L'objectif de la thèse est de caractériser la variabilité climatique de la période Holocène (10 000-0 ans) en analysant des séries climatiques d'enregistrements marins, continentaux, glaciaires. Les enregistrements d'Atlantique Nord et Sud ainsi que l'océan Austral ont permis d'identifier deux types de fréquences millénaires : les premières s'expriment pendant le début de l'Holocène (10 000-5 000 BP) et sont similaires aux fréquences solaires, les secondes, pendant la fin de l'Holocène, suggèrent un forçage interne océanique. Ce schéma Holocène avec une circulation océanique qui s'établit à un régime stable à partir de 5 000 ans coïncide avec l'établissement du niveau marin à son niveau proche de l'actuel, en lien avec la disparition de la calotte Laurentides et les drainages d'eau douce en Atlantique Nord. À partir de 5 000 ans, les flux d'eau douce ne perturbent plus le gradient de salinité permettant l'établissement de la circulation thermohaline à son régime stable. En Antarctique, de nouvelles séries de données poussières couvrant les 2000 dernières années à Dôme C et Vostok ont été produites. Sur la période Holocène en analysant l'ensemble des données disponibles (isotopes stables, excès en Deutérium, poussières) pour différents sites sur le plateau Antarctique, il n'apparaît aucune structure persistante significative pour aucun des proxies. Au Groenland, les seules fréquences significatives dans le deutérium sont l'empreinte spectrale de l'événement 8 200 ans. Le signal climatique déduit des calottes polaires pour la période Holocène est masqué par des processus tels que les effets locaux, la sensibilité des proxy,...

Emerald Pond (26° 32' 12" N, 77° 06' 32" W) is a vertical-walled solution hole in the pine rocklands of Great Abaco Island, The Bahamas. In 2006, Sally Horn, Ken Orvis, and students recovered an 8.7 m-long sediment core from the center of the pond using a Colinvaux-Vohnout locking piston corer. AMS radiocarbon dates on macrofossils are in stratigraphic order and indicate that the sequence extends to ca. 8400 cal yr BP. Basal deposits consist of aeolian sands topped by a soil and then pond sediment, suggesting that the site began as a sheltered, dry hole during a Late Pleistocene low sea level stand, and became moister as climate changed and rising sea level pushed up the freshwater table. The limestone rockland surrounding the site is presently dominated by Bahamian pine (Pinus caribaea Morelet var. bahamensis (Griseb.) W.H. Barrett & Golfari) with an understory of hardwoods and several palm species. Pollen analyses on the sediments of Emerald Pond indicate significant environmental change at the site. Pines and palms have dominated for much of the record, with some variation in relative importance. Pine pollen shows a non-uniform, general increase over the record, with highest values reached in a section of the upper meter of the record that contains abundant microscopic charcoal that may be related to anthropogenic activities. Palm pollen is well represented in all but this upper section of the core. The shifts in pollen percentages in the upper meter of the core suggest a generally drier environment during the last two millennia at Emerald Pond.

