This thesis presents a multi-proxy paleoenvironmental reconstruction from the sedimentary archives of Lilandsvatnet, a small arctic lake on Vestvågøy, in the Lofoten Islands, Norway. Lofoten has a rich history of human settlements existing throughout the Holocene. The catchment of Lilandsvatnet was the location of a prominent Viking chieftain farm that existed throughout the Iron Age, and the sedimentary archive contains a strong signal of prehistoric and historic human settlements and land-use practices. Paleoenvironmental reconstructions in this thesis show evidence for Holocene environmental variability in response to both natural and anthropogenic forcing. Cryptotephra deposits from Icelandic eruptions further contrain sediment chronology in the study, allowing reconstructions of subtle changes in the landscape with excellent chronological control during the late Holocene period of settlement. Additionally, I attempt to improve existing methods for crypto-tephrochronology through the development of new techniques.

This study was designed with the overriding goal of improving our understanding of the nature, causes, and impacts of past climatic conditions in the High Arctic and to evaluate the potential impacts of future climatic warming. Specifically, the focus of this project was centered on Upper and Lower Murray Lakes (81° 21’ N, 69° 32’ W) on northern Ellesmere Island, Nunavut, Canada. Sediment cores were collected from each of the lakes in order to reconstruct past climate and environmental variability and space-borne synthetic aperture radar (SAR) data were used to evaluate recent variability in the ice cover of these lakes. The climatic setting and physical characteristics of Lower Murray Lake has led to the formation and preservation of annually laminated sediments (varves). Varve deposition began ca. 5200 calendar years BP and continued through 2004 AD, providing an annual record of sediment accumulation spanning the past 5200+ years. Annual mass accumulation was correlated to regional July temperatures providing a means of quantitatively evaluating past temperature changes in the region. The temperature reconstruction suggests that recent temperatures are ~2.6°C higher than minimum temperatures observed during the Little Ice Age, maximum temperatures during the past 5200 years exceeded modern values by ~0.6°C, and that minimum temperatures observed approximately 2900 varve years BC were ~3.5°C colder than recent conditions. SAR observations of the ice cover Upper and Lower Murray Lake were used to assess the potential effects of past and future temperatures on lake-ice conditions. Under current climatic conditions the lakes average several weeks of ice-free conditions in August and early September, although in some years a continuous ice cover persists throughout the year. The relationship between summer temperature and ice melt at the lakes suggests that recent warming in the High Arctic has forced the lakes across a threshold from a state of perennial ice cover to seasonal melting. Projected future warming will significantly increase the duration of ice free conditions on Upper and Lower Murray Lakes. Ice-out is predicted to occur between 6 and 28 days earlier for every 1°C of warming.

No description available.

<p> This investigation is intended to explore and trace the trend in the development of muskeg (organic terrain), of which water is an essential factor. The work proceeded as follows: field work and laboratory pollen macerations, identification of pollen and spores and pollen counting; and finally the analysis of the results obtained. </p> <p> The results do not favour the establishment of a strong relationship between water in muskeg and vegetation in situ. However, this needs further test. On the other hand, there are relationships found between pollen species, and also interesting natural grouping was observed to exist in the bogs studied, due to unknown factors. </p> / Thesis / Master of Science (MSc)

The Mississippi Sound is underlain by late Pleistocene aged sediments of the Biloxi, Prairie, and Gulfport Formations topped by an erosional unconformity, which was an exposed land surface during the sea level low-stand of the last glacial maximum. During that period, rivers and streams draining upland watersheds cut across the exposed coastal plain incising a network of distributary fluvial channels. Subsequent sea level rise covered the incised drainage network with a relatively thin (10-20 m) layer of reworked Holocene aged sediments. Here, an extensive database of archived and newly collected seismic reflection profile data, as well as archived core data, is analyzed to map the paleotopography and the paleo-drainage network of the Pleistocene-Holocene unconformity surface beneath the western Mississippi Sound. Approximately 255 km of seismic data was acquired with a 2-16 kHz chirp sub-bottom profiling sonar. Additionally, 978 km of seismic data was accessed through a United States Geological Survey archive along with over 20 historical cores. Results indicate that the Pleistocene-Holocene unconformity under the western Mississippi Sound is gently dipping to the southeast (<0.05°) and contains a complex network of incised paleofluvial channels with relief ranging from 5-10 m and widths ranging from 0.3–2 km. A conceptual model for paleo-channel incision and infilling as well as modern analogue depositional environments are presented.

