THE OCEAN.

 

 

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The Ocean.

194. Composition. —The water of the ocean

- contains a number of various saline ingredients,

which give it a bitter taste and render it heavier

. than fresh water in the proportion of 1.027 to 1.

Every hundred pounds of ocean-water contains

about three and one-third pounds of various
saline ingredients.

Chloride of sodium, or common salt, chloride of magne-
sium, sulphates and carbonates of lime, magnesia, and
potassa, and various bromides, chlorides, and iodides, are
the principal saline ingredients,

195. Origin of the Saltness of the Ocean.—The
rivers are constantly dissolving from their channels large
quantities of mineral matters, and pouring them into the
ocean. Besides this, fully three-fourths of the earth’s sur-
face is covered permanently by the oceanic waters. In
this way immense quantities of mineral ingredients have
been dissolved out from the crust. The latter cause was
especially active during the geological past, when frequent
convulsions brought fresh portions of the crust into con-
‘tact with the warm waters.

The ocean is salter in those parts where the evaporation
exceeds the rainfall, or at about the latitude of the tropics;
where the rainfall exceeds the evaporation, the water is
slightly fresher than at the equator.

In inland seas, like the Mediterranean or the Red Sea,

which, though connected with the ocean, yet lose much"

more of their waters by evaporation than by outflow, the
proportion of salt is slightly greater than in the ocean.
In such cases a current generally flows into the sea from
the ocean. In colder latitudes, inland seas, like the Bal-
tic, receiving the waters of large rivers, contain rather
less salt than the open sea, and a current generally flows
from them into the ocean.

196. Color—Though transparent and colorless
in small quantities, yet in large masses the color
of sea-water is.a deep blue. The same is true
of fresh water. Over limited portions of the
ocean the waters are sometimes of a reddish or
a greenish hue, from the presence of numberless
minute organisms.

Sometimes a pale light or phosphorescence,
visible only at night, and due to the presence of
animalcule, appears where the air comes into con-

. tact with the water, as in the wake of a vessel or
on the crests of the waves.

  

OCEANIC WATERS.

——050300——_

197. Temperature.—The salts dissolved in
ocean-water lower the temperature of its freez-
ing-point. Ordinary ocean-water freezes at about
27° F. In places where the water is salter, the
temperature of its freezing-point is lower.

Ice formed from ocean-water is comparatively
fresh, nearly all the salt being separated as the
water freezes or crystallizes. The salt, thus thrown
out from the frozen water, is dissolved by the
water below, lowers the temperature of its freez-
ing-point, and thus increases its density. In this
manner the water below the ice may have a tem-
perature lower than that at which the surface-
water freezes, and yet remain liquid.

In the polar regions the water below the sur-
face is at a temperature lower than that of the
freezing-point of the surface-water. This cold
water, from its greater density, spreads over the
floor of the ocean in all latitudes, so that, except
where stirred by deep currents, the entire bottom
of the ocean is covered with a layer of dense,
heavy water, the temperature of which is nearly
constant.

The temperature of this water is about 35° F. Near
the poles it is somewhat lower : about 29°, or a little higher
than its maximum density of the surface-waters.

The upper limit of this line of invariable temperature
varies with the latitude. Near the equator, where the
waters are heated to great depths, it is found at about
10,000 feet below the surface. Toward the poles, it comes
nearer the surface, reaching it at about Lat. 60°, from
which point it again sinks, being found at Lat. 70° at
about 4500 feet below the surface.

In the tropics the temperature of the surface-water
is about 80° F.; in the polar regions it is near the
freezing-point. The ice which forms in the polar
regions collects in vast ice-fields or floes.

198. Shape of the Bottom of the Ocean.—The
bed of the ocean, though diversified like the sur-
face of the land, contains fewer irregularities,
Numerous soundings show that it extends for
immense distances in long undulations and slopes.
Its plateaus and plains, therefore, are of great
size, compared with those of the continents.
Submerged mountain-ranges occur both in the
deep ocean and along the shores. The latter