Atlantic Ocean

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Atlantic Ocean

[Lat.,=of Atlas], second largest ocean (c.31,800,000 sq mi/82,362,000 sq km; c.36,000,000 sq mi/93,240,000 sq km with marginal seas).

Physical Geography

Extent and Seas

The Atlantic Ocean extends in an S shape from the arctic to the antarctic regions between North and South America on the west and Europe and Africa on the east. It is connected with the Arctic Ocean by the Greenland Sea and Smith Sound; with the Pacific Ocean by Drake Passage, the Straits of Magellan, and the Panama Canal; and with the Indian Ocean by the Suez Canal and the expanse between Africa and Antarctica. The shortest distance across the Atlantic Ocean (c.1,600 mi/2,575 km) is between SW Senegal, W Africa, and NE Brazil, E South America. The principal arms of the Atlantic Ocean are Hudson and Baffin bays, the Gulf of Mexico, and the Caribbean Sea in the west; the Baltic, North, Mediterranean, and Black seas in the east; and the Weddell Sea in the south. More large rivers, including the Mississippi, the Congo, and the Amazon, drain into the Atlantic than into any other ocean.

Islands

The Atlantic has relatively few islands, with the greatest concentration found in the Caribbean region. Most of the islands are structurally part of the continents, such as the British Isles, Falkland Islands, Canary Islands, and Newfoundland. Iceland, the Azores, the islands of Cape Verde, Ascension, the South Sandwich Islands, the West Indies, and Bermuda are exposed tops of submarine ridges. The Bahamas are low coral islands that sit on the Blake Plateau, while the Madeiras are high volcanic islands.

Ocean Floor

The floor of the Atlantic has an average depth of c.12,000 ft (3,660 m). It is separated from that of the Arctic Ocean by a submarine ridge extending from SE Greenland to N Scotland; part of the floor (c.3,000 ft/910 m deep) is known as "telegraph plateau" because of the network of cables laid there. A shallow submarine ridge across the Strait of Gibraltar separates the Mediterranean basin from the Atlantic and limits the exchange of water between the two bodies. The Mid-Atlantic Ridge (c.300–600 mi/480–970 km wide), a submarine mountain range extending c.10,000 mi (16,100 km) from Iceland to near the Antarctic Circle, generally follows the trend of the coastlines of the continents. It rises to an average height of c.10,000 ft (3,050 m), and a few peaks emerge as islands. The ridge, which is the center of volcanic activity and earthquakes, has a great rift that is constantly widening (see seafloor spreadingseafloor spreading,
theory of lithospheric evolution that holds that the ocean floors are spreading outward from vast underwater ridges. First proposed in the early 1960s by the American geologist Harry H.
..... Click the link for more information.
) and filling with molten rock from the earth's interior. As a result the Western Hemisphere and Europe and Africa are moving away from each other. The Mid-Atlantic Ridge divides the floor of the Atlantic Ocean into eastern and western sections that are composed of a series of deep-sea basins (abyssal plains). The greatest depth (c.28,000 ft/8,530 m) is the Milwaukee Deep, in the Puerto Rico Trench, N of Puerto Rico. Scientific knowledge of the ocean floor dates from the Challenger expeditionChallenger expedition,
British oceanographic expedition under the direction of the Scottish professor Charles Wyville Thompson and the British naturalist Sir John Murray. Taking place from 1872 to 1876, it opened the era of descriptive oceanography.
..... Click the link for more information.
 (1872–76).

Currents

Because of its shape, the Atlantic may be divided into two basins—North Atlantic Ocean and South Atlantic Ocean—each with a distinct circulation system. The clockwise-moving currents of the North Atlantic (North Equatorial Current, Antilles Current, Gulf Stream, North Atlantic Drift, Canaries Current) and the counterclockwise-moving currents of the South Atlantic (South Equatorial Current, Brazil Current, West Wind Drift, Benguela Current) are separated from each other by the Equatorial Counter Current; the Guinea Current off W Africa is a link between the two systems. At the Grand Banks off Newfoundland heavy fogs form along the front where the warm Gulf Stream meets the cold Labrador Current. The surface waters in the Atlantic's trade wind belts attain the highest salinity known in ocean water.

Commerce and Shipping

The North Atlantic Ocean has some of the world's busiest shipping lanes; the northern lanes are patrolled for icebergs. Commerce between the Mediterranean Sea and the NE Atlantic Ocean was initiated by the Carthaginians. From the 7th cent. A.D., Scandinavians navigated the Atlantic; they probably reached North America c.1000. Trade routes along the coast of Africa were opened by Portugal in the 15th cent. and to the Western Hemisphere by Spain after the voyages of Columbus. The Grand Banks have traditionally contained some of the world's best commercial fishing grounds, but by the early 1990s the area had been overfished, and many species were depleted.

Bibliography

See V. H. Cassidy, The Sea around Them: The Atlantic Ocean, A.D. 1250 (1968); K. F. George, The Atlantic Ocean (1977); K. O. Emery and E. Uchupi, The Geology of the Atlantic Ocean (1984); S. Winchester, Atlantic (2010).

Atlantic Ocean

 

(the Latin name Mare Atlanticum and Greek name Atlantis designated the stretch between the Strait of Gibraltar and the Canary Islands; the entire ocean was called Oceanus Occidentalis—Western Ocean).

Islands. The main island groups originated as part of the mainland and are located off coasts (such as Great Britain, Ireland, Newfoundland, the Greater Antilles and, partially, the Lesser Antilles, the Canary Islands, Cape Verde, and the Falklands). There are few islands in the open part of the ocean; they are all of volcanic origin (the Azores, St. Helena, Tristan de Cunha, and others).

Coasts. The coastal line is strongly dissected in the northern part of the Atlantic Ocean. Almost all the internal seas and large gulfs (Biscay, Guinea, Fundy, and others) are located here. The coasts are weakly dissected in the southern part of the Atlantic Ocean; only the outlying Weddell Sea (off Antarctica) and small gulfs off the coasts of South America (La Plata, San Matías, and others) are found here. To the east, the coasts are predominantly original; alluvial coasts predominate to the west, and glacial coasts in the antarctic region.

