If a headband should be put on the earth
to measure its length, it is approximately 40,000 kilometers though there is
a little difference in length between the lines around the equator and passing
over North and South Poles.
The sea has a mean water depth of 3,800 meters reportedly. This depth is so
significant that the earth would be covered with the sea at a water depth of
2,400 meters all over the surface if the land were ground off to fill up the
sea.
The sea covers 70% or more of the earth surface area,
or an area of approximately 368 million square kilometers.
The Pacific Ocean plate sinks under the Japanese Islands. And its sinking port
found to be every deep is called the Japan Deep.
High and low tides are up and down motions of the seawater on the surface due
to the force of gravitation (tide-generating force) of the moon (and the sun).
A tidal action will be largest when the moon and the sun are arranged straight
toward the earth. And it will be smallest when the moon and the sun are positioned
at the right angle to the earth. This tide-generating force has the magnitude
to which the moon is force of gravitation contributes more than the sun. Eventually
the earth has the center distance vertically extended on the surface facing
the moon (and on the earth surface opposite thereto).
The sea has a color naturally affected by the colors of sky and
cloud and by a condition of waves. Without their influence, however, the sea
looks blue in reality. While it is advancing into the seawater, the light will
gradually fade as a result of being absorbed by the seawater. Such absorption
has a ratio vary from color to color (wavelength). The red light (which has
a longer wavelength) is absorbed most, being followed by yellow which has a
little shorter wavelength than red. Thus, the seawater selectively absorbs a
color. While it is advancing in the seawater, therefore, the light will have
its red color decreased gradually. In contrast, the blue light remains mostly
unchanged. As a result, the light is turning bluish more and more. The sea color
we usually look at is such bluish light that has returned onto the surface again
as a result of being reflected by the fine parties (Plankton and soil particles)
suspended in the sea water. A certain sea, among others, may not look blue.
In a shallow sea (along the coast), there is little light absorbable. With the
yellow light reflected by phytoplankton, the sea may look greenish if the yellow
light should be mixed with the blue of seawater. The reason why the Black Sea
has the water look black is because it contains a scarce amount of oxygen but
a high concentration of hydrogen sulfide. The reason why the Red Sea looks red
is because those seaweeds which dye the water in red on the surface are growing
thick from season to season. The Yellow Sea, moreover, looks yellow because
the water flowing in from its rivers contains yellow soil.
Usually, the sea has a variety of substances dissolved at a rate of 32 thru
38 grams per liter. And eighty percent thereof is occupied by these sodium and
chlorine ions, which are an origin of table salt. This is the reason why the
seawater is salty. Now, why the seawater contains much salt is because both
sodium and chlorine ions are readily soluble in water, existing very stably
in the seawater as compared with any other substances. And these ions are scarcely
removed either as a result of chemical reaction or by any creatures.
95% or more of the ocean in the world has a salt concentration fall within a range of 3.3 thru 3.7%, being averaged at approximately 3.5%. The water in the subtropical zone of the sea area to the north of the Atlantic Ocean is very salty, having a salt concentration of as high as 3.79%. The Pacific Ocean has a little lower salt concentration (approximately 3.4% at the depths of the Pacific Ocean), with the lowest salt concentration seen in the Arctic and Antarctic Oceans). A large amount of fresh water enters the sea if ice melts, when there is a large of inflow from rivers, and/or where it rains heavily. In such a case, the seawater will have a salt concentration decreased. The saltiest seawater could be seen in the sea into which either rain or river scarcely flows in while the water is evaporating actively. The Persian Gulf and the Red Sea, for example, have a salt concentration of as high as 4.2% or more.
・Sound is the Best in the Sea.：
To communicate with a remote partner, electric waves and beams have been being
used on land. How about the sea? Neither radio waves nor beams are unserviceable
to communicate with a remote partner in the seawater because they will disappear
soon, being absorbed in the seawater. Nevertheless, the sound can arrive remotely
in the seawater. This allows us to understand why whales and dolphins use the
sound to talk with each other and to find out their feed. The sound advances
approximately 340 meters per second in the air. In the seawater, it accelerates,
reaching approximately 1,500 meters per second. This is also advantageous for
communications. The sound in the seawater, moreover, will fade away all the
less at the lower frequency. A tactful use of low frequencies, therefore, would
permit the sound to reach up to several thousand kilometers. Besides, the sound
has been being used to measure the depth on the sea and to find out a group
of fish in the sea.
