The World Ocean, or the Sea is the earth’s unique saltwater reservoir and subdivided into smaller geographical units named oceans and seas. The World Ocean corresponds to the largest part of the planet’s hydrosphere as it represents approx 97% of the water on earth. The ocean covers more than two thirds (71%) of the earth’s surface, 90% of its biosphere and plays a crucial role for our life on earth. Nonetheless, it is estimated that less than 5% of the World Ocean has been explored.
The World Ocean is commonly subdivided into the three main oceans (Pacific, Atlantic & Indian Oceans), whose limits vary if the Southern and Arctic Oceans are taken into account. Each of these oceans is further subdivided into several seas that are defined by more or less enclosed divisions of an ocean.