Page:The New International Encyclopædia 1st ed. v. 14.djvu/852

OCEAN. 724 OCEAN. bromide. 0.22 per cent. ; and calcium car- Ijuiiale, 0.34 per teiil. 8iiiall amounts of various other sulistanees. including silicon, phospho- rus, fluorine, iodine, boron, aluminum. Iiarium. strontiiun. manganese, iron, copper, nickel, lead, and even of the much rarer metals, gold and silver, are also known to be i)resent. The slight portion of dissolved calcium carl)onate is of great importance to marine life, Ijeing the source from which the corals and shell-building organ- isms derive their supplies of lime. The amount of salts dissolved in the water varies in dillerent localities, though the range of such variation is small. In regions of heavy rainfall, such as the equatorial calms and oil' the nKUiths of large river.s, tlic salinity is lowered, as it is also in high latitudes, where evaporation takes I)laee slowly. On the other hand, the waters of inclosed seas, like the Ked Sea and the Mediter- ranean, and of trade-wind belts which receive little precipitation and are subject to rapid evaporation, are slightly above the average in salinity. The freezing point for sea-water of aver- age salinity is 28° F., which is also the point of ma.vimum density, while fresh water attains its greatest density at 3')' F. As the surface of the ocean is cooled its density increases steadily, so that the upper la.yers by siid<ing distribute the low temperature throughout the mass. Owing to the ocean currents which tend to cqtialize the temperatures and to chemical changes which low- er the freezing point, the ocean, however, never freezes solid even in the coldest regions. Its sur- face waters show a smaller range of temperature than does the air over it and much smaller than the land in the same latitudes. This tendency to preserve an ecpiable temperature has great influence upon the climate, esjiecially as it tem- pers the winds which blow ovei- its surface. In the polar regions when the sirface waters are freezing, the minimum temperature is somewhat le.ss than ."iO". while the waters of the Ked Sea at- tain a maximum of more than 00°, .showing an extreme range between the warmest and the cold- est parts of over 00° F. The greatest annual variation in any one locality is probably off the coast of Newfoundland, a region alTccted at different seasons by cold currents from tlic north and by warm currents from the tropics. With depth there is a rapid decrease in temperature (more rapid in regions near the eijuator) until a depth of about 400 fathoms is reached, when there is a very gradual lowering to the bottom. where the temperature remains ]nactically uni- form at from 32° to 35° and is independent of latitude. In inclosed seas shut oil' from com- munication with the deeper ])arts of the ocean by slialliiw barriers, the temperature corresponds to that of the ocean only in the upper portions above the level of the barrier: below this depth the temperature remains constant to the bottom and is determined by the C(ddest surface waters in winter or by the influx of waters at the deep- est inlet. Thus the ^fediterranenn shows a uni- form temperature of 55° below 1!)0 fathoms (the depth of the Strait of Oibraltar) to the bottom in 2400 fathom*, while the .tlantic at the latter dejith has a temperature of 35°. The Oulf nf Mexico anil the f'aribbean Sea. with inlets 700 fathoms cleep. have bottom tempi'mture* of 30°. nnd the T?ed Sea below 200 fathoms, which is the extreme depth of the Strait of fJab-el Mandeb. has a temperature of 70^ The abnormally high tem- perature of the Ked Sea is due to the cnncentra- tion of its surface waters by evaporation, caus- ing them to sink and thus to maintain a con- stant vertical circidaliou. The averagi' density of sea-water is 1.020. there being a slight variation corresponding to the dill'erence in salinity. Between the surface and great depths the densit.v shows no material change, notwithstanding the enormous pressure exerted upon the lower layers. The color of pure ocean water, examined b.v transmitted white light, is pale blue, but becomes a deep Idue, changing to sk.v-blue, when it reflects the light of the clear sky, and to grav or almost black under heavy storm clinids. Along the shore, however, it mav assume a brown or .vi'Uowisli color from suspended mud, while in shallow portions or near the coast it is green, ilinute vegetable and ani- mal organisms sometimes lend a whitish or reil- dish color to the surface. ilovEiiKMs OF Ocean Waters. The surface waters of the ocean are in constant motion under the influence of waves, tides, currents, and drifts. Waves are vertical oscillations caused by the winds, and liave little movement of translation except in shallow water when the upper portions rush forward with great force. Great waves caused by earthi|uakes move across the oceans. (See E.UiTUguAKE.) Tides resemble waves in their motion, but they owe their origin to the at- tractive force of the sun and moon. (See Tioes.) The horizontal moventents of the surface waters are known as drifts and currents. A drift is a general movement under the influence of the wind, hut slower and more changeable in direction than a current. (See Ocean Ccrrents.) Inclosed seas also have circulator.v movements, usuall.v arising from the fact that their waters dill'er in densit.v from the ocean. Thus in the Baltic Sea the waters arc so freshened b.v the contributions of the numerous rivers that thi>y flow out iilto the Xorth Sea as a surface current, while the heav- ier ocean water sets in as an undercurrent. The waters of the Red Sea and the Mediterranean, on the other hand, are salter and denser than the ocean, and as their level is lowered by evapora- tion a surface current flows in from the ocean, and the heavier waters move out along the bottom. Origix of the Oceans. The study of the geo- logical history of the oceans is largely specula- tive. It is apparent, however, that the form of the oceanic basins has undergone changes cor- res|)onding to the variations in the continental outlines (sec C'oxtixent) . and it is also ))robable that the submarine portion of the lith(is]iher(' is involved in similar oscillations to those afTecling the areas above sea-level. According to Suess, the Atlantic Ocean has resulteil from the en- largement northward ami southward of the medi- terranean sea which during the f'enozoic era extended from Central .merica to Southeastern Europe. The Pacific Ocean in recent geological times has increase<l its area by encroachment >ipon Australia: and the island chains of Poly- nesia, which are largely of coral formation, may also mark an area of svdimergence. The Indian Ocean probablv occupies a dejiression in a fiuMner land surface (Ooinlwnnaland) that once ex- tended from Central .frica to India. Bim,lO(:RAlMlY. Keclus. Thr Ormn. Afninf!- phnc o»i</ Life, translated by Woodward (Lon-