This thesis is an analysis and synthesis of the geologic and archaeological history of the Dickie Carr site, 41PR26, on Mill Creek in north central Texas. Included are analyses of the stratigraphy, sedimentary environments, and soils of the locality. A regional comparison is made with respect to the Late Quaternary geology of the upper Trinity River basin, Texas to interpret the geologic data. Two stratigraphic units were identified that record the Pleistocene-Holocene transition. The buried lower unit is comprised of terrace, floodplain, and channel deposits with extensive pedogenesis. The unit is Late Pleistocene in age and contains the remains of Mammuthus columbi. The upper stratigraphic unit is comprised of terrace and floodplain sediments with well-expressed pedogenesis. The unit is Early Holocene in age with Late Paleoindian and Late Archaic occupations. The archaeological components are compared and contrasted with documented sites from the Elm and East Forks of the Trinity River. The occupations are examined in a geoarchaeological context. The Late Paleoindian occupation is post-depositional and located in terrace deposits. The Late Archaic occupation is syndepositional and located in floodplain deposits.

The stability of Mammoth Cave’s microclimate has never undergone extensive investigation. The Snowball Dining Room area was chosen to measure the microclimate of the cave and to determine if food preparation, human presence and surface temperature variations alter this microclimate. Three portable weather stations containing a temperature / humidity probe, datalogger and microbarograph were placed in various locations along three passageways leading away from the dining room. Readings were taken 24 hours per day for four months. Plotting temperature readings in graph form show a correlation between temperature of the passageway and distance from the dining room.

South-central Kentucky has one of the world’s most intensively studied karstareas, with most work focusing on the Mammoth Cave System and related caves and aquifers. However, slightly higher in the stratigraphic section than Mammoth Cave, the Haney Limestone is a locally important but less well studied carbonate aquifer. This research provides the most comprehensive synthesis to date of the karst hydrogeology of the Haney Limestone of south-central Kentucky, focusing on the distribution and controls on cave and karst features developed within. In contrast to drainage systems within the major limestones below, joints are the most dominant control on passage development in the Haney Limestone within the study area and the orientation of these joints is consistent with that of regional joint sets. Bedding planes and the presence of insoluble rock at the base of the Haney also exert control on conduit development in the Haney Limestone. Most of the caves of the study area developed in the Haney Limestone are singleconduit caves that receive water through direct, allogenic sources. Cave entrances are frequently perennial spring resurgences and the presence of active streams suggests that the caves function within the contemporary landscape, acting as drains for localized recharge areas. The hydrology of the Haney Limestone plays an important, if localized, role in the regional hydrology of south-central Kentucky, integrated into the current system of surface and subsurface drainage of the regional karst landscape. Evidence supports the idea that caves of the Haney Limestone are, geologically, relatively recent phenomena. A majority of the cave passages in the study area are hydrologically active, the water resurging from the sampled springs is typically undersaturated with respect to limestone, and the caves in some case appear to be developed along potential stress release fractures associated with small, apparently young valleys. This suggests that caves in the Haney Limestone were not directly influenced by the incision of the Green River over vast periods, like Mammoth Cave, but that cave development is a largely contemporary process.

Understanding the potential for karst aquifer contamination by sediment-sorbed pesticides is important for cave conservation efforts in agricultural landscapes. Flow rate, water quality parameters and suspended sediment concentrations were measured in Logsdon River, a ~10km karst conduit within the Turnhole Spring Groundwater Basin of Mammoth Cave National Park to determine characteristics of storm-period transport of sediment-sorbed atrazine through a conduit-flow karst aquifer. Analysis of two independent precipitation events occurring in the Spring of 2008 from May 2-4 and May 27-29 demonstrated the rapid response of the Logsdon River to precipitation events with detections of atrazine increasing during the initial turbidity peak and decline in spC, indicating that the atrazine arrives with the initial flush of surface waters that enters the conduit. Distinct peaks of atrazine did not coincide with fine grained (silt and clay-sized) sediment peaks and concentrations of atrazine remained elevated on the falling limb of the hydrograph as turbidity declined. In addition, no systematic relation between filtered and unfiltered samples was evident. There was also exceedingly weak correlation between the concentration of atrazine and suspended sediment, suggesting that if atrazine is sorbed to fine sediment particles this sorption involves only the fractions finer than 0.22 μm.

