Introduction to Oceans
Oceans cover 70% of the Earth's surface. The
oceans contain about 97% of the Earth's water-supply.
The oceans of the Earth are unique in the solar
system and in other parts of the solar system, there is no
liquid water. Origin of the existing creatures was the sea and
the oceans continue to be the home of many animals at present.
The oceans affect the weather and temperature of
the Earth. By absorbing solar radiation, the oceans moderate the
weather on the earth. The ocean currents distribute this
absorbed energy around the globe. This heats the land and air
during winter and cools it during summer.
OCEANS
The Earth's oceans are connected to each other.
There are five oceans on the Earth: The Pacific, Atlantic,
Indian, Arctic and the Southern Ocean.
There are many seas. Seas are enclosed by land.
The largest seas are the South China Sea, the Caribbean Sea, and
the Mediterranean Sea.
|
Ocean |
Area (square
miles) |
Average
Depth (ft) |
Deepest
depth (ft) |
|
Pacific
Ocean |
64,186,000 |
15,215 |
Mariana
Trench, 36,200 ft deep |
|
Atlantic
Ocean |
33,420,000 |
12,881 |
Puerto
Rico Trench, 28,231 ft deep |
|
Indian
Ocean |
28,350,000 |
13,002 |
Java
Trench, 25,344 ft deep |
|
Southern
Ocean |
7,848,300
sq. miles (20.327 million sq km ) |
13,100 -
16,400 ft deep (4,000 to 5,000 meters) |
the
southern end of the South Sandwich Trench, 23,736 ft (7,235
m) deep |
|
Arctic
Ocean |
5,106,000 |
3,953 |
Eurasia
Basin, 17,881 ft deep |
Salty Ocean
All water contains "salts." But not all water tastes
salty. Water is fresh or salty according to one's taste,
and in making this decision man is more convinced by his
sense of taste than by a laboratory experiment. It is
one's taste result that prefers this water and rejects
another.
An easy experiment illustrates this. Fill three glasses
with water from the kitchen valve. Drink one and it tastes
fresh even though some dissolved salts are naturally
there. Add a bit of table salt to the second, and the
water may taste fresh or slightly salty depending on a
personal taste threshold and on the quantity of salt held
in a "pinch."
But
add a teaspoon of salt to the third and your taste tell
you that this water is too salty to drink; this glass of
water has about the same salt content of a glass of sea
water.
The ocean water contains too much amounts of dissolved
chemicals and it is too salty for human to eat.
Some scientists guess that the oceans contain as much as
50 quadrillion tons (50 million billion tons) of dissolved
solids.
If the salt in the sea could be extracted and dispersed
evenly over the Earth's land surface, it would form a
layer more than 500 feet thick, about the height of a
40-story office building. The saltiness of the ocean is
further realized when compared by means of the salt
content of a lake. For instance, when 1 cubic foot of sea
water evaporates about 2.2 pounds of salt is remained, but
1 cubic foot of fresh water from Lake Michigan contains
only one one-hundredth (0.01) of a pound of salt, or about
one sixth of an ounce. Thus, sea water is 220 times
saltier than the new lake water.
What
arouses the scientist's interest is not so much why the
ocean is salty, but why it isn't fresh like the rivers and
streams that empty into it. Further, what is the origin of
the sea and of its "salts"? And how does one explain ocean
water's remarkably uniform chemical composition? To these
and related questions, scientists seek answers.
In public words, "ocean" and "sea"
are used interchangeably. Today's seas are the North and
South Pacific, North and South Atlantic, Indian and Arctic
Oceans and the Antarctic waters or seas.
Scientists consider that the seas are as much as 500
million years old. About the origin of the seas, there are
several theories but no single theory explains all aspects
of this puzzle. Many earth scientists agree with the
hypothesis that both the atmosphere and the oceans have
accumulated slowly through geologic time from some
development of "degassing" of the Earth's interior.
According to this theory, the
ocean had its origin from the escape of water steam and
other gases from the molten igneous rocks of the Earth to
the clouds surrounding the cooling Earth. Following the
Earth's surface had cooled to a temperature below the
boiling point of water; rain began to fall and continued
to fall for centuries. As the water drained into the great
hollows in the Earth's surface, the ocean came into
existence. The forces of gravity prevented the water to
leave the planet.
Sea water is defined as a answer of almost everything.
