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  • The magnetic properties of a sediment core from a high altitude lake in the Swiss Alps were compared with palynological and geochemical data to link climatic and mineral magnetic variations. According to pollen data, the sediments extend from the present to the Younger Dryas, i.e., they cover more than 10,000 years of environmental change in the Alps. The major change in magnetic properties corresponds to the climatic warming of the early Holocene. High-coercivity magnetic minerals that characterize the Late Glacial period almost disappeared during the Holocene and the concentration of ferrimagnetic minerals increased sharply. The contribution of superparamagnetic grains also decreased in the Holocene sediments. Similar variations in {SP} content and coercivity, of smaller magnitude, are found in the Holocene and are interpreted to represent minor climatic variations. Comparison with the historical record of the last 1000 years confirms this interpretation. The magnetic mineralogy, the superparamagnetic contents, and the {IRM} intensity in the coarse-grained, Late Glacial sediments are similar to those measured in the catchment bedrock. This indicates a detrital origin. The different properties and the higher concentration of magnetic minerals in the Holocene sediments are due to authigenic phases. Magnetic properties provide a high resolution record of climatic change. They are sensitive even to small variations that are not recorded in the pollen or {LOI} data. Magnetic parameters show fine-scale variation and constitute a valuable supplement to conventional climatic indicators.
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    • Document
  • Abstract. Here we present stable isotope data from three sediment records from lakes that lie along the Macedonian- Albanian border (Lake Prespa: 1 core, and Lake Ohrid: 2 cores). The records only overlap for the last 40 kyr, although the longest record contains the MIS 5/6 transition (Lake Ohrid). The sedimentary characteristics of both lakes differ significantly between the glacial and interglacial phases. At the end of MIS 6 Lake Ohrid’s water level was low (high �18Ocalcite) and, although productivity was increasing (high calcite content), the carbon supply was mainly from inorganic catchment rock sources (high �13Ccarb). During the last interglacial, calcite and TOC production and preservation increased, progressively lower �18Ocalcite suggest increase in humidity and lake levels until around 115 ka. During ca. 80 ka to 11 ka the lake records suggest cold conditions as indicated by negligible calcite precipitation and low organic matter content. In Lake Ohrid, �13Corg are complacent; in contrast, Lake Prespa shows consistently higher �13Corg suggesting a low oxidation of 13C-depleted organic matter in agreement with a general deterioration of climate conditions during the glacial. From 15 ka to the onset of the Holocene, calcite and TOC begin to increase, suggesting lake levels were probably low (high �18Ocalcite). In the Holocene (11 ka to present) enhanced productivity is manifested by high calcite and organic matter content. All three cores show an early Holocene characterised by low �18Ocalcite, apart from the very early Holocene phase in Prespa where the lowest �18Ocalcite occurs at ca. 7.5 ka, suggesting a phase of higher lake level only in (the more sensitive) Lake Prespa. From 6 ka, �18Ocalcite suggest progressive aridification, in agreement with many other records in the Mediterranean, although the uppermost sediments in one core records low �18Ocalcite which we interpret as a result of human activity. Overall, the isotope data present here confirm that these two big lakes have captured the large scale, low frequency palaeoclimate variation that is seen in Mediterranean lakes, although in detail there is much palaeoclimate information that could be gained, especially small scale, high frequency differences between this region and the Mediterranean.
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  • Detailed knowledge of the past climate and environmental variability is vital in order to predict future scenarios with more confidence. High resolution and highly-resolved natural archives are therefore in growing demand (PAGES report, 2009). This thesis is part of a coordinated effort, STALCLIM project, where a series of state-of-theart methods in speleothems proxies were used in order to develop the full potential of speleothemsas paleoclimate and paleoenvironmental archive. The thesis investigates climate variations as recorded by speleothems from Schafsloch and Milandre caves, spanning time intervals of high scientific interest: 0 to 14 550 years BP and 130 000 to 230 000 years BP. The locations of the caves, Jura Mountains and the Alpstein Mountains (Swiss Alps) are regions highly sensitive to climate-induced changes in temperature, atmospheric pathways and/or environment evolution. In order to establish new climate records and resolve the paleoclimate questions, continuous geochemical analyses were applied, with high resolution stable isotopic and trace elements analysis and 230Th age measurements, and these were combined with thin section analysis of the calcite petrology. Where possible, we conducted continuous and temporal measurements in the caves where the samples were collected, to provide a better understanding of the cave environment. Chapters 2 and 3 highlight the sensitivity of high altitude speleothem proxies to small changes in temperature and water availability, both induced by internal and external climate drivers. The MF3 stalagmite, from Schafsloch Cave, provides a unique opportunity to investigate a regional expression of millennial-scale climate variability in Central Europe during MIS 6 and Late MIS 7. The sample records in high detail the structure of the penultimate deglaciation in the Alps, and brings new evidence regarding the nature of this important climatic transition. Chapters 4 and 5 show the high resolution composite δ18O record and elemental composition of speleothems from Milandre Cave, covering the Lateglacial- Holocene interval. A detailed comparison with Greenland ice cores and Gerzensee lake sediments (Central Switzerland) indicates similarities in the long timescale changes of atmospheric circulation patterns in the whole North Atlantic region after the last deglaciation. In contrast, during the Holocene, the signature pattern in the isotopic calcite δ18O data differs to that seen in Central Europe. This provides important insights into the regional teleconnections and local environmental reaction to changes in the temperature, seasonality of precipitation and atmospheric processes. The use of a robust δ18O/temperature transfer function has enabled a high resolution temperature reconstruction of the autumn to spring temperatures at the Milandre site for the last 14 550 y BP. In summary, this thesis provides new results on environmental and climatic variability in Switzerland during specific intervals over the last 230 000 years. It suports large teleconnections over the northern hemisphere and emphasizes the role of insolation and obliquity as important climate triggers in the region. These new high-resolution and precisely dated records of δ18O and cold season temperature reconstruction for the Jura Mountains over the last 14 550 y BP, are proposed as being representative for Central Europe.
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    • Document