The Sea Around Us

The Global Thermostat

WHEN THE BUILDING of the Panama Canal was first suggested, the project was severely criticized in Europe. The French, especially, complained that such a canal would allow the waters of the Equatorial Current to escape into the Pacific, that there would then be no Gulf Stream, and that the winter climate of Europe would become unbearably frigid. The alarmed Frenchmen were completely wrong in their forecast of oceanographic events, but they were right in their recognition of a general principle—the close relation between climate and the pattern of ocean circulation.

There are recurrent schemes for deliberately changing—or attempting to change—the pattern of the currents and so modifying climate at will. We hear of projects for diverting the cold Oyashio from the Asiatic coast, and of others for controlling the Gulf Stream. About 1912 the Congress of the United States was asked to appropriate money to build a jetty from Cape Race eastward across the Grand Banks to obstruct the cold water flowing south from the Arctic. Advocates of the plan believed that the Gulf Stream would then swing in nearer the mainland of the northern United States and would presumably bring us warmer winters. The appropriation was not granted. Even if the money had been provided, there is little reason to suppose that engineers then—or later—could have succeeded in controlling the sweep of the ocean’s currents. And fortunately so, for most of these plans would have effects different from those popularly expected. Bringing the Gulf Stream closer to the American east coast, for example, would make our winters worse instead of better. Along the Atlantic coast of North America, the prevailing winds blow eastward, across the land toward the sea. The air masses that have lain over the Gulf Stream seldom reach us. But the Stream, with its mass of warm water, does have something to do with bringing our weather to us. The cold winds of winter are pushed by gravity toward the low-pressure areas over the warm water. The winter of 1916, when Stream temperatures were above normal, was long remembered for its cold and snowy weather along the east coast. If we could move the Stream inshore, the result in winter would be colder, stronger winds from the interior of the continent—not milder weather.

But if the eastern North American climate is not dominated by the Gulf Stream, it is far otherwise for the lands lying ‘down-stream.’ From the Newfoundland Banks, as we have seen, the warm water of the Stream drifts eastward, pushed along by the prevailing westerly winds. Almost immediately, however, it divides into several branches. One flows north to the western shore of Greenland; there the warm water attacks the ice brought around Cape Farewell by the East Greenland Current. Another passes to the southwest coast of Iceland, and, before losing itself in arctic waters, brings a gentling influence to the southern shores of that island. But the main branch of the Gulf Stream or North Atlantic Drift flows eastward. Soon it divides again. The southernmost of these branches turns toward Spain and Africa and re-enters the Equatorial Current. The northernmost branch, hurried eastward by the winds blowing around the Icelandic ‘low,’ piles up against the coast of Europe the warmest water found at comparable latitudes anywhere in the world. From the Bay of Biscay north its influence is felt. And as the current rolls northeastward along the Scandinavian coast, it sends off many lateral branches that curve back westward to bring the breath of warm water to the arctic islands and to mingle with other currents in intricate whirls and eddies. The west coast of Spitsbergen, warmed by one of these lateral streams, is bright with flowers in the arctic summer; the east coast, with its polar current, remains barren and forbidding. Passing around the North Cape, the warm currents keep open such harbors as Hammerfest and Murmansk, although Riga, 800 miles farther south on the shores of the Baltic, is choked with ice. Somewhere in the Arctic Sea, near the island of Novaya Zemlya, the last traces of Atlantic water disappear, losing themselves at last in the overwhelming sweep of the icy northern sea.

It is always a warm-water current, but the temperature of the Gulf Stream nevertheless varies from year to year, and a seemingly slight change profoundly affects the air temperatures of Europe. The British meteorologist, C. E. P. Brooks, compares the North Atlantic to ‘a great bath, with a hot tap and two cold taps.’ The hot tap is the Gulf Stream; the cold taps are the East Greenland Current and the Labrador Current. Both the volume and the temperature of the hot-water tap vary. The cold taps are nearly constant in temperature but vary immensely in volume. The adjustment of the three taps determines surface temperatures in the eastern Atlantic and has a great deal to do with the weather of Europe and with happenings in arctic seas. A very slight winter warming of the eastern Atlantic temperatures means, for example, that the snow cover of northwestern Europe will melt earlier, that there will be an earlier thawing of the ground, that spring plowing may begin earlier, and that the harvest will be better. It means, too, that there will be relatively little ice near Iceland in the spring and that the amount of drift ice in the Barents Sea will diminish a year or two later. These relations have been clearly established by European scientists. Someday long-range weather forecasts for the continent of Europe will probably be based in part on ocean temperatures. But at present there are no means for collecting the temperatures over a large enough area, at frequent enough intervals.[27]

For the globe as a whole, the ocean is the great regulator, the great stabilizer of temperatures. It has been described as ‘a savings bank for solar energy, receiving deposits in seasons of excessive insolation and paying them back in seasons of want.’ Without the ocean, our world would be visited by unthinkably harsh extremes of temperature. For the water that covers three-fourths of the earth’s surface with an enveloping mantle is a substance of remarkable qualities. It is an excellent absorber and radiator of heat. Because of its enormous heat capacity, the ocean can absorb a great deal of heat from the sun without becoming what we would consider ‘hot,’ or it can lose much of its heat without becoming ‘cold.’

Through the agency of ocean currents, heat and cold may be distributed over thousands of miles. It is possible to follow the course of a mass of warm water that originates in the trade-wind belt of the Southern Hemisphere and remains recognizable for a year and a half, through a course of more than 7000 miles. This redistributing function of the ocean tends to make up for the uneven heating of the globe by the sun. As it is, ocean currents carry hot equatorial water toward the poles and return cold water equator-ward by such surface drifts as the Labrador Current and Oyashio, and even more importantly by deep currents. The redistribution of heat for the whole earth is accomplished about half by the ocean currents, and half by the winds.

At that thin interface between the ocean of water and the ocean of overlying air, lying as they do in direct contact over by far the greater part of the earth, there are continuous interactions of tremendous importance.

The atmosphere warms or cools the ocean. It receives vapors through evaporation, leaving most of the salts in the sea and so increasing the salinity of the water. With the changing weight of that whole mass of air that envelops the earth, the atmosphere brings variable pressure to bear on the surface of the sea, which is depressed under areas of high pressure and springs up in compensation under the atmospheric lows. With the moving force of the winds, the air grips the surface of the ocean and raises it into waves, drives the currents onward, lowers sea levels on windward shores, and raises it on lee shores.

But even more does the ocean dominate the air. Its effect on the temperature and humidity of the atmosphere is far greater than the small transfer of heat from air to sea. It takes 3000 times as much heat to warm a given volume of water 1° as to warm an equal volume of air by the same amount. The heat lost by a cubic meter of water on cooling 1° C. would raise the temperature of 3000 cubic meters of air by the same amount. Or to use another example, a layer of water a meter deep, on cooling .1° could warm a layer of air 33 meters thick by 10°. The temperature of the air is intimately related to atmospheric pressure. Where the air is cold, pressure tends to be high; warm air favors low pressures. The transfer of heat between ocean and air therefore alters the belts of high and low pressure; this profoundly affects the direction and strength of the winds and directs the storms on their paths.

There are six more or less permanent centers of high pressure over the oceans, three in each hemisphere. Not only do these areas play a controlling part in the climate of surrounding lands, but they affect the whole world because they are the birthplaces of most of the dominant winds of the globe. The trade winds originate in high-pressure belts of the Northern and Southern hemispheres. Over all the vast extent of ocean across which they blow, these great winds retain their identity; it is only over the continents that they become interrupted, confused, and modified.

In other ocean areas there are belts of low pressure, which develop, especially in winter, over waters that are then warmer than the surrounding lands. Traveling barometric depressions or cyclonic storms are attracted by these areas; they move rapidly across them or skirt around their edges. So winter storms take a path across the Icelandic ‘low’ and over the Shetlands and Orkneys into the North Sea and the Norwegian Sea; other storms are directed by still other low-pressure areas over the Skagerrak and the Baltic into the interior of Europe. Perhaps more than any other condition, the low-pressure area over the warm water south of Iceland dominates the winter climate of Europe.

And most of the rains that fall on sea and land alike were raised from the sea. They are carried as vapor in the winds, and then with change of temperature the rains fall. Most of the European rain comes from evaporation of Atlantic water. In the United States, vapor and warm air from the Gulf of Mexico and the tropical waters of the western Atlantic ride the winds up the wide valley of the Mississippi and provide rains for much of the eastern part of North America.

Whether any place will know the harsh extremes of a continental climate or the moderating effect of the sea depends less on its nearness to the ocean than on the pattern of currents and winds and the relief of the continents. The east coast of North America receives little benefit from the sea, because the prevailing winds are from the west. The Pacific coast, on the other hand, lies in the path of the westerly winds that have blown across thousands of miles of ocean. The moist breath of the Pacific brings climatic mildness and creates the dense rain forests of British Columbia, Washington, and Oregon; but its full influence is largely restricted to a narrow strip by the coast ranges that follow a course parallel to the sea. Europe, in contrast, is wide open to the sea, and ‘Atlantic weather’ carries hundreds of miles into the interior.

By a seeming paradox, there are parts of the world that owe their desert dryness to their nearness to the ocean. The aridity of the Atacama and Kalahari deserts is curiously related to the sea. Wherever such marine deserts occur, there is found this combination of circumstances: a western coast in the path of the prevailing winds, and a cold coastwise current. So on the west coast of South America the cold Humboldt streams northward off the shores of Chile and Peru—the great return flow of Pacific waters seeking the equator. The Humboldt, it will be remembered, is cold because it is continuously being reinforced by the upwelling of deeper water. The presence of this cold water offshore helps create the aridity of the region. The onshore breezes that push in toward the hot land in the afternoons are formed of cool air that has lain over a cool sea. As they reach the land they are forced to rise into the high coastal mountains—the ascent cooling them more than the land can warm them. So there is little condensation of water vapor, and although the cloud banks and the fogs forever seem to promise rain, the promise is not fulfilled so long as the Humboldt rolls on its accustomed course along these shores. On the stretch from Arica to Caldera there is normally less than an inch of rain in a year. It is a beautifully balanced system—as long as it remains in balance. What happens when the Humboldt is temporarily displaced is nothing short of catastrophic.

At irregular intervals the Humboldt is deflected away from the South American continent by a warm current of tropical water that comes down from the north. These are years of disaster. The whole economy of the area is adjusted to the normal aridity of climate. In the years of El Niño, as the warm current is called, torrential rains fall—the downpouring rains of the equatorial regions let loose upon the dust-dry hillsides of the Peruvian coast. The soil washes away, the mud huts literally dissolve and collapse, crops are destroyed. Even worse things happen at sea. The cold-water fauna of the Humboldt sickens and dies in the warm water, and the birds that fish the cold sea for a living must either migrate or starve.