Relief and geological structure of the floor. The characterist; element of the relief of the floor of the Atlantic Ocean is the vast meridional Mid-Atlantic Ridge, which divides the ocean into eastern and western sections.

Underwater plateaus (Bermuda, Rio Grande), ridges (Southern Antilles, Kitovyi), and elevations (Rockall and Sierra Leone) are located to the west and east of the Mid-Atlantic Ridge in the region of the ocean bed. Elevations of the floor demarcate vast basins: the Labrador, North America, Guiana, Brazil, Argentine, and other basins in the west; the West Europe, North Africa, Guinea, Angola, Cape, and Agulhas basins in the east; and the African-Antarctic Basin in the south. The depth of the basins ranges from 3,000 to 7,200–7,300 m. The maximum depths of the Atlantic Ocean are linked to deepwater trenches which border on mountain systems of island arcs—the Greater Antilles (the Puerto Rico Trench, 8,385 m) and the South Sandwich Islands (South Sandwich Trench, 8,428 m). The Greater and Lesser Antilles island arcs separate the Mexican, Yucatan (with Cayman Trench), Colombian, and Venezuelan basins from open portions of the Atlantic Ocean; the threshold of the Strait of Gibraltar separates the Mediterranean Sea. The basin floors are composed of hilly or virtually flat abyssal plains; only here and there are they complicated by underwater mountains. Occasionally, mountain peaks project above the water in the form of volcanic islands (Bermuda, Azores, Canary, Cape Verde, Fernando de Noronha, Martin Vaz, St. Helena, Tristan de Cunha, Gough, and other islands). The largest seamounts include Altair, Anti-Altair, Milne, Kelvin, San Pablo, Rehoboth, Ronkevei, Yakutat, Atlantis, Plateau, Cruizer, Great Meteor, Josephine, Amper, Davis, Columbia, Discovery, Schmitt-Ott Bank, Meteor, and Alfred Mers.

The underwater outskirts of the continents surrounding the basin of the Atlantic Ocean are characterized by gently inclined plains of continental embankments and steep continental slopes. The latter are cut by underwater canyons, which are situated, for the most part, along extensions of river valleys of the land mass. The width of continental embankments ranges from several dozen kilometers (off the coasts of Argentina and North America) to several hundred (the North, Baltic, and other seas). The depth of the external region of the continental shelves ranges from 100 to 500 m.

The bottom deposits of the Atlantic Ocean, which attain maximum thicknesses of 800–1,000 m at the bottoms of basins, can be divided into several types according to their origin. Terrigenous sediments (gravelly-pebbly, sandy, and oozy material) are distributed primarily on the underwater outskirts of the continents. Biogenous sediments are represented by calcareous (more than 30 percent CaCO3) and siliceous (more than 10 percent amorphous SiO2) deposits. Calcareous deposits (65 percent of the area of the bottom) cover the slopes of the Mid-Atlantic Ridge, sizable extents of the floor of basins, and slopes of submarine elevations within the basins. Siliceous deposits (about 10 percent of the area of the bottom) are prevalent only in the southern part of the ocean, near Antarctica. Polygenous deposits (about 26 percent of the area of the bottom) are of mixed origin; they are represented by red deepwater clays which cover the deepest parts of the basins. Volcanogenic deposits—deposits with admixtures of volcanic ashes—are prevalent in regions of volcanic islands.

The so-called rift deposits are related to rift ravines of the axial zone of the Mid-Atlantic Ridge; they represent the products of the disintegration of plutonic rocks. Chemogenic deposits are developed in the form of glauconites and phosphate nodules in the region of the underwater outskirts of continents and in the form of ferrous manganese nodules on the floor of deep basins. In the northern and southern parts of the Atlantic Ocean, the dispersion of coarsely fragmented material by floating ice and icebergs has an important influence on the composition of bottom deposits. Deposits of suspended currents play an important role among the sediments of deep basins.

Outcrops of indigenous rocks are encountered on continental slopes in the form of sedimentary and metamorphic formations of different ages up to the Cretaceous. Tholeiitic and alkali basalts are found on volcanic mountains and islands; on the summits of chains of the Mid-Atlantic Ridge are basalts and plutonic rocks of basic composition (gabbro) and ultrabasic composition (dunites, peridotites). Serpentin-ites developing on peridotites are evident, as are greenstone rocks, which formed as a result of regional metamor-phism of basalts and gabbro at the bottom of the crust. Rocks of ultrabasic composition compose the island of Sao Paolo. It is conjectured that they are of plutonic (mantle) origin and that their age is on the order of 4.5 billion years (nearly the age of the earth).

Tectonic structure. Characteristic of the submarine outskirts of the continents are the continental type of crust and continental platform structures which, as a rule, are broken by the continental slopes. The extension of these continental features into the domain of the ocean has been traced only in the gulfs of Biscay and Mexico; in other places, this extension is unknown. The bottom of a basin is covered over with a crust of the oceanic type which consists of three strata: the stratum of porous deposits; the so-called second stratum, which is characterized by seismic waves of velocities around 5.0 km/sec and which may be made up of sedimentary volcanogenic or magmatic rocks; and the “basaltic” stratum, which is characterized by velocities of seismic waves on the order of 6.7 km/sec and which is probably composed of basic rocks of the gabbro-basaltic type and serpentinized ultrabasic rocks. Lower down, rocks of the upper mantle are deposited; they are characterized by velocities of seismic waves on the order of 8.3 km/sec and are represented by peridotites and dunites. The sedimentary stratum is virtually absent in the structure of the Mid-Atlantic Ridge, while the second and basaltic strata are thinned and ^occasionally faulted in the rift zone, so that ultrabasic rocks are exposed on the bottom. Here, according to seismic data, decompressed rocks of the upper mantle, characterized by velocities of waves on the order of 7.3–7.6 km/sec, are deposited.

