Atlantic Ocean

I

Introduction

Atlantic Ocean, the second-largest of the Earth's five oceans and the most heavily travelled. Only the Pacific Ocean is larger. The Atlantic is divided into two nominal sections: the part north of the equator is called the North Atlantic; the part south of the equator, the South Atlantic. The ocean's name is derived from Atlas, one of the Titans of Greek mythology.

II

Boundaries and Size

The Atlantic Ocean is essentially an S-shaped north-south channel, extending from the Arctic Ocean in the north to Antarctica in the south and situated between the eastern coast of North and South America and the western coasts of Europe and Africa. The Atlantic Ocean proper has a surface area of about 82 million sq km (31.7 million sq mi). Including its marginal seas—the Gulf of Mexico-Caribbean Sea, the Arctic Ocean, and the North, Baltic, Mediterranean, and Black seas—the total area is about 106,190,000 sq km (41 million sq mi). It covers 24 per cent of the global ocean area.

The boundary between the North Atlantic and the Arctic Ocean is arbitrarily designated as lying along a system of submarine ridges that extend between the land masses of Baffin Island, Greenland, and Scotland. More clearly defined is the boundary with the Mediterranean Sea at the Strait of Gibraltar and with the Caribbean Sea along the arc of the Antilles. The South Atlantic is arbitrarily separated from the Indian Ocean on the east by the 20° east meridian and from the Pacific on the west along the line of shallowest depth between Cape Horn and the Antarctic Peninsula.

III

Geological Formation and Structural Features

The Atlantic began to form during the Jurassic period, about 150 million years ago, when a rift opened up in the supercontinent of Gondwanaland, resulting in the separation of South America and Africa. The separation continues today at the rate of several centimetres a year along the Mid-Atlantic Ridge. Part of the midoceanic ridge system that girdles the world, it is a submarine ridge extending north to south in a sinuous path midway between the continents. Roughly 1,500 km (930 mi) wide, the ridge has a more rugged topography than any mountain range on land, and is a frequent site of volcanic eruptions and earthquakes. The ridge ranges from about 1 to 3 km (0.6 to 2 mi) above the ocean bottom.

Along the American, Antarctic, African, and European coasts are the continental shelves—embankments of the debris washed from the continents. Submarine ridges and rises extend roughly east-west between the continental shelves and the Mid-Atlantic Ridge, dividing the eastern and western ocean floors into a series of basins, also known as abyssal plains. The three basins on the American side of the Mid-Atlantic Ridge are more than 5,000 m (16,400 ft) deep: the North American Basin, the Brazil Basin, and the Argentina Basin. The Eurafrican side is marked by several basins that are smaller but just as deep: the Iberia, Canaries, Cape Verde, Sierra Leone, Guinea, Angola, Cape, and Agulhas basins. The large Atlantic-Antarctic Basin lies between the southernmost extension of the Mid-Atlantic Ridge and Antarctica.

The Atlantic Ocean has an average depth of 3,926 m (12,881 ft). At its deepest point, in the Puerto Rico Trench, the bottom is 8,742 m (28,681 ft) below the surface.

IV

Islands

The largest islands of the Atlantic Ocean lie on the continental shelves. Newfoundland is the principal island on the North American shelf; the British Isles are the major island group of the Eurafrican shelf. Other continental islands include the Falkland Islands (Islas Malvinas), the only major group on the South American shelf, and the South Sandwich Islands on the Antarctic shelf.

Oceanic islands, usually of volcanic origin, are less common in the Atlantic Ocean than in the Pacific. Among these are the island arc of the Antilles (including Puerto Rico, Hispaniola, Jamaica, and Cuba). In the eastern Atlantic, the Madeiras, Canaries, Cape Verde, and the São Tomé-Príncipe group are the peaks of submarine ridges. The Azores, St Paul's Rocks, Ascension, and the Tristan da Cunha group are isolated peaks of the Mid-Atlantic Ridge system; the large island of Iceland is also the result of volcanic action at the Mid-Atlantic Ridge. Bermuda rises from the floor of the North American Basin, and St Helena from the Angola Basin.