Which sea is the only sea on Earth with no land boundary?

The Sargasso Sea is the only sea on Earth with no land boundary, being defined by ocean currents instead.

It lies in the North Atlantic and is surrounded by four major currents: the Gulf Stream to the west, the North Atlantic Current to the north, the Canary Current to the east and the North Atlantic Equatorial Current to the south. These currents form a large rotating system called the North Atlantic subtropical gyre.

The sea is named for Sargassum, a floating brown seaweed that gathers in extensive mats at the surface. Unlike coastal seas, the Sargasso has no fixed shoreline, so its precise edges can shift with changing currents.

The area has long been linked in popular culture with stories of ships becoming trapped in calm waters. It is also ecologically important: floating Sargassum provides habitat for young eels, sea turtles, fish and seabirds.