Atlantic Ocean

(Map) Atlantic Ocean

ATLANTIC OCEAN (the Latin name is "Mare Atlanticum", the Greek name is "Atlantís", it designated originally the space between the Strait of Gibraltar and the Canary Islands, the entire ocean was called the "Oceanus Occidentalis" (Western Ocean); RU: Атлантический океан) is the basin of the world ocean, which is bounded at the west by the shores of America, at the east by those of Europe and Africa, at the south by the Antarctica (map).

General facts. It is the second in size basin of the world ocean, the area with the seas is 91.6 million square kilometres; the average depth is 3926 metres; the volume of water is 337 million cubic metres. It includes: the inland seas (the Baltic, North, Mediterranean, Black, Azov, Caribbean with the Gulf of Mexico), the partially isolated seas (at the North, the Baffin Bay, Labrador; near the Antarctica, the Scotia, Weddell, Lazarev, Riser-Larsen), the large bays (the Guinea, Biscay, Hudson, Saint Lawrence). The islands of the Atlantic Ocean are: Greenland (2176 thousand square kilometres), Iceland (103 thousand square kilometres), Great Britain (230 thousand square kilometres), Greater and Lesser Antilles (220 thousand square kilometres), Ireland (84 thousand square kilometres), Cape Verde (4 thousand square kilometres), Faroe (1.4 thousand square kilometres), Shetland (1.4 thousand square kilometres), Azores (2.3 thousand square kilometres), Madeira (797 square kilometres), Bermuda (53.3 square kilometres), and others (see the map).

Historical outline. Atlantic has become the subject of navigation since the 2nd millennium BC. During the 6th century BC, the Phoenician ships sailed around Africa. The ancient Greek navigator Pytheas has accomplished during the 4th century BC the voyage into the North Atlantic. During the 10th century AD, the Norman navigator Erik the Red has explored the coast of Greenland. During the Age of Discovery (15-16 centuries), the Portuguese people master the way into the Indian Ocean along the shores of Africa (Vasco da Gama, 1497-98). There have been discovered by the Genoese person H.Columbus (1492, 1493-96, 1498-1500, 1502-1504) the islands of the Caribbean sea and the South America. During these and subsequent travels, there have been for the first time determined the outlines and character of the shores, determined the coastal depths, directions and speeds of the currents, climatic characteristics of the Atlantic Ocean. The first soil samples have been obtained by the British scientist J.Ross within the Baffin Bay (1817-1818, and others). The determinations of temperature, transparency, and other measurements have been performed by the expeditions of the Russian navigators Y.F.Lisyansky and I.F.Krusenstern (1803-06), O.E.Kotzebue (1817-18). Antarctica has been discovered during the 1820 by the Russian expedition of F.F.Bellingshausen and M.P.Lazarev. The interest to the studying of the relief and soils of the Atlantic Ocean has increased during the middle of the 19th century in association with the need of the laying of the transoceanic telegraphic cables. Tens of vessels measured the depths and retrieved the samples of the soils (the American ships "Arctic", "Cyclops"; the English ships "Lighting", "Porcupine"; the German ships "Gazelle", "Valdivia", "Gauss"; the French ships "Travailleur", "Talisman"; and others).

There has played the great role for the study of the Atlantic Ocean the British expedition on the ship "Challenger" (1872-76), according to the materials of which, with the usage of other data, there have been compiled the first maps of the relief and soils of the world ocean. The most important expeditions of the 1st half of the 20th century are: the German one on the "Meteor" (1925-38), the American one on the "Atlantis" (the 30-ies), the Swedish one on the "Albatross" (1947-48). During the start of the 50-ies, the series of the countries, primarily the USSR and the USA, have unfolded the extensive researches of the relief and geological structure of the bottom of the Atlantic Ocean, with the usage of the precision echo sounders, most modern geophysical methods, automatic and controlled underwater apparatuses. The extensive works have been conducted by the modern expeditions on the ships "Mikhail Lomonosov", "Vityaz", "Zarya", "Sedov", "Ekvator", "Ob", "Akademik Kurchatov", "Akademik Vernadsky", "Dmitry Mendeleev", and others. Since the 1968, there has been started the deepwater drilling from the board of the American vessel "Glomar Challenger".

