DEEP-SEA EXPLORATION. While
the beginnings of our knowledge of the surface
of the sea date back to the earliest recorded
voyage of discovery, the physical conditions
obtaining in the depths of the great oceans have
been ascertained chiefly during the past half
century.
The modern science of oceanography (q.v.) is based largely upon the voyages of a score or more of vessels sent out by various governments for the special purpose of making physical and biological investigations of the oceanic basins.
As late as Captain Cook's time the ocean had
been sounded no deeper than a few hundred
fathoms. For scientific attempts to ascertain
depths far from land, it is scarcely necessary
to go back farther than a century and a
half, and it was not until the day of submarine
cables that systematic soundings were taken.
The dredge has been employed by naturalists
in obtaining marine forms in shallow water for
a century and a half, but its use in ocean depths
has been limited to about half that period.
The governments that have participated
largely in modern deep-sea exploration are the
English, French, German, Austrian, Dutch, Russian, Norwegian, Swedish, and by no means the least, that of the United States. The foundations of oceanography as a science were laid by the British in the publication of the results of the famous Challenger Expedition. The investigations of this vessel were followed by those of American vessels, one of which, the Albatross, is perhaps better equipped for such work than any other vessel afloat, and has been in commission for more than thirty years.
Deep-sea explorations have now been carried
into all seas and the general conditions of
temperature, depths, and animal life in the
great oceanic areas are no longer unknown, while the literature of oceanography occupies an important place in science.
The deep-sea exploring vessel of the present
time might properly be described as a floating
laboratory, equipped for hydrographical, meteorological, geological and biological investigations. The equipment would include not
merely that of a general scientific laboratory, but also the heavy apparatus necessary for sounding and dredging. The ship machinery for deep-sea work has been gradually brought to a state of high efficiency. Soundings formerly made with rope are now made with a single strand of wire, and instead of the stout rope cable for dredging, light wire rope of great strength is employed. Various self-recording instruments have gradually been perfected for quick and accurate work in taking deep sea temperatures and in the collecting of small forms of life at intermediate depths.
Sounding.— During the course of deep-sea
exploration, many soundings have been made in
depths exceeding 3,000 fathoms. More than
50 great depressions, or “deeps” as they have
been called, are now known, varying from
3,000 to 5,000 fathoms. Ten of these exceed
4,000 fathoms. It is only in the western Pacific
that depths exceeding 5,000 fathoms have been
found. The greatest depth known was
discovered in July 1913 by the German survey
ship Planet, about 40 miles east of northern
Mindanao, where a sounding was made of
5,348 fathoms, or 406 feet more than six miles. This depth exceeds by 3,000 feet the height of the loftiest mountain peak. The deeps now known are distributed over the Atlantic, Pacific and Indian oceans. While many of them are far out in great ocean basins, some of them are close to the continental slopes. One exceeding 3,000 fathoms (Bartlett Deep) lies in the Caribbean Sea between Honduras and Cuba. Some of the deeps are now known to extend over thousands of square miles while others are apparently mere holes. Enough sounding has already been done to indicate that the greatest depths have probably been discovered.
Deep-sea sounding has shown that the floor
of the ocean has not only its depressions, but its
elevations. Many islands are merely the
projecting summits of submarine peaks, their bases
often resting on an ocean floor lying 3,000
fathoms deep. Submarine ridges of great
extent have been discovered in the north and
south Atlantic. The average depth of the
ocean is probably not less than 2,200 fathoms.