An international team of researchers led by the University of Barcelona, in collaboration with the University of the Aegean and the Hellenic Centre for Marine Research, has uncovered evidence showing that a massive outflow of low-salinity water from the Black Sea into the Aegean Sea during the Early Holocene (approximately 11,000-6,000 years ago) played a much more important role in shaping the Eastern Mediterranean than previously thought.
The study, published in the Nature Portfolio journal Communications Earth & Environment , demonstrates that freshwater exported from the Black Sea enhanced surface-water stratification in the Aegean Sea, suppressing the formation of deep waters and contributing to the development of the so-called Sapropel 1 , a widespread organic-rich sediment layer deposited across the Eastern Mediterranean during the Early Holocene.
The findings extend beyond the Eastern Mediterranean’s past. By demonstrating how large freshwater inputs can disrupt deep-water formation and reorganize marine circulation, the study offers valuable insights into the links between climate, hydrology and ocean circulation during warm periods, helping scientists better understand the potential consequences of future climate change.
The Black Sea: More important than previously thought
For decades, scientists have largely attributed the formation of Sapropel 1 to increased freshwater input from North African rivers and enhanced precipitation over the northern Mediterranean region. These processes were thought to reduce deep-water formation and promote conditions favourable for the accumulation of organic-rich sediments on the seafloor. The new findings challenge this long-standing view by identifying the Black Sea as a major and previously underestimated driver of these environmental changes.
The results reveal that the combination of intensified meltwater input and increased precipitation across the vast Black Sea drainage basin during the Early Holocene strengthened the export of low-salinity water through the Dardanelles Strait. This freshwater pulse triggered a major reorganization of water masses in the northern and central Aegean Sea, increasing stratification of the water column and reducing the formation of deep waters.
“Our findings show that the formation of Sapropel 1 cannot be explained solely by changes in North African river discharge and regional precipitation,” explains Dimitris Evangelinos, lead author of the study and member of the Marine Geosciences Research Group (Gmar) at the UB’s Faculty of Earth Sciences.
“The Black Sea acted as a powerful source of freshwater that fundamentally altered ocean circulation in the Aegean Sea and played a decisive role in the environmental transformation of the Eastern Mediterranean”, explains Evangelinos, from the UB’s Department of Earth and Ocean Dynamics.
More than 42,000 years of environmental history
To reach these conclusions, the researchers analysed a marine sediment core recovered from the central Aegean Sea, close to key deep-water formation areas in the northern Aegean. The sediment archive preserves more than 42,000 years of environmental history. The study relied on a suite of advanced analyses carried out in state-of-the-art laboratories at the UB and its Science and Technology Centres (CCiTUB). By combining multiple innovative approaches, including grain-size analysis, X-ray fluorescence scanning, radiogenic isotopes and stable isotope geochemistry, the team reconstructed past changes in ocean circulation and distinguish the influence of Black Sea outflow from other climatic and hydrological processes.
This research was supported by the MORIA project (2023-2027), and received funding from the the State Research Agency of the Ministry of Science, Innovation and Universities, the European Research Council Consolidator Grant and the NextGenerationEU programme, among other institutions.
Communications Earth & Environment
Experimental study
Not applicable
Early Holocene vigorous Black Sea outflow and the onset of sluggish Aegean deep-water convection
20-Jun-2026