OCEAN WATER. By the continuous process of interchange between the surface waters of the land and the ocean, the latter has become a de pository of vast quantities of mineral matter that have been dissolved out of rocks through the agency of springs and streall). The principal constituents of sea-water are the more soluble salts—time chlorides and sulphates of the alkalies and alkaline earths. The less easily soluble com pounds, although playing it much more important ride in the formation of rocks, are present in sea water in only minute quantities. On the average 100 parts of water contain 3.5 parts of solid ma terials whose composition is about as follows: Sodium chloride. 77.76 per cent.: magnesium chloride, 10.S8 per cent.: magnesium sulphate, 4.74 per cent.; calcium sulphate, 3.60 per cent.: potassium Aulphate, 2.46 per cent ; magnesium bromide. 0.22 per cent.; and calcium hona.le, gel' cent. small amounts of various other substances. including silicon. rus. fluorine. iodine, boron, aluminum. barium, strontium. manganese. iron, copper, nickel, lead. and even of the much rarer metals, gold and silver, are also known to be present. Tiiw slight p,rium of dissolved calcium carbonate is of great importance to marine life, being the source from which the corms and shell-building isms derive their supplies of lime. the amount of salts dissolved in the water in localities. though the range of such variation is small. in regions of heavy rainfall. such as the equatorial calms and off the mouths of large ricers, the salinity is lowered. as it is also in high latitudes, Nlhere evaporation takes place slowly. (hi the other hand, the waters of inclosed seas, like the Red Sea and the Mediter ranean, and of trade-wind belts which receive little precipitation and are subject to rapid evap oration. are slightly above the average in The freezing point for sea-water of aver age salinity '35° F., which is also the point of maximum density, while fresh water attains its greatest density at F. As the surface of the ocean is cooled its density increases steadily, so that the upper layers by sinking distribute the low temperature throughout the mass. ()wing to the Ocean currents which tend to equalize the and to chemical changes which 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 loos the air over it and much smaller than the land in the same latitudes. This tendency to preserve an equable temperature has great influence upon the climate, especially as it pers the winds which blow over its surface. In
the polar regions when the surface waters are freezing, the minimum temperature is somewhat les- than 30 . while the Waters of the Rod Sea tain a maximum of more than showing an extreme range between the warmest and the •I parts of over F. The greatest animal variation in any one locality is probably off the of Newfoundland, a region alreetrd at different seasons by cold currents front the north and by warm currents from the tropics. With depth there is a rapid decrease in temperature (more rapid in regions near the equator) until a depth of about 4o0 fathoms is reaehed. when there is a Very gradual lowering to the bottom, where the temperature remains practically uni form at from to and is independent of latitude. In inelosed seas shut off from cont. noinivation with the deeper parts of the ocean by shallow barriers, the temperature corresponds to that of the /wean only in the upper portions above the level of the barrier; below this depth the temperature remains eonstant to the bottom and is determined hy the oddest surface waters in winter or by the influx of waters at the deep est inlet. Thus the shows a uni form temperature of 55' below 190 fothoms 'the depth of the Strait of to the bottom in 2400 fathoms. while the Atlant ie at the latter depth has a temperature of The Null of llexieo and the Caribbean Sea, with inlets 700 fathoms deep, have bottom temperatures o f and the fled Sea below 200 fathoms, which is the extreme depth of the Strait of flab-el "Mandeb, has a temperature of ;W. The abnormally high tem perature of the Red Sea is due to the tion of its surface waters by evaporation, ing them to sink and thus to maintain a stant vertical eireulation.
The average density of is Deli, there being a slight variation corresponding to the difference in salinity. Between the surface and great depths the density shows no material change, notwithstanding the enormous pressure exerted upon the lower layers. The color of pure invun water, examined by transmitted white light, is pale blue. hit beeomes a deep blue, changing to sky-blue, when it reflects the light of the clear sky, and to gray or almost black under heavy storm Clouds. Along the shore, however, it May assuulo It brunt) or yellowish (•0101* front suspended 11111d. While in shallow portions or near the coast it is green. Alinute vegetable and ani mal organisms sometimes lend a whitish or dish color to the surface.