Climate controlled ostracod preservation in Lake Ohrid (Albania, Macedonia)

Abstract

Lake Ohrid (Albania, Macedonia) is probably the oldest existing lake in Europe and thus of great interest for palaeo-environmental and genetic studies. Within more than 220 endemic faunal species known to live in the lake, ostracods are outstanding due to the potentially very long fossil record. They can provide geochemical information over a period exceeding the entire Quaternary and direct evidence for radiation. Here we discuss the ostracod record and the calcite concentration along a 10-m-long sediment core taken at 100 m water depth in the south-eastern, Albanian part of Lake Ohrid. Well preserved ostracod valves representing in-situ fauna only occur from 0 cm to 105 cm and from 476 cm to 933 cm core depth, corresponding to the last interglacial and the Holocene, respectively. Those periods are also characterized by high concentrations of endogen calcite. There is no significant difference in the faunal composition of the two periods separated by several tens of thousand years and we found non-calcitic ostracod remains, especially the strongly chitinised mandibles, throughout the glacial period. Therefore, we conclude that ostracods were present in the lake throughout the entire period represented by the sediment core, but with poor or lacking preservation of their calcite valves during the glacial period. Calcite precipitation and ostracod preservation were most likely inhibited by the complete interruption of Calcium supply from karsts springs, which were inactive during the glacial periods due to permafrost in large parts of the calcareous mountains.