Those parts of the coast of Africa that are bathed by the cool Benguela Current also lie between mountains and sea. The easterly winds are dry, descending winds, and the cool breezes from the sea have their moisture capacity increased by contact with the hot land. Mists form over the cold waters and roll in over the coast, but in a whole year the rainfall is the meagerest token. The mean rainfall at Swakopmund in Walvis Bay is 0.7 inches a year. But again this is true only as long as the Benguela holds sway along the coast, for there are times when the cold stream falters as does the Humboldt, and here also these are years of disaster.

The transforming influence of the sea is portrayed with beautiful clarity in the striking differences between the Arctic and Antarctic regions. As everyone knows, the Arctic is a nearly landlocked sea; the Antarctic, a continent surrounded by ocean. Whether this global balancing of a land pole against a water pole has a deep significance in the physics of the earth is uncertain; but the bearing of the fact on the climates of the two regions is plainly evident.

The ice-covered Antarctic continent, bathed by seas of uniform coldness, is in the grip of the polar anticyclone. High winds blow from the land and repel any warming influence that might seek to penetrate it. The mean temperature of this bitter world is never above the freezing point. On exposed rocks the lichens grow, covering the barrenness of cliffs with their gray or orange growths, and here and there over the snow is the red dust of the hardier algae. Mosses hide in the valleys and crevices less exposed to the winds, but of the higher plants only a few impoverished stands of grasses have managed to invade this land. There are no land mammals; the fauna of the Antarctic continent consists only of birds, wingless mosquitoes, a few flies, and microscopic mites.

In sharp contrast are the arctic summers, where the tundra is bright with many-colored flowers. Everywhere except on the Greenland icecap and some of the arctic islands, summer temperatures are high enough for the growth of plants, packing a year’s development into the short, warm, arctic summer. The polar limit of plant growth is set not by latitude, but by the sea. For the influence of the warm Atlantic penetrates strongly within the Arctic Sea, entering, as we have seen, through the one large break in the land girdle, the Greenland Sea. But the streams of warm Atlantic water that enter the icy northern seas bring the gentling touch that makes the Arctic, in climate as well as in geography, a world apart from the Antarctic.

So, day by day and season by season, the ocean dominates the world’s climate. Can it also be an agent in bringing about the long-period swings of climatic change that we know have occurred throughout the long history of the earth—the alternating periods of heat and cold, of drought and flood? There is a fascinating theory that it can. This theory links events in the deep, hidden places of the ocean with the cyclic changes of climate and their effects on human history. It was developed by the distinguished Swedish oceanographer, Otto Pettersson, whose almost century-long life closed in 1941. In many papers, Pettersson presented the different facets of his theory as he pieced it together, bit by bit. Many of his fellow scientists were impressed, others doubted. In those days few men could conceive of the dynamics of water movements in the deep sea. Now the theory is being re-examined in the light of modern oceanography and meteorology, and only recently C. E. P. Brooks said, ‘It seems that there is good support for Pettersson’s theory as well as for that of solar activity, and that the actual variations of climate since about 3000 B.C. may have been to a large extent the result of these two agents.’

To review the Pettersson theory is to review also a pageant of human history, of men and nations in the control of elemental forces whose nature they never understood and whose very existence they never recognized. Pettersson’s work was perhaps a natural outcome of the circumstances of his life. He was born—as he died 93 years later—on the shores of the Baltic, a sea of complex and wonderful hydrography. In his laboratory atop a sheer cliff overlooking the deep waters of the Gulmarfiord, instruments recorded strange phenomena in the depths of this gateway to the Baltic. As the ocean water presses in toward that inland sea it dips down and lets the fresh surface water roll out above it; and at that deep level where salt and fresh water come into contact there is a sharp layer of discontinuity, like the surface film between water and air. Each day Pettersson’s instruments revealed a strong, pulsing movement of that deep layer—the pressing inward of great submarine waves, of moving mountains of water. The movement was strongest every twelfth hour of the day, and between the 12-hour intervals it subsided. Pettersson soon established a link between these submarine waves and the daily tides. ‘Moon waves,’ he called them, and as he measured their height and timed their pulsing beat through the months and years, their relation to the ever-changing cycles of the tides became crystal clear.

Some of these deep waves of the Gulmarfiord were giants nearly 100 feet high. Pettersson believed they were formed by the impact of the oceanic tide wave on the submarine ridges of the North Atlantic, as though the waters moving to the pull of the sun and moon, far down in the lower levels of the sea, broke and spilled over in mountains of highly saline water to enter the fiords and sounds of the coast.

From the submarine tide waves, Pettersson’s mind moved logically to another problem—the changing fortunes of the Swedish herring fishery. His native Bohuslan had been the site of the great Hanseatic herring fisheries of the Middle Ages. All through the thirteenth, fourteenth, and fifteenth centuries this great sea fishery was pursued in the Sund and the Belts, the narrow passageways into the Baltic. The towns of Skanor and Falsterbo knew unheard-of prosperity, for there seemed no end of the silvery, wealth-bringing fish. Then suddenly the fishery ceased, for the herring withdrew into the North Sea and came no more into the gateways of the Baltic—this to the enrichment of Holland and the impoverishment of Sweden. Why did the herring cease to come? Pettersson thought he knew, and the reason was intimately related to that moving pen in his laboratory, the pen that traced on a revolving drum the movements of the submarine waves far down in the depths of Gulmarfiord.

He had found that the submarine waves varied in height and power as the tide-producing power of the moon and sun varied. From astronomical calculations he learned that the tides must have been at their greatest strength during the closing centuries of the Middle Ages—those centuries when the Baltic herring fishery was flourishing. The sun, moon, and earth came into such a position at the time of the winter solstice that they exerted the greatest possible attracting force upon the sea. Only about every eighteen centuries do the heavenly bodies assume this particular relation. But in that period of the Middle Ages, the great underwater waves pressed with unusual force into the narrow passages to the Baltic, and with the ‘water mountains’ went the herring shoals. Later, when the tides became weaker, the herring remained outside the Baltic, in the North Sea.

Then Pettersson realized another fact of extreme significance—that those centuries of great tides had been a period of ‘startling and unusual occurrences’ in the world of nature. Polar ice blocked much of the North Atlantic. The coasts of the North Sea and the Baltic were laid waste by violent storm floods. The winters were of ‘unexplained severity’ and in consequence of the climatic rigors political and economic catastrophes occurred all over the populated regions of the earth. Could there be a connection between these events and those moving mountains of unseen water? Could the deep tides affect the lives of men as well as of herring?

From this germ of an idea, Pettersson’s fertile mind evolved a theory of climatic variation, which he set forth in 1912 in an extraordinarily interesting document called Climatic Variations in Historic and Prehistoric Time.[28] Marshalling scientific, historic, and literary evidence, he showed that there are alternating periods of mild and severe climates which correspond to the long-period cycles of the oceanic tides. The world’s most recent period of maximum tides, and most rigorous climate, occurred about 1433, its effect being felt, however, for several centuries before and after that year. The minimum tidal effect prevailed about A.D. 550, and it will occur again about the year 2400.

During the latest period of benevolent climate, snow and ice were little known on the coast of Europe and in the seas about Iceland and Greenland. Then the Vikings sailed freely over the northern seas, monks went back and forth between Ireland and ‘Thyle’ or Iceland, and there was easy intercourse between Great Britain and the Scandinavian countries. When Eric the Red voyaged to Greenland, according to the Sagas, he ‘came from the sea to land at the middle glacier—from thence he went south along the coast to see if the land was habitable. The first year he wintered on Erik’s Island…’ This was probably in the year 984. There is no mention in the Sagas that Eric was hampered by drift ice in the several years of his exploration of the island; nor is there mention of drift ice anywhere about Greenland, or between Greenland and Wineland. Eric’s route as described in the Sagas— proceeding directly west from Iceland and then down the east coast of Greenland—is one that would have been impossible during recent centuries. In the thirteenth century the Sagas contain for the first time a warning that those who sail for Greenland should not make the coast too directly west of Iceland on account of the ice in the sea, but no new route is then recommended. At the end of the fourteenth century, however, the old sailing route was abandoned and new sailing directions were given for a more southwesterly course that would avoid the ice.

The early Sagas spoke, too, of the abundant fruit of excellent quality growing in Greenland, and of the number of cattle that could be pastured there. The Norwegian settlements were located in places that are now at the foot of glaciers. There are Eskimo legends of old houses and churches buried under the ice. The Danish Archaeological Expedition sent out by the National Museum of Copenhagen was never able to find all of the villages mentioned in the old records. But its excavations indicated clearly that the colonists lived in a climate definitely milder than the present one.

But these bland climatic conditions begin to deteriorate in the thirteenth century. The Eskimos began to make troublesome raids, perhaps because their northern sealing grounds were frozen over and they were hungry. They attacked the western settlement near the present Ameralik Fiord, and when an official mission went out from the eastern colony about 1342, not a single colonist could be found—only a few cattle remained. The eastern settlement was wiped out some time after 1418 and the houses and churches destroyed by fire. Perhaps the fate of the Greenland colonies was in part due to the fact that ships from Iceland and Europe were finding it increasingly difficult to reach Greenland, and the colonists had to be left to their own resources.

The climatic rigors experienced in Greenland in the thirteenth and fourteenth centuries were felt also in Europe in a series of unusual events and extraordinary catastrophes. The seacoast of Holland was devastated by storm floods. Old Icelandic records say that, in the winters by the early 1300’s, packs of wolves crossed on the ice from Norway to Denmark. The entire Baltic froze over, forming a bridge of solid ice between Sweden and the Danish islands. Pedestrians and carriages crossed the frozen sea and hostelries were put up on the ice to accommodate them. The freezing of the Baltic seems to have shifted the course of storms originating in the low-pressure belt south of Iceland. In southern Europe, as a result, there were unusual storms, crop failures, famine, and distress. Icelandic literature abounds in tales of volcanic eruptions and other violent natural catastrophes that occurred during the fourteenth century.

What of the previous era of cold and storms, which should have occurred about the third or fourth century B.C., according too the tidal theory? There are shadowy hints in early literature and folklore. The dark and brooding poetry of the Edda deals with a great catastrophe, the Fimbul-winter or Götterdämmerung, when frost and snow ruled the world for generations. When Pytheas journeyed to the seas north of Iceland in 330 B.C., he spoke of the mare pigrum, a sluggish, congealed sea. Early history contains striking suggestions that the restless movements of the tribes of northern Europe—the southward migrations of the ‘barbarians’ who shook the power of Rome—coincided with periods of storms, floods, and other climatic catastrophes that forced their migrations. Large-scale inundations of the sea destroyed the homelands of the Teutons and Cimbrians in Jutland and sent them southward into Gaul. Tradition among the Druids said that their ancestors had been expelled from their lands on the far side of the Rhine by enemy tribes and by ‘a great invasion of the ocean.’ And about the year 700 B.C. the trade routes for amber, found on the coasts of the North Sea, were suddenly shifted to the east. The old route came down along the Elbe, the Weser, and the Danube, through the Brenner Pass to Italy. The new route followed the Vistula, suggesting that the source of supply was then the Baltic. Perhaps storm floods had destroyed the earlier amber districts, as they invaded these same regions eighteen centuries later.

