The Atlantic is the ocean most maps put at the centre of the world, which makes it oddly easy to overlook. It is also the ocean whose shape tells the clearest story about how continents move: its two coastlines still fit together like torn paper, and the seam they tore along runs right down the middle of the sea floor.
How big it is
According to the US National Oceanic and Atmospheric Administration, the Atlantic covers about 106,460,000 square kilometres, roughly 41.1 million square miles, or about 20 percent of the Earth’s surface. That makes it the second largest ocean basin after the Pacific, and NOAA notes it is only slightly larger than half the size of the Pacific.
The shape: a long S
The Atlantic runs from the Arctic in the north to the Southern Ocean around Antarctica, and it is much longer than it is wide. Its outline traces a rough S, following the bulge of West Africa and the matching curve of north-eastern South America. Put the two coasts next to each other and Brazil tucks into the Gulf of Guinea, which is the first clue to the ocean’s history.
The equator splits it into the North Atlantic and the South Atlantic, which behave differently. The north is ringed by busy coasts, crossed by some of the busiest shipping lanes in the world, and fed by large seas. The south is wider, emptier and has far fewer islands.
The Mid-Atlantic Ridge
The most important feature on a map of the Atlantic is underwater. The Mid-Atlantic Ridge runs down the middle of the ocean, from near the Arctic to the far South Atlantic, following the same S shape as the coasts. It is part of the global mid-ocean ridge system, which NOAA describes as nearly 65,000 kilometres long, with more than 90 percent of it in the deep ocean.
Along the ridge, the sea floor is pulling apart. NOAA puts the Mid-Atlantic Ridge among the slow spreading ridges, opening at 2 to 5 centimetres a year, and says its central rift valley is about the depth and width of the Grand Canyon. In practical terms, Europe and North America drift a little further apart every year, and the Atlantic is still widening.
In a few places the ridge breaks the surface. Iceland sits on top of it, which is why the island has active volcanoes and visible rift valleys on land. The Azores, in the middle of the North Atlantic, are another part of the ridge that rises above sea level.
The seas that branch off
Much of what people call “the Atlantic” in daily life is one of its marginal seas or gulfs:
- The Caribbean Sea and the Gulf of Mexico on the American side.
- The Mediterranean, connected through the narrow Strait of Gibraltar.
- The North Sea and the Baltic in northern Europe.
- The Labrador Sea between Canada and Greenland.
- The Gulf of Guinea along the West African coast.
One sea in the middle of the North Atlantic has no coast at all. The Sargasso Sea is defined by currents rather than land, and it is known for its floating mats of seaweed.
The islands of the Atlantic
Most Atlantic islands sit close to the continents or on the ridge. Reading from north to south:
- Iceland and the Faroe Islands in the far north.
- Bermuda, alone in the western North Atlantic.
- The Azores, Madeira and the Canary Islands, off Europe and North Africa.
- Cape Verde, off the coast of Senegal.
- Ascension, Saint Helena and Tristan da Cunha, scattered across the empty South Atlantic.
- The Falkland Islands and South Georgia, in the far south-west.
Currents that shape the climate
The Gulf Stream carries warm water from the Caribbean region up the east coast of North America and across toward Europe, which is part of the reason western Europe is milder than places at the same latitude in Canada. In the south, the Benguela Current runs cold up the coast of south-western Africa. Both appear on a good physical map as arrows, and both explain more about the weather on either shore than the shape of the coastline does.
Reading the Atlantic with its neighbours
Several of the Atlantic’s arms have their own guides on this site. The map of the Caribbean covers the island chains on its western edge, and the map of the Mediterranean explains the sea behind Gibraltar. To the north, the map of the Arctic shows where the Atlantic meets the polar sea, and the map of West Africa covers the coast that once lay against South America.
NOAA’s short fact page on the Atlantic is the reference for its size and rank.