G. B. UDINTSEV

Climate. The great longitudinal stretch of the Atlantic Ocean determines the diversity of climatic conditions on its surface. The ocean is located in all climatic belts, from the equatorial to the subarctic in the north and the antarctic in the south. The great area of the Atlantic Ocean, between approximately 40° N lat. and 40° S lat., is located in the equatorial, tropical, and subtropical climate belts. Four main centers of action of the atmosphere are developed over the Atlantic Ocean—the Icelandic and Antarctic minimums and the North Atlantic and South Atlantic maximums, divided at the equator by a zone of depressed atmospheric pressure. Interacting with the regions of pressure which develop over adjacent continents, these centers produce the dominance of strong west winds in temperate latitudes and of northeast and southeast winds (trade winds) in subtropical and tropical latitudes in the northern and southern hemispheres respectively. Winds attain their maximum strength in the temperate latitudes, especially in the southern part of the Atlantic Ocean. Storms are so frequent here that the southern temperate latitudes got the name the Roaring Forties. Strong winds are also characteristic of the Bay of Biscay. In northern tropical latitudes, tropical (so-called West Indies) hurricanes, which traverse the ocean from east to west, are characteristic from June to October-November. They achieve their maximum force over the Caribbean Sea and the Gulf of Mexico. The air temperature in winter, in February (August in the southern part of the Atlantic Ocean), varies from 25° C at the equator to 0° C at 60° N lat. and from -8° C to -10° C at 60° S lat. In the extreme northwest and the south, the temperature drops to -25° C and below. In summer, in August (in February in the southern part of the Atlantic Ocean), the temperature is 26°-28° C at the equator, 8°-12° C at 60° N lat. and 0°-2° C at 60° S lat. In the south, the temperature of the Weddell Sea is between -4° and -6° C. There is a perceptible difference between the air temperature of the eastern and western parts of the ocean throughout the area situated to the north of 40° S lat.; it is caused by the dominance of warm or cold currents. North of 30° N lat. the temperature in the west is 10° C lower than in the east, whereas between 30° N lat. and 40° S lat. the temperature in the west is 5° C higher than in the east. The average annual cloudiness in regions of low atmospheric pressure is 60–80 percent in northern temperate, high southern, and equatorial latitudes; in regions of high pressure in the sub-tropics, the figure decreases to 30–40 percent. The mean annual precipitation on the equator is more than 2,000 mm; in the temperate latitudes, it is 1,000–1,500 mm; in subtropical latitudes and in the antarctic, it decreases to 250–500 mm; in regions adjoining the desert shores of Africa, it decreases to 100 mm; and in the southern part of the ocean, it is less than 100 mm. Fogs are characteristic of regions where warm and cold waters meet (such as the Grand Banks of Newfoundland and near the mouth of the gulf of the Rio de la Plata); fog is also characteristic of southern temperate latitudes, where warm air passes over the cool surface of the ocean. Dusty hazes, borne by the northeast trade wind from the Sahara, are recorded in the region of the Cape Verde Islands.

The hydrologic conditions of the Atlantic Ocean form under the influence of climatic conditions, water exchange with adjoining oceans and the Mediterranean Sea, and peculiarities of the configuration of the surrounding land. Under the influence of atmospheric circulation, the surface currents of the Atlantic Ocean form anticyclonal cycles in subtropical and tropical latitudes and cyclonal cycles in northern temperate and high southern latitudes. A characteristic feature of the Atlantic Ocean is the powerful system of warm currents—the so-called Gulf Stream system—which develops in its northern part. The Gulf Stream and its extension, the North Atlantic current, form respectively the western and northern peripheries of the northern anticyclonal cycle. The eastern periphery of this cycle is formed by the cold Canaries Current, the southern periphery by the warm North Equatorial Current. The northern cyclonal cycle is formed by the warm North Atlantic and Irminger currents and the cold Labrador Current, which enters from Baffin Bay. In the southern part of the Atlantic Ocean, the anticyclonal cycle is formed by the warm South Equatorial and Brazil currents on the north and west respectively and the cold Southern Ocean and Benguela currents in the south and east. Cyclonic circulation develops south of 50° S lat. with its center in the Weddell Sea. In summer, anticyclonal circulations of the northern and southern parts of the Atlantic Ocean are divided, north of the equator, by the Equatorial (Inter-trade-wind) Countercurrent; in the winter, these circulations are replaced by the general western transfer of surface waters. The subsurface Lomonosov Countercurrent is a more permanent boundary at the equator.

Currents are the primary redistributors of the solar heat absorbed by the surface of the ocean. The thermal balance of the Atlantic Ocean is formed from the radiation balance, heat loss by evaporation, and turbulent heat exchange with the atmosphere. The greatest positive thermal balance, amounting to 2.5–3.3 gigajoules /(m2-yr), equivalent to 60–80 kilocalories /(cm2-yr), is recorded at the equator; it approaches 0 at 30° N lat. and S lat. As the latitude increases, the thermal balance becomes negative. Thus, the surface of the Atlantic Ocean absorbs heat primarily between latitudes 30° N and S; over the rest of its area, the ocean gives off heat to the atmosphere. The water temperature on the surface of the Atlantic Ocean in winter (February; August in the southern part of the ocean) is 27°-28° C at the equator, 6° C at 60° N lat., and -1° C at 60° S lat. In the summer (August; February in the southern part of the ocean) the temperature is 26° C at the equator, 10° C at 60° N lat., and about 0° C at 60° S lat. Under the influence of warm and cold currents, great differences in temperature are created within latitudinal zones. North of 30° N lat., the temperature in the west is about 10° C lower than in the east. Between 30° N lat. and 40° S lat., on the other hand, the temperature in the west is 5° C higher than in the east. South of 40° S lat., where a zonal current of surface water predominates, this difference disappears.