All these ancient records of climatic variations seemed to Pettersson an indication that cyclic changes in the oceanic circulation and in the conditions of the Atlantic had occurred. ‘No geologic alteration that could influence the climate has occurred for the past six or seven centuries,’ he wrote. The very nature of these phenomena—floods, inundations, ice blockades—suggested to him a dislocation of the oceanic circulation. Applying the discoveries in his laboratory on Gulmarfiord, he believed that the climatic changes were brought about as the tide-induced submarine waves disturbed the deep waters of polar seas. Although tidal movements are often weak at the surface of these seas, they set up strong pulsations at the submarine boundaries, where there is a layer of comparatively fresh, cold water lying upon a layer of salty, warmer water. In the years or the centuries of strong tidal forces, unusual quantities of warm Atlantic water press into the Arctic Sea at deep levels, moving in under the ice. Then thousands of square miles of ice that normally remain solidly frozen undergo partial thawing and break up. Drift ice, in extraordinary volume, enters the Labrador Current and is carried southward into the Atlantic. This changes the pattern of surface circulation, which is so intimately related to the winds, the rainfall, and the air temperatures. For the drift ice then attacks the Gulf Stream south of Newfoundland and sends it on a more easterly course, deflecting the streams of warm surface water that usually bring a softening effect to the climate of Greenland, Iceland, Spitsbergen, and northern Europe. The position of the low-pressure belt south of Iceland is also shifted, with further direct effect on European climate.

Although the really catastrophic disturbances of the polar regime come only every eighteen centuries, according to Pettersson, there are also rhythmically occurring periods that fall at varying intervals—for example, every 9, 18, or 36 years. These correspond to other tidal cycles. They produce climatic variations of shorter period and of less drastic nature.

The year 1903, for instance, was memorable for its outbursts of polar ice in the Arctic and for the repercussions on Scandinavian fisheries. There was ‘a general failure of cod, herring, and other fish along the coast from Finmarken and Lofoten to the Skagerrak and Kattegat. The greater part of the Barents Sea was covered with pack ice up to May, the ice border approaching closer to the Murman and Finmarken coasts than ever before. Herds of arctic seals visited these coasts, and some species of the arctic whitefish extended their migrations to the Christiana Fiord and even entered into the Baltic.’ This outbreak of ice came in a year when earth, moon, and sun were in a relative position that gives a secondary maximum of the tide-producing forces. The similar constellation of 1912 was another great ice year in the Labrador Current—a year that brought the disaster of the Titantic.

Now in our own lifetime we are witnessing a startling alteration of climate, and it is intriguing to apply Otto Pettersson’s ideas as a possible explanation. It is now established beyond question that a definite change in the arctic climate set in about 1900, that it became astonishingly marked about 1930, and that it is now spreading into sub-arctic and temperate regions. The frigid top of the world is very clearly warming up.

The trend toward a milder climate in the Arctic is perhaps most strikingly apparent in the greater ease of navigation in the North Atlantic and the Arctic Sea. In 1932, for example, the Knipowitsch sailed around Franz Josef Land for the first time in the history of arctic voyaging. And three years later the Russian ice-breaker Sadko went from the northern tip of Novaya Zemlya to a point north of Severnaya Zemlya (Northern Land) and thence to 82° 41’ north latitude—the northernmost point ever reached by a ship under its own power.

In 1940 the whole northern coast of Europe and Asia was remarkably free from ice during the summer months, and more than 100 vessels engaged in trade via the arctic routes. In 1942 a vessel unloaded supplies at the west Greenland port of Upernivik (latitude 72° 43’ N) during Christmas week ‘in almost complete winter darkness.’ During the ’forties the season for shipping coal from West Spitsbergen ports lengthened to seven months, compared with three at the beginning of the century. The season when pack ice lies about Iceland became shorter by about two months that it was a century ago. Drift ice in the Russian sector of the Arctic Sea decreased by a million square kilometers between 1924 and 1944, and in the Laptev Sea two islands of fossil ice melted away completely, their position being marked by submarine shoals.

Activities in the nonhuman world also reflect the warming of the Arctic—the changed habits and migrations of many fishes, birds, land mammals, and whales.

Many new birds are appearing in far northern lands for the first time in our records. The long list of southern visitors—birds never reported in Greenland before 1920—includes the American velvet scoter, the greater yellowlegs, American avocet, black-browed albatross, northern cliff swallow, ovenbird, common crossbill, Baltimore oriole, and Canada warbler. Some high-arctic forms, which thrive in cold climates, have shown their distaste for the warmer temperatures by visiting Greenland in sharply decreasing numbers. Such abstainers include the northern horned lark, the grey plover, and the pectoral sandpiper. Iceland, too, has had an extraordinary number of boreal and even subtropical avian visitors since 1935, coming from both America and Europe. Wood warblers, skylarks, and Siberian rubythroats, scarlet grosbeaks, pipits, and thrushes now provide exciting fare for Icelandic bird watchers.

When the cod first appeared in Angmagssalik in Greenland in 1912, it was a new and strange fish to the Eskimos and Danes. Within their memory it had never before appeared on the east coast of the island. But they began to catch it, and by the 1930’s it supported so substantial a fishery in the area that the natives had become dependent upon it for food. They were also using its oil as fuel for their lamps and to heat their houses.

On the west coast of Greenland, too, the cod was a rarity at the turn of the century, although there was a small fishery, taking about 500 tons a year, at a few places on the southwest coast. About 1919 the cod began to move north along the west Greenland coast and to become more abundant. The center of the fishery has moved 300 miles farther north, and the catch is now about 15,000 tons a year.

Other fishes seldom or never before reported in Greenland have appeared there. The coalfish or green cod is a European fish so foreign to Greenland waters that when two of them were caught in 1831 they were promptly preserved in salt and sent to the Co-penhagen Zoological Museum. But since 1924 this fish has often been found among the cod shoals. The haddock, cusk, and ling, unknown in Greenland waters until about 1930, are now taken regularly. Iceland, too, has strange visitors—warmth-loving southern fishes, like the basking shark, the grotesque sunfish, the six-gilled shark, the swordfish, and the horse mackerel. Some of these same species have penetrated into the Barents and White seas and along the Murman coast.

As the chill of the northern waters has abated and the fish have moved poleward, the fisheries around Iceland have expanded enormously, and it has become profitable for trawlers to push on to Bear Island, Spitsbergen, and the Barents Sea. These waters now yield perhaps two billion pounds of cod a year—the largest catch of a single species by any fishery in the world. But its existence is tenuous. If the cycle turns, the waters begin to chill, and the ice floes creep southward again, there is nothing man can do that will preserve the arctic fisheries.

But for the present, the evidence that the top of the world is growing warmer is to be found on every hand. The recession of the northern glaciers is going on at such a rate that many smaller ones have already disappeared. If the present rate of melting continues others will soon follow them.

The melting away of the snowfields in the Opdal Mountains in Norway has exposed wooden-shafted arrows of a type used about A.D. 400 to 500. This suggests that the snow cover in this region must now be less than it has been at any time within the past 1400 to 1500 years.

The glaciologist Hans Ahlmann reports that most Norwegian glaciers ‘are living only on their own mass without receiving any annual fresh supply of snow’; that in the Alps there has been a general retreat and shrinkage of glaciers during the last decades, which became ‘catastrophic’ in the summer of 1947; and that all glaciers around the Northern Atlantic coasts are shrinking. The most rapid recession of all is occurring in Alaska, where the Muir Glacier receded about 10½ kilometers in 12 years.

At present the vast antarctic glaciers are an enigma; no one can say whether they also are melting away, or at what rate. But reports from other parts of the world show that the northern glaciers are not the only ones that are receding. The glaciers of several East African high volcanoes have been diminishing since they were first studied in the 1800’s—very rapidly since 1920—and there is glacial shrinkage in the Andes and also in the high mountains of central Asia.

The milder arctic and sub-arctic climate seems already to have resulted in longer growing seasons and better crops. The cultivation of oats has improved in Iceland. In Norway good seed years are now the rule rather than the exception, and even in northern Scandinavia the trees have spread rapidly above their former timber lines, and both pine and spruce are making a quicker annual growth than they have for some time.

The countries where the most striking changes are taking place are those whose climate is most directly under the control of the North Atlantic currents. Greenland, Iceland, Spitsbergen, and all of northern Europe, as we have seen, experience heat and cold, drought and flood in accordance with the varying strength and warmth of the eastward and northward-moving currents of the Atlantic. Oceanographers who have been studying the matter during the 1940’s have discovered many significant changes in the temperature and distribution of great masses of ocean water. Apparently the branch of the Gulf Stream that flows past Spitsbergen has so increased in volume that it now brings in a great body of warm water. Surface waters of the North Atlantic show rising temperatures; so do the deeper layers around Iceland and Spitsbergen. Sea temperatures in the North Sea and along the coast of Norway have been growing warmer since the 1920’s.

Unquestionably, there are other agents at work in bringing about the climatic changes in the Arctic and sub-Arctic regions. For one thing, it is almost certainly true that we are still in the warming-up stage following the last Pleistocene glaciation—that the world’s climate, over the next thousands of years, will grow considerably warmer before beginning a downward swing into another Ice Age. But what we are experiencing now is perhaps a climatic change of shorter duration, measurable only in decades or centuries. Some scientists say that there must have been a small increase in solar activity, changing the patterns of air circulation and causing the southerly winds to blow more frequently in Scandinavia and Spitsbergen; changes in ocean currents, according to this view, are secondary effects of the shift of prevailing winds.

But if, as Professor Brooks thinks, the Pettersson tidal theory has as good a foundation as that of changing solar radiation, then it is interesting to calculate where our twentieth-century situation fits into the cosmic scheme of the shifting cycles of the tides. The great tides at the close of the Middle Ages, with their accompanying snow and ice, furious winds, and inundating floods, are more than five centuries behind us. The era of weakest tidal movements, with a climate as benign as that of the early Middle Ages, is about four centuries ahead. We have therefore begun to move strongly into a period of warmer, milder weather. There will be fluctuations, as earth and sun and moon move through space and the tidal power waxes and wanes. But the long trend is toward a warmer earth; the pendulum is swinging.

Wealth from the Salt Seas

THE OCEAN IS THE earth’s greatest storehouse of minerals. In a single cubic mile of sea water there are, on the average, 166 million tons of dissolved salts, and in all the ocean waters of the earth there are about 50 quadrillion tons. And it is in the nature of things for this quantity to be gradually increasing over the millennia, for although the earth is constantly shifting her component materials from place to place, the heaviest movements are forever seaward.

