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Earth's oceans
(World Ocean)

The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about 106.4 million square kilometres (41.1 million square miles), it covers approximately twenty percent of the Earth's surface and about twenty-six percent of its water surface area. The first part of its name refers to the Atlas of Greek mythology, making the Atlantic the "Sea of Atlas".

The oldest known mention of this name is contained in The Histories of Herodotus around 450 BC (I 202); see also: Atlas Mountains. Another name historically used was the ancient term Ethiopic Ocean, derived from Ethiopia, whose name was sometimes used as a synonym for all of Africa and thus for the ocean. Before Europeans discovered other oceans, the term "ocean" itself was to them synonymous with the waters beyond Western Europe that we now know as the Atlantic and which the Greeks had believed to be a gigantic river encircling the world; see Oceanus.

The Atlantic Ocean occupies an elongated, S-shaped basin extending longitudinally between the Americas to the west, and Eurasia and Africa to the east. As one component of the interconnected global ocean, it is connected in the north to the Arctic Ocean (which is sometimes considered a sea of the Atlantic), to the Pacific Ocean in the southwest, the Indian Ocean in the southeast, and the Southern Ocean in the south. (Other definitions describe the Atlantic as extending southward to Antarctica.) The equator subdivides it into the North Atlantic Ocean and South Atlantic Ocean.

The Atlantic Ocean, not including Arctic and Antarctic regions.

Contents

Geography

Photo of surf breaking on rocky shore
The Atlantic Ocean as seen from the western coast of Portugal

The Atlantic Ocean is bounded on the west by North and South America. It connects to the Arctic Ocean through the Denmark Strait, Greenland Sea, Norwegian Sea and Barents Sea. To the east, the boundaries of the ocean proper are Europe, the Strait of Gibraltar (where it connects with the Mediterranean Sea, one of its marginal seas and, in turn, the Black Sea) and Africa.

In the southeast, the Atlantic merges into the Indian Ocean. The 20° East meridian, running south from Cape Agulhas to Antarctica defines its border. Some authorities show it extending south to Antarctica, while others show it bounded at the 60° parallel by the Southern Ocean.[1]

In the southwest, the Drake Passage connects it to the Pacific Ocean. The man-made Panama Canal links the Atlantic and Pacific. Besides those mentioned, other large bodies of water adjacent to the Atlantic are the Caribbean Sea, the Gulf of Mexico, Hudson Bay, the Arctic Ocean, the Mediterranean Sea, the North Sea, the Baltic Sea, and the Celtic Sea.

Covering approximately 22% of Earth's surface, the Atlantic is second in size to the Pacific. With its adjacent seas it occupies an area of about 106,400,000 square kilometres (41,100,000 sq mi); without them, it has an area of 82,400,000 square kilometres (31,800,000 sq mi). The land that drains into the Atlantic covers four times that of either the Pacific or Indian oceans. The volume of the Atlantic with its adjacent seas is 354,700,000 cubic kilometers (85,100,000 cu mi) and without them 323,600,000 cubic kilometres (77,640,000 cu mi).

The average depth of the Atlantic, with its adjacent seas, is 3,339 metres (10,955 ft); without them it is 3,926 metres (12,881 ft). The greatest depth, 8,605 metres (28,232 ft), is in the Puerto Rico Trench. The Atlantic's width varies from 2,848 kilometres (1,770 mi) between Brazil and Sierra Leone to over 6,400 km (4,000 mi) in the south.

Extent

The 3rd edition of the International Hydrographic Organization's (IHO) Limits of Oceans and Seas defines the limits of the North Atlantic Ocean as follows:[2]

On the West. The Eastern limits of the Caribbean Sea, the Southeastern limits of the Gulf of Mexico from the North coast of Cuba to Key West, the Southwestern limit of the Bay of Fundy and the Southeastern and Northeastern limits of the Gulf of St. Lawrence.

On the North. The Southern limit of Davis Strait from the coast of Labrador to Greenland and the Southwestern limit of the Greenland Sea and Norwegian Sea from Greenland to the Shetland Islands.

On the East. The Northwestern limit of the North Sea, the Northern and Western limits of the Scottish Seas, the Southern limit of the Irish Sea, the Western limits of the Bristol and English Channels, of the Bay of Biscay and of the Mediterranean Sea.

On the South. The equator, from the coast of Brazil to the Southwestern limit of the Gulf of Guinea.

And the South Atlantic Ocean is defined as:

On the Southwest. The meridian of Cape Horn, Chile (67°16'W) from Tierra del Fuego to the Antarctic Continent; a line from Cape Virgins (52°21′S 68°21′W / 52.35°S 68.35°W / -52.35; -68.35) to Cape Espiritu Santo, Tierra del Fuego, the Eastern entrance to Magellan Strait, Chile

On the West. The limit of the Rio de La Plata.

On the North. The Southern limit of the North Atlantic Ocean.

On the Northeast. The limit of the Gulf of Guinea.

On the Southeast. From Cape Agulhas along the meridian of 20° East to the Antarctic continent.

On the South. The Antarctic Continent.

Note that these definitions exclude any marginal waterbodies that are separately defined by the IHO (such as the Bay of Biscay and Gulf of Guinea), though these are usually considered to be part of the Atlantic Ocean.

