Convection in the Black Sea during cold winters

We investigate the effects of initial conditions and atmospheric forcing on the penetration depth of winter convection in the strongly stratified environment of the Black Sea. The amount of Cold Intermediate Water (CIW) formed annually in the Black Sea, and the amount entrained into the euphotic zone from below, largely depend on the convective activity in the cold season. Seasonal thermohaline evolution of the mixed layer has been simulated using a one-dimensional mixed layer model driven by the ECMWF meteorological data, and initial conditions based on hydrographic data collected in the northwestern Black Sea in autumn. Simulations have been carried out for three different regions with typical hydrological conditions. The results were compared with data obtained in the spring seasons of successive years. Convection events, primarily responsible for the replenishment of the CIW, are shown to last for several days and coinciding with severe storms. The model results suggest that inhomogeneities in the CIW density and thickness could be a consequence of initial stratification in different parts of the Black Sea. In all of our experiments, convection had limited effect in modifying thermal and density structure of the main pycnocline.