It has been assumed that the first seas were only faintly saline and that their saltiness has been growing over the eons of time. For the primary source of the ocean’s salt is the rocky mantle of the continents. When those first rains came—the centuries-long rains that fell from the heavy clouds enveloping the young earth—they began the processes of wearing away the rocks and carrying their contained minerals to the sea. The annual flow of water seaward is believed to be about 6500 cubic miles, this inflow of river water adding to the ocean several billion tons of salts.

It is a curious fact that there is little similarity between the chemical composition of river water and that of sea water. The various elements are present in entirely different proportions. The rivers bring in four times as much calcium as chloride, for example, yet in the ocean the proportions are strongly reversed—46 times as much chloride as calcium. An important reason for the difference is that immense amounts of calcium salts are constantly being withdrawn from the sea water by marine animals and are used for building shells and skeletons—for the microscopic shells that house the foraminifera, for the massive structures of the coral reefs, and for the shells of oysters and clams and other mollusks. Another reason is the precipitation of calcium from sea water. There is a striking difference, too, in the silicon content of river and sea water—about 500 per cent greater in rivers than in the sea. The silica is required by diatoms to make their shells, and so the immense quantities brought in by rivers are largely utilized by these ubiquitous plants of the sea. Often there are exceptionally heavy growths of diatoms off the mouths of rivers. Because of the enormous total chemical requirements of all the fauna and flora of the sea, only a small part of the salts annually brought in by rivers goes to increasing the quantity of dissolved minerals in the water. The inequalities of chemical make-up are further reduced by reactions that are set in motion immediately the fresh water is discharged into the sea, and by the enormous disparities of volume between the incoming fresh water and the ocean.

There are other agencies by which minerals are added to the sea—from obscure sources buried deep within the earth. From every volcano chlorine and other gases escape into the atmosphere and are carried down in rain onto the surface of land and sea. Volcanic ash and rock bring up other materials. And all the submarine volcanoes, discharging through unseen craters directly into the sea, pour in boron, chlorine, sulphur, and iodine.

All this is a one-way flow of minerals to the sea. Only to a very limited extent is there any return of salts to the land. We attempt to recover some of them directly by chemical extraction and mining, and indirectly by harvesting the sea’s plants and animals. There is another way, in the long, recurring cycles of the earth, by which the sea itself gives back to the land what it has received. This happens when the ocean waters rise over the lands, deposit their sediments, and at last withdraw, leaving over the continent another layer of sedimentary rocks. These contain some of the water and salts of the sea. But it is only a temporary loan of minerals to the land and the return payment begins at once by way of the old, familiar channels—rain, erosion, run-off to the rivers, transport to the sea.

There are other curious little exchanges of materials between sea and land. While the process of evaporation, which raises water vapor into the air, leaves most of the salts behind, a surprising amount of salt does intrude itself into the atmosphere and rides long distances on the wind. The so-called ‘cyclic salt’ is picked up by the winds from the spray of a rough, cresting sea or breaking surf and is blown inland, then brought down in rain and returned by rivers to the ocean. These tiny, invisible particles of sea salt drifting in the atmosphere are, in fact, one of the many forms of atmospheric nuclei around which raindrops form. Areas nearest the sea, in general, receive the most salt. Published figures have listed 24 to 36 pounds per acre per year for England and more than 100 pounds for British Guiana. But the most astounding example of long-distance, large-scale transport of cyclic salts is furnished by Sambhar Salt Lake in northern India. It receives 3000 tons of salt a year, carried to it on the hot dry monsoons of summer from the sea, 400 miles away.

The plants and animals of the sea are very much better chemists than men, and so far our own efforts to extract the mineral wealth of the sea have been feeble compared with those of lower forms of life. They have been able to find and to utilize elements present in such minute traces that human chemists could not detect their presence until, very recently, highly refined methods of spectroscopic analysis were developed.

We did not know, for example, that vanadium occurred in the sea until it was discovered in the blood of certain sluggish and sedentary sea creatures, the holothurians (of which sea cucumbers are an example) and the ascidians. Relatively huge quantities of cobalt are extracted by lobsters and mussels, and nickel is utilized by various mollusks, yet it is only within recent years that we have been able to recover even traces of these elements. Copper is recoverable only as about a hundredth part in a million of sea water, yet it helps to constitute the life blood of lobsters, entering into their respiratory pigments as iron does into human blood.

In contrast to the accomplishments of invertebrate chemists, we have so far had only limited success in extracting sea salts in quantities we can use for commercial purposes, despite their prodigious quantity and considerable variety. We have recovered about fifty of the known elements by chemical analysis, and shall perhaps find that all the others are there, when we can develop proper methods to discover them. Five salts predominate and are present in fixed proportions. As we would expect, sodium chloride is by far the most abundant, making up 77.8 per cent of the total salts; magnesium chloride follows, with 10.9 per cent; then magnesium sulphate, 4.7 per cent; calcium sulphate, 3.6 per cent; and potassium sulphate, 2.5 per cent. All others combined make up the remaining .5 per cent.

Of all the elements present in the sea, probably none has stirred men’s dreams more than gold. It is there—in all the waters covering the greater part of the earth’s surface—enough in total quantity to make every person in the world a millionaire. But how can the sea be made to yield it? The most determined attempt to wrest a substantial quantity of gold from ocean waters—and also the most complete study of the gold in sea water—was made by the German chemist Fritz Haber after the First World War. Haber conceived the idea of extracting enough gold from the sea to pay the German war debt and his dream resulted in the German South Atlantic Expedition of the Meteor. The Meteor was equipped with a laboratory and filtration plant, and between the years 1924 and 1928 the vessel crossed and recrossed the Atlantic, sampling the water. But the quantity found was less than had been expected, and the cost of extraction far greater than the value of the gold recovered. The practical economics of the matter are about as follows: in a cubic mile of sea water there is about $93,000,000 in gold and $8,500,000 in silver. But to treat this volume of water in a year would require the twice-daily filling and emptying of 200 tanks of water, each 500 feet square and 5 feet deep. Probably this is no greater feat, relatively, than is accomplished regularly by corals, sponges, and oysters, but by human standards it is not economically feasible.

Most mysterious, perhaps, of all substances in the sea is iodine. In sea water it is one of the scarcest of the nonmetals, difficult to detect and resisting exact analysis. Yet it is found in almost every marine plant and animal. Sponges, corals, and certain seaweeds accumulate vast quantities of it. Apparently the iodine in the sea is in a constant state of chemical change, sometimes being oxidized, sometimes reduced, again entering into organic combinations. There seem to be constant interchanges between air and sea, the iodine in some form perhaps being carried into the air in spray, for the air at sea level contains detectable quantities, which decrease with altitude. From the time living things first made iodine a part of the chemistry of their tissues, they seem to have become increasingly dependent on it; now we ourselves could not exist without it as a regulator of the basal metabolism of our bodies, through the thyroid gland which accumulates it.

All commercial iodine was formerly obtained from seaweeds; then the deposits of crude nitrate of soda from the high deserts of North Chile were discovered. Probably the original source of this raw material—called ‘caliche’— was some prehistoric sea filled with marine vegetation, but that is a subject of controversy. Iodine is obtained also from brine deposits and from the subterranean waters of oil-bearing rocks—all indirectly of marine origin.

A monopoly on the world’s bromine is held by the ocean, where 99 per cent of it is now concentrated. The tiny fraction present in rocks was originally deposited there by the sea. First we obtained it from the brines left in subterranean pools by prehistoric oceans; now there are large plants on the seacoasts—especially in the United States—which use ocean water as their raw material and extract the bromine directly. Thanks to modern methods of commercial production of bromine we have high-test gasoline for our cars. There is a long list of other uses, including the manufacture of sedatives, fire extinguishers, photographic chemicals, dyestuffs, and chemical warfare materials.

One of the oldest bromine derivatives known to man was Tyrian purple, which the Phoenicians made in their dyehouses from the purple snail, Murex. This snail may be linked in a curious and wonderful way with the prodigious and seemingly unreasonable quantities of bromine found today in the Dead Sea, which contains, it is estimated, some 850 million tons of the chemical. The concentration of bromine in Dead Sea water is 100 times that in the ocean. Apparently the supply is constantly renewed by underground hot springs, which discharge into the bottom of the Sea of Galilee, which in turn sends its waters to the Dead Sea by way of the River Jordan. Some authorities believe that the source of the bromine in the hot springs is a deposit of billions of ancient snails, laid down by the sea of a bygone age, in a stratum long since buried.

Magnesium is another mineral we now obtain by collecting huge volumes of ocean water and treating it with chemicals, although originally it was derived only from brines or from the treatment of such magnesium-containing rocks as dolomite, of which whole mountain ranges are composed. In a cubic mile of sea water there are about 4 million tons of magnesium. Since the direct extraction method was developed about 1941, production has increased enormously. It was magnesium from the sea that made possible the wartime growth of the aviation industry, for every airplane made in the United States (and in most other countries as well) contains about half a ton of magnesium metal. And it has innumerable uses in other industries where a light-weight metal is desired, besides its long-standing utility as an insulating material, and its use in printing inks, medicines, and toothpastes, and in such war implements as incendiary bombs, star shells, and tracer ammunition.

Wherever climate has permitted it, men have evaporated salt from sea water for many centuries. Under the burning sun of the tropics the ancient Greeks, Romans, and Egyptians harvested the salt men and animals everywhere must have in order to live. Even today in parts of the world that are hot and dry and where drying winds blow, solar evaporation of salt is practiced—on the shores of the Persian Gulf, in China, India, and Japan, in the Philippines, and on the coast of California and the alkali flats of Utah.

Here and there are natural basins where the action of sun and wind and sea combine to carry on evaporation of salt on a scale far greater than human industry could accomplish. Such a natural basin is the Rann of Cutch on the west coast of India. The Rann is a flat plain, some 60 by 185 miles, separated from the sea by the island of Cutch. When the southwest monsoons blow, sea water is carried in by way of a channel to cover the plain. But in summer, in the season when the hot northeast monsoon blows from the desert, no more water enters, and that which is collected in pools over the plain evaporates into a salt crust, in some places several feet thick.

Where the sea has come in over the land, laid down its deposits, and then withdrawn, there have been created reservoirs of chemicals, upon which we can draw with comparatively little trouble. Hidden deep under the surface of our earth are pools of ‘fossil salt water,’ the brine of ancient seas; ‘fossil deserts,’ the salt of old seas that evaporated away under conditions of extreme heat and dryness; and layers of sedimentary rock in which are contained the organic sediments and the dissolved salts of the sea that deposited them.

