The Sargasso Sea is the subject of both legend and scientific research

This edited article about the Sargasso Sea originally appeared in Look and Learn issue number 738 published on 6 March 1976.

The Sargasso Sea and its abundant sea-weed

The crews of Christopher Columbus’s little ships gazed in astonishment. As far as the eye could see, the surface of the ocean was covered by tangled mats of brown seaweed.

Their first thought was that they had reached shallow waters, and that land could not be far away. But their landfall in the Bahamas was still hundreds of miles distant; and the part of the Atlantic where they found themselves reaches depths of more than 15,000 feet (4,572 m.).

Nowhere else in the world is there anything to compare with this vast sea of weed, which we call the Sargasso Sea. Though Columbus found the seaweed no obstacle, its strange and sinister appearance struck fear into the hearts of many old-time sailors. Stories were told of ships becoming entangled in the weeds, with the crews dying of thirst and starvation in their trapped vessels.

Another belief widely held was that the Sargasso was the “graveyard of the ocean”, to which all drifting ships in the Atlantic eventually found their way.

We now know that these were no more than superstitious seamen’s tales; though the true facts about the Sargasso Sea are interesting enough.

It is part of the Atlantic Ocean lying to the east of the Bahamas. Roughly oval in shape, it stretches about 2,000 miles (3,200 km.) from west to east, and has an area about eight times that of France.

The Sargasso has been compared to the hub of a wheel, the great Atlantic currents forming the rim. Running north-east from the Gulf of Mexico is the Gulf Stream. This links in the eastern Atlantic with the southward-flowing Canaries current, part of whose waters swing westward with the Northern Equatorial current. The circle is completed in the west by the Antilles Current, which joins up with the Gulf Stream again.

The Sargasso Sea lies within this vast circle of currents. It is itself relatively free of currents, and it lies in an area in which strong winds are rare.

The sargassum, or gulfweed, which gives it its name is related to species that grow along the shores of North America and the Caribbean. It was no doubt first carried there by the currents that scour the shores, but the Sargasso weed long ago evolved distinctive forms.

It has branches growing from a short central stem. From these branches grow smaller ones, some of which bear the little bladders, or “berries”, that keep it afloat. The original Portuguese word for the weed was sarga√ßo, the name of a small grape which the bladders were thought to resemble.

The evaporation rate in the Sargasso Sea is high, which makes the salt content greater than average. To a depth of about 3,000 feet (919 m.), its waters are several degrees warmer than normal in those latitudes. The effect of this is that minerals that would in the ordinary way rise from the sea-bed are trapped in the cold bottom layers of water. Without these nourishing minerals, there is a shortage of plankton and other minute marine life, on which many sea creatures depend for food. As a result, the Sargasso Sea, beneath its weed-strewn surface, is almost empty of life, and has been called a marine desert. It is this which makes the water exceptionally clear, and blue.

If the waters below are almost devoid of life, the floating islands of weed are teeming with it, in some cases forms which are normally found close to the shore. The branches of weed are infested with sargassum sea-slugs which are themselves branched and coloured to resemble the weed.

Another remarkable creature camouflaged to blend with this background is the sargassum fish. Even at close range it is almost indistinguishable from its background, as it crawls among the weeds on stumpy fins. It does not grow longer than about three inches (75 mm.), but it has an insatiable appetite for other small fish – even some larger than itself.

Dozens of other creatures find a living in the gulfweed, including shrimps, sea-horses and porcupine fish, while between the patches float Portuguese man-of-war jelly-fish, trailing their stinging tentacles through the water.

The fact that many species have evolved habits and characteristics to suit these unusual conditions shows that the Sargasso Sea is very old. Even before the time of Columbus, its existence was known. It should have come as no surprise to him, as an Italian map drawn half a century before his voyage, shows a “sea of berries” in the Atlantic.

It is easy to understand how the Sargasso gained its grim reputation. Not only did it present a forbidding sight to ignorant sailors voyaging far from their homelands. When their ships were becalmed there for long periods, they may have thought that it was the weed that held their vessels captive, rather than the lack of wind.

It is also likely that any wrecked or abandoned ship that did drift into the Sargasso would tend to stay there. Such would be the origin of the “ships’ graveyard” legend.

Now it is no longer regarded as a menace to shipping, but a curiosity to be studied by oceanographers and observers of marine life.