Spatial and temporal temperature and moisture patterns across the Tibetan Plateau are very complex. The onset and magnitude of the Holocene climate optimum in the Asian monsoon realm, in particular, is a subject of considerable debate as this time period is often used as an analogue for recent global warming. In the light of contradictory inferences regarding past climate and environmental change on the Tibetan Plateau, I have attempted to explain mismatches in the timing and magnitude of change. Therefore, I analysed the temporal variation of fossil pollen and diatom spectra and the geochemical record from palaeo-ecological records covering different time scales (late Quaternary and the last 200 years) from two core regions in the NE and SE Tibetan Plateau. For interpretation purposes I combined my data with other available palaeo-ecological data to set up corresponding aquatic and terrestrial proxy data sets of two lake pairs and two sets of sites. I focused on the direct comparison of proxies representing lacustrine response to climate signals (e.g., diatoms, ostracods, geochemical record) and proxies representing changes in the terrestrial environment (i.e., terrestrial pollen), in order to asses whether the lake and its catchments respond at similar times and magnitudes to environmental changes. Therefore, I introduced the established numerical technique procrustes rotation as a new approach in palaeoecology to quantitatively compare raw data of any two sedimentary records of interest in order to assess their degree of concordance. Focusing on the late Quaternary, sediment cores from two lakes (Kuhai Lake 35.3°N; 99.2°E; 4150 m asl; and Koucha Lake 34.0°N; 97.2°E; 4540 m asl) on the semi-arid northeastern Tibetan Plateau were analysed to identify post-glacial vegetation and environmental changes, and to investigate the responses of lake ecosystems to such changes. Based on the pollen record, five major vegetation and climate changes could be identified: (1) A shift from alpine desert to alpine steppe indicates a change from cold, dry conditions to warmer and more moist conditions at 14.8 cal. ka BP, (2) alpine steppe with tundra elements points to conditions of higher effective moisture and a stepwise warming climate at 13.6 cal. ka BP, (3) the appearance of high-alpine meadow vegetation indicates a further change towards increased moisture, but with colder temperatures, at 7.0 cal. ka BP, (4) the reoccurrence of alpine steppe with desert elements suggests a return to a significantly colder and drier phase at 6.3 cal. ka BP, and (5) the establishment of alpine steppe-meadow vegetation indicates a change back to relatively moist conditions at 2.2 cal. ka BP. To place the reconstructed climate inferences from the NE Tibetan Plateau into the context of Holocene moisture evolution across the Tibetan Plateau, I applied a five-scale moisture index and average link clustering to all available continuous pollen and non-pollen palaeoclimate records from the Tibetan Plateau, in an attempt to detect coherent regional and temporal patterns of moisture evolution on the Plateau. However, no common temporal or spatial pattern of moisture evolution during the Holocene could be detected, which can be assigned to the complex responses of different proxies to environmental changes in an already very heterogeneous mountain landscape, where minor differences in elevation can result in marked variations in microenvironments. Focusing on the past 200 years, I analysed the sedimentary records (LC6 Lake 29.5°N, 94.3°E, 4132 m asl; and Wuxu Lake 29.9°N, 101.1°E, 3705 m asl) from the southeastern Tibetan Plateau. I found that despite presumed significant temperature increases over that period, pollen and diatom records from the SE Tibetan Plateau reveal only very subtle changes throughout their profiles. The compositional species turnover investigated over the last 200 years appears relatively low in comparison to the species reorganisations during the Holocene. The results indicate that climatically induced ecological thresholds are not yet crossed, but that human activity has an increasing influence, particularly on the terrestrial ecosystem. Forest clearances and reforestation have not caused forest decline in our study area, but a conversion of natural forests to semi-natural secondary forests. The results from the numerical proxy comparison of the two sets of two pairs of Tibetan lakes indicate that the use of different proxies and the work with palaeo-ecological records from different lake types can cause deviant stories of inferred