Ocean water is certainly a compound solution of stone
salts and of decayed biologic matter in the seas. Most of
the ocean's salts were resulting from steady processes
such the breaking up of the cooled igneous rocks of the
Earth's crust by weathering and erosion, the wearing down
of mountains, and the dissolving action of rains and
streams which transported their mineral washings to the
sea.
Some
of the ocean's salts have been dissolved from rocks and
sediments below its floor. Other sources of salts include
the solid and gaseous materials that escaped from the
Earth's crust through volcanic eruptions or that
originated in the atmosphere.
The
Mississippi, Amazon, and Yukon Rivers empty respectively
into the Gulf of Mexico, the Atlantic Ocean, and the
Pacific Ocean, all of which are salty. Why aren't the
oceans as fresh as the river waters that flows into them?
Because the saltiness of the ocean is the result of
several natural phenomena and processes, the salt load of
the streams entering the ocean is just one of these
factors.
The primeval seas must have been only somewhat salty. But
ever since the first rains descended upon the young Earth
hundreds of millions of years ago and ran over the land
breaking up rocks and transporting their raw materials to
the seas, the ocean has become saltier. It is predictable
that the rivers and streams flowing from the United States
alone discharge 225 million tons of dissolved solids and
513 million tons of suspended deposit yearly to the sea.
New calculations show load of dissolved solids from other
land masses that range from about 6 tons per square mile
for Australia to about 120 tons per square mile for
Europe.
all through the world, rivers carry an estimated 4 billion
tons of dissolved salts to the ocean annually. About the
same tonnage of salt from the ocean water probably is
deposited as sediment on the ocean bottom, and thus,
yearly gains may offset yearly losses. In other words, the
oceans today probably have a balanced salt input and
outgo.
Past accumulations of dissolved and floating solids in
the sea do not explain completely why the ocean is salty.
Salts become intense in the sea because the Sun's heat
distills or vaporizes almost pure water from the surface
of the sea and leaves the salts behind. This process is
part of the repeated exchange of water between the Earth
and the atmosphere that is called the hydrologic cycle.
Water vapor rises from the ocean surface and is carried
landward by the winds.
When the vapor collides with a colder mass of air, it
condenses (changes from a gas to a liquid) and falls to
Earth as rain. The rain runs off into streams which in
turn transport water to the ocean. Evaporation from both
the land and the ocean again causes water to return to the
atmosphere as vapor and the cycle starts anew. The ocean,
then, is not fresh like river water because of the huge
buildup of salts by evaporation and the contribution of
raw salts from the land. In fact, since the first
rainfall, the seas have become saltier.
Scientists have studied the ocean's water for more than a
century, but they still do not have a complete perceptive
of its chemical composition. This is partly because of the
lack of precise methods and procedures for measuring the
materials in sea water. Some of the problems confronting
scientists result from the huge size of the oceans, which
cover about 70 percent of the Earth's surface, and the
complex chemical system in a marine surroundings in which
constituents of sea water have intermingled over periods
of time. At least 72 chemical elements have been
recognized in sea water, most in particularly small
amounts.
Probably
all the Earth's elements exist in the sea. Elements may
combine in various ways and form insoluble products that
sink to the ocean floor. But even these are subject to
chemical alteration because of the overlying sea water
which continues to exert its environmental influence.
Oceanographers report salinity and the concentrations of
individual chemical constituents in sea water. The
salinity of ocean water varies. It is affected by such
items as melting of ice, inflow of river water,
evaporation, rain, snowfall, wind, wave motion, and ocean
currents that cause horizontal and vertical mixing of the
saltwater.
The saltiest water (40 ‰) occurs in the Red Sea and the
Persian Gulf, where evaporation rates are very high. Of
major oceans, the North Atlantic is the saltiest; its
salinity averages about 37.9 ‰. Within the North Atlantic,
the saltiest part is the Sargasso Sea, an area of about 2
million square miles, located about 2,000 miles west of
the Canary Islands.
The Sargasso Sea is separated from the open ocean by
floating brown seaweed "sargassum" from which the sea gets
its name. The saltiness of this sea is due in part to the
high water temperature (up to 83º F) causing a high rate
of evaporation and in part to its remoteness from land;
because it is so far from land, it receives no fresh-water
inflow.
Low salinities happen in polar seas where the salt water
is weak by melting ice and continued precipitation. Partly
closed in seas or coastal inlet that receive considerable
runoff from precipitation falling on the land also may
have low salinities. The Baltic Sea ranges in salinity
from about 5 to 15‰. The salinity of the Black Sea is less
than 20‰. Water of the Puget Sound in the Tacoma, washes
the area ranging in salt content from 21‰ to about 27‰.
