Atlantic Ocean

The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe and Asia from the "New World" of the Americas in the European perception of the World.

The Atlantic Ocean occupies an elongated, S-shaped basin extending longitudinally between Europe and Africa to the east, and North and South America to the west. As one component of the interconnected World Ocean, it is connected in the north to the Arctic Ocean, 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 Atlantic Ocean is divided in two parts, by the Equatorial Counter Current, with the North(ern) Atlantic Ocean and the South(ern) Atlantic Ocean split at about 8°N.

Scientific explorations of the Atlantic include the ''Challenger'' expedition, the German ''Meteor'' expedition, Columbia University's Lamont–Doherty Earth Observatory and the United States Navy Hydrographic Office.

Toponymy

The oldest known mentions of an "Atlantic" sea come from Stesichorus around mid-sixth century BC (Sch. A. R. 1. 211): (Greek: ; English: 'the Atlantic sea'; etym. 'Sea of Atlas') and in '' The Histories'' of Herodotus around 450 BC (Hdt. 1.202.4): (Greek: ; English: 'Sea of Atlas' or 'the Atlantic sea') where the name refers to "the sea beyond the pillars of Heracles" which is said to be part of the sea that surrounds all land. In these uses, the name refers to Atlas, the Titan in Greek mythology, who supported the heavens and who later appeared as a frontispiece in Medieval maps and also lent his name to modern atlases. On the other hand, to early Greek sailors and in Ancient Greek mythological literature such as the ''Iliad'' and the ''Odyssey'', this all-encompassing ocean was instead known as Oceanus, the gigantic river that encircled the world; in contrast to the enclosed seas well known to the Greeks: the Mediterranean and the Black Sea. In contrast, the term "Atlantic" originally referred specifically to the Atlas Mountains in Morocco and the sea off the Strait of Gibraltar and the North African coast. The Greek word has been reused by scientists for the huge Panthalassa ocean that surrounded the supercontinent Pangaea hundreds of millions of years ago.

The term "Aethiopian Ocean", derived from Ancient Ethiopia, was applied to the Southern Atlantic as late as the mid-19th century. During the Age of Discovery, the Atlantic was also known to English cartographers as the Great Western Ocean.

The pond is a term often used by British and American speakers in reference to the Northern Atlantic Ocean, as a form of meiosis, or ironic understatement. It is used mostly when referring to events or circumstances "on this side of the pond" or "on the other side of the pond", rather than to discuss the ocean itself. The term dates to 1640, first appearing in print in pamphlet released during the reign of Charles I, and reproduced in 1869 in Nehemiah Wallington's ''Historical Notices of Events Occurring Chiefly in The Reign of Charles I'', where "great Pond" is used in reference to the Atlantic Ocean by Francis Windebank, Charles I's Secretary of State.

Extent and data

The International Hydrographic Organization (IHO) defined the limits of the oceans and seas in 1953, but some of these definitions have been revised since then and some are not used by various authorities, institutions, and countries, see for example the CIA World Factbook. Correspondingly, the extent and number of oceans and seas vary.

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, both of which also touch upon Asia) 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. In the 1953 definition it extends south to Antarctica, while in later maps it is bounded at the 60° parallel by the Southern Ocean.

The Atlantic has irregular coasts indented by numerous bays, gulfs and seas. These include the Baltic Sea, Black Sea, Caribbean Sea, Davis Strait, Denmark Strait, part of the Drake Passage, Gulf of Mexico, Labrador Sea, Mediterranean Sea, North Sea, Norwegian Sea, almost all of the Scotia Sea, and other tributary water bodies. Including these marginal seas the coast line of the Atlantic measures compared to for the Pacific.

Including its marginal seas, the Atlantic covers an area of or 23.5% of the global ocean and has a volume of or 23.3% of the total volume of the earth's oceans. Excluding its marginal seas, the Atlantic covers and has a volume of . The North Atlantic covers (11.5%) and the South Atlantic (11.1%). The average depth is and the maximum depth, the Milwaukee Deep in the Puerto Rico Trench, is .