Rewilding aims at the restoration of lost ecosystems by re-introducing large herbivores. In northern Siberia, the demise of the mammoth steppe ecosystem at the end of the Pleistocene has been related to the loss of megafauna due to human overhunting. Others argue that climate change at the beginning of the Holocene has triggered the shift from dry, cold steppe vegetation to wet and low productive tundra and taiga vegetation. Despite many different opinions and ongoing discussions on the topic, few case studies are available to test the proposed hypotheses. In this thesis I try to bridge the theoretical backgrounds of palaeoecology and contemporary grazing ecology, and apply these to new data from grazed steppes and surrounding vegetation in Yakutia. This study region is suitable to shed light on the importance of grazers for the (mammoth) steppe vegetation because Yakutia was dominated by mammoth steppe in Pleistocene glacials, and the extrazonal steppes of today are considered potential relics; permafrost deposits in close proximity to these steppes allow palaeobotanical reconstructions of vegetation from the same area; and two game parks, one in Central Yakutia, one in northeastern Yakutia, allow to study grazing impact on contemporary vegetation, specifically steppes. The first part of the thesis focuses on current grassland and steppe vegetation in Russia in general and in Yakutia specifically. Chapter highlights the biological diversity of Russia´s grasslands under diverse climatic and edaphic consditions. It highlights the value of Russian steppes for nature conservation, shows that most grasslands are of agricultural origin and that cessation of land use can pose a threat to both natural and secondary grasslands. Chapter 2 focuses on the phytosociology of extrazonal steppes and other grasslands of Yakutia, and on the harsh climatic and the special edaphic conditions they inhabit. It demonstrates relationships to southern zonal steppes, despite lower species diversity and unique associations with a high contribution of alpine plants. The second part of the thesis addresses the evidence of grazing in the palaorecord as well as effects and importance of grazing for contemporary vegetation. Chapter 3 aims at a comparison of current vegetation with Pleistocene fossil remains in order to find the closest analogues of mammoth steppe vegetation. It demonstrates that meadow steppes formed large parts of the vegetation in both cold and warm stages, only shifting in proportions. Disturbance indicators from grazing animals were more common in the fossil record than today. Chapter 4 discusses the influence of grazing on current vegetation under the given harsh climate; on plant species and trait composition, as well as on vegetation productivity. Climate and soil conditions seem to be the most important determinants of steppe and surrounding vegetation. Large grazers like bison can alter vegetation structure and plant communities on the local scale, but do not alter composition dramatically nor do they increase vegetation productivity in the given settings. In summary, steppes are an important part of biodiversity in Russia and specifically in Yakutia today. The extrazonal steppes of Yakutia are no direct relics of the mammoth steppe, and are not dependent on grazing. However, grazing of large herbivores, such as bison, can locally open up vegetation, and in a continental climate, drive grasslands towards a more steppic character. Further research is needed to investigate the details of these processes and how they could translate to the landscape