In 2000 the IHO redefined the Atlantic Ocean, moving its southern limit to 60°S, with the waters south of that line identified as the Southern Ocean. This new definition has not yet been ratified (a reservation has been lodged by Australia[3]) though it is in use by the IHO and others. If and when adopted, the 2000 definition will be published in the 4th edition of Limits of Oceans and Seas, restoring the Southern Ocean as originally outlined in the 2nd edition and subsequently omitted from the 3rd edition.

Cultural significance

Transatlantic travel played a major role in the expansion of Western civilization into the Americas. Today, it can be referred to in a humorously diminutive way as the Pond in idioms, in reference to the geographical and cultural divide between North America and Europe. Some British people refer to the USA as "across the pond".[4]

Ocean bottom

Map that uses color to show ocean depth

The principal feature of the bathymetry (bottom topography) is a submarine mountain range called the Mid-Atlantic Ridge[5]. It extends from Iceland in the north to approximately 58° South latitude, reaching a maximum width of about 1,600 kilometres (990 mi). A great rift valley also extends along the ridge over most of its length. The depth of water at the apex of the ridge is less than 2,700 metres (8,900 ft) in most places, the bottom of the ridge is three times as deep and of course several peaks rise above the water and form islands.[6] The South Atlantic Ocean has an additional submarine ridge, the Walvis Ridge[7].

The Mid-Atlantic Ridge separates the Atlantic Ocean into two large troughs with depths from 3,700–5,500 metres (12,100–18,000 ft). Transverse ridges running between the continents and the Mid-Atlantic Ridge divide the ocean floor into numerous basins. Some of the larger basins are the Blake, Guiana, North American, Cape Verde, and Canaries basins in the North Atlantic. The largest South Atlantic basins are the Angola, Cape, Argentina, and Brazil basins.

The deep ocean floor is thought to be fairly flat with occasional deeps, trenches, seamounts and some guyots. Various shelves along the margins of the continents constitute about 11% of the bottom topography with few deep channels cut across the continental rise.

Ocean floor trenches and seamounts:

Ocean sediments are composed of:

  • Terrigenous deposits with land origins, consisting of sand, mud, and rock particles formed by erosion, weathering, and volcanic activity on land washed to sea. These materials are found mostly on the continental shelves and are thickest near large river mouths or off desert coasts.
  • Pelagic deposits, which contain the remains of organisms that sink to the ocean floor, include red clays and Globigerina, pteropod, and siliceous oozes. Covering most of the ocean floor and ranging in thickness from 60–3,300 metres (200–10,830 ft) they are thickest in the convergence belts, notably at the Hamilton Ridge and in upwelling zones.
  • Authigenic deposits consist of such materials as manganese nodules. They occur where sedimentation proceeds slowly or where currents sort the deposits, such as in the Hewett Curve.

Water characteristics

Map displaying a looping line with arrows indicating that water flows eastward in the far Southern ocean, angling north east of Australia, turning sough after passing Alaska, then crossing the mid-Pacific to flow north of Australia, continuing west below Africa, then turning northwest until reaching eastern Canada, then angling east to southern Europe, then finally turning south just below Greenland and flowing down the Americas' eastern coast, and resuming its flow eastward to complete the circle
Path of the thermohaline circulation. Purple paths represent deep-water currents, while blue paths represent surface currents.
Map showing 5 circles. The first is between western Australia and eastern Africa. The second is between eastern Australia and western South America. The third is between Japan and western North America. Of the two in the Atlantic, one is in hemisphere.
Map of the five major ocean gyres

On average, the Atlantic is the saltiest major ocean; surface water salinity in the open ocean ranges from 33 to 37 parts per thousand (3.3 - 3.7%) by mass and varies with latitude and season. Evaporation, precipitation, river inflow and sea ice melting influence surface salinity values. Although the salinity values are just north of the equator (because of heavy tropical rainfall), in general the lowest values are in the high latitudes and along coasts where large rivers enter. Maximum salinity values occur at about 25° north and south, in subtropical regions with low rainfall and high evaporation.

Surface water temperatures, which vary with latitude, current systems, and season and reflect the latitudinal distribution of solar energy, range from below −2 °C (28.4 °F). Maximum temperatures occur north of the equator, and minimum values are found in the polar regions. In the middle latitudes, the area of maximum temperature variations, values may vary by 7-8 °C (12-15 °F).

The Atlantic Ocean consists of four major water masses. The North and South Atlantic central waters make up the surface. The sub-Antarctic intermediate water extends to depths of 1,000 metres (3,300 ft). The North Atlantic Deep Water reaches depths of as much as 4,000 metres (13,000 ft). The Antarctic Bottom Water occupies ocean basins at depths greater than 4,000 meters.

Within the North Atlantic, ocean currents isolate the Sargasso Sea, a large elongated body of water, with above average salinity. The Sargasso Sea contains large amounts of seaweed and is also the spawning ground for both the European eel and the American eel.

The Coriolis effect circulates North Atlantic water in a clockwise direction, whereas South Atlantic water circulates counter-clockwise. The south tides in the Atlantic Ocean are semi-diurnal; that is, two high tides occur during each 24 lunar hours. In latitudes above 40° North some east-west oscillation occurs.