Dans lhémisphère Sud, les reconstitutions paléoclimatiques à haute résolution sont encore relativement rares. Cette partie du monde joue pourtant un rôle essentiel dans la compréhension des changements climatiques terrestres. Le Sud du Chili étant suffisamment éloigné des calottes glaciaires de lhémisphère Nord et de linfluence de la circulation thermohaline, il constitue une région idéale en vue détudier les changements paléoclimatiques de lhémisphère Sud. Dans ce travail, le remplissage sédimentaire de deux lacs chiliens dorigine glaciaire a été étudié par une analyse multi-paramètres de carottes prélevées lors de lété austral 2002 dans le cadre du projet SSTC ENSO-Chili. Dans le lac Puyehue (164 km², 40°S, altitude 185 m), la carotte la plus prometteuse a été prélevée au site PU-II, localisé sur un cordon morainique sous-aquatique, dominé par les courants intermédiaires du Rio Golgol. Les sédiments de ce site sont finement laminés et faiblement perturbés par les activités volcanique et sismique. Premièrement, une carotte courte du site PU-II a été étudiée de manière détaillée en vue de (1) tester différentes techniques de mesure de la densité et du contenu sédimentaire en matière organique et en silice biogénique, et (2) reconstituer les changements climatiques régionaux au cours des 600 dernières années. Plusieurs traceurs ont été utilisés : la granulométrie, la susceptibilité magnétique, la géochimie des éléments majeurs, les concentrations en silice biogénique ainsi que les concentrations et les propriétés géochimiques de la matière organique (C/N, d13C). Ces analyses sont utilisées pour reconstituer les variations de paléoproductivité et de paléoprécipitations aux alentours de 40°S. Les résultats démontrent que, durant les 600 dernières années, les plus forts taux daccumulation massique en particules terrigènes sont enregistrés dans lintervalle 1490 1700 AD. Ce résultat est interprété comme une période humide associée à la mise en place du Petit Age Glaciaire européen (LIA). Les fortes précipitations caractérisant cette période pourraient être la signature locale du LIA. Le LIA serait donc un évènement global qui nest pas restreint à lhémisphère Nord. Les traceurs sélectionnés ont ensuite été appliqués à une carotte de 11 m de longueur prélevée au site PU-II. Le modèle dâge de cette carotte a été élaboré à partir de 9 datations radiocarbone et prouve que cette séquence sédimentaire couvre la dernière déglaciation et lHolocène. Les résultats démontrent que la granulométrie est hautement corrélée avec le contenu biogénique du sédiment et peut ainsi être utilisée comme traceur de paléoproductivité lacustre. La susceptibilité magnétique quant à elle est fortement corrélée avec les concentrations en aluminium et en titane et constitue un indicateur des apports terrigènes. Les variations temporelles de la composition du sédiment démontrent que, depuis le Dernier Maximum Glaciaire, la Région des Lacs chilienne a été soumise à trois changements climatiques abrupts survenus lors dune évolution climatique à plus long terme. Ces changements climatiques rapides sont : (1) la fin du Dernier Maximum Glaciaire à 17.300 cal. yr. BP ; (2) un évènement froid entre 13.100 et 12.300 cal. yr. BP, caractérisé par une terminaison abrupte et interprété comme léquivalent local de la période froide caractéristique du Dryas Récent et (3) une instabilité climatique à 3400 2900 cal. yr. BP probablement à mettre en relation avec une faible activité solaire. Lâge de lévènement froid à 13.100 12.300 cal. yr. BP est comparé aux datations obtenues sur des enregistrements similaires dans les deux hémisphères. Cette comparaison démontre que lévènement enregistré à Puyehue précède denviron 500 à 1000 ans lévènement froid caractéristique de la période du Dryas Récent dans lhémisphère Nord. Lenregistrement sédimentaire du lac Icalma (11,65 km², 38°S, altitude 1140 m) est fortement perturbé par les évènements sismiques et volcaniques. Lexistence de particules sédimentaires grossières nous a amenés à développer une méthode de mesure granulométrique combinant diffraction laser et tamisage par voie sèche. Les descriptions macroscopiques, les analyses granulométriques, les profils de susceptibilité magnétique et les résultats minéralogiques ont permis de décrire quatre types de dépôts évènementiels probablement engendrés par des séismes (homogénites, turbidites, slumps et dépôts chaotiques). Ces analyses démontrent également que les turbidites et les homogénites sont engendrées par un mécanisme similaire et que des dépôts texturalement intermédiaires existent. Ils peuvent être regroupés sous le terme turbidite s.l. et, dans ce cas, une homogénite serait léquivalent dune turbidite déposée sous linfluence dun effet de seiche. La séismite la plus récente décrite dans les sédiments du lac Icalma est un dépôt de slump ubiquiste de 6 cm dépaisseur daté à 1100 AD. Bien que la région ait été affectée par de nombreux séismes de magnitude importante au cours de la période historique (1500 2000 AD), il semble quaucun dentre eux nait engendré une séismite dans le lac Icalma. Daprès les résultats obtenus sur deux carottes longues (8 m), la région dIcalma a été soumise à une importante activité sismo-tectonique entre 3000 et 2200 cal. yr. BP.

