The long-term climatic and environmental history of Southeast Asia is still fragmentary. This thesis therefore aims at studying lake sediment/peat sequences using a multi-proxy approach to reconstruct the environmental history and the impact of past changes in monsoon variability and intensity on lake ecosystems in Thailand. The study focuses on two lakes located in northeast Thailand: the larger Lake Kumphawapi and the smaller Lake Pa Kho. The comparison of multiple sediment sequences and their proxies from Kumphawapi suggests a strengthening of the summer monsoon between c. 10,000 and 7000 cal yr BP. Parts of the lake had been transformed into a wetland/peatland by c. 7000 cal yr BP, while the deeper part of the basin still contained areas of shallow water until c. 6600 cal yr BP. This gradual lowering of the lake level can point to a weakening of the summer monsoon. Paleoenvironmental information for the time interval between 6200 and 1800 cal yr BP is limited due to a several thousand-year long hiatus. This new investigation demonstrates that arguments using the phytolith and pollen record of Lake Kumphawapi to support claims of early rice agriculture in the region or an early start of the Bronze Age are not valid, because these were based upon the assumption of continuous deposition. The lithostratigraphy and multi-proxy reconstructions for Pa Kho support a strengthened summer monsoon between 2120-1580 cal yr BP, 1150-980 cal yr BP, and after 500 cal yr BP; and a weakening of the summer monsoon between 1580-1150 cal yr BP and between 650-500 cal yr BP. The increase in run-off and higher nutrient supply after AD 1700 can be linked to agricultural intensification in the region. Conclusively, the Holocene records from northeast Thailand add important paleoclimatic information for Southeast Asia and allow discussing past monsoon variability and movements of the Intertropical Convergence Zone in greater detail. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Accepted. Paper 5: Manuscript.</p>

Le Bergsee offre une séquence sédimentaire terrestre et continue sur l’histoire environnementale de l’Europe de l’Ouest entre 50 ka BP et aujourd’hui.Un enregistrement pollinique continu et séculaire permet la construction de l’évolution de la végétation et du climat sur la dernière période glaciaire.Outre l’opposition entre le Stade Isotopique Marin 3 et 2 (le second étant plus steppique), la succession de stades et d’interstades courts nord-atlantiques est reflétée par l’alternance de steppes (i.e. climat froid/sec) et de courts épisodes forestiers (i.e. réchauffements). Des phases glaciaires plus prononcées attestent de Stades de Heinrich en Europe de l’Ouest.Ces résultats sont validés par : 1) la confrontation avec des études européennes et 2) l’approche multi-proxy (chironomes, alkanes, géochimie) appliquée à des épisodes clés.Une comparaison avec les données archéologiques montre finalement le potentiel de contribution du contexte climato-environnemental du Bergsee à la compréhension des changements sociétaux du Paléolithique Supérieur. / Bergsee Lake provides a terrestrial and continuous sediment record of environmental changes in Western Europe for the last 50 ka.A continuous pollen record established at secular resolution allow to reconstruct the vegetation and climate variability of the Last Glacial period.Contrasted climate/vegetation is recorded between Marine Isotope Stages 3 and 2 (more steppic for the second one), and the north-Atlantic stadial/interstadial succession is also reflected by alternating steppe (i.e. cold/dry climate) and short forested episodes (i.e. warming). Moreover, Heinrich Stadials are evidenced as pronounced glacial phases by the Bergsee record.These results are supported by 1) comparison with other European records and 2) the multi-proxy approach (chironomids, alkanes, sedimentary data) applied on key climatic periods.Finally, comparison with archaeological data highlights the great potential contribution of the Bergsee record to the understanding of society changes of the Late Palaeolithic.