change. Irrespective of the timescale (Holocene or last 200 years) or region (SE or NE Tibetan Plateau) analysed, the agreement in terms of the direction, timing, and magnitude of change between the corresponding terrestrial data sets is generally better than the match between the corresponding lacustrine data sets, suggesting that lacustrine proxies may partly be influenced by in-lake or local catchment processes whereas the terrestrial proxy reflects a more regional climatic signal. The current disaccord on coherent temporal and spatial climate patterns on the Tibetan Plateau can partly be ascribed to the complexity of proxy response and lake systems on the Tibetan Plateau. Therefore, a multi-proxy, multi-site approach is important in order to gain a reliable climate interpretation for the complex mountain landscape of the Tibetan Plateau. / Die räumlichen und zeitlichen Temperatur- und Feuchtigkeitsmuster auf dem Tibet-Plateau sind sehr komplex. Im Einzugsbereich der asiatischen Monsune sind insbesondere der Beginn und das Ausmaß des Klimaoptimums während des Holozäns von wissenschaftlichem Interesse, da diese Periode oft als Analogie für die derzeitige globale Klimaerwärmung herangezogen wird. In Hinblick auf sich teilweise widersprechende Paläoklima- und Umweltrekonstruktionen für das Tibet-Plateau, ist es mein Ziel, die bestehenden Unstimmigkeiten bezüglich des Zeitpunktes und des Ausmaßes des Umweltwandels zu erklären. Dafür wurden von mir zeitliche Variationen fossiler Pollen- und Diatomeenspektren und geochemische Untersuchungen an Seesedimenten unterschiedlicher Zeitskalen (Spätquartär und die letzten 200 Jahre) aus zwei Kernregionen auf dem NO und SO Tibet-Plateau analysiert. Zur Unterstützung der Interpretation wurden die hier erhobenen Daten mit bereits vorhandenen paläoökologischen Aufzeichnungen der Lokalitäten kombiniert, um Datensätze der entsprechenden aquatischen und terrestrischen Proxy-Daten (Stellvertreterdaten) zweier Seenpaare aus den beiden Regionen gegenüberstellen zu können. Hierbei konzentrierte ich mich auf den direkten Vergleich von Proxies, die die Seenentwicklung reflektieren (z.B. Diatomeen, Ostracoden, geochemische Eigenschaften), mit Proxies, die Veränderungen der terrestrischen Umgebung des Sees beschreiben (terrestrische Pollen). Durch diesen Vergleich lässt sich beurteilen, ob Veränderungen im See selbst mit Umweltveränderungen in dem jeweiligen Einzugsgebiet zeitlich übereinstimmen. Dafür habe ich die bereits etablierte numerische Methode Procrustes-Rotation als neuen Ansatz in der Paläoökologie eingeführt. Damit ist ein quantitativer Vergleich von Rohdaten zweier beliebiger sedimentärer Datensätze möglich, um den Grad der Übereinstimmung zu prüfen. Um die in dieser Arbeit rekonstruierten Umwelt- und Klimaereignisse des nordöstlichen Tibet-Plateaus in einen größeren Zusammenhang hinsichtlich holozäner Klimaentwicklung des gesamten Plateaus setzen zu können, und um schlüssige zeitliche und räumliche Klimatrends auf dem Plateau erkennen zu können, habe ich auf alle vorhandenen Paläoklimadatensätze einen Fünf-Skalen Feuchtigkeitsindex und eine Clusteranalyse angewandt. Es konnten jedoch keine einheitlichen zeitlichen und räumlichen Trends der holozänen Klimaentwicklung nachgewiesen werden, was meiner Analyse entsprechend, auf die komplexen Reaktionen verschiedener Proxies auf Umweltveränderungen in einer ohnehin sehr heterogen Berglandschaft, zurückgeführt werden kann. Die Ergebnisse des numerischen Proxy-Vergleichs beider Seenpaare zeigen, dass die Verwendung von verschiedenen Proxies und die Arbeit mit paläo-ökologischen Datensätzen unterschiedlicher See-Typen zu abweichenden Klimaableitungen führen können. Unabhängig vom untersuchten Zeitraum (Holozän oder die letzten 200 Jahren) oder der Region (SO oder NO Tibet-Plateau), ist die Übereinstimmung zweier Datensätze hinsichtlich der Richtung, des Zeitpunktes und des Ausmaßes der abgeleiteten Paläo-Umweltverhältnisse in der Regel zwischen den entsprechenden terrestrischen Datensätzen besser als zwischen den entsprechenden lakustrinen Datensätzen. Die derzeitige Uneinigkeit über stimmige zeitliche und räumliche Klimatrends auf dem Tibet-Plateau kann daher teilweise der Komplexität der verschieden Proxies und ihrer individuellen Empfindlichkeiten gegenüber Umweltveränderungen sowie der unterschiedlichen Reaktionsweise verschiedenartiger See-Systeme auf dem Plateau zugeschrieben werden. Meine Ergebnisse zeigen, dass ein „Multi-Proxy-Multi-Site-Ansatz“ für zuverlässige Paläoklimaableitungen für das Tibet-Plateau von zentraler Bedeutung ist.

