What is the only sea with no coastline, lying within the North Atlantic Ocean?

The Sargasso Sea is the only sea with no coastline, lying within the North Atlantic Ocean.

Instead of being enclosed by land, the Sargasso Sea is defined by ocean currents. Its approximate boundaries are formed by 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 create a large rotating system known as the North Atlantic subtropical gyre.

The region is famous for floating mats of Sargassum, a brown seaweed that gives the sea its name. Unlike many seaweeds, Sargassum can remain afloat and provide shelter and food for fish, crabs, shrimp, and other organisms. Young sea turtles also use the habitat during parts of their development.

Christopher Columbus described the seaweed during his first voyage across the Atlantic in 1492. The Sargasso Sea’s position and boundaries shift with ocean conditions, so it is not a sharply outlined geographic basin. It is also important in the life cycle of European and American eels, which migrate there to spawn.