The Sea Around Us

1

For this special edition of The Sea Around Us, Rachel Carson’s notes have been placed at the end of each corresponding chapter.

2

Our concept of the age of the earth is constantly undergoing revision as older and older rocks are discovered and as methods of study are refined. The oldest rocks now known in North America are in the Canadian Shield area. Their precise age has not been determined, but some from Manitoba and Ontario are believed to have been formed about 3 billion years ago. Even older rocks have been discovered in the Karelia Peninsula in the U.S.S.R., and in South Africa. Geologists are generally of the opinion that present concepts of geologic time will be considerably lengthened in the future. Tentative adjustments of the length of the various periods have already been made (see chart above) and the age of the Cambrian has been pushed back 100 million years compared with the dating assigned to it a decade ago. It is in that immense and shadowy time that preceded the Cambrian, however, that the greatest uncertainty exists. This is the time of the pre-fossiliferous rocks. Whatever life may have inhabited the earth during that time has left few traces, although by indirect evidence we may infer that life existed in some abundance before its record was written in the rocks.

By studies of the rocks themselves geologists have established a few good benchmarks standing out in those vast stretches of time indicated on the chart as the Proterozoic and Archeozoic Eras. These indicate a billion-year age for the ancient Grenville Mountains of eastern North America. Where these rocks are exposed at the surface, as in Ontario, they contain large amounts of graphite, giving silent testimony to the abundance of plant life when these rocks were forming, for plants are a common source of carbon. An age-reading of 1,700,000,000 years has been obtained in the Penokean Mountains of Minnesota and Ontario, formerly known to geologists as the Killarney Mountains. The remains of these once lofty mountains are still to be seen as low, rolling hills. The discovery of even older rocks in Canada, Russia, and Africa, dating back more than 3 billion years, suggests that the earth itself may have been formed about 4½ billion years ago.

3

From The Condor, vol. 36, no. 5, Sept.–Oct. 1934, pp. 186–7.

4

From Charles Darwin’s Diary of the Voyage of H.M.S. Beagle, edited by Nora Barlow, 1934 edition, Cambridge University Press, p. 107.

5

From The Mirror of the Sea, Kent edition, 1925, Doubleday-Page, p. 71.

6

From The Depths of the Ocean, by Sir John Murray and Johan Hjort, 1912 edition, Macmillan & Co., p. 649.

7

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.

8

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.

9

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.

10

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.

11

The range of echo-sounding instruments has now been so greatly extended that under ideal conditions the most powerful of them are capable of sounding the maximum depths of the sea. Factors such as the nature of the underlying bottom and conditions in the intervening water layers influence the effectiveness with which the sounding devices operate under actual conditions at sea. Nevertheless, the potential range necessary for charting all parts of the sea is now at the command of oceanographers.

12

In the ten years that have elapsed since this account of the canyons was written much more has been learned about them, but it may still be said that there is no general agreement about their origin. Many of the resources of the modern oceanographer have been brought to bear on the problem. Divers have engaged in direct exploration of the shallow heads of some of the California canyons, collecting samples of their walls and photographing them. Other canyons have been studied by oceanographers using deep-sea corers or dredges to obtain samples of rocks and sediments. Precision depth recorders have given much new information about their shapes. As a result of these studies it is now known that there are at least five types of canyons, so different in their characteristics that almost certainly they have different origins. No single theory may be expected to explain all of them. Professor Francis S. Shepard, the marine geologist who originally put forward the theory that the canyons had been cut by rivers and later submerged, now feels this explanation is adequate for some canyons but not for others. For example, some marine valleys, trough-shaped and straight-walled and occurring in areas where the earth’s crust is in a state of unrest, probably represent a fault or fracture of the rocky floor. The theory that some of the canyons have been cut by vast sediment flows called turbidity currents has gained support as a result of new concepts of dynamic activity on the floor of the sea. Further detailed study of all types of these extraordinarily fascinating features of the sea floor should not only clarify their own history but add greatly to our understanding of the history of the earth.

