Ecological Systems and Devices Annotation << Back RESEARCH OF THE STRUCTURE AND MOTION OF WATER MASSES IN THE FOURTH KURIL STRAIT ON THE BASIS OF EXPEDITION DATA E.A. Tikhonchuk Hydrological characteristics in the straits of the Kuril Islands have signifi cant spatial diversity and variability. Tidal processes are decisive in the formation of the structure and dynamics of waters in the considered area. The features of the hydrophysical characteristics and the structure of the sea waters in the Fourth Kuril Strait are determined in this paper, and the nonuniformity of the temperature field and the sound velocity is revealed. The influence of tides on the water structure formation in the Fourth Kuril Strait is considered. It was noted the formation of the second minimum of the cold intermediate layer, which is characteristic of all large straits of the Kuril chain. An analysis of the vertical distribution of the sound velocity values showed the presence of the underwater sound channel. Keywords: the Fourth Kuril Strait, hydrological characteristics, Sea of Okhotsk, water masses, tides, intermediate layer, salinity, temperature, the sound velocity. DOI: 10.25791/esip.6.2023.1378 Pp. 52-58.