Popular Science Monthly/Volume 29/September 1886/The Antarctic Ocean
|THE ANTARCTIC OCEAN.|
THE Antarctic Ocean occupies a position around the south pole similar to that of the Arctic Ocean at the opposite end of the earth. It fills all the space to the south of the Antarctic Circle. It differs vastly, however, from its northern homologue, for, instead of having land at its outer circumference, it has water. While the North American, the European, and the Asiatic coasts encircle the Northern Ocean, the Pacific, the Atlantic, and the Indian Oceans mingle their waters with those of the frozen zone at the south.
As it differs in physical conditions, so also it differs in having received much less attention from the world at large. While the aim of innumerable expeditions for the past four hundred years has been to find a northwest passage to Asia, to plant a flag at latitude 90°, or to rescue some unfortunate commander and his crew from a horrible fate, and while thousands of dollars have been expended, and hundreds of lives have been lost, there is a strange contrast offered when we turn to the far south. The expeditions which have been sent out by the great nations of the world to explore the vast watery expanse about the southern pole are so few as to be counted on the fingers of one hand, and all the ships which have left records of any extensive explorations beyond the Antarctic Circle might be counted on the fingers of two. hands. And yet "within the periphery of the Antarctic Circle," says Lieutenant Maury, "is included an area equal in extent to one sixth of the entire land-surface of our planet. Most of this immense area is as unknown to the inhabitants of the earth as the interior of one of Jupiter's satellites. . . . For the last two hundred years the Arctic Ocean has been a theatre of exploration; but, as for the Antarctic, no expedition has attempted to make any persistent exploration, or even to winter there." It is noteworthy, too, that in the voyages which have been made not a ship nor a life has been lost south of the circle. "It does not appear," says one writer, "that Antarctic voyages would be attended with any excessive degree of danger. . . . It may even be found that the Antarctic barriers are impenetrable; but this has certainly not as yet been demonstrated."
In consequence of this limited exploration, comparatively little is known of the physical condition of this part of the globe. It has been conjectured that a vast continent exist in it. But, if it is there, only mere outlying parts of it have been seen, and those that are known are of such a character as to preclude their being of any value to the world. "Consider for a moment," says Captain Hogg, in his account of the second voyage of Captain Cook, "what thick fogs, snows, storms, intense cold, and everything dangerous to navigation, must be encountered by every hardy adventurer; behold the horrid aspect of a country impenetrable by the animating heat of the sun's rays; a country doomed to be immersed in everlasting snow! See the islands and floats on the coast, and the continual falls of the ice-cliffs in the ports; these difficulties, which might be heightened by others not less dangerous, are sufficient to deter any one from the rash attempt of proceeding farther to the south than our expert and brave commander has done, in search of unknown countries, which, when discovered, will answer no valuable purpose whatever."
The discoveries of Gheritk, Cook, Weddell, Bisco, D'Urville, Wilkes, and Ross—and, if to these we add the Challenger Expedition, we have the whole number of explorers—have revealed the existence of a certain amount of land within the Antarctic Circle. In the year 1600 Theodoric de Gheritk was driven during a gale as far as 64° south latitude, and reported land in that neighborhood. In his second voyage, Captain Cook penetrated during the summer seasons of 1773-'75 to 71° south without finding land previously reported in certain districts; yet he, as well as most of the earlier geographers and navigators, believed firmly in the existence of a southern continent, of little use, as he supposed it to be, for "the ice that is spread over this vast Southern Ocean must originate," in Cook's opinion, "in a track [tract] of land. . . which lies near the pole, and extends farthest to the north opposite the South Atlantic and Indian Oceans; for, ice being found in these farther to the north than anywhere else, . . . land of considerable extent must exist near the south."
This land was largely conjectural until the expeditions sent out by the French, American, and English Governments under D'Urville, Wilkes, and Ross, respectively, between the years 1838 and 1840. D'Urville left the Strait of Magellan in January, 1838, with two vessels. He penetrated with great difficulty the ice-fields which surround the pole, and reported land as lying about two hundred miles south of the Orkney Islands. The next year he attempted to explore from an opposite quarter, and reported a further discovery which he called Adelia's Land. It seems probable that most of his discoveries were only huge cliffs of ice, though he is said to have landed on a little islet off the coast in one place, and carried away quartz and gneiss rocks torn from the cliffs. He coasted along the ice-cliffs for a distance of more than one hundred miles, and thus describes their appearance:
"The walls of these blocks of ice far exceeded our masts and rigging in height; they overhung our ships, whose dimensions seemed ridiculously curtailed. We seemed to be traversing the narrow streets of some city of giants. At the foot of these gigantic mountains we perceived vast caverns hollowed by the waves, which were there ingulfed with a crashing tumult. The sun darted his oblique rays upon the immense walls of ice, making them look as if they were crystal, and presenting effects of light and shade truly magical and startling. From the summit of these mountains numerous brooks, fed by the melting ice produced by the summer heat of a January sun in these regions, threw themselves in cascades into the icy sea. Occasionally these icebergs would approach each other so as to conceal the land entirely, and we could only perceive two walls of threatening ice whose sonorous echoes sent back the word of command of the officers. The corvette which followed the Astrolabe appeared so small, and its masts so slender, that the ship's crew were seized with terror. For nearly an hour we only saw vertical walls of ice."
