The main aim of this thesis was to contribute with detailed information of regional environmental change during the Holocene through studies of speleothems and their growth environments from two caves, Korallgrottan and Labyrintgrottan in northwestern Sweden, and a cellar vault in Uppsala. This was done through studies of stable isotopes and luminescence properties in the speleothems in combination with a detailed monitoring study in Korallgrottan. The monitoring study suggests that stalagmites fed by stalactites with slow and stable drip rates from deep inside the cave may be suitable as palaeoclimate archives. Similarities between oxygen isotope signals of contemporary samples from Labyrintgrottan and Korallgrottan emphasize the potential of speleothems from Labyrintgrottan to also provide high resolution regional palaeoclimate information. Except for a number of cold events stalagmite δ18O records from northern Scandinavia indicate that temperatures were warmer than today between 9500 and 6000 years ago. During this period the interval between 7800 and 6000 years ago seems to have been the warmest. The area above Labyrintgrottan was most likely covered by much denser vegetation than today at the time of stalagmite growth (9500-7500 years ago) and was, unlike today, probably situated below the local tree-limit between 9000 and 8000 years ago. The δ18O record of a stalagmite from Korallgrottan covering the last 4000 years agrees with the concept of a warmer period, the so called Medieval Warm Period, centred around AD1000 and a colder period, the so called Little Ice Age, somewhere between AD1000 and today. Studies of luminescence properties in fast growing speleothems from Uppsala indicate that the variations in luminescence intensity are annual and that the annual lamiae of the luminescent record represent a flush of organic material.

Stable isotopes in ice cores drilled in the polar and high-mountain region have been used intensively to reconstruct past climatic changes and atmospheric dynamics. However, no similar studies have been conducted on perennial ice accumulations in caves due to a limited understanding of the links between the external and cave environments, and the way in which the climatic signal can be recorded by the cave ice. In this thesis, we successfully designed and build a research methodology for the reconstruction of past climatic changes based on perennial ice accumulation in caves, using as example the Scarisoara Ice Cave, Romania. The ice block in this cave preserves a large variety of candidate proxies for both past climate and environmental changes, the most significant ones being the stable isotopic composition of the ice (a proxy for air temperature) and pollen remains. The ice block has formed by the successive accumulation of layers formed by the freezing of water accumulated from late summer through mid-autumn precipitation. An original method has been developed for the reconstruction of the stable isotopic composition of water before freezing, and further, of the late summer air temperature. Pollen in the ice has been found to reflect changes in surface vegetation at both local and regional scale. A 22 m long ice core has been extracted from the ice block, and stable isotope analyses were performed at high resolution on its entire length. Twenty-sex radiocarbon ages have been used to derive a precise depth-age model for this core. The stable isotope data covers almost the entire Holocene, between 0.09 and 9.75 ka BP. The first order fluctuation broadly follows the orbitally induced Northern Hemisphere September insolation, with a minimum in the early Holocene, a slow climb towards a maximum at ~5.0 ka, followed by a very slow cooling towards the present, accentuated after ~0.5 ka. Superimposed on the long-term variations a series of rapid cooling events (RCE) are recorde, the most notable ones being at 9.5 ka, 8.2 ka, 7.9 ka, 6 ka, 4.2 ka, 3.2 ka and 0.9 ka. The timing of these RCEs agrees remarkably well with the Holocene rapid climatic changes and the ice rafted debris (IRD) events in the North Atlantic (NA). Our data suggests that the general trends of temperature changes in mainland Europe during the Holocene were governed by changes in solar output. RCEs were synchronous with NA IRD events, the NA climatic signal originating from sea surface temperature changes and being amplified by atmospheric dynamics. The stable isotope data spanning the past 2000 years clearly shows four climatic events over this interval, attributed to the Roman Warm period (RWP), the Dark Ages Cold Period (DACP), Medieval Warm Period (MWP) and the Little Ice Age (LIA). Our data suggests that air temperature was highly variable during the LIA and more stable during the warm MWP and RWP. As ice caves were described in many parts of the world otherwise poorly represented in ice-based paleoclimatology, the results of this study could open a new direction in paleoclimatic research, so that an array of significant paleoclimate data can be developed based on their study.

