The Sargasso Sea is a vast patch of ocean named for a genus of free-floating seaweed called Sargassum. It was discovered in 1492 by Columbus, who was delayed in it for a fortnight. For centuries afterwards weird tales were told of ships being caught and lost in this dreaded tangle of Gulf-weed. In fiction, the region becomes a plot device starting in the late 19th century with Julius Chambers’ In Sargasso (1896) and Thomas A. Janvier’s In the Sargasso Sea (1898). In Lost Worlds, L. Sprague de Camp describes the latter work: "Some odd ideas are current about the Sargasso Sea because in 1896 [sic] the novelist T.A. Janvier wrote a gripping novel, In the Sargasso Sea, in which he described the tract as an impenetrable tangle of weed holding fast the remains of ships of all ages from Spanish galleons down."
The “impenetrable tangle” would become a distinctly supernatural “borderland” in the Sargasso Sea cycle of William Hope Hodgson, a collection of short stories published between 1906 and 1920. But in 1910, the Norwegian Government sent an expedition to explore the Sargasso Sea. It was then found that the weed did not extend in one dense mass, but that it occurred in patches, some of them covering an immense area.
While there are many different types of seaweed found floating in the ocean all around world, the Sargasso Sea is unique in that it harbors species of sargassum that are 'holopelagi' - this means that they not only freely float around the ocean, but it reproduces vegetatively on the high seas. Other seaweeds reproduce and begin life on the floor of the ocean.
Sargassum provides a home to an amazing variety of marine species. Turtles use sargassum mats as nurseries where hatchlings have food and shelter. Sargassum also provides essential habitat for shrimp, crab, fish, and other marine species that have adapted specifically to this floating algae. The Sargasso Sea is a spawning site for threatened and endangered eels, as well as white marlin, porbeagle shark, and dolphinfish. Humpback whales annually migrate through the Sargasso Sea. Commercial fish, such as tuna, and birds also migrate through the Sargasso Sea and depend on it for food.
Seas are smaller than oceans and are usually located where the land and ocean meet. Typically, seas are partially enclosed by land. While all other seas in the world are defined at least in part by land boundaries, the Sargasso Sea is defined only by ocean currents. It lies within the Northern Atlantic Subtropical Gyre. The Gulf Stream establishes the Sargasso Sea's western boundary, while the Sea is further defined to the north by the North Atlantic Current, to the east by the Canary Current, and to the south by the North Atlantic Equatorial Current. Since this area is defined by boundary currents, its borders are dynamic, correlating roughly with the Azores High Pressure Center for any particular season.
The open-ocean ecosystem of the Sargasso Sea generally lies beyond the jurisdiction of any country. One exception is the portion of the Sargasso Sea surrounding Bermuda. Although Bermuda is undertaking various steps to protect the sea within its jurisdiction, improved protection of the Sargasso Sea requires international coordination.
By 2015 many islands in the Caribbean were suffering from an invasion of sargassum, a type of brown seaweed that stinks when in washes ashore and starts to rot. In the French overseas territory of Guadeloupe, residents are complaining about the seaweed’s effect on the environment, as well as on the local economy. Some are even worried about their health.
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