IN OCEAN DEPTHS
“My soul is full of longing
For the secret of the Sea.”--LONGFELLOW.
“Of the old Sea some reverential fear
Is with me.”--WORDSWORTH.
Through ages of the world’s history, man knew nothing of the Ocean
beyond its surface.
He could sail on the sea; he could bathe in the shallow waters near
land. If a good swimmer, he might go farther out, and might even dive
for one or two minutes out of sight. In more recent times, with the
help of a diving-bell, he could descend thirty or forty feet; and in a
diving-dress he might even, if experienced, get from one to two hundred
feet down.
But that was all. Of the vast depths beyond he was sublimely ignorant.
He did not so much as know of their existence. Until the late
scientific expedition made in the vessel _Challenger_, that great world
of the Under-Ocean was swathed in mystery.
Nothing is known of it now by direct personal observation. No living
man may penetrate those depths. The only mode in which we can learn
what is, what lives, what happens there, is by means of “soundings,” by
sending down and drawing up specially prepared instruments, the reading
of which gives us information about that Under-world.
Soundings made in earlier times did little more than tell navigators
how deep the sea thereabout might be. Such instruments as were then
used could neither work beyond a limited depth, nor say their say with
accuracy.
Of late years immense improvements have taken place, both in the make
of the machines employed, and in the methods of working them. Past
soundings were few and unsystematic; whereas now they are many and
by rule. Thermometers have been made which bring up from the bottom
of the sea reports of the prevailing heat or cold, moving unaffected
through warm or cold layers between. Specimens of the materials which
lie on the ocean-floor have been brought to light, and analysed. Living
creatures in great numbers have been hauled from their own domains,
examined and classified.
All this means progress. And though, no doubt, fifty or a hundred years
hence, that which we now know will be looked upon as the barest A B
C of the science, still our knowledge is growing year by year. The
Under-Ocean is no longer a vague fairy-land of possible mermaids, or a
waste region of death.
A region of death in one sense it is and must be. All living creatures
that die in the sea, unless devoured by other creatures, sink to the
bottom, there to find a tomb. Covered at first by a vast winding-sheet
of water, they may be slowly buried under the shifting mud and sand.
But in this sense the whole Crust of Earth may be called one vast
sepulchre, wherein all animals that die are entombed.
People are slow to realise how modern is our knowledge of ocean-depths.
About three hundred years ago a famous navigator made the first
sounding which went below two hundred fathoms--that is, about one
hundred feet deeper than the height of Beachy Head from the shore.
He at once decided that, by a happy chance, he had alighted upon the
uttermost depth in the ocean.
To him it was an awe-inspiring profundity. Yet, when viewed beside
such abysses as have been recently discovered, depths of five and six
miles, his little “deep” was as a saucer beside a lake.
It is not easy to picture to ourselves the changeless calm of those
abysses--those five or six miles of under-water, with nothing from
sea-level to sea-floor to break the dead monotony.
Throughout such regions storms, no matter how terrible, have no power.
Winds cannot reach them. When Ocean’s surface is lashed by a hurricane
into wild commotion, that commotion is superficial. It means a furious
stirring and flurry of upper layers; and it means no more.
If at the height of some fierce tornado, a sailor could leave his
tossing straining ship, and could dive far into the sea, keeping
breath and sense and life, he would soon quit the turmoil, and would
find himself in a scene of deep repose. Strange to say, the idea of
submarine ships actually doing this has been mooted, as one of the new
projects in the beginning of the Twentieth Century.
Wave-motion does not descend much below the surface. It is believed
that the depth of water affected by a wave is usually about equal to
the space which divides crest from crest. So, if we are looking at
little ripples, flowing one after another, with crests perhaps one
foot apart, we may suppose that the water is disturbed by those ripples
to a depth of about one foot. Or, if we are watching larger waves, with
crests twenty feet apart, we may suppose the disturbance to reach down
to a depth of some twenty feet. And if our gaze is fixed on dignified
Atlantic rollers, with crests six or eight hundred feet apart, we may
suppose that the sea is affected to a depth of six or eight hundred
feet--less and less affected the deeper we go down.