The salinity of the water depends on the water balance, which on the average forms as follows for the surface of the Atlantic Ocean: evaporation of 1,040 mm per year, precipitation of 780 mm per year, and continental drainage of 200 mm per year. The continental drainage is of importance primarily in the narrow coastal strip off estuarine sections of the ocean. In the open ocean, salinity is determined by the correlation of evaporation and precipitation. Maximum evaporation (1,640–1,660 mm per year) is in tropical and subtropical latitudes; at the equator, it decreases to 1,400 mm per year; at 60° N lat., 780 mm per year; and at 60° S lat., 320 mm per year. The greatest quantity of precipitation—about 1,770 mm per year—occurs at the equator; at 20° N lat. the quantity decreases to 640 mm per year, and at 20° S lat. to 270 mm. In the temperate latitudes, precipitation increases again up to 1,100–1,200 mm per year. Correspondingly, the maximum salinity, 37.25 parts per thousand (‰), is recorded in tropical and subtropical latitudes; at the equator, salinity decreases to 35‰, in southern temperate latitudes, to 34‰, and in the Antarctic region, to 33.6–33.8‰; in northern temperate latitudes it is 32‰ in the west and 35.5‰ in the east.

The greatest density of water is observed in the northeast and south of the ocean, where it exceeds 1,027 kg/m3; the figure decreases to 1,022.5 kg/m3 toward the equator. The oxygen content in the surface stratum of the Atlantic Ocean changes from 4 liters /m3 at the equator to 5 liters/m3 in high latitudes. The water color in subtropical and tropical latitudes is dark blue and blue; in temperate and high latitudes, green shades predominate. The greatest transparency of the water is 66 m, in the Sargasso Sea.

Tides are primarily semidiurnal. Their greatest magnitude (for the entire world ocean) of 18 m is recorded in the Bay of Fundy. In the open part of the Atlantic Ocean, the height of tides is about 1 m (the island of St. Helena, 0.8 m; Ascension Island, 0.6 m). In various regions, tides are compound and diurnal; their magnitudes range from 0.5 to 2.2 m.

In the northern part of the Atlantic Ocean, ice forms only in internal seas of temperate latitudes (the Baltic, Azov, and Black seas, the Gulf of St. Lawrence, and others); the ice forms yearly. In the open ocean, a great quantity of ice and many icebergs are carried from the Arctic Ocean (Baffin Bay and Greenland Sea). The average boundary of ice and icebergs passes approximately along 40° N lat., but in certain cases icebergs are encountered in the western part of the Atlantic Ocean at 31° N lat. In the southern part of the ocean, marine ice and icebergs form off the continent of Antarctica and in the Weddell Sea. Icebergs are most prevalent during November and December, when their boundary passes along 40° S lat. in the middle part of the ocean and 35° S lat. in the west and the east. The greatest prevalence of marine ice is observed during August and September, when it is carried by winds and currents approximately to 55° S lat. During February and March (summer in the southern hemisphere) it is encountered only in the narrow coastal zone of Antarctica and in the Weddell Sea.

Deep-sea circulation and the vertical structure of the Atlantic Ocean are formed by waters that sink as a result of their density increase occurring in zones of convergence of surface currents in antarctic latitudes, as well as by deep waters which enter from the Mediterranean Sea and Arctic Ocean. Densification occurs in zones of convergence as a result of the mixing of waters of different temperatures and salinity. The greater the temperature and salinity difference of the mixed waters and the lower their temperature, the greater the increase in the density of the water. Accordingly, waters which sink in higher latitudes occupy lower strata in the ocean. Subsurface waters sink in subtropical latitudes and occupy the layer below surface waters in the ocean (from depths of 100–150 m to 400–500 m). Their temperature is between 10° and 22° C; they have high salinity of 34.8–36.0°/oo and are characterized in different places by low oxygen content (toward the east in the southern subtropical latitudes, 1.0–1.5 liters [/] per m3). Over the remaining area of the ocean, the quantity of oxygen is 4.0–5.5 //m3; it reaches 7.0 //m3 in the south. Intermediate waters sink in subpolar zones of convergence and are located at depths of 400–500 m to 1,000 -1,500 m. Their temperature is between 3° and 7° C; their salinity has the lowest value in the vertical distribution (of 34.0–34.9*/oo), and their oxygen content is 3.0–6.2 //m3, which decreases at the continental slope of Africa to 1–2.5 //m3. Subsurface and intermediate waters complete an-ticyclonic circulations, along whose eastern peripheries the characteristics of these waters are transferred toward the equator.

In the northern part of the Atlantic Ocean, a role in the formation of deep waters is played by the deep water of the Mediterranean Sea—which determines the high salinity of the Atlantic waters—and the deep water of the Greenland Sea, the influence of which is limited, however, to the extreme northern part of the ocean. Deep waters are distributed in the stratum from 1,000–1,500 m to 3,500 m in the southern direction. Their temperature is between 2.5° and 3° C, their salinity 34.71–34.99°/oo, and their oxygen content 4.5–6.4 Urn3.The densest waters form in antarctic latitudes, where they sink to the bottom and follow in the level adjacent to the bottom in a northerly direction. They are characterized by temperatures of 1° C-2.5° C (below 0° C in high southern latitudes), salinity of 34.64–34.89°/oo and oxygen content of 4.5–5.9 //m3. Thus, in the vertical structure of the Atlantic Ocean, subsurface and deep-sea maximums and intermediate minimums of salinity and intermediate minimums of oxygen are recorded.

A. M. MUROMTSEV

Flora. The vegetable life of the Atlantic Ocean is very diverse. Bottom vegetation (phytobenthos), which occupies the coastal zone down to depths of 100 m (about 2 percent of the total area of the ocean bottom), includes brown, green, and red algae; flowering vegetation (phyllospadix, Zostera, poseidonia) also inhabits the salt water.

There are similarities between the bottom vegetation of the northern and southern parts of the Atlantic Ocean, but the leading forms are represented by different species and sometimes different genuses. Similarities are expressed more clearly among the vegetation of the western and eastern shores.