Climate

Map of Caribbean showing 7 approximately parallel westward-pointing arrows that extend from east of the Virgin Islands to Cuba. The southern arrows bend northward just east of the Dominican Republic before straightening out again.
Waves in the trade winds in the Atlantic Ocean—areas of converging winds that move along the same track as the prevailing wind—create instabilities in the atmosphere that may lead to the formation of hurricanes

Climate is influenced by the temperatures of the surface waters and water currents as well as winds. Because of the ocean's great heat retention capacity, maritime climates are more moderate and have less extreme seasonal variations than inland climates. Precipitation can be approximated from coastal weather data and air temperature from water temperatures.

The oceans are the major source of the atmospheric moisture that is obtained through evaporation. Climatic zones vary with latitude; the warmest zones stretch across the Atlantic north of the equator. The coldest zones are in high latitudes, with the coldest regions corresponding to the areas covered by sea ice. Ocean currents influence climate by transporting warm and cold waters to other regions. The winds that are cooled or warmed when blowing over these currents influence adjacent land areas.

The Gulf Stream and its northern extension towards Europe, the North Atlantic Drift, for example, warms the atmosphere of the British Isles and north-western Europe, and the cold water currents contribute to heavy fog off the coast of eastern Canada (the Grand Banks of Newfoundland area) and Africa's north-western coast. In general, winds transport moisture and air over land areas. Hurricanes develop in the southern part of the North Atlantic Ocean.

History

Animation showing the continents separating from a single mass, making creating the Atlantic in the process
Animation of showing the separation of Pangaea, which formed the Atlantic Ocean known today

The Atlantic Ocean appears to be the second youngest of the five oceans. Apparently it did not exist prior to 130 million years ago, when the continents that formed from the breakup of the ancestral super continent, Pangaea, were drifting apart from seafloor spreading. The Atlantic has been extensively explored since the earliest settlements along its shores.

The Vikings, the Portuguese, and Christopher Columbus were the most famous among early explorers. After Columbus, European exploration rapidly accelerated, and many new trade routes were established.

As a result, the Atlantic became and remains the major artery between Europe and the Americas (known as transatlantic trade). Scientific explorations include the Challenger expedition, the German Meteor expedition, Columbia University's Lamont-Doherty Earth Observatory and the United States Navy Hydrographic Office.

Notable crossings

Ethiopic Ocean

The Ethiopic Ocean or Ethiopian Ocean (Okeanos Aithiopos) is an old name for what is now called the South Atlantic Ocean, which is separated from the North Atlantic Ocean by a narrow region between Natal, Brazil and Monrovia, Liberia. Use of this term illustrates a past trend towards referring to the whole continent of Africa by the name Aethiopia. The modern nation of Ethiopia, in northeast Africa, is nowhere near the Ethiopic Ocean, which would be said to lie off the west coast of Africa. The term Ethiopian Ocean sometimes appeared until the mid-19th century.[citation needed]

Economy

The Atlantic has contributed significantly to the development and economy of surrounding countries. Besides major transatlantic transportation and communication routes, the Atlantic offers abundant petroleum deposits in the sedimentary rocks of the continental shelves. The Atlantic hosts the world's richest fishing resources, especially in the waters covering the shelves. The major fish are cod, haddock, hake, herring, and mackerel.

The most productive areas include Newfoundland's Grand Banks, the Nova Scotia shelf , Georges Bank off Cape Cod, the Bahama Banks, the waters around Iceland, the Irish Sea, the Dogger Bank of the North Sea, and the Falkland Banks. Eel, lobster, and whales appear in great quantities. Because environmental threats from oil spills, marine debris, and the incineration of toxic wastes at sea, various international treaties attempt to reduce pollution.

Terrain

From October to June the surface is usually covered with sea ice in the Labrador Sea, Denmark Strait, and Baltic Sea. A clockwise warm-water gyre occupies the northern Atlantic, and a counter-clockwise warm-water gyre appears in the southern Atlantic. The Mid-Atlantic Ridge , a rugged north-south centerline for the entire Atlantic basin, first discovered by the Challenger Expedition dominates the ocean floor. This was formed by the vulcanism that also formed the ocean floor and the islands rising from it.

The Atlantic has irregular coasts indented by numerous bays, gulfs, and seas. These include the Norwegian Sea, Baltic Sea, North Sea, Labrador Sea, Black Sea, Gulf of Saint Lawrence, Bay of Fundy, Gulf of Maine, Mediterranean Sea, Gulf of Mexico, and Caribbean Sea.

Islands include Greenland, Iceland, Faroe Islands, Great Britain (including numerous surrounding islands), Ireland, Rockall, Newfoundland, Sable Island, Azores, Madeira, Bermuda, Canary Islands, Caribbean, Cape Verde, São Tomé and Príncipe, Annobón Province, St. Peter Island, Fernando de Noronha, Rocas Atoll, Ascension Island, Saint Helena, The Islands of Trindad, Tristan da Cunha, Gough Island (Also known as Diego Alvarez), Falkland Islands, Tierra del Fuego, South Georgia Island, South Sandwich Islands, and Bouvet Island.

Natural resources

The Atlantic harbors petroleum and gas fields, fish, marine mammals (seals and whales), sand and gravel aggregates, placer deposits, polymetallic nodules, and precious stones.