Unclear predictions surrounding climate change, associated sea-level rise and potential impacts upon coastal environments have placed an emphasis on the importance of sea-level change. Past sea-level fluctuations have been measured using biological and geomorphological forms of evidence. One such biological proxy is salt-marsh foraminifera, which have been used as a high-resolution indicator of past sea-level change, based on the assumption that surface foraminiferal assemblages are similar in composition to buried fossil foraminifera. In South Africa, there is ongoing research seeking to produce high-resolution records of sealevel change, however foraminifera remain an underutilized source of proxy evidence. This research applies salt-marsh foraminifera as precise indicators of relative sea-level change at Kariega Estuary on the Eastern Cape coastline of South Africa. Distributions of modern foraminiferal assemblages were investigated, revealing vertical zonation across the intertidal zone. The foraminiferal and marsh vegetation zones were in part similar and overlapped to a certain extent, identifying three zones; high, low and tidal flats. This suggested foraminiferal distribution is a direct function of elevation relative to tidal fluctuation. A 94 cm core consisting of peat, sand and clay sediments was extracted from the salt marsh. A chronological framework for the core was based on five AMS radiocarbon age determinations of both bulk sediment and shell fragment samples placing the record within the last 1500 years Before Present (BP). The basal shell age was a clear outlier to all bulk sediment ages, possibly as a result of shell recrystallisation. The bulk sediment age determinations suggested two possible age reversals, potentially linked to sedimentary hiatus or contamination. These inconsistencies in the chronology were best viewed as separate age models. The core was analysed at a high resolution, whereby fossil foraminifera were extracted every 2 cm’s down the core. A transfer function was applied to calculate the former elevation at which each core sample once existed, to produce a relative sea-level reconstruction. The reconstruction was related to the age models to produce two possible sea-level curve scenarios. Reconstructed curves from both scenarios depict a 0.5 m (±0.16 m) sealevel highstand at 1500 cal years BP followed by a lowstand of -0.6 m (±0.03 m). Scenario One reached its lowest recorded sea-level between 600 cal years BP and 500 cal years BP and then fluctuated below present day levels. Scenario Two reached its lowest recorded sea-level around 1200 cal years BP, followed by low amplitude fluctuations and a relatively stable period from 100 cal years BP till the present day. The 1500 cal years BP highstand recorded for both scenarios correlates well with existing palaeoenvironmental literature from the southern African coastline. Chronological limitations associated with the remainder of the record hinder inter-comparison with previous studies. The outcomes of this research suggest that intertidal saltmarsh foraminifera demonstrate enormous potential for the high-resolution reconstruction of relative sealevel change in the South African context. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.