This area is exhausted by a number of fresh-water streams
which discharge an average of about 4.1 billion gallons of
water per day into Puget Sound.
Salinity
of sea water along the coastal areas of the conterminous
United States varies with the month of the year as well as
with geographic location. For example, the salinity of the
ocean water off Miami Beach, Fla., varies from about 34.8‰
in October to 36.4‰ in May and June, while diagonally
across the country, off the coast of Astoria, Oregon, the
salinity of sea water varies from 0.3‰ in April and May to
2.6‰ in October.
The
water off the coast of Miami Beach has a high salt content
because it is undiluted sea water. Off the coast of
Astoria, however, the sea water is less salty because it
is mixed with the fresh water of the mighty Columbia.
Sometimes river water travels far from coast before it
mixes with sea water. This is shown by data gathered from
a study of the Columbia River, which, in an standard year,
carries to the ocean enough water to cover an area of 1
million acres to a depth of 197 feet. Using a radio-
active tracer, scientists at Oregon State University have
followed the river's water from its mouth near Astoria to
a point southwest of Coos Bay, 217 miles away.
The salt content of the open oceans, free from land
influences, is rarely less than 33‰ and seldom more than
38‰. Throughout the earth, the salinity of sea water
averages about 35‰. This average salinity was obtained by
William Dittmar in 1884 from chemical analyses of 77 sea
water samples collected from many parts of the world
during the scientific expedition of the British corvette,
H.M.S. Challenger.
The Challenger journey, organized by the British
Government at the proposal of the Royal Society, set out
to study the biology of the sea, examine the chemical and
physical properties of the water, sample deposits on the
ocean floor, and evaluate water temperatures. The voyage
began in 1872 and ended almost 4 years later after
covering 68,890 miles.
This expedition remains today the longest continuous
scientific investigation of the ocean basins. Dittmar's 77
samples are still the only worldwide set of samples of sea
water for which complete data (each principal constituent)
on chemical composition are available. More recent data,
reflecting improvements in analytical and sampling
techniques, show slight deviations from Dittmar's results,
but these changes do not affect the overall usefulness of
his work.
The salinity of water in the open sea is not fixed at 35‰
even in areas distant from land; that figure is only an
average. On a universal basis, a maximum salinity of 36‰
occurs at about latitudes 20º N. and 20º S. The average
salinity of sea water, 35‰, occurs at the Equator. A
minimum salinity of 31‰ corresponds approximately with
latitude 60º N., whereas lowest salinities of 33‰ in the
Southern Hemisphere occur at latitude 60º S.
At
the Equator, where salinity is 35‰, the strength of sea
water by rain is offset by the loss of water by
evaporation. But in the latitudes bordering the Equator
the opposite condition prevails
As much as the oceans receive most of their water from the
rivers, the ratios (as distinguished from the total
amounts) of different chemical constituents should be
about the same in both in spite of total salt content but
this is not so.
Sea water and river water obviously are very different
from each
other:
(1) Sodium and chloride (the components of common table
salt) constitute a little more than 85 percent of the
dissolved solids in ocean water and give to the water its
characteristic salty taste, but they represent less than
16 percent of the salt content of river water.
(2) Rivers carry to the sea more calcium than chloride,
but the oceans nevertheless contain about 46 times more
chloride than calcium.
(3) Silica is an important ingredient of river water but
not of sea water.
(4) Calcium and bicarbonate account for nearly 50 percent
of the dissolved solids in river water yet constitute less
than 2 percent of the dissolved solids in ocean water.
These variations seem contrary to what one would expect.
Part of the clarification is the role played by marine.
Sea water is not simply a solution of salts and dissolved
gases unchanged by living organisms in the sea. Mollusks
(oysters, clams, and mussels, for example) extract calcium
from the sea to build their shells and skeletons.
Foraminifers (very small
one-celled sea animals) and
crustaceans (such as crabs,
shrimp, lobsters, and barnacles) likewise take out large
amounts of calcium salts to build their bodies. Coral
reefs, ordinary in warm tropical seas, consist mostly of
limestone (calcium carbonate) formed over millions of
years from the skeletons of billions of small corals and
other sea animals.
