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Atlantic Ocean
From Wikipedia, the free encyclopedia
(World Ocean)
- Arctic Ocean
- Atlantic Ocean
- Indian Ocean
- Pacific Ocean
- Southern 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.
Geography
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 ( 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
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:
- Puerto Rico Trench, in the North Atlantic, is the deepest trench at 8,605 metres (28,232 ft)[8]
- Laurentian Abyss is found off the eastern coast of Canada
- South Sandwich Trench reaches a depth of 8,428 metres (27,651 ft)
- Romanche Trench is located near the equator and reaches a depth of about 7,454 metres (24,455 ft)
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