A clear geographic succession of the main forms of phytobenthos is observed with variation in latitude. In high arctic latitudes of the Atlantic Ocean, where the surface is covered with ice for much of the time, the littoral is devoid of vegetation. The bulk of phytobenthos in the sublittoral is made up of Laminaria with an admixture of red algae. In the temperate zone, along the American and European shores of the northern Atlantic, brown development of phytobenthos is characteristic. Brown algae (Fucus and Ascophyllum) predominate sharply on the littoral; in the sublittoral they are replaced by forms of Laminaria, Alaria, Desmarestia, and red algae (such as Furtselliaria, Ahnfeltia, Lithothamnion, and Rhodimenia). Zostera is prevalent on soft bottoms. Brown algae, Laminaria in particular, predominate in the temperate and cold zones of the southern hemisphere. Vegetation is virtually absent on the littoral and in the upper strata of the sublittoral in the tropical zone because of strong heating and intensive insolation.

The so-called Sargasso Sea is situated between 20° N lat. and 40° N lat. and 30° W long, and 60° W long, in the Atlantic Ocean. It is characterized by the constant presence of a mass of floating brown algae—Sargassum.

As distinct from phytobenthos, phytoplankton is developed over the entire area of the ocean in the upper 100-meter stratum; it achieves its maximum concentration, however, in the upper 40- to 50-meter layer.

Phytoplankton consists of small one-celled algae (diatoms, dinoflagellates, blue-green algae, Silicoflagellatae, coccolith-ophores). The mass of phytoplankton varies between I and 100 mg/m3, and in the high latitudes (50°-60° lat.) of the northern and southern hemispheres it reaches 10 g/m3 and above during the period of mass development (blooming).

In the cold and temperate zones of the northern and southern parts of the Atlantic Ocean, diatoms predominate, forming the bulk of phytoplankton. The mass development of phaeosystis (from brown algae) in the spring is characteristic of the coastal regions of the North Atlantic. In the tropics, different species of coccolithophores and blue-green Trichodesmium are very widespread.

The greatest quantitative development of phytoplankton in the high latitudes of the Atlantic Ocean is observed in the summer during the period of most intensive solar radiation. Two peaks are characteristic of the development of phytoplankton in the temperate region. The spring blooming has the maximum biomass. During the autumn blooming, the biomass is considerably less than in the spring. In the tropical region the development of phytoplankton proceeds year round, but the biomass is small throughout the year.

The floral world of the tropical region of the Atlantic Ocean is marked by great diversity in kind but smaller quantitative development than the floral world of the temperate and cold zones.

Fauna. Animal organisms inhabit the entire depth of the water of the Atlantic Ocean. The diversity in fauna increases in the direction of the tropics. In the cold and temperate belts, the fauna includes thousands of species; in the tropics, tens of thousands. Characteristic animals of the cold and temperate belts are whales, seals, and walruses, among mammals; and among fish, herring, cod, perch, and flounder. Among zooplankton, a sharp predominance of Copepoda crustaceans and sometimes Pteropoda mollusks is noted. Great similarity is evident among the fauna of the moderate belts of both hemispheres. Not fewer than 100 species of animals are of the bipolar variety—that is, they are characteristic of cold and temperate belts and are absent in the tropics. These include hair seals, northern fur seals, whales, sprats, sardines, anchovies, and many invertebrates, including mussels. Characteristic of the tropical belts of the Atlantic Ocean are sperm whales, sea turtles, crustaceans, sharks, flying fish, crabs, coral polyps, jellyfish, Siphonophora, and Radiolaria. The fauna of the Sargasso Sea is distinctive. This area is inhabited both by free-swimming animals (such as mackerel, flying fish, pipe fish, and crabs) and by animals which attach to seaweeds (sea anemones, Bryozoa).

The deep-sea fauna of the Atlantic Ocean is richly represented by sponges, corals, echinoderms, crustaceans, fish, and others. This fauna stands out in the independent Atlantic deep-sea region.

REFERENCES

Zenkevich, L. A. Fauna i biologicheskaia produktivnost’ moria, vol. 2. Moscow, 1947.
Kharitonov, D. G. Gidrometeorologicheskaia kharakteristika severnoi chasti Atlanticheskogo okeana. Moscow-Leningrad, 1948.
Muromtsev, A. M. “Opyt raionirovaniia Mirovogo okeana.” Tr. Gos. okeanograficheskogo in-ta, 1951, no. 10.
Heezen, B., M. Tharp, and M. Ewing. Dno Atlanticheskogo okeana, part 1. Moscow, 1962. (Translated from English.)
Demenitskaia, R. M. Kora i mantiia Zemli. Moscow, 1967.
Leont’ev, O. K. Kratkii kurs morskoi geologii. Moscow, 1963.
Fiziko-geograficheskii atlas mira. Moscow, 1964.
Schott, G. Geographic des Atlantischen Ozeans, 3rd ed. Hamburg, 1942.
The Encyclopedia of Oceanography. (Encyclopedia of the Earth Sciences, vol. 1.) New York, 1966.
The Sea, vol. 3. New York, 1963.