Natural hazards

Overhead photo of iceberg
Iceberg A22A in the South Atlantic Ocean

Icebergs are common from February to August in the Davis Strait, Denmark Strait, and the northwestern Atlantic and have been spotted as far south as Bermuda and Madeira. Ships are subject to superstructure icing in the extreme north from October to May. Persistent fog can be a maritime hazard from May to September, as can hurricanes north of the equator (May to December).

The United States' southeast coast has a long history of shipwrecks due to its many shoals and reefs. The Virginia and North Carolina coasts were particularly dangerous.

The Bermuda Triangle is popularly believed to be the site of numerous aviation and shipping incidents because of unexplained and supposedly mysterious causes, but Coast Guard records do not support this belief.

Current environmental issues

Endangered marine species include the manatee, seals, sea lions, turtles, and whales. Drift net fishing can kill dolphins, albatrosses and other seabirds (petrels, auks), hastening the fish stock decline and contributing to international disputes.[11] Municipal pollution comes from the eastern United States, southern Brazil, and eastern Argentina; oil pollution in the Caribbean Sea, Gulf of Mexico, Lake Maracaibo, Mediterranean Sea, and North Sea; and industrial waste and municipal sewage pollution in the Baltic Sea, North Sea, and Mediterranean Sea.

In 2005, there was some concern that warm northern European currents were slowing down, but no scientific consensus formed from that evidence.[12]

On June 7, 2006, Florida's wildlife commission voted to take the manatee off the state's endangered species list. Some environmentalists worry that this could erode safeguards for the popular sea creature.

Marine pollution

Marine pollution is a generic term for the entry into the ocean of potentially hazardous chemicals or particles. The biggest culprits are rivers and with them many agriculture fertilizer chemicals as well as livestock and human waste. The excess of oxygen-depleting chemicals leads to hypoxia and the creation of a dead zone.[13]

Marine debris, also known as marine litter, describes human-created waste floating in a body of water. Oceanic debris tends to accumulate at the center of gyres and coastlines, frequently washing aground where it is known as beach litter.

Major ports and harbours

See also

References

  1. ^ Limits of Oceans and Seas. International Hydrographic Organization Special Publication No. 23, 1953.
  2. ^ "Limits of Oceans and Seas, 3rd edition". International Hydrographic Organization. 1953. http://www.iho-ohi.net/iho_pubs/standard/S-23/S23_1953.pdf. Retrieved 6 February 2010. 
  3. ^ Darby, Andrew (22 December 2003). "Canberra all at sea over position of Southern Ocean". The Age. http://www.theage.com.au/articles/2003/12/21/1071941610556.html. Retrieved 21 December 2009. 
  4. ^ Example: BBC Click - Episode 04 April 2009
  5. ^ Hsü, Kenneth J. (1992) Challenger at Sea, Princeton, Princeton University Press, page 57
  6. ^ The Mediterranean Was a Desert" by Kenneth J. Hsü, illustration 13.
  7. ^ National Geographic Atlas of the World: Revised Sixth Edition, National Geographic Society, 1992
  8. ^ http://www.sea-seek.com/site/Milwaukee_Deep
  9. ^ http://ap.google.com/article/ALeqM5gtFxhb2bKIQLIxaRF0qB0x7k4yvgD93RLE680
  10. ^ "Introduction" U-Boat Operations of the Second World War—Vol 1 by Wynn, Kenneth, 1998 p. 1
  11. ^ animallaw.info: Problems and Prospects for the Pelagic Driftnet
  12. ^ Atlantic Ocean's 'Heat Engine' Chills Down by Christopher Joyce. All Things Considered, National Public Radio, 30 Nov, 2005.
  13. ^ Gerlach: Marine Pollution, Springer, Berlin (1975)

http://www.cartage.org.lb/en/themes/geoghist/histories/history/hiscountries/A/atlanticocean.html

http://www.mnsu.edu/emuseum/information/oceans/atlantic.html

Much of this article comes from the public domain site http://oceanographer.navy.mil/atlantic.html (dead link). It is now accessible from the Internet Archive at http://web.archive.org/web/20020221215514/http%3a//oceanographer.navy.mil/atlantic.html.

External links


Travel guide

Up to date as of January 14, 2010
(Redirected to Islands of the Atlantic Ocean article)

From Wikitravel

Sete Cidades twin lakes on São Miguel, Azores
Sete Cidades twin lakes on São Miguel, Azores

The islands of the Atlantic Ocean are - except for those in one concentrated region - scattered far and wide, with little in common but their relative obscurity.

The most numerous group of islands are the so-called West Indies and their neighbors, located southeast of North America, east of Central America, and north of South America. Although part of the Atlantic, this sea forms its own region: the Caribbean.

The near-polar islands to the far north and south are covered here among the islands of the Arctic Ocean and Southern Ocean.

