Which sea is the only sea on Earth without a coastline?

The Sargasso Sea is the only sea on Earth without a coastline.

It is a region of the North Atlantic Ocean defined by ocean currents rather than land boundaries. The North Atlantic Current forms its northern edge, the Canary Current its eastern edge, the North Atlantic Equatorial Current its southern edge and the Gulf Stream its western edge. These currents create the clockwise North Atlantic subtropical gyre.

The sea is named for Sargassum, a floating brown seaweed that forms large mats on the surface. Portuguese sailors noticed the seaweed during voyages in the Atlantic, and Christopher Columbus recorded seeing it in 1492. Sargassum provides shelter and feeding areas for young sea turtles, fish, crabs and other marine life.

The Sargasso Sea is not a sharply outlined body like a lake or a coastal sea. Its boundaries shift with currents and seasons. It has also been linked in popular culture to legends about ships disappearing, although the region is a real oceanographic area rather than a supernatural zone.