Launching a light against the dark in the seawater will make you see something
whitish like snow. This is marine snow. About 50 years ago, it was named by
a Japanese researcher. The marine snow takes a variety of shapes, i.e. ball,
string, potato, paper piece or the like. Usually, the marine snow is decreasing
according to an increase in water depth. Nevertheless, a large number of marine
snow particles may be seen at a water depth of approximately 500 meters. Their
number varies from location to location, ranging from several hundred to one
only per litter. The marine snow is sinking at a rate of several ten meters
thru several hundred meters per day. Finally, it turns out as the feed for creatures
in the deep sea. The substances on the superficial surface of the sea are carried
to the seabed in the form of marine snow.
If you go on diving into the sea aboard a submersible survey vessel, the light
is decreasing gradually. At a water depth of approximately 400 meters, the sea
blacks out. Looking at the seawater through the window of a diving submersible
survey vessel will cause you to be aware of something illuminated glitteringly.
This is the marine star (star in the sea). It was so designated by a certain
team, who had been operating a submersible survey vessel. The marine stars are
really those luminous bacteria, which have been attached to the marine snow.
A moving submersible survey vessel disturbs the marine snow suspended in the
seawater in the periphery. And the bacteria attached thereto emit the light
as a result of being surprised at such disturbance. The luminous bacteria could
be found anywhere in the sea and would emit the light in response to a physical
or chemical stimulus.
・Is There Fish at the Deepest Portion of Sea?：
In 1960, an American submarine (Trieste) cruised underwater and reached the
deepermost part on the seabed all over the world, or seabed in the Mariana Deep.
On that occasion, it was reported that a fish like a dab had been found to exist
there. Experts, however, were doubtful of this report.
In March 1995, "Kaikoh" an unmanned surveyor vessel owned by Ocean Science and
Technology Center, reached the seabed at a depth of 10,911 meters in the Mariana
Deep. On that occasion, fish feed was placed on the seabed and gathering creatures
were observed. Some creatures like the fish resembling the medic were observed
coming and swimming around the feed. The people watching the situations on a
TV set aboard the vessel were very pleased to know that there were fish at the
deepermost part of the world. Later, the TV images were shown to experts, who
in turn found the creatures not to be fish but to belong to a family of shrimps.
Is there a fish anyway at the deepest part all over the world? The fish so far
sampled was caught at a water depth of 8,370 meters. Fish experts think that
there is no fish living at the deepest portion in the sea. Nevertheless, our
knowledge to date is limited. In the future, it may fall short of this prediction.
・Sperm Whales are Sounding into the Deep Sea.：
A sperm whale is able to sound as deep as 2,000 meters or more. In the stomach
of a sperm whale, the mouthpiece of a large shellfish may have been left behind.
This evidences the fact that the sperm whale has eaten the shellfish in the
deep sea. The hard mouthpiece remained although the shellfish body had been
digested.
・How Could Submersible Survey Vessel Dive Deep?：
The submersible survey vessel is a vessel, which can move freely in the seawater,
with people onboard. No cable is attached to the vessel. It is driven by the
energy that a built-in cell has. The hull of a submersible survey vessel is
afloat on the sea. To dive into the water, the vessel has an iron weight filled
on the bottom so that the hull will be heavier than the seawater. The vessel's
own weight only makes the vessel dive into the water. Near the seabed, the vessel
has its weight partially dropped so as to gradually slow down diving. Around
the seabed, the vessel has a weight equalized with that of the seawater there.
Then, the vessel will neither dive nor float. Now, the vessel will start moving,
using the screw for the first time. A submersible survey vessel is provided
with a special tank, through which the seawater can be taken in and out in the
deep sea. Using this tank allows the hull to get heavier than the seawater so
as to reach the seabed or to be lighter so that it can get afloat again. To
get afloat onto the sea surface, the vessel throws away all of the weights.
