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.
*During the 1950’s enormous advances were made in the development of instruments for the recording of water temperatures. A continuous recording of water temperatures to a depth of several hundred feet may be obtained by towing a thermistor chain behind a vessel. The electronic bathythermograph is potentially capable of obtaining temperatures at any depth, depending on the length of cable available. It is a vast improvement over the original bathythermograph because a recorder on deck traces a continuous graph of the temperatures being registered while the vessel is under way. An even more revolutionary development in the study of sea temperatures is the airborne radiation thermometer which, while flown above the sea, registers the surface temperature with an accuracy of a fraction of a degree. Oceanographers regard this instrument as still in the developmental stage, with further refinement of accuracy possible. However, in such work as tracing the edge of the Gulf Stream these airborne thermometers have already proven themselves enormously useful. During a 1960 survey of the Gulf Stream conducted by the Woods Hold Oceanographic Institution, a low-flying plane covered some 30,000 miles, obtaining surface temperatures in various areas of the Stream.
* Svenska Hydrog.-Biol. Komm. Skrifter, No. 5, 1912.
Wealth from the Salt Seas
A sea change into something rich and strange.
SHAKESPEARE
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, re
curring 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.
The Sea Around Us Page 21