The objectives of this thesis are to establish a chronological framework for environmental changes during the last 15,000 years in northwest Romania, to reconstruct the vegetation development, and to evaluate the underlying processes for forest dynamics. Furthermore, an overview of earlier and ongoing pollenstratigraphic work in Romania is provided. Sediments from two former crater lakes, Preluca Tiganului and Steregoiu, situated in the Gutaiului Mountains, on the western extremity of the Eastern Carpathians at 730 m and 790 m a.s.l., respectively were obtained and analysed for high-resolution pollen, macrofossils, charcoal, mineral magnetic parameters and organic matter. The chronostratigraphic framework was provided by dense AMS 14C measurements. Cold and dry climatic conditions are indicated by the occurrence of open vegetation with shrubs and herbs, and cold lake water prior to 14,700 cal. yr BP. The climatic improvement at the beginning of the Lateglacial interstadial (around 14,700 cal. yr BP) is seen by the development of open forests. These were dominated by Pinus and Betula, but contained also new arriving tree taxa, such as Populus, Alnus and Prunus. The gradual establishment of forests may have led to a stabilization of the soils in the catchment. Between ca. 14,100 and 13,800 cal. yr BP the forest density became reduced to stands of Pinus, Betula, Alnus, Larix and Populus trees and grassland expanded, suggesting colder climatic conditions. Picea arrived as a new taxon at around 13,800 cal. yr BP, and between 13,800 and 12,900 cal. yr BP, the surroundings of the sites were predominantly covered by Picea forest. This forest included Betula, Pinus, Alnus, Larix and Populus and, from 13,200 cal. yr BP onwards also Ulmus. At ca. 12,900 cal. yr BP, the forest became significantly reduced and at 12,600 cal. yr BP, a recurrence of open vegetation with stands of Larix, Pinus, Betula, Salix and Alnus is documented, lasting until 11,500 cal. yr BP. This distinct change in vegetation may by taken as a strong decline in temperature and moisture availability. At the transition to the Holocene, at ca. 11,500 cal. yr BP, Pinus, Betula and Larix quickly expanded (from small local stands) and formed open forests, probably as a response to warmer and more humid climatic conditions. At 11,250 cal. yr BP Ulmus and Picea expanded and the landscape became completely forested. The rapid increase of Ulmus and Picea after 11,500 cal. yr BP may suggest the existence of small residual populations close to the study sites during the preceding cold interval. Ulmus was the first and most prominent deciduous taxa in the early Holocene in the Gutaiului Mountains. From ca. 10,750 cal. yr BP onwards Quercus, Tilia, Fraxinus and Acer expanded and Corylus arrived. A highly diverse, predominantly deciduous forest with Ulmus, Quercus, Tilia, Fraxinus, Acer, Corylus and Picea developed between 10,700 and 8200 cal. yr BP, which possibly signifies more continental climatic conditions. The development of a Picea-Corylus dominated forest between 8200 and 5700 cal. yr BP is likely connected to a more humid and cooler climate. The establishment of Carpinus and Fagus was dated to 5750 cal. yr BP and 5200 cal. yr BP, respectively. The dominance of Fagus during the late Holocene, from 4000 cal. yr BP onwards, may have been related to cooler and more humid climatic conditions. First signs of human activities are recorded around 2300 cal. yr BP, but only during the last 300 years did local human impact become significant. The vegetation development recorded in the Gutaiului Mountains during the Lateglacial is very similar to reconstructions based on lowland sites, whereas higher elevation sites seem not to have always experienced visible vegetation changes. The time of tree arrival and expansion during the past 11,500 cal. yr BP seems to have occurred almost synchronously across Romania. The composition of the forests during the Holocene in the Gutaiului Mountains is consistent with that reconstructed at mid-elevation sites, but differs from the forest composition at higher elevations. Important differences between the Gutaiului Mountains and other studied sites in Romania are a low representation of Carpinus and a late and weak human impact. The available data sets for Romania give evidence for the presence of coniferous and cold-tolerant deciduous trees before 14,700 cal. yr BP. Glacial refugia for Ulmus may have occurred in different parts of Romania, whereas the existence of Quercus, Tilia, Corylus and Fraxinus has not been corroborated.

