A comparison of modelled and measured Chernobyl 90Sr distributions in the Black Sea

Strontium-90 data are used to verify the mixing and ventilation patterns simulated in a circulation model of the Black Sea. We trace physical processes using 90Sr which was delivered after the Chernobyl accident, primarily via riverine discharges in the Northwest shelf region. The results used for the verification of our model simulations were obtained from samples collected between 1986 and 1992. A three-dimensional circulation/transport model coupled with a tracer model simulates the transport of 90Sr and its penetration into the intermediate and deep layers. Though most of the 90Sr is introduced in the model at the sea surface by river runoff in the NW shelf area, the concentration patterns suggest that a large amount of this signal penetrates the halocline in the Bosphorus area and along the southern coast. This fundamental spatial characteristic of mixing in the Black Sea is associated with the entrainment of surface and intermediate waters in the vicinity of the Bosphorus strait, and with vertical exchanges along the southern coast resulting from the anticyclonic circulation patterns. Another important fraction of the river water penetrates intermediate layers at the shelf edge in the NW Black Sea. Higher model resolution and more elaborated forcing functions would be needed in order to more accurately define mesoscale features in this basin.