Growth rates, δ18O and δ13C of five stalagmites from the west coasts of North and South Islands, New Zealand, provide records of millennial-scale climate variability over the last ~75 kyr. Thirty-five uranium-series ages were used to provide the chronology. δ18O of stalagmite calcite was influenced by changes in moisture source region, temperature and both δ18O and δ13C primarily display a negative relationship with rainfall. To assist interpretation of climatic signals δ18O profiles were adjusted for the ice-volume effect. Changes in these proxies reflect changes in the strength of the circumpolar westerly circulation and the frequency of southwesterly flow across New Zealand. MIS 4 was a period of wet and cool climate lasting from 67.7 to 61.3 kyr B.P., expressed in the stalagmites by an interval of strongly negative isotope ratios and increased growth rate. This contrasts with less negative δ18O and δ13C, and slow growth, interpreted as dry and cold climate, during much of MIS 2. This difference between MIS 2 and MIS 4 provides an explanation for why glacial moraines in the Southern Alps of MIS 4 age lie beyond those deposited during the last glacial maximum (MIS 2). Heinrich events, with the exception of H0 (the Younger Dryas), are interpreted from high-resolution South Island stalagmite HW05-3, from Hollywood Cave, West Coast, as times of wetter and cooler climate. Minima in δ18O and δ13C (wet periods) occurred at 67.7-61.0, 56-55, 50.5-47.5, 40-39, 30.5-29, 25.5-24.3 and 16.1-15. kyr B.P. matching Heinrich events H6-H1 (including H5a) respectively. This demonstrates a robust teleconnection between events in the North Atlantic and New Zealand climate. Minima in δ18O also occurred at similar times in less well-dated North Island stalagmite RK05-3 from Ruakuri Cave, Waitomo. Speleothems from low-latitudes have revealed that Heinrich events forced southerly displacement of the Intertropical Convergence Zone. This caused steepening of the temperature gradient across mid-southern latitudes, increased westerly circulation and resulted in wet conditions on the west coast of both islands. Immediately following H1 in the HW05-3 stable isotope profiles is another excursion to more negative isotopic values, suggesting wet and cold climate, lasting from 14.6 to 13.0 kyr B.P. Such a climate on the West Coast at this time has been previously suggested from glacier advance (e.g. Waiho Loop moraine) and decreased abundance of tall trees on the landscape. This event occurred too early to be a response to H0, but is synchronous with a return to cool climate in Antarctica. Thus West Coast climate appears to have been sensitive to changes in Antarctica as well as the North Atlantic. Isotopic minima (wet and cool climate) in South Island stalagmite GT05-5, which formed during the Holocene, first occurred 4.6 kyr B.P. This began a series of four oscillations in isotope ratios, the last terminating when the stalagmite was collected (2006). Onset of these oscillations is associated with initiation of ice advance in the Southern Alps, and beginning of the Neoglacial. The last oscillation displays enriched isotope ratios lasting from 1.2 to 0.8 kyr B.P. succeeded by depleted ratios lasting until 0.15 kyr B.P., mirroring the Medieval Climate Optimum and Little Ice Age, respectively, of European palaeoclimate records.

En 2000, une carotte de 15 m a été prélevée dans le lac d'Annecy : celle-ci a fait l'objet d'une étude permettant d'une part, d'établir une chronologie annuelle de la sédimentation et d'autre part, de reconstruire l'évolution hydrologique du lac d'Annecy associée aux grands événements climatiques des 15 000 dernières années. La chronologie des sédiments récents a été établie à partir de mesures radiochronologiques (137Cs et 210Pb), comptage de varves et grâce à la reconnaissance de crues historiques. Au-delà du Petit Age de Glace, le comptage de varves a été précisé grâce à des datations 14C SMA, à l'identification de téphras et aux variations de d18O des ostracodes benthiques. Le modèle d'âge à résolution infradécennale recouvre l'ensemble de l'Holocène et du Tardiglaciaire (âge estimé de la base 15380 calBP). La sédimentologie et les propriétés physiques du sédiment (SM, IRM, ARM, Spectrocolorimètrie, etc...) attestent de la sensibilité du bassin versant et de son hydrologie aux évènements majeurs de l'Holocène et du Tardiglaciaire (Oscillations climatiques Tardiglaciaire, Dryas récent, évènement 8.2 ka, optimum Holocène, Petit âge de Glace). On observe de plus dans les sédiments les traces de l'impact humain dès 2700 calBP.