This thesis investigates how variations in the oxygen isotopic composition of lake waters in northern Fennoscandia are recorded in lake sediment archives, especially diatoms, and how these variations can be used to infer past changes in climate and atmospheric circulation. Results from analyses of the oxygen isotopic composition of lake water samples (δ18Olakew) collected between 2001 and 2006 show that δ18O of northern Fennoscandian lakes is mainly controlled by the isotopic composition of the precipitation (δ18Op). Changes in local δ18Op depend on variations in ambient air temperature and changes in atmospheric circulation that lead to changes in moisture source, vapour transport efficiency, or winter to summer precipitation distribution. This study demonstrates that the amount of isotopic variation in lake water δ18O is determined by a combination of the original δ18Olakew, the amount and timing of the snowmelt, the amount of seasonally specific precipitation and groundwater, any evaporation effects, and lake water residence time. The fact that the same isotope shifts have been detected in various δ18Olakew proxies, derived from hydrologically different lakes, suggests that these records reflect regional atmospheric circulation changes. The results indicate that diatom biogenic silica isotope (δ18Odiatom) records can provide important information about changes in atmospheric circulation that can help explain temperature and precipitation changes during the Holocene. The reconstructed long-term Holocene decreasing δ18Op trend was likely forced by a shift from strong zonal westerly airflow (relatively high δ18Op) in the early Holocene to a more meridional flow pattern (relatively low δ18Op). The large δ18Olakew depletion recorded in the δ18O records around ca. 500 cal yr BP (AD 1450) may be due to a shift to more intense meridional airflow over northern Fennoscandia resulting in an increasing proportion of winter precipitation from the north or southeast. This climate shift probably marks the onset of the so-called Little Ice Age in this region. / At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: In press. Paper 2: Submitted. Paper 5: In progress.

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.

The Optimal Foraging Theory, rooted in the processual archaeology, uses a measuring methodology where the foraging strategy that gives the highest payoff measured as the highest ratio of energy gain per time unit is analysed (Mac Arthur & Pianca 1966, Emlen 1966). The theory is a branch of evolutionary ecology why much attention is paid to the interdependence of humans and preys and environmental conditions caused by climatologically and geographical changes or by overexploitation or other changes caused by humans. The analysis of Early Mesolithic pioneers onGotland, who settle in a transforming landscape, leaves indications of a Maglemose culture origin, probably from flooded original settlements in the south/southwest Baltic basin. The pioneers have to adapt to a seal-hunting economy dominated by grey seal which give the best cost-benefit outcome as big terrestrial mammals are missing and only mountain hare is available. The diet is narrow and there is a great risk for deficiency diseases as well as for acquiring hypervitaminosis and osteoporosis caused by excess of seal food. There is a hiatus c. 5000-4500 BC in the archaeological records on Gotland and the south-western Baltic region, and the master thesis hypothesises that Littorina Transgression I with a severe cold dip called the “8.2 ka BP cold event” has a delayed, but such a severe impact also on fauna and flora on Gotland, that the ecological system is destroyed. The possibility for humans to survive in a sustainable society is questionable. The extremely cold winters during this c. 400 years cold event, with glaciers moving southwards, delayed the blooming season, diminished the harvest and changed both flora and fauna. When the ecological niche for the grey seal is destroyed with flooded