North Sea

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North Sea,

arm of the Atlantic Ocean, c.222,000 sq mi (574,980 sq km), c.600 mi (1,000 km) long and c.400 mi (640 km) wide, NW of Central Europe. It washes the shores of Great Britain, Norway, Denmark, Germany, the Netherlands, Belgium, and the northern tip of France. In the south the Strait of Dover connects it with the English Channel. The North Sea is deepest (c.2,165 ft/660 m) along the coast of Norway and contains several shallows, the largest of which is the Dogger Bank, midway between England and Denmark. The herring fisheries of the North Sea are economically important, but the cod and haddock stocks have declined significantly. In 1970 oil was discovered under the seafloor. During the 1970s the oil resources were garnered by Great Britain, West Germany (now Germany), Denmark, Norway, and the Netherlands.

North Sea

 

a marginal sea of the Atlantic Ocean.

Physical geography. The North Sea lies between the British Isles and the Orkney and Shetland islands in the west, the Scandinavian and Jutland peninsulas in the east, and the coast of Europe in the south. In the north it merges with the Norwegian Sea; in the east it is connected with the Baltic Sea through the Skagerrak, Kattegat, Øresund, Store Belt, and Langelands Belt; in the southwest it is linked with the Atlantic Ocean through the Strait of Dover and the English Channel; and in the northwest it is connected with the Atlantic by straits between the islands. The North Sea is bounded by Great Britain, France, Belgium, the Netherlands, the Federal Republic of Germany, Denmark, and Norway. It has an area of 544,000 sq km, an average depth of 96 m, and a volume of 42,000 cu km.

COAST. The North Sea has a highly diverse coastline. In contrast to the northeast (Norway) coast, broken by fjords and fringed by a large number of small islands, the southeast coast is generally even and everywhere low and sandy. In the south there is a lagoon coastline with some tidal marshes, and in the west are found many large and small bays and several estuaries, notably that of the Thames River. The eastern shore (Netherlands), subject to flooding, has been almost entirely lined with dikes. There are no islands in the open sea; along the southeastern coast stretch the Friesian Islands with Helgoland to the north.

TOPOGRAPHY AND GEOLOGICAL STRUCTURE OF THE FLOOR. The North Sea lies on the continental shelf. The surface of the sea floor, a plain dipping slightly to the north with depths ranging from 20–30 m to 150–170 m, has many small banks (the largest being Dogger Bank) composed of the products of the erosion of moraine deposits from the glacier that covered the entire sea floor during the Pleistocene. Small sand and gravel ridges created by tidal currents extend in a northeasterly direction in the southwestern part of the sea. There are also narrow troughs, the remains of ancient river valleys, with depths exceeding 200 m. Along the coast of Norway stretches a troughlike trench formed along fault lines; it has an average depth of 300–400 m, descending to 800 m in the Skagerrak.

The sea floor is composed of sedimentary layers as much as 10–12 km thick dating from Permian (possibly earlier) to Anthropogenic times (including glacial deposits). The deposits form a system of gentle rises and depressions in the platform mantle. The largest rises are the Jutland Rise and Dogger Bank, and the major depressions are the Northern, North Danish, and English basins. The rises and their slopes are complicated by archlike and domelike bends in the layers, which are associated with large deposits of petroleum and gas. (Some of the deposits, notably Ekofisk in the Norwegian part of the sea, are being worked.) The Permian beds include large salt deposits forming numerous domes and anticlines that penetrate overlying layers and extend from north to south.

The sedimentary mantle of the sea floor covers a folded basement that is not of the same age throughout: the margin of the Precambrian Eastern European Platform in the east, the boundary between the Caledonian mountains of Norway and Scotland in the northwest, and a region of Baikal folding (which extends from Central Europe to Great Britain) in the middle.

CLIMATE. The North Sea has a temperate climate that is directly influenced by the warm North Atlantic Current and the cyclonic activity of the Icelandic low. Winters are short and relatively mild, and summers are cool. Westerly and southwesterly winds prevail throughout the year, reaching their greatest force in winter. Storms occur with maximum frequency between November and March. The frequent succession of cyclones and anticyclones causes unstable weather in all seasons.