Un total de cinq séquences a été étudié sur le Mont Lozère afin de reconstruire la dynamique paysagère et les usages du sol sur la longue durée. L’approche multiproxy utilisé a permis de déterminer les principaux rythmes d’anthropisation et de déterminer son caractère régional et/ou local. Ce travail mené à haute résolution spatiale, chronologique et analytique a permis d’intégrer les résultats avec les données obtenus dans le cadre du PCR-Mont Lozère, afin de caractériser les modes d’occupation de la montagne qui ont modelé ce paysage culturel depuis le Néolithique jusqu’à nos jours. Une longue histoire des interactions socio-environnementales a été mise en évidence au Mont Lozère, avec une première phase à caractère agropastoral dès le Néolithique ancien, vers ca. 4550-4400 cal BC. Le Néolithique final est une période clé caractérisée par un important impact agropastoral fondé sur l’utilisation du feu pour l’ouverture de clairières. Pendant l’Âge du Fer, un déboisement marqué dans les espaces d’altitude et de piedmont coïncide avec un développement des activités agropastorales et métallurgiques. Le Haut Moyen Âge se caractérise par l’amplification des déforestations, contemporaines d’un essor des activités agropastorales. Durant le Moyen Âge Central, un système diversifié d’exploitation des ressources naturelles inclue de la métallurgie, l’agriculture, le pastoralisme, l’extraction minière et le charbonnage. Le développement agropastoral du Bas Moyen Âge aboutit à une déforestation marquée du massif qui s’étend jusqu’à la moitié du 19ème siècle, quand commencent la déprise agropastorale et les reboisements au Mont Lozère. L’histoire de la nardaie qui caractérise les espaces sommitaux suit ces phases majeures de l’anthropisation et dévoile le rôle clé qu’a joué l’agropastoralisme dans la genèse et l’évolution de ce paysage culturel de moyenne montagne. / Five sedimentary sequences have been studied in the Mont Lozère with the aim to reconstruct the landscape dynamics and the land-use through the longue durée. The use of a multi-proxy analysis has allowed us both to identify distinct rhythms of human-induced landscape shift and to establish the local/regional extent of these changes. The use of high spatial, chronological and analytical resolution has enabled a correct integration of the results of this research with those supplied by the PCR-Mont Lozère project. As a result, a series of land-uses in a mountain environment from the Neolithic to present time has been proposed. A long history of socio-environmental interactions in Mont-Lozère is evidenced. A first shepherding phase in Early Neolithic (4550-4400 cal BC) has been evidenced. During Late Neolithic pastoral practices and related slash-and-burn strategies attain its highest activity. In the Iron Age Period a noticeable deforestation of both foothills and higher environments takes place as a consequence of the overall increase farming and metallurgical activities. Forest clearances increase even more during High-Medieval times, at the same time that farming activities reinforce. During the Middle Ages a more complex and diversified land-use system, including farming, metallurgy, mining and charcoal production, is recorded. The development of farming activities in the Late Medieval resulted in a more evident forest clearance of the Massif. This area remained unchanged until the 19th century, when the decay of agriculture and shepherding occurs and forest replanting in Mont Lozère is recorded. The history of highland herb communities of Nardus stricta correctly matches the main phases of land-use and underlines the key-role of farming in the genesis and evolution of this cultural landscape. / Se han estudiado cinco secuencias sedimentarias en el Mont Lozère con el objetivo de reconstruir la dinámica paisajística y los usos del suelo en la longue durée. La utilización de un análisis multiproxy ha permitido determinar los principales ritmos de antropización y establecer su carácter regional y/o local. La alta resolución espacial, cronológica y analítica hapermitido la integración de resultados con aquellos obtenidos en el marco del PCR-Mont Lozère y proponer los usos de la montaña que han modelado el paisaje cultural desde el Neolítico hasta la actualidad. Se ha evidenciado una larga historia de las interacciones socioambientales en el Mont Lozère, con una primera fase de carácter agropastoral en el Neolítico Antiguo, en ca. 4550-4400 cal BC. El Neolítico Final es una fase de marcado impacto agropastoral en la que se generalizan las quemas para abrir claros en el bosque. En la Edad del Hierro se inicia una marcada deforestación en el piedemonte y los espacios de altitud, coincidiendo con un desarrollo agropastoral y metalúrgico. En el periodo altomedieval se amplifican las deforestaciones coincidiendo con un marcado incremento de las actividades agropastorales. En la Plena Edad Media se evidencia un sistema diversificado que implica metalurgia, agricultura, pastoreo, minería y carboneo. El desarrollo agropastoral de la Baja Edad Media supone una marcada deforestación en el macizo que se extiende hasta mitad del s. XIX, momento en que se inicia el declive del agropastoralismo y empiezan las reforestaciones en el Mont Lozère. La historia de las formaciones herbosas con Nardus stricta de los espacios somitales sigue estas principales fases de antropización y revela el papel clave del agropastoralismo en la génesis y evolución de este paisaje cultural.

