Сhanges of the Structure Indicators and the Salinity Field Average Value in the Sea of Azov

Abstract

Purpose. The work is aimed at continuing the started in the previous papers investigations of structure of the Azov Sea salinity field based on the oceanographic survey data collected since 2000. Interest in studying this parameter is conditioned by its anomalous increase after 2006. Methods and Results. The data of 49 seasonal oceanographic surveys carried out in the Sea of Azov by the Azov-Black Sea Branch of "VNIRO" ("AzNIIRKH") from 2001 to 2016 permitted to calculate the following: the radii in the concentration region of the field spatial correlation function in the meridional and zonal directions for the surface and bottom layers (the characteristic of the field homogeneity); the ratio between these radii; the sea-average values of salinity field for the surface and bottom layers. The time graphical and the paired correlation analyses of the calculated indicators’ series were done. The average values of the meridional and zonal radii of the concentration region of the spatial correlation function (42.5 and 47.1 km) testify presence of two relatively isolated zones in the sea related to the water circulation. These zones are formed under the conditions of the eastern winds dominating in the region. The average values of the above-mentioned radii the near-bottom sea layer were approximately equal, whereas in the surface layer, the average zonal radii exceeded the meridional ones. In spring and summer, the meridional radius in the bottom layer surpassed the zonal one. Long-term variability shows that in the surface layer, the meridional radius values tend to increase, and in the bottom layer, the zonal radius ones – to decrease. These trends demonstrate a change in the nature of water exchange in the sea, namely from predominance of the zonal transport to that of the meridional one. Conclusions. Since 2006, the changes in the structure of the Azov Sea water salinity field (trends towards decrease of the zonal radii and increase of the meridional ones in the concentration region of the field spatial correlation function) resulted from decrease in the river water inflow and increase of water exchange with the Kerch Strait, and were accompanied by growth of average salinity. Water exchange with the Kerch Strait in the bottom layer was the most active in spring and summer. The anticipatory shift of the field structural characteristics by 1 and 2 years relative to its average values makes it possible to forecast them with a two-year advance time.