13

Somewhat greater depths have more recently been recorded in the Mariana Trench off the island of Guam, the trench into which the bathyscaphe Trieste made its record-breaking descent to the bottom. In this trench the Challenger in 1951 recorded a depth of 10,863 meters or about 6.7 miles. Since the exact location of the Challenger echo sounding was given, this depth is capable of verification and so is regarded as the maximum depth of which we have authentic record. In 1958, however, Russian scientists aboard the Vitiaz reported a finding of slightly greater depths (11,034 meters or 6.8 miles) also in the Mariana Trench, but at an unspecified location.

14

From The Changing World of the Ice Age, 1934 edition, Yale University Press, p. 116.

15

The supposition that the Atlantic Ridge may extend across the Arctic basin has been confirmed in exciting new developments in marine geology. Indeed, it is now suggested by some geologists that the whole mid-Atlantic ridge is part of a continuous range of mountains that runs for 40,000 miles across the bottom of the Atlantic, the Arctic, the Pacific, and the Indian Oceans (see Preface).

As for the exploration of the Arctic basin itself—the charting of details so long unknown and merely guessed at—the revolutionary development that made it possible to substitute fact for theory was the use of American nuclear-powered submarines to pass beneath the ice cover and directly explore the depths of this ocean. In 1957 the Nautilus (bearing the same name as Wilkin’s conventional submarine) first penetrated beneath Arctic ice in a preliminary exploration designed to discover whether it was feasible to explore these regions by submarines. The Nautilus remained submerged for 74 hours and covered a distance of almost 1000 miles. A vast amount of data was collected, including depth soundings and measurements of the thickness of the overlying ice. Then in 1958 the Nautilus crossed the entire Arctic basin from Point Barrow in Alaska to the North Pole and thence to the Atlantic. In the course of this historic voyage it made the first continuously recorded echo-sounder profile across the center of the Arctic basin. Other nuclear submarines have subsequently contributed to our knowledge of the Arctic. It is now clear, from the work of the nuclear submarines and from other, more conventional explorations, that the bottom topography of the Arctic Ocean is for the most part that of a normal oceanic basin, with flat abyssal plains, scattered sea mounts, and rugged mountains. The greatest depth so far discovered is somewhat more than three miles. The shelf break (from which a steeper descent begins) falls at the unusually shallow depth of 35 fathoms off Alaska. From samplings by coring tubes and dredges and from deep-sea photography it was discovered during the International Geophysical Year that the bottom is widely covered with rocks, pebbles, and shells, the latter chiefly of shallow-water forms. The present ice cover seems to be carrying little or no material such as rock fragments and sand, so the material now found in bottom samples must have come from ice rafted in from surrounding continents during some past geologic time, when the Arctic was relatively open water.

Russian scientists, who have done rather extensive work in marine biology, obtained interesting data which seem to disprove Nansen’s earlier belief that the waters of the central Arctic are extremely poor in both plant and animal life. Data collected from the drifting station “North Pole” indicate that both plant and animal plankton in great variety exist in the region of the Pole. Little-studied organisms develop on the surface of the ice; these contain much fat and tint the ice shades of yellow and red. Diatoms are not found in the surface of the ice but develop (along with other plankton) in the lakes that form on the surface of the ice as it melts. By absorbing a great amount of energy from the sun, the abundant diatom colonies contribute to further melting of the ice cover. The wealth of plankton during the Arctic summer attracts numbers of birds and various mammals.

16

Now that the sediments have been measured over much greater areas of the ocean floor, the reaction of oceanographers is one of considerable amazement— but their surprise concerns the fact that on the whole the mantle of sediments is so much thinner than related facts would lead them to expect. Over vast areas of the Pacific the average thickness of the sediments (unconsolidated sediments plus sedimentary rock) is only about a quarter of a mile. It is little thicker over much of the Atlantic. (These are average figures; some much deeper deposits of course exist.) In some areas there has been almost no sedimentation. A few years ago several oceanographers obtained photographs of manganese nodules lying on the floor of the Atlantic at great depths and of others on the Easter Island Ridge of the southeast Pacific. Sharks’ teeth dating from the Tertiary, hence possibly as much as 70 million years old, sometimes form the nuclei of these nodules. Certainly their growth, by deposit of successive layers around the nuclei, must be very slow. Hans Pettersson has estimated a growth of about 1 mm. per thousand years. Yet during the period these nodules have lain on the ocean floor, sediments deep enough to cover them have not been accumulated.

