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The Sargasso Sea

a region of the Atlantic Ocean known for its clear water, extreme saltiness, and masses of seaweed

A line drawn from the mouth of the Chesapeake Bay to Gibraltar would skirt the northern border of the Sargasso Sea; another from Haiti to Dakar would mark its southern boundary. It extends more than halfway across the Atlantic, and has an area roughly the size of the United States (about 2 million square miles).

location of the Sargasso Sea
location of theSargasso Sea

The Sargasso is a creation of the great currents of the North Atlantic that encircle it and bring into it the millions of tons of floating sargassum weed, from which the place takes its name. Under the seldom-clouded skies, the waters of the Sargasso Sea grow warm and heavy with salt. There is no fresh water coming in to dilute its saltiness, for it is far from coastal rivers and from polar ice. The only inflow is of salty water from the nearby currents, especially from the Gulf Stream. And with the little inflowing streams come the plants and animals that for months or years have drifted in the Gulf Stream.

a wide-angle aerial view of the Sargasso Sea showing many, many masses of sargassum
bird's-eye view of the Sargasso Sea

Where exactly the sargassum originates is not known. Some say that the supply is kept up by weeds recently torn away from coastal beds. Others say the sargassum fields of the West Indies and Florida are too limited to supply the immense sea of the Sargasso and that the community of plants within the sea maintains itself. The plants have become adapted to life in the open sea, need no roots or holdfasts for attachment, and are able to propagate by breaking off bits to grow into new plants. There is probably truth in both ideas.

No matter how they get there, sargassum plants that reach the calm of the Sargasso seem to live forever. The individual plants may live for decades, if not centuries, depending on specific species. It is estimated that there may be 10 million tons of sargassum weeds within the Sargasso Sea. But this, of course, is distributed over so large an area that most of the Sargasso is open water. The dense fields of weeds which sailors once believed were waiting to entrap a vessel never existed except in their imagination.

Many small marine animals have adapted themselves to growing on and among the weeds, including tiny crabs, shrimps, and barnacles. Fish can see at depths as great as 1,200 feet in the Sargasso Sea, the deepest that fish can see in any ocean. Sargassum fish are difficult to distinguish from Sargassum weeds, because the fish have taken on the colors and patterns of the weeds.

The waters of the Sargasso Sea have many distinctive features -- an unusually deep blue color, a high salt content (3.7 per cent), a high temperature (up to 83 F.), and extreme clearness. These features result chiefly from the location of the sea and its great depth, averaging over 3 miles. Also, there are no islands nearby except for Bermuda.

Sargasso Sea from the surface, showing the extremely blue water and some of the characteristic sargassum
Sargasso Sea at the surface


Our Wonderful World New York: Grolier Incorporated, 1965

See Also

Gulf Stream

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The Robinson Library >> Oceanography

This page was last updated on 10/16/2018.