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SDD-01 Scientific drilling
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Towards an understanding of the evolutionary and environmental history of ancient Lake Ohrid
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Bernd Wagner, University of Cologne (Germany)
Tom Wilke, Justus Liebig University Giessen (Germany)
Christian Albrecht, Justus Liebig University Giessen (Germany)
Andy Lotter, Universiteit Utrecht (Netherlands)
Goce Kostoski, Hydrobiological Institute (Macedonia, Fyrom)
Gerhard Daut, University of Jena (Germany)
Sebastian Krastel, Universität Bremen (Germany)
Jane Reed, University of Hull (United Kingdom)
Klaus Reicherter, RWTH Aachen (Germany)
Antje Schwalb, TU Braunschweig (Germany)
Roberto Sulpizio, Universita die Pisa (Italy)
Giovanni Zanchetta, Universita die Pisa (Italy)
Sasho Trajanovski, Hydrobiological Institute (Macedonia, Fyrom)
Hendrik Vogel, University of Cologne (Germany)
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Lake Ohrid is a transboundary lake between the Republics of Albania and Macedonia. The lake is located in a deep graben of tectonic origin and is considered to be the oldest present-day lake in Europe, formed some 3-5 million years ago. In addition to the presumed old age, an extraordinary high level of endemism with more than 200 endemic species described make Lake Ohrid a site of global importance. Recently, the age of Lake Ohrid and of major evolutionary events were estimated by molecular clock analyses of mitochondrial DNA genes from endemic species and their sister groups. The reasons for the evolutionary history of Lake Ohrid and processes leading to the unique fauna are however largely unknown, because a sedimentary record covering the complete history of the lake is lacking.
Up to 14 m long sediment sequences were recovered from different sites in Lake Ohrid between 2005 and 2007. The occurrence of several tephras in these sequences indicates that Lake Ohrid is a valuable archive of volcanic ash dispersion in the Mediterranean region. The tephras also provide a valuable basis for chronological constraints on sediment sequences from the lake. The sediment sequences recovered to date comprise the last glacial / interglacial cycle and record sensitively climate changes and human impact in the region.
Shallow hydro-acoustic seismic surveys carried out in 2004 and 2007 indicate faults and sediment redeposition, particularly at the steep sub-aquatic slopes close to the shore of Lake Ohrid. The faults and sediment redeposition are likely due to tectonic activities, such as they are documented in numerous earthquakes in the region, and to significant lake-level changes, which likely have occurred in the past. The results from the shallow hydro-acoustic surveys match with those achieved by an airgun survey in autumn 2007, which revealed c. 600 m of relatively undisturbed sediment fill in the central part of the lake. Since major erosive discordances were not observed in the central part of the lake, the sediments from this part likely contain the complete and continuous lake history. Based on these results, the study of sediment sequences recovered from Lake Ohrid within the scope of a future deep-drilling project would allow to obtain valuable information about the age and the origin of the lake, to achieve a continuous record of tectonic and volcanic activity and of climatic changes in the region, and to test if the evolution in Lake Ohrid is triggered by long-term stability or by rapid changes.
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