Hydrological variability in the Black Sea region during the last 670,000 years recorded in multi-proxy speleothem records from northern Türkiye

Changes in the hydrological balance of the Black Sea play a crucial role in the hydrological cycle and exert a strong influence on the isotopic composition of precipitation in the Black Sea region. However, the timing, duration and driving factors of hydrological shifts in the Black Sea region remain poorly constrained. Here, we present several new speleothem records from Sofular Cave in northern Türkiye to reconstruct hydroclimate fluctuations during the last 670,000 years, thereby expanding the previously published discontinuous isotope records. Stable oxygen isotopes of speleothem calcite (δ¹⁸O_ca) reflect variations in the isotopic composition of the Black Sea surface water, providing information on the timing, origin and duration of Black Sea water exchange with the Mediterranean and Caspian Seas, inflow of meltwater from the Eurasian ice sheet (EIS), and configuration of the Black Sea paleodrainage basin and EIS during the last 670,000 years. The comparison between stable water isotopes of modern precipitation and paleo-precipitation trapped inside speleothem fluid inclusions demonstrates that the modern Local Meteoric Water Line (LMWL) is representative for the isotopic composition of precipitation during glacial and interglacial climate conditions. Furthermore, speleothem fluid inclusion deuterium excess values were higher during glacial periods compared to interglacial periods, which is most likely related to atmospheric changes affecting the evaporative conditions above the moisture source.