Then, the hull will be lighter than the seawater so that the vessel can move
up. What weight a submersible survey vessel should be loaded with varies from
submarine voyage to submarine voyage. It depends upon the crew's body weight
and upon the load of observation equipment.
・How Long Can Submersible Survey Vessel Dive Deep?：
How long a submersible survey vessel is capable of continuing to dive depends
upon two factors: one is the capacity of cells owned by the vessel and the other
is to what fatigue the crew may have during the voyage. Electricity is essential
for the submersible survey vessel to carry out its mission. The electric power
is used to turn the screw and to illuminate the seabed with intensive light.
A quantity of the electricity available for a submersible survey vessel is limited.
And three persons usually embark a pressure resistant cube of the submersible
survey vessel. Since the pressure-resistant cube is very narrow (with an inside
diameter of 2 meters only), the crew cannot pass a long time in the interior.
Now, for what time has a submersible survey vessel been diving in reality? Assume
that "Shinkai 6500" will drive down to a water depth of 6,500 meters. First
of all, 30 minutes are required for the vessel to start diving after the crew
has embarked the pressure-resistant cube. Subsequently, two hours and a half
are required for the vessel to reach the seabed. For 3 hours subsequent thereto,
the screw surveyed the seabed. And another two hours and a half are required
for the vessel to get afloat up to the sea surface. Finally, 30 minutes are
taken for the crew to get out of the cube after the vessel has been recovered
by the mother boat. In the long run, nine hours are required for the crew to
get out of the pressure-resistant cube after their embarkation.
・Does Submersible Survey Vessel Have Water Closet?：
The deep sea, moreover, has a temperature lower than
that in a refrigerator but the vessel is not provided with any heater. Why will
be described below. In water, you should experience a pressure felt pressed
in the surroundings. This is the hydraulic pressure. The deeper diving, the
higher the hydraulic pressure will be. If you drive down to a water depth of
up to 6,500 meters aboard "Shinkai 6500," for example, the hydraulic pressure
then acting thereon will be equivalent to the weight of ten human adults working
on the thumb. The higher the hydraulic pressure receiving surface, moreover,
the larger force will have to be received as a whole. If the palm is used entirely,
for example, the force equal to or more than 100 times that on the thumb will
be received by the palm. In other words, the pressure-resistant cube embarked
by the crew must have the smallest possible size since the hydraulic pressure
is extremely high in the deep sea. "Shinkai 6500" has a pressure-resistant cube
with a diameter of 2 meters only. In addition, the survey vessel is filled up
with the mechanisms required to operate the submersible survey vessel for observation
purposes. With three persons embarking thereon, the pressure-resistant cube
has no sufficient room. Although no water closet is available, please do not
be worried since a special bag is available in emergency.
When viewing the horizon while standing on the coast, you have a distance of
approximately 4.5 kilometers to the horizon.
Unit in which the speed of a vessel is expressed; it is a rate of advancing
1 sea mile per hour, or approximately 1.85 kilometers. One sea mile is approximately
1,852 meters, length of one minute in latitude.
・What are the
Seven Seas? ：
At present, they include "Arctic Sea, Antarctic Sea, Indian Ocean, North Atlantic
Ocean, North Pacific Ocean, South Atlantic Ocean and South Pacific Ocean." The
seven seas, however, have changed historically. Some say they have originated
from a myth in ancient India. When there was no geographical recognition of
the world, there was a thought in the myths of ancient India that the world
had seven seas surrounding seven continents. Besides, "7" meant the "whole"
or "world" in the language used in ancient Mesopotamia. Such world views are
considered to have brought about the thought that all the seas should be called
"7 seas." Under such thought, the world has had the sea divided into seven.
In the 15th century and before, i.e. prior to the Large Voyages Times, the seven
seas were "Red Sea, Mediterranean Sea, Persian Gulf, Black Sea, Adriatic Sea,
Caspian Sea and Indian Sea."