Ocean

Three quarters of the surface of the Earth is covered by ocean. This global, interconnected body of salt water is divided by the continents and larger archipelagos into five oceans as follows:

• Arctic Ocean
• Atlantic Ocean
• Indian Ocean
• Pacific Ocean
• Southern Ocean

The boundaries between the oceans are set by the International Hydrographic Organization; e.g., the Southern Ocean extends from the coast of Antarctica to 60 degrees south latitude. Smaller regions of the oceans are known as seas, gulfs, straits, etc.

See sea water for a detailed discussion of ocean water composition, most notably its salinity.

Exploration

Study of Earth's oceans is called oceanography. Travel on the surface of the ocean through the use of boats dates back to prehistoric times, but only in modern times has extensive underwater travel become possible.

The deepest point in the ocean is the Marianas Trench located in the Pacific Ocean near the Northern Mariana Islands. It has a maximum depth of 10,924 m (35,838 ft). It was fully surveyed in 1951 by the British navy vessel, "Challenger II" which gave its name to the deepest part of the trench, the "Challenger Deep".

Climate

One of the most dramatic forms of weather occurs over the oceans: hurricanes (called typhoons in the eastern Pacific Ocean). Ocean currents greatly affect Earth's climate.

Ecology

The oceans are home to many forms of life, such as:

• fish
• cetacea such as whales, dolphins and porpoises,
• cephalopods such as the octopus
• crustaceans such as lobsters and shrimp
• marine worms
• plankton
• krill

Economy

The oceans are essential to transportation: a huge portion of the world's goods is moved by ship between the world's seaports. Important ship canals include the Saint Lawrence Seaway, Panama Canal, and Suez Canal.

Extraterrestrial oceans

Earth is the only planet known with liquid water on its surface, and is certainly the only such in our own solar system. However, liquid water is thought to be present under the surface of several moons, most notably Europa. Other icy moons may have once had internal oceans that have now frozen, such as Triton. There is currently much debate over whether Mars once had an ocean of water, and over what happened to it if it did. The planets Uranus and Neptune may also possess large oceans of liquid water under their thick atmospheres, though their internal structure is not well understood at this time.

Liquid hydrocarbons are thought to be present on the surface of Titan, though it may be more accurate to describe them as "lakes" rather than an "ocean". The distribution of these liquid regions will hopefully be better known after the arrival of the Cassini probe.

External link

• Why is the ocean salty?

Referenced By