a semienclosed sea of the Pacific Ocean, situated between the Eurasian continent and the Korean Peninsula on the west and the islands of Japan and Sakhalin Island on the east and southeast. It is bounded by the USSR, the People’s Democratic Republic of Korea, South Korea, and Japan. The total length of the coastline is 7,600 km, of which 3,240 km lie within the USSR.

General information. The Sea of Japan is connected with the East China and Yellow seas in the south through the Korea Strait, with the Pacific Ocean in the east through Tsugaru Strait, and with the Sea of Okhotsk in the north and northeast through La Perouse and Nevel’skoi straits. It measures 2,255 km from north to south and has a maximum width of about 1,070 km. Its area is 1.062 million sq km, with an average depth of 1,536 m and a water volume of 1.630 million cu km (according to some data, 978,000 sq km, 1,750 m, and 1.713 million cu km, respectively). The coasts, which are weakly indented, are high and steep. The largest inlets are Petr Velikii Bay, East Korea Bay, Ishikari Bay (the island of Hokkaido), and Toyama and Wakasa bays (island of Honshu). There are no large islands in the Sea of Japan, and all the islands except Ullung lie close to the shore, including Rebun, Rishiri, Okushiri, Sado, and Oki. River discharge into the sea is insignificant; the largest river that empties into the Sea is the Turnen.

Topography and geological structure of the bottom. Four elements are distinguished on the floor of the Sea of Japan: the shelf, the continental slope, abyssal basins, and underwater banks. The abyssal basin is divided by the Yamato, Kita-Oki, and Oki banks into three depressions: the Central (maximum depth, 3,699 m), Honshu (3,063 m), and Tsushima (2,300 m) depressions. The crust beneath the abyssal basins is suboceanic crust (8–12 km thick), consisting chiefly of two layers, a sedimentary layer (1.5–2.5 km) and a “basaltic” layer. The crust beneath the banks is thinned continental-type crust (18–22 km).

The basin of the Sea of Japan was apparently formed in the Cenozoic or Late Cretaceous as a result of the drifting apart of continental blocks that had broken off from the continent or as a result of the subsidence and basification of the continental crust; another possibility is that the basin is a relict of the Pacific Ocean. At present, it is in an active stage of a geosynclinal process, accompanied by sea-floor volcanic and seismic activity. Most of the mineral resources, including petroleum, gas, and marine placers of gold and cassiterite, are located on the shelf.

Climate. The Sea of Japan has a temperate monsoonal climate. The northwestern monsoon prevails in the winter, bringing cold, dry air from Asia; wind velocity is 5–12 m/sec. In the summer, the weak, unstable winds of the southeastern monsoon predominate, bringing warm, humid air from the ocean; at the same time, the force of the wind drops to 4 m/sec. Typhoons occur between May and October and are especially frequent and powerful in the southeastern part of the sea, where one or two typhoons occur per month between July and September. The average air temperature in February ranges from – 15°C in the north to 6°C in the south; the August temperatures are 17° and 25°C, respectively. The average annual precipitation increases from 310–500 mm in the northwest to 1,500–2,000 mm in the southeast. Fog is common in the spring and summer.

Hydrology. The surface layer of water, formed by incoming Pacific Ocean waters, encompasses depths to 150–200 m, and the primary cyclonic water circulation forms within it. The warm Tsushima Current enters from the south through the Korea Strait and flows northward in the eastern part of the sea, issuing branches through the straits into the Pacific Ocean and Sea of Okhotsk. At the Tatar Strait, the Tsushima Current is deflected to the west and becomes the Maritime Province Cold Current, which flows southward in the western part of the sea. In the southern part of the sea it turns eastward, thus completing the counterclockwise circulation. In the winter, the southern current issues a weak branch into the Korea Strait. Several secondary circulations moving in the same direction form in the central part of the sea between the northern and southern flows of surface water.

The water balance of the Sea of Japan in an average year is governed primarily by the influx of water through the Korea Strait with the Tsushima Current (52,200 cu km) and the discharge of water through Tsugaru Strait (34,610 cu km) and La Perouse Strait (10,380 cu km). Precipitation, continental runoff, and evaporation are of secondary importance in the water balance.

The surface water temperature in the winter ranges from – 1.3° to 0°C in the north and northwest to H°–12°C in the south and southeast. In the summer the temperature ranges from 17°C in the north to 26°C in the south. The eastern part of the sea is 2°–3°C warmer than the western part.

Salinity is 34.1–34.8% in the east and 33.7–33.9%c in the west, dropping to 27.5%c in certain parts in the north. The water density in the winter is 1.0270 g/cm³ in the north and 1.0255 g/cm³ in the south; in the summer the corresponding figures are 1.0253 and 1.0215 g/cm³.

Ice appears in the northern part of the sea and in the closed inlets and bays in the west in November and lasts until March or April; in the bays of the north it lasts until May. Floating ice reaches its maximum extent in February, when the southern boundary of the ice extends approximately from the northwestern coast of Hokkaido to the coast of the continent at 42°N lat.

