(also known as Lam Sea, Kamchatka Sea), a semienclosed sea in the northwestern Pacific, bounded by the east coast of Asia from Cape Lazarev to the mouth of the Penzhina River and by the Kamchatka Peninsula, the Kuril Islands, Hokkaido, and Sakhalin Island. The coasts of the USSR and Japan (Hokkaido) are washed by the Sea of Okhotsk, which is connected with the Pacific by the Kuril Strait and with the Sea of Japan by the Nevel’skoi and La Perouse straits. The Sea of Okhotsk stretches 2,445 km from north to south and attains a maximum width of 1,407 km. It has an area of 1,583,000 sq km, an average volume of 1,365,000 cu km, an average depth of 777 m, and a maximum depth of 3,372 m (Kuril Depression).

The sea’s 10,460-km coastline is only slightly indented. The largest gulfs and bays are the Shelikhov Gulf (with the Gizhiga and Penzhina bays), Sakhalin Gulf, Uda Bay, Taui Bay, and Akademiia Gulf. The Gulfs of Aniva and Terpenie are found on the southeastern coast of Sakhalin. Most of the northern, northwestern, and northeastern coast is high and rocky. At the mouths of the great rivers, along the western Kamchatka Peninsula, and along the northern parts of Sakhalin and Hokkaido the shore is low-lying. Almost all the islands—Shantar, Zav’ialov, Spafar’ev, lama, and others—lie near the coast; only the Island of lona is in the open sea. Such great rivers as the Amur, Uda, Okhota, Gizhiga, and Penzhina flow into the sea.

Relief and geology of the bottom. The Sea of Okhotsk lies in a transition zone between the continent and the ocean floor. Its basin is divided into a northern and a southern part. The northern part constitutes a continental shelf up to 1,000 m deep on which are found two underwater heights, named after the Academy of Sciences of the USSR and the Institute of Oceanology, and the depressions of Deriugin (near Sakhalin) and Tinro (near Kamchatka). The underwater heights occupy the central part of the sea. The southern part of the sea has the deep-water Kuril Depression, separated from the ocean by the ridge of the Kuril Islands. Whereas the coastal sediments are terrigenous and coarse-grained, the bottom deposits in the central part of the sea are diatomaceous silt. The earth’s crust under the sea is continental and subcontinental in the north and sub-oceanic in the south. The northern part of the sea basin was formed in anthropogenic times through the subsidence of large blocks of the earth’s crust. The more ancient Kuril Depression was formed either by the subsidence of a continental block or by the separation of part of the ocean floor.

Climate. The Sea of Okhotsk lies in the monsoon zone of the temperate latitudes. For most of the year dry cold winds from the continent chill the northern half of the sea. From October to April the air temperature is below zero, and the sea is icebound. In January and February the average monthly air temperature ranges from —14° to — 20°C in the northeast, from -20° to -24°C in the north and west, and from -5° to -7°C in the south and east. The average monthly temperatures in July and August are 10°-12°C, 11°-14°C, and 11°-18°C, respectively. The annual precipitation ranges from 300–500 mm in the north to 600–800 mm in the west; in the south and southeast it exceeds 1,000 mm. The cloud cover, less in the north than in the south, increases from west to east.

Continental drainage, precipitation, and evaporation play a negligible role in the sea’s water balance, which is chiefly determined by incoming and outgoing Pacific waters and the influx of water from the Sea of Japan through the La Pérouse Strait. Deep Pacific waters enter the sea through the Kuril Strait at depths of more than 1,000–1,300 m. During the year there is little change in this water’s temperature (about 1.8°-2.3°C) or salinity (about 34.4–34.7 parts per thousand). The sea’s surface layer, 300–500 m thick, is found everywhere but in coastal areas. It has a winter temperature of — 1.8°-2°C, a summer temperature of -1.5° to 15°C, and a salinity of 32.8–33.8 parts per thousand. Winter convection between the lower boundary of the surface water and the upper boundary of the deep water produces an intermediate layer 150–900 m thick with a temperature ranging seasonally from –1.7° to 2.2°C and a salinity of 33.2 to 34.5 parts per thousand.