The history of the exploration of the Atlantic Ocean can be divided into three periods: (1) from ancient voyages to 1749, (2) 1749–1872, and (3) from 1872 to the present. The first period was characterized by the study of the distribution of ocean waters and dry land in this part of the world, the determination of the continental boundaries of the Atlantic Ocean, and the determination of its connections with the other oceans. In the course of the first known voyages of the Phoenicians (1200 B.C.), the Carthaginians (fifth century B.C), the Greeks (fourth to second centuries B.C.), and the Romans (third to first centuries B.C.), information was obtained about the Atlantic’s coastal waters adjoining the shores of Europe and North Africa. During the ninth and tenth centuries the Normans sailed toward Iceland, Greenland, and North America. During the Middle Ages, Slavic tribes completed voyages on the Baltic Sea. In the 15th century Spanish and Portuguese sailors began to make distant voyages in search of routes to India and China. The most outstanding voyages during this period were made by the Portuguese B. Dias (1487), C. Columbus (1492–1503), the Englishman J. Cabot (1497), and the Portuguese Vasco da Gama (1498). In 1520, F. Magellan, in the first circumnavigation of the world, passed through the Strait of Magellan from the Atlantic to the Pacific Ocean. European navigators also opened up the coasts of North America in the 16th and 17th centuries (J. Davis, 1576–78; H. Hudson, 1610; W. Baffin, 1616; and others). By the turn of the 18th century, much of the expanse of the Atlantic Ocean had been studied. However, its southern boundary—the continent of Antarctica—was discovered only in 1819–21 by the first Russian antarctic expedition of F. F. Bellingshausen and M. P. Lazarev.

The second period was characterized by the initiation of the study of the physical properties of the water and by deep-sea exploration. In 1749, H. Ellis carried out the first temperature measurements at different depths. These were repeated by J. Cook (1772), H. Saussure (1780), I. F. Krusenshtern (1803), and others. Krusenshtern’s observations during the first Russian circumnavigational expedition (1803–06) occupy a special place. E. Lentz, who participated in the Russian expedition on the Predpriiatie, first used the bathometer (an apparatus for taking specimens of water from different depths) and made the first observations of the specific gravity of the water in the ocean. The material collected during the second period made it possible to compile maps of the Gulf Stream (B. Franklin, 1770), the depths of the northern part of the Atlantic Ocean (M. F. Maury, 1854), and the winds and currents of the Atlantic Ocean (M. F. Maury, 1849–60), and to carry out other investigations.

In the third period, comprehensive oceanographic investigations of the Atlantic Ocean carried out with specially equipped expeditionary ships began. The English expedition on the ship Challenger (1872–76) carried out physical, chemical, and biological observations; as a result, an enormous body of material was collected and was published by J. Murray in 50 volumes. Expeditions on the ships Gazelle (1874–76), Vitiaz’ (1886–89), Valdivia (1898–99), Gauss (1901–03), and others followed. The most significant work was carried out on the ships Meteor (1925–38), Discovery II (since 1931; still active today), iht Atlantis (since 1933), and others. The unification of oceanographic exploration in the study of the Atlantic Ocean during the International Geophysical Year (1957–58) was of great importance. Soviet expeditions (the ships M. Lomonosov, Sedov, Ekvator, and others) participated actively.

Work carried out on the basis of the program of the International Geophysical Year initiated broad international contacts in the study of the ocean, which proceeded at first on the basis of the program of international geophysical cooperation and then by the program of the Intergovernmental Oceanographic Commission (since 1960). In 1963–64 the latter carried out a major expedition—on the Equilant—to explore the equatorial and tropical zones of the Atlantic Ocean; the USSR, the USA, Brazil, and other countries participated. Since then, the study of the Atlantic Ocean has been conducted primarily by international expeditions working in accordance with the programs of the Intergovernmental Oceanographic Commission and also by expeditions of individual countries—the USSR, Britain, France, the Netherlands, the USA, Brazil, Argentina, and others.

A. M. MUROMTSEV

The Atlantic’s importance on the economic and political maps of the world is determined by the fact that situated on its shores and the shores of adjoining seas (such as the Baltic, North, Mediterranean, and Caribbean) are socialist countries, the large capitalist states of Europe and North America, smaller capitalist states, and the developing countries of Europe, Latin America, and Africa. The great industrial production, the wealth of raw materials and productive resources, and the huge foreign trade operations of the countries of the Atlantic basin, together with progress in shipbuilding, aircraft construction, and communications have given the Atlantic Ocean its extraordinarily great economic importance in the world economy.

About 40 percent of the population of the world, producing over 80 percent of the world industrial output, is concentrated in the countries washed by the waters of the Atlantic Ocean and its seas. About two-thirds of the freight turnover of world navigation passes along sea routes of the Atlantic Ocean. The waters of the Atlantic and its seas account for 40 percent of the world fishing catch.

Freight traffic and navigation. In 1965 over 1 billion tons of freight were transported across the Atlantic Ocean; in contrast, 300–350 million tons a year were shipped in the years preceding World War II. Growth has been particularly notable in the transport of liquid fuel and metallurgical raw materials. Oil and oil products constitute over 50 percent of the total freight turnover, iron ore about 10 percent, grain and coal in the area of 4–5 percent, bauxites and alumina about 2 percent. General goods make up about 25 percent of all freight transported on the Atlantic Ocean. Oil is sent primarily to the USA and Western Europe from Venezuela and other countries of the Caribbean Sea and also from the countries of the Near and Middle East and North and West Africa. Because of the constricted passage of the Suez Canal (allowing tankers with complete load capacities [deadweight] of up to 60,000 tons to pass through the canal) and its closing after Israel seized various Arab regions in 1967, the transport of oil from the countries of the Near and Middle East to Western Europe around Africa in large-tonnage oil tankers has increased. Much oil is transported between the ports of the USA on the Gulf of Mexico and those on the northeastern coast. The main flow of iron ore goes from the countries of Latin America (Venezuela, Brazil) and North and West Africa to the USA and Western Europe, which also receive ore from the ports of northern Scandinavia. Coal goes from the USA to Western Europe, bauxites and alumina from the countries of the Caribbean Sea and West Africa to the USA and Canada, and grain from Canada, the USA, and Argentina to Western Europe. The transport of general goods (machines and equipment, cotton, and paper and pulp goods) is carried on between the ports of Europe and North America. The main sea route in the Atlantic Ocean (in terms of quantity of ship and freight turnover and passenger transport) passes between the ports of Western Europe and the northeastern USA. The length of passage between London and New York is five to six days for passenger liners and ten to 12 days for freight vessels. The transport of passengers across the ocean between Europe and North America reached a maximum of 1 million persons per year in 1956–57, but the number has since decreased because of the influence of competition by air transport (in 1968 about 800,000 persons traveled the ocean between Europe and North America). Other major directions in the freight traffic on the Atlantic Ocean are the route between the ports of Western Europe and the Gulf of Mexico, the Caribbean, and the Panama Canal; the route between the ports of Western Europe and those of the Atlantic coast of Latin America; the route between the ports of the Atlantic coast of the USA and Canada and those of the Gulf of Mexico, the Caribbean, and the Panama Canal; the route between the ports of the Atlantic coast of the USA and Canada and the Atlantic coast of Latin America; the route from the ports of Western Europe and the Atlantic coast of North America through the Strait of Gibraltar and the Mediterranean Sea to the Suez Canal; and the route from the ports of Western Europe and the Atlantic coast of North America to the ports of West Africa and beyond, around the Cape of Good Hope to the Indian Ocean. (The construction of large-tonnage vessels has increased the importance of this route.) After the modernization of the water route along the St. Lawrence River, the goods traffic between the ports on this river and the Great Lakes and the ports of Western Europe increased.