scale.:Chapter 1: General Introduction 1 1.1. Large mammal extinctions and the onset of the Anthropocene 1 1.2. The 'mammoth steppe' 3 1.2.1. Definitions and concepts 3 1.2.2. Environmental conditions 4 1.2.3. Vegetation of the mammoth steppe 6 1.2.4. Megafauna and suggested ecosystem processes of the mammoth steppe 7 1.2.5. The demise of the mammoth steppe 9 1.3. Grazing ecology 11 1.3.1. Effects of herbivores on vegetation 11 1.3.2. Effects of herbivores on ecosystem processes 14 1.4. Study area 15 1.4.1. Central and northeastern Yakutia 15 1.4.2. Pleistocene Park and the Ust-Buotoma Bisonary 18 1.5. Chapter outline 19 Chapter 2: Land Use of Natural and Secondary Grasslands in Russia 20 2.1. Introduction 21 2.2. Origin and types of grasslands 26 2.2.1. Natural grasslands 26 2.2.1.1. Steppes 26 2.2.1.2. Alpine grasslands 32 2.2.1.3. Azonal grasslands 33 2.2.2. Secondary grasslands 34 2.3. Agronomic Use of grasslands 34 2.3.1. History of land use 34 2.3.2. Current practice of grassland management 38 2.4. Ecological and economic value of grasslands 40 2.5. Threats to grasslands 43 2.6. Conservation of grasslands 48 2.6.1. Legal aspects 48 2.6.2. Prioritization 50 2.6.3. Conservation of grasslands: Protected Areas (PAs) 51 2.7. Conclusions 53 Chapter 3: Extrazonal steppes and other temperate grasslands of northern Siberia - Phytosociological classification and ecological characterization 55 3.1. Introduction 57 3.2. Methods 60 3.3. Results 61 3.3.1. Overview: classification and ordination 61 3.3.2. Description of communities 67 3.3.2.1. Meadows and wet grasslands 67 3.3.2.2. Steppes 68 3.3.3. Phytosociological synopsis 73 3.4. Discussion 75 3.4.1. Meadows 75 3.4.2. Steppes 76 3.4.3. Tundra steppes 80 3.5. Conclusions 81 Cahpter 4: Woodlands and steppes: Pleistocene vegetation in Yakutia´s most continental part recorded in the Batagay permafrost sequence 82 4.1. Introduction 84 4.1.1. Regional setting 86 4.2. Material and methods 87 4.2.1. Material 87 4.2.2. Sampling and preparation 90 4.2.3. Macrofossil preparation and identification 91 4.2.4. Charcoal 91 4.2.5. Palynology preparation and identification 91 4.2.6. Invertebrate sampling and identification 92 4.2.7. Reconstruction of palaeo-vegetation 92 4.3. Results 94 4.3.1. Vegetation of the last cold stage 95 4.3.2. Vegetation of the last interglacial 107 4.3.3. History of local vegetation and environment throughout the sequence 113 4.3.3.1. Unit IV 113 4.3.3.2. Unit III 114 4.3.3.3. Unit II 114 4.4. Discussion 121 4.4.1. Steppes persistent throughout the investigated timespan 121 4.4.2. Steppes in northeast Siberia: Pleistocene survivors or Holocene immigrants? 124 4.4.3. Climatic implications 126 4.5. Conclusions 129 Chapter 5: Grazing at the limit 􀂱 effects of large herbivore grazing on relics of presumed mammoth steppe in NE-Siberia 131 5.1. Introduction 133 5.2. Methods 137 5.2.1. Field sampling and data collection 137 5.2.2. Data analysis 138 5.2.2.1. Species composition 138 5.2.2.2. Plant trait composition 138 5.2.2.3. Taxonomic and functional diversity 139 5.2.2.4. Productivity and chemical composition of vegetation 139 5.3. Results 139 5.3.1. Species composition 140 5.3.2. Trait composition 142 5.3.3. Taxonomic and functional diversity 143 5.3.4. Productivity and chemical composition of vegetation 144 5.4. Discussion 145 5.4.1. Effect of microclimate 145 5.4.2. Grazing effects 146 5.4.3. Implications for rewilding in Siberia 149 Chapter 6: Synthesis - Yakutian steppes and rewilding the mammoth steppe 151 6.1. Contemporary grasslands and herbivore pastures in Yakutia 151 6.2. Contemporary steppes and tundra steppes 152 6.2.1. Relics of the mammoth steppe?! 