The mean February temperature ranges from 0°C in the east to 5°C in the west, and the mean August temperature ranges from 15°C in the north to 17°C in the south. In winter, when north winds blow, the temperature may drop to -23°C. The mean annual cloudiness is 60–70 percent with a winter maximum. Precipitation ranges from 600–700 mm in the south to 1,000 mm in the north. Snow storms are frequent during the winter and may be accompanied by strong squalls. Fog is typical. During the summer the frequency of fog increases from south to north, and at other times it increases from north to south.

HYDROLOGY. The hydrological conditions of the North Sea are determined by its geographic position, climate, water exchange with the Atlantic Ocean and Baltic Sea, and continental runoff. The warm saline Atlantic waters entering the North Sea in two streams, one between the Shetland Islands and the northern tip of Great Britain and the other through the Strait of Dover, are responsible for the increased salinity in adjacent parts of the North Sea. The less saline waters of the Baltic Sea enter in the northeast through the Skagerrak. Continental runoff is most important in the southeast, where the Elbe, Weser, Ems, Rhine, Meuse, Schelde, and Thames flow into the North Sea. The waters entering the sea create a general cyclonic (counterclockwise) circulation over which local cyclonic gyres are superimposed. Most of the surface water flows out of the North Sea into the Norwegian Sea between the Scandinavian Peninsula and the Shetland Islands. The velocity of the surface currents usually does not exceed 0.3 m per sec, although winds may cause significant changes in direction and velocity.

Semidiurnal tidal currents play an important part. The primary wave enters the sea from the north and reaches the southern shores six hours later; here it meets the weaker wave, which enters through the English Channel. The velocity of the tidal currents reaches 18 km per hr near the Shetland Islands. The tidal currents, which affect the entire body of water, cause intensive mixing and a vertical equalization of temperature and salinity. Wind-causing mixing, which occurs with the development of wind-driven waves, may be observed primarily in the shallow southern part of the sea.

During the winter the mean surface winter temperature is 5°-6°C, dropping to 2°C under the influence of cold continental waters in the southeast. In the summer the temperature is about 12°C in the north, 16°-17°C in the central part, and up to 18°-19°C in the southeast. In the streams of Atlantic waters in the northwest and southwest the salinity is 34.7–35.3‰, and in the central part of the sea it is 34.5–34.7‰;. In the northeast, where Baltic waters enter the sea, the salinity drops to 31.0–32.0‰, and in the southeast it is 29–31‰. In most parts of the sea the temperatures and salinity at depth differ little from those at the surface.

Tides are semidiurnal, ranging from 0.6 m to 7.6 m, depending on the region. In the south, surges may raise the water level by more than 3 m or lower it by as much as 2.1 m. Under the combined influence of the tide and strong surge winds, disastrous floods may occur, inundating large parts of the low-lying coast of the Netherlands, Belgium, Great Britain, and Denmark. During storms wind-driven waves reach heights of 8–10 m in the north and 6–7 m in the south. Ice is encountered along the coast between December and March, and in severe winters the ice sheet may last a month or more. The waters of the North Sea have been polluted by industrial wastes, petroleum waste products, and, with the development of offshore drilling, petroleum.

A. M. MUROMTSEV

PLANT AND ANIMAL LIFE. The fauna of the North Sea is typical for the boreal North Atlantic zoogeographic region. It is similar to that of the Barents Sea, but has a greater diversity owing to warm-water forms. Arctic species constitute up to 20 percent of some groups. Some 300 plant species and more than 1,500 animal species inhabit the sea. Diatomaceous algae predominate in the north, and peridiniaceous planktonic algae and green, brown, and red macrophytes occur everywhere. Among animals, crustaceans (roughly 600 species), worms, mollusks (about 300 species), coelenterates, and fish (more than 100 species) are especially numerous. Common birds include marine solans, gulls, and murres.

