The application of radiotracers to a study of Black Sea circulation: Validation of numerical simulations against observed weapons testing and Chernobyl Cs-137 data

In this paper, we use the distribution of the artificial radionuclide, Cs-1 37, to investigate mixing and ventilation in the Black Sea. Timeseries data of vertical radionuclide distributions are combined with model simulations in order to follow the magnitude and depth of penetration of surface oxic water into intermediate depths, below the oxic/anoxic interface. Simulated data are produced by a three-dimensional circulation model that includes a new parameterization of the Bosphorus inflow/plume to simulate the effects of Mediterranean water on internal mixing, A radioactive tracer model for p re-Chernobyl Cs-137 (weapons testing Cs-137) and Chernobyl Cs-137 is couple d to the circulation model. The model results are compared to field data co llected between 1986 and 1992. The main output from the simulations is the identification of the contribution of entrainment in the mixing of surface waters into subsurface layers. The trend of tracer penetration into the dee per layers following isopycnal surfaces is well demonstrated in the model a nd is consistent with the known circulation and physics of the Black Sea. T he correlation between the activities of radionuclides and salinity, found in the field data, is supported by the simulations. These model results ill ustrate that the time-space abundance of the existing field data is suffici ent for reconstructing the distribution of tracers in space and time, provi ded reliable estimates of Black Sea circulation exist.