Speleothems (cave carbonate deposits) have been recognized as a multi-proxy paleoclimate archive. Variations in carbon and oxygen isotopes in speleothems can record past climate changes (e.g., temperature, rainfall and vegetation) under isotopic equilibrium conditions. However, non-climatic noises caused by in-cave processes may affect these stable isotope records under non-equilibrium isotopic conditions. The identification of equilibrium and non-equilibrium isotopic conditions in speleothems is still disputed in the speleothem research community; however, this is a prerequisite for the interpretation of carbon and oxygen isotope records in speleothems as paleoclimate proxies. In this Ph.D. thesis, a series of laboratory experiments under cave-analogue conditions were performed to simulate the formation of speleothems in natural caves. The results of these experiments demonstrate that stable isotope equilibrium in speleothems is achieved under slow carbonate precipitation in pool-like settings (pool carbonates). On the basis of these pool carbonates, equilibrium carbon and oxygen isotope fractionation factors between calcite and water (or DIC for carbon) were determined. Our experiments show larger carbon and oxygen isotope non-equilibrium fractionations between calcite and water (or DIC for carbon) in stalagmite-like settings (fast carbonate precipitate) than those determined in pool-like settings. The flow rate of drip water above the surface of stalagmite appears to control the magnitude of these non-equilibrium isotope effects which increase with decreasing the flow rate. Furthermore, a natural speleothem sample was examined as a paleoclimate archive in this thesis. The growth of a double stalagmite (WS-5d) in Wadi Sannur Cave from the Northeastern Sahara was used to infer the greening of the Sahara (intensive rainfall and vegetation). The U/Th dating in the WS-5d stalagmite suggests that greening conditions extended widely in the Sahara during the interglacial Marine Isotope Stages MIS 5.5, MIS 7.3, and the early MIS 9. Based upon oxygen isotope compositions from the WS-5d, we attributed the source of these greening periods to long-traveling rains from the Atlantic Ocean that were delivered via the West African monsoon system. Our study suggests that the two youngest greening periods were concurrent with the arrival of Homo sapiens in the Levant and an earlier possible change in human population at 244 ka, indicating a key role of the Sahara route in early human dispersal out of Africa. Finally, clumped isotope measurements (Δ47) on carbonate-derived CO2 have been shown to reflect the formation temperature of the carbonate minerals. The absolute Δ47 values of these isotopic measurements seem to be sensitive to the standardization methods (heated CO2 gases and water-equilibrated CO2 gases) that are used to normalize the raw Δ47 measurements. Neither the hypothetical base for the heated CO2 gas standardization method nor the theoretical base for the water-equilibrated CO2 gas standardization method has been experimentally tested. A series of CO2 gases were heated in pre-dehumidified quartz tubes to obtain equilibrium Δ47 values of these CO2 gases at temperature range of 50 – 1100 °C. Consequently, the first experimentally derived Δ47 – T calibration in a CO2 gas phase was proposed. This experimental calibration provides a validated base for the standardization of the raw Δ47 data. Moreover, heating CO2 in a pre-humidified quartz tube enables us to easily prepare a CO2 standard gas of a similar Δ47 value to the CO2 sample (i.e., similar Δ47 correction matrix). This will lead to an improvement in the correction scheme of the carbonate clumped isotope thermometry and reliably adjust the absolute Δ47 scale. / Thesis / Doctor of Philosophy (PhD)

Two conceptual approaches which offer promise for improved understanding of biological invasions are conceptualizing the invasion process as a series of distinct stages and explicitly incorporating human actions into analyses. This study explores the utility of these approaches for understanding the invasion of Trifolium (true clover) species in New Zealand. From the published literature, I collected a range of Trifolium species attributes, including aspects of global transport and use by humans, opportunistic association with humans in New Zealand, native range attributes, habitat characteristics, and biological traits. I also searched historical records to estimate the extent to which each species had been planted in New Zealand, a search facilitated by the enormous importance of Trifolium in New Zealand’s pastoral agriculture system. Regression analysis and structural equation modelling were then used to relate these variables to success at each invasion stage. Fifty-four of the 228 species in the genus Trifolium were intentionally introduced to New Zealand. Species introduced for commercial agriculture were characterised by a large number of economic uses and presence in Britain, while species introduced for horticulture or experimental agriculture were characterised by a large native range area. Nine of these 54 intentionally introduced species subsequently naturalised in New Zealand. The species that successfully naturalised were those that had been planted extensively by humans and that were well-matched to the New Zealand climate. A further 16 species (from the pool of 174 species that were never intentionally introduced) arrived and naturalised in New Zealand without any recorded intentional aid of humans. Several attributes appeared to assist species in unintentional introduction-naturalisation, including a good match to the New Zealand climate, a large native range area, presence in human-influenced habitats, a widespread distribution in Britain, and self-pollination capability. The 25 total naturalised species varied greatly in their current distributions and in the rates at which they had spread to achieve those distributions. Species that had spread quickly and are currently more widespread had been frequent contaminants in the pasture seed supply and have a long flowering period in New Zealand. Other biological traits and native range attributes played supporting roles in the spread process. Attributes facilitating success clearly varied among invasion stages. Humans played a dominant role at all stages of this invasion, although biological traits had increasing importance as a species moved through the invasion sequence. My findings suggest that incorporation of human actions and the stage-based framework provide valuable insight into the invasion process. I discuss potential avenues by which these approaches might be integrated into predictive invasion models.

