Far from being the original home of life, the deep sea has probably been inhabited for a relatively short time. While life was developing and flourishing in the surface waters, along the shores, and perhaps in the rivers and swamps, two immense regions of the earth still forbade invasion by living things. These were the continents and the abyss. As we have seen, the immense difficulties of surviving on land were first overcome by colonists from the sea about 300 million years ago. The abyss, with its unending darkness, its crushing pressures, its glacial cold, presented even more formidable difficulties. Probably the successful invasion of this region—at least by higher forms of life—occurred somewhat later.
Yet in recent years there have been one or two significant happenings that have kept alive the hope that the deep sea may, after all, conceal strange links with the past. In December 1938, off the southeast tip of Africa, an amazing fish was caught alive in a trawl—a fish that was supposed to have been dead for at least 60 million years! This is to say, the last known fossil remains of its kind date from the Cretaceous, and no living example had been recognized in historic time until this lucky net-haul.
The fishermen who brought it up in their trawl from a depth of only 40 fathoms realized that this five-foot, bright blue fish, with its large head and strangely shaped scales, fins, and tail, was different from anything they had ever caught before, and on their return to port they took it to the nearest museum. This single specimen of Latimeria, as the fish was christened, is so far the only one that has been captured, and it seems a reasonable guess that it may inhabit depths below those ordinarily fished, and that the South African specimen was a stray from its usual habitat.*
Occasionally a very primitive type of shark, known from its puckered gills as a ‘frillshark,’ is taken in waters between a quarter of a mile and half a mile down. Most of these have been caught in Norwegian and Japanese waters—there are only about 50 preserved in the museums of Europe and America—but recently one was captured off Santa Barbara, California. The frillshark has many anatomical features similar to those of the ancient sharks that lived 25 to 30 million years ago. It has too many gills and too few dorsal fins for a modern shark, and its teeth, like those of fossil sharks, are three-pronged and briarlike. Some ichthyologists regard it as a relic derived from very ancient shark ancestors that have died out in the upper waters but, through this single species, are still carrying on their struggle for earthly survival, in the quiet of the deep sea.
Possibly there are other such anachronisms lurking down in these regions of which we know so little, but they are likely to be few and scattered. The terms of existence in these deep waters are far too uncompromising to support life unless that life is plastic, molding itself constantly to the harsh conditions, seizing every advantage that makes possible the survival of living protoplasm in a world only a little less hostile than the black reaches of interplanetary space.
* Man’s dream of personally exploring the deepest recesses of the sea has been realized during the past decade. Persistent effort, imaginative vision, and engineering skill have produced a type of underwater craft capable of withstanding the enormous stresses imposed by the greatest depths of the sea and of carrying human observers into these realms that only a few years ago would have seemed beyond the reach of man.
The pioneer in this area of deep ocean exploration was Professor Auguste Piccard, the Swiss physicist who had already attained fame through his ascent into the stratosphere in a balloon. Professor Piccard proposed a depth-exploring vehicle which, instead of being suspended at the end of a cable like the bathysphere, would move freely, independent of control from the surface. Three such bathyscaphes (depth boats) have now been constructed. Observers ride in a pressure-resisting ball suspended from a metal envelope containing high-octane gasoline, an extremely light, almost incompressible fluid. Silos loaded with iron pellets provide ballast; the pellets are held by electomagnets, to be released by the touch of a button when the divers are ready to return to the surface. The first bathyscaphe, provided by the Fonds National de la Recherche Scientifique, which is the Belgian scientific research fund, was known as the FNRS-2. (The FNRS-1 was the stratosphere balloon, which the Fund also provided for Piccard.) The FNRS-2, in experimental unmanned dives, revealed great promise but also had certain defects which were remedied in the craft built later. The second bathyscaphe, the FNRS-3, was built under a treaty between the Belgian and French governments, under the direction of Piccard and Jacques Cousteau. Before the completion of this bathyscaphe, Professor Piccard went to Italy to begin the building of a third bathyscaphe, to be christened Trieste.
The FRNS-3 and the Trieste made the history-making descents of the 1950’s that carried man to the deepest parts of the abyss. In September 1953, Professor Piccard and his son Jacques descended in the Trieste to a depth of 10,395 feet in the Mediterranean. This was more than double the previous record. Then in 1954 two Frenchmen in the FNRS-3, Georges Houot and Pierre-Henri Willm, penetrated even deeper into the sea, to depths of 13,287 feet in the open ocean off Dakar on the coast of Africa. In 1958 the Trieste was purchased from the Piccards by the United States Office of Naval Research. The following year the Trieste was taken to Guam, in the vicinity of which lies the great Mariana Trench, in which echo soundings have revealed the deepest hole now known in any part of the ocean. On January 23, 1960, manned by Jacques Piccard and Don Walsh, the Trieste descended to the bottom of this trench, 35,800 feet (or nearly seven miles) beneath the surface.
* From The Depths of the Ocean, by Sir John Murray and Johan Hjort, 1912 edition, Macmillan & Co., p. 649.