Peatlands in Southern South America (SSA), in the path of the Southern Westerly Wind belt (SWW), offer the potential of reliable palaeoclimate archives. This investigation aimed to test the late-Holocene climate signal related to variability of the SWW. Three sites were investigated: San Juan and Karukinka bog, southernmost Chile and San Carlos, a Sphagnum dominated bog, discovered in the Falkland Islands, to form a regional comparison. A multi-proxy approach was used, combining both palaeoecological and stable isotopic methods. At one site, Karukinka, intra-site replicability was tested across three profiles located along a microtopographical gradient. A low number of statistically significant correlations between proxies were evident. KAR-EM-1, the low-hummock profile, displayed the highest number of significant correlations, suggesting an optimal coring location. Chronological uncertainty in the high-hummock profile, KAR-EM-3, was the focus of discussion. Intra-site replicability between the palaeoecological records was improved by plotting the records against a ‘master chronology’, from the mid-hummock profile, KAR-EM-2, assuming a synchronous acrotelm-catotelm boundary across the profiles. The testate amoeba inferred depth to water table (WTD) reconstructions offered the highest intra-site coherence, while the stable isotope records suggested generally poor intra-site replicability. A semi-quantitative method of intra-site comparison was carried out which resulted in a number of climate scenarios. The inter-site comparison assessed correlations between the records from the three sites. A lack of significant correlations between the sites may have been due to regional climate variations and differences in the temporal resolution of the records. Robust climatic inferences were limited to the last 300 years. The WTD reconstructions displayed the highest inter-site coherence and suggested a drying trend after AD 1930 due to a southerly shift of the SWW. Late-Holocene climate variability was inferred from the palaeoecological records from Karukinka. Two periods were identified: a MCA period of generally wetter conditions (AD 750-1100) and a LIA period of overall drier conditions (~AD 1100-1900) during a southerly and northerly shifted SWW respectively, driven by solar variability and polar cell strengthening.

No description available.

The characterization of natural climate variability is important in order to understand the climate response to natural forcings and to identify anthropogenic influences. The aim of this thesis is to reconstruct climate changes in the southwest of France, a region which is characterised by recurrent drought periods, where high resolution proxy records of the last millennia were lacking.The reconstruction is based on multiple proxies from two continental archives: speleothems and tree rings. Their combination can make use of the strengths of each archive while compensating their weaknesses. There are two principal objectives: first, to gain a better understanding of the climatic and non-climatic influences on each proxy; and second, to reconstruct drought periods in the past.The oxygen isotopic composition (δ18O) of speleothem fluid inclusions and tree ring cellulose is controlled to a large extent by the δ18O of precipitation, which can serve as a tracer of the atmospheric circulation. In order to interpret these proxies in terms of climate, it is necessary to understand how the climate signal becomes recorded in the proxy, and which processes modify the original signal during the formation of the archive.Measurements of δ18O in precipitation, cave drip water, and fluid inclusions in modern speleothem samples from Villars Cave demonstrated that the isotopic composition of cave drip water corresponds to the pluri-annual average precipitation. The speleothem fluid inclusions, in turn, preserve the isotopic composition of the drip water. Based on this calibration, it is possible to reconstruct drip water isotope variability using fluid inclusions in a more than 2000 year old stalagmite, which has been dated by laminae counting, as well as U-Th and 14C measurements. Changes in the cave environment, e.g. the vegetation cover, are indicated by other proxies from the same stalagmite (stable isotopes in calcite and trace element concentrations), but these changes do not seem to impact the fluid inclusion δ18O significantly.The isotopic composition of tree ring cellulose from Quercus spp. in the study area is strongly influenced by climate conditions during the summer. However, non-climatic influences on the isotopic composition of cellulose are identified. They are linked to the age of the trees and to site hydrology, and must be accounted for in the sampling and analytical procedures. Crossdated cores from living trees and timber wood in historic buildings near Angoulême are used to build an annually resolved chronology of cellulose δ18O. Significant correlations with meteorological data enable a calibration and a reconstruction of drought periods since 1360 AD.Lastly, this thesis explores a novel approach of integrating oxygen isotope records from speleothem fluid inclusions and tree ring cellulose from closely located sites to reconstruct both high- and low-frequency variability of droughts in the past.

Climate north of the Atlas Mountain belt in NW Africa is dominated by extratropical disturbances. However, climatic controls to the south, where climate transitions from extratropical to tropical regimes, are poorly understood due to a paucity of both instrumental and palaeoclimate data. In this thesis past climate change between the High Atlas Mountains and Sahara Desert is reconstructed using the stable isotopic composition and radiometric dating of speleothems. A high-resolution record from the mid-Holocene and a discontinuous record covering the past 400,000 years are developed. Supplemented by U-Th dating of a further four samples, these records indicate increased humidity in this area concomitant with the wider African Humid Period, and indicate a link between the West African Monsoon and humidity north of 30°N. Reconstructed glacial-interglacial scale increases in humidity overlap with "green Sahara" conditions and evidence a recurrent humid corridor connecting NW Africa and the central Sahara that is highly relevant to discussions of prehistoric human migrations. Evidence for a strong influence of high-latitude and solar forcing on decadal to millennial time- scales in this area is also presented. Further to this work, the potential of cadmium-to-calcite ratios as a novel proxy for palaeo-hydrology is confirmed using an annually-resolved trace element, stable isotope and calcite fabric dataset from a North Moroccan stalagmite. The first measurements of cadmium-to-calcite ratios in natural speleothem are here presented, and the palaeoclimatic significance and potential of this proxy for aiding the quantitative reconstruction of changes in calcite precipitation behaviour are demonstrated.

