OVERVIEW

The sea covers more than 70 percent of the Earth's surface with liquid water.^[1] Seen from space, our planet appears as a "blue marble" of various forms of water: salty oceans, sea ice, clouds.^[2] The science fiction author Arthur C. Clarke once suggested that "Earth" should have been named "Ocean" as the sea is its dominant feature.^[1]

The sea is from one point of view the World Ocean, the interconnected system of all the Earth's oceanic waters.^[3] About 97.2 percent of the Earth's water is found in the sea, some 326 million cubic miles (1360 million cubic kilometres) of salty water.^[4] Of the rest, 2.15 percent is accounted for by ice in glaciers, surface deposits and sea ice, and 0.65 percent is in the form of vapour or liquid fresh water in lakes, rivers, the ground and air.^[4]

The word "sea" can also be used for specific, much smaller bodies of water, such as the North Sea or the Red Sea. There is no sharp distinction between seas and oceans, though generally seas are smaller, and are often partly (as marginal seas) or wholly (as inland seas) bordered by land.^[5] However, the Sargasso Sea has no coastline and lies within a circular current, the North Atlantic Gyre. It is a distinctive body of water with brown Sargassum seaweed and calm blue water, very different from the rest of the Atlantic Ocean.^[6][7] Seas are generally larger than lakes and contain salt water rather than freshwater, but some geographic entities known as "seas" are enclosed inland bodies of water that are not salty: for instance, the Sea of Galilee is a freshwater lake.^[7][a] The Law of the Sea states that all of the ocean is "sea".^{[11][12][13][b]}

"Freedom of the seas" is a principle in international law dating from the seventeenth century. It stresses freedom to navigate the oceans and disapproves of war fought in international waters.^[15] Today, this concept is enshrined in the United Nations Convention on the Law of the Sea, which came into force in 1994. Article 87(1) states: "The high seas are open to all states, whether coastal or land-locked." Article 87(1) (a) to (f) gives a non-exhaustive list of freedoms including navigation, overflight, the laying of submarine cables, building artificial islands, fishing and scientific research. Territorial waters extend to 12 nautical miles (22 kilometres; 14 miles) from the coastline and in these waters, the coastal state is free to set laws, regulate use and exploit any resource.^[15]