During the Permian period, which was a time of great heat and dryness and widespread deserts, a vast inland sea formed over much of Europe, covering parts of the present Britain, France, Germany, and Poland. Rains came seldom and the rate of evaporation was high. The sea became exceedingly salty, and it began to deposit layers of salts. For a period covering thousands of years, only gypsum was deposited, perhaps representing a time when water fresh from the ocean occasionally entered the inland sea to mix with its strong brine. Alternating with the gypsum were thicker beds of salt. Later, as its area shrank and the sea grew still more concentrated, deposits of potassium and magnesium sulphates were formed (this stage representing perhaps 500 years); still later, and perhaps for another 500 years, there were laid down mixed potassium and magnesium chlorides or carnallite. After the sea had completely evaporated, desert conditions prevailed, and soon the salt deposits were buried under sand. The richest beds form the famous deposits of Stassfurt and Alsace; toward the outskirts of the original area of the old sea (as, for example, in England) there are only beds of salt. The Stassfurt beds are about 2500 feet thick; their springs of brine have been known since the thirteenth century, and the salts have been mined since the seventeenth century.

At an even earlier geological period—the Silurian—a great salt basin was deposited in the northern part of the United States, extending from central New York State across Michigan, including northern Pennsylvania and Ohio and part of southern Ontario. Because of the hot, dry climate of that time, the inland sea lying over this place grew so salty that beds of salt and gypsum were deposited over a great area covering about 100,000 square miles. There are seven distinct beds of salt at Ithaca, New York, the uppermost lying at a depth of about half a mile. In southern Michigan some of the individual salt beds are more than 500 feet thick, and the aggregate thickness of salt in the center of the Michigan Basin is approximately 2000 feet. In some places rock salt is mined; in others wells are dug, water is forced down, and the resulting brine is pumped to the surface and evaporated to recover the salt.

One of the greatest stock piles of minerals in the world came from the evaporation of a great inland sea in the western United States. This is Searles Lake in the Mohave Desert of California. An arm of the sea that overlay this region was cut off from the ocean by the thrusting up of a range of mountains; as the lake evaporated away, the water that remained became ever more salty through the inwash of materials from all the surrounding land. Perhaps Searles Lake began its slow transformation from a landlocked sea to a ‘frozen’ lake—a lake of solid minerals—only a few thousand years ago; now its surface is a hard crust of salts over which a car may be driven. The crystals of salts form a layer 50 to 70 feet deep. Below that is mud. Engineers have recently discovered a second layer of salts and brine, probably at least as thick as the upper layer, underlying the mud. Searles Lake was first worked in the 1870’s for borax; then teams of 20 mules each carried the borax across desert and mountains to the railroads. In the 1930’s the recovery of other substances from the lake began—bromine, lithium, and salts of potassium and sodium. Now Searles Lake yields 40 per cent of the production of potassium chloride in the United States and a large share of all the borax and lithium salts produced in the world.

In some future era the Dead Sea will probably repeat the history of Searles Lake, as the centuries pass and evaporation continues. The Dead Sea as we know it is all that remains of a much larger inland sea that once filled the entire Jordan Valley and was about 190 miles long; now it has shrunk to about a fourth of this length and a fourth of its former volume. And with the shrinkage and the evaporation in the hot dry climate has come the concentration of salts that makes the Dead Sea a great reservoir of minerals. No animal life can exist in its brine; such luckless fish as are brought down by the River Jordan die and provide food for the sea birds. It is 1300 feet below the Mediterranean, lying farther below sea level than any other body of water in the world. It occupies the lowest part of the rift valley of the Jordan, which was created by a down-slipping of a block of the earth’s crust. The water of the Dead Sea is warmer than the air, a condition favoring evaporation, and clouds of its vapor float, nebulous and half formed, above it, while its brine grows more bitter and the salts accumulate.

Of all legacies of the ancient seas the most valuable is petroleum. Exactly what geologic processes have created the precious pools of liquid deep within the earth no one knows with enough certainty to describe the whole sequence of events. But this much seems to be true: Petroleum is a result of fundamental earth processes that have been operating ever since an abundant and varied life was developed in the sea—at least since the beginning of Paleozoic time, probably longer. Exceptional and catastrophic occurrences may now and then aid its formation but they are not essential; the mechanism that regularly generates petroleum consists of the normal processes of earth and sea—the living and dying of creatures, the deposit of sediments, the advance and retreat of the seas over the continents, the upward and downward foldings of the earth’s crust.

The old inorganic theory that linked petroleum formation with volcanic action has been abandoned by most geologists. The origin of petroleum is most likely to be found in the bodies of plants and animals buried under the fine-grained sediments of former seas and there subjected to slow decomposition.

Perhaps the essence of conditions favoring petroleum production is represented by the stagnant waters of the Black Sea or of certain Norwegian fiords. The surprisingly abundant life of the Black Sea is confined to the upper layers; the deeper and especially the bottom waters are devoid of oxygen and are often permeated with hydrogen sulphide. In these poisoned waters there can be no bottom scavengers to devour the bodies of marine animals that drift down from above, so they are entombed in the fine sediments. In many Norwegian fiords the deep layers are foul and oxygenless because the mouth of the fiord is cut off from the circulation of the open sea by a shallow sill. The bottom layers of such fiords are poisoned by the hydrogen sulphide from decomposing organic matter. Sometimes storms drive in unusual quantities of oceanic water and through turbulence of waves stir deeply the waters of these lethal pools; the mixing of the water layers that follows brings death to hordes of fishes and invertebrates living near the surface. Such a catastrophe leads to the deposit of a rich layer of organic material on the bottom.

Wherever great oil fields are found, they are related to past or present seas. This is true of the inland fields as well as of those near the present seacoast. The great quantities of oil that have been obtained from the Oklahoma fields, for example, were trapped in spaces within sedimentary rocks laid down under seas that invaded this part of North America in Paleozoic time.

The search for petroleum has also led geologists repeatedly to those ‘unstable belts, covered much of the time by shallow seas, which lie around the margins of the main continental platforms, between them and the great oceanic deeps.’

An example of such a depressed segment of crust lying between continental masses is the one between Europe and the Near East, occupied in part by the Persian Gulf, the Red, Black, and Caspian seas, and the Mediterranean Sea. The Gulf of Mexico and the Caribbean Sea lie in another basin or shallow sea between the Americas. A shallow, island-studded sea lies between the continents of Asia and Australia. Lastly, there is the nearly landlocked sea of the Arctic. In past ages all of these areas have been alternately raised and depressed, belonging at one time to the land, at another to the encroaching sea. During their periods of submersion they have received thick deposits of sediments, and in their waters a rich marine fauna has lived, died, and drifted down into the soft sediment carpet.

There are vast oil deposits in all these areas. In the Near East are the great fields of Saudi Arabia, Iran, and Iraq. The shallow depression between Asia and Australia yields the oil of Java, Sumatra, Borneo, and New Guinea. The American mediterranean is the center of oil production in the Western Hemisphere—half the proved resources of the United States come from the northern shore of the Gulf of Mexico, and Colombia, Venezuela, and Mexico have rich oil fields along the western and southern margins of the Gulf. The Arctic is one of the unproved frontiers of the petroleum industry, but oil seepages in northern Alaska, on islands north of the Canadian mainland, and along the Arctic coast of Siberia hint that this land recently raised from the sea may be one of the great oil fields of the future.

In recent years, the speculations of petroleum geologists have been focused in a new direction—under sea. By no means all of the land resources of petroleum have been discovered, but probably the richest and most easily worked fields are being tapped, and their possible production is known. The ancient seas gave us the oil that is now being drawn out of the earth. Can the ocean today be induced to give up some of the oil that must be trapped in sedimentary rocks under its floor, covered by water scores or hundreds of fathoms deep?

Oil is already being produced from offshore wells, on the continental shelf. Off California, Texas, and Louisiana, oil companies have drilled into the sediments of the shelf and are obtaining oil. In the United States the most active exploration has been centered in the Gulf of Mexico. Judging from its geologic history, this area has rich promise. For eons of time it was either dry land or a very shallow sea basin, receiving the sediments that washed into it from high lands to the north. Finally, about the middle of the Cretaceous period, the floor of the Gulf began to sink under the load of sediments and in time it acquired its present deep central basin.

By geophysical exploration, we can see that the layers of sedimentary rock underlying the coastal plain tilt steeply downward and pass under the broad continental shelf of the Gulf. Down in the layers deposited in the Jurassic period is a thick salt bed of enormous extent, probably formed when this part of the earth was hot and dry, a place of shrinking seas and encroaching deserts. In Louisiana and Texas, and also, it now appears, out in the Gulf itself, extraordinary features known as salt domes are associated with this deposit. These are fingerlike plugs of salt, usually less than a mile across, pushing up from the deep layer toward the earth’s surface. They have been described by geologists as ‘driven up through 5000 to 15,000 feet of sediments by earth pressures, like nails through a board.’ In the states bordering the Gulf such structures have often been associated with oil. It seems probable that on the continental shelf, also, the salt domes may mark large oil deposits.

In exploring the Gulf for oil, therefore, geologists search for the salt domes where the larger oil fields are likely to lie. They use an instrument known as a magnetometer, which measures the variations in magnetic intensity brought about by the salt domes. Gravity meters also help locate the domes by measuring the variation in gravity near them, the specific gravity of salt being less than that of the surrounding sediments. The actual location and outline of the dome are discovered by seismographic exploration, which traces the inclination of the rock strata by recording the reflection of sound waves produced by dynamite explosions. These methods of exploration have been used on land for some years, but only since about 1945 have they been adapted to use in off-shore Gulf waters. The magnetometer has been so improved that it will map continuously while being towed behind a boat or carried in or suspended from a plane. A gravity meter can now be lowered rapidly to the bottom and readings made by remote control. (Once an operator had to descend with it in a diving bell.) Seismic crews may shoot off their dynamite charges and make continuous recordings while their boats are under way.

Despite all these improvements which allow exploration to proceed rapidly, it is no simple matter to obtain oil from undersea fields. Prospecting must be followed by the leasing of potential oil-producing areas, and then by drilling to see whether oil is actually there. Offshore drilling platforms rest on piles that must be driven as far as 250 feet into the floor of the Gulf to withstand the force of waves, especially during the season for hurricanes. Winds, storm waves, fogs, the corrosive gnawing of sea water upon metal structures—all these are hazards that must be faced and overcome. Yet the technical difficulties of far more extensive offshore operations than any now attempted do not discourage specialists in petroleum engineering.

So our search for mineral wealth often leads us back to the seas of ancient times—to the oil pressed from the bodies of fishes, seaweeds, and other forms of plant and animal life and then stored away in ancient rocks; to the rich brines hidden in subterranean pools where the fossil water of old seas still remains; to the layers of salts that are the mineral substances of those old seas laid down as a covering mantle over the continents. Perhaps in time, as we learn the chemical secrets of the corals and sponges and diatoms, we shall depend less on the stored wealth of prehistoric seas and shall go more and more directly to the ocean and the rocks now forming under its shallow waters.