Although there are numerous local deviations, the Sea of Okhotsk has a well-defined cyclonic system of currents with low velocities (2–10 cm per sec) away from the coasts. There are strong tidal currents in the narrows and straits; in the Kuril Strait and near the Shantar Islands the currents reach 3.5 m per sec. Mixed tides, mainly irregular daily ones, predominate. The strongest tide (12.9 m) occurs in the Penzhina Bay, and the weakest tide (0.8 m) is found near southeastern Sakhalin Island. In November the northern part of the sea is covered with ice; the middle and southern parts, influenced by incoming cyclones and sometimes typhoons, have severe storms lasting seven to ten days. Away from the coast, the water is transparent for 10–17 m; near the shore the transparency decreases to 6–8 m or less. There is luminescence of the water and ice.

Flora and fauna. The species inhabiting the sea give it an arctic character. Because of the warming influence of the oceanic waters, species of the temperate (boreal) belt are found primarily in the south and southeast. The phytoplankton is dominated by diatomaceous algae, and the zooplankton consists mostly of copepods, medusas, and the larvae of mollusks and worms. On the littoral there are numerous mussels, Litorina, and other mollusks, acorn barnacles, sea urchins, amphipods, and crabs. At great depths there is a rich fauna of fish and such invertebrates as glass sponges, holothurians, octocorals, and decapod crustaceans. The brown algae are the richest in species and most common group of plant organisms in the littoral zone. Red algae and, in the northwest, green algae are also abundant. The most valuable fish are of the salmon family: dog salmon, pink salmon, coho salmon, chinook salmon, and sockeye salmon. Also commercially important are herring, pollack, plaice, cod, navaga, capelin, and smelts. Marine mammals include whales, seals, sea lions, and fur seals. The Sea of Okhotsk’s salmon and Kamchatka spider and blue crabs are of great economic importance; the sea has the world’s largest supply of commercial crabs.

The sea is crossed by important routes linking Vladivostok with the northern regions of the Far East and the Kuril Islands. The largest ports are Magadan (in Nagaev Bay) and Okhotsk on the mainland, Korsakov on Sakhalin Island, and Severo-Kuril’sk on the Kuril Islands.

The Sea of Okhotsk was discovered in the second quarter of the 17th century by the Russian explorers I. Iu. Moskvitin and V. D. Poiarkov. In 1733 the Second Kamchatka Expedition was launched, whose members mapped almost the entire coast of the Sea of Okhotsk. In 1805,1. F. Kruzenshtern described the eastern coast of Sakhalin Island, and from 1849 to 1855, G. I. Ne-vel’skoi explored the sea’s southwestern coast and the mouth of the Amur River, demonstrating that a strait existed between Sakhalin Island and the continent. S. O. Makarov gave the first complete account of the sea’s hydrology in 1894. The best early 20th-century studies of the region’s fauna are those of V. K. Brazhnikov (1899–1902) and N. K. Soldatov (1907–13). Of the foreign expeditions of the late 19th and early 20th centuries, the most imporant are the voyages of the Americans Ringgold and Rogers, the US Fishing Commission’s expedition on the Albatross, and the Japanese expedition of 1915–17 led by H. Marukawa.

After the October Revolution of 1917, K. M. Deriugin and P. Iu. Shmidt conducted comprehensive studies of the sea. In 1932 the State Hydrological Institute and the Pacific Ocean Institute of Fisheries sponsored extensive research on the Gagara. After this expedition, systematic investigations were conducted for a number of years by the Pacific Ocean Research Institute of Fisheries and Oceanography. Since 1947 expeditions have been sponsored by the Institute of Oceanology of the Academy of Sciences of the USSR (on the Vitiaz’, 1949–54), by the State Oceanographie Institute, and by the Vladivostok Bureau of Hydrometeorology.