The Sefidrud has developed a large delta in the south west of the Caspian Sea. Its delta is characterized by rapid sedimentation rate (20 mm/yr) in the delta plain and low sedimentation rate (1.67 mm/yr) in a very steep delta front. Sefidrud Delta evolution depends upon sediment supply by river and longshore current under rapid Caspian Sea Level (CSL) fluctuation and tectonic setting at the point of entry to the basin. The tectonic setting caused a very steep slope in the delta front. Sediment supply is variable and affected by river avulsion and dam construction. The CSL has undergone significant changes during the last millennium. Therefore, the Sefidrud Delta evolution during the last millennium is explained based on CSL fluctuations. This fluctuation has major impacts not only on coastal lagoons, but also more inland in wetlands when the CSL rose up to at least -21.44 m (i.e. >6 m above the present water level) during the early Little Ice Age. Although previous studies in the southern coast of the Caspian Sea have detected a high-stand during the Little Ice Age period, this study presents the first evidence that this high-stand reached so far inland and at such a high altitude. This study also examines the interdependence of different factors in the evolution of coastal lagoons as a part of delta evolution. Dam flushing operations and rapid sea–level rise (~3 m between 1977 and 1995) have accelerated the infilling of the coastal lagoon system. This rapid infilling (31 mm/yr) makes the whole system more prone to sediment encroachment in the short term. Because the lagoons are short-lived and have dynamic evolution, the impact of the Anthropocene is also visible in the delta evolution.

A lack of well-distributed, high-resolution records of Late Quaternary Asian palaeomonsoon variability remains an outstanding issue for palaeoclimatologists, and is especially marked in remote regions such as the mountains of southwestern China (Wang et al., 2005). Characterising the nature, timing and magnitude of climate variability in southwestern China is essential for understanding the regional climate as a whole, and the potential social, economic and environmental impacts that may result from Asian monsoon system changes. The NERC-funded research presented in this thesis focuses on a high altitude lake sediment record obtained from Lake Shudu, Yunnan Province, China. The lake is located on the southeastern edge of the Tibetan Plateau. The primary aims of this research were to identify and examine key environmental and climatic shifts which occurred in southwestern China during the Late Pleistocene (Dali) - Early Holocene Period; to examine the possible drivers of these changes; and to compare the findings with other regional proxy records in order to better understand climate dynamics in southwestern China. These aims were chosen in order to test the hypothesis that Late Quaternary millennial to centennial scale climatic and environmental changes in southwestern China were driven by changes in solar insolation and / or glacial climate boundary conditions, characterised by stepwise increases in palaeomonsoon intensity. AMS 14C radiocarbon dates obtained from bulk sediment samples and pollen concentrations indicated that the seven metre core (06SD) that forms the focus of this research spans the last c. 22.6 ka cal. yr BP, making it one of the longest high-resolution Late Quaternary records available for southwestern China. 06SD was examined using a multi-proxy approach incorporating physical, organic and palaeoecological analyses. The record captures the shift from colder, drier Pleistocene (Dali) conditions to warmer, wetter Holocene conditions and is punctuated by two events. The first event, centred at c. 17.3 ka cal. yr BP, possibly represents a phase of warmer and / or wetter conditions in response to rising solar insolation during the deglacial period. The second event, commencing at c. 11.7 ka cal. yr BP, possibly denotes the Pleistocene - Holocene Boundary. Overall, the findings of this research support the view that during the Late Pleistocene, Asian summer monsoon strengthening was non-linear and driven by changes in glacial dynamics and / or solar insolation.

Late Pleistocene sediments recovered from ODP Leg 175, Site 1085 are used to generate a high-resolution (500 yr) record of continental climate change in Southern Africa. The location of Site 1085, the SW African continental slope, provides a continuous hemipelagic section with a significant terrigenous component. Terrigenous sediments are transported via fluvial and/or eolian transport mechanisms with MIS 1 being dominated by eolian transport. Analyses, including grain-size, color reflectance, biogenic sediment geochemistry (%CaCO3, %TOC, and C/N), bulk sediment geochemistry, and clay mineralogy, are used to identify continental climate conditions in southern Africa. Analyses indicate glacial/interglacial variation. Median grain-size peaks are associated with changes in transport. Clay mineralogy indicates the presence of kaolinite, smectite, and illite in varying percentages. Smectite and illite dominate the clay mineral assemblages except during MIS 2. Maximum kaolinite was found during MIS 2 and is associated with poleward transport by the Angola Counter Current.

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.

The palaeoecological development of alum mire since early Eneolithic on the basis of the results of macro-remains, pollen, and chemical analysis. The developement of local vegetation and nearest surrounding area was studied.