154 6.3. The role of grazers today - and their proposed role in the mammoth steppe 157 6.4. Outlook on rewilding 166 Chapter 7: Conclusions 174 Chapter 8: Summary 175 Chapter 9: Zusammenfassung 177 II. References 179 III. Appendix 207 IV. List of abbreviations 263 V. Curriculum vitae 270 / Mit der Auswilderung von Großherbivoren wird oft das Ziel verfolgt, ein lange vergangenes Ökosystem wiederherzustellen. In Nordsibirien ist das die Mammutsteppe, deren Verlust auf die Ausrottung der Großherbivoren-Fauna durch menschliche Überjagung zurückgeführt wurde. Andererseits könnte auch der Klimawandel am Beginn des Holozäns für den Vegetationswandel von trockener, kalter Steppe zu feuchter und wenig produktiver Tundra und Taiga verantwortlich sein. Das Thema wird von verschiedenen Meinungen beherrscht und die Diskussion darüber dauert an; doch konkrete Studien, die diese Hypothesen überprüfen würden, sind selten. In meiner Dissertation versuche ich, eine Brücke zwischen Theorien aus der Paläoökologie und der rezenten Beweidungsökologie zu schlagen und diese auf die beweideten Steppen Yakutiens und deren umgebende Vegetation anzuwenden. Diese Studie liefert Erkenntnisse zur Bedeutung von Weidetieren für die (Mammut-)steppenvegetation, da Yakutien in Pleistozänen Kaltzeiten von Mammutsteppe bedeckt war und die rezenten, extrazonalen Steppen als potenzielle Reliktvegetation angesehen werden; Permafrostaufschlüsse in direkter Umgebung dieser Steppen die paläobotanische Rekonstruktion des selben Gebietes erlauben; und zwei Wildparks, einer in Zentralyakutien, einer im Nordosten Yakutiens, die Erforschung von Beweidungseffekten auf die rezente Vegetation, vor allem Steppenvegetation, ermöglichen. Der erste Teil meiner Dissertation bezieht sich auf die rezente Grasland- und Steppenvegetation Russlands mit Fokus auf Yakutien. Kapitel 1 stellt die biologische Vielfalt der Russischen Grasländer unter verschiedensten klimatischen und edaphischen Bedingungen heraus. Dabei steht die Bedeutung der Russischen Steppen für den Naturschutz im Fokus. Es wird deutlich, dass der Großteil der Grasländer auf landwirtschaftliche Nutzung zurückzuführen ist und dass eine Nutzungsaufgabe sowohl natürliche als auch sekundäre Grasländer bedroht. Kapitel 2 beschäftigt sich mit der Pflanzensozologie der extrazonalen Steppen und anderer Grasländer Yakutiens, sowie mit den speziellen klimatischen und edaphischen Bedingungen, unter denen sie existieren. Ich zeige die verwandtschaftlichen Beziehungen dieser Steppen mit den südlichen, zonalen Steppen, trotz ihrer geringeren Artenvielfalt und ihrer einzigartigen Assoziationen mit hohem Anteil alpiner Arten. Der zweite Teil meiner Dissertation beschäftigt sich mit den Hinweisen auf Beweidung in paläobotanischen Rekonstruktionen der Vegetation, sowie der Bedeutung von Beweidung in der rezenten Vegetation. Kapitel 3 stellt einen Vergleich zwischen der Artenzusammensetzung Pleistozäner Pflanzenfossilien mit denen rezenter Pflanzengesellschaften an, um die Vegetation zu definieren, die der Mammutsteppe am ähnlichsten ist. Dieser Vergleich zeigt, dass Wiesensteppen sowohl in Kalt- als auch in Warmzeiten vorkamen und nur in ihrem Anteil an der Gesamtvegetation schwankten. Störungszeiger für Beweidung waren häufiger in den fossilen Pflanzenresten zu finden als in rezenten Pflanzengesellschaften. Kapitel 4 diskutiert schließlich den Einfluss von Beweidung auf die rezente Vegetation unter den gegebenen extremen Klimaverhältnissen; auf die Zusammensetzung von