HOLOCENE BENTHIC FORAMINIFERS FROM THE MARMARA SEA: CLUES TO THE INTENSITY OF THE BLACK SEA OUTFLOW

The eutrophic Marmara Sea is an unusual exception in the extreme oligotrophic eastern Mediterranean, due to the outflow of low saline and nutrient rich Black Sea Water (BSW). It was suggested that stronger than today outflow of BSW contributed to the deposition of Sapropel S1 in the Eastern Mediterranean. Modern benthic foraminiferal assemblages from the modern Marmara Sea are restricted by permanent low-oxygen stress caused by the stable stratification of the water column; thus any change in the BSW outflow must have a significant impact on the assemblages. Our results based on high-resolution records of foraminifers and oxygen stable isotopes from the Marmara Sea suggest that the BWS outflow during S1 was absent or weak. Rich and highly diverse benthic assemblages and the lesser importance of the low oxygen indicator Chilostomella oolina indicate well-oxygenated conditions during S1. After the end of S1, the assemblages are more similar to the modern ones, with diminished diversities and stronger dominance of C. oolina, implying that the BSW outflow was established at that time. The second important outcome of our investigations are the distinct oscillations of the Bolivina dilatata assemblage with a periodicity of ~ 900 years. This assemblage requires higher oxygen contents than C. oolina. We suggest that waxing and waning of the BSW outflow during the last 7000 years allowed temporarily higher oxygenation of the seafloor and thus thriving of B. dilatata. Since recently other authors discovered cycles of similar duration in the North Atlantic, the forcing mechanism of the cycle in the Marmara Sea may be connected with the intensity of the North Atlantic Oscillation.