La caractérisation de la variabilité naturelle du climat est importante pour comprendre la réponse de celui-ci aux forçages naturels et pour identifier les influences anthropiques. L'objectif de cette thèse est de reconstituer les changements climatiques dans le sud-ouest de la France, une région qui se caractérise par des périodes de sécheresse récurrentes, où les reconstitutions millénaires basées sur des « proxies » à haute résolution font défaut.La reconstruction est basée sur plusieurs proxies dans deux archives continentales : les spéléothèmes et les cernes d'arbre. Leur combinaison permet de tirer avantage de leurs points forts tout en compensant leurs faiblesses. Il y a deux objectifs principaux : d’une part de mieux comprendre les influences climatiques et non climatiques qui s’exercent sur chaque proxy ; et, d'autre part, de reconstituer les périodes de sécheresse dans le passé.La composition isotopique en oxygène (δ18O) des inclusions fluides des spéléothèmes et de la cellulose des cernes d’arbre est contrôlée dans une large mesure par le δ18O des précipitations, qui peut servir de traceur de la circulation atmosphérique. Pour interpréter ces proxies en termes de climat, il est nécessaire de comprendre comment le signal climatique est enregistré dans le proxy, et quels processus modifient ce signal lors de la formation de l'archive.Les mesures de δ18O dans les précipitations, l'eau d’infiltration, et les inclusions fluides dans des échantillons de spéléothèmes modernes de la Grotte de Villars démontrent que la composition isotopique de l'eau d’infiltration dans la grotte correspond à une moyenne pluriannuelle des précipitations, et que les inclusions fluides des spéléothèmes préservent la composition isotopique de cette eau d’infiltration. Sur la base de cette calibration, il est possible de reconstituer les variations de la composition isotopique de l'eau d’infiltration à partir de celles des inclusions fluides d’une stalagmite vieille de plus de 2000 ans, datée par comptage de lamines, et par des mesures U-Th et 14C. Des changements dans l'environnement de la grotte, par exemple du couvert végétal, sont indiqués par d'autres proxies de la même stalagmite (les isotopes stables dans la calcite et les concentrations d'éléments traces), mais ces changements n'ont pas d'incidence significative sur le δ18O des inclusions fluides.La composition isotopique de la cellulose des cernes d'arbre de Quercus spp. dans la zone d'étude est fortement influencée par les conditions climatiques estivales. Cependant, des influences non-climatiques sur la composition isotopique de la cellulose sont identifiées ; elles sont liées à l'âge de l'arbre et à l'hydrologie du site, et doivent être prises en compte dans l'échantillonnage et dans les procédures analytiques. Grace à l’inter-datation de carottes d’arbres vivants et de poutre de bâtiments historiques des environs d'Angoulême, une chronologie de δ18O dans la cellulose à résolution annuelle a été établie. Des corrélations significatives avec les données météorologiques permettent une calibration des données isotopiques et une reconstruction des périodes de sécheresse depuis 1360 AD.Enfin, cette thèse explore une nouvelle approche intégrant les enregistrements isotopiques de l'oxygène dans les inclusions fluides des spéléothèmes et dans la cellulose des cernes d’arbre de sites proches pour reconstruire la variabilité à la fois haute et basse fréquence des sécheresses dans le passé. / The characterization of natural climate variability is important in order to understand the climate response to natural forcings and to identify anthropogenic influences. The aim of this thesis is to reconstruct climate changes in the southwest of France, a region which is characterised by recurrent drought periods, where high resolution proxy records of the last millennia were lacking.The reconstruction is based on multiple proxies from two continental archives: speleothems and tree rings. Their combination can make use of the strengths of each archive while compensating their weaknesses. There are two principal objectives: first, to gain a better understanding of the climatic and non-climatic influences on each proxy; and second, to reconstruct drought periods in the past.The oxygen isotopic composition (δ18O) of speleothem fluid inclusions and tree ring cellulose is controlled to a large extent by the δ18O of precipitation, which can serve as a tracer of the atmospheric circulation. In order to interpret these proxies in terms of climate, it is necessary to understand how the climate signal becomes recorded in the proxy, and which processes modify the original signal during the formation of the archive.Measurements of δ18O in precipitation, cave drip water, and fluid inclusions in modern speleothem samples from Villars Cave demonstrated that the isotopic composition of cave drip water corresponds to the pluri-annual average precipitation. The speleothem fluid inclusions, in turn, preserve the isotopic composition of the drip water. Based on this calibration, it is possible to reconstruct drip water isotope variability using fluid inclusions in a more than 2000 year old stalagmite, which has been dated by laminae counting, as well as U-Th and 14C measurements. Changes in the cave environment, e.g. the vegetation cover, are indicated by other proxies from the same stalagmite (stable isotopes in calcite and trace element concentrations), but these changes do not seem to impact the fluid inclusion δ18O significantly.The isotopic composition of tree ring cellulose from Quercus spp. in the study area is strongly influenced by climate conditions during the summer. However, non-climatic influences on the isotopic composition of cellulose are identified. They are linked to the age of the trees and to site hydrology, and must be accounted for in the sampling and analytical procedures. Crossdated cores from living trees and timber wood in historic buildings near Angoulême are used to build an annually resolved chronology of cellulose δ18O. Significant correlations with meteorological data enable a calibration and a reconstruction of drought periods since 1360 AD.Lastly, this thesis explores a novel approach of integrating oxygen isotope records from speleothem fluid inclusions and tree ring cellulose from closely located sites to reconstruct both high- and low-frequency variability of droughts in the past.