Most of the major ports of the world are located in the basin of the Atlantic Ocean. These include the following (with annual freight turnover in millions of tons for 1966–68 given in parentheses): in Western Europe, Rotterdam (157), Marseille (80), Antwerp (72), London (61), Liverpool (47), Genoa (51), Le Havre (43), Hamburg (38), Augusta (35), Southampton (30), Wilhelmshaven, Trieste, Dunkerque, Bremen, Venice, Göteborg (in the area of 20–25), Amsterdam and Naples (about 18), and Nantes-St. Nazaire and Copenhagen (about 12); in North America, New York (95), Houston (52), Philadelphia (50), Baltimore (45), Norfolk-Newport (42), Montreal and Boston (around 25), and New Orleans (17); in South America, Maracaibo, Rio de Janeiro, Santos, and Buenos Aires; and in Africa, Dakar, Abidjan, and Cape Town. New oil ports to receive the supertankers bringing oil from the Persian Gulf around Africa are being built in Bantry Bay (in the southwest of Ireland) and in the regions of Rotterdam, Brest, and Marseille. The largest ports of the USSR in the basin of the Atlantic Ocean are Leningrad, Riga, Odessa-Il’ichevsk, and Novorossiisk.

Air transport plays the main role in passenger communications across the Atlantic Ocean between Europe and North America. In 1968, over 5 million persons were transported by air in both directions—five-sixths of the total number of passengers transported in these directions by air and sea transport. Air freight shipment between Europe and North America amounted to 200,000 tons in 1967. For the most part, transatlantic airlines pass over the North Atlantic (over the islands of Iceland and Newfoundland) and link London, Paris, Amsterdam, and other European capitals with New York and other cities of the USA and Canada. Another air communications route between Europe and North America passes over Lisbon, the Azores, and the Bermuda Islands. Air routes from Europe to South America pass over Lisbon and Dakar and continue over the narrowest part of the Atlantic Ocean to Rio de Janeiro. Moscow is linked by nonstop air lines over the Atlantic Ocean with New York, Montreal, and Havana. The air route joining the USA and Africa passes over the Bahama Islands, Dakar, and Robertsfield (Liberia).

Telegraph communications across the Atlantic Ocean are carried out by means of a dense network of underwater cables, the total length of which is over 200,000 km; of these, 16 transatlantic cables (seven of which belong to the USA, six to Great Britain, and three to France) link Europe with America. The first underwater cable between Europe and North America was laid in 1866; in 1882 Europe and South America were joined by cable. Cables have also been laid between Western Europe and South Africa (in 1888), the USA and South America, Dakar and Rio de Janeiro, and Buenos Aires and Capetown. A 128-channel telephone cable is in operation between Great Britain and the USA. There are many radio stations located on the shores and islands of the Atlantic Ocean. The Early Bird satellites began to function in 1965 for communications between the USA and Western Europe.

A line of tropospheric dispersion, which operates within the limits of the warning and communications system of NATO, passes over the North Atlantic (the Hebrides—Faeroe Islands—Iceland-Greenland-Labrador); it interconnects land radio relay and cable lines of NATO on territories of the countries of Western Europe and North America adjoining the Atlantic Ocean.

M. N. SOKOLOV

Fishing and marine industry. In 1967, 22 million tons of products of the sea (excluding whales)—that is, 41.3 percent of the catch in the world’s seas—were caught in the basin of the Atlantic Ocean, which occupies 27 percent of the total area of the world ocean. Although the total catch in the Pacific Ocean grew to surpass that in the Atlantic Ocean during the postwar period, the average catch per sq km in the Atlantic Ocean (0.21 tons) considerably exceeds that of the Pacific (0.14 tons) and Indian (0.03 tons) oceans.

The greatest part of the catch (86 percent) consists of fish—first and foremost, varieties of the herring family (such as herring, menhaden and sardines), cod family (such as cod, haddock, hake, pollack, whiting, and navaga), perch family (bass), flounder family (flounder, halibut), and others, constituting about 70 percent of the total catch. The catch of invertebrates—especially of different mollusks (oysters, mussels, and squid) and crustaceans (lobsters, crabs)—is of considerable importance in the total (8 percent). Whales, seals, and walruses provide 5 percent of the catch and plants 1 percent.

