In the very heart of the Atlantic Ocean, midway between the Bahamas and the Azores, lies the great body of water known as the Sargasso Sea. The designation of this part of the Atlantic as a “sea” is at first glance something of a paradox, for no land boundaries of any kind mark it off from the rest of the open ocean. There is, however, justification for the designation in the fact that the characteristics of this tract of water are so marked as to confer upon it a distinct individuality.
Its name, which is derived from the Portuguese word for seaweed, it owes to the prevalence of seaweed or gulfweed floating over its surface. Legend and myth have covered this area with islands of thickly- matted seaweed many miles in extent, peopled it with strange monsters and made of it the graveyard of missing ships. Even now, it is not uncommon to find it stated in serious publications that in certain parts, the Sargasso Sea is so thickly matted over with seaweed that vessels passing through are much retarded in their speed.
Not only is it differentiated from the rest of the Atlantic Ocean by the prevalence of gulfweed on its surface, but its waters likewise exhibit distinctive characteristics. Surrounded by great current systems which include the mighty Gulf Stream, the waters of the Sargasso Sea are relatively motionless. It is further marked off by the exceptionally high salinity and high temperature of its water as well as by its unusually deep blue color—rivaling indeed the blueness of the sunny skies above it. And coupled with this is great transparency. Here a white disc about six feet in diameter was clearly seen with the naked eye when lowered 200 feet below the surface.
Whether the Sargasso Sea was known prior to the discovery of America is still an open question. There appear to be grounds for believing that those remarkably hardy navigators of ancient times, the Phoenicians, were acquainted with it. Before the beginning of the Christian era there are references to the sea west of the Pillars of Hercules, certain parts of which are represented as being unnavigable because of seaweed. And there is a record of the fact that a Portuguese sailor told Columbus prior to his eventful journey that one of the obstacles to be overcome in the westward voyage to India was the grasses.
It appears not at all improbable that some vague knowledge of this sea existed before 1492. To Columbus, however, must be credited its discovery and the first authentic notice of the occurrence of gulfweed in this region. On his first voyage westward he encountered gulfweed for a number of days; and likewise on his return journey. In his log we find that the great navigator carefully recorded the occurrence of the gulfweed.
Viewed from the small vessels of Columbus and the other navigators of that time, the patches of gulfweed undoubtedly looked vastly more formidable than they really were. This region is one of light winds; hence a sailing vessel here made slow progress. It is therefore little wonder that stories of wide-spreading meadows of thickly-matted gulfweed which seriously impeded the progress of vessels became current. These stories, it is of interest to note, originated not with Columbus, but with his followers. Columbus himself records the occurrence of the gulfweed in a characteristically accurate manner.
The belief in the existence of great areas of thickly-matted gulfweed in the Sargasso Sea has persisted down to the present time. But with the accumulation of carefully recorded observations this has been proven to have no basis in fact. The gulfweed occurs in scattered masses up to one hundred feet in diameter, although patches covering an acre or even a little more have been seen occasionally. Sometimes under the action of the wind long strips of gulfweed are formed which follow the direction of the wind. But it has been definitely proven that there are no islands of gulfweed miles in extent, and that it is nowhere so dense as to interfere with a ship’s movements.
What explains the decided individuality of this great body of deep water lying out in the open ocean? It is upon a vast stage— measured in millions of square miles—that the activities of the Sargasso Sea take place. Many details are still unknown, and these can come only as the result of patient oceanographic research. Enough, however, is known to give an understanding of the forces and factors that give rise to the larger distinguishing features of the Sargasso Sea.
Primarily the Sargasso Sea owes its existence to the current systems that surround it. If we glance at a map showing the circulation in the North Atlantic Ocean—for example, that drawn up by Lieutenant J. C. Soley, U.S.N., and issued as a supplement to the Pilot Charts of the Hydrographic Office —it will be seen that three great current systems bound this area. On the south is the North Equatorial Current flowing westward, on the west and north is the Gulf Stream flowing northward and then eastward, and on the east is the Canary Current flowing southward. These currents thus make a closed circuit about the Sargasso Sea, and within this shelter the waters have developed a distinct individuality of their own.
The high salinity of the water is due to the concurrence of a number of factors. Situated at a considerable distance from any coast, there is no dilution by the less saline waters poured into the ocean by continental rivers. Nor is such water brought into the region by any currents, for the ocean circulation is about this sea and not into it. Freedom from melting ice likewise removes a factor that tends to lower salinity. Moreover the region is one of relatively high temperature, favoring evaporation and therefore increased salinity of the water. This latter factor is further augmented by the relatively high percentage of sunny days.
Obviously a number of the factors that bring about the high salinity are also instrumental in bringing about a relatively high temperature of the water. Its position in lower latitudes, coupled with freedom from strong currents, permits the sunny skies to maintain a heightened temperature of the water. Furthermore, it is to be noted that the girdle formed by the great current systems prevents the entrance of any considerable quantity of colder water from higher latitudes.