Arten und Artmerkmalen einer Pflanzengesellschaft, sowie auf deren Produktivität. Die klimatischen und edaphischen Bedingungen scheinen ausschlaggebend für die Steppen- und umgebende Vegetation zu sein. Großherbivoren wie das Bison können allerdings lokal Veränderungen in der Vegetationsstruktur und Pflanzengesellschaften bewirken, wenn auch, unter den gegebenen Umständen, weder Artenzusammensetzung noch Produktivität drastisch verändert wurden. Steppen stellen einen bedeutenden Anteil der Russischen, und besonders Yakutischen, Biodiversität dar. Die extrazonalen Steppen Yakutiens sind keine unmittelbaren Relikte der Mammutsteppe und sind heute nicht auf Beweidung angewiesen. Trotzdem können Großherbivoren wie das Bison lokale Veränderungen bewirken: sie vermögen Baumbestände aufzulichten und, unter kontinentalem Klima, Wiesen hin zu einem mehr steppen-artigen Charakter zu verändern. Weitere Forschung ist nötig, um die Details der beobachteten Prozesse zu erkunden und ihre Übertragbarkeit auf die Landschaftsebene zu überprüfen.:Chapter 1: General Introduction 1 1.1. Large mammal extinctions and the onset of the Anthropocene 1 1.2. The 'mammoth steppe' 3 1.2.1. Definitions and concepts 3 1.2.2. Environmental conditions 4 1.2.3. Vegetation of the mammoth steppe 6 1.2.4. Megafauna and suggested ecosystem processes of the mammoth steppe 7 1.2.5. The demise of the mammoth steppe 9 1.3. Grazing ecology 11 1.3.1. Effects of herbivores on vegetation 11 1.3.2. Effects of herbivores on ecosystem processes 14 1.4. Study area 15 1.4.1. Central and northeastern Yakutia 15 1.4.2. Pleistocene Park and the Ust-Buotoma Bisonary 18 1.5. Chapter outline 19 Chapter 2: Land Use of Natural and Secondary Grasslands in Russia 20 2.1. Introduction 21 2.2. Origin and types of grasslands 26 2.2.1. Natural grasslands 26 2.2.1.1. Steppes 26 2.2.1.2. Alpine grasslands 32 2.2.1.3. Azonal grasslands 33 2.2.2. Secondary grasslands 34 2.3. Agronomic Use of grasslands 34 2.3.1. History of land use 34 2.3.2. Current practice of grassland management 38 2.4. Ecological and economic value of grasslands 40 2.5. Threats to grasslands 43 2.6. Conservation of grasslands 48 2.6.1. Legal aspects 48 2.6.2. Prioritization 50 2.6.3. Conservation of grasslands: Protected Areas (PAs) 51 2.7. Conclusions 53 Chapter 3: Extrazonal steppes and other temperate grasslands of northern Siberia - Phytosociological classification and ecological characterization 55 3.1. Introduction 57 3.2. Methods 60 3.3. Results 61 3.3.1. Overview: classification and ordination 61 3.3.2. Description of communities 67 3.3.2.1. Meadows and wet grasslands 67 3.3.2.2. Steppes 68 3.3.3. Phytosociological synopsis 73 3.4. Discussion 75 3.4.1. Meadows 75 3.4.2. Steppes 76 3.4.3. Tundra steppes 80 3.5. Conclusions 81 Cahpter 4: Woodlands and steppes: Pleistocene vegetation in Yakutia´s most continental part recorded in the Batagay permafrost sequence 82 4.1. Introduction 84 4.1.1. Regional setting 86 4.2. Material and methods 87 4.2.1. Material 87 4.2.2. Sampling and preparation 90 4.2.3. Macrofossil preparation and identification 91 4.2.4. Charcoal 91 4.2.5. Palynology preparation and identification 91 4.2.6. Invertebrate sampling and identification 92 4.2.7. Reconstruction of palaeo-vegetation 92 4.3. Results 94 4.3.1. Vegetation of the last cold stage 95 4.3.2. Vegetation of the last interglacial 107 4.3.3. History of local vegetation and environment throughout the sequence 113 4.3.3.1. Unit IV 113 4.3.3.2. Unit III 114 4.3.3.3. Unit II 114 4.4. Discussion 121 4.4.1. Steppes persistent throughout the investigated timespan 121 4.4.2. Steppes in northeast Siberia: Pleistocene survivors or Holocene immigrants? 