Some idea of the rate of sedimentation during post-glacial time has been gained by observation of the rate of radioactive decay of some of the components of the sediments. If this sedimentation rate had prevailed during the supposed life of the oceans, the average thickness of the sediments would be enormously greater than it now appears to be. Did much of the deposited sediments dissolve? Were most of the present land masses submerged for far greater periods than we now assume, with consequently long periods of slight erosion? These and other explanations of the mystery of the sediments have been suggested, but none seems wholly satisfying. Possibly the dramatic project of boring holes in the floor of the ocean down to the Mohorovicic discontinuity (Project Mohole; see Preface) will provide the explanation that is now lacking.

17

From The Changing World of the Ice Age, 1934 edition, Yale University Press, p. 210.

18

From Transactions, Geol. Soc. Cornwall, vol. v, 1843.

19

From Annual Rept., Smithsonian Inst., 1947.

20

From the time of its establishment up to 1960, the warning system has issued eight alerts warning residents of the Hawaiian Islands of the approach of seismic waves. On three of these occasions, waves of major proportions have in fact struck the islands. None have been so large or so destructive, however, as those of May 23, 1960, which spread out across the Pacific from their place of origin in violent earthquakes on the coast of Chile. Without such warning the loss of life would almost certainly have been enormous. As soon as the seismograph at the Honolulu Observatory recorded the first of the Chilean quakes the system went into operation. Reports from the scattered tide stations gave ample notice that a seismic wave had formed and was spreading out across the Pacific. By early news bulletins and later by an official “sea wave warning” the Observatory alerted residents of the area and predicted the time the wave would arrive and the areas to be affected. These predictions proved to be accurate within reasonable limits, and although property damage was heavy, loss of life was limited to the few who disregarded the warnings. Sea wave activity was reported as far west as New Zealand and as far north as Alaska. The Japanese coasts were struck by heavy waves. Although the United States warning system does not now include other nations, officials at Honolulu sent to Japan warnings of the wave which, unfortunately, were disregarded.

The warning system now (in 1960) consists of eight seismograph stations at points on both eastern and western shores of the Pacific and on certain islands, and of twenty widely scattered wave stations, four of which are equipped with automatic wave detectors. The Coast and Geodetic Survey feels that additional wave-reporting tide stations would improve the effectiveness of the system. Its principal defect now, however, is the fact that it is not possible to predict the height of a wave as it reaches any particular shore, and therefore the same alert must be issued for all approaching seismic waves. Research on methods of forecasting wave height is therefore needed. Even with its present limitations, however, the system has filled so great a need that there is strong international interest in extending it to other parts of the world.

21

The flood of ocean waters that overwhelmed the coast of the Netherlands on February 1, 1953, deserves a place in the history of great storm waves. A winter gale that formed west of Iceland swept across the Atlantic and into the North Sea. All its force was ultimately brought to bear on the first land mass to obstruct the course of its center—the southwestern corner of Holland. The storm-driven waves and tides battered against the dikes in such bitter violence that these ancient defenses were breached in a hundred places, through which the flood rushed in to inundate farms and villages. The storm struck on Saturday, January 31, and by midday of Sunday one-eighth of Holland was under water. The toll included about half a million acres of Holland’s best agricultural land—ravaged by water and permeated with salt—thousands of buildings, hundreds of thousands of live stock, and an estimated 1400 people. In all the long history of Holland’s struggle against the sea, there has been no comparable assault by ocean waters.

22

From Am. Phil. Soc. Trans., vol. 2, 1786.

