THE DEPIHS OF THE SEA.

Otago Witness, Issue 3101, 20 August 1913, Page 75

THE DEPIHS OF THE SEA.

Soundings in the shallow waters of our home seas show that the British Isles are really the upper parts of elevations rising from a submarine plateau which a comparatively small uplift would bring above sea level, making it a part of the European mainland, as it doubtless was in a time long past. In most inland seas the water’s are comparatively shallow; but in the great oceans they are in parts so deep that high mountain ridges rising from vast plains or bordering great valleys never reach the surface, or even come near it. The greatest hollow known yet is in the Pacific Ocean off New Zealand, and in this Mount Everest or its rival heights could be hidden safely while ships passed through the waters far above, which means that the deep must there extend nearly six miles downward from the surface of the ocean. In sea-measurement it is actually over 5200 fathoms, and there are a few other deep hollows exceeding 4000 fathoms or 24,000 ft, one of which occurs in the Atlantic, among the West Indies. The average depth of the water-world is about 12,600 ft.

-—The Submarine Climate. —

As to climate, the recording thermometers show that this varies considerably, the temperature falling as it sinks farther and farther down away' from the sun’s warming influence, falling also where cold polar currents flow, and rising where a tropical current exerts its influence, just as cold and hot winds modify air temperatures over the land. In tropical regions the surface water is sometimes SOdeg Fahr. ; but water being a bad conductor of heat, the sun’s power diminishes fairly rapidly downwards, while cold undercurrents from the Poles also lower the temperature in deep waters, and at 1000 fathoms even in these tropical seas the temperature is not much above freezing point. Travelling polewards, the line of ice-cold water rises higher and higher, until in Arctic and Antarctic regions it joins the snow-line of the land, and snow and ice prevail. —Soil of the Water World. — Similarly the soil of the water world varies in different parts. In the shallower water round continents there is a region where land-iscourings of mud, sand, and coarser gravel, their character depending on the geological formation of the land itself, form the sea-bed. The heavier fragments and particles settle first, the finer mud being carried farther out, and these deposits affect the character of the sea-floor for a distance probably of about 250 miles, though the mud of the greatest rivers can be traced much farther out than this, that of the Ganges, for example, for 1000 miles. The remains of animal and plant life also contribute their quota to the sea-floor, as the bit of shore alternately exposed and submerged by the tide shows, and locally other contributions are made—e.g., lava, volcanic mud. and waterlogged pumice, where active volcanoes are near enough to the. sea, and detritus carried by melting icebergs such as builds up the banks off Newfoundland. Farther out, in the depths of the ocean, the soil is of different character. The land deposits do not generally carry so far, and the larger inhabitants of deep waters do not contribute shells, skeletons, etc., to the sea floor, as do those of shallower seas. But there is a continuous rain of the shells of microscopic creatures which swarm in the surface waters and sink as they die, and this builds up a fine ocean ooze or mud known variously as Globigerina. Pteropod, Radiolarian, or Diatom, according to the predominating kind of shell, as shown by the microscope. These ocean muds, dirty white, yellowish, brown, or red in tint, are found, on examination

under the microscope, to rank among the marvels of Nature’s handiwork, each particle being a shell, or fragment of shell of beautiful workmanship. In some parte of the deepest waters this ooze carpet gives place to one of grey or red clay owing its origin not mainly to plant or animal life, but to volcanic activity, and perhaps also to meteors. Volcanic dust carried far out by winds and upper air currents, and pumice floating by virtue of its lightness far over the ocean, come finally to rest in the deep waters, where also the burnt-out dust of “shooting stars” finds a resting place. —Life in the Depths.—

With all these different conditions there is, as we should expect, a great variety of plant and animal life 'in the ocean. Even holiday rambles along British shores show us that the shallow waters round these islands have often a tangle of seaweeds of many forms, amid which endless and quaint varieties of animals find a suitable home. Many other varieties axe found in the sand and gravel regions, the “deserts,” as it were, of the ocean world, with structure modified according to their environment. Others are rockdwellers equipped with suckers and feelers, and yet others swim about in surface waters and are well known to the mariner and naturalist, the fisherman, and those who appreciate his-spoil. But the inhabitants of the deep waters of the ocean are less well known. In fact, until the beginning of the last century, when scientific deep-sea investigations began, it was believed that no animals could live in the depths of the great oceans. The modern dredge, however, has shown that there is a rich life in these regions, representing the groups of marine creatures found in shallow waters, but with peculiarities developed by the conditions which exist there.

Remembering what these conditions are —the tremendous pressure of the overlying waters, amounting from two and a-half to four or five tons square inch, the low temperature, into which no ray of sunlight penetrates ever—it is easily understood that the life-forms developed are different in various ways from those in any other environment. —Phosphorescent Monsters.—

Vegetable life is entirely lacking, as might be expected, in these sunless regions; but in the depths strange fairylike polyps, rooted firmly and growing to a height of 12ft to 10ft, wave about like some giant pampas-grass, of amethyst shades, and glowing with the soft phosphorescence with which Nature enables some of the deep-sea creatures to enlighten their dark habitation. Strange forms, able to resist the heavy weight of water, creep and swim, about in this forest, as in the tangle of sea weeds in shallow waters, and many of them shed light, probably of many colours, in their track, and meet scintillating flashes from branching polyps as they pass. Light-givers, indeed, appear to abound, some having little organs like bull's-eye lamps, in rows along their bodies, others sending out flashes or pouring forth clouds of splendour from tentacles and feelers or emitting a white radiance from their skins, while some are furnished with will-o’-the-wisp lights round cavernous mouths, to lure their smaller prey along the way of destruction. Of many sizes and forms are these deepsea creatures, with peculiarities of structure which are extremely interesting when considered in relation to environment. In fact, the deep waters which little more than a generation ago were regarded as the deserts of the ocean, practically devoid of life, are now known to he the home of a characteristic fauna, though no extraordinary species, such as the fabulous creatures reported of old, have yet been found.