Dans les systèmes chevauchants la tectonique, l'érosion et la sédimentation interagissent pour créer des reliefs et des bassins syntectoniques. Le but de ce travail est d'aider à mieux comprendre et quantifier le contrôle exercé par ces trois phénomènes sur 1) la morphologie des reliefs; 2) la localisation des dépôts sédimentaires et les types de dépôt; 3) la localisation de la déformation. Dans ce but, et dans la première partie de mon travail, j'ai procédé au développement d'un modèle numérique comportant une simulation de la croissance incrémentale des plis par propagation de faille, couplée à une loi de diffusion rendant compte des transports superficiels (érosion et sédimentation). Ceci permet d'étudier la répartition de l'érosion et de la sédimentation en fonction de l'activité tectonique et des relations entre plissement/chevauchement. La mise en oeuvre des modélisations permet aussi une analyse de l'évolution des systèmes chevauchants. L'application à l'exemple du Subandin de Bolivie, montre que 1) L'évolution du prisme tectonique et la formation des grands bassins sont pour une grande part contrôlées par la géométrie du prisme initial ainsi que par celle du plan de décollement régional; 2) Les phénomènes superficiels qui permettent la formation de vastes bassins syntectoniques influencent la localisation de la déformation, en contrôlant la géométrie de la surface du prisme. Dans la seconde partie de ce travail la méthodologie mise au point, est appliquée aux Siwalik de l'Ouest Népal. Dans cette région, où le système chevauchant est de mieux en mieux contraint par des études de terrain, on observe également de vastes bassins transportés inégalement répartis sur la zone d'étude. Les modélisations montrent que le paramètre contrôlant au premier ordre le développement des bassins transportés est le pendage du plan de décollement. Un fort pendage du plan de décollement, qui induit une forte épaisseur des écailles tectoniques, favorise l'apparition de vastes bassins transportés. Dans le cas contraire, où le pendage du plan de décollement est faible, la forte pente de surface du prisme favorise l'érosion et les réactivations hors séquence. Ces résultats sont confirmés grâce aux coupes équilibrées effectuées dans l'Ouest Népal qui montrent que les bassins transportés se développent au-dessus d'un prisme tectonique épais (5500 m), alors que là où le système tectonique, incorporant des écailles, n'est plus épais que de 4000 m, on observe des réactivations d'un chevauchement interne. Les modélisations montrent , aussi, que le développement latéral des structures frontales par le biais de plis par propagation de faille, contrôle les morphologies du synclinal et du crêt situes en position interne. Ceci est confirmé par une étude morphostructurale qui montre que la structure frontale est constituée de tronçons assez courts qui se relaient et que la sédimentation et la morphologie du système sont contrôlés par ces relais. Dans les Siwalik de l'Ouest Népal, existe une lacune de sismicité, et les vitesses de raccourcissement instantanées sont faibles (2-7 mm/an). L'étude des terrasses alluviales des bassins syntectoniques, montre 1) que le remplissage holocène du Dun de Deukhury est largement dépendant de la localisation de l'activité tectonique le long des chevauchements limitant ces bassins, et formant des "barrages tectoniques"; 2) que l'enregistrement des variations climatiques est masqué par l'importance des phénomènes tectoniques; 3) que les vitesses de surrection de ces terrasses alluviales, déduites de datations au C14, permettent de calculer des vitesses moyennes de raccourcissement de l'ordre de 15 à 20 mm/an pour la période holocène; 4) qu'il existe de nombreuses réactivations hors séquence, se localisant le long d'un chevauchement intermédiaire, le MDT. Les faibles déformations actuelles déduites de mesures GPS ne sont donc pas représentatives de la déformation de cette partie de la chaîne himalayenne sur une longue période. Ces différences de vitesses entre déformations actuelles et déformations moyennes telles qu'elles sont enregistrées dans cette partie du Népal, témoignent d'un rallentissement momentané de la déformation qui pourrait être en accord avec une période intersismique d'un cycle sismique. Des périodes de relatif calme tectonique comme la période actuelle pourraient être suivies de période où l'activité tectonique est plus intense (le futur proche?). L'alternance de la localisation du raccourcissement le long des structures chevauchantes, frontales ou en position plus interne, suivrait un cycle de quelques milliers d'années. Une étape du cycle serait caractérisée par une activité tectonique concentrée sur le chevauchement frontal; une autre étape verrait l'activité tectonique se répartir équitablement entre la structurefrontale et un chevauchement en position interne.

