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.
An elevated ridge rising to an average height of about 1,900 fathoms [3,500 m; 11,400 ft] below the surface traverses the basins of the North and South Atlantic in a meridianal direction from Cape Farewell, probably its far south at least as Gough Island, following roughly the outlines of the coasts of the Old and the New Worlds.
Most of the MAR runs under water but where it reaches the surfaces it has produced volcanic islands.
1.202.4): Atlantis thalassa (Greek: Ἀτλαντὶς θάλασσα; English: 'Sea of Atlantis' or 'the Atlantis sea' Thus, on one hand, 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.
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 varies.The Equatorial Counter Current subdivides it into the North Atlantic Ocean and the South Atlantic Ocean 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.The MAR produces basaltic volcanoes in Eyjafjallajökull, Iceland, and pillow lava on the ocean floor.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.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.