Particle Deposition in the Present and Holocene Black Sea

T H E BLACK SEA represents a fascinating environment for detailed particle deposition studies. The basin is comparatively small, yet over 2,000 m deep. It is nearly completely enclosed and only connected through the shallow Bosporus to the world's oceans. The hydrography and the sediment input parameters from the surrounding rivers are comparatively well known. The seasonal changes in sedimentation are preserved in the bottom sediments in the form of laminated sequences, since the absence of oxygen in the deep water interface prohibits bioturbation. Once deposited, the sediments in the abyssal Black Sea remain in place: redistribution processes on the basin floor are comparatively insignificant. The current biogeochemical conditions of the Black Sea, however, are not stable. About 5000-7000 years ago the Black Sea was a fresh water lake. With the inflow of saline Mediterranean water through the Bosporus, the salinity gradually increased until reaching its present value of about 18 ppt in the surface waters. The constant change in salinity forced constant readjustment of the planktonic assemblages in the struggle for the adaptational edge, The salinity may not have risen linearly. Due to the delicate balance between riverine fresh water and Mediterranean saline water inflow as a function of sea level and climate variability, there may have been a significant second-order component in the salinity increase. Temporal changes in precipitation and rainfall patterns most likely left their mark in the accumulation rates of terrigenous matter in the bottom sediments (e.g., Hay, 1988), The laminated sediments in the abyssal Black Sea were discovered during one of the first scientific cruises in the Black Sea about 100 years ago (Andrusov, 1890). The high concentration of the coccolithophorid species Emiliania huxleyi in the white laminae was not recognized, however, until the first international landmark cruise with the R/V Atlantis / / in 1969 (e.g. Degens and Ross, 1974). The uppermost sediment sequences were then grouped into sediment units I (coccolith ooze) and II (sapropel) (Ross and Degens, 1974). The R]V Atlantis H cruise was succeeded by a shorter R/V Chain cruise in 1975, when a number of undisturbed laminated cores