The sediment record of Lake Ohrid (Albania/Macedonia) � new methodological approaches, tephrostratigraphy, chronology, and inferences of past climatic and environmental changes

This thesis had two primary objectives: One objective was to explore and develop applications of Fourier transform infrared spectroscopy (FTIRS) for the quantification of biogeochemical properties in lake sediment; the other objective was to assess the Lake Ohrid (Albania/Macedonia) sediment record with an emphasis on tephrostratigraphy and inferences of climatic and environmental changes using a 15 m long sediment succession (core Co1202) from the north-eastern part of the lake. Studies presented in this thesis were conducted within the scope of an envisaged deep drilling campaign at Lake Ohrid and therefore represent important preliminary studies. FTIR spectra of lacustrine sediment samples were calibrated to infer concentrations of total organic carbon (TOC), total inorganic carbon (TIC), total nitrogen (TN), and biogenic silica (BSi). To test the applicability of the FTIRS technique, site-specific FTIRS calibrations and FTIRS calibrations based on a surface sediment dataset from 94 northern Swedish lakes were constructed. Both approaches demonstrated significant correlations between FTIRS-inferred and conventionally assessed biogeochemical property concentrations, ranging between R2 = 0.79 � 0.99 for TOC, R2 = 0.85 � 0.99 for TIC, R2 = 0.62 � 0.84 for TN, and R2 = 0.68 � 0.94 for BSi. These results, in combination with the small amount of sample material (0.01 g) required, negligible sample pre-treatments, and low costs of analysis, show that FTIRS is a promising analytical alternative to infer biogeochemical properties, especially when large sample quantities need to be analysed. The finding of ten tephra and cryptotephra layers throughout the Co1202 sediment succession and their correlation with explosive eruptions of Italian volcanoes provided new data on the dispersal of ash originating from these eruptions. The relatively well-known ages of these tephra and cryptotephra layers combined with seven radiocarbon dates, enabled a chronological framework for core Co1202 to be established. Based on these chronological constrains, the Co1202 succession covers the last glacial-interglacial cycle back to 136 ka, except for a hiatus between 97.6 and 81.7 ka. Assessment of climatic and environmental changes using lithological, sedimentological, geochemical, and physical indicators revealed that Lake Ohrid´s sediments sensitively recorded both long- and short-term climatic fluctuations over the past 136 kyrs. Despite some minor discrepancies, the climate fluctuations documented in the Lake Ohrid sediment record are well correlated with other climate records in the wider Mediterranean region. These studies emphasise the potential of Lake Ohrid as a valuable archive of dispersed volcanic products from Italian volcanoes and for climatic and environmental changes in the northern-central Mediterranean region