Purpose. The study is aimed at identifying possible physical mechanisms for the variability of available potential energy density and buoyancy fluxes in the upper active layer of the Black Sea.

Methods and Results. Spatial distribution of the available potential energy density and buoyancy fluxes was studied based on analyzing the thermohaline characteristics of the Black Sea circulation in 2011 and 2016 resulted from the numerical experiments performed using the Black Sea dynamics model developed in the Marine Hydrophysical Institute. The model included the EMODNet bathymetry and the SKIRON system data on wind velocity, heat fluxes, precipitation, evaporation, and sea surface temperature. The numerical experiments provided the daily fields of current velocities, temperature and salinity based on which the density of available potential energy and the buoyancy work were calculated. It is shown that the spatial-temporal variability of the available potential energy density in the Black Sea was formed by the mechanisms different for the upper 30-m layer and for the main halocline layer. The buoyancy work was revealed to be of seasonal variability.

Conclusions. In the upper layer, the variability of the available potential energy density is related primarily to the propagation of freshened river waters, whereas in the main halocline layer (75–150 m), the field structure is conditioned by mesoscale dynamics. In the first case, the increased values of the available potential energy density are observed during a year on the northwestern shelf and on the basin periphery; in the central part of the sea, the distribution of available potential energy density is determined by the atmospheric conditions. In the layer below 75 m, the maximum values of the available potential energy density correspond to the anticyclonic eddies. In consequence of the intensive water mixing in the upper active layer during the cold period of a year, the buoyancy work is conditioned by vertical velocity. In a spring-summer period, a two-layer structure of the field is observed which governed by the sign of density anomalies. The upper layer thickness constitutes 20–30 m and corresponds to the depth of seasonal thermocline. In the main halocline, the highest absolute values of the buoyancy work are observed in the zones of intense mesoscale anticyclones.