Two conceptual approaches which offer promise for improved understanding of biological invasions are conceptualizing the invasion process as a series of distinct stages and explicitly incorporating human actions into analyses. This study explores the utility of these approaches for understanding the invasion of Trifolium (true clover) species in New Zealand. From the published literature, I collected a range of Trifolium species attributes, including aspects of global transport and use by humans, opportunistic association with humans in New Zealand, native range attributes, habitat characteristics, and biological traits. I also searched historical records to estimate the extent to which each species had been planted in New Zealand, a search facilitated by the enormous importance of Trifolium in New Zealand's pastoral agriculture system. Regression analysis and structural equation modelling were then used to relate these variables to success at each invasion stage. Fifty-four of the 228 species in the genus Trifolium were intentionally introduced to New Zealand. Species introduced for commercial agriculture were characterised by a large number of economic uses and presence in Britain, while species introduced for horticulture or experimental agriculture were characterised by a large native range area. Nine of these 54 intentionally introduced species subsequently naturalised in New Zealand. The species that successfully naturalised were those that had been planted extensively by humans and that were well-matched to the New Zealand climate. A further 16 species (from the pool of 174 species that were never intentionally introduced) arrived and naturalised in New Zealand without any recorded intentional aid of humans. Several attributes appeared to assist species in unintentional introduction-naturalisation, including a good match to the New Zealand climate, a large native range area, presence in human-influenced habitats, a widespread distribution in Britain, and self-pollination capability. The 25 total naturalised species varied greatly in their current distributions and in the rates at which they had spread to achieve those distributions. Species that had spread quickly and are currently more widespread had been frequent contaminants in the pasture seed supply and have a long flowering period in New Zealand. Other biological traits and native range attributes played supporting roles in the spread process. Attributes facilitating success clearly varied among invasion stages. Humans played a dominant role at all stages of this invasion, although biological traits had increasing importance as a species moved through the invasion sequence. My findings suggest that incorporation of human actions and the stage-based framework provide valuable insight into the invasion process. I discuss potential avenues by which these approaches might be integrated into predictive invasion models.

Les travaux de recherche décrits dans cette thèse s’intéressent aux conditions environnementales qui ont vu les premières dispersions humaines du technocomplexe de l’Aurignacien en Europe, au début du Paléolithique supérieur. En d’autres mots, ce projet contribue aux discussions sur la transition entre le Paléolithique moyen et le Paléolithique supérieur, une période qui a vu le remplacement des populations néanderthaliennes d’Europe par les populations d’humains anatomiquement modernes (HAM) arrivantes. Ce tournant de l’histoire de notre espèce s’est déroulé durant le stade isotopique marin 3 (MIS 3), une période de changements climatiques répétés et cycliques entre 60 000 et 24 000 années avant aujourd’hui. L’impact de ces changements climatiques sur les dynamiques populationnelles est un sujet vivement discuté chez les chercheurs. Cette recherche fait une contribution certaine à ce discours par l’évaluation de la sensibilité des HAM aux changements climatiques et au risque écologique, ainsi que par l’investigation des impacts des différentes conditions climatiques du MIS 3 sur leurs comportements spatiaux et sur leurs dispersions initiales en Europe. La thèse s’articule autour de trois articles de recherche. Le premier article fait office de collecte de données et vise la sélection d’un corpus d’assemblages archéologiques fiables et bien contrôlés chronologiquement. En effet, un obstacle de l’étude des interactions humain- environnement durant le MIS 3 est l’association claire entre les occupations archéologiques et les événements climatiques millénaires. Une revue critique des datations publiées pour la culture archéologique de l’Aurignacien, un recensement des études environnementales reliées aux niveaux datés et une classification bayésienne de ces datations et occupations archéologiques dans les différents cycles froids et chauds de cette période ont été réalisés. La base de données ainsi produite a servi, dans le cadre du second article, à la production de modèles d’habitat propice (habitat suitability) pour les interstadiaires et les stadiaires du MIS 3. Ces modèles utilisent des données paléoclimatiques de fine résolution (15km, interpolées à 1km) qui représentent les tendances de précipitation et de température, ainsi que la variabilité interannuelle de celles-ci (une cinquantaine de prédicteurs sont