<p>The objective of the thesis was to explore the potential of diatoms (<i>Bacillariophyceae</i>) as indicators of Holocene climate and environmental change in northern Sweden (Abisko region, 68°21'N, 18°49'E). A modern surface-sediment calibration set including 100 lakes was developed and lake-water pH, sedimentary organic content (assessed by loss-on-ignition) and temperature were identified as most powerful environmental variables explaining the variance within the diatom assemblages. Transfer functions based on unimodal species response models (WA-PLS) were developed for lake-water pH and mean July air temperature (July T), yielding coefficients of determination of 0.77 and 0.70, and prediction errors based on leave-one-out cross-validation of 0.19 pH units and 0.96 °C for lake-water pH and July T, respectively. The transfer functions were validated with monitoring data covering two open-water seasons (lake-water pH) and meteorological records covering the 20th century (July T). The good agreement between diatom-based inferences and measured monitoring data confirmed the prediction ability of the developed transfer functions. </p><p>Analysing a Holocene sediment core from a lake nearby Abisko (Vuoskkujávri), diatoms infer a linearly decreasing July T trend (1.5 °C) since 6,000 cal. BP, which compares well with inferences based on chironomids and pollen from the same sediment core. The lake-water pH inference shows a pattern of moderate natural acidification (c. 0.5 pH units) since the early Holocene, reaching present-day pH values at c. 5,000 cal. BP. By fitting fossil diatom samples to the modern calibration set by means of residual distance assessment within canonical correspondence analysis (CCA), the early Holocene (between 10,600 and 6,000 cal. BP) was identified as a problematic time-period for diatom-based inferences and, consequently, reconstructions during this period are tentative. Pollen-based inferences also show 'poor' fit between 10,600 and 7,500 cal. BP and chironomids probably provide the most reliable July T reconstruction at Vuoskkujávri, with 'poor' fit only during the initial part of the Holocene (between 10,600 and 10,250 cal. BP). </p><p>Possible factors confounding diatom-based July T inferences were investigated. Using detrended CCA (DCCA), Holocene sediment sequences from five lakes indicate that during the early Holocene, mainly physical factors such as high minerogenic erosion rates, high temperature and low light availability may have regulated diatom assemblages, favouring <i>Fragilaria</i> species. In all five lakes, diatom assemblages developed in a directional manner, but timing and scale of development differed substantially between lakes. The differences are attributed primarily to the geological properties of the lake catchments (with strong effects on lake-water pH), but other factors such as climatic change, vegetation, hydrologic setting and in-lake processes appear to regulate diatom communities in each lake differently. The influence of long-term natural acidification on diatom assemblages progressively declined during the Holocene with corresponding increase of the influence of climatic factors.</p>

Throughout the Holocene, appreciable changes in bathymetry are hypothesized to have resulted in large changes to tidal datums in coastal and estuarine areas. An understanding of tidal change is an important contribution to the knowledge of relative historical sea-level change and future coastal planning. To test this hypothesis, the Advanced Circulation (ADCIRC) model was used, with representative bathymetric grids based on glacial isostatic adjustment models and semi-empirical sea level rise predictions, in order to model the time-varying tidal behavior of the Delaware Bay. Model runs were conducted at various time slices between 10,000 years before present and 300 years into the future on high resolution grids that allowed for inundation moving forward in time. Open boundary tidal forcing was held constant in time to highlight the effect of the changing regional bathymetry. With each change in sea level, the shape of the Delaware Bay was considerably altered, leading to changes in the tides. Resonance and shallow water dissipation appeared to be the primary mechanisms behind these changes. Results showed that tidal ranges have nearly doubled in the upper Delaware Bay over the past 3000 years, while decreasing in the lower bay by 8%. Tidal range change represents a possible correction to past sea level rise estimates from the geologic record. Scenarios incorporating future sea level predictions primarily showed a small decrease in tidal range, potentially impacting future water levels and tidal sediment transport. Trends modeled were consistent with field measurements of relative change over similar time periods. / Graduation date: 2012