Biggest seas in Atlantic Ocean

Top large seas:

# Sargasso Sea - 3.5 million km²
# Caribbean Sea - 2.754 million km²
# Mediterranean Sea - 2.510 million km²
# Gulf of Guinea - 2.35 million km²
# Gulf of Mexico - 1.550 million km²
# Norwegian Sea - 1.383 million km²
# Hudson Bay - 1.23 million km²
# Greenland Sea - 1.205 million km²
# Argentine Sea - 1 million km²
# Labrador Sea - 841,000 km²
# Irminger Sea - 780,000 km²
# Baffin Bay - 689,000 km²
# North Sea - 575,000 km²
# Black Sea - 436,000 km²
# Baltic Sea - 377,000 km²
# Libyan Sea - 350,000 km²
# Levantine Sea - 320,000 km²
# Celtic Sea - 300,000 km²
# Tyrrhenian Sea - 275,000 km²
# Gulf of Saint Lawrence - 226,000 km²
# Bay of Biscay - 223,000 km²
# Aegean Sea - 214,000 km²
# Ionian Sea - 169,000 km²
# Balearic Sea - 150,000 km²
# Adriatic Sea - 138,000 km²
# Gulf of Bothnia - 116,300 km²
# Sea of Crete - 95,000 km²
# Gulf of Maine - 93,000 km²
# Ligurian Sea - 80,000 km²
# English Channel - 75,000 km²
# James Bay - 68,300 km²
# Bothnian Sea - 66,000 km²
# Gulf of Sidra - 57,000 km²
# Sea of the Hebrides - 47,000 km²
# Irish Sea - 46,000 km²
# Sea of Azov - 39,000 km²
# Bothnian Bay - 36,800 km²
# Gulf of Venezuela - 17,840 km²
# Bay of Campeche - 16,000 km²
# Gulf of Lion - 15,000 km²
# Sea of Marmara - 11,350 km²
# Wadden Sea - 10,000 km²
# Archipelago Sea - 8,300 km²

Bathymetry

The bathymetry of the Atlantic is dominated by a submarine mountain range called the Mid-Atlantic Ridge (MAR). It runs from 87°N or south of the North Pole to the subantarctic Bouvet Island at 54°S.

Mid-Atlantic Ridge

The MAR divides the Atlantic longitudinally into two halves, in each of which a series of basins are delimited by secondary, transverse ridges. The MAR reaches above along most of its length, but is interrupted by larger transform faults at two places: the Romanche Trench near the Equator and the Gibbs Fracture Zone at 53°N. The MAR is a barrier for bottom water, but at these two transform faults deep water currents can pass from one side to the other.

The MAR rises above the surrounding ocean floor and its rift valley is the divergent boundary between the North American and Eurasian plates in the North Atlantic and the South American and African plates in the South Atlantic. The MAR produces basaltic volcanoes in Eyjafjallajökull, Iceland, and pillow lava on the ocean floor. The depth of water at the apex of the ridge is less than in most places, while the bottom of the ridge is three times as deep.

The MAR is intersected by two perpendicular ridges: the Azores–Gibraltar Transform Fault, the boundary between the Nubian and Eurasian plates, intersects the MAR at the Azores Triple Junction, on either side of the Azores microplate, near the 40°N. A much vaguer, nameless boundary, between the North American and South American plates, intersects the MAR near or just north of the Fifteen-Twenty Fracture Zone, approximately at 16°N.

In the 1870s, the ''Challenger'' expedition discovered parts of what is now known as the Mid-Atlantic Ridge, or:
The remainder of the ridge was discovered in the 1920s by the German ''Meteor'' expedition using echo-sounding equipment. The exploration of the MAR in the 1950s led to the general acceptance of seafloor spreading and plate tectonics.

Most of the MAR runs under water but where it reaches the surfaces it has produced volcanic islands. While nine of these have collectively been nominated a World Heritage Site for their geological value, four of them are considered of "Outstanding Universal Value" based on their cultural and natural criteria: Þingvellir, Iceland; Landscape of the Pico Island Vineyard Culture, Portugal; Gough and Inaccessible Islands, United Kingdom; and Brazilian Atlantic Islands: Fernando de Noronha and Atol das Rocas Reserves, Brazil.

Ocean floor

Continental shelves in the Atlantic are wide off Newfoundland, southernmost South America, and north-eastern Europe.
In the western Atlantic carbonate platforms dominate large areas, for example, the Blake Plateau and Bermuda Rise.
The Atlantic is surrounded by passive margins except at a few locations where active margins form deep trenches: the Puerto Rico Trench ( maximum depth) in the western Atlantic and South Sandwich Trench () in the South Atlantic. There are numerous submarine canyons off north-eastern North America, western Europe, and north-western Africa. Some of these canyons extend along the continental rises and farther into the abyssal plains as deep-sea channels.

In 1922, a historic moment in cartography and oceanography occurred. The USS ''Stewart'' used a Navy Sonic Depth Finder to draw a continuous map across the bed of the Atlantic. This involved little guesswork because the idea of sonar is straightforward with pulses being sent from the vessel, which bounce off the ocean floor, then return to the vessel. The deep ocean floor is thought to be fairly flat with occasional deeps, abyssal plains, trenches, seamounts, basins, plateaus, canyons, and some guyot