Which sea is defined by ocean currents rather than a coastline?

The Sargasso Sea is defined by ocean currents rather than a coastline.

It lies in the North Atlantic Ocean and is bounded by the circular system of currents known as the North Atlantic Subtropical Gyre. The Gulf Stream forms its western boundary, the North Atlantic Current its northern boundary, the Canary Current its eastern boundary and the North Atlantic Equatorial Current its southern boundary.

The sea is named for Sargassum, a brown seaweed that floats at the surface in large mats. Portuguese sailors noticed the vegetation during the Age of Discovery and called the region the Sargasso Sea. Unlike almost every other named sea, it has no land boundary.

The Sargasso Sea is an important habitat for young eels, which travel thousands of kilometres from European and North American rivers to spawn in the region. Oceanographers also study its floating seaweed communities as shelter and food sources for marine animals.