The North Sea is one of the world’s most productive seas. In its littoral zone are found many fucoid thickets and large colonies of mussels, barnacles, lugworms, and amphipods. At greater depths there are marine grasses of the genus Zostera and many large mollusks, including bearded mussels, sea scallops, and oysters. The benthic biomass averages 350 g per sq km. In 1912 ships brought the Chinese crab into the North Sea. It multiplied rapidly and became a pest in the south, where its burrows destroy the banks. The North Sea is a region of highly intensive fishing. The catch includes plaice, cod, haddock, coalfish, mackerel, herring, sprats, and some species of skates and sharks.

N. G. VINOGRADOVA

Economic geography. The North Sea owes its economic importance to the presence on its shores of the most advanced industrial countries of Western Europe (Great Britain, France, the Federal Republic of Germany, Belgium, the Netherlands, and the Scandinavian countries) and to the fact that it is crossed by important trade routes from the Baltic to the Atlantic and has major fish resources and deposits of petroleum and natural gas.

The countries adjacent to the North Sea have more than 200 million inhabitants and produce more than one-fifth of the capitalist world’s gross national product and about one-quarter of its industrial output. The ports on the North Sea coast, the English Channel, Skagerrak, Kattegat, and Øresund handled more than 800 million tons of cargo in 1973. Most of the foreign trade cargo and coastal shipments of the West European countries pass through the North Sea. The chief cargoes are petroleum and petroleum products, coal, iron ore, timber, metals, pulp and paper, and machinery. The largest ports are Rotterdam, which handles more cargo than any other port in the world (more than 250 million tons in 1973), and Amsterdam in the Netherlands; Antwerp in Belgium; London, Immingham, and Hull in Great Britain; Hamburg, Bremen, and Wilhelms-haven in the Federal Republic of Germany; Göteborg in Sweden; and Oslo and Bergen in Norway.

The North Sea is one of the major fishing grounds of Western Europe, providing an annual catch of 4 million tons, chiefly herring, cod, and mackerel. Most of the fishing is done on the banks off the coast of Great Britain, the Netherlands, Norway, and Denmark. Important fishing ports and fish-processing centers are Aberdeen and Yarmouth in Great Britain, Esbjerg in Denmark, and Stavanger and Haugesund in Norway. Natural gas is extracted in the British sector of the North Sea, along the Yorkshire and Scottish coast (33 billion cu m in 1974). Both petroleum and natural gas are extracted from the Ekofisk deposit in the Norwegian sector, which produced roughly 2 million tons of petroleum in 1974. Gas extraction began in the Dutch sector in 1975.

REFERENCES

Selitskaia, E. S. Osnovnye cherty gidrologicheskogo rezhima Severnogo moria. Leningrad, 1957. (Trudy Gos. okeanograficheskogo in-ta, fasc. 39.)
Gidrometeorologicheskii spravochnik Severnogo moria. Leningrad, 1964.
Neftegazonosnost’ morei i okeanov. Moscow, 1973.
Muratov, M. V. “Sredne-Evropeiskaia plita i ee sootnoshenie s Vostochno-Evropeiskoi platformoi.” Biull. Mosk. ob-va ispytatelei prirody: Otd. geol., 1975, no. 3.
Dietrich, G. “Die natürlichen Regionen von Nord-und Ostsee auf hydrographischer Grundlage.” Kieler Meeresforschungen, 1950, vol. 7, no. 2.
Korringa, P. “Biological Consequences of Marine Pollution With Special Reference to the North Sea Fisheries.” Helgoländer wissenschaftliche Meeresuntersuchungen, 1968, vol. 17, nos. 1–4.

A. M. MUROMSTEV, M. V. MURATOV, V. M. LITVIN (topography and geological structure of the floor), and M. N. SOKOLOV (economic geography)

North Sea

an arm of the Atlantic between Great Britain and the N European mainland. Area: about 569 800 sq. km (220 000 sq. miles)
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