(Map) Geomorphological map of the Atlantic Ocean

Hydrological regime. There are distinguished within the upper layer of the Atlantic Ocean the 4 large-scale circulations: the Northern cyclonic one (from 45 degrees of the north latitude to the north), the anticyclonic circulation of the Northern hemisphere (from 45 degrees of the north latitude to 5 degrees of the south latitude), the anticyclonic circulation of the Southern hemisphere (from 5 degrees of the south latitude to 45 degrees of the south latitude), the Antarctic circumpolar current of the cyclonic rotation (from 45 degrees of the south latitude to Antarctica). There are situated at the western periphery of the circulations the narrow but powerful currents (2-6 kilometres per hour): Labradorian current at the North cyclonic circulation; Gulf Stream (the most powerful current of the Atlantic Ocean), Guiana current at the North anticyclonic circulation; Brazilian current at the South anticyclonic circulation. Within the central and eastern regions of the ocean, the currents are relatively weak, with the exception of the equatorial zone.

The bottom waters form themselves during the descent of the surface waters within the polar latitudes (their average temperature is 1.6 degrees Celsius). Within the certain places, they move themselves with high speeds (up to 1.6 kilometres per hour), and are able to erode (by washing) the sediments, and transfer the suspended material, thus creating the underwater valleys, and the large bottom accumulative forms of the relief. The cold and slightly saltish bottom Antarctic waters penetrate along the bottoms of the basins within the western regions of the Atlantic Ocean up to 42 degrees of the north latitude. The average temperature of the Atlantic Ocean at the surface is 16.53 degrees Celsius (South Atlantic is 6 degrees Celsius colder than the North one). The warmest waters with the average temperature of 26.7 degrees Celsius are observed at 5-10 degrees of the north latitude (the thermal equator). Nearer to Greenland and Antarctica, the temperature of the water decreases to 0 degrees Celsius. The salinity of the waters of the Atlantic Ocean is 34.0-37.3 permille, the greatest density of the water is more than 1027 kilograms per cubic metre at the north-east and south, and nearer to the equator decreases to 1022.5 kilograms per cubic metre. There prevail the semi-diurnal tides (the greatest magnitude is 18 metres within the Bay of Fundy); there are observed within the certain regions the mixed and diurnal tides with magnitude of 0.5-2.2 metres.

Ices. Within the northern part of the Atlantic Ocean, the ices form themselves only within the inland seas of the temperate latitudes (Baltic, North Sea and Azov Sea, Gulf of Saint Lawrence); the large quantity of the ices and icebergs is carried out from the North Arctic Ocean (from the Greenland and Baffin Bay seas). Within the southern part of the Atlantic Ocean, the ices and icebergs form themselves near the shores of Antarctica and within the Weddell Sea.

Relief and geological structure. There are distinguished within the limits of the Atlantic Ocean the powerful mountainous system, which is stretching from north to south, namely, the Mid-Atlantic Ridge, which is the element of the global system of the mid-oceanic ridges, and also the deep-water basins and trenches (map). The Mid-Atlantic Ridge stretches for 17 thousand kilometres with the width of up to 1000 kilometres. Its crest is dissected within many places by the longitudinal gorges, namely, by the rift valleys, and also by the transverse depressions, namely, by the transformational faults, which divide it into the separate blocks with latitudinal displacement relative to the axis of the ridge. The relief of the ridge, which is very much dissected within the axial zone, flattens itself nearer to the periphery on the account of the burying of the sediments. The epicentres of the shallow-focus earthquakes localize themselves within the axial zone, along the crest of the ridge, and at the places of the transformational faults. At the outskirts of the ridge, there are situated the deep-water basins: at the west, the Labradorian, Newfoundland, North American, Brazilian, Argentine ones; at the east, the European (including Icelandic, Iberian ones, and Irish trench), North African (including the Canary Islands, and Cape Verde ones), Sierra Leone, Guinea, Angola, and Cape ones. Within the limits of the bed of the ocean, there are distinguished the abyssal plains, zones of the hills, uplifts, and underwater mountains (map). The abyssal plains stretch as two discontinuous bands within the adjacent to the mainland parts of the deep-water basins. They are the most flat places of the Earth's surface, the primary relief of which is flattened by the sediments with the thickness of 3-3.5 kilometres. Nearer to the axis of the Mid-Atlantic Ridge, at the depth of 5.5-6 kilometres, there are situated the zones of the abyssal hills. The oceanic uplifts are located between the mainlands and mid-oceanic ridge, and divide the basins. The largest uplifts are: the Bermuda, Rio Grande, Rockall, Sierra Leone, Whale Ridge, Canaries, Madeira, Cape Verde, and others.