The Encircling Sea

TO THE ANCIENT GREEKS the ocean was an endless stream that flowed forever around the border of the world, ceaselessly turning upon itself like a wheel, the end of earth, the beginning of heaven. This ocean was boundless; it was infinite. If a person were to venture far out upon it—were such a course thinkable—he would pass through gathering darkness and obscuring fog and would come at last to a dreadful and chaotic blending of sea and sky, a place where whirlpools and yawning abysses waited to draw the traveler down into a dark world from which there was no return.

These ideas are found, in varying form, in much of the literature of the ten centuries before the Christian era, and in later years they keep recurring even through the greater part of the Middle Ages. To the Greeks the familiar Mediterranean was The Sea. Outside, bathing the periphery of the land world, was Oceanus. Perhaps somewhere in its uttermost expanse was the home of the gods and of departed spirits, the Elysian fields. So we meet the ideas of unattainable continents or of beautiful islands in the distant ocean, confusedly mingled with references to a bottomless gulf at the edge of the world—but always around the disc of the habitable world was the vast ocean, encircling all.

Perhaps some word-of-mouth tales of the mysterious northern world, filtering down by way of the early trade routes for amber and tin, colored the conceptions of the early legends, so that the boundary of the land world came to be pictured as a place of fog and storms and darkness. Homer’s Odyssey described the Cimmerians as dwelling in a distant realm of mist and darkness on the shores of Oceanus, and they told of the shepherds who lived in the land of the long day, where the paths of day and night were close. And again perhaps the early poets and historians derived some of their ideas of the ocean from the Phoenicians, whose craft roamed the shores of Europe, Asia, and Africa in search of gold, silver, gems, spices, and wood for their commerce with kings and emperors. It may well be that these sailor-merchants were the first ever to cross an ocean, but history does not record the fact. For at least 2000 years before Christ—probably longer—the flourishing trade of the Phoenicians was plied along the shores of the Red Sea to Syria, to Somaliland, to Arabia, even to India and perhaps to China. Herodotus wrote that they circumnavigated Africa from east to west about 600 B.C., reaching Egypt via the Straits of the Pillars and the Mediterranean. But the Phoenicians themselves said and wrote little or nothing of their voyagings, keeping their trade routes and the sources of their precious cargoes secret. So there are only the vaguest rumors, sketchily supported by archaeological findings, that the Phoenicians may have launched out into the open Pacific.

Nor are there anything but rumors and highly plausible suppositions that the Phoenicians, on their coastwise journeys along western Europe, may have sailed as far north as the Scandinavian peninsula and the Baltic, source of the precious amber. There are no definite traces of any such visits by them, and of course the Phoenicians have left no written record of any. Of one of their European voyages, however, there is a secondhand account. This was the expedition under Himlico of Carthage, which sailed northward along the European coast about the year 500 B.C. Himlico apparently wrote an account of this voyage, although his manuscript was not preserved. But his descriptions are quoted by the Roman Avienus, writing nearly a thousand years later. According to Avienus, Himlico painted a discouraging picture of the coastwise seas of Europe:

Perhaps the ‘wild beasts’ are the whales of the Bay of Biscay, later to become a famous whaling ground; the shallow water areas that so impressed Himlico may have been the flats alternately exposed and covered by the ebb and flow of the great tides of the French coast—a strange phenomenon to one from the almost tide-less Mediterranean. But Himlico also had ideas of the open ocean to the west, if the account of Avienus is to be trusted: ‘Farther to the west from these Pillars there is boundless sea… None has sailed ships over these waters, because propelling winds are lacking on these deeps… likewise because darkness screens the light of day with a sort of clothing, and because a fog always conceals the sea.’ Whether these descriptive details are touches of Phoenician canniness or merely the old ideas reasserting themselves it is hard to say, but much the same conceptions appear again and again in later accounts, echoing down the centuries to the very threshold of modern times.

So far as historical records are concerned, the first great voyage of marine exploration was by Pytheas of Massilia about 330 B.C. Unfortunately his writings, including one called On the Ocean, are lost and their substance is preserved for us only in fragmentary quotations passed on by later writers. We know very little of the controlling circumstances of the northward voyage of this astronomer and geographer, but probably Pytheas wished to see how far the oecumene or land world extended, to learn the position of the Arctic Circle, and to see the land of midnight sun. Some of these things he may have heard of through the merchants who brought down tin and amber from the Baltic lands by the overland trade routes.

Since Pytheas was the first to use astronomical measurements to determine the geographic location of a place and in other ways had proved his competence as an astronomer, he brought more than ordinary skill to an exploratory voyage. He seems to have sailed around Great Britain, to have reached the Shetland Islands, and then to have launched out into the open ocean to the north, coming at last to ‘Thule,’ the land of midnight sun. In this country, he is quoted as reporting, ‘the nights were very short, in some places two, in others three hours long, so that the sun rose again a short time after it had set.’ The country was inhabited by ‘barbarians’ who showed Pytheas ‘the place where the sun goes to rest.’ The location of ‘Thule’ is a point much disputed by later authorities, some believing it to have been Iceland, while others believe that Pytheas crossed the North Sea to Norway. Pytheas is also said to have described a ‘congealed sea’ lying north of Thule, which accords better with Iceland.

But the Dark Ages were settling down over the civilized world, and little of the knowledge of distant places acquired by Pytheas on his voyagings seems to have impressed the learned men who followed him. The geographer Posidonius wrote of the ocean that ‘stretched to infinity’ and from Rhodes he undertook a journey all the way to Gadir (Cadiz) to see the ocean, measure its tides, and determine the truth of the belief that the sun dropped with the hissing of a red-hot body into the great western sea.

Not for about 1200 years after Pytheas do we have another clear account of marine exploration—this time by the Norwegian Ottar. Ottar described his voyagings in northern seas to King Alfred, who recorded them in a straightforward narrative of geographic exploration strikingly free from sea monsters and other imaginary terrors. Ottar, on the basis of this account, was the first known explorer to round the North Cape, to enter the Polar or Barents Sea, and later to enter the White Sea. He found the coasts of these seas inhabited by people of whom he seems to have heard previously. According to the narrative, he went there ‘chiefly to explore the country, and for the sake of the walrus, for they have much valuable bone in their tusks.’ This voyage was probably made between A.D. 870 and 890.

Meanwhile the age of the Vikings had dawned. The beginning of their more important expeditions is usually considered to be the end of the eighth century. But long before that time they had visited other countries of northern Europe. ‘As early as the third century and until the close of the fifth century,’ wrote Fridtjof Nansen, ‘the roving Eruli sailed from Scandinavia, sometimes in company with Saxon pirates, over the seas of western Europe, ravaging the coasts of Gaul and Spain, and indeed penetrating in 455 into the Mediterranean as far as Lucca in Italy.’ As early as the sixth century the Vikings must have crossed the North Sea to the land of the Franks, and probably to southern Britain. They may have established themselves in Shetland by the beginning of the seventh century, and plundered the Hebrides and northwest Ireland about the same time. Later they sailed to the Faroes and to Iceland; in the last quarter of the tenth century they established two colonies in Greenland, and shortly thereafter they steered across the intervening Atlantic waters to North America. Of the place of these voyages in history Nansen writes:

But only the vaguest rumors of any of these things had reached the ‘civilized world’ of the Mediterranean. While the sagas of the Norsemen were giving clear and factual directions for the passage across oceans, from known to unknown worlds, the writings of the scholars of the medieval world dealt still with that outermost encircling ocean, the dread Sea of Darkness. About the year 1154 the noted Arab geographer Edrisi wrote for the Norman king of Sicily, Roger II, a description of the earth, accompanied by 70 maps, which portrayed on the outside of all the known earth the Dark Sea, forming the limit of the world. He wrote of the sea about the British Isles that it is ‘impossible to penetrate very far into this ocean.’ He hinted at the existence of far islands but thought the approach to them difficult because of the ‘fog and deep darkness that prevails on this sea.’ The scholarly Adam of Bremen, writing in the eleventh century, knew of the existence of Greenland and Wineland as distant islands in the great ocean, but could not separate the reality from the old ideas of that sea, ‘infinite and fearful to behold, which encompasses the whole world,’ that ocean flowing ‘endlessly around the circle of the earth.’ And even the Norsemen themselves, as they discovered lands across the Atlantic, seem merely to have pushed back the boundaries of the place where still there began that outermost ocean, for the idea of the outer ocean surrounding the disc of the earth appears in such Northern chronicles as the Kings Mirror and the Heimskringla. And so over that Western Ocean into which Columbus and his men set out there hung still the legend of a dead and stagnant sea, of monsters and entrapping weeds, of fog and gloom and ever present danger.

Yet centuries before Columbus—no one knows how many centuries—men on the opposite side of the world had laid aside whatever fears the ocean may have inspired and were boldly sailing their craft across the Pacific. We know little of the hardships, the difficulties, and the fears that may have beset the Polynesian colonists—we know only that somehow they came from the mainland to those islands, remote from any shore. Perhaps the aspect of these central Pacific waters was kindlier than that of the North Atlantic—it must have been—for in their open canoes they entrusted themselves to the stars and the signposts of the sea and found their way from island to island.

We do not know when the first Polynesian voyages took place. Concerning the later ones, there is some evidence that the last important colonizing voyage to the Hawaiian Islands was made in the thirteenth century, and that about the middle of the fourteenth century a fleet from Tahiti permanently colonized New Zealand. But again, all those things were unknown in Europe, and long after the Polynesians had mastered the art of navigating unknown seas, the European sailors still regard the Pillars of Hercules as the gateway to a dreaded sea of darkness.

Once Columbus had shown the way to the West Indies and the Americas, once Balboa had seen the Pacific and Magellan had sailed around the globe, there arose, and long persisted, two new ideas. One concerned the existence of a northern passage by sea to Asia; the other had to do with a great southern continent generally believed to lie below the then-known lands.

Magellan, while sailing through the strait that now bears his name, had seen land to the south of him through all the thirty-seven days required for the passage through the strait. At night the lights of many fires glowed from the shores of this land, which Magellan named Tierra del Fuego—Land of Fires. He supposed that these were the near shores of that great land which the theoretical geographers had already decided should lie to the south.

Many voyagers after Magellan reported land they assumed to be outlying regions of the sought-for continent, but all proved to be islands. The locations of some, like Bouvet, were so indefinitely described that they were found and lost again many times before being definitely fixed on maps. Kerguelen believed firmly that the bleak, forbidding land he discovered in 1772 was the Southern Continent and so reported it to the French government. When, on a later voyage, he learned that he had found merely another island, Kerguelen unhappily named it ‘Isle of Desolation.’ Later geographers, however, gave his own name to it.

