An international team led by the Centro Nacional de Investigación sobre la Evolución Humana (CENIEH) has just published a paper in the journal Quaternary Science Reviews reconstructing episodes of highstands of the Black Sea during the last glacial period, based on the analysis of coastal terraces in the eastern Sinop Peninsula (Turkey). These findings reveal alternating connections of the Black Sea with the Mediterranean and the Caspian Sea, refining the history of its highstands during the Late Pleistocene.

The study has identified three major highstand episodes of the Black Sea: the first approximately between 105 and 95 ka, the second between 85 and 69 ka, and the third between 45 and 35 ka. These episodes are recorded in a staircase of three uplifted coastal terraces near the town of Gerze, which constitute a key archive for reconstructing sea-level changes during the Late Pleistocene.

To carry out this research, the team combined high-resolution geomorphological mapping with multiple dating techniques, including Optically Stimulated Luminescence (OSL), radiocarbon, and Uranium-Thorium (U-Th). In addition, fossil mollusc assemblages and strontium isotope ratios (87Sr/86Sr) were analysed.

“These analyses allowed us to distinguish phases dominated by Mediterranean influence from others linked to Caspian inputs,” explains Altug Hasözbek, researcher in charge of the Uranium-Series Laboratory, where carbonate shells were dated using the U-Th method.

The results show that the Black Sea behaved in a much more complex way than indicated by global eustatic sea-level (ESL) curves. Rather than following a uniform pattern, it experienced significant variability driven by intermittent interbasinal connectivity within the Black Sea–Mediterranean–Caspian system. In this regard, the youngest terrace records marine conditions with clear Mediterranean influence, whereas the intermediate terrace provides the first direct coastal evidence of a Caspian water incursion into the Black Sea around 69 ka. The oldest terrace is also associated with a Mediterranean connection.

At a regional scale, the timing of these highstands coincides with phases of retreat of the Eurasian Ice Sheet, suggesting that meltwater inputs played a key role in raising Black Sea levels. These results highlight the importance of hydrological thresholds such as the Bosphorus, as well as the reorganization of the Ponto-Caspian system, in controlling these fluctuations.

“This study provides a solid framework for understanding Eurasian hydroclimatic dynamics during glacial–interglacial transitions, as well as connectivity between major continental basins during glacial periods,” concludes Mehmet Korhan Erturaç, first author of the study.