In the recent past it has become evident that the Earth's climate is changing, and that human activity play a significant role in these changes. One of the regions where the ongoing climate change has been most evident is in the Arctic: the surface temperature has increased twice as much in this region as compared to the global average, in addition, a significant decline in the Arctic sea-ice extent has been observed in the past decades. Climate model studies of past climates are important tools to understand the ongoing climate change and how the Earth's climate may respond to changes in the forcing. This thesis includes studies of the Arctic climate in simulations of the early and mid-Holocene, 9 000 and 6 000 years before present. Changes in the Earth's orbital parameters resulted in increased summer insolation as compared to present day, especially at high northern latitudes. Geological data imply that the surface temperatures in the early to mid Holocene were similar to those projected for the near future. In addition, the geological data implies that the Arctic sea ice cover was significantly reduced in this period. This makes the early to mid-Holocene an interesting period to study with respect to the changes observed in the region at present. Several model studies of the mid-Holocene have been performed through the Paleoclimate Modeling Intercomparison Project (PMIP1 to PMIP3). The simulations have been performed with climate models of varying complexity, from atmosphere-only models in the first phase to fully coupled models with the same resolution as used for future climate simulations in the third phase. The first part of this thesis investigates the simulated sea ice in the pre-industrial and mid-Holocene simulations included in the PMIP2 and PMIP3 ensemble. As the complexity of the models increases, the models simulate smaller extents and thinner sea ice in the Arctic; the sea-ice extent suggested by the proxy data for the mid-Holocene is however not reproduced by the majority of the models. One possible explanation for the discrepancy between the simulated and reconstructed Arctic sea ice extent is missing or inadequate representations of important processes. The representation of atmospheric aerosol direct and indirect effects in past climates is a candidate process. Previous studies of deeper time periods have concluded that the representation of the direct and indirect effects of the atmospheric aerosols can influence the simulated climates, and reduce the equator to pole temperature gradient in past warm climates, in better agreement with reconstructions. The second part of the thesis investigates the influence of aerosol on the early Holocene climate. The indirect effect of reduced aerosol concentrations as compared to the present day is found to cause an amplification of the warming, especially in the Arctic region. A better agreement with reconstructed Arctic sea ice extent is thus achieved. / Under senare tid har det blivit uppenbart att jordens klimat håller på att förändras, och att mänsklig aktivitet spelar en viktig roll för dessa ändringar. Ett av de områden där den pägäende klimatfärändringen har varit tydligast är Arktis: temperaturen vid ytan har ökat dubbelt så mycket här jämfört med det globala genomsnittet. Dessutom har man observerat en betydande nedgång i havsisens utbredning i Arktis de senaste decennierna. Simuleringar gjorda med klimatmodeller av forntida klimat är viktiga verktyg för att förstå de pågående klimatförändringarna och hur jordens klimat påverkas av ändringar i klimatsystemets drivningar. Denna avhandling består av studier av det arktiska klimatet i modellsimuleringar av tidig och mid-holocen, ca. 9 000 och 6 000 år före nutid. Förändringar i jordens bana kring solen resulterade i en ökad sommar-solinstrålning jämfört med nutid, särskilt vid höga nordliga breddgrader. Geologiska data antyder att jordens temperatur vid ytan under denna period kan jämföras med dem vi förväntar för den närmaste framtiden. Vidare indikerar geologiska data att havsisen i Arktisk var kraftigt reducerad under denna period. Detta gör tidig till mid-holocen till en intressant period att studera, med avseende på de förändringar som för närvarande har observerats i området. Flera modellstudier av mitt-holocen har utförts i de olika faserna av Paleoclimate Modeling Intercomparison Project (PMIP1 till PMIP3). Simuleringarna har utförts med klimatmodeller av varierande komplexitet, från atmosfärsmodeller i den första fasen, till fullt kopplade modeller med hög rumslig upplösning i den tredje fasen. I den första delen av denna avhandling undersöks den simulerade havsisen i de förindustriella och mid-holocen simuleringar som ingår i PMIP2 och PMIP3 ensemblerna. Modellerna simulerar mindre utbredning och tunnare havsis i Arktis i den senare PMIP ensemblen, men fortfarande återskapar inte modellerna generelt den havsisutbredning som de geologiska data indikerar. En möjlig förklaring till skillnaderna mellan den simulerade och rekonstruerade havsisutsträckningen kan vara att viktiga processer i klimatsystemet saknas eller inte är tillräckligt väl beskrivna i modellerna. Beskrivningen av atmosfäriska aerosoler och dess effekter på klimatet är en möjlig kandidatprocess. Från studier av forntida varma tidsperioder har man dragit slutsatsen att beskrivningen av aerosoleffekterna påverkar det simulerade klimatet. Bland annat kan man minska temperaturgradienten mellan ekvator och polerna i tidigare varma klimat, vilket bättre överensstämmer med temperaturrekonstruktioner. Den andra delen av avhandlingen undersöker påverkan av aerosoler på klimatet under tidig holocen. Den indirekta effekten som följer av lägre aerosolkoncentrationer i tidig holocen jämfört med i dag, visar sig orsaka en förstärkning av uppvärmningen, särskilt i det arktiska områet, vilket stämmer bättre med havsisrekonstruktioner från denna period. / <p>QC 20130910</p>

