Polar ice cap

“ It so happens, however, that the fluctuating polar ice cap hovers over the single narrow bridge to the New World and the part it has played in the story of the primates is truly wonderful. The reader familiar with the recent literature on Paleolithic man need not be told that the pulsation of this ice cap is proving the only reliable time clock for human culture. At four intervals, at least, this ice field crept down into North America and into the Old World, each time greatly modifying the distribution of mammalian life. ”

“ He further suggested a probable analogy between the Antarctic ice-cap, some 25,000 miles in diameter, and the polar ice-cap of glacial times, and mentioned Croll's estimate that the former is twelve miles thick at its center. In speaking of a polar ice-cap, he did not mean to imply, however, that the ice was necessarily thickest on the pole, but that in Greenland, Labrador, the Hudson Bay region, or elsewhere, there may have been centers from which glaciers grew finally to coalesce into one mass of ice, the top strata of which flowed southward to the great terminal moraine. ”

“ In consequence, the moist air which reaches the south frigid zone is greatly in excess of that which reaches the northern zone of cold, and the snow-fall there must be very much more considerable. It is estimated that the south polar ice-cap can not be less than three miles and may be twelve miles in height. The thrust of this vast ice mountain upon the viscid material beneath it is necessarily enormous, and a lofty ice-cliff is pushed off the land at a rate of not less than a quarter of a mile annually, and this around a circle of great extent. ”

“ While it is melting it takes all the heat available and so preserves the fresh-water ice, which melts after all the salt-water ice is gone. In old hummocky ice this process of purification has been going on intermittently whenever the weather was warm enough. I trust I have made these matters plain, but it is impossible by words to give a true idea of the marvellous colour and beauty of the ice in polar seas, or of its irresistible power when driven hither and thither by sea and wind. There can be no more terrific experience than a storm in a living polar pack. ”

“ Wind and weather may pack it closer together, the plastic new ice giving way with the old ice embedded in its matrix. The whole becomes a solid floe, and many floes unite and form great "fields" of ice. This field ice is more formidable than the fields and floes of new ice that are formed during a single winter, and which during the following summer are known by polar voyagers as "one-year ice." At the beginning of winter they may show a thickness of possibly five or perhaps ten feet, and in places there will be even thicker pieces. ”

“ It is well known that similar causes produce similar effects in the warmer regions of the earth. In the midst of the tropical ocean, the mariner sees verdant islands rise from the waters, and in the treeless desert fantastic palm-groves wave their fronds, as if in mockery of the thirsty caravan.
When we consider the intense cold which reigns during the greatest part of the year in the Arctic regions, we might naturally, expect to find the whole of the Polar Sea covered, during the winter at least, with one solid unbroken sheet of ice. ”

“ In low temperature new ice forms rapidly. This offers an obstruction to the drift of the old ice. As the heavy central pack is pressed against the unyielding land pack the small ice is ground to splinters, and even heavy floes are crushed. This reduced mass of small ice is pasted and cemented along the shores of the Big Lead, leaving a broad band of troublesome surface as a serious barrier to sled travel. It seems quite probable that this lead, or a condition similar to it, extends entirely around the Polar sea as a buffer between the land and the middle pack. ”

“ It has been demonstrated that an ice-cap resting several thousand years over any considerable portion of the surface would so reduce the subjacent temperature of the earth that for many centuries after the disappearance of the ice, a decrease of temperature would be discovered in penetrating downward. Even centuries later, so much cold would still remain within the earth, that the rate of increase of temperature would be less than if the ice-cap had not existed ”

“ Those of greater bulk, taking the ground, offer a resistance against which the lesser masses can only strain and grind; but away out in the unfathomable depths of the Polar Sea there is no chance of the [Pg 192] ice ever grounding. It is always floating, and so always susceptible to the force of wind, tide, and current. Consequently it is always moving and feeling the pressure of the water below, of the grinding strain of the drift, and of the surface disturbances brought about by the constant displacement. ”

“ His view about the ice-cap will be seen from the following quotations (l. c., p. 475) : “After crossing the eighty-fifth degree of latitude, the traveller will come to that immovable ice-cap which will in all probability prove to be a palaeocrystic sea of ice and snow. We should have a clear, unbroken surface to travel upon, subject, of course, to fissures and shrinkage cracks.” P. 476, he says, “The countless million square miles of ice annually expelled from the Arctic OCean alone prove the fallacy of a ‘palaeocrystic sea of ice;’” p. ”

“ Fresh snow is all the while falling, and adding to the whole. Blizzards come and drive the powdery loose snow from one place to another, and the hard-driving wind binds the powder into solid ice. Imagine all this on an enormous scale! Not over an area of a dozen or a hundred, or even a thousand square miles, but over an area as large as Europe and Australia combined, then we have a picture of what is happening over the length and breadth of Antarctica! The ice thus accumulated from snowfall, thus consolidated from loose snow into solid ice by pressure, gets pushed ultimately into the sea. ”

“ As winter sets in within the Arctic Circle, the sea which flows between the northern coasts of Europe, Asia, and America becomes covered with ice to the shores, thus forming an enormous field of ice some two thousand miles across. This, lying on the surface of the water, often having a thickness of from thirty to fifty feet, checks, but cannot control the tides. The ebb, on one hand, leaves vast tracks of ice, previously afloat, straining on the ground, cracking so as to form enormous fissures and weakening the surface resistance. ”

“ During the winter, frost and snow thicken them, and wind piles them into hummocks. Sometimes part of the ice lasts for more than one year—thus whalers talk of ice of one or more seasons old. But the floes of the Polar Sea are perennial. They bear the plainest evidences of great age. They grow from above, and are stratified by seasonal deposits of snow slowly converted into ice. Excepting in insignificant spots along shore, the surface of the Polar Sea never freezes into new floe; it is never long enough exposed. ”

