Currents of the Indian Ocean.

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becoming warmer owing to tropical heat, it turns westward about 20° S. lat., and merges into the great equatorial current of the Pacific. This last-named current, formed of a northern and southern part like the equatorial current of the Atlantic, occupies the entire width of the Torrid Zone, and is driven westwards by the trade winds to the East Indian islands. Here it is broken up into several parts, one of which passes into the Indian Ocean, while another turns southwards and carries warm water past Eastern Australia and New Zealand. The main branch, however, turns north past the Philippine Islands, and then flowing north-east, becomes the great KuroSiwo, or Japanese Current. The Kuro-Siwo is thus formed in a similar manner to the Gulf Stream, and resembles it in course and character. Its warm waters sweep along the eastern shores of Asia, and, after passing Japan, it divides into several branches. One of these reaches British Columbia, whose winter temperature is thus raised, just as the Gulf Stream raises that of the British Isles and North-west Europe.

201. Currents of the Indian Ocean. In the Indian Ocean a cool West Australian current unites with a current that comes between Australia and Java to form a south equatorial current that flows west to the coast of Madagascar. A portion of this passes along the east of Cape Colony as the Agulhas Current. In winter, when the north-east monsoon is blowing, a north equatorial current flows westward from Sumatra, curving upwards in the Bay of Bengal, and then passing to North-east Africa, where it is turned southward. At this time also a counter equatorial current flows eastward from Zanzibar towards Java between the other two equatorial currents. In summer, during the south-west monsoon, the currents of the northern part of the Indian Ocean are reversed,

CHAPTER XVIII.

THE POLAR REGIONS AND THE ICE OF THE SEA.

202. Arctic Ocean.-The Arctic Ocean includes that portion of the sea surrounding the north pole, and bounded on the ⚫ south by the northern coasts of Europe, Asia, and America. It does not therefore exactly coincide with the Arctic circle, which is 231 from the pole, as it reaches further south at the north of the Old World, and at the North Cape where it joins the Atlantic. With the Atlantic it has two gateways of communication, the wide opening between Norway and Greenland, and the narrower passages through Davis Strait between Greenland and the great archipelago of islands on the north of America. With the Pacific it has only a narrow connection of sixty miles at Behring Strait. The passage between the Atlantic and Pacific along the ice-encumbered channels between the islands on the northern shores of America is called the " North-west Passage," and was once much sought after as a route to India and the East. The passage along the northern shores of Europe and Asia through Behring Strait is called the "North-east Passage." This circular basin included within the above limits is but very partially known. From the parallel of 72° north, which skirts its southern land limit, up to the parallel of 80° it has been often explored, but only a few expeditions have proceeded farther north. This is on account of the sea beyond being so blocked with ice that ships are not able to make progress. 1875 Sir George Nares reached the latitude of 80° 10' N. in H.M.S. Alert, and from that ship a sledge party, under Commander Markham, succeeded in planting the British flag in latitude 83° 20′ 26′′ N., 400 miles from the pole. Instead of finding the "open polar sea," the ice was found to be of most

In

unusual age and thickness, and to this region the name Palaocrystic Sea, or sea of ancient ice, has been given. Owing to the absence of land trending northward, and the polar pack not being navigable, Sir George Nares concluded that no ship could be carried north on either side of Smith's Sound beyond the position they had attained. Dr. Nansen in his famous voyage with the Fram (1893-1896) reached, however, a latitude of 86° 14' N. His soundings showed a depth of over

2000 fathoms in most cases, so that the deep hollow of the Atlantic passes towards the pole between Greenland and Spitzbergen.

203. Marine Ice.-On approaching the ice of the polar regions, its presence is indicated to the mariner by a brilliant band of yellowish-white light along the horizon called the ice-blink. The ice-blink is produced by the reflection of the light from the snow-covered ice. The ice of the Arctic seas is of two different kinds, the one being formed in the sea, and the other coming from the surface of land. The intense cold of the Arctic winter freezes the water on the surface of the sea, but the restless movements of the waves seldom allow a thick covering of level ice to be

formed, large stretches having an uneven surface being produced.

Such an expanse of marine ice having no visible limit is called an ice-field. An ice-field, then, does not consist of a level sheet, but is an immense irregular expanse, having deep hollows and large mounds called "hummocks," or hills, and is often interspersed with fissures, which are sometimes filled with drifted snow. In the winter this frozen sea is kept within its narrowest limits, but at the beginning of summer the ice-field, which may be continuous for hundreds of miles, begins to break up, the smaller detached portions of a field being called floes, and a number of floes closely compacted together is known as pack-ice. It is this pack ice which so often forms a barrier impassable to ships even in summer, though at times it opens out into channels through which a bold adventurer steers. In 1806 Captain Scoresby forced his way through 250 miles of pack-ice until he reached the latitude of 81° 50′ Ñ. A pack is sometimes broken up into loose masses called drift ice. The ice-fields detached from the frozen seas during the summer are carried forwards by waves and currents, and sometimes crash together with such force as to produce a scene of terrible grandeur, huge floes being broken off at the edges, and an enormous pile of fragments being squeezed together into a mass.

Many a good ship has been crumpled up like matchwood or lifted bodily on to the ice by such an icy embrace. In 1869 the Hansa, a German exploring vessel, was so damaged by the pressure of the ice on the east coast of Greenland that she sank. The crew with their boats and provisions established themselves on an ice-floe about two miles in diameter. For 200 days they resided on this drifting mass surrounded by other floes, and were carried southwards during the summer by the currents for a distance of 1300 miles. At this time the floe had diminished greatly in size, but fortunately an opportunity of escape to the coast then presented itself.

204. The Ice-foot. There is still another form of sea ice. This is formed by the sea freezing along the margin of the land, so that a layer lifted up by the tide becomes frozen to the shore. Such a shelf of ice formed along a shore, as on the edge of North Greenland and other islands, is called the ice-foot (Fig. 177). The ice formed by the freezing of the Arctic seas seldom exceeds seven or eight feet in thickness, but on the coast it rises in long rugged ridges to a height of 30 or 40 feet. This shore ice not only carries loose débris attached underneath, but often receives a mass of stones and rubbish from the overhanging cliffs. Much of this icefoot may remain attached to the shores for years, but during the warmth of summer the loose bergs and floes driving against it sometimes detach large masses, which float away with their load of materials. These are either carried until the ice melts and deposits its cargo of blocks and rubbish, or the floating raft of ice from the ice-belt becomes caught again in the ice of the succeeding winter.

205. Frozen Sea Water contains very little Salt.-During the process of freezing the sea water throws out nearly all the salts it contains, so that the ice when thawed furnishes fresh water which can be drunk.

Weyprecht observes, "When the growth of ice is carried on quickly in times of intense cold a great number of crystals are formed, whose salt particles are not only drawn downwards in the water, but scattered round on all sides. In consequence of this the original melted ice consists of crystals loosely adhering together, and mixed with the solution of salt which has been rejected from them all. As the ice grows harder by the freezing together of the separate ice-crystals, this solution also freezes with