The World Ocean or Global Ocean (colloquially the sea or the ocean) is the interconnected system of Earth’s oceanic waters, and comprises the bulk of the hydrosphere, covering 361,132,000 square kilometres or 139,434,000 square miles (70.8%) of Earth’s surface, with a total volume of roughly 1,332,000,000 cubic kilometres (320,000,000 cubic miles). The unity and continuity of the World Ocean, with relatively free interchange among its parts, is of fundamental importance to oceanography. It is divided into a number of principal oceanic areas that are delimited by the continents and various oceanographic features: these divisions are the Atlantic Ocean, Arctic Ocean (sometimes considered an estuary of the Atlantic), Indian Ocean, Pacific Ocean, and Southern Ocean, defined by the International Hydrographic Organization (IHO) in 2000, based on evidence that this region of the World Ocean has a distinct ecosystem and a unique impact on global climate.