124 4.4.3. Climatic implications 126 4.5. Conclusions 129 Chapter 5: Grazing at the limit 􀂱 effects of large herbivore grazing on relics of presumed mammoth steppe in NE-Siberia 131 5.1. Introduction 133 5.2. Methods 137 5.2.1. Field sampling and data collection 137 5.2.2. Data analysis 138 5.2.2.1. Species composition 138 5.2.2.2. Plant trait composition 138 5.2.2.3. Taxonomic and functional diversity 139 5.2.2.4. Productivity and chemical composition of vegetation 139 5.3. Results 139 5.3.1. Species composition 140 5.3.2. Trait composition 142 5.3.3. Taxonomic and functional diversity 143 5.3.4. Productivity and chemical composition of vegetation 144 5.4. Discussion 145 5.4.1. Effect of microclimate 145 5.4.2. Grazing effects 146 5.4.3. Implications for rewilding in Siberia 149 Chapter 6: Synthesis - Yakutian steppes and rewilding the mammoth steppe 151 6.1. Contemporary grasslands and herbivore pastures in Yakutia 151 6.2. Contemporary steppes and tundra steppes 152 6.2.1. Relics of the mammoth steppe?! 154 6.3. The role of grazers today - and their proposed role in the mammoth steppe 157 6.4. Outlook on rewilding 166 Chapter 7: Conclusions 174 Chapter 8: Summary 175 Chapter 9: Zusammenfassung 177 II. References 179 III. Appendix 207 IV. List of abbreviations 263 V. Curriculum vitae 270

Aim: Identifying how climate change, habitat loss, and corridors interact to influence species survival or extinction is critical to understanding macro-scale biodiversity dynamics under changing environments. In North America, the ice-free corridor was the only major pathway for northward migration by megafaunal species during the last deglaciation. However, the timing and interplay among the late Quaternary megafaunal extinctions, climate change, habitat structure, and the opening and reforestation of the ice-free corridor have been unclear. Location: North America. Time period: 15–10 ka. Major taxa studied: Woolly mammoth (Mammuthus primigenius). Methods: For central North America and the ice-free corridor between 15 and 10 ka, we used a series of models and continental-scale datasets to reconstruct habitat characteristics and assess habitat suitability. The models and datasets include biophysical and statistical niche models Niche Mapper and Maxent, downscaled climate simulations from CCSM3 SynTraCE, LPJ-GUESS simulations of net primary productivity (NPP) and woody cover, and woody cover based upon fossil pollen from Neotoma. Results: The ice-free corridor may have been of limited suitability for traversal by mammoths and other grazers due to persistently low productivity by herbaceous plants and quick reforestation after opening 14 ka. Simultaneously, rapid reforestation and decreased forage productivity may have led to declining habitat suitability in central North America. This was possibly amplified by a positive feedback loop driven by reduced herbivory pressures, as mammoth population decline led to the further loss of open habitat. Main conclusions: Declining habitat availability south of the Laurentide Ice Sheet and limited habitat availability in the ice-free corridor were contributing factors in North American extinctions of woolly mammoths and other large grazers that likely operated synergistically with anthropogenic pressures. The role of habitat loss and attenuated corridor suitability for the woolly mammoth extinction reinforce the critical importance of protected habitat connectivity during changing climates, particularly for large vertebrates.