beaches close to the pioneers, human overexploitation is reinforced. With a diminishing population of mountain hare, which eventually gets extinct at the end of the Mesolithic, there are no alternatives but some birds and fish, hard to catch. Probably the pioneers abandon Gotland or move to a higher level on Gotland but no records are yet found why the period is called a hiatus. Extinction is the worst scenario or survival in such a small number that a sustainable society is lost. If so, new population groups repopulatedGotlandafter the Littorina transgressions. The origin is still unknown of the Pitted-ware and Funnelbeaker cultures that are populating Gotland after the transgressions. This master thesis can not confirm an affluent life style but rather a suffering starving society flooded by Littorina transgressions and struggling with the severe cold, caused by the “8.2 ka cold event” that makes the environmental conditions even worse. The subsistence economy is successively destroyed which probably causes the hiatus in archaeological records. The Littorina Transgression I with the “8.2 cold event” and the lack of terrestrial big animals are bottle necks. / Optimal Foraging Theory, med sina rötter i den processuella arkeologin, använder en metodik utgående från mätningar där insamlingsstrategin som ger den högsta avkastningen per tidsenhet analyseras (Mac Arthur & Pianca 1966, Emlen 1966). Teorin är en undergrupp inom den evolutionära ekologin och därför ägnas stor tid åt att uppmärksamma det ömsesidiga beroendet och påverkan som sker i miljön p.g.a. klimatologiska och geologiska orsaker men också p.g.a. mänsklig påverkan som exempelvis överförbrukning.  Analysen av tidigmesolitiska pionjärbosättare på Gotland, som möter ett landskap i förvandling, lämnar spår efter sig som tyder på ett ursprung i Maglemosekulturen i södra/sydvästra Östersjöregionen. De tvingas bli adapterade till en säljägarekonomi dominerad av gråsäl som ger det bästa energiutbytet, eftersom stora landdäggdjur saknas och endast bergshare finns tillgänglig. Dietvalet är smalt och det föreligger stor risk för både bristsjukdomar och A-vitaminförgiftning och osteoporos p.g.a. överkonsumtion av sälprodukter. Det finns ett uppehåll i de arkeologiska fynden c. 5000-4500 BC på Gotland liksom i södra Östersjöområdet. Magisteruppsatsens hypotes är att den kalla perioden med temperatursänkning som kallas ”8.2 ka BP cold event” under Littorinatransgression I har en fördröjd men så kraftigt övergripande effekt, på både djur- och växtliv på Gotland, att den förstör det ekologiska systemet och därmed möjligheten för människor att överleva i ett hållbart samhälle. De mycket hårda vintrarna under de c. 400 årens ”cold event” medför att glaciärerna dras sig söderut, blomningssäsongen fördröjs, skörden minskar och både fauna och flora förändras. När den ekologiska nischen för gråsälen förstörs av översvämmade stränder nära bosättarna förstärks överexploateringen, och då det inte finns någon alternativ föda utom en minskande harstam, svårfångade fåglar och fiskar, blir situationen fatal för de tidigmesolitiska bosättarna. Troligtvis flyttar de till andra platser inom Östersjönätverket eller till en högre nivå på Gotland, men fynd saknas hittills varför detta tomrum benämns ”hiatus”. Det värsta scenariot är att bosättarna dör ut eller överlever i ett så litet antal att det hållbara samhället går under.Om så är fallet återbefokas Gotland av gropkeramisk kultur och trattbägarkultur i anslutning till Littorinatrasgressionernas slut. Denna magisteruppsats kan inte konfirmera en livsstil i överflöd, utan snarare ett lidande svältande samhälle som översvämmas av Littorinatransgressioner med miljömässiga förhållanden som förvärras av den allvarliga kylan orsakad av ”8.2 ka cold event”.  Försörjningsmöjligheterna förstörs succesivt och befolkningen försvinner vilket troligen orsakar ett hiatus i de arkeologiska fynden. Littorina Transgression I med ”8.2 ka cold event” och bristen på stora landdjur är stora flaskhalsar.