Lake sediments contain the remains of midge communities that may be used as biological proxies for inferring past environmental changes. Freshwater midges, including Chironomidae and Chaoboridae, from two alpine tarns (Pyramid Lake and Bullwinkle Lake) in the Cassiar Mountains of northern British Columbia were used to estimate Holocene palaeotemperature changes, and more specifically, to test for the presence of the Milankovitch thermal maximum, an early Holocene warm interval coinciding with peak Holocene summer solar insolation. Mean July air temperatures were reconstructed using midge-inference models developed via weighted averaging-partial least squares (WA-PLS) regression. Cold-tolerant midge taxa dominate the stratigraphies from both Pyramid and Bullwinkle Lakes; however, warm-adapted species are more common in Bullwinkle Lake. Early Holocene warming is apparent at both lakes, however it is unclear whether this is indicative of the Milankovitch thermal maximum. A decrease in temperature occurs from 8,700-7,900 cal. yr BP at Pyramid Lake, around the same time that the 8,200 cal. yr BP cooling event occurred in the northern hemisphere. During the middle Holocene, records from Pyramid Lake indicate an overall decrease in temperature, with a short period of warmer temperatures that peak at 5,100 cal. yr BP. Temperatures fluctuate little during this time at Bullwinkle Lake. A short warming phase is apparent at both lakes during the late Holocene. July temperatures are highest at 2,000 cal. yr BP (10.5°C) in Pyramid Lake and at 1,200 cal. yr BP (13°C) in Bullwinkle Lake. Thereafter, temperatures return to what they were before the warming occurred, and at Bullwinkle Lake, vary little throughout the remainder of the Holocene.

Lake sediments contain the remains of midge communities that may be used as biological proxies for inferring past environmental changes. Freshwater midges, including Chironomidae and Chaoboridae, from two alpine tarns (Pyramid Lake and Bullwinkle Lake) in the Cassiar Mountains of northern British Columbia were used to estimate Holocene palaeotemperature changes, and more specifically, to test for the presence of the Milankovitch thermal maximum, an early Holocene warm interval coinciding with peak Holocene summer solar insolation. Mean July air temperatures were reconstructed using midge-inference models developed via weighted averaging-partial least squares (WA-PLS) regression. Cold-tolerant midge taxa dominate the stratigraphies from both Pyramid and Bullwinkle Lakes; however, warm-adapted species are more common in Bullwinkle Lake. Early Holocene warming is apparent at both lakes, however it is unclear whether this is indicative of the Milankovitch thermal maximum. A decrease in temperature occurs from 8,700-7,900 cal. yr BP at Pyramid Lake, around the same time that the 8,200 cal. yr BP cooling event occurred in the northern hemisphere. During the middle Holocene, records from Pyramid Lake indicate an overall decrease in temperature, with a short period of warmer temperatures that peak at 5,100 cal. yr BP. Temperatures fluctuate little during this time at Bullwinkle Lake. A short warming phase is apparent at both lakes during the late Holocene. July temperatures are highest at 2,000 cal. yr BP (10.5°C) in Pyramid Lake and at 1,200 cal. yr BP (13°C) in Bullwinkle Lake. Thereafter, temperatures return to what they were before the warming occurred, and at Bullwinkle Lake, vary little throughout the remainder of the Holocene.

Research Doctorate - Doctor of Philosophy (PhD) / The 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.