ainsi testés). L’approche utilisée 4 pour la production des modèles est l’algorithme d’apprentissage automatique (machine learning) Random Forest, lequel a permis de sélectionner des prédicteurs forts de l’occupation humaine selon les conditions climatiques en place. Le troisième article décrit une étude exploratoire qui bâtit sur les modèles d’adéquation de l’habitat produits ci-avant dans la réalisation d’analyses mixtes de chemins de moindre coût (least-cost path analysis). Grâce à ces modèles, il a été possible de comparer les routes potentielles pour l’entrée des HAM en Europe selon les conditions climatiques chaude ou froide, en plus d’étudier l’impact de ces oscillations sur les axes de mobilité au sein du continent et sur l’interconnexion des différentes régions habitables. Les analyses effectuées dans le cadre de cette thèse montrent que les HAM du début du Paléolithique supérieur étaient bel et bien sensibles aux changements climatiques et au risque écologique. Les détériorations environnementales associées aux périodes stadiaires ont considérablement réduit la taille de leur espace vital en Europe, en plus d’avoir limité la connectivité entre les régions habitables. Dans le même ordre d’idées, la prise de décision spatiale était sensible à la variabilité climatique, et donc à la prédictibilité des ressources dans le paysage. Cette gestion du risque écologique chez Homo sapiens, en plus de sa capacité à s’adapter aux changements climatiques, s’inscrit parmi les capacités adaptatives qui ont plausiblement joué un rôle important dans la survie et le succès de l’espèce. Finalement, selon les résultats, les HAMs ont probablement profité d’une extension de leur habitat durant un épisode stadiaire pour se disperser en Europe. / The research described in this thesis focuses on the environmental conditions that saw the first human dispersal from the Aurignacian technocomplex in Europe, at the beginning of the Upper Paleolithic. In other words, this project contributes to discussions on the transition from the Middle Paleolithic to the Upper Paleolithic, a period that saw the replacement of Europe’s Neanderthal populations by incoming populations of anatomically modern humans (AMHs). This turning point in the history of our species took place during Marine Isotope Stage 3 (MIS 3), a period of repeated and cyclical climate change between 60,000 and 24,000 years before present. The impact of these climatic changes on population dynamics is a widely discussed topic among researchers. This research makes a definite contribution to this discourse by assessing the sensitivity of HAMs to climate change and ecological risk, as well as investigating the impacts of the different MIS 3 climatic conditions on their spatial behaviour and initial dispersal in Europe. The thesis is structured around three research articles. The first article acts as a data collection step and aims to select a corpus of reliable, chronologically controlled archaeological assemblages. Indeed, an obstacle to the study of human-environment interactions during MIS 3 is the clear association between archaeological occupations and millennial climatic events. A critical review of published dates for the Aurignacian archaeological culture, a survey of environmental studies related to dated levels and a Bayesian classification of these dates and archaeological layers within the different cold and warm cycles of this period were carried out. In the second article, the resulting database was used to produce habitat suitability models for the interstadials and stadials of MIS 3. These models use fine-resolution paleoclimatic reconstructions(15 km, interpolated to 1 km) representing precipitation and temperature trends, as well as their interannual variability (some 50 predictors were tested). The models were produced using the Random Forest machine learning algorithm, which was used to select strong predictors of human occupation based on prevailing climatic conditions. The third article describes an exploratory study that builds on the habitat suitability models produced above in carrying out least-cost path analysis. Thanks to these models, it was 6 possible to compare potential routes for HAMs to enter Europe under warm and cold climatic conditions, and to study the impact of these oscillations on mobility routes within the continent and on the interconnection of different habitable regions. The analyses carried out as part of this thesis show that early Upper Palaeolithic HAMs were indeed sensitive to climate change and ecological risk. Environmental deterioration associated with stadial periods considerably reduced the size of their suitable landmassin Europe, in addition to limiting connectivity between habitable regions. Similarly, spatial decision-making was sensitive to climatic variability, and therefore to the predictability of resources in the landscape. This ecological risk management in Homo sapiens, as well as their ability to adapt to climate change, are plausibly part of the adaptive capacities that played an important role in the survival and success of the species. Finally, according to the results, HAMs probably took advantage of an extension of their habitat during a stadial episode to disperse across Europe.