microstructure with climate and produced inconclusive results. Distributions of leaf wax n-alkanes have great potential as a proxy for palaeoclimate. Results presented here support the use of n-alkane ACL variation to detect aridity rather than temperature.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2015
Fitchett, Jennifer Myfanwy. "Towards a multi-proxy holocene palaeoenvironmental and palaeoclimatic reconstruction for Eastern Lesotho." Thesis, 2016. http://hdl.handle.net/10539/19361.
Повний текст джерелаThe eastern Lesotho highlands observe climate patterns distinct from adjacent lower altitude regions, representing a niche environment with unique biodiversity, comprising well-adapted but restricted biomes. With a heavy reliance on subsistence agriculture, Lesotho faces risks to both the economy and individual livelihoods, should current rates of climate change persist or intensify. Furthermore, eastern Lesotho serves as southern Africa’s primary water catchment, with precipitation exceeding evaporation. Any changes in the climate and hydrological systems, as are likely under climate change scenarios, would compromise biomes, livelihoods, and water security both locally and regionally. Climate change research in eastern Lesotho, is thus of particular value, yet meteorological data are sparse and the palaeoenvironmental history remains poorly resolved. This research presents the first multi-proxy Holocene palaeoenvironmental and palaeoclimatic reconstruction for eastern Lesotho. This reconstruction is developed from the results from pollen, diatom and sediment analyses, extracted from sediment cores obtained from two peat bogs at Sani Valley (~2,800 m.asl) and Mafadi Wetland (~3,390 m.asl), and from an exposed gully-sidewall profile at Sekhokong (~2,950 m.asl), approximately 1km south of the Sani Valley site. The reconstructions are temporally constrained by AMS radiocarbon dates obtained for all three sites. Mafadi Wetland demonstrates marked differences to the lower altitude sites, including slower sedimentation rates, a decrease in pollen and diatom taxa diversity, and an increase in the relative abundance of ice-tolerant diatom taxa. The microtopography of the three sites influences the rates of sedimentation, sediment properties, pollen composition, and distinct palaeoenvironmental and palaeoclimatic reconstructions for each site. The Sekhokong record commences in the late Pleistocene, with a wet period from ~13,180-10,850 cal. yr BP, interrupted by a dry period from ~13,080-12,830 cal. yr BP. From ~10,550-6,420 cal. yr BP, the Sekhokong record indicates a drier climate with a slow transition to warmer, wetter conditions. The Mafadi Wetland record commences with cold, wet conditions from ~8,140-7,580 cal. yr BP, followed by a warmer, drier period from ~7,520-6,680 cal. yr BP. Thereafter, greater microclimatic differences are apparent. For Sekhokong, warmer, dry conditions are inferred for ~6,420-6,000 cal. yr BP, followed by cold, wet conditions from ~6,000-5,450 cal. yr BP. Warmer, dry conditions commence earlier at Mafadi Wetland, from ~6,160-5,700 cal. yr BP, coinciding with the initiation of a longer wet period at Sani Valley, from ~6,200-4,900 cal. yr BP. At Sekhokong, a dry, warmer period follows from ~5,450-3,700 cal. yr BP. At Sani Valley, drier conditions are evident from ~4,770-4,470 cal. yr BP, followed by a cold, wet period from ~4,460-2,260 cal. yr BP. For Mafadi Wetland, these cold, wet conditions endure longer, from ~5,600-1,100 cal. yr BP. This overlaps with similarly cool, wet conditions at Sekhokong, from ~3,650- 1,200 cal. yr BP. By contrast, dry conditions are evident at Sani Valley, from ~2,260-1,350 cal. yr BP. For all three sites, ~1,000 cal. yr BP to present is characterised by progressive drying, with discrete wet events. Pronounced cold events are detected at ~12,660 cal. yr BP, ~8,400-8,000 cal. yr BP and ~150 cal. yr BP. The results of this study indicate similarities with records from adjacent studies in western Lesotho and South Africa, although with notable variability in the timing of events. The palaeoenvironmental reconstructions for eastern Lesotho, and their comparison with existing studies, provide valuable information to improve the understanding of southern African Holocene climates, and to facilitate the development of high resolution, accurate climate models for the eastern Lesotho region.