Before the creation of Mammoth Cave National Park, this area was home to numerous communities, each with a sense of identity. To prepare for the creation of the National Park, all residents living within these communities were relocated, and many of these communities were lost to the passage of time. Today, public memory of these lost communities is being fostered by the descendents of the pre-park area. Through the use of a Historical Geographic Information System, 1920 Edmonson County manuscript census data, and statistical analysis, the demographic composition of these lost communities was explored. This project not only brought to light a past that is not well known, but also built interest in sustaining public memory of the Mammoth Cave pre-park area through the use of historical GIS and public participation.

The study of flaked mammoth bone tools from the Late Pleistocene is a topic that has inspired great interest in the archaeological community for the last 40 years. The interpretation of evidence of culturally modified mammoth bone tools has varied widely across both time and space. At different times and in different places, flaked bone toolmaking has been interpreted across the geographic expanse of the North American continent, from Beringia to central Mexico, and through a vast timeframe, from 120,000 years ago, until as recently as 10,000 years ago. The study of these purported flaked bone tool assemblages has taken many forms, and has involved efforts to understand broken mammoth bone assemblages by drawing analogies to stone toolmaking strategies, by understanding the multitude of taphonomic processes that affect archaeological bone assemblages, and by attempting to differentiate the effects of natural and cultural processes. This thesis reports on a series of experiments designed to lend new actualistic evidence to the debate surrounding flaked bone toolmaking. These experiments include investigations into the effect of different environmental conditions on the degradation of bones, the flaking characteristics of both fresh and frozen bones, and the effect of rockfall as a taphonomic process on bones exposed to different real-world environments. These experiments, paired with a body of previous research, provide a basis in actualistic and taphonomic research that allows for the reassessment of archaeological and paleontological broken mammoth bone assemblages. This thesis includes the reassessment and detailed taphonomic analysis of four mammoth bone assemblages relevant to understanding cultural bone modification and the effect of non-cultural taphonomic processes. New interpretations of zooarchaeological assemblages from Lange/Ferguson (South Dakota, USA), Owl Cave (Idaho, USA), Inglewood (Maryland, USA), and Kent’s Cavern (Devon, UK) reveal new data that revise the understanding of the nature of these assemblages, and the effect of both natural and cultural bone fracturing agencies.

The poems in Carved take the reader on a journey of self-discovery and explore the inequalities of human relationships: between being silent and the discovery of one's voice. The collection also addresses humanity's destructive imprint and the resiliency of nature in reclaiming what humanity sought to exploit and conquer. The poems expose the ironies in how we imagine things to be, compared to their reality. Some of the poems also draw parallels between the process of going underground and that of being reborn, as well as the spiritual experience of caving.

