Ostracod-based isotope record from Lake Ohrid (Balkan Peninsula) over the last 140 ka

The stable isotope composition of benthic ostracods from a deep-lake sediment core (JO2004-1) recovered from Lake Ohrid (Albania-Macedonia) was studied to investigate regional responses to climate change at the interface between the north-central European and Mediterranean climate systems. Ostracod valves are present only during interglacial intervals, during the Marine Isotope Stage (MIS) 5 and 1. The ostracod oxygen isotope values (δ18O) quantitatively reflect changes in the oxygen isotope signal of the lake water (δ18OL). The interpretation of this record however, is far from straight forward. δ18OL variations throughout MIS 5/6 transition (TII), MIS 5 and MIS 1 appear to be controlled by site specific hydrological processes as shown by modern isotope hydrology. The δ18OL trends at TII, MIS 5 and MIS 1 match the timing and the main structural feature of the major regional climate records (Corchia cave δ18O, Iberian margin Sea Surface Temperature) suggesting that the Ohrid δ18OL responded to global-scale climate changes, although it seems certain that the lake experienced a significant degree of evaporation and varying moisture availability.The carbon isotope signal (δ13C) seems to respond more accurately to climate changes in agreement with other JO2004-1 proxies. δ13C of the ostracod calcite is directly linked to the δ13C of the dissolved inorganic carbon (DIC) in the lake, which in this case is controlled by the isotopic composition of the DIC in the incoming water and by the internal processes of the lake. High δ13C during cold periods and low values during warm periods reflect changing vegetation cover and soil activity. These results suggest that Lake Ohrid has the potential to capture a long record of regional environment related-temperature trends during interglacial periods, particularly given the exceptional thickness of the lake sediment covering probably the entire Quaternary.