Which sea has no land boundaries and is defined by ocean currents?

The Sargasso Sea has no land boundaries and is defined by ocean currents.

The Sargasso Sea is a region of the North Atlantic Ocean surrounded by the rotating currents of the North Atlantic Gyre. Its boundaries are commonly described 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. Unlike conventional seas, it has no coastline.

The region is named for Sargassum, a floating brown seaweed that forms large mats at the surface. Christopher Columbus described seeing abundant floating vegetation in the area during his 1492 voyage, which contributed to sailors’ concerns about slow progress.

Sargassum provides shelter and food for many marine organisms. European and American eels also use the wider Sargasso Sea region as part of their extraordinary migration and breeding cycle, although details of that life cycle remain difficult to observe directly.