Modeling of wind upwellings on the northwest shelf of the Black Sea near local features of the bottom topography

UDC 551.465 We discuss the results of numerical experiments aimed at the investigation of the process of formation of the three-dimensional structure of the zones of upwelling on the northwest shelf of the Black Sea depending on the direction of the wind. We perform the detailed analysis of three zones (I, II, and III) with fairly well pronounced inhomogeneities of the bottom topography. Zone I is located in the north part of the shelf and, in this region, we observe a narrow depression to the southwest of the Tendrovskaya Spit. In zone II located in the near-Danube zone, we observe a height reaching the sea surface (Zmeinyi Island). Zone III is located in the east part of the shelf and corresponds to a sharp drop of depths with specific curvature of the coastal line of the Kalamitskii Bay and Gerakleiskii Peninsula. The performed analysis enables us to conclude that, in the vicinity of the local features of the bottom topography and coastal line (such as underwater heights, depressions, and capes), we observe the appearance of the zones of upwelling of waters, especially pronounced in the deep-water layers of the sea. The northwest shelf of the Black Sea attracts significant attention of researchers in various fields as a promising object of industrial and economic utilization. Hence, the problem of investigation of the circulation of water masses in this region under the action of various external factors seems to be of high importance [1–9]. The processes running on the shelf strongly differ from the processes observed in the abyssal regions of the sea. In the shallow-water coastal zone, the currents are, as a rule, quite strong and the role of bottom friction (insignificant in the open sea) becomes noticeable. The presence of the coastal line imposes restrictions on the motion of waters and leads to the formation of surges. The river discharge promotes the process of freshening of seawater near the coast, i.e., decreases its salinity and, hence, density and, in this way, affects the currents. The influence of external thermal factors on the shelf is also characterized by certain specific features. Thus, for the same heat fluxes through the sea surface, the shallow-water coastal zones suffer greater temperature variations than the abyssal regions. On the boundary of the shelf and the abyssal part of the sea, there is a drop of depths, where the bottom slope sharply increases. Large slopes of the bottom lead to a special character of circulation responsible for the formation of frontal zones and intense jet currents. In turn, the process of meandering of these currents, promotes the formation of eddies and the appearance of upwellings and downwellings. In general, the northwest shelf can be regarded as a striking example of a region (with three-dimensional structure of circulation and thermohaline fields) interacting with the abyssal part of the sea. The phenomenon of upwelling observed both near the coasts and in the open sea is one of the most typical but insufficiently studied phenomena in this region. In this region, a large part of the events of upwelling, especially near the coasts, has mainly the wind character. This means that they are caused by the wind-induced deviations of pure drift currents from the coast toward the open sea with subsequent elevation of the abyssal waters to the surface.