* Even today the mystery of the scattering layer has not been completely revolved. Through an ingenious combination of new techniques, however, the picture is gradually becoming clearer. It now appears that at least in some areas—as over the continental shelf off New England—fishes may compose a substantial part of the layer. This has been determined by studying it with a sound source that embraces many frequencies (the ordinary echo sounder is a single-frequency device). This method not only reveals the vertical migration but brings out the fact that the very nature of the scattering changes with depth. Such changes are best interpreted as originating in the swim bladders of fishes, which are compressed under the increasing pressure of a descent into deeper levels of the sea but which expand with ascent toward the surface and consequent lessening of pressure. The formerly held objection that fishes could not possibly be abundant enough to account for the very widespread occurrence of the scattering layer has melted away in the light of information new techniques have given us. It was formerly supposed that a strong echo implied a very dense concentration of whatever creatures were returning the echo. Now it is realized that the tracings recorded by the echo sounder do not necessarily indicate the density of the animals in the scattering layer, so that actually a dark tracing on the record may be produced by only a few strong scatterers passing through the beam in any particular instant of time.
One of the study methods increasingly used during the 1950’s was an underwater camera correlated with an echo sounder. All pictures of fishes so obtained have been accompanied by strong echoes. None of these findings rule out the possibility that other organisms may also help to compose the scattering layer. They do furnish rather convincing evidence that fishes compose an important part of a phenomenon that, in all probability, lends itself to no single explanation, but varies as to the species composing it over the vast areas of the ocean.
*In 1957 Bruce C. Heezen of the Lamont Geological Observatory published a fascinating compilation of fourteen instances of whales entangled in submarine cables between 1877 and 1955. Ten of these accidents occurred off the Pacific coast of Central and South America, two in the South Atlantic, one in the North Atlantic, and one in the Persian Gulf. All entanglements involved sperm whales and it is possible the concentration of reports off the coasts of Ecuador and Peru may be related to a seasonal migration of these whales. The greatest depth at which a
whale was found entangled was 620 fathoms or nearly two-thirds of a mile. More whales were trapped by cables at about 500 fathoms than at any other depth, suggesting that the natural food of the sperm whale may be concentrated at about this level. Two significant details were observed in most of these cases: the entanglement occurred near the site of earlier repairs where slack cable lay on the bottom, and the cable was usually wrapped around the whale’s jaw. Heezen suggests that as a whale skims along the ocean bottom in search of food its lower jaw may become entangled in a slack loop of cable lying on the bottom. The struggles of the whale to free itself could easily result in its complete entanglement in the cable.
*For years people have speculated as to the function served by sound production on the part of marine species. It has been known for at least 20 years that the bat finds its way about in lightless caves and on dark nights by means of a physiological equivalent of radar, emitting a stream of high-frequency sound, which returns to it as echoes from any obstructions in its path. Could the sounds produced by certain fishes and marine mammals serve a similar purpose, aiding inhabitants of deep waters to swim in darkness and to find prey? Among the early tape recordings of underwater sound obtained by the Woods Hole Oceanographic Institution was a recording of some mysterious calls that emanated from waters so deep as surely to be lightless. They were distinguished by the fact that each call was followed by a faint echo of itself, so that for want of a better name the unknown author of these eerie sounds was christened the “echo fish.” Actual evidence of anything similar to the bat’s echo location or echo ranging has come only recently in the form of ingenious experiments performed on captive porpoises by W. N. Kellogg of Florida State University. Dr. Kellogg finds that the porpoises emit streams of underwater sound pulses by which they are able to swim accurately through a field of obstructions without collision. They could do this in water too turbid for vision or in darkness. When the experimenters introduced any object into the tank the porpoises gave forth bursts of sound signals by which the animals appeared to be trying to locate the object. Splashing on the surface, as from a hose or a shower of rain, “produced great disturbance, loud sound signals, undulating porpoise ‘alarm’ whistles, and ‘flight’ swimming reactions.” When food fish were introduced into the tank under such circumstances that they could not be located visually, the porpoises located them by streams of sound signals, turning their heads to right and left as the returning echoes allowed them to fix the exact location of their target.
* Latimeria was identified as a coelacanth, or one of an incredibly ancient group of fishes that first appeared in the seas some 300 million years ago. Rocks representing the next 200 million and more years of earth history yielded fossil coelacanths; then, in the Cretaceous, the record of these fishes off South Africa was at first considered a mysterious and extraordinary incident, not likely to be repeated. An ichthyologist in South Africa, Professor J. L. B. Smith, did not share this view. Believing there must be other coelacanths in the sea, he began a patient search that went on 14 years before it was successful. Then, in December 1952, a second fish of this group was captured near the island of Anjouan, off the north-western tip of Madagascar. The search was then taken up by Professor J. Millot, Director of the Research Institute in Madagascar. By 1958 Professor Millot had obtained ten more specimens, consisting of seven males and three females.