There are known within the Atlantic Ocean thousands of the underwater mountains; almost all of them are probably the volcanic structures. It is characteristical for the Atlantic Ocean the unconformal cutting of the geological structures of the mainlands by the coastline. The depth of the edge of the coastal shelf is 100-200 metres, within the near-polar regions is 200-350 metres, the width is from several kilometres to several hundred kilometres. The most extensive regions of the coastal shelf are near the island of Newfoundland, within the North Sea, Gulf of Mexico, and near the shores of Argentina. There are characteristical for the relief of the coastal shelf the longitudinal trenches, and the banks along the outer edge. The mainland slope of the Atlantic Ocean has the inclination of several degrees, the height of 2-4 kilometres, there are characteristical the terrace-shaped ledges and transverse canyons. There tapers within the limits of the inclined plain (the mainland rise) the "granitic" layer of the continental Earth's crust. They refer to the transitional zone with the special structure of the crust the deep-water trenches at the edges: Puerto Rico (the maximal depth is 8742 metres), the South Sandwich (8325 metres), Cayman (7090 metres), Oriente (up to 6795 metres), within the limits of which are observed both the shallow-focus and deep-focus earthquakes (map).

The thickness of the Earth's crust within the transitional zone of the Atlantic Ocean decreases from 30-40 kilometres on the mainlands to 5-7 kilometres within the ocean (it increases under the certain uplifts); the type of the Earth's crust changes from the mainland one to the oceanic one. The lower layer of the crust (the layer #3, or oceanic) is characterized by the velocities of the longitudinal seismic waves of 6.5-7.1 kilometres per second, and by the thickness of approximately 5 kilometres; it consists of the deep basic and ultrabasic rocks. Above the layer #3 lies the layer #2 ("basement"), with the velocities of the waves of 4.5-5.5 kilometres per second, and with the thickness of 1.5-1.7 kilometres; it is represented mainly by the basalts. Above lies the layer #1 (sedimentary), with the average velocity of approximately 2.5 kilometres per second, and with the average thickness of 0.7 kilometres. Within the region of the axial zone of the ridge the layer #3 has not been detected, directly under the layer #2 lies the uncompacted mantle. The heat flow through the bottom of the ocean has the increased values within the axial zone of the mid-oceanic ridge (0.1 Watts per square metre), and the lowest values (0.04 Watts per square metre) within the trenches at the edges.

(Map) Atlantic OceanThe overwhelming majority of the magmatic rocks of the oceanic bottom is represented by the tholeiitic basalts of the underwater effusions and by the pillow lavas. There are developed on the islands the alkaline varieties (basalts, trachytes, andesites). There have been found within the deep trenches and zones of the transformational faults the magmatic basic and ultrabasic rocks, there may be found the metamorphic rocks (serpentinized peridotites, and others). The sediments within the axial zone of the mid-oceanic ridge are thin, from 0 to several metres, at the distance of 100-400 kilometres from the axis are up to 200 metres, within the zone of the abyssal hills are several tens of metres, nearer to the mainlands are up to 1 kilometre, within the region of the mainland rise and slope are several kilometres. The great thicknesses of the sediments (up to several kilometres) have been detected on the certain uplifts (Whale Ridge, Bermuda, and others), and within the downfolds on the coastal shelf. The most ancient sediments of the bed of the ocean are the Middle Jurassic ones (150 million years), which have been uncovered by the drilling near the shores of the North America. Nearer to the axis of the mid-oceanic ridge, the age of the foundation of the sediments sequentially decreases till the Quaternary one. The increase of the thickness of the sediments near the mainlands is explained as both the increase of the age of their basement, and the terrigenous alluvial drift from the land. There has been uncovered within the cross section of the sediments the change of the facies with the general tendency of overlaying the biogenic carbonatic ones by the deep-water clayish ones, there are characteristical the significant stratigraphic interruptions. More than 67% of the surface of the bottom of the Atlantic Ocean is covered by the calcareous biogenic silts, which are consisting of the shells of the planktonic foraminifera and coccoliths. There are developed near the shores of Antarctica and the South-Western Africa the diatomaceous oozes (6.7%). There cover the bottoms of the deep-water basins the deep-water clayish silts (the "red clays", and similar ones) - 25.8%. There are distributed near the mainlands the terrigenous sediments.