The objective of the thesis was to explore the potential of diatoms (Bacillariophyceae) as indicators of Holocene climate and environmental change in northern Sweden (Abisko region, 68°21'N, 18°49'E). A modern surface-sediment calibration set including 100 lakes was developed and lake-water pH, sedimentary organic content (assessed by loss-on-ignition) and temperature were identified as most powerful environmental variables explaining the variance within the diatom assemblages. Transfer functions based on unimodal species response models (WA-PLS) were developed for lake-water pH and mean July air temperature (July T), yielding coefficients of determination of 0.77 and 0.70, and prediction errors based on leave-one-out cross-validation of 0.19 pH units and 0.96 °C for lake-water pH and July T, respectively. The transfer functions were validated with monitoring data covering two open-water seasons (lake-water pH) and meteorological records covering the 20th century (July T). The good agreement between diatom-based inferences and measured monitoring data confirmed the prediction ability of the developed transfer functions. Analysing a Holocene sediment core from a lake nearby Abisko (Vuoskkujávri), diatoms infer a linearly decreasing July T trend (1.5 °C) since 6,000 cal. BP, which compares well with inferences based on chironomids and pollen from the same sediment core. The lake-water pH inference shows a pattern of moderate natural acidification (c. 0.5 pH units) since the early Holocene, reaching present-day pH values at c. 5,000 cal. BP. By fitting fossil diatom samples to the modern calibration set by means of residual distance assessment within canonical correspondence analysis (CCA), the early Holocene (between 10,600 and 6,000 cal. BP) was identified as a problematic time-period for diatom-based inferences and, consequently, reconstructions during this period are tentative. Pollen-based inferences also show 'poor' fit between 10,600 and 7,500 cal. BP and chironomids probably provide the most reliable July T reconstruction at Vuoskkujávri, with 'poor' fit only during the initial part of the Holocene (between 10,600 and 10,250 cal. BP). Possible factors confounding diatom-based July T inferences were investigated. Using detrended CCA (DCCA), Holocene sediment sequences from five lakes indicate that during the early Holocene, mainly physical factors such as high minerogenic erosion rates, high temperature and low light availability may have regulated diatom assemblages, favouring Fragilaria species. In all five lakes, diatom assemblages developed in a directional manner, but timing and scale of development differed substantially between lakes. The differences are attributed primarily to the geological properties of the lake catchments (with strong effects on lake-water pH), but other factors such as climatic change, vegetation, hydrologic setting and in-lake processes appear to regulate diatom communities in each lake differently. The influence of long-term natural acidification on diatom assemblages progressively declined during the Holocene with corresponding increase of the influence of climatic factors.

Previous studies showed that sea surface salinity (SSS) in the Florida Straits as well as Florida Current transport covaried with changes in North Atlantic climate over the past two millennia. However, little is known about earlier Holocene variability in the Florida Straits. Here, we combine Mg/Ca-paleothermometry and stable oxygen isotope measurements on the planktonic foraminifera Globigerinoides ruber (white variety) from Florida Straits sediment core KNR166-2 JPC 51 (24 degrees 24.70? N, 83 degrees 13.14?W, 198m deep) to reconstruct a high-resolution (~30 yr/sample) early to mid Holocene record of sea surface temperature and delta18OSW (a proxy for SSS) variability. We also measured Ba/Ca ratios in the same shell material as a proxy for riverine input into the Gulf of Mexico over the same time interval. After removing the influence of global delta18OSW change due to continental ice volume variability, we propose that early Holocene SSS enrichments were caused by increased evaporation/precipitation ratios in the Florida Straits associated with periods of reduced solar output, increased ice rafted debris in the North Atlantic and the development of more permanent El Nino-like conditions in the eastern equatorial Pacific. When considered with previous high-resolution reconstructions of early Holocene tropical atmospheric circulation changes, our results provide evidence that solar output variability over the Holocene had a significant impact on the global tropical hydrologic cycle over the last 10,000 years.

