Ocean is a vast body of salt water on Earth, mostly separated by continents. It is a principal component of the global hydrosphere, essential to life on Earth and its climate, and – as a huge heat reservoir – influences weather patterns. The ocean also plays a critical role in the carbon cycle, and it provides a substantial portion of Earth’s oxygen.
Scientists use the term ocean to refer to the whole of the world’s marine waters, not just those waters that are close to land. This includes the Arctic, Atlantic, Indian, Pacific, and Southern Oceans. Oceanographers generally do not distinguish between these regions based on water properties or ocean currents; instead, they use the geographical boundaries of the continents that frame them.
The ancient Greeks believed that the name for the ocean came from a Titan named Oceanus (). The word ocean is actually derived from two Latin words: oceanus, meaning “large sea”, and marinus, meaning “of or belonging to the sea”.
The world’s oceans are a vital part of our planet. They provide food for fish, whales and other animals, and help to stabilize the planet’s temperature, balance its chemical composition, and regulate its atmosphere. Oceans are also important sources of raw materials for industry, transportation and communication.
In addition to the water itself, the ocean contains a great deal of organic matter – including dead organisms and their shells. This material, known as detritus or organic debris, makes up a significant fraction of the total mass of the ocean. It is a source of much of the pollution that enters the ocean and contributes to ocean acidification, which erodes the shells of corals and other marine creatures.
Human activities on and around the ocean are widespread, varied, and often destructive. These activities include exploration and navigation, naval warfare, trade and shipping, fishing and whaling, recreational boating and scuba diving, marine leisure (e.g., cruising, sailing and beachcombing), sport fishing and yacht racing, aquaculture, offshore oil and gas drilling and deep sea mining, and the production of freshwater through desalination.
Marine species range in size from microscopic phytoplankton, the basis of the ocean’s food chain, to massive cetaceans like blue whales that can be 33 m or 108 ft long. The resulting ecological interactions are studied by scientists in the fields of marine biology and biological oceanography.
The oceans cover 71 percent of the planet and are a major source of energy for living things. They are also a significant repository of carbon dioxide, a greenhouse gas that traps radiation and raises Earth’s temperatures. The increasing level of carbon dioxide in the atmosphere, due to human activity, is contributing to ocean warming and acidification. This threatens the survival of many ocean ecosystems. The scientific community recognizes the need to understand these environmental changes and develop strategies to protect and conserve the world’s oceans. These issues are addressed by the United Nations Division for Ocean Affairs and the Law of the Sea, and other organizations.