To its great depth, freedom from islands and distance from the continents is to be ascribed the exceptional transparency of the water in the Sargasso Sea. The greater part of this region is between 2,000 and 3,000 fathoms in depth—altogether too deep for any storm waves to stir the sediments lying at the bottom. And because of its distance from the coast, all sediments brought down by continental rivers are precipitated long before they can reach this region.
Another factor that makes for the great transparency of the water and at the same time helps explain the deep blue color is the poverty of the Sargasso Sea in the minute plant and animal life that goes under the name of plankton. This term has come into use to describe the minute marine organisms that without volition are carried hither and thither by currents. It has been found in general that waters rich in plankton appear green, while waters poor in plankton appear blue. And oceanographic research has shown that the Sargasso Sea is poorer in plankton than any other region in the North Atlantic.
The origin of the seaweed or gulfweed found in these waters has been a matter of controversy from the very beginning. A plausible theory which was early accepted was that it grew on submarine banks near the Azores and Bermuda from which it was torn loose by the action of the waves and spread over the area by current and wind. The sounding lead, however, soon showed the depth in this region to be altogether too great for the existence of such banks. The well known expedition under Lieutenant S. P. Lee in the U. S. Brig Dolphin during the years 1851 and 1852, which found depths here always exceeding 2,000 fathoms, made the theory of submarine banks in the Sargasso Sea supporting a growth of gulfweed altogether untenable.
Following this, it was thought for many years—down to the present time in fact—that the gulfweed came from the shores of the West Indies and the Bahamas. Under this theory the gulfweed was represented as being torn loose by wind and wave and, coming within the sweep of the Gulf stream, being borne into the Sargasso Sea. Here it drifted for a year or more; and, dying, sank beneath the waves, the place of this dying gulfweed being taken by a new crop brought in by the Gulf Stream from its place of birth.
It was known, however, that the gulfweed drifting in the Sargasso Sea was destitute of the ordinary organs of reproduction which are found on the gulfweed that grows attached along the coast. This raised the question whether the Sargasso Sea gulfweed is not a different species which is born, lives, and dies in the open sea. This is answered in the affirmative by the most competent authorities of the present day. According to the latest theory, therefore, the gulfweed in the Sargasso Sea is an adaptation of the plant to the open sea. It does not come from the coast but lives and propagates vegetatively or by partition year after year. Some replenishment from coastal plants is conceded, but such replenishment is regarded as of very minor importance in the maintenance of the Sargasso Sea as a whole.
If the gulfweed within this sea originated in the shallow waters along the Bahamas and West Indies it is reasonable to expect that some of the floating plants would be found with roots attached. But it is a curious fact that the gulfweed in the Sargasso Sea has no roots or other organs of attachment. It floats on the water supported by the small air sacks with which it is provided. This absence of roots is therefore another point in favor of the independent origin of the gulfweed in this region.
The gulfweed occurs most frequently and in the greatest quantity within the central part of the sea. Farther out it occurs less and less frequently. Drifting patches may under the action of varying winds and current be carried to places which at other times are free from gulfweed. Where, therefore, shall the limits of the Sargasso Sea be set? For practical purposes they may be extended to cover the region bounded by the twentieth and fortieth parallels of north latitude and by the thirty-fifth and seventy-fifth meridians west of Greenwich. These limits will cover the area within which gulfweed may be expected to occur, and within these limits the Sargasso Sea occupies an area of approximately 3,000,000 square miles.
How large a quantity of gulfweed is there in the region? Occurring as it does in scattered patches over so large an area it is obvious that to answer this question with any pretense at precision would require rather extensive observations. It is an interesting question, however, and one navigator familiar with this region has estimated the floating gulfweed in this region to aggregate 20,000,000 tons.
A varied and specially adapted animal life is found in the Sargasso Sea. This special adaptation may be taken to testify not only to the independent origin of the gulfweed here, but as testimony also to the great age of the Sargasso Sea. But, curiously enough, it has been discovered that this sea is singularly poor in bird life. To be sure, the greater part of this region is at a considerable distance from land; but in other regions of the North Atlantic which are just as far from land the frequency of birds is many times that in the Sargasso Sea. The explanation of the scarcity of birds here appears to be that the masses of drifting gulfweed afford a hiding place for the fishes and crabs that serve as food for birds, making capture more difficult than in areas free from gulfweed.
In recent years a further discovery has been made that marks the Sargasso Sea off from other regions of the open ocean. It has been found that the European eels, which occur in great numbers in the North Sea, in the Baltic and in the Mediterranean, have their breeding grounds within the warm and saline waters of the Sargasso Sea. Here at the close of winter the eels spawn. In the course of the following year the larvae disappear from the spawning grounds, having moved into the central Atlantic region, and a year later they appear on the western shores of Europe and in the Mediterranean.