Purpose. The study is purposed at analyzing the available potential energy and its budget components in the Black Sea based on the results of numerical circulation modeling using a new temperature and salinity approximation scheme in the advective transport operator.

Methods and Results. Two numerical experiments were carried out based on the MHI model versions differing from each other in their approximation schemes of advective terms. The difference between the schemes is that in experiment 1, the condition of conserving temperature and salinity in the first and second degrees is satisfied, whereas in experiment 2 – temperature in the first and third degrees and salinity in the first and fifth degrees are conserved. It is found that application of the new scheme is accompanied by an increase in the available potential energy reserve by on average 30% over a year. The difference is conditioned by a decrease in both horizontal diffusion in a warm season and consumption of available potential energy through the buoyancy work in a cold season. The modeling results validated by the temperature and salinity measurement data from the MHI Oceanographic Data Bank show that application of the new approximation scheme permits to specify the density field and the energy characteristics in the Black Sea upper layer. Below the 300 m horizon, the discrepancies between the model and in-situ thermohaline fields in two experiments are minor, whereas the qualitative and quantitative distinctions in energy fields are significant: difference in the values of available potential energy in the basin central and periphery parts as well as the area of zones with the extreme buoyancy work values increase.

Conclusions. Application of the new approximation scheme of temperature and salinity in the advective transport operator makes it possible to specify the field density and, as a consequence, to obtain more accurate estimates of the available potential energy of sea circulation. In the Black Sea upper layer (the main pycnocline layer and above), the difference between the fields of energy characteristics calculated in two experiments is due to the differences in spatial distribution of density anomalies, at that the anomaly absolute values and the maximum energy values in the experiments are close in their magnitudes. Below the pycnocline layer, application of the new scheme is followed by the growth of available potential energy since the temperature and salinity changes lead to an increase in the gradients of density anomalies normal to the coast.