The remaining islands of the Atlantic run rather intermittently from the southwestern tip of Europe, past West Africa, across the equator, to the open waters of the South Atlantic:

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1911 encyclopedia

Up to date as of January 14, 2010

From LoveToKnow 1911

ATLANTIC OCEAN, a belt of water, roughly of an S-shape, between the western coasts of Europe and Africa and the eastern coasts of North and South America. It extends E northward to the Arctic Basin and southward to the Great Southern Ocean. For purposes of measurement the polar boundaries are taken to be the Arctic and Antarctic circles, although in discussing the configuration and circulation it is impossible to adhere strictly to these limits. The Atlantic Ocean consists of two characteristic divisions, the geographical equator forming a fairly satisfactory line of division into North and South Atlantic. The North Atlantic, by far the best-known of the main divisions of the hydrosphere, is remarkable for the immense length of its coast-line and for the large number of enclosed seas connected with it, including on the western side the Caribbean Sea and Gulf of Mexico, the Gulf of St Lawrence and Hudson Bay, and on the eastern side the Mediterranean and Black Sea, the North Sea and the Baltic. The North Atlantic is connected with the Arctic Basin by four main channels: (1) Hudson Strait, about 60 m. wide, communicating with the gulfs and straits of the North American Arctic archipelago; (2) Davis Strait, about 200 m. wide, leading to Baffin Bay; (3) Denmark Strait, between Greenland and Iceland, 130 m. wide; and (4) the " Norwegian Sea," about 400 m. wide, extending from Iceland to the Faeroe Islands, the Shetland Islands and the coast of Norway. The width of the North Atlantic in lat. 60°, approximately where it breaks up into the branches just named, is nearly 2000 m.; in about lat. 50° N. the coasts of Ireland and Newfoundland approach to 1750 m.; the breadth then increases rapidly to lat. 40° N., and attains its maximum of 4500 m. in lat. 25° N.; farther south the minimum breadth is reached between Africa and South America, Cape Palmas being only 1600 m. distant from Cape St Roque. In marked contrast to this, the South Atlantic is distinguished by great simplicity of coast-line; inland seas there are none, and it attains its greatest breadth as it merges with the Southern Ocean; in lat. 35° S. the width is 3700 m.

The total area of the North Atlantic, not counting inland seas connected with it, is, according to G. Karstens, 36,438,000 sq. kilometres, o$ io,588,000 sq. m.; including the inland seas the area is 45,641,000 sq. kilometres or 13,262,000 sq. m. The area of the South Atlantic is 43,455, 000 sq. kilometres, or 12,627,000 sq. m. Although not the most extensive of the great oceans, the Atlantic has by far the largest drainage area. The " long slopes " of the continents on both sides are directed towards the Atlantic, which accordingly receives the waters of a large proportion of the great rivers of the world, including the St Lawrence, the Mississippi, the Orinoco, the Amazon, the rivers of the La Plata, the Congo, the Niger, the Loire, the Rhine, the Elbe and the great rivers of the Mediterranean and the Baltic. Sir J. Murray estimates the total area of land draining to the Atlantic to be 13,432,000 sq. m., or with the Arctic area nearly 20,000,000 sq. m., nearly four times the area draining to the Pacific Ocean, and almost precisely four times the area draining to the Indian Ocean. Murray's calculations give the amount of precipitation received on this area at 15,800 cub. m. annually, and the river discharge from it at 3900 cub. m.

The dominant feature of the relief of the Atlantic basin is a submarine ridge running from north to south from about lat. 50° N. to lat. 40° S., almost exactly in the central line, and following the S-shape of the coasts. Over g p this ridge the average depth is about 1700 fathoms.

Towards its northern end the ridge widens and rises to the plateau of the Azores, and in about 50° N. lat. it merges with the " Telegraph Plateau," which extends across nearly the whole ocean from Ireland to Newfoundland. North of the fiftieth parallel the depths diminish towards the north-east, two long submarine ridges of volcanic origin extend north-eastwards to the southwest of Iceland and to the Faeroe Islands, and these, with their intervening valleys, end in a transverse ridge connecting Greenland, through Iceland and the Faeroe Islands, with Northwestern Scotland and the continental mass of Europe. The mean depth over this ridge is about 250 fathoms, and the maximum depth nowhere reaches 500 fathoms. The main basin of the Atlantic is thus cut off from the Arctic basin, with which the area north of the ridge has complete deep-water communication. This intermediate region, which has Atlantic characteristics down to 300 fathoms, and at greater depths belongs more properly to the Arctic Sea, commonly receives the name of Norwegian Sea. On both sides of the central ridge deep troughs extend southwards from the Telegraph plateau to the Southern Ocean, the deep water coming close to the land all the way down on both sides. In these troughs the depth is seldom much less than 3000 fathoms, and this is exceeded in a series of patches to which Murray has given the name of " Deeps." In the eastern trough the Peake Deep lies off the Bay of Biscay in 20° W. long., Monaco Deep and Chun Deep off the north-west of Africa, Moseley Deep off the Cape Verde Islands, Krech Deep off the Liberian coast, and Buchanan Deep off the mouth of the Congo. The western trough extends northwards into Davis Strait, forming a depression in the Telegraph plateau; to the south of Newfoundland and Nova Scotia are Sigsbee Deep, Libbey Deep and Suhm Deep, each of small area; north-east of the Bahamas Nares Deep forms the largest and deepest depression in the Atlantic, in which a sounding of 4561 fathoms was obtained (70 m. north of Porto Rico) by the U.S. ship " Blake " in 1883. Immediately to the south of Nares Deep lies the smaller Makarov Deep; and off the coast of South America are Tizard Deep and Havergal Deep.

