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Kara Sea(kär`ə), Rus. Karskoye More, shallow section of the Arctic Ocean, off N Russia, between Severnaya Zemlya and Novaya Zemlya. It has an average depth of 420 ft (128 m). It receives the Ob, the Yenisei, the Pyasina, and the Taimyra rivers, and is important as a fishing ground. Its main ports are Novyy Port and Dikson, but the ice-locked sea is navigable only during August and September.
The Kara Sea is located on the continental shelf; thus, approximately 40 percent of it is less than 50 m deep and only 2 percent is more than 500 m deep. The shelf is cut in the north by two wide, deepwater troughs—St. Anne’s Trough, which lies along the eastern shore of Franz Josef Land and is up to 620 m deep, and the Voronin Trough, which lies along the western shore of Severnaia Zemlia and is up to 450 m deep. Between the troughs is the underwater Central Kara Rise (less than 50 m deep) from which Vize and Ushakov islands protrude. The Novaia Zemlia Trough (200–418 m deep) stretches along the eastern shore of Novaia Zemlia.
The water area of the Kara Sea has had transgressions numerous times and assumed its present shape as the result of the retreat of Pleistocene glaciation. Traces of this glaciation are found under a thin layer of sediments—brown, gray, and light blue silts in troughs and deepwater hollows and sandy silts on underwater heights and in shallow areas. Rocky soils are found in the northeastern part of the sea. Sand predominates on shoals and near the coast of the mainland.
The climate is a severe arctic one. The polar night lasts for three to four months of the year, and the polar day lasts two to three months. The air temperature remains below 0°C for nine to ten months in the northern part of the sea and for seven to eight months in the south. The average temperature in January is from −20° to −28°C; the minimum temperature is −46°C. The average temperature in July is from 6° to −1°C; the maximum temperature is 16°C. The number of days in July during which the temperature drops below freezing ranges from six in the south to 20 in the north. Gale winds and snowstorms are common in the winter and snow squalls and fogs in the summer. The sea is covered with ice for most of the year, with ice first forming in September in the north and in October in the south. During the winter, fast ice forms near the coast and between the islands, and beyond that there is floe ice. As summer approaches the fast ice breaks up, and the ice in the southern and northern parts of the sea forms stable masses. In years when conditions for navigation are unfavorable, ice floes cover almost the entire sea during the summer; in other years there are large ice-free expanses.
The water masses are extremely cold and stratified. Most of the water has a temperature that is below −1.5°C; only in the troughs do warm Atlantic waters enter from the Arctic Basin. At depths of 150–200 m their temperature is up to 2.5°C. In the winter the temperature of the layer of water under the ice is from —1.5° to — 1.7°C. In the summer the temperature of the surface water between the ice floes is only slightly higher; in regions that have become ice-free the temperature reaches 6°C in the southwestern part of the sea and 2°C in the northern. The upper layer of water is very fresh as a result of river inflow and summer thawing. In one year the river waters could form a freshwater layer 160 cm thick, the greatest of any sea in the world. (In the world ocean the average thickness of this layer is only 10 cm.) Salinity of the water near the mouths of the Ob’ and Enisei is 10–12 parts per thousand (‰ near Zhelanie Cape it rises to 30‰, and near Franz Josef Land it reaches 33‰. In the southwestern part of the sea the salinity of surface waters ranges from 20 to 25‰, increasing toward the southern straits to 30–31‰.
The currents move in two slow counterclockwise rotations in the southwestern and northeastern parts of the sea. Tides are primarily semidiurnal, with an average height of 0.5–0.8 m. Owing to the wind the water level in the inlets may vary by as much as 2 m.
The Kara Sea is rich in invertebrates and semi-anadromous fish (arctic cisco, muksun, nelma, arctic char, navaga, and flounder). Marine mammals inhabiting the Kara Sea include the ringed seal, walrus, bearded seal, and beluga. There are many birds on the islands (primarily guillemots, razorbills, and little auks), where they form colonies. Land animals that visit the islands are the polar bear and the polar fox.
The Kara Sea is part of the Northern Sea Route. The chief port is Dikson. Seagoing vessels also travel up the Enisei to the cities of Igarka and Dudinka. The principal items shipped are timber, building materials, furs, and foodstuffs. With the discovery of major deposits of petroleum and natural gas in the Ob’-Enisei region, the Kara Sea routes have become much more important.
REFERENCESVize, V. Iu. Moria Sovetskoi: Arktiki [3rd ed.]. Moscow-Leningrad, 1948.
Sovetskaia Arktika: Moria i ostrova Severnogo Ledovitogo okeana. Moscow, 1970.
E. G. NIKIFOROV and A. O. SHPATKHER