Early Holocene vigorous Black Sea outflow and the onset of sluggish Aegean deep-water convection.

The Eastern Mediterranean Sea underwent profound hydrographic changes from the late glacial to the Early Holocene, culminating in deep-water stagnation and the deposition of the most recent organic-rich sediment layer (sapropel S1). While this event has traditionally been attributed to riverine discharge from North Africa and enhanced precipitation over the northern Mediterranean borderlands, the role of Black Sea outflow remains overlooked. Here, we present high-resolution multi-proxy records from a central Aegean sediment core spanning the past 42,500 years. Combining grain size, X-ray fluorescence, radiogenic and stable isotope records, we show that a shift in sedimentation ~ 11,000 years ago marked the onset of silt-rich detrital input predominantly sourced from the Dardanelles-Marmara region, accompanied by surface freshening and an enhanced influx of isotopically light dissolved inorganic carbon. We propose that vigorous Black Sea outflow enhanced stratification and suppressed Aegean deep-water convection, playing a more critical role than previously recognised in sapropel S1 formation.