Comparative analysis of two simulations of the Black Sea hydrophysical fields' long-term variability in 1993-2012 is performed. Two reanalyses are done using various methods of parametrizing the vertical turbulent exchange in the circulation model. The first variant implies a simple parameterization including the constant coefficient of vertical turbulent viscosity and the coefficient of vertical turbulent diffusion in a form of climatic profiles. The second simulation includes the turbulence model of the Mellor-Yamada type to parametrize the vertical exchange processes. Having been compared, the reanalysis results and the measurement data show that application of the turbulent model for parametrizing the vertical exchange yields a better description of the Black Sea water thermohaline structure. In particular, structure of the summer seasonal thermocline and location of the main halocline (in both of them maximum deviations of the model temperature and salinity from the in-situ measurement data are observed) are reproduced more accurately. Different methods of parametrizing the momentum vertical exchange influence the horizontal circulation vertical structure.The first variant of simulation shows that a significant part of the currents' kinetic energy is concentrated in the thin 10-m layer, and this fact affects the circulation features of shallow water on the northwestern shelf; whereas the simulation based on the turbulent model implies more intensive transfer of the kinetic energy to the lower layers. The carried out investigation shows that the results of the hydrophysical fields' reanalysis depend on accurate description of the thermodynamic processes in the sea upper layer and the vertical turbulent exchange ones, in particular.Acknowledgements: the investigation is carried out within the framework of the state task on the theme No. 0827-2018-0002 "Development of the methods of operational oceanology based on the inter-disciplinary studies of the marine environment formation and evolution processes, and mathematical modeling using the data of remote and direct measurements" (code "Operational oceanology") (numerical modeling with satellite data assimilation) under support of the RSF No.17-77-30001 "New methods and supercomputer technologies of the World Ocean and Arctic basin nowcast and forecast" (analysis of the obtained results).For citation: Sukhikh, L.I. and Dorofeyev, V.L., 2018. Influence of the vertical turbulent exchange parameterization on the results of reanalysis

Purpose. The study represents analysis of the features of the Black Sea ecosystem components transfer from the northwestern shelf to the deep-sea part and its dependence on circulation in the sea upper layer. Methods and Results. The fluxes of water mass, nutrients and bioproduction from the shelf zone to the deep part of the sea were calculated using the current fields and biogeochemical ones resulted from the reanalysis, which, in its turn, was carried out due to the Black Sea ecosystem model including assimilation of remote sensing data both in the numerical circulation model and in the biogeochemical block. Numerical modeling permitted to calculate the fluxes through three sections that bound the shelf zone (by the capes Kaliakra and Chersonesus, and along the 200 m isobath). Behavior of the RIM Current jet and, consequently, direction and magnitude of the flows through the boundaries of the northwestern shelf depend on the wind stress vorticity over the western part of the Black Sea. The type of circulation with the intense RIM Current jet pressed to the shelf edge, is characterized by the pattern of distribution of the inorganic nitrogen and phytoplankton surface concentration as a narrow strip of its high values along the Black Sea western and partially southern coasts. When the RIM Current jet is weak or moves from the shelf edge (that corresponds to the low values of the wind stress vorticity) the increased concentration values are located on the northwestern shelf. Conclusions. Direction, magnitude and character of horizontal distribution of the nutrient and bioproduction fluxes are determined mainly by circulation in the sea upper layer. The magnitude of these flows is significantly affected by difference between the nutrient and bioproduction concentrations in the shelf zone and in the deep part of the Black Sea.

Purpose. The work is aimed at studying the features of currents on the Black Sea northwestern shelf based of the reanalysis results, and at analyzing the reasons of these features. Methods and Results. To analyze the currents on the northwestern shelf, applied were the results of physical reanalysis of the Black Sea fields performed by the authors earlier, namely, the arrays of hydrodynamic fields on a regular grid with the 21-year duration (1992–2012). Surface currents on the northwestern shelf of the Black Sea are directed mainly to the southwest. Throughout the whole year (except for the summer months when the wind effect weakens), an intensive compensatory current directed to the south is formed along the western coast. The waters near the western coast are highly horizontally stratified that is caused by fresh water inflowing with the river runoffs. In winter seasons, the stratification is most pronounced, whereas in summer, the horizontal density gradient decreases. The horizontal density stratification leads to the following: starting from the depth ~ 20 m, the pressure gradient changes its sign and the along-coastal jet countercurrent directed to the north, occurs. Conclusions. The performed studies have shown that the water circulation on the Black Sea northwestern shelf is determined mainly by the following factors: the wind-induced water flows across the shelf boundary and strong horizontal water stratification near the western coast resulted from the river runoffs. As the currents on the sea surface are directed mainly to the southwest, the compensatory current directed to the south is formed near the western coast. Due to the strong horizontal stratification resulted from the river runoffs, a countercurrent directed to the north is formed in the subsurface layer near the western coast. In case the seawater flows to the shelf are extremely high, the countercurrent may be absent.