Atlantic Ocean

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Atlantic 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 one-fifth of the Earth's surface and about one-quarter of its water surface area. The first part of its name refers to the Atlas of Greek mythology, making the Atl...

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 one-fifth of the Earth's surface and about one-quarter 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 BCE (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.

Geography
The Atlantic Ocean as seen from the western coast of PortugalThe 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. 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 (10,950 ft); without them it is 3,926 metres (12,880 ft). The greatest depth, 8,605 metres (28,230 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.

Extents
The 3rd edition of the International Hydrographic Organization's Limits of Oceans and Seas defines the limits of the North Atlantic Ocean as follows:

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 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. (Now redefined as 60°S

On the Southwest. The meridian of Cape Horn (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. (These limits have not yet been officially accepted by Argentina and Chile.)

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

Following a decision in 2000, the International Hydrographic Organization plans to define the southern limit of the Atlantic Ocean as terminating at 60°S, with the waters south of that point identified as the Southern Ocean. However, this change has not yet been ratified due to a reservation lodged by Australia. When adopted, it 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".

Ocean bottom
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Map that uses color to show ocean depthThe principal feature of the bathymetry (bottom topography) is a submarine mountain range called the Mid-Atlantic Ridge. 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 over the ridge is less than 2,700 metres (8,900 ft) in most places, and several mountain peaks rise above the water and form islands. The South Atlantic Ocean has an additional submarine ridge, the Walvis Ridge.

The Mid-Atlantic Ridge separates the Atlantic Ocean into two large troughs with depths from 3,700–5,500 metres (12,000–18,000 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, although numerous seamounts and some guyots exist. Several deeps or trenches are also found on the ocean floor. The Puerto Rico Trench, in the North Atlantic, is the deepest at 8,605 metres (28,230 ft). The Laurentian Abyss is found off the eastern coast of Canada. In the South Atlantic, the South Sandwich Trench reaches a depth of 8,428 metres (27,650 ft). A third major trench, the Romanche Trench, is located near the equator and reaches a depth of about 7,454 metres (24,460 ft). The shelves along the margins of the continents constitute about 11% of the bottom topography. Several deep channels cut across the continental rise.

Ocean sediments are composed of terrigenous, pelagic, and authigenic material. Terrigenous deposits consist of sand, mud, and rock particles formed by erosion, weathering, and volcanic activity on land and then 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 (200–10,800 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
Path of the thermohaline circulation. Purple paths represent deep-water currents, while blue paths represent surface currents.
Map of the five major ocean gyresOn 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 (45–46 °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
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 hurricanesClimate 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 of showing the separation of Pangaea, which formed the Atlantic Ocean known todayThe 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
In 1000, the Icelander, Leif Ericson was the first European to discover North America's Atlantic coast, including Vinland. The Norse discovery was documented in the 13th century Icelandic Sagas and was corroborated by recent archeological evidence.
In 1003, Thorfinnr Karlsefni led an attempted Viking settlement in North America but was driven off by the natives.
In 1004, Snorri Thorfinnsson was the first European born on the American continent.
In 1419 and 1427, Portuguese navigators reached Madeira and Azores, respectively.
From 1415 to 1488, Portuguese navigators sailed along the Western African coast, reaching the Cape of Good Hope.
In 1492, Christopher Columbus landed somewhere in The Bahamas.
From 1499 to 1502, Amerigo Vespucci mapped South America's east coast, proving that the Americas are not Asia's east edge.
In 1500, Pedro Álvares Cabral reached Brazil.
Saint Brendan may have crossed the Atlantic Ocean between 512 and 530.
In 1524, Italian explorer Giovanni da Verrazzano discovered the United States of America east coast.
In 1764 William Harrison (the son of John Harrison) sailed aboard the HMS Tartar, with the H-4 time piece. The voyage became the basis for the invention of the global system of Longitude.
In 1858, Cyrus West Field laid the first transatlantic telegraph cable (it quickly failed).
In 1865 Brunel's ship the SS Great Eastern laid the first successful transatlantic telegraph cable .
On April 15, 1912 the RMS Titanic sank after hitting an iceberg with a loss of more than 1,500 lives
1914-1918, the First Battle of the Atlantic took place.
In 1919, the American NC-4 became the first fixed-wing aircraft (seaplane) to cross the Atlantic (though it made a couple of landings on islands and the sea along the way, and taxied several hundred miles).
Later in 1919, a British aeroplane piloted by Alcock and Brown made the first non-stop transatlantic flight, from Newfoundland to Ireland.
In 1921, the British were the first to cross the North Atlantic in an airship.
In 1922, Sacadura Cabral and Gago Coutinho were the first to cross the South Atlantic in an airship.
In 1927, Charles Lindbergh made the first solo non-stop transatlantic flight in an aircraft (between New York City and Paris).
In 1932, Amelia Earhart became the first female to make a solo flight across the Atlantic
1939-1945, the Second Battle of the Atlantic. Nearly 3,700 Allied ships were sunk at a cost of 783 German U-boats.
In 1952, Ann Davison was the first woman to single-handedly sail the Atlantic Ocean.
In 1975, Fons Oerlemans crossed the Atlantic in 82 days, starting from Safi (Morocco) to Trinidad and Tobago, on a selfmade raft.
In 1980, Gérard d'Aboville was the first man to cross the Atlantic Ocean rowing.
In 1994, Guy Delage was the first man to allegedly swim across the Atlantic Ocean (with the help of a kick board, from Cape Verde to Barbados).
In 1998, Benoît Lecomte was the first man to swim across the northern Atlantic Ocean without a kick board, stopping for only one week in the Azores.
In 1999, after rowing for 81 days and 4,767 kilometres (2,962 mi), Tori Murden became the first woman to cross the Atlantic Ocean by rowboat alone when she reached Guadeloupe from the Canary Islands.

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.

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
Iceberg A22A in the South Atlantic OceanIcebergs 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.

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