23

It is now the fashion among oceanographers to speak of the Gulf Stream System, reflecting the discovery that east of Cape Hatteras there is no longer a continuous river of warm water but a “series of overlapping currents arranged somewhat like the shingles on a roof.” Not only do the streams “overlap” but they are narrow and swift. The main branches of the stream that have long been recognized east of the Grand Banks are now known to originate far to westward of the Banks, developing not as branches in the ordinary sense but as a series of new currents, each to the north of the next older one.

As oceanographers study more about the dynamics of circulation in the sea, they are more and more struck by parallels between the ocean of water and the ocean of air. One of the leading students of the Gulf Stream, Columbus Iselin, has commented on the branching of the Stream in terms of a fascinating analogy: “Much the same phenomena seem to be present in the jet streams found at high elevations in the great belts of prevailing westerly winds of mid-latitudes,” he says, “although each atmospheric jet has greater dimensions than the overlapping subdivision of the Gulf Stream System.”

24

One of the most exciting recent events in oceanography was the discovery of a powerful current running under the South Equatorial current but in the opposite direction. The core of the counter current lies about 300 feet below the surface (although shallower near its eastern terminal in the vicinity of the Galapagos Islands). This subsurface current is about 250 miles wide and it flows at least 3500 miles eastward along the equator at a speed of about 3 knots. (The speed of the surface current is only about one knot.) The existence of the current was discovered in 1952 by Townsend Cromwell in the course of a U.S. Fish and Wildlife Service investigation of methods of tuna fishing. Cromwell observed that long lines set for tuna at the equator did not move westward with the surface current, as would be expected, but drifted rapidly in the opposite direction. It was not until 1958, however, that an extensive survey of the current was made by the Scripps Institution of Oceanography and its impressive dimensions measured. This same survey gave further proof that the deep circulation of the ocean is far more complicated than has generally been realized, for beneath the swift-flowing eastward current was still another, flowing to the west. In only the uppermost half mile of Pacific equatorial waters, therefore, there are three great rivers of water, one above the other, each flowing on its own course independent of the other. When such surveys can be extended all the way to the floor of the ocean an even more complex picture will undoubtedly be revealed.

Only a year before the detailed charting of this Pacific current, British and American oceanographers discovered a south-flowing counter current running from the North to the South Atlantic under the Gulf Stream and the Brazil Current. The techniques that make such discoveries possible have only very recently become available to oceanographers. As their use becomes more widespread our almost complete ignorance of the deep circulation of the ocean will be dispelled.

25

From Bulletin, U.S. Bureau of Fisheries, vol. XXVIII, part 1, 1908, p. 338.

26

From Natural History, vol. LIII, no. 8, 1944, p. 356. ?

27

During the 1950’s enormous advances were made in the development of instruments for the recording of water temperatures. A continuous recording of water temperatures to a depth of several hundred feet may be obtained by towing a thermistor chain behind a vessel. The electronic bathythermograph is potentially capable of obtaining temperatures at any depth, depending on the length of cable available. It is a vast improvement over the original bathythermograph because a recorder on deck traces a continuous graph of the temperatures being registered while the vessel is under way. An even more revolutionary development in the study of sea temperatures is the airborne radiation thermometer which, while flown above the sea, registers the surface temperature with an accuracy of a fraction of a degree. Oceanographers regard this instrument as still in the developmental stage, with further refinement of accuracy possible. However, in such work as tracing the edge of the Gulf Stream these airborne thermometers have already proven themselves enormously useful. During a 1960 survey of the Gulf Stream conducted by the Woods Hold Oceanographic Institution, a low-flying plane covered some 30,000 miles, obtaining surface temperatures in various areas of the Stream.

28

Svenska Hydrog.-Biol. Komm. Skrifter, No. 5, 1912.

29

From In Northern Mists, 1912 edition, A. H. Clark, vol. 1, pp. 234 and 247.

30

Many of the old basic works on the sea are now out of print but they are well worth pursuing in libraries for the excellent background they provide.