The Potential of Lake Ohrid for Long-Term Paleoenvironmental Reconstructions

Lake Ohrid at the Macedonian/Albanian border is thought to be one of the oldest lakes in Europe, being tectonically formed during the Tertiary. Since only a few studies to the potential of Lake Ohrid sediments for long-term palaeoenvironmental reconstructions so far exist, a transect of surface sediments was investigated for chronology, physical properties, grain-size composition, and biogeochemistry. The results obtained indicate a conform sedimentation in the central part of the lake basin with mean sedimentation rates of c. 0.5 mm/yr. The sediment composition is dominated by fine clastic matter, i.e., mainly carbonates. Diatoms or diatom fragments form the major part of organic matter deposits, as it is indicated in relatively high contents of biogenic opal and low contents of total organic carbon and total nitrogen. Towards the lateral parts of the basin, sedimentation is increasingly influenced by local inflows. The results of the sedimentological investigations are compared with those of a hydroacoustic shallow seismic survey that allowed to indicate regions of undisturbed sediment deposition particularly in the central basin and lateral regions of high tectonic activity and sediment redeposition. A 11 m long piston core was recovered in spring 2005 from the southern part of Lake Ohrid and studied with a multidisciplinary geoscientific approach. Bioturbation is common throughout the core and hampers palaeoenvironmental reconstructions on an annual or decadal scale. However, significant changes in sediment color, composition, and structure indicate that long-term changes in the hydrological and sedimentological conditions have occurred during the Late Pleistocene and Holocene. Thus, the palaeoenvironmental record from Lake Ohrid may form a valuable link between long-term records from the Mediterranean Sea and the adjacent terrestrial regions.