Before the Antarctic expeditions of 1903-1904 our knowledge of the form of the sea bottom south of 40° S. lat. was almost wholly derived from the soundings of the expedition of Sir J. C. Ross in the " Erebus " and " Terror " (1839-1843), and the bathymetrical maps published were largely the result of deductions based on one sounding taken -by Ross in 68° 34' S. lat., 12° 49' W. long., in which he recorded a depth exceeding 4000 fathoms. The Scottish Antarctic expedition has shown this sounding to be erroneous; the " Scotia " obtained samples of bottom, in almost the same spot, from a depth of 2660 fathoms. Combining the results of recent soundings, Dr W. S. Bruce, the leader of the Scottish expedition, finds that there is a ridge " extending in a curve from Madagascar to Bouvet Island, and from Bouvet Island to the Sandwich group, whence there is a forked connexion through the South Orkneys to Graham's Land, and through South Georgia to the Falkland Islands and the South American continent." Again, the central ridge of the South Atlantic extends a thousand miles farther south than was supposed, joining the east and west ridge, just described, between the Bouvet Islands and the Sandwich group.

The foundations of our knowledge of the relief of the Atlantic basin may be said to have been laid by the work of H.M.S. " Challenger " (1873-1876), and the German ship " Gazelle " (1874-1876), the French expedition in the " Travailleur " (1880), and the U.S. surveying vessel " Blake " (1877 and later). Large numbers of additional soundings have been made in recent years by cable ships, by the expeditions of H.S.H. the prince of Monaco, the German " Valdivia " expedition under Professor Chun (1898), and the combined Antarctic expeditions (1903-1904).

The Atlantic Ocean contains a relatively small number of islands. The only continental groups, besides some islands in. the Mediterranean, are Iceland, the British Isles, Islands. Newfoundland, the West Indies, and the Falklands, and the chief oceanic islands are the Azores, Madeira, the Canaries, the Cape Verde Islands, Ascension, St Helena, Tristan da Cunha and Bouvet Island.

The mean depth of the North Atlantic is, according to G. Mean Karstens, 2047 fathoms. If we include the enclosed depth, and seas, the North Atlantic has a mean depth of 1800 bottom fathoms. The South Atlantic has a mean depth of deposits. 2067 fathoms.' The greater part of the bottom of the Atlantic is covered by a deposit of Globigerina ooze, roughly the area between l000 and 3000 fathoms, or about 60% of the whole. At a depth of about 3000 fathoms, i.e. in the " Deeps," the Globigerina ooze gradually gives place to red clay. In the shallower tropical waters, especially on the central ridge, considerable areas are covered by Pteropod ooze, a deposit consisting largely of the shells of pelagic molluscs. Diatom ooze is the characteristic deposit in high southern latitudes. The terrigenous deposits consist of blue muds, red muds (abundant along the coast of Brazil, where the amount of organic matter present is insufficient to reduce the iron in the matter brought down by the great rivers to produce blue muds), green muds and sands, and volcanic and coral detritus.

The question of the origin of the Atlantic basin, like that of the other great divisions of the hydrosphere, is still unsettled. Most geologists include the Atlantic with the other oceans in the view they adopt as to its age; but E. Suess and Ri. Neumayr, while they regard the basin of the Pacific as of great antiquity, believe the Atlantic to date only from the Mesozoic age. Neumayr finds evidence of the existence of a continent between Africa and South America, which protruded into the central North Atlantic, in Jurassic times. F. Kossmat has shown that the Atlantic had substantially its present form during the Cretaceous period. In describing the mean distribution of temperature in the waters of the Atlantic it is necessary to treat the northern and southern divisions separately. The heat equator, or line of maximum mean surface temperature, starts from the African coast in about 5° N. lat., and closely follows that parallel to 40° W. long., where it bends northwards to the Caribbean Sea. North of this line, near which the temperature is a little over 80° F., the gradient trends somewhat to the east of north, and the temperature is slightly higher on the western than on the eastern side until, in 4 5° N. lat., the isothermal of 60° F. runs nearly east and west. Beyond this parallel the gradient is directed towards the north-west, and temperatures are much higher on the European than on the American side. From the surface to 500 fathoms the general form of the isothermals remains the same, except that instead of an equatorial maximum belt there is a focus of maximum temperature off the eastern coast of the United States. This focus occupies a larger area and becomes of greater relative intensity as the depth increases until, at 500 fathoms, it becomes an elongated belt extending right across the ocean in about 30° N. lat. Below 500 fathoms the western centres of maximum disappear, and higher temperatures occur in the eastern Atlantic off the Iberian peninsula and north-western Africa down to at least 1000 fathoms; at still greater depths temperature gradually becomes more and more uniform. The communication between the Atlantic and Arctic basins being cut off, as already described, at a depth of about 300 fathoms, the temperatures in the Norwegian Sea below that level are essentially Arctic, usually below the freezing-point of fresh water, except where the distribution is modified by the surface circulation. The isothermals of mean surface temperature in the South Atlantic are in the lower latitudes of an cn- shape, temperatures being higher on the American than on the African side. In latitudes south of 30 S. the curved form tends to disappear, the lines running more and more directly east and west. Below the surface a focus of maximum temperature appears off the coast of South America in about 30 S. lat., and of minimum temperature north and northeast of this maximum. This distribution is most marked at about 300 fathoms, and disappears at soo fathoms, beyond which depth the lines tend to become parallel and to run east and west, the gradient slowly diminishing.