Six or eight hundred feet, compared with six miles, are hardly more
than a man’s skin compared with his body. And beyond the shallow depths
where wind and wave have sway, we come to a region of profound calm.
This repose does not mean stagnation. Ocean’s waters are ever on the
move, travelling this way and that way. Currents exist far below,
as well as at the surface; but they are generally slow and placid,
not rough and hurrying. Old Ocean’s excitability lies all outside.
Superficially he is soon upset; but deep down he is composed.
A great deal of discussion has taken place as to possibilities of Light
in those depths. Are they black with midnight darkness? or do faint
glimmers of daylight creep through?
Ocean-water, like other water, is transparent. Any substance is
transparent, when thin enough,--even gold. A very thin film of water
is not, however, needed for transparency. Many feet, even many yards,
may be seen through, if clear and pure. Few of us have not, at one time
or another, looked down from a boat, to see golden sand, variegated
pebbles, small fishes swimming about, at a considerable depth.
Thus with water, as with denser materials, transparency is merely a
question of thickness. As the thickness increases, more and more rays
of sunlight are taken captive, and the water becomes less and less
translucent, till at length, if we could get deep enough, we should
find ourselves to be surrounded with blackness.
Another feature of ocean-depths is that of immense pressure.
We bear a certain degree of it in that other and lighter ocean--the
Atmosphere. A man of medium size has upon his body about thirty
thousand pounds’ weight, or some fifteen pounds to the square inch. But
this is nothing to what he would have to endure down in ocean-waters.
At a depth of one mile, an extra ton would be piled upon each square
inch of his body; two miles down, would mean two extra tons on each
square inch; three miles down, three extra tons; and so on. The load
would soon become intolerable.
For many years scientists maintained that in such depths no life could
exist, since no bodies could withstand the awful pressure. Yet we now
know that frail jelly-fish, fragile shell-inhabitants, do withstand it,
flourishing there by myriads.
Perhaps the fact was somewhat overlooked, that the pressure upon a
living creature is not only inwards from without, but also is outwards
from within. This is true of ourselves in the ocean of air, breathing
air. It is true of creatures in the ocean of water, breathing water.
Much less than the weight of thirty thousand pounds might crush a man
flat, were it not for the resisting pressure from within. If for one
instant he could empty his body of all inner air and liquids, and could
so harden his skin that no air should squeeze through its pores, he
would be pressed as flat as a pancake by the surrounding atmosphere.
A story has been told, illustrative of this. Once upon a time a clever
fellow started an original idea. He proposed to make a balloon, which
should mount skywards, not from being full of hydrogen gas, but from
being emptied of air. Being then lighter than the atmosphere, it would,
he said, of course rise.
So far as the reasoning went, it was faultless. It only did not go far
enough.
The balloon being made, he named a day for its ascent, and asked
many friends to witness his triumph. At the last moment, all air was
withdrawn; and everybody waited in expectation, hoping to see the novel
balloon skim lightly above their heads.
But the inventor, while using strong materials, had failed to make full
allowance for the tremendous pressure of the air, when counteractive
pressure from within should have been done away with. As the air was
drawn out, the sides of the balloon collapsed, being crushed together
as an empty egg-shell may be smashed in a boy’s hand. Instead of
soaring gaily upward, the would-be aeronaut stood on earth, scanning
with disappointed eyes a flattened and useless shell.
A diver going down into the sea has a much increased weight upon his
body; but he does not suffer from it to a serious extent, provided that
he is not raised or lowered too fast. Much depends upon this. Both
men and beasts can endure a good deal of alteration in the degree of
pressure, whether from air or from water; but they cannot bear very
abrupt changes. Hearts and lungs need time for growing accustomed to a
fresh condition. In early days of diving this was not understood, and
some divers lost their lives through being too hurriedly hauled up.
The same has been noticed in animals brought quickly from great depths.
They have been constantly found in the net or trawl, dying or dead,
their bodies swollen and even bursting from the lessening of pressure.
It was natural that at first the belief should arise of Life being in
those parts impossible. Now we know that animals die in the act of
being drawn up, and that they live and flourish in profound depths,
unaffected by the vast load of water.