“ In order fully to appreciate the power and magnitude of this ice-movement, it must be borne in mind that a very large proportion of the ice is of very ancient formation,—old floes or ice-fields of immense thickness and miles in extent, as well as of icebergs discharged from Humboldt Glacier. These vast masses, tearing along with the current in the early winter through the sea as it is closing up and new ice is making rapidly, are as irresistible as a tornado among the autumn leaves. ”

“ But although the mean temperature of the whole earth might be somewhat lowered by such a disposition of the land, there can be little doubt that it would render all extremes of temperature impossible, and that even during a period of high excentricity there would be no glacial epochs, and perhaps no such thing as ice anywhere produced. This would result from there being no land near the poles to retain snow, while the constant interchange of water by means of currents between the polar and tropical regions would most likely prevent ice from ever forming in the sea. ”

“ It is more commonly used to describe huge floating masses of ice that drift from polar regions into navigable waters. They are occasionally encountered far beyond the polar regions, rising into beautiful forms with breakers roaring into their caves and streams of water pouring from their pinnacles in the warmer air. When, however, they rest in comparatively warm water, melting takes place most rapidly at the base and they frequently overturn. Only one-ninth of the mass of ice is seen above water. ”

“ At first it seemed impossible that the great masses grounded along the shore could be mere fragments of sea ice we saw spread before us. We mistook them for icebergs. Like them, they were stratified. They grew in the same way, only the land is the parent of one, and the sea of the other. The Polar floes are in fact a floating glacier, and we accordingly called the fragments floebergs. In this the sea before us differed from ordinary frozen seas. Baffin’s Bay, for example, renews its ice year by year. Every summer great part of it is, as we saw it, free from ice ”

“ Then comes a whole winter's intense frost, snow falls and adds to the weight and thickness, and when this ice breaks up the following spring we have a really formidable pack to encounter. When such pack ice is not very open, but still open enough for a protected ship to work its way through, the ship has to be handled with the greatest care even when navigating through it in fine weather. This ice cannot be charged indiscriminately like one-year ice, and one must be able to distinguish between one piece of ice and another. ”

“ Under the conditions of low temperature which have been described, even if there is only a very slight snowfall in the heart of Antarctica, there must be a constant accumulation of snow upon the land. This snow by its own incumbent weight gets compressed into ice, which fills corries and glens, and covers any flat land there may be with a great depth of solid ice. But the accumulation cannot go on indefinitely, and the ice begins to flow, first down the steeper glens, then down even the least inclined stretches of the land, forced by the great mass of ice always accumulating from behind. ”

“ It can be seen that this ice is much more plastic than fresh-water ice. Fresh-water ice is relatively brittle, even in thin layers. Fresh-water ice, of the thickness of about 21⁄2 or 3 inches, will bear the weight of a man, but a child's foot would sink through sea ice of similar thickness, as if going through a layer of tough glue. ”

“ The Arctic navigators have given various names to these movable shoals,46 which are the cause of so much delay and danger. They are icebergs when they tower to a considerable height above the waters, and ice-fields when they have a vast horizontal extension. A floe is a detached portion of a field; pack-ice, a large area of floes or smaller fragments closely driven together so as to oppose a firm barrier to the progress of a ship; and drift-ice, loose ice in motion, but not so firmly packed as to prevent a vessel from making her way through its yielding masses. ”

“ The colder surface-waters almost perpetually exposed to a chilly air, and frequently covered, even in summer, with floating ice, are indeed unfavorable to the development of organic life; but this adverse influence is modified by the higher temperature which constantly prevails at a greater depth; for, contrary to what takes place in the equatorial seas, we find in the Polar Ocean an increase of temperature from the surface downward, in consequence of the warmer under-currents, flowing from the south northward, and passing beneath the cold waters of the superficial Arctic current. ”

“ The closeness and quantity of the ice in the Polar Seas vary much in different years; but, should it be in the same state that we found it, I would not recommend a ship's leaving Icy Cape earlier than the middle of August, for after that period the ice was not only broken up within the sphere of our vision, but a heavy swell rolling from the northward, indicated a sea unsheltered by islands, and not much encumbered by ice. ”

“ Here the pack of the central polar sea meets the land-adhering ice. The movement of the land pack is intermittent and usually along the coast. The shallows, grounded ice and projecting points interfere with a steady drift. The movement of the central pack is quite constant, in almost every direction, the tides, currents and winds each giving momentum to the floating mass. The lead is thus the breaking line between the two bodies of ice. It widens as the pack separates, and narrows or widens with an easterly or westerly drift, according to the pressure of the central pack. ”

“ At no point within the Arctic Circle has there been found an ice-belt extending, either in winter or in summer, more than from fifty to a hundred miles from land. And even in the narrow channels separating the islands of the Parry Archipelago, in Baffin Bay, in the North Water, and the mouth of Smith Sound,—everywhere, indeed, within the broad area of the Frigid Zone, the waters will not freeze except when sheltered by the land, or when an ice-pack, accumulated by a long continuance of winds from one quarter, affords the same protection. ”

“ There was, indeed, a certain logical consequence in the belief of an inner Polar Sea, as long as it was unknown that ice is formed on the open sea as well as on the coasts. There was also one argument, which made the existence of such a sea not altogether improbable. It might be assumed, that the formation of ice renewed every year in the Arctic regions, would necessarily produce eternal bulwarks of congelation and destroy all organic life, unless sea-currents modified these extremes of climate. ”