If you had to draw the boundaries of the Earth's oceans on a map, would you be able to? The answer is no—because there is really only one "world ocean."

Oceanographers have divided the world ocean into four principal areas: the Pacific, Atlantic, Indian, and Arctic Oceans. The Atlantic, Indian, and Pacific Oceans merge into icy waters around Antarctica. Some oceanographers define this as a fifth ocean, usually called the Antarctic or Southern Ocean.

Water, animals, plants, pollution, and people can move throughout the world ocean. This makes ocean stewardship challenging.

National Geographic Explorer-in-Residence Enric Sala discusses the five areas of the world ocean in this collection of videos. The videos are taken from the interactive online game, My Ocean. Test your ocean knowledge and learn about the different ocean basins of the world ocean by playing here.