Propagation of the Azov Sea waters in the Black sea under impact of variable winds, geostrophic currents and exchange in the Kerch Strait

Abstract

Satellite and hydrological data were used to study the propagation of the Azov waters (Azov plume - AP) in the Black Sea, its relation to wind forcing, eddy dynamics, and water balance in the Azov and Black Seas. Strong north winds increase the inflow of the Azov waters in the basin and their further transport to the west along the Crimean coast. AP usually extends from the Kerch Strait to the west up to cape Chauda and Feodosiya Bay over the shallow areas less than 30 m deep. In winter-early spring, when northeast storms and the Rim Current are the most intense, they penetrate further up to cape Meganom or even to the southwestern Crimean coast. Near the capes, AP may detach from the coast and get trapped in the mesoscale anticyclones formed beyond the capes. Salinity gradients between the AP and the Black Sea waters induce the formation of frontal geostrophic currents, reaching 10 cm/s, which can constitute half of the total geostrophic velocity in this part of the basin. During the strong south winds, AP is transported both to the east and west of the Kerch Strait, or the inflow of the Azov waters is completely blocked. These storms are the reason of the highest turbidity in the vicinity of the Kerch Strait, which is related to the wave-induced coastal erosion and resuspension of bottom sediments over the shallow Kerch-Taman shelf.Altimetry and in-situ data on sea level difference in the two basins were used to study the variability of the barotropic transport near the Kerch Strait, and its dependence on the water balance in the two basins, wind direction and magnitude. The greatest difference between mean sea level in the Azov Sea and the Black Sea in winter increases the inflow of the Azov waters in cold season. Rise of the dynamic sea level over the coastal part of the Black Sea in winter caused by the intensification of cyclonic circulation partly compensates this difference and decreases the exchange. North, and northwest winds with magnitude 12–16 m/s increase the barotropic velocity in the strait by 30–40 cm/s, while south, and southwest winds with the same magnitude decrease it by 20–30 cm/s. Turbidity near the strait that is an indicator of AP has significant interannual variability. In 2003–2015 it declines over the whole Kerch-Taman shelf, which is related to the decrease of the inflow of the Azov waters into the Black Sea in this period.