Within the Atlantic Ocean is the world's only sea without shores, its borders defined by the currents of the North Atlantic gyre. The Sargasso Sea takes its name from sargassum, a free-floating golden brown seaweed that is a haven for hatchling sea turtles and hundreds of other marine species who use it to feed, grow and hide from predators.
But the sargassum is now home to objects wholly unnatural too.