Until relatively recently, the view of Late Pleistocene hunter-gatherers in the Americas was dominated by the “Clovis-first” paradigm. However, recent discoveries have challenged traditional views and forced reconsiderations of the timing, processes, and scales used in modeling the settlement of the Americas. Chief among these discoveries has been the recognition of a wide range of early cultural diversity throughout the Americas that is inconsistent with previously held notions of cultural homogeneity. During the Late Pleistocene-Early Holocene, the development of widely varying economic, technological and mobility strategies in distinct environments is suggestive of a range of different adaptations and traditions. It is argued that colonization was a disjointed process involving alternative, perhaps competing strategies at local and regional levels. Individual groups likely employed distinct strategies for settling new landscapes. These different strategies are reflected in the cultural variability that has been documented in the Late Pleistocene-Early Holocene archaeological records of South and North America. A scalar framework for conceptualizing and modeling this variability on local, regional, and continental scales is introduced. Although primarily focused on local and regional reconstructions, the results can be integrated with other regional studies to generate more comprehensive, continental-scale models of the peopling of the New World. This research provides insight into the local and regional variability—in terms of settlement patterns and economic and technological strategies—present in the archaeological record of at least two formally recognized Late Pleistocene-Early Holocene complexes (Fishtail and Paiján complexes) in the Quebradas del Batán and Talambo of the lower Jequetepeque Valley, northern Perú. Results of extensive survey, excavation, and materials analyses are used to characterize mobility strategies and settlement organization. This research indicates that two distinct patterns of site types, settlement, subsistence, and technology existed at the local level between the Fishtail (ca. 11,200-10,200 B.P.) and Paiján (ca. 10,800-9,000 B.P.); these patterns are indicative of differing regional strategies of colonization. Lastly, it is suggested that the adaptations and behaviors pursued during regional settlement, particularly by Paiján groups, set in motion an increasing reliance on plant foods and an early trend toward sedentism that carried forward into the Holocene period.

La région du lac Mégantic est probablement la première zone à s'être déglacée au Québec, ce qui lui confère un intérêt particulier. L'analyse pollinique et anthracologique des sédiments des trois lacs situés à ses abords, soit les lacs Clinton, Dubuc et des Joncs ont permis de reconstituer l'histoire locale et régionale de la végétation et des feux. La présence d'un gradient altitudinal a entrainé des décalages surtout dans l'instauration des premières phases forestières. La région s'est déglacée vers 13 500 ans AA, et une toundra s'y est installée. Le début de l'afforestation est marqué par l'arrivée du sapin baumier et de l'épinette noire. Par la multiplication de leurs populations, la forêt s'est fermée vers 10 000 ans AA pour constituer une forêt boréale qui fût alors perturbée par plusieurs épisodes de feux. Vers 8000 ans AA, les nouvelles conditions climatiques favorisent les espèces feuillues et instaurent une érablière à bouleau jaune et une diminution de la fréquence des feux. Les résultats obtenus permettent d'enrichir les connaissances paléophytogéographiques et anthracologiques du Québec. / The Lac Mégantic area is probably the first deglaciated in Quebec (13,500 cal. BP) which gives it a special interest. The pollen and charcoal analysis in sediments of three lakes located in its vicinity, Clinton, Dubuc and des Joncs Lakes, helped to reconstruct postglacial vegetation and fire, locally and regionally. The presence of an altitudinal gradient resulted in some delays in the introduction of various forest stages especially at the beginning. At start, tundra established in the region. The start of the afforestation is marked by the arrival of the balsam fir and black spruce. By multiplying their populations, the forest closed around 10,000 years cal. BP to build a boreal forest and was also disturbed by multiple fires. By 8,000 years cal. BP, new conditions favored deciduous species and created a sugar maple and yellow birch forest associated with lower fire frequencies. This study offers new perspectives in fire and forest reconstitutions by using proximal sites.