No description available.

Small peat basins (c. 10-50 m diameter) were used to obtain fine spatial resolution pollen-stratigraphic records of Holocene vegetation and land-use history in upland West Glen Affric and adjacent lowland Kintail, north-western Scottish Highlands. These data provide evidence for remarkably diverse and dynamic early to mid-Holocene vegetational mosaic and sustained later Holocene upland land-use. While acidophilous Pinus sylvestris-Betula-Calluna vulgaris communities on lower hillslopes appear comparable with other areas of the Highlands, data from floodplain and alluvial fan sediments in West Affric indicate a greater woodland diversity. Betula-dominated alluvial woods included a species-rich mix of arboreal, fen, tall-herb and ruderal herbaceous taxa, with Pinus forming small populations, confined to marginal soils. Ulmus was an important component of the lowland Betula-Alnus woods. Spatial differences in soil forming processes, particularly nutrient and base status, played a primary role in determining community composition, structure, dynamics, species diversity and stability. Inferred climatic shifts during the mid-Holocene, initially to drier, more continental conditions, followed by increased oceanicity, are suggested to have made woodland communities increasingly vulnerable to low intensity grazing disturbance and anthropogenic interference during the later Neolithic and early Bronze Age. These stresses resulted in widespread woodland decline, including that of Pinus, with the spread of blanket peat and heath on poorer hillside soils, and grassland communities on alluvial sediment. Bronze Age agricultural expansion is followed by several phases of expansion and/or intensification, with sustained pastoral and arable activity in the lowlands and on small 'islands' of richer soils in the uplands. There is little evidence for abandonment and the longevity of agricultural activity, particularly cultivation, above 250 m OD clearly indicates that the unqualified assumption of upland marginality is inappropriate. The implications for the interpretation of land-use in the Highlands from conventional palynological and archaeological records are discussed. The level of spatial and temporal detail regarding the palaeoecology of plant communities and adaptive land management evident in the present study is not afforded by conventional pollen analyses. This suggests that fine-spatial resolution palynology has the potential to contribute previously unrecognised information at scales which are directly applicable to ecological and human understanding and which can be more successfully integrated with neoecological and archaeological research, fostering closer collaboration between the disciplines.