Against the background of past, recent and future climate change, the present thesis addresses elevational shifts of alpine treelines in the Swedish Scandes. By definition, treeline refers to the elevation (m a.s.l.) at a specific site of the upper trees of a specific tree species, at least 2 m tall. Based on historical records, the first part of the thesis reports and analyzes the magnitude of treeline displacements for the main trees species (Betula pubescens ssp. czerepanovii, Picea abies and Pinus sylvestris) since the early 20th century. The study covered a large and heterogeneous region and more than 100 sites. Concurrent with temperature rise by c. 1.4 °C over the past century, maximum treeline advances of all species amount to about 200 m. That is virtually what should be predicted from the recorded temperature change over the same period of time. Thus, it appears that under ideal conditions, treelines respond in close equilibrium with air temperature evolution. However, over most parts of the landscape, conditions are not that ideal and treeline upshifts have therefore been much smaller. The main reason for that discrepancy was found to be topoclimatic constraints, i.e. the combined action of geomorphology, wind, snow distribution, soil depth, etc., which over large parts of the alpine landscape preclude treelines to reach their potential thermal limit. Recorded treeline advance by maximum 200 m or so over the past century emerges as a truly anomalous event in late Holocene vegetation history. The second part of the thesis is focused more on long-term changes of treelines and one specific and prevalent mechanism of treeline change. The first part of the thesis revealed that for Picea and Betula, treeline shift was accomplished largely by phenotypic transformation of old-established stunted and prostrate individuals (krummholz) growing high above the treeline. In obvious response to climate warming over the past century, such individuals have transformed into erect tree form, whereby the treeline (as defined here) has risen. As a means for deeper understanding of this mode of positional treeline change, extant clonal spruces, growing around the treeline, were radiocarbon dated from megafossil remains preserved in the soil underneath their canopies. It turned out that Picea abies in particular may attain almost eternal life due to its capability for vegetative reproduction and phenotypic plasticity. Some living clones were in fact inferred to have existed already 9500 years ago, and have thus persisted at the same spot throughout almost the entire Holocene. This contrasts with other tree species, which have left no living relicts from the early Holocene, when they actually grew equally high as the spruce. Thereafter they retracted by more than 300 m in elevation supporting that also on that temporal scale, treelines are highly responsive to climate change. The early appearance of Picea in the Scandes, suggests that Picea “hibernated” the last glacial phase much closer to Scandinavia than earlier thought. It has also immigrated to northern Sweden much earlier than the old-established wisdom. The experiences gained in this thesis should constitute essential components of any model striving to the project landscape ecological consequences of possible future climate shifts.

Title from PDF of title page. / Document formatted into pages; contains 113 pages. / Thesis (M.S.)--University of South Florida, 1983. / Includes bibliographical references. / Text (Electronic thesis) in PDF format. / ABSTRACT: Bunces Key, a narrow, linear, barrier island on the west-central coast of Florida, was formed in 1961. Its growth and development since that time is well documented by aerial photography. Cores taken from the Key and surrounding areas reveal a stratigraphic succession of facies reflecting rapid vertical aggradation. Sedimentation began on a gently sloping platform through the landward migration of large scale bedforms (sand waves) during fair weather periods. Migration of these bedforms ceased when emergence and lack of continued overwash precluded further movement. / Vertical accretion to supratidal levels resulted from the continued onshore transport of sediment and subsequent welding to the previously formed bars. Stratigraphically, the barrier exhibits a "layer-cake" type of stratigraphy, with nearshore sediments overlain by foreshore, backbeach, and dune deposits. The backbarrier generally exhibits muddy lagoon sediments intercalated with washover and channel margin sediments.Fining upward washover sequences reflect the unstable nature of the island. / Low pressure systems commonly cause overtopping of the barrier, with the subsequent formation of tidal inlets and washover fans. Aerial photographs document the formation of an initial barrier that was breached twice prior to 1973. A second barrier formed in late 1973 just seaward of the initial island and subsequently grew through littoral drift to a length of 1.8 km. A narrow inlet (30 m) formed through the northern end of the island in 1982. / System requirements: World Wide Web browser and PDF reader. / Mode of access: World Wide Web.

