SCIENCE EXPLORER
Why is the Sea Salty
IF ALL the salt
in the sea were spread evenly over the land, it would form a layer more than
500 feet [150 m] thick—about 45 stories high! Where
does all that salt come from, especially considering that countless freshwater
streams and rivers empty into the oceans? Scientists have discovered a number
of sources.
One source is
the ground beneath our feet. As rainwater seeps through soil and rocks, it
dissolves tiny amounts of minerals, including salts and their chemical
constituents, and carries them out to sea by means of streams and rivers (1). This process is called weathering.
Of course, the concentration of salt in freshwater is very low, so we cannot
taste it.
Another source
is salt-forming minerals in the earth’s crust beneath the oceans. Water
penetrates the seafloor through cracks, gets superheated, and returns to the
surface with its cargo of dissolved minerals. Hydrothermal vents—some forming
deep-sea geysers—disgorge the resulting chemical soup into the sea (2).
In a reverse
process that has a similar end result, undersea volcanoes eject large amounts
of hot rock into the oceans, where the rock releases chemicals into the water (3). An additional source of minerals
is the wind, which carries particles from land out to sea (4). All these processes make seawater a solution of practically
every element known. The major salt component, however, is sodium
chloride—common table salt. It makes up 85 percent of the dissolved salts
and is the primary reason why seawater tastes salty.
What Keeps Salt Levels Stable?
Salts are
concentrated in the sea because the water that evaporates from the ocean is
almost pure. The minerals are left behind. At the same time, more minerals
continue to enter the oceans; yet, the salt level remains stable at about 35
parts per thousand of seawater. Evidently, then, salts and other minerals are
being added and removed at about the same rate. This raises the question, Where
do the salts go?
Many salt
components are absorbed into the bodies of living organisms. For instance,
coral polyps, mollusks, and crustaceans harvest calcium, a salt component, for
their shells and skeletons. Microscopic algas called diatoms extract silica.
Bacteria and other organisms consume dissolved organic matter. When these
organisms die or are eaten, the salts and minerals in their bodies eventually
settle to the seafloor as dead matter or feces (5).
Many salts not
removed by biochemical processes are disposed of in other ways. For example,
clay and other terrestrial materials that find their way into the oceans by
means of rivers, land runoff, and volcanic fallout may bind certain salts and
carry them down to the seafloor. Some salts also bind to rock. Thus, through a
number of processes, much of the salt ends up being added to the seafloor (6).
Many researchers
believe that geophysical processes complete the cycle, albeit over aeons of
time. The earth’s crust is made up of gigantic plates. Some of these meet at
subduction zones, where one plate plunges beneath its neighbor and sinks into
the hot mantle. Usually, the denser oceanic plate sinks beneath its lighter
continental neighbor, at the same time carrying its cargo of salty sediments
with it like a great conveyor belt. In this way much of the earth’s crust
slowly gets recycled (7).
Earthquakes, volcanoes, and rift zones are three manifestations of this
process.
Amazing Stability
Ocean salinity
varies from place to place and sometimes from season to season. The saltiest
unenclosed waters are in the Persian Gulf and the Red Sea,
where evaporation is very high. Regions of ocean that receive freshwater from
large rivers or much rainfall are less salty than average. So, too, is seawater
near melting polar ice, which is frozen freshwater. Conversely, when ice forms,
nearby seawater becomes more saline. Overall, though, ocean salinity is very
stable.
Seawater also
has a relatively stable pH, which is a measure of the acidity or alkalinity of
a substance, 7 being neutral. The pH of seawater ranges between 7.4 and 8.3,
which is slightly alkaline. (Human blood has a pH of about 7.4.) If the pH were
to go out of this range, the oceans would be in big trouble. In fact, this is
what some scientists now fear. Much of the carbon dioxide that humans are
adding to the atmosphere ends up in the oceans, where it reacts with water to
form carbonic acid. So human activity may be slowly acidifying the oceans. Many
of the mechanisms that keep seawater chemically stable are not completely
understood. Still, what we have learned underscores the vast wisdom of the
Creator, who cares about his handiwork.—Revelation 11:18.
See the article
"The Ocean Floor—Its Secrets Revealed,” in the November 22, 2000,
issue of Awake!
Rain
↓↓
↓↓
4 Wind
1 Minerals
↓
in
rocks ↓
6 Volcanic
………………↓…………………………………………………………………………↓……………………………………………………………………………………………………………………………………………………………………fallout…………
3 Oceanic 5
Diatoms ↓
OCEAN eruption ↓ ↓
↑ ↓ ↓
2 Hydrothermal ↑ ↓ ↓
vent ↑ ↓ ↓
……………………………………………………↑………………………………………………………………↑………………OCEAN FLOOR……………………↓………… …………………………↓……………………
↑ ↑ 7
←← SUBDUCTION
↑
EARTH’S CRUST ←←
ZONE
↑ ←←
………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………
Salts Found
in the Sea
Even though scientists have studied seawater for
over a century, they still have incomplete knowledge of its chemical
composition. However, they have been able to isolate the various dissolved salt
constituents and to calculate their proportions. These components include:
55% Chloride
30.6 Sodium
7.7 Sulfate
3.7 Magnesium
1.2 Calcium
1.1 Potassium
0.4 Bicarbonate
0.2 Bromide
and a number of
others, such as borate, strontium, and fluoride.
Saltier Than
the Ocean
Some inland bodies of water are saltier than the
ocean. A prime example is the Dead Sea, the
saltiest body of water on earth. Water flows into the Dead Sea, called the Salt Sea
in Bible times, carrying dissolved salts and other minerals. (Numbers
34:3, 12) Because the shore of the Dead Sea is the lowest dry spot on
earth, water can leave only one way—through evaporation, which can reduce the
sea level as much as one inch [25 mm] a day in summer.
Consequently, the salt content of the upper
layer of water is about 30 percent—nearly ten times that of the Mediterranean Sea. Because water density increases with
salinity, swimmers float very high in the water. In fact, they can lie on their
back and read a newspaper without the aid of a flotation device.
Salt Helps
Clean the Air
Research has shown that pollution particles in
air suppress precipitation from clouds over land. Polluted clouds over the
ocean, however, more readily produce rain. The difference is attributed to
sea-salt aerosols, which originate in sea spray.
Water droplets that form on pollution particles
in the atmosphere tend to be too small to fall as raindrops; hence, they just
stay in suspension. Sea-salt aerosols seed oceanic clouds by attracting these
small droplets and forming larger ones. The result is rain, which also helps to
purify the atmosphere of pollutants.
Courtesy: Awake!
Feedback to sexplorer.exced@gmail.com
|