Wilkes, as the commander of the American expedition, charted lands which subsequent navigators failed to find. The Challenger sought in vain for what he named Termination Land, but could find only open sea. He explored the ocean for a distance of fifteen hundred miles east and west, skirting a barrier of ice often one hundred and fifty feet or more in height, and sometimes extending in an unbroken line for fifty miles.
Lastly, Sir James Ross, the commander of the English expedition, penetrated from an opposite quarter to Wilkes, and in the same year, and succeeded in reaching latitude 78°, the highest before or since attained. He found a continent which he called Victoria Land, and he describes its first appearance as follows: "On January 11, 1841, in about latitude 71° south and longitude 171° east, the Antarctic Continent was first seen, the general outline of which at once indicated its volcanic character, rising steeply from the ocean in a stupendous mountain-range, peak above peak enveloped in perpetual snow, and clustered together in countless groups resembling a vast mass of crystallization, which, as the sun's rays were reflected on it, exhibited a scene of such unequaled magnificence and splendor as would baffle all language to portray, or give the faintest conception of. One very remarkable peak, in shape like a huge crystal of quartz, rose to the height of 7,867 feet, another to 9,096, and a third to 8,444 feet above the level of the sea. From these peaks ridges descended to the coast, terminating in bold capes and promontories. . . . On the 28th, in latitude 77° 31' and longitude 167 1', the burning volcano, Mount Erebus, was discovered, covered with ice and snow from its base to its summit, from which a dense column of black smoke towered high above the other numerous lofty cones and crateriferous peaks with which this extraordinary land is studded from the seventy-third to the seventy-eighth degree of latitude. Its height above the sea is 12,367 feet, and Mount Terror, an extinct crater, near to it, . . . attains an altitude little inferior, being 10,884 feet in height, and ending in a cape, from which a vast barrier of ice extended in an easterly direction, checking all further progress south. This continuous perpendicular wall of ice, varying in height from two hundred to one hundred feet, its summit presenting an almost unvarying level outline, we traced for three hundred miles, when the pack-ice obstructed all further progress."
From 1841 up to 1874 when the Challenger visited the Antarctic Circle, no vessel has spent any lengthy period in this region; so, having thus reviewed the discoveries of the various explorers, let us turn to that element which is so much more abundant than land, the water, and examine its form in a solid state. The icy barrier of which we hear so much is thus described by Sir James Ross: "As we approached the land, . . . we perceived a low white line extending from its extreme eastern point as far as the eye could perceive to the eastward. It presented an extraordinary appearance, gradually increasing in height as we got nearer to it, and proving at length to be a perpendicular cliff of ice between 150 and 200 feet above the level of the sea, perfectly flat and level at the top, and without any fissures or promontories on its even seaward face." This barrier extended for a distance of 450 miles, and nowhere was there any opening of consequence by which it could be penetrated.
Where such immense quantities of solid ice exist, there are icebergs in abundance. The ones floating in these seas are of enormous size, and present a vastly different appearance from those seen at the north. There they are commonly jagged and sharp-pointed from their first leaving the parent glacier, afterward assuming all sorts of weird shapes. But at the south they are at first, and for a long while afterward, flat-topped, with square-cut sides, and with a stratified structure. The top stratum is from ten to twelve inches thick. The thickness of the strata gradually decreases toward the bottom, and at the level of the water is not more than two inches. A line of clear, blue ice marks the boundary of each layer, produced, in the opinion of various writers, by the melting of the top portion of the snow-fall of a previous winter, while the white part represents the unmelted part of the snow-fall. Wilkes estimates the snow-fall in this region at thirty feet in the year, and, as only a very small part of this can be melted in the course of the short summer, an immense accumulation must go on. The small part of each year's fall that is melted will be clear ice, and this is represented by the line of blue in the berg; so that, by counting the number of layers in a berg, some idea can be had of its age.
Sir Wyville Thomson says that the reduction in thickness of the layers from top to bottom is due mostly to compression, and estimates that at a depth of 1,400 feet enough heat will be generated to melt the ice. On the other hand, Croll contends that the temperature of the bottom of the immense icebergs, which sometimes tower 700 and 1,000 feet above the water, is 20° or 22° Fahr., and when we remember that ice floats with from six to seven times its height below water, and that the bottom of a 1,000-foot berg would be 6,000 or 7,000 feet below the surface, it is easily seen that no melting would occur on the bottom of an ice-sheet only 1,400 feet thick. The reason assigned by Croll for the gradual thinning of the ice-layers toward the bottom is, that, instead of being due solely to compression, it is due mainly to what he terms dispersion. In other words, if, at 85° south, a mass of ice covers one square foot of surface, it will, in its gradual passage north, be made to cover two square feet at 80° latitude; at 70° it will occupy four square feet, and, at 60° south, six square feet; that is to say, a stratum which was one foot thick in 85° latitude will be only two inches thick when it has reached 60° latitude.
