Late Glacial–Holocene palaeoceanography of the Sea of Marmara: timing of connections with the Mediterranean and the Black Seas

Stratigraphic analysis of Late Quaternary sediments of the Sea of Marmara Basin (SMB) indicates that it was a freshwater lake during the late glacial to ca 12,000 yr BP, depositing sediments with a Neoeuxinian fauna characteristic of the Black Sea Basin. At ca 12,000 yr BP, it was inundated by the Mediterranean waters and gradually converted into a marine realm as indicated by the presence above the Neoeuxinian sediments of a mixed layer, containing both marine and freshwater fauna. A sapropelic sediment layer was deposited between 10,600 and 6400 yr BP under suboxic bottom water conditions. This layer roughly corresponds in time to S1 sapropel unit of the eastern Mediterranean, suggesting a common origin. Its presence in the SMB, therefore, supports the hypothesis that a large influx of freshwaters from the Black Sea was an important factor in sapropel formation in the eastern Mediterranean. A second sapropelic layer formed in the SMB during 4750 to 3200 yr BP. The earliest known record of Mediterranean water in the Bosphorus is at ca 5300 yr BP, suggesting a later marine inundation than the 7150 yr BP event suggested by Ryan and co-workers. An abrupt drowning of Black Sea shelf at 7.5 kyr BP, Geo-Eco-Marina, 2, Proc. Int. Workshop on Fluvial–Marine Interactions, Mainas, Romania, 1–7 October, 1997, pp. 115–125 and Ryan, W.B.F., Pitman III, W.C., Major, C.O., Shimkus, K., Moskalenko, V., Jones, J.A., Dimitrov, P., Görür, N., Sakinç, M., Yüce, H., 1997b An abrupt drowning of Black Sea shelf, Mar. Geol. 138 (1997) 119–126). This implies that either earlier marine connections with the Black Sea were through a different waterway or the earlier marine record in the strait has been eroded. The present two-layer flow system was established at 4000 yr BP.