The vertical profiles of 137Cs were determined in the North Aegean, Marmara and Black Seas, to assess inventories and fluxes of the radionuclide in these basins. The inventory of 137Cs in the Western Black Sea integrated from the surface down to 400m water depth is 3.4±0.1kBqm-2, which is surprisingly close to the amount determined in 1988, decay corrected to 2007 (2.9±0.1kBqm-2). On the other hand, based on the comparison of profiles roughly 20years apart, it is estimated that about 1kBqm-2 has been transferred from above the halocline to depths below the halocline, emphasizing the effective redistribution of tracers within the same period. We estimate that about 12TBqy-1 of 137Cs presently leaves the Black Sea with the upper layer flow through the Bosphorus and only 2TBqy-1 is returned with the lower layer inflow of Mediterranean water from the Marmara Sea. Accounting for river fluxes, estimated on the order of 2TBqy-1 few years after the Chernobyl accident, and possibly decreased by now, we can thus estimate a net rate of loss of about 8-10TBqy-1.Investigating the effective redistribution in the upper water column, the supply by the inflowing Mediterranean water alone does not explain the increase of 137Cs concentration and inventory at intermediate depths in the Western Black Sea. The most important mechanism transferring 137Cs and dissolved contaminants from the surface water to the sub-pycnocline layer appears to be the turbulent entrainment of a larger quantity of Black Sea water into the inflowing plume of Mediterranean water through mixing processes on the southwestern shelf and continental slope following its exit from the Bosphorus. This process produces an extra export of some10TBqy-1 of 137Cs from the surface to the sub-pycnocline depths of the Black Sea, a quantity comparable in magnitude to the total export out from the basin. It is the entrainment flux resulting from the mixing, and the further advection and penetration of this water into the Black Sea deeper layer (200-600m) that seems to maintain the inventory with little change over time. Through these two processes the Black Sea surface layer (0-50m) loses every year about 4% of its total inventory of 137Cs. © 2013 Elsevier B.V.

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