An average long-term distribution of temperature and salinity is analyzed for different months (May-November) computed on the basis of materials accumulated at standard oceanological sections of the northern part of the Tatar Strait. The main attention is paid to the section Korsakov Cape-Cape Syurkum crossing the water area under study practically in the middle. In early spring, the cold waters with salinity of more than 33‰ are registered at the section Korsakov Cape-Cape Syurkum. The waters with smaller salinity are revealed only in late spring, in June. In the same period, the intensification of cold intermediate layer occurs, first of all, in the western part of the section. The waters in the surface layer near the Sakhalin coast are warmed more than at the continental shelf. During the summer, this difference gradually decreases and the surface layer temperature becomes even in September. On the contrary, the spatial salinity gradients increase. In the fall, under the influence of northern and northwestern winds being typical of this period, the upwelling is formed near the Sakhalin coast and the cold dense waters emerge in the narrow coastal strip. The direction of alongshore flow changes from northern to the southern one. At the section Korsakov Cape-Cape Syurkum in November, the influence of small-salinity waters associated with the Amur River runoff is significantly revealed.
The seasonal variability of oceanographic conditions in the southern part of the Sea of Okhotsk is described based on long-term mean temperature T and salinity S from observations along a standard oceanographic section Cape Aniva-Cape Dokuchaev (May-November). It is shown that the Soya Current is relatively weak in spring, with low temperature and salinity gradients along the section. The Sea of Okhotsk low-salinity water mass is observed in the upper layer. It was formed as a result of melting of a large amount of ice brought here with the East Sakhalin Current from the northwestern part of the Sea of Okhotsk. A cold intermediate layer (CIL) at depths of 50-150 m extends along the entire section. The cold intermediate layer core with a temperature at the edge of the Sakhalin shelf of about -1.3°C is retained during a period of maximum warming in August; however, in October-November the intensified flow of the East Sakhalin Current (up to 50 cm/s) results in a situation when relatively warm low-salinity waters, connected with the Amur River runoff, dissipate CIL. The results of 12 surveys conducted by the Sakhalin Research Institute for Fisheries and Oceanography in 1998-2004 show significant deviations of T and S [10] in different years from the calculated values. Generally, maximum anomalies (DT > 4°C and DS > 0.55‰) are observed in the surface layer.Their values and statistical significance decrease with depth. However, the situation is opposite in some cases. The maximum deviation from normal was observed in June 1999, when warm and salt waters were located much further seaward from the Kunashir shelf, which is most likely connected with the Soya Current meandering. Fig. 1. Bathymetric chart of the area. Circles denote the location of stations of the standard oceanographic section Cape Aniva-Cape Dokuchaev, and rhombs denote additional stations 8a and 8b.
The materials of satellite observations of the sea surface temperature in the study area (1998–2020) were also analyzed by statistical methods and by decomposition according to the EOF. The amplitude of the averaged curve of the annual variation of the ocean surface temperature (SST) as a whole for the region was estimated, which was 7° (the contribution of the semiannual component with an amplitude of 1°С is small), as well as the most significant anomalies that reached 4°С in cold August 2002 and 3°С in warm September 2012. A quasiperiodic course of the envelope of summer maximums with a period of 5–6 years was revealed. It is shown that there is negligible trend in the thermal regime in the study area. Based on the analysis of materials from 10 oceanological surveys, seasonal variations in hydrological conditions in the area of South Kuril Islands were studied. It is shown that the areas of the Kunashirsky and Yuzhno-Kurilsky Straits in the warm season are filled with warm and salty waters of the Soya Current, and in winter and spring - with freshened modified water from the Amur River runoff transported by the East Sakhalin Current. Annual salinity variations exceed 1.5 psu here.
Seasonal variations of hydrological conditions in the area adjoining the southeastern coast of Sakhalin Island are described based on the analysis of monthly mean temperature and salinity obtained over standard oceanic sections Makarov-Cape Georgii and Cape Svobodny-the sea and from nine oceanic surveys. The Poronai River runoff that promotes the formation of a warm surface layer with low salinity largely influences the water area of Terpeniya Bay in the northern part of the area studied. In spring, these waters primarily spread southward along the coast; in summer, they flow southeastward, forming a weak vortex structure at 144°E. In the fall, major changes occur below 20 m, where waters of the cold intermediate layer are replaced by warmer waters (4-6°C) of low salinity connected with the Amur River runoff. The destruction of the CIL core near the shelf edge at depths of about 100 m resulting from the fall intensification of the East Sakhalin Current is pronounced in the southern, abyssal part of the region. The coastal area is covered by waters with salinity below 32‰ connected with the Amur River runoff. The volume of low-salinity waters coming through the Cape Svobodny-the sea section into the southern part of the Sea of Okhotsk is estimated at 3000 km 3 taking into account instrumental measurements of flow rates.
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