One of the major subdivisions of the interconnected body of salt water that occupies almost three-quarters of the Earth's surface. Earth is the only planet in the solar system whose surface is covered with significant quantities of water. Of the nearly 1.4 billion cubic kilometers of water found either on the surface or in relatively accessible underground supplies, more than 97% is in the oceans. Oceanography

Oceans and the seas that connect them cover some 73% of the surface of the Earth, with a mean depth of 3729 m (12,234 ft) (see table). More than 70% of the oceans have a depth between 3000 and 6000 m (10,000 and 20,000 ft). Less than 0.2% of the oceans have depths as great as 7000 m (23,000 ft).

The oceans are cold and salty. Some 50% have a temperature between 0 and 2°C (32 and 36°F) and a salinity between 34.0 and 35.0. To a high degree of approximation, a salinity of 34 is the equivalent of 34 grams of salt in a kilogram of seawater. Water with a temperature above a few degrees Celsius is confined to a relatively thin surface layer of the ocean. Seawater

Ocean salinity is primarily controlled by the balance of precipitation, river runoff, and evaporation of water at the sea surface. The highest salinities are found in major evaporation basins with little rainfall or river runoff, such as the Red Sea. The lowest salinities are found near the mouths of major rivers such as the Amazon. Red sea

Nearly all elements known to humankind have been found dissolved in seawater, and those that have not are assumed to be present. However, all but a few are found in very small amounts. Sodium chloride accounts for some 85% of the dissolved salts, and an additional four ions (sulfate, magnesium, calcium, and potassium) bring the total to more than 99.3%. The ratio of ions is remarkably constant from one ocean to another and from top to bottom of each.

The oceans are continually transporting excess heat (warm water) from the tropics toward the Poles and returning colder water toward the tropics. This process of moving excess heat from lower (south of 40°) to higher (north of 40°) latitudes is shared approximately equally by the oceans and the atmosphere. A significant part of the ocean heat exchange process is carried out by the major ocean currents, the “named” currents such as the Gulf Stream, Brazil Current, California Current, and Kuroshio. These currents are primarily driven by the winds, and there is considerable similarity in their pattern from one ocean basin to another. Gulf stream

The average winds over the North and South Atlantic as well as the North and South Pacific oceans come out of the west (westerlies) at the middle latitudes and from the east at the lower latitudes (trade winds). The frictional drag of these winds on the surface of the water imparts a spin or torque to the surface of the ocean, clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. The major exception is the Indian Ocean north of the Equator, where the circulation is strongly influenced by the winds of the seasonal monsoon.Atlantic ocean Equatorial currents Indian ocean Ocean circulation Pacific ocean