A plausible explanation of the sixty-million-year gap in the occurrence of fossil coelacanths has been put forward by Dr. Bobb Schaeffer of the American Museum of Natural History. Dr. Schaeffer points out that the earliest coelacanths, from pre-Jurassic time, seem to have inhabited a variety of environments, including freshwater swamps as well as seas. From the Jurassic to the present time, on the other hand, they seem to have been exclusively marine. At the close of the Cretaceous, the great withdrawal of the sea from the continental areas it had overflowed may have confined the coelacanths to the permanent ocean basins. There, in the bottom sediments, their fossils would be so inaccessible that the chance of their discovery would be exceedingly remote.
Hidden Lands
Sand-strewn caverns, cool and deep,
Where the winds are all asleep.
MATTHEW ARNOLD
THE FIRST EUROPEAN ever to sail across the wide Pacific was curious about the hidden worlds beneath his ship. Between the two coral islands of St. Paul and Los Tiburones in the Tuamotu Archipelago, Magellan ordered his sounding line to be lowered. It was the conventional line used by explorers of the day, no more than 200 fathoms long. It did not touch bottom, and Magellan declared that he was over the deepest part of the ocean. Of course he was completely mistaken, but the occasion was none the less historic. It was the first time in the history of the world that a navigator had attempted to sound the depths of the open ocean. Three centuries later, in the year 1839, Sir James Clark Ross set out from England in command of two ships with names of dark foreboding, the Erebus and the Terror, bound for the ‘utmost navigable limits of the Antarctic Ocean.’ As he proceeded on his course he tried repeatedly to obtain soundings, but failed for lack of a proper line. Finally he had one constructed on board, of ‘three thousand six hundred fathoms, or rather more than four miles in length. … On the 3rd of January, in latitude 27° 26’ S., longitude 17° 29’ W., the weather and all other circumstances being propitious, we succeeded in obtaining soundings with two thousand four hundred and twenty-five fathoms of line, a depression of the bed of the ocean beneath its surface very little short of the elevation of Mount Blanc above it.’ This was the first successful abyssal sounding.
But taking soundings in the deep ocean was, and long remained, a laborious and time-consuming task, and knowledge of the undersea topography lagged considerably behind our acquaintance with the landscape of the near side of the moon. Over the years, methods were improved. For the heavy hemp line used by Ross, Maury of the United States Navy substituted a strong twine, and in 1870 Lord Kelvin used piano wire. Even with improved gear a deep-water sounding required several hours or sometimes an entire day. By 1854, when Maury collected all available records, only 180 deep soundings were available from the Atlantic, and by the time that modern echo sounding was developed, the total that had been taken from all the ocean basins of the world was only about 15,000. This is roughly one sounding for an area of 6000 square miles.
Now hundreds of vessels are equipped with sonic sounding instruments that trace a continuous profile of the bottom beneath the moving ship (although only a few can obtain profiles at depths greater than 2000 fathoms*). Soundings are accumulating much faster than they can be plotted on the charts. Little by little, like the details of a huge map being filled in by an artist, the hidden contours of the ocean are emerging. But, even with this recent progress, it will be years before an accurate and detailed relief map of the ocean basins can be constructed.
The general bottom topography is, however, well established. Once we have passed the tide lines, the three great geographic provinces of ocean are the continental shelves, the continental slopes, and the floor of the deep sea. Each of these regions is as different from the others as an arctic tundra from a range of the Rocky Mountains.
The continental shelf is of the sea, yet of all regions of the ocean it is most like the land. Sunlight penetrates to all but its deepest parts. Plants drift in the waters above it; seaweeds cling to its rocks and sway to the passage of the waves. Familiar fishes—unlike the weird monsters of the abyss—move over its plains like herds of cattle. Much of its substance is derived from the land—the sand and the rock fragments and the rich topsoil carried by running water to the sea and gently deposited on the shelf. Its submerged valleys and hills, in appropriate parts of the world, have been carved by glaciers into a topography much like the northern landscapes we know and the terrain is strewn with rocks and gravel deposited by the moving ice sheets. Indeed many parts (or perhaps all) of the shelf have been dry land in the geologic past, for a comparatively slight fall of sea level has sufficed, time an
d again, to expose it to wind and sun and rain. The Grand Banks of Newfoundland rose above the ancient seas and were submerged again. The Dogger Bank of the North Sea shelf was once a forested land inhabited by prehistoric beasts; now its ‘forests’ are seaweeds and its ‘beasts’ are fishes.
Of all parts of the sea, the continental shelves are perhaps most directly important to man as a source of material things. The great fisheries of the world, with only a few exceptions, are confined to the relatively shallow waters over the continental shelves. Seaweeds are gathered from their submerged plains to make scores of substances used in foods, drugs, and articles of commerce. As the petroleum reserves left on continental areas by ancient seas become depleted, petroleum geologists look more and more to the oil that may lie, as yet unmapped and unexploited, under these bordering lands of the sea.
The shelves begin at the tidelines and extend seaward as gently sloping plains. The 100-fathom contour used to be taken as the boundary between the continental shelf and the slope; now it is customary to place the division wherever the gentle declivity of the shelf changes abruptly to a steeper descent toward abyssal depths. The world over, the average depth at which this change occurs is about 72 fathoms; the greatest depth of any shelf is probably 200 to 300 fathoms.
The Sea Around Us Page 7