Une molécule soumise à un champ laser infra-rouge intense (dans la gamme des 10 14 W.cm−2) peut être ionisée par effet tunnel. Le paquet d’ondes électroniques (POE) ainsi libéré est alors accéléré par le champ laser et, lorsqu’il repasse à proximité de l’ion parent, il a une certaine probabilité de se recombiner dans son état fondamental. Lors de cette recombinaison, le POE libère son énergie sous la forme d’un flash attoseconde (1as=10 −18s) de rayons XUV. Cette émission cohérente est produite à chaque demi-cycle laser résultant en un train d’impulsions attosecondes. Dans le domaine spectral, ce train correspond à un spectre discret d’harmoniques de la fréquence lasers. L’étape de recombinaison de l’électron avec l’ion parent peut être considérée comme une sonde de la structure des orbitales de valence moléculaires participant à la génération d’harmoniques et de la dynamique ayant lieu dans l’ion pendant l’excursion de l’électron dans le continuum. En caractérisant en amplitude, phase et polarisation, l’émission harmonique associée à cette recombinaison, il est possible de remonter à ces informations structurales et dynamiques avec une précision de l’ordre de l’Ångström et une résolution attoseconde. En particulier, la phase de l’émission harmonique qui est difficile à caractériser, encode des informations indispensables à la bonne compréhension des processus ayant lieu dans le milieu de génération. Nous présentons les principes et testons de nouvelles techniques permet tant de caractériser la phase de l’émission attoseconde suivant plusieurs dimensions à la fois et dans un laps de temps optimisé. Dans une première partie, nous présentons une méthode permettant de caractériser rapidement la phase spectrale de l’émission harmonique, fondée sur un modèle en champ fort de la photoionisation à deux couleurs (RABBIT). Nous introduisons ensuite une nouveau dispositif interférométrique à deux sources, permettant de mesurer les variations de phase de l’émission attoseconde induites par l’excitation d’un paquet d’ondes rotationnelles ou vibrationnelles. Ce dispositif très stable, compact et sobre énergétiquement repose sur l’utilisation d’un élément optique de diffraction (DOE) binaire. Après avoir qualifié notre dispositif par des simulations numériques et des expériences préliminaires, nous montrons qu’il est si sensible qu’il permet de mesurer les variations de phase en fonction du paramètre d’excitation pour différentes trajectoires électroniques dans le continuum. Pour l’azote et le dioxyde de carbone, les mesures expérimentales montrent des variations de phase très différentes pour les deux premières trajectoires électroniques. Ce DOE est ensuite utilisé pour mesurer la phase de l’émission harmonique dans les molécules alignées dans les mêmes conditions expérimentales que le RABBIT. Les deux expériences menées successivement donnent des résultats compatibles que nous combinons par deux méthodes différentes : le CHASSEUR et le MAMMOTH. Enfin, nous proposons de combiner le DOE avec un réseau transitoire pour caractériser simultanément la phase de l'émission attoseconde moléculaire suivant deux axes de polarisation différents. Ces différentes techniques de mesure de phase nous ont permis d’étudier précisément l’émission harmonique suivant différentes dimensions (angle d’alignement, intensité de génération, trajectoire électronique) et d’en tirer de nouvelles informations sur le mécanisme de génération dans les molécules. / When a low-frequency laser pulse is focused to a high intensity into a gas, the electric field of the laser light may become of comparable strength to that felt by the electrons bound in an atom or molecule. A valence electron can then be 'freed' by tunnel ionization, accelerated by the strong oscillating laser field and can eventually recollide and recombine with the ion. The gained kinetic energy is then released as a burst of coherent XUV light which is spectrally organized as harmonics of the fundamental driving field frequency.In high-harmonic molecular spectroscopy, the recombining electron wave-packet probes the structure of the molecule and the dynamics occurring in the ion left after tunnel ionization. The XUV burst is imprinted with this information which can be retrieved through an accurate characterization of the amplitude, phase and polarization of the harmonics. In the case of small molecules as nitrogen and carbon dioxide, impulsive alignment allows to change the direction of recombination of the electron wave-packet with respect to the molecular axis. The XUV burst from the molecular sample should then be characterized both along the spectral dimension and the alignment angle one, and this for the two polarization components. In this report, we present a new experimental scheme to perform two-source interferometry to measure the phase of the emission in aligned molecules along the alignment angle dimension. We how a refined spatio-spectral analysis of the fringe patterns obtained with this very stable interferometer allows one to extend high-harmonic spectroscopy from short to long trajectories. We then show how the combination of this setup together with RABBIT gives access to a bidimensionnal (spectrum and alignment angle) phase map with no arbitrary constant. Finally comparing two-source interferometry with transient grating spectroscopy leads to inconsistent results that can be interpreted taking into consideration polarization effects.