Reconstruction of the Late Quaternary climatic and environmental history of the northern Mediterranean region by a multidisciplinary study of sediment cores from Lake Ohrid, Macedonia and Albania
Zusammenfassung der Projektergebnisse
Based on the geological material and geophysical data gathered during numerous field campaigns since 2004 to Lake Ohrid in combination with a large array of methodological and analytical techniques the following conclusions can be drawn from this project. FTIR spectra of lacustrine sediment samples were successfully 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, sitespecific FTIRS calibrations and FTIRS calibrations based on a surface sediment dataset from 94 northern Swedish lakes were constructed. Both approaches demonstrated significant correlations between FTlRS-inferred and conventionally assessed biogeochemical property concentrations, ranging between R2 = 0.79 - 0.99 for TOC, R^ = 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. Modern sedimentation in the Lake Ohrid basin is controlled by a complex interaction of multiple processes. Analysis of biogeochemical bulk parameters, selected metals, pigment concentrations as well as grain size distributions revealed a significant spatial heterogeneity in surface sediment composition. It implies that sedimentation in Lake Ohrid is controlled by an interaction of multiple natural and anthropogenic factors and processes. Major factors controlling surface sediment composition are related to differences in geological catchment characteristics, anthropogenic land use, and a counterclockwise rotating surface water current. Frequent occurrences of well-dated tephra and cryptotephra layers as well as radiocarbon, electron spin resonance, and luminescence dating allowed the establishment of a chronological framework for the recovered sediment successions. These data revealed that the sediment successions recovered se far in part reach well back into MIS 6 and prove that Lake Ohrid hosts a very valuable tephrostratigraphic and paleoclimatic archive. Despite distinct spatial differences, Lake Ohrid appears to have reacted uniformly to climatic forcing on changes in catchment configuration, limnology and hydrology in the past as evidenced by contemporaneous changes in sediment composition in long sediment successions from different parts of the lake basin. The interplay of climatic forced factors has varied significantly in the course of the last glacial-interglacial cycle and led to distinctly different sediment characteristics during glacial and interglacial phases at Lake Ohrid. Interglacial sediments appear as calcareous clayey-sandy silt and glacial sediments are dominated by clastic clayey-sandy silt. Apart from this general pattern tied to high amplitude climate fluctuations, short-term climatic fluctuations of reduced amplitude are also recorded in the sediment successions and generally well correlated to other paleoclimate records in the Mediterranean. As the results, revealed that Lake Ohrid is a key site to better understand the dispersal of tephras, the climatic and tectonic history in the northern Mediterranean region and te link geological events and endemism, an ICDP project has been established during the past years. The deep drilling campaign is scheduled for 2011. Ongoing research on Lake Ohrid, will improve the already existing knowledge significantly.