The discharge of icebergs from the extremity of the ice-field takes place constantly, and they are sometimes huge. Croll has collected notices of bergs which towered 400, 580, 720, 960, and 1,000 feet above the sea-level, and, as six or seven times the bulk above water floats below, some adequate idea can be formed of the contents of a berg three, four, or five miles in length. As the ice-field must have an onward motion to cause this discharge, it has been calculated that one foot in 211 is the smallest slope which will be effectual, and that the ice moves here at the rate of about one quarter of a mile per annum. As it is impossible that thirty or forty feet of snow can be melted in a single short summer's season, it follows that there must be a rapid accumulation all the time. This accumulation will probably be greatest at the pole, and Croll estimates that here the ice has attained a thickness of about seven miles. Allowing this estimate to be correct, and it does not seem excessive, when it is remembered that the thickness of the ice-sheet over Northern New England, during the Glacial period, was 6,000 feet, the question arises, Upon what sort of land is this immense mass of ice piled? It is a question not easy to answer definitely, because no one has ever seen it. The idea has generally been that the continent is high land. But it has been urged with justness that, had the glaciers descended from a mountainous country, they would bear upon their surfaces, or in their mass, stones to indicate the sort of rock of which the mountains were made. But such is not the case. It is said that stones are never found on the Antarctic bergs, and Captain Cook states expressly his idea that the bergs are formed at the mouths of rivers or cataracts, "because we never found any of the ice which we took up in the least incorporated or connected with earth." He goes on to say: "The ice-islands. . . must be formed from snow and sleet consolidated, which gather by degrees, and are drifted from the mountains. In the winter, the seas or the ice-cliffs must fill up the bays if they are ever so large. The fall of snow occasions the accumulation of these cliffs, till they can support their weight no longer, and large pieces break off from these ice-islands. We are inclined to believe that these ice-cliffs, where they are sheltered from the violence of the winds, extend a great way into the sea."
The discovery, by Sir James Ross, of the Parry Mountains and Mounts Erebus and Terror, in latitude 78°, tended to confirm the prevailing notion of a high and mountainous land forming the Antarctic Continent. But the Parry Mountains are merely conjectural, having been seen only at a distance, and it is well known that the coasts charted by some navigators have been proved by subsequent ones to have been either clouds merely or else islands of ice. The most recent idea is, that the land about the pole consists of a cluster of low islands, rising but little above the sea-level, but united by masses of ice. The gradual accumulation of snow for centuries has raised a cap, as before stated, seven miles thick, and from this cap the ice flows away in all directions, forced onward by the pressure of the enormous mass behind.
The immense size of the icebergs seen in the Antarctic Ocean is without a parallel elsewhere. Croll in a late essay gives a list of the largest of which there is record, and we find they range from 400 to 1,000 feet above the water. The one 1,000 feet high was observed in latitude 37° 32' south, and was nearly five miles long. When these bergs are first broken off and float away they all have the tabular form, but, as they grow old and drift northward into warmer airs and waters, they become fissured and seamed in all directions; pinnacles and domes and caverns appear, and they become beautiful objects. Wilkes describes one as exhibiting "lofty arches of many-colored tints, leading into deep caverns open to the swell of the sea, which, rushing in, produced loud and distant thunderings. . . . Every noise on board, even our own voices, reverberated from the massive and pure white walls. These tabular bergs are like masses of beautiful alabaster. ... If an immense city of ruined alabaster palaces can be imagined, of every variety of shape and tint, and composed of huge piles of buildings grouped together, with long lanes or streets winding irregularly through them, some faint idea may be formed of the beauty and grandeur of the spectacle."
Dredging and trawling in the Antarctic Ocean have not been extensive. The Challenger Expedition penetrated to 66° south latitude, and dredged and sounded frequently. The temperature of the surface-water ranged from 29·5° to 34·5°, while at 200 fathoms it varied from 30° to 35·5°. Wherever the dredge or trawl was used, quantities of stones, rounded and polished, of basalt and other rocks, were brought to the surface, dropped to the sea-bottom, presumably by icebergs. Life is not abundant, but what exists seems related to that of the northern ocean. Ross, in 1840, dredged in 1,620 feet in latitude 73°, and found several forms of life, of which he says: "It was interesting among these creatures to recognize several that I had been in the habit of taking in equally high northern latitudes; and, although contrary to the general belief of naturalists" (quite modified in the past ten years, however), "I have no doubt that, from however great a depth we may be able to bring up the mud and stones of the bed of the ocean, we shall find them teeming with animal life; the extreme pressure at the greatest depths does not appear to affect these creatures. Hitherto we have not been able to determine this point beyond a thousand fathoms, but from that depth several shell-fish have been brought up with the mud" (volume i, page 202).
- Quoted in Somerville's "Physical Geography," London, I, pp. 282-284.