The weight that a man can endure is not to be compared with what
fragile sea-creatures thrive under. Beyond a depth of some two hundred
feet or more, the pressure becomes too great for any human beings; yet
animals are found at depths of three or four miles. But the fact that
man breathes air, and that animals in the sea breathe, in a sense,
water, makes an enormous difference in their power to resist pressure.
One might suppose that the terrific weight of miles of water would
squeeze lower layers to a smaller bulk. Water is, however, very
difficult to compress; unlike air.
At the bottom of the sea, four or five miles deep, the weight is said
to be equal to about four tons upon the square inch. If this tremendous
load were pressing upon a mass of air, eleven thousand cubic feet in
quantity, the whole would be crushed together into only twenty-two
cubic feet. But the same weight pressing upon the same quantity of
sea-water, would merely reduce its size to ten thousand cubic feet. So
there is not much difference between the make of sea-water near the
surface and sea-water at a great depth.
Not only are ocean’s depths calm and free from storms; not only are
they black with midnight darkness; not only are they heavy with the
weight of miles of water overhead; but also for the most part they are
cold.
Changes from season to season, like changes of weather, are
superficial. At a depth of about six hundred feet, Seasons have ceased
to be. There, summer and winter, autumn and spring, exist no longer.
The dead level of calm and darkness is also a dead level of uniform
weather and unalterable climate. Where changes of cold and heat do
come about, they are very uncertain, and usually they are due to other
causes than those which bring about the succession of seasons upon
Earth.
Many remarkable facts have lately come to light with respect to Ocean’s
temperatures. In far northern and far southern regions, near the two
poles, the whole sea is very cold. One might expect the converse of
this in tropical regions--a whole sea intensely warm. But this we do
not find. The shallower parts--those included in the hundred-fathom
limit--may be nearly as warm below as above. When, however, deep-sea
soundings are made, when the registering thermometer is despatched on
its mission of inquiry miles below the surface, then the report brought
up is generally of great cold.
In almost all deeper parts, the tale is told of a frigid
under-layer,--of water nearly and sometimes quite down to the
freezing-point of fresh water. This, not only in Polar Seas, not only
in Temperate Oceans, but in the hottest portions of the Tropics. The
Atlantic, near the equator, is icy in its depths.
A reckoning has been made that, if the floor of the whole ocean,
omitting shallower parts, could be divided into one hundred equal
portions, ninety-two of those portions would be found covered by water
at a temperature of less than 40°; and only eight of them would lie
under warm water. The vast mass of the ocean is cold, with a thin warm
layer over certain districts.
Little doubt can there be that this under-layer is largely fed from
polar regions.
We know that cold ocean-rivers pour from north-polar regions to the
south, both in the Atlantic and in the Pacific. A general creeping
under-flow of icy waters towards the equator evidently balances the
general surface drift of warm waters towards the poles. Since cold
water is heavier than warm, it would naturally find its way to lower
depths, leaving the warm light liquid to float on the top.
In the Mediterranean Sea a marked contrast is found. There no ice-cold
layer is spread over the bottom; and the water in its uttermost
depths--over two miles and a quarter--does not sink below the
temperature of 54° F. The heat of the sun in South Europe can hardly be
compared with the heat of the sun over the Indian Ocean. Yet the latter
has water far below the surface down to at least 35°.
Practically the Mediterranean, despite its depth, may be looked upon as
an inland sea. The one opening which connects it with the open ocean is
not only comparatively narrow, but also is shallow, being less than two
hundred fathoms deep. The water on this dividing ridge remains at about
55°, and the Mediterranean throughout, to its greatest depths, keeps to
about that same degree of warmth. No entrance is afforded to the heavy
cold currents from polar regions.
The Red Sea is separated from the Indian Ocean by a similar ridge, and
the same result is seen there. Over the floor of the Indian Ocean lies
a carpet of chill water. But the whole body of the Red Sea never sinks,
in summer or winter, below 70° F. Here, too, the cold streams are not
able to surmount the barrier.
In many deep mid-ocean hollows, cut off by surrounding sub-ocean walls
of rock, the same is found again--warm water within the hollow, cold
water on the ocean-bed outside.