137Cs vertical distribution at the deep basins of the North and Central Aegean Sea, Greece

•Three deep basins were studied using 137Cs as a tracer.•Deep waters constitute 137Cs repositories due to deep water formation followed Chernobyl accident.•Diffusivities, as well as particulate 137Cs settling speeds are estimated.

Large volume seawater samples were collected for the determination of 137Cs concentration along with depth in the deep basins of North and Central Aegean Sea. The vertical 137Cs distribution showed maximum concentration at the bottom of the basins, while the minimum values corresponded to the intermediate layer, where Levantine water exists. The surface 137Cs activity is found to lie between the two limits and is originated from the Black Sea waters. The typical oceanographic advection–diffusion balance model is modified to a diffusion-settling-decay balance model to better understand the vertical distribution and variation of the 137Cs concentration in the deep basins. In addition, the diffusivity of each basin, as well as the settling speed of particulate 137Cs is also estimated. The results are compared with theoretical approach as well as with previous data.