Plankton (tiny floating animal
and plant life) also exerts control on the composition of
sea water. Diatoms, members of the
plankton community, require silica to form their shells
and they draw heavily on the ocean's silica for this
purpose.
Some marine organisms concentrate or secrete chemical
basics that are there in such minute amounts in sea water
as to be almost untraceable: Lobsters think copper and
cobalt; snails secrete lead; the sea cucumber extracts
vanadium; and sponges and certain seaweeds remove iodine
from the sea.
Sea life has a strong control on the composition of sea
water. However, some elements in sea water are not
affected to any apparent extent by plant or animal life.
For example, no known biological process removes the
element sodium from the sea.
In addition to biological influences, the factors of
solubility and physical-chemical reaction rates also help
to explain the composition of sea water. The solubility of
a constituent may limit its concentration in sea water.
Excess calcium (more calcium than the water can hold) may
be precipitated out of the water and deposited on the sea
floor as calcium carbonate. Presumably as a result of
physical-chemical reactions not well understood, the metal
manganese occurs as nodules in many places on the ocean
floor. Similarly,
phosphorite (phosphate rock) is
found in large amounts on the sea bottom off southern
California and in lesser amounts in several other places.
Although the composition of sea water differs from that of
river water, the proportions of the major constituents of
sea water are almost constant all through the world.
Dittmar's 77 samples showed no significant global
differences in relative composition, and his average
concentrations are used today to represent the ratios of
major constituents in sea water.
The analyses, which Dittmar made over a period of 9 years,
further showed that chloride, sodium, magnesium, sulfate,
calcium, and potassium make up 99 percent of the dissolved
solids in sea water. Dittmar's result may be uttered in
another way: although the salinity or total salt content
may vary from place to place, the ratio of any one major
constituent of sea water (chloride as an instance) to the
total content is nearly constant.
However,
the ratios of the less abundant elements (aluminum,
copper, tin, and bismuth, for example) to total salt
content are not constant nor are those of dissolved gases
such as oxygen, carbon dioxide, and nitrogen. But
establishment of the near constancy of the ratios of major
constituents of sea water is important because it enables
scientists to measure one principal element and then, by
projection of ratios and correction for temperature and
pressure, to calculate the other components in the water,
thereby shaping its salinity.
Conclusions:
Because of the slow build up of dissolved chemicals worn
from the Earth's crust and washed into the sea, the marine
is salty. Solid and gaseous explosion from volcanoes,
floating particles swept to the ocean from the land by
onshore winds, and materials dissolved from sediments
deposited on the ocean floor have also contributed.
Salinity is increased by evaporation or by freezing of sea
ice and it is decreased as a result of rainfall, runoff,
or the melting of ice. The average salinity of sea water
is 35‰, but concentrations as high as 40‰ are observed in
the Red Sea and the Persian Gulf. Salinities are much less
than average in coastal waters, in the polar seas, and
near the mouths of large rivers.
Not only sea water is much saltier than river water but
also differs in the proportion of the various salts.
Sodium and chloride constitute 85 percent of the dissolved
solids in sea water and account for the characteristic
salty taste. Certain constituents in sea water, such as
calcium, magnesium, bicarbonate, and silica, are partly
taken out of solution by biological organisms, chemical
precipitation, or physical-chemical reactions. In open
water the chemical composition of sea water is almost
constant. Because of the steady ratios of the main
constituents to total salt content, the determination of
one major ingredient can be used to calculate sea water
salinity. For minor constituents and dissolved gases the
composition is variable and so ratios cannot be used to
calculate salt Circulation and mixing, density and ocean
currents, wind action, water temperature, solubility, and
biochemical reactions are some of the factors that explain
why the composition of water in the open sea is
approximately constant from place to place.
BLUE OCEAN
The ocean appears blue because it reflects the
blue color of the sky. On a cloudy, gray day,
the ocean appears gray.
The Red Sea often looks red because of red algae that live
in this sea.
The Black Sea looks roughly black because it has a high
focus of hydrogen sulfide.
Ocean Waves
Waves on the surface of the ocean are caused by the winds.
Through friction between the air molecules and the water
molecules, the wind transfers some of its energy to the
water,. Stronger winds (like storm surges) cause larger
waves. You can make your own small waves by blowing across
the surface of a pot of water.
Waves of water do not move straight, they only move up and
down.
Tsunamis (sometimes called tidal waves) are
different from surface waves; they are usually caused by
underwater earthquakes, volcanic eruptions, or landslides.