This study deploys compound-specific multi-proxy isotopic study of lipid biomarkers to understand Neogene climatic and ecological variabilities in the Himalayan foreland. The investigation of compound-specific carbon and hydrogen isotopes along with glycerol dialkyl glycerol tetraether (GDGT) is the first of its kind for the Nepalese Siwalik. A total of 49 mudstone (and some paleosol) samples were collected from the paleomagnetically age-constrained Siwalik strata in the Surai Khola and Karnali River sections. δ13C results suggest a domination of C3 trees between 12 and 8.5 Ma, and a stepwise expansion of C4 grasses starting gradually at 8.5 Ma and culminating rapidly around 5.5 Ma. δD results show an overall gradual increase in rainfall since 12 Ma, with a rapid intensification around 5.5 Ma. The negative correlation between rainfall and GDGT-derived paleotemperature prior to 5.5 Ma indicates that the region experienced higher rainfalls during colder periods and vice versa. We propose that this negative correlation could be related to the strong presence of mid-latitude westerlies in the region because of the subdued Himalayas, when summer monsoon winds were weaker, that brought enhanced winter-precipitation particularly during colder periods. After 5.5 Ma, our data show a conspicuous positive correlation between rainfall and annual temperature, indicating the onset of modern-style seasonality in rainfall in the Indian subcontinent, which generates more rainfall during summer than during winter. Notably, this initiation of the Indian monsoon around 5.5 Ma favored the dominance of C4 grasses over C3 trees that is reflected in our δ13C data.

Palaeoenvironmental investigations from the Lake Plav catchment of the Prokletije Mountains in Montenegro and Albania, allowed primarily climatic change and anthropogenic influences during the Late Holocene and particularly the Little Ice Age (LIA) to be identified. Three sediment cores were analysed, two from Lake Plav (904 m a.s.l., cores LPCA and LPCB) and one from the upper catchment site of Lake C in Buni i Jezerces (1754 m a.s.l., core BJC1). These sediments were analysed for a variety of proxies including pollen, ostracoda, organic content, magnetic susceptibility and particle size. Chronologies for each sediment core were constructed using AMS radiocarbon, 210Pb and 137Cs dating techniques. The lower sites provided a record of past flood events, anthropogenic influences, lake development and infilling that have occurred since c. AD 500. Core BJC1 provided longer-term data since c. 2720 BC, providing complementary records of Pediastrum and thermophilous arboreal types, identified following a catchment vegetation survey. Glacial geomorphological mapping of the Maja e Koljaet glacier in Buni i Jezerces, Albania, enabled a catchment specific palaeotemperature record to be constructed from AD 1859 to the present. Glacial features were dated using lichenometry before degree-day modelling enabled temperature reconstruction. The palaeotemperature reconstruction for the Albanian Little Ice Age glacial maximum (LIAGM) suggests that temperatures were 0.9°C below the 1980-2008 annual temperature mean. This work also provided the first record of glacial extent during the LIA in Albania, indicating that the Albania LIAGM occurred c. AD 1859, around a decade after the European LIAGM and two decades before that of Montenegro. Anthropogenic indicators were used to reconstruct human activity in the catchment, which suggested that arable farming was pursued throughout the Medieval Warm Period (MWP; c. AD 800-1090) and continued during a period of transition to the LIA, between c. AD 1090 and AD 1300. The LIA (c. AD 1300 - 1860) was characterised by an abrupt Alnus decline, thought to be the result of anthropogenic clearance of the floodplain and reduction of both arable and thermophilous types. During the LIA sedimentation rates were up to 1.41 + 0.17 cm yr-1 at Lake Plav causing lake infilling and shallowing allowing wetland expansion c. AD 1570. The result of lake infilling is highlighted during the early 20th century, when the lake extent fell by around 42% as a result of climatic amelioration post-LIA causing lake levels to fall and wetland indicators to decline. The inferred past climatic changes from the Lake Plav catchment are compared to data from around the Mediterranean and Southern Europe. This allows identification of the climatic influences affecting the site during the Late Holocene. Catchment records have provided evidence of cooler and wetter conditions coeval to the occurrence of solar minima such as the Wolf, Spörer and Maunder minima. Overall, the records suggest that continental atmospheric circulation patterns such as the North Sea-Caspian Pattern (NCP) and East Atlantic-West Russia pattern (EA-WR), dominated the site until the late 1800s, when records become more synchronous with the NAO index and Mediterranean/Southern European data.