The Sargasso Sea is the only sea defined by ocean currents rather than land coastlines.
It lies in the North Atlantic Ocean and is bounded by the clockwise circulation of the North Atlantic subtropical gyre. The surrounding currents include the Gulf Stream, the North Atlantic Current, the Canary Current, and the North Atlantic Equatorial Current.
The sea is named for Sargassum, a floating brown seaweed that forms large mats at the surface. Portuguese sailors encountered the seaweed during early Atlantic voyages and gave it names related to grapes because of the plant’s berry-like air bladders.
The Sargasso Sea is important habitat for animals including eels, sea turtles, and seabirds. Its boundaries shift with the currents, so it is not a fixed region enclosed by coastlines like the Mediterranean or Caribbean seas.