Discovery of the southern land was one of the objects of Captain Cook’s voyages, but instead of a continent, he discovered an ocean. By making an almost complete circumnavigation of the globe in high southern latitudes, Cook revealed the existence of a stormy ocean running completely around the earth south of Africa, Australia, and South America. Perhaps he believed that the islands of the South Sandwich group were part of the Antarctic mainland, but it is by no means sure that he was the first to see these or other islands of the Antarctic Ocean. American sealers had quite possibly been there before him, yet this chapter of Antarctic exploration contains many blank pages. The Yankee sealers did not want their competitors to find the rich sealing grounds, and they kept the details of their voyages secret. Evidently they had operated in the vicinity of the outer Antarctic islands for many years before the beginning of the nineteenth century, because most of the fur seals in these waters had been exterminated by 1820. It was in this year that the Antarctic continent was first sighted, by Captain N. B. Palmer in command of the Hero, one of a fleet of eight sealers from Connecticut ports. A century later, explorers were still making fresh discoveries about the nature of that Southern Continent, dreamed of by the old geographers, so long searched for, then branded a myth, and finally established as one of the great continental masses of the earth.

At the opposite pole, meanwhile, the dream of a northern passage to the riches of Asia lured one expedition after another into the frozen seas of the north. Cabot, Frobisher, and Davis sought the passage to the northwest, failed, and turned back. Hudson was left by a mutinous crew to die in an open boat. Sir John Franklin set out with the Erebus and Terror in 1845, apparently entered the labyrinth of Arctic islands by what later proved a feasible route, but then lost his ships and perished with all his men. Later rescue ships coming from east and west met in Melville Sound and thus the Northwest Passage was established.

Meanwhile there had been repeated efforts to find a way to India by sailing eastward through the Arctic Sea. The Norwegians seem to have hunted walruses in the White Sea and had probably reached the coasts of Novaya Zemlya by the time of Ottar; they may have discovered Spitsbergen in 1194, although this is usually credited to Barents in 1596. The Russians had hunted seals in the polar seas as early as the sixteenth century, and whalers began to operate out of Spitsbergen soon after Hudson, in 1607, called attention to the great number of whales in the sea between Spitsbergen and Greenland. So at least the threshold of the ice-filled northern ocean was known when the British and Dutch traders began their desperate attempt to find a sea road north of Europe and Asia. There were many attempts, but few got beyond the coasts of Novaya Zemlya; the sixteenth and seventeenth centuries were marked by the wreckage of hopes as well as of vessels, and by the death of such brilliant navigators as William Barents under the hardships met by expeditions ill prepared for arctic winters. Finally the effort was abandoned. It was not until 1879, after the practical need for such a passage had largely disappeared, that Baron Nordenskiöld, in the Swedish Vega, passed from Gothenburg to Bering Strait.

So, little by little, through many voyages undertaken over many centuries, the fog and the frightening obscurity of the unknown were lifted from all the surface of the Sea of Darkness. How did they accomplish it—those first voyagers, who had not even the simplest instruments of navigation, who had never seen a nautical chart, to whom the modern miracles of loran, radar, and sonic sounding would have been fantasied beyond belief? Who was the first man to use a mariner’s compass, and what were the embryonic beginnings of the charts and the sailing directions that are taken for granted today? None of these questions can be answered with finality; we know only enough to want to know more.

Of the methods of those secretive master mariners, the Phoenicians, we cannot even guess. We have more basis for conjecture about the Polynesians, for we can study their descendants today, and those who have done so find hints of the methods that led the ancient colonizers of the Pacific on their course from island to island. Certainly they seem to have followed the stars, which burned brightly in the heavens over those calm Pacific regions, which are so unlike the stormy and fog-bound northern seas. The Polynesians considered the stars as moving bands of light that passed across the inverted pit of the sky, and they sailed toward the stars which they knew passed over the islands of their destination. All the language of the sea was understood by them: the varying color of the water, the haze of surf breaking on rocks yet below the horizon, and the cloud patches that hang over every islet of the tropic seas and sometimes seem even to reflect the color of a lagoon within a coral atoll.

Students of primitive navigation believe that the migrations of birds had meaning for the Polynesians, and that they learned much from watching the flocks that gathered each year in the spring and fall, launched out over the ocean, and returned later out of the emptiness into which they had vanished. Harold Gatty believes the Hawaiians may have found their islands by following the spring migration of the golden plover from Tahiti to the Hawaiian chain, as the birds returned to the North American mainland. He has also suggested that the migratory path of the shining cuckoo may have guided other colonists from the Solomons to New Zealand.

Tradition and written records tell us that primitive navigators often carried with them birds which they would release and follow to land. The frigate bird or man-of-war bird was the shoresighting bird of the Polynesians (even in recent times it has been used to carry messages between islands), and in the Norse Sagas we have an account of the use of ‘ravens’ by Floki Vilgerdarson to show him the way to Iceland, ‘since seafaring men had no loadstone at that time in the north… Thence he sailed out to sea with the three ravens… And when he let loose the first it flew back astern. The second flew up into the air and back to the ship. The third flew forward over the prow, where they found land.’

In thick and foggy weather, according to repeated statements in the Sagas, the Norsemen drifted for days without knowing where they were. Then they often had to rely on observing the flight of birds to judge the direction of land. The Landnamabok says that on the course from Norway to Greenland the voyager should keep far enough to the south of Iceland to have birds and whales from there. In shallow waters it appears that the Norsemen took some sort of soundings, for the Historia Norwegiae records that Ingolf and Hjorleif found Iceland ‘by probing the waves with the lead.’

The first mention of the use of the magnetic needle as a guide to mariners occurs in the twelfth century after Christ, but as much as a century later scholars were expressing doubt that sailors would entrust their lives to an instrument so obviously invented by the devil. There is fair evidence, however, that the compass was in use in the Mediterranean about the end of the twelfth century, and in northern Europe within the next hundred years.

For navigating the known seas, there had been the equivalent of our modern Sailing Directions for a great many centuries before this. The portolano and the peripli guided the mariners of antiquity about the Mediterranean and Black seas. The portolano were harbor-finding charts, designed to accompany the coast pilots or peripli, and it is not known which of the two was developed first. The Periplus of Scylax is the oldest and most complete of these ancient Coast Pilots that have survived the hazards of the intervening centuries and are preserved for us. The chart which presumably accompanied it no longer exists, but the two were, in effect, a guide to navigation of the Mediterranean in the fourth or fifth century B.C.

The periplus called Stadiasmus, or circumnavigation of the great sea dates from about the fifth century after Christ but reads surprisingly like a modern Pilot, giving distances between points, the winds with which the various islands might be approached, and the facilities for anchorage or for obtaining fresh water. So for example, we read, ‘From Hermaea to Leuce Acte, 20 stadia hereby lies a low islet at a distance of two stadia from the land, there is anchorage for cargo boats, to be put into with west wind; but by the shore below the promontory is a wide anchoring-road for all kinds of vessels. Temple of Apollo, a famous oracle; by the temple there is water.’

Lloyd Brown, in his Story of Maps, says that no true mariners’ chart of the first thousand years after Christ has been preserved or is definitely known to have existed. This he ascribes to the fact that early mariners carefully guarded the secrets of how they made their passages from place to place; that sea charts were ‘keys to empire’ and a ‘way to wealth’ and as such were secret, hidden documents. Therefore, because the earliest specimen of such a chart now extant was made by Petrus Vesconte in 1311 does not mean that many had not existed before it.

It was a Dutchman who produced the first collection of navigational charts bound together in book form—Lucas Janssz Waghenaer. The Mariner’s Mirror of Waghenaer, first published in 1584, covered the navigation of the western coast of Europe from the Zuyder Zee to Cadiz. Soon it was issued in several languages. For many years ‘Waggoners’ guided Dutch, English, Scandinavian, and German navigators through eastern Atlantic waters, from the Canaries to Spitsbergen, for succeeding editions had extended the areas covered to include the Shetland and Faroe islands and even the northern coast of Russia as far as Novaya Zemlya.

In the sixteenth and seventeenth centuries, under the stimulus of fierce competition for the wealth of the East Indies, the finest charts were prepared not by governmental agencies, but by private enterprise. The East India companies employed their own hydro-graphers, prepared secret atlases, and generally guarded their knowledge of the sailing passages to the East as one of the most precious secrets of their trade. But in 1795 the East India Company’s hydrographer, Alexander Dalrymple, became official hydrographer to the Admiralty, and under his direction the British Admiralty began its survey of the coasts of the world from which the modern Admiralty Pilots stem.

Shortly thereafter a young man joined the United States Navy—Matthew Fontaine Maury. In only a few years Lieutenant Maury was to make his influence felt on navigation all over the world, and was to write a book, The Physical Geography of the Sea, which is now considered the foundation of the science of oceanography. After a number of years at sea, Maury assumed charge of the Depot of Charts and Instruments—the forerunner of the present Hydrographic Office—and began a practical study of winds and currents from the standpoint of the navigator. Through his energy and initiative a world-wide co-operative system was organized. Ships’ officers of all nations sent in the logs of their voyages, from which Maury assembled and organized information, which he incorporated in navigational charts. In return, the co-operating mariner received copies of the charts. Soon Maury’s sailing directions were attracting world notice: he had shortened the passage for American east-coast vessels to Rio de Janeiro by 10 days, to Australia by 20 days, and around the Horn to California by 30 days. The co-operative exchange of information sponsored by Maury remains in effect today, and the Pilot Charts of the Hydrographic Office, the lineal descendants of Maury’s charts, carry the inscription: ‘Founded on the researches of Matthew Fontaine Maury while serving as a Lieutenant in the United States Navy.’

In the modern Sailing Directions and Coast Pilots now issued by every maritime nation of the world we find the most complete information that is available to guide the navigator over the ocean. Yet in these writings of the sea there is a pleasing blend of modernity and antiquity, with unmistakable touches by which we may trace their lineage back to the sailing directions of the sagas or the peripli of the ancient Mediterranean seamen.

It is surprising, but pleasant, that sailing directions of one and the same vintage should contain instructions for obtaining position by the use of loran, and should also counsel the navigator to be guided, like the Norsemen a millennium ago, by the flight of birds and the behavior of whales in making land in foggy weather. In the Norway Pilot we read as follows:

And the ultra-modern United States Pilot for Antarctica says:

Sometimes the Pilots for remote areas of the sea can report only what the whalers or sealers or some old-time fisherman has said about the navigability of a channel or the set of the tidal currents; or they must include a chart prepared half a century ago by the last vessel to take soundings in the area. Often they must caution the navigator not to proceed without seeking information of those having ‘local knowledge.’ In phrases like these we get the feel of the unknown and the mysterious that never quite separates itself from the sea: ‘It is said that there was once an island there… such information as could be secured from reports of men with local knowledge… their position has been disputed… a bank reported by an old-time sealer.’