The similarity of the contours and geological structure of the mainlands, which are surrounding the Atlantic Ocean, and also the increase of the age of the basalt bed, of the thickness and age of the sediments, with the increase of the distance from the axis of the mid-oceanic ridge, have served as the basis for the explaination of the origin of the ocean within the framework of the concept of Mobilism. It is supposed, that the North Atlantic has formed itself during the Triassic (200 million years ago), during the tearing of the North America from the North-Western Africa, and the South America has formed itself 120-105 million years ago, during the separation of Africa and the South America. The unification of the basins has occurred approximately 90 million years ago (the youngest age of the bottom, approximately 60 million years, has been identified at the north-east from the southern end of Greenland). Later, the Atlantic Ocean expanded itself with the continuous new creation of the crust on the account of the effusions and intrusions of the basalts within the axial zone of the mid-oceanic ridge, and with its partial submersion into the mantle within the trenches at the edges.

Mineral resources. Among the mineral resources of the Atlantic Ocean, there have the most important significance the oil and gas (the map for the "World Ocean" article). Near the North America, there are oil-and-gas-bearing the coastal shelves of the Labrador Sea, and the bays: Saint Lawrence, Nova Scotia, Georges Bank. The reserves of oil on the eastern coastal shelf of Canada are estimated at 2.5 billion tonnes, and of gas at 3.3 trillion cubic metres, on the eastern coastal shelf and on the mainland slope of the USA at up to 0.54 billion tonnes of oil and 0.39 trillion cubic metres of gas. There have been discovered on the southern coastal shelf of the USA more than 280 fields, near the shores of Mexico more than 20 fields (see the "Gulf of Mexico oil-and-gas-bearing basin" article). There is extracted within the Maracaibo lagoon more than 60% of the oil of Venezuela (see the "Maracaibo oil-and-gas-bearing basin" article). There are actively used the fields of the Gulf of Paria (Trinidad island). The total reserves of the coastal shelves of the Caribbean sea amount to up to 13 billion tonnes of oil and 8.5 trillion cubic metres of gas. The oil-and-gas-bearing regions have been identified on the coastal shelves of Brazil (the Todos-os-Santos Bay) and Argentina (the San Jorge Gulf). The fields of oil have been discovered within the North (114 fields) and Irish seas, the Gulf of Guinea (50 on the coastal shelf of Nigeria, 37 near Gabon, 3 near Congo, and so on).

The forecasted reserves of the oil on the coastal shelf of the Mediterranean sea are estimated at 110-120 billion tonnes. There are known the fields within the Aegean, Adriatic, Ionian seas, near the shores of Tunisia, Egypt, Spain, and others. Sulfur is extracted within the salt-dome structures of the Gulf of Mexico. With the help of the horizontal underground workings from the onshore mines, coal is extracted at the marine extensions of the continental basins, within the Great Britain (up to 10% of the national extraction) and Canada. Near the eastern coast of the island of Newfoundland, there is located the Wabana largest iron ore deposit (the total reserves are approximately 2 billion tonnes). The tin ore deposits are being developed near the shores of Great Britain (Cornwall peninsula). Heavy minerals (ilmenite, rutile, zircon, monazite) are extracted near the coast of Florida, within the Gulf of Mexico, near the shores of Brazil, Uruguay, Argentina, Scandinavian and Iberian peninsulas, Senegal, South Africa. The coastal shelf of the South-Western Africa is the region of the industrial extraction of diamonds (the reserves are 12 million carats). The gold-bearing placer deposits have been uncovered near the Nova Scotia peninsula. Phosphorites have been found on the coastal shelves of the USA, Morocco, Liberia, on the Agulhas Bank. The largest fields of the ferromanganese nodules within the Atlantic Ocean are located within the North American basin and on the Blake plateau near Florida; their extraction is yet unprofitable. The major marine ways within the Atlantic Ocean, along which are transported mineral raw materials, have mainly formed themselves during the 18-19 centuries. During the 60th, Atlantic Ocean accounted for 69% of all maritime transportation; besides the floating crafts, they are using pipelines for the transportation of oil and gas from the marine productive fields onto the shore. Atlantic Ocean is being increasingly polluted with oil products, waste waters of the industrial substances of enterprises, which are containing copper, mercury, cobalt, phosphorus, lead, poisonous chemicals, radioactive and other substances, which bring harm to the marine flora and fauna, concentrate themselves within the marine nutritional products, thus representing the great danger for the humanity, which requires the adoption of the effective measures for the prevention of the further pollution of the oceanic environment.