This thesis contributes to increased knowledge on Holocene climate and environmental variability from two complex and sparsely studied areas. Using a speleothem from Gasparee Cave, Trinidad, as a paleoclimate archive, the local expression of the 8.2 ka (thousand years before 1950) climate event and associated patterns of the inter-tropical convergence zone (ITCZ) and rainfall is provided. Subsequent speleothem studies using multi-proxy analysis of stalagmites from Kapsia Cave and Alepotrypa Cave, Greece, provide records of climate, vegetation and human induced changes in the cave environment during parts of the Holocene. The speleothems from the well-studied Neolithic habitation site, Alepotrypa Cave, have produced a climate and habitation record which covers the period of 6.3-1.0 ka. The cave was inhabited between 8.0-5.2 ka and was closed by a tectonic event, which has preserved the settlement. The stable oxygen record shows the first well-dated and robust expression of the 4.2 ka dry event in the Peloponnese, places the timing of the 3.2 ka dry event within an ongoing dry period, and shows a final dry event at 1.6 ka. The North Atlantic as well as more regional drivers, such as the North Sea Caspian Pattern Index is proposed to, in a complex interplay, govern many of the climate trends and events observed. Trace element variation after the site is abandoned indicate what is interpreted as two volcanic eruptions, the Minoan eruption of Thera (Santorini) around 3.6 ka and the 2.7 ka eruption of Somma (Vesuvius). Variations in trace elements during the habitation period show clear human influence, indicating an association with specific cave activities. One of the most interesting prospects for continued work on Alepotrypa Cave is this successful marriage of speleothem studies and archeology. A framework of dates which constrain some behavior of people living in the cave is only the beginning, and there is great potential to continue finding new clues in the speleothem data. / Denna avhandling bidrar till ökad kunskap om klimatets variationer och miljön i två geografiskt skilda områden på låga breddgrader och under tidsperioder inom den Holocena epoken. Genom att använda en droppsten (stalagmit) från Gasparee-grottan, Trinidad, som ett paleoklimatarkiv, har det bland annat varit möjligt att visa att Trinidad upplevde torrare förhållanden under den snabba klimatförändring som observerats ske för 8200 år sedan på många platser i världen. Denna torrare klimatsituation i Trinidad föreslås vara ett resultat av en sydlig förflyttning av den intertropiska konvergenszonen. Övriga stalagmiter som studerats för denna avhandling kommer från Kapsia-grottan och Alepotrypa-grottan som finns på Peloponnesos-halvön i Grekland. Resultaten därifrån speglar dels klimat- och vegetationsvariatoner och dels graden av mänsklig aktivitet, under tiden för ca 8000 år sedan till för 1000 år sedan. Alepotrypa-grottan är känd för att vara en av de större Neolitiska boplatserna i Grekland. Isotop- och spårämnesanalyser av stalagmiterna har bidragit med ny kunskap om tidpunkten för mänsklig aktivitet, hur människorna påverkade grott-miljön samt hur klimatet varierat efter det att grottan, genom en tektonisk händelse, stängdes för människans inverkan. Snabba klimatförändringar, för 4200 och 3200 år sedan, observerade i andra regioner, rekonstrueras här för första gången på Peloponnesos. En snabb förändring mot torrare förhållanden observeras även för 1600 år sedan. De klimatstyrande processerna föreslås vara en kombination av storskaliga processer som den nordatlantiska oscillationen och mer regionala processer som det så kallade North Sea Caspian Pattern Index. Variationer i spårämnen i stalagmiterna efter att Alepotrypa-grottan stängdes kan kopplas till två vulkaniska utbrott, nämligen det Minoiska utbrottet av Thera på ön Santorini kring 3600 år sedan och utbrottet av Somma (Vesuvius) kring 2700 år sedan. Spårämnesvariationer under bo-perioden ger tydliga indikationer på människans påverkan på grottmiljön och som delvis kan länkas till specifika aktiviteter, som eldning av dynga i grottan. Avhandlingen är ett resultat av en framgångsrik kombination av klimatstudier och arkeologisk kunskap och utgör ett viktigt underlag för fördjupat interdisciplinärt forskningssamarbete i Alepotrypa-grottan. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 4: Manuscript. Paper 5: Manuscript. Paper 6: Manuscript.</p>