So here and there, in a few out-of-the-way places, the darkness of antiquity still lingers over the surface of the waters. But it is rapidly being dispelled and most of the length and breadth of the ocean is known; it is only in thinking of its third dimension that we can still apply the concept of the Sea of Darkness. It took centuries to chart the surface of the sea; our progress in delineating the unseen world beneath it seems by comparison phenomenally rapid. But even with all our modern instruments for probing and sampling the deep ocean, no one now can say that we shall ever resolve the last, the ultimate mysteries of the sea.

In its broader meaning, that other concept of the ancients remains. For the sea lies all about us. The commerce of all lands must cross it. The very winds that move over the lands have been cradled on its broad expanse and seek ever to return to it. The continents themselves dissolve and pass to the sea, in grain after grain of eroded land. So the rains that rose from it return again in rivers. In its mysterious past it encompasses all the dim origins of life and receives in the end, after, it may be, many transmutations, the dead husks of that same life. For all at last return to the sea— to Oceanus, the ocean river, like the ever-flowing stream of time, the beginning and the end.

Suggestions for Further Reading[30]

Bigelow, Henry B. and Edmonson, W. T. Wind Waves at Sea, Breakers and Surf, U.S. Navy, Hydrographic Office Pub. no. 602, Washington, U.S. Government Printing Office, 1947. 177 pp. Extremely readable; full of interesting and practical information about waves at sea and along coasts.

Johnson, Douglas W. Shore Processes and Shoreline Development. New York, John Wiley and Sons, 1919. 584 pp. Primarily for geologists and engineers concerned with shoreline changes, yet the chapter, The Work of Waves, is unmatched for sheer interest. Out of print.

Marmer, H. A. The Tide. New York, D. Appleton and Co., 1926. 282 pp. In this book the late outstanding American authority on tidal phenomena explains the complex behavior of the tides. Out of print.

Maury, Matthew Fontaine. Physical Geography of the Sea. New York, Harper and Brothers, 1855. 287 pp. Marks the foundation of the science of oceanography, as the first book to consider the sea as a dynamic whole. Out of print.

Murray, Sir John, and Hjort, Johan. The Depths of the Ocean. London, Macmillan, 1912. 822 pp. Based chiefly on the work of the Norwegian research vessel Michael Sars in the North Atlantic, this work was for many years the bible of oceanography. It is now out of print and copies are rare.

Ommaney, F. D. The Ocean. London, Oxford University Press, 1949. 238 pp. A thoughtful and pleasantly written account of the ocean and its life, for the general reader.

Russell, F. S. and Yonge, C. M. The Seas. London, Frederick Warne and Co., 1928. 379 pp. Written chiefly from the biological point of view, this is one of the best general treatments of the subject.

Sverdrup, H. U., Fleming, Richard, and Johnson, Martin W. The Oceans. New York, Prentice-Hall, Inc., 1942. 1087 pp. The standard modern textbook of oceanography.

Some of the most rewarding sources of information about the sea are the Sailing Directions of the U.S. Hydrographic Office (for waters outside of the United States) and the Coast Pilots of the U.S. Coast and Geodetic Survey (for United States shores). Besides giving detailed accounts of the coastlines and coastal waters of the world, these books are repositories of fascinating information on icebergs and sea ice, storms, and fog at sea. Some approach the character of regional geographies. Those dealing with remote and inaccessible coasts are especially interesting. They may be purchased from the issuing agency. The British Admiralty publishes a similar series, as do the appropriate authorities of most maritime nations.

Hardy, Alister. The Open Sea. Part I, The World of Plankton. Boston, Houghton Mifflin Co., 1956. 335 pp. Part II, Fish and Fisheries, Boston, Houghton Mifflin Co., 1959. 322 pp. A two-part study of marine biology, describing first the little-known creatures of the true sea world beyond the coastal areas, and then the fishes that depend on them.

Hesse, Richard, Allee, W. C, and Schmidt, Karl P. Ecological Animal Geography. New York, John Wiley and Sons (2nd Ed., 1951). 597 pp. This is an excellent source of information on the intricate relations of living things to their environment, with profuse references to source material. About a fourth of the book is concerned with marine animals.

Murphy, Robert Cushman. Oceanic Birds of South America. New York, Macmillan, 1948. 1245 pp. 2 vols. (originally issued by American Museum of Natural History, 1936). Highly recommended for an understanding of the relation of birds to the sea and of marine organisms to their environment. It describes little-known shores and islands in extremely readable prose, and contains an extensive bibliography. Out of print.

Wallace, Alfred Russell, Island Life. London, Macmillan, 1880. 526 pp. Deals in interesting fashion with the basic biology of island life. Out of print.

Yonge, C. M. The Sea Shore. London, Collins, 1949. 311 pp. For the general reader, a charming and authoritative account of the life of the shore; based chiefly on British localities. Out of print.

Ricketts, E. F. and Gavin, Jack. Between Pacific Tides. Stanford, Stanford University Press, 1948. 365 pp. An ideal companion for exploring American Pacific shores.

Babcock, William H. Legendary Islands of the Atlantic; a study in medieval geography. New York, American Geographical Society, 1922. 385 pp. Deals with early exploration of the sea and the search for distant lands. Out of print.

Beebe, William. Half Mile Down. New York, Harcourt Brace, 1934. 344 . pp. Stands alone as a vivid eyewitness account of the sea half a mile below the surface.

Brown, Lloyd A. The Story of Maps. Boston, Little, Brown, 1940. 397 pp. Contains, especially in the chapter, The Haven Finding Art, much of interest about early voyages.

Challenger Staff. Report on the Scientific Results of the Exploring Voyage of H. M. S. Challenger, 1873—76. 40 vols. See especially volume 1, parts 1 and 2—Narrative of the Cruise—which gives an interesting account of this historic expedition. Consult in libraries.

Cousteau, Jacques-Yves and Frederic Dumas. The Silent World. New York, Harper and Brothers, 1953. 288 pp. A fascinating book in which the reader shares Cousteau’s long and remarkable experience undersea.

Darwin, Charles. The Diary of the Voyage of H. M. S. Beagle. Edited from the manuscript by Nora Barlow. Cambridge, Cambridge University Press, 1934. 451 pp. A fresh and charming account, as Darwin actually set it down in the course of the Beagle voyage.

Dugan, James. Man Under the Sea. New York, Harper and Brothers, 1956. 332 pp. An interesting and useful account of man’s explorations undersea during the past 5000 years.

Heyerdahl, Thor. Kon-Tiki. Chicago, Rand McNally & Co., 1950. 304 pp. The Odyssey of six modern Vikings who crossed the Pacific on a primitive raft—one of the great books of the sea.

Brooks, C. E. P. Climate Through the Ages. New York, McGraw-Hill, 1949. 395 pp. Interprets clearly and readably the climatic changes of past ages. Out of print.

Coleman, A. P. Ice Ages, Recent and Ancient. New York, Macmillan 1926. 296 pp. An account of Pleistocene glaciation, and also of earlier glacial epochs. Out of print.

Daly, Reginald. The Changing World of the Ice Age. New Haven, Yale University Press, 1934. 271 pp. A fresh, stimulating, and vigorous treatment of the subject, more easily read, however, against some background of geology. Out of print.

Our Mobile Earth. New York, Charles Scribner’s Sons, 1926. 342 pp. For the general reader; an excellent picture of the earth’s continuing development. Out of print.

Hussy, Russell C. Historical Geology: The Geological History of North America. New York and London, McGraw-Hill, 1947. 465 pp. Out of print.

Miller, William J. An Introduction to Historical Geology, with Special Reference to North America. New York, D. Van Nostrand Co., 6th Ed. 1952. 499 pp.

Schuchert, Charles, and Dunbar, Carl O. Outlines of Historical Geology. New York, John Wiley and Sons, 1941. 291 pp. Any one of these three books will give the general reader a good conception of this fascinating subject; the treatment by the various authors differs enough that all may be read with profit.

Shepard, Francis P. Submarine Geology. New York, Harper and Brothers, 1948. 348 pp. The first textbook in a field which is still in the pioneering stages.

These books are listed because each, in one way or another, captures the sea’s varied and always changing moods; all are among my own favorite volumes.

Beston, Henry. The Outermost House: A Year of Life on the Great Beach of Cape Cod. New York, Rinehart and Company, 1949. 222 pp.

Conrad, Joseph. The Mirror of the Sea. New York, Doubleday, Anchor Books, 1960. 304 pp. (Combined with Conrad’s A Personal Record.)

Hughes, Richard. In Hazard. New York, Harper and Brothers, 1938. 279 pp. (also published by Penguin Books, 1943).

Melville, Herman. Moby Dick. Available in many editions, as Modern Library, New American Library, Pocket Books.

Nordhoff, Charles, and Hall, James Norman. Men Against the Sea. Boston, Little, Brown, 1934. 251 pp. (also published by Pocket Books, 1946).

Tomlinson, H. M. The Sea and the Jungle. New York, Modern Library, 1928. 332 pp. Paper: Dutton (Everyman).

These books provide further details about the topics discussed in the Afterword.

Kennett, J. Marine Geology. Englewood Cliffs, Prentice-Hall, 1982. An excellent textbook introducing the student to a vast subject.

Scientific American. Ocean Science. San Francisco, W. H. Freeman, 1977. A book of readings about the ocean for the educated layman.

The Global Thermostat

Dansgaard, W., J. W. C. White, and S. J. Johnsen. The abrupt termination of the Younger Dryas climate event. Nature v. 339, 1989, pp. 532–5. A short technical account of the rapidity of climatic change at the end of the last glacial age.

Houghton, R. A. and G. M. Woodwell. Global climatic change. Scientific American. v. 260, 1989, pp. 36–44. An account of the significance of the burning of fossil fuels and deforestation to world climate.

Imbrie, John, and Katherine Palmer Imbrie. Ice Ages: Solving the Mystery. Short Hills, Enslow Publishers, 1979. An historical account of the astronomical theories of the ice ages.

Jones, P. D., T. M. L. Wigley, and P. B. Wright. Global temperature variations between 1861 and 1984. Nature v. 322, 1986, pp. 430–434. A technical account of global warming over the last century.

Stanley, S. M. Extinction. New York: Freeman, 1987.

Migrations and Larval Transport

Childress, R. J. and M. Trim. Pacific Salmon. University of Washington Press, 1979. A beautifully illustrated popular description of the migrations and general biology of the Pacific salmon.

Harden Jones, F. R. Fish Migration. London: Edward Arnold, 1968.

Strathman, R. R. Feeding and nonfeeding larval development and life-history evolution in marine invertebrates. Annual Review of Ecology and Systematics, v. 16, 1985, pp. 339–361. An excellent technical account of the nature of marine invertebrate larval development and dispersal.

Birkeland, C. The Faustian traits of the crown-of-thorns starfish. American Scientist, volume 77, 1989, pp. 154–163.

Levinton, J. S. 1982. Marine Ecology. Englewood Cliffs, Prentice-Hall, 1982. Chapters 20 and 21 cover the biology of coral reefs.