Turbulence in the Sea of Japan is generally moderate. The frequency of waves with a force of 1–3 is 64 percent in the winter and no more than 79 percent in the summer; corresponding figures for waves with a force of higher than 6 are 9–11 percent and no more than 3 percent, respectively. Tides are mixed in the open part of the sea, reaching 0.5 m; tides in the Tatar Strait are primarily semidiurnal, reaching 2.3 m.

The color of the water varies from light blue to greenish blue. The transparency of the water is more than 10 m. The abyssal waters, which are formed as a result of the transformation of surface waters during the autumn and winter cooling in the northern part of the sea, gradually creep down the continental slope, filling all depths of more than 150–200 m. They are characterized by a high degree of physical homogeneity. Their temperature is 0.1°–0.2°C in the winter and 0.3°–0.5°C in the summer. Salinity is 34.01–34.15%., and the density is 1.0273–1.0274 g/cm³.

A characteristic feature of the water of the Sea of Japan is the high content of dissolved oxygen at all depths—about 95 percent in the surface waters and about 70 percent at a depth of 3,000 m.

Flora and fauna. More than 800 species of plants and more than 3,500 species of animals inhabit the Sea of Japan, including more than 900 species of crustaceans, about 1,000 fish species, and 26 species of mammals. The coastal regions are highly productive, with a biomass totaling as much as several kilograms per square meter. The most abundant bottom plants are Zostera, Phyllospadix, brown algae (laminarias, fucuses, sargassums, and others), and red algae (Ahnfeltia and others). Among the valuable animals are crustaceans (shrimps and crabs), mollusks (oysters, scallops, mussels, cuttlefish, and squid), echinoderms (trepangs), and fish (flounder, herring, saury, cod, walleye pollock, mackerel, and smelt). Because the straits connecting the sea with the ocean are comparatively shallow, the Sea of Japan does not have a true pelagic ocean fauna. Its depths are populated with secondary pelagic species of local origin.

Intensive fishing and crabbing are carried on in the Sea of Japan, as well as the gathering of trepangs, algae, and other products. Large fishing enterprises are located along the coast. The Sea of Japan is very important for transportation; it is crisscrossed by routes linking the countries bordering on it with all the ports of the world. There are important coastwise shipping routes linking the northern and northeastern parts of the USSR, Sakhalin, and the Kuril Islands. The principal ports are Vladivostok, Nakhodka, Sovetskaia Gavan’, Aleksandrovsk-Sakhalinskii, and Kholmsk (USSR), Niigata, Tsuruga, and Maizuru (Japan), and Wonsan, Hungnam, and Chongjin (the People’s Democratic Republic of Korea).

Exploration. The study of the Sea of Japan in Russia was begun in the period 1733-43 by several groups of the Great Northern, or Second Kamchatka, expedition, which determined the geographic position of the islands of Japan and Sakhalin and conducted partial surveys of their coastlines. In 1806 the sea’s eastern shore was surveyed by the expedition of I. F. Kruzenshtern and Iu. F. Lisianskii to circumnavigate the globe (1803–06). Of importance was the discovery in 1849 of a strait between the Eurasian continent and Sakhalin by G. I. Nevel’skoi, who at the same time conducted a geographic survey of the Amur Estuary and the northern part of the Tatar Strait. The permanent Hydro-graphic Expedition began its work in 1880, helping compile precise navigation charts. Along with hydrographic studies, observations of water temperature and surface currents were made, and the results were summarized in 1874 by L. I. Shrenk in The Currents of the Seas of Okhotsk and Japan and Adjacent Seas. Deep-water studies were begun by S. O. Makarov, who was the first, during the expedition on the Vitiaz’ (1886–89), to note the cyclonic character of the circulation of the surface waters. The biological study of the sea was begun at about the same time by V. K. Brazhnikov (1899–1902), P. Iu. Shmidt (1903–04), and others.

In the 1920’s the Marine Observatory, State Hydrologic Institute, and Pacific Biological Station (later the Pacific Ocean Scientific Research Institute of Fisheries and Oceanography) conducted studies of the Sea of Japan. Standard cross sections were established in the 1930’s for systematic, monthly hydrological observations. In the late 1940’s and subsequent years, standard cross sections were established for virtually the entire sea. At this time, the Pacific ocean department of the Institute of Oceanography of the Academy of Sciences of the USSR (later renamed the Pacific Oceanographic Institute) and the Far East Scientific Research Hydrometeorological Institute became involved in the study of the Sea of Japan; in the late 1960’s the Institute of Marine Biology also began studying the Sea of Japan.

Japanese scientific research institutions began studying the Sea of Japan in 1915, but systematic investigations were only organized in the mid-1920’s; major studies were conducted in the 1930’s by the expeditions on the Syunpu Mam (1928–38) and Sintoku Maru (1930–39).

Since 1947 observations have been carried out primarily on standard cross sections.