The industry is carried on most intensively and effectively in the northeastern part of the ocean, including the Barents, Norwegian, North, and Baltic seas (catch, 10.2 million tons, primarily herring, cod, hake, and bass). Large-scale fishing of cod, herring, hake, and other fish (4 million tons) is carried on in the northwest of the ocean and on the Grand Banks of Newfoundland, and near the shores of Greenland, Labrador, and Nova Scotia. In the western part of the ocean—the Caribbean Sea, the Gulf of Mexico, and along the coast of Florida—estuarine herring (menhaden) is the primary catch (1.3 million tons); in the southeastern part of the ocean, near the southwestern shores of Africa, the catch (2.5 million tons) is dominated by the South African sardine. In recent years, there has been intensive development in fishing for hake, crucian carp, and other fish on the Patagonian shelf, which stretches along the eastern coast of South America and is the most promising region for further development of the industry. Whales are now hunted in the waters off Antarctica, where the catch is primarily of common rorquals, sei whales, and sperm whales. Seals are taken on the ice of the White, Norwegian, and Barents seas. In a number of northern parts of the Atlantic Ocean, intensive fishing has led to decreased supplies of certain catches (such as whales, flounder in the North Sea, bass in the Grand Banks, and tuna in the central part of the ocean). Several international conventions on fishing have been established and operate in the basin of the Atlantic Ocean; their aim is the rational and effective exploitation of biological resources on the basis of the application of scientifically grounded measures for the regulation of the industry.

A diverse marine industry is carried on in the Atlantic Ocean by 155 countries. The greatest catches (1967) were obtained by the USSR (2.70 million tons), Norway (2.21 million), the USA (1.40 million), Spain (1.43 million), Iceland (900,000), Great Britain (1.03 million), Denmark (1.07 million), France (820,000), and Canada (780,000).

P. A. MOISEEV

The exploitation of the mineral and energy resources of the Atlantic Ocean is in its initial stage. There is oil drilling on the continental shelves of the Gulf of Mexico; in the southern part of the Caribbean; in the Bay of Biscay and the Mediterranean; and in the North Sea, where large reserves of gas have also been located. Marine petroleum has been discovered off the coast of West Africa (Gabon, Nigeria, and Angola); industrial extraction of sulfur is conducted in the Gulf of Mexico, and of iron ore off the island of Newfoundland. On the continental shelf of South Africa, diamonds are obtained from marine alluvial deposits. Near the Florida peninsula, the continental shelf is rich in phosphate nodules; much attention is being devoted to the possibilities of exploiting ferrous manganese nodules associated with the bottoms of oceanic basins. A tidal electric power station has been built in Saint-Malo (France), and projects have been developed for tidal electric power stations in the mouths of the Ranee (France) and Severn (Great Britain) rivers and on the coast of the USA and Canada.

M. N. SOKOLOV

The first colonies arose on the American and African shores of the Atlantic Ocean after the geographical discoveries of the 15th and 16th centuries. The first colonial powers—Spain and Portugal—held the dominant positions on the Atlantic Ocean. From that time, the Atlantic became a major region of sea communications and world trade. In the era of initial accumulation of capital, caravelles with groups of conquistadors set out on the Atlantic from Europe westward to the shores of America, returning laden with silver and gold. Merchant vessels moved south around Africa to the countries of South Asia for spices. Slaves were brought on slave ships from the shores of West Africa to the plantations of the West Indies. From the end of the 16th century, the Netherlands and England disputed the primacy of a weakened Spain on the Atlantic. During the late 17th and early 18th centuries, England pressed the Netherlands, and in the 18th century their other rival on the sea, France, as well. In the 19th century, the USA entered the struggle for domination on the Atlantic Ocean; in the early 20th century it achieved a dominant position in the western Atlantic. Around this time, Great Britain and France held the strongest positions in the eastern part of the Atlantic Ocean; as a result of the colonial partition and redistribution of the world they seized vast territories on the coast of Africa. On the eve of World War I, the goods traffic on the Atlantic Ocean constituted as much as three-fourths of the world sea transport. After World War II, in the context of the ruin of the colonial system of imperialism, Great Britain, France, and the Netherlands as well, managed to retain various possessions—for the most part, islands—in the western Atlantic.

The political and strategic importance of the Atlantic Ocean grew sharply in the era of imperialism. It was an important naval theater of military actions during World Wars I and II. Its strategic value was determined, first of all, by the extraordinarily large role of sea transport of military goods (especially for Great Britain) and troops (primarily from the USA) and also by the necessity of defending the shores of the countries bordering on the Atlantic Ocean. This situation defined the activities of the German naval command: during World Wars I and II it unleashed active operations of submarines and, to some extent, cruisers against naval communications in the Atlantic Ocean. The German actions prompted extensive retaliatory measures such as the organization of convoys and antisubmarine defense, active struggle against the submarines and cruisers of the enemy, and the laying of mine fields.

The Atlantic Ocean plays an important role in the military plans of NATO. During World War II, the USA acquired or strengthened its control over approximately 70 million sq km of the Atlantic Ocean area; in this basin, it created a ramified system of naval and air force bases and then rocket and nuclear bases as well. On the basis of 99-year leases concluded in 1940 the USA controls bases on Bermuda, the Bahamas, and the Antilles; it has the Guantanamo base on Cuba; by agreement with Spain and Portugal after World War II, American military bases were established in the eastern part of the Atlantic—on the Azores and Canary Islands, the island of Fernando Po, and the coast of Rio Muni. Special bases to service atomic submarines armed with rockets have been constructed at Holy Loch in Scotland (Great Britain) and Rota (Spain). There are air bases for strategic aviation in the North Atlantic: Goose Bay on the Labrador Peninsula and Keflavik, Iceland. A system of radar stations for the distant detection of planes and rockets has been established on the coasts of Greenland, Scotland, Norway, and the islands of the North Atlantic. The central part of the Atlantic Ocean (from the rocket base on Cape Kennedy in Florida in a southeast direction toward Ascension Island) is used by the USA for testing strategic intercontinental rockets and spaceships.

M. N. SOKOLOV

Atlantic Ocean

[ət′lan·tik ′ō·shən]
(geography)
The large body of water separating the continents of North and South America from Europe and Africa and extending from the Arctic Ocean to the continent of Antarctica.

Atlantic Ocean

the world's second largest ocean, bounded in the north by the Arctic, in the south by the Antarctic, in the west by North and South America, and in the east by Europe and Africa. Greatest depth: 9220 m (30 246 ft.). Area: about 81 585 000 sq. km (31 500 000 sq. miles)