Highstands of the Black Sea during the last glacial: Timing, duration, and implications for inter-basin connectivity

Abstract

The timing and nature of the Black Sea's connections to the global ocean and the Caspian Sea during the late Pleistocene remain poorly constrained, limiting our understanding of Eurasian hydroclimate dynamics. This study presents a multi-proxy investigation of a three-step coastal terrace staircase on the Sinop Peninsula (southern Black Sea) to reconstruct the history of Black Sea highstands during the last glacial period. By integrating detailed geomorphological mapping, optically stimulated luminescence (OSL; n = 9), U-Th (n = 2), and radiocarbon (n = 1) dating with analyses of mollusc assemblages and strontium isotopes, we identify and chronologically constrain three major depositional phases related to highstands at 45–35 ka (T1; n = 4), 85–69 ka (T2; n = 6), and 105–95 ka (T3; n = 2). The base of T1 terrace contains marine fauna indicative of Mediterranean inflow and salinities of ∼28-35‰. In contrast, the top of T2 terrace hosts a unique assemblage of Caspian endemic molluscs, providing the first direct coastal faunal evidence for a Caspian incursion into the Black Sea at ∼69 ka. The age of the T3 terrace represents a highstand likely associated with Mediterranean connectivity during MIS 5c. Modeled uplift rates (0.6–0.8 mm yr−1) indicate that these highstands reached elevations close to the present sea level, diverging from global eustatic reconstructions for equivalent periods. Our results refine the late Pleistocene Black Sea sea-level curve and reveal that its evolution was marked by episodic, high-amplitude fluctuations driven by alternating connections with the Mediterranean and Caspian seas, likely modulated by meltwater routing from the retreating Eurasian Ice Sheet during interstadials.