The Atlantic is by far the saltest of the great oceans. Its saltest waters are found at the surface in two belts, one extending east and west in the North Atlantic between 20° and 30 N. lat., and another of almost equal salinity extending eastwards from the coast of South America in 10 to 20° S. lat. In the equatorial region between these belts the salinity is markedly less, especially in the eastern part. North of the North Atlantic maximum the waters become steadily fresher as latitude increases until the channels opening into the Arctic basin are reached. In all of these water of relatively high salinity usually appears for a long distance towards the north on the eastern side of the channel, while on the western side the water is comparatively fresh; but great variations occur at different seasons and in different years. In the higher latitudes of the South Atlantic the salinity diminishes steadily and tends to be uniform from east to west, except near the southern extremity of South America, where the surface waters are very fresh. Our knowledge of the salinity of waters below the surface is as yet very defective, large areas being still unrepresented by a single observation. The chief facts already established are the greater saltness of the North Atlantic compared with the South Atlantic at all.depths, and the low salinity at all depths in the eastern equatorial region, off the Gulf of Guinea.

The wind circulation over the Atlantic is of a very definite character. In the South Atlantic the narrow land surfaces of Africa and South America produce comparatively little effect in disturbing the normal planetary circulation. Meteor- g P Y The tropical belt of high atmospheric pressure is very marked in winter; it is weaker during the summer months, and at that season the greater relative fall of pressure over the land cuts it off into an oval-shaped anticyclone, the centre of which rests on the coolest part of the sea surface in that latitude, near the Gulf of Guinea. South of this anticyclone, from about the latitude of the Cape, we find the region where, on account of the uninterrupted sea surface right round the globe, the planetary circulation is developed to the greatest extent known; the pressure gradient is steep, and the region is swept continuously by strong westerly winds - the " roaring forties." In the North Atlantic the distribution of pressure and resulting wind circulation are very largely modified by the enormous areas of land and frozen sea which surround the ocean on three sides. The tropical belt of high pressure persists all the year tion of ture. Salinity. round, but the immense demand for air to supply the ascending currents over the heated land surfaces in summer causes the normal descending movement to be largely reinforced; hence the " North Altantic anticyclone is much larger, and its circulation more vigorous, in summer than in winter. Again, during the winter months pressure is relatively high over North America, Western Eurasia and the Arctic regions; hence vast quantities of air are brought down to the surface, and circulation must be kept up by ascending currents over the ocean. The Atlantic anticyclone is, therefore, at its weakest in winter, and on its polar side the polar eddy becomes a trough of low pressure, extending roughly from Labrador to Iceland and Jan Mayen, and traversed by a constant succession of cyclones. The net effect of the surrounding land is, in fact, to reverse the seasonal variations of the planetary circulation, but without destroying its type. In the intermediate belt between the two high-pressure areas the meteorological equator remains permanently north of the geographical equator, moving between it and about i r° N. lat.

The part of this atmospheric circulation which is steadiest in its action is the trade winds, and this is, therefore, the most effective in producing drift movement of the surface waters. The trade winds give rise, in the region most exposed to their influence, to two westward-moving drifts - the equatorial currents, which are separated in parts of their course by currents moving in the opposite direction along the equatorial belt. These last may be of the nature of " reaction " currents; they are collectively known as the equatorial counter-current. On reaching the South American coast, the southern equatorial current splits into two parts at Cape St Roque: one branch, the Brazil current, is deflected southwards and follows Currents. the coast as a true stream current at least as far as the river Plate. The second branch proceeds north-westwards towards the West Indies, where it mingles with the waters of the northern equatorial; and the two drifts, blocked by the <-shape of the land, raise the level of the surface in the Gulf of Mexico, the Caribbean Sea, and in the whole area outside the West Indies. This congestion is relieved by what is probably the most rapid and most voluminous stream current in the world, the Gulf Stream, which runs along the coast of North America, separated from it by a narrow strip of cold water, the " cold wall," to a point off the south-east of Newfoundland. At this point the Gulf Stream water mixes with that from the Labrador current (see below), and a drift current eastwards is set up under the influence of the prevailing westerly winds: this is generally called the Gulf Stream drift. When the Gulf Stream drift approaches the eastern side of the Atlantic it splits into two parts, one going southwards along the north-west coast of Africa, the Canaries current, and another turning northwards and passing to the west of the British Isles. Most of the Canaries current re-enters the northern equatorial, but a certain proportion keeps to the African coast, unites with the equatorial return currents, and penetrates into the Gulf of Guinea. This last feature of the circulation is still somewhat obscure; it is probably to be accounted for by the fact that on this part of the coast the prevailing winds, although to a considerable extent monsoonal, are off-shore winds, blowing the surface waters out to sea, and the place of the water thus removed is filled up by water derived either from lower levels or from " reaction " currents.

