GEOGRAPHY

About seventy per cent of the surface of the Earth is covered by the oceans. More than one-fifth of the surface is covered by the Atlantic Ocean, the second largest ocean in the world.

The Atlantic Ocean lies between North America and Europe in the north and Africa and South America in the south, stretching from the Arctic to the Antartic. At its margins are seas such as the Gulf of Mexico. Waters from many of the greatest rivers of the world including the Amazon, Congo and Niger flow into the Atlantic.

The average depth of the Atlantic Ocean is 3,900 meters (12,800 ft). The ocean bed is made up of hills, mountains, tablelands and valleys just as on dry land.

TIDES/CURRENTS AND TEMPERATURE

The waters of the Atlantic ocean, like those of all the world's seas and oceans, are moved by tides and currents.

The currents of the ocean folllow the paths of the prevailing winds.

In the North Atlantic the currents move clockwise, the most famous being the Gulf Stream which carries warm water from the Caribbean and the Gulf of Mexico up the east coast of the USA and then out across to the British Isles.

In the South Atlantic the currents run counter-clockwise.

The currents affect the land temperature of the countries whose shores they pass; they also carry plankton and other marine life, with the cold currents such as the South Atlantic's Benguela Current particularly important to the fishing industry.

Where the Gulf Stream meets the cold Labrador Current off Newfoundland the mixing of warm and cold produces thick fogs and the rich marine life supports the huge fish stocks of the Grand Banks. The Labrador Current also brings icebergs, one of which was responsible for the Atlantic's most famous shipwreck, the Titanic.

While the surface currents of warm water move in one direction, deep below them the colder waters are moving in the opposite direction.

HISTORY

The Atlantic Ocean was formed in the Jurassic Period approximately 150 million years ago.

Between two hundred and three hundred and fifty million years ago, when the Atlantic Ocean did not exist, all today's continents were joined together in one giant continent - Pangaea. The irregular coast lines of America (North and South) and Africa show, as they can almost be fitted together like pieces from a jigsaw puzzle, the way in which the giant continent broke apart.

Down the middle of the Atlantic, throughout its length, runs an undersea mountain range called the Mid Atlantic Ridge. The valleys, or trenches, on either side of the Ridge mark the edges of the great plates which float on the earth's molten core and carry the continents. Along the centre of the mid-Atlantic ridge the sea floor is still cracking and moving apart - the cracking causes earthquakes.

The undersea mountains have become the islands of the Atlantic such as St Helena.The volcanic activity continues today as we can see in the eruptions that have driven people from their homes in Montserrat.

It is believed that the first explorers to venture beyond the Straits of Gibraltar were the Phoenicians. The Carthaginians sailed down the west coast of Africa, reaching further than the Gambia River. In the North Atlantic the Vikings colonised Iceland and then sailed to Greenland. It is believed that they also sailed, from Greenland, to North America.

Christopher Columbus, searching for a quicker way to the important markets of India and China, sailed westwards and landed on islands in the Caribbean (1492). Although he was mistaken in his belief that he had discovered a new way to the Indies, his voyages led to the discovery and colonisation of North, Central and South America.

LIFE IN THE ATLANTIC OCEAN

The Atlantic is the home of a wide range of creatures. In the shallow waters of the continental shelf, before the sea bed drops away to the ocean depths there is the familiar marine life such as crabs, lobsters and shrimps, molluscs (clams, mussels, snails). On the rocks and reefs live sea anemones, sponges and corals. The shallow waters are also the home of many varieties of fish, and of eels, octopus and squid. These are fed on by creatures higher up the food chain, for example, seals and dolphins.

In the deeper ocean, beyond the continental shelf, the waters are cold, and dark. At greater depths life must be able to withstand greater water pressure and survive without light. Animals living on or near the sea bed rely on food which drifts down from above or on eating smaller creatures. Microscopic organisms, known as plankton drift on the ocean currents and provide a food for creatures higher up the food chain such as whales and dolphins.

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