The movements of the northern branch of the Gulf Stream drift have been the object of more careful and more extended study than all the other currents of the ocean put together, except, perhaps, the Gulf Stream itself. The cruises of the " Porcupine " and " Lightning," which led directly to the despatch of the " Challenger " expedition, were altogether within its " sphere of influence "; so also was the great Norwegian Atlantic expedition. More recently, the area has been further explored by the German expedition in the ss. " National, " the Danish " Ingolf " expedition, and the minor expeditions of the " Michael Sars," " Jackal," " Research," &c., and since 1902 it has been periodically examined by the International Council for the Study of the Sea. Much has also been done by the discussion of observations made on board vessels belonging to the mercantile marine of various countries. It may now be taken as generally admitted that the current referred to breaks into three main branches. The first passes northwards, most of it between the Faeroe and Shetland Islands, to the coast of Norway, and so on to the Arctic basin, which, as Nansen has shown, it fills to a great depth. The second, the Irminger stream, passes up the west side of Iceland; and the third goes up the Greenland side of Davis Strait to Baffin Bay. These branches are separated from one another at the surface by currents moving southwards: one passes east of Iceland; the second, the Greenland current, skirts the east coast of Greenland; and the third, the Labrador current already mentioned, follows the western side of Davis Strait.

The development of the equatorial and the Brazil currents in the South Atlantic has already been described. On the polar side of the high-pressure area a west wind drift is under the control of the " roaring forties," and on reaching South Africa part of this is deflected and sent northwards along the west coast as the cold Benguella current which rejoins the equatorial. In the central parts of the two high-pressure areas there is practically no surface circulation. In the North Atlantic this region is covered by enormous banks of gulf-weed (Sargassum bucciferum), hence the name Sargasso Sea. The Sargasso Sea is bounded, roughly, by the lines of 20°-35° N. lat. and 40°-75° W. long.

The sub-surface circulation in the Atlantic may be regarded as consisting of two parts. Where surface water is banked up against the land, as by the equatorial and Gulf Stream drift currents, it appears to penetrate to very considerable depths; the escaping stream currents are at first of great vertical thickness and part of the water at their sources has a downward movement. In the case of the Gulf Stream, which is not much impeded by the land, this descending motion is relatively slight, being perhaps largely due to the greater specific gravity of the water; it ceases to be perceptible beyond about 500 fathoms. On the European-African side the descending movement is more marked, partly because the coast-line is much more irregular and the northward current is deflected against it by the earth's rotation, and partly because of the outflow of salt water from the Mediterranean; here the movement is traceable to at least 1000 fathoms. The northward movement of water across the Norwegian Sea extends down from the surface to the IcelandShetland ridge, where it is sharply cut off; the lower levels of the Norwegian Sea are filled with ice-cold Arctic water, close down to the ridge. The south-moving currents originating from melting ice are probably quite shallow. The second part of the circulation in the depth is the slow " creep " of water of very low temperature along the bottom. The North Atlantic being altogether cut off from the Arctic regions, and the vertical circulation being active, this movement is here practically non-existent; but in the South Atlantic, where communication with the Southern Ocean is perfectly open, Antarctic water can be traced to the equator and even beyond.

The tides of the Atlantic Ocean are of great complexity. The tidal wave of the Southern Ocean, which sweeps uninterruptedly round the globe from east to west, generates a secondary wave between Africa and South America, which travels north at a rate dependent only on the depth of the ocean. With this " free " wave is combined a " forced " wave, generated, by the direct action of the sun and moon, within the Atlantic area itself. Nothing is known about the relative importance of these two waves. (H. N. D.) See also Ocean And Oceanogra Phy.


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Wiktionary

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English

The Atlantic Ocean.

Proper noun

Singular
Atlantic Ocean

Plural
-

Atlantic Ocean

  1. The ocean lying between the Americas to the west and Europe and Africa to the east.

Synonyms

Derived terms

Translations


Genealogy

Up to date as of February 01, 2010

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The Atlantic Ocean lies east of North America and South America and west of Europe and Africa.

At least one individual who has a page on this site was born on shipboard there.


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Simple English

Earth's oceans
(World Ocean)

The Atlantic Ocean is the body of water bordered

Scientists say that millions of years ago, there was only one ocean, and that most of the land in the world was joined together over where the Atlantic Ocean is now. Eventually, they think an enormous crack developed in the ground due to volcanic forces, and that the continents started ever so slowly drifting away from each other. The crack would have filled with water from rivers, and eventually the sea might have broken through from the north and the south. Even to this day, the east coast of the Americas is shaped somewhat like the west coast of Africa, but the difference is actually much greater than it might appear, so it is not really an exact fit or even a close one. The Atlantic Ocean is still growing now, because of sea-floor spreading from the mid-Atlantic Ridge, while the Pacific Ocean is said to be shrinking because the sea floor is folding under itself.

Gulf Stream

The Atlantic Ocean has important ocean currents. One of these, called the Gulf Stream, flows across the North Atlantic. Water gets heated by the sun in the Caribbean Sea and then moves northwest toward the North Pole. This makes France, Ireland, Britain, Iceland, and Norway in Europe much warmer in winter than Newfoundland and Nova Scotia in Canada. Without the Gulf Stream, the climates of northeast Canada and northwest Europe might be the same, because these places are about the same distance from the North Pole.

There are currents in the South Atlantic too, but the shape of this sea means that it has less effect on South Africa.

frr:Atlantische Oseåån

rue:Атлантічный океан








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