لطفا منتظر باشید ...
Water-Salt water and fresh water seas
The contiguity and clash of two seas , two
water currents , or two kinds of water
have long occupied the minds of interpretors
of Quran ; on the basis of the scientific
knowledge of the time , they have given
different interpretations in connection whit
the these verses , such as metaphormic and
figurative interpretations,the two Roman and
Persian seas , and underground deposits and
oceans.What is far sure is that wonderful sea
currents such as the Gulf stream,which flows
like a gigantic river that is 150 km.Wide and
a few hundred meters deep , sparkles for ever
in the midst of the Atlantic ocean , and what
is more it does not mix whit its adjacent
waters. This huge water current is one of the
mysteries of creation and also a mgnificent
scene of the incarnation of the Lord's
greatness which follows its course apart from
any interpretation.
Anyhow,many research studies concerning
sea and water currents have so far been
carried on.The results obtained from such
studies are briefly taken up in two section:
factors involved in the emergence of water
currents,and kinds of water currents.
Factors involved in the emergence of sea
currents.
1- Tides :
It has been proved that the Moon , like
the Earth has a gravitational field , and
exerts a force of attraction on the Earth.
Considering the greatness of the size of
the Earth in relation to that of the Moon,
the hemisphere of the Earth which is closer
to the Moon is more under the Moon's
gravitational force than the other one.
On the other hand,it is quite obvious that
ocean water is closer to the Moon that the
land at is bottom and is , therefore, more
under the Moon's gravitational force.
Consequently ocean water is convexly
attracted towards the Moon.Because of the
movement of the Earth and the Moon , this
condition changes every few hours and cause
currents known as flow and ebb currents.
2- The Earth's rotation :
The Earth rotates around its axis once every
24 hours , and hence we , on the Earth , are
turning towards the east at the speed of 82
kilometers per second.The tow elements of air
and water however , are not attached to the
Earth , therefore , they don't turn with the
Earth at the same speed so they roll away in
wave form causing sea currents and winds.
These currents lean towards the right in the
north hemisphere,and to the left in the south
hemisphere this fact was first recognized
and stated by Coriolis , a french engineer,
and is therefore known as Coriolis force .
3- convection :
The sea water around the pole becomes cold
and as a result hevier , so it moves down;
to take its place ,the warmer water on the
surface of the sea moves towards the pole.
The reverse of this process occurs in the
equator and causes water currents . This
exchange of warm equatorial water whit cold
polar water is one of the most important
water movements in oceans.
4 - Winds :
Convectional currents of the air cause wind,
and because of the cold air in the pole and
the warm air in the equator , winds , on the
surface of the seas are always blowing from
the pole towards the equator,these winds are
known as prevailing winds,they,inturn,cause
water currents.
5 - Water pressure :
When water passes a narrow passage,it moves
faster Bernoullis' principle ; this fact
is also true for sea water ,and cause water
current.This phenomenon is more seen at the
mouth of gulfs and straits.
6 - Water density :
The relative density of sea water is the
ratio of the weight of the unit volume of
sea water is to the weight of distillted
water of equal volume at 4 degree c.
Density is effective in the formation of
currents because it regulates the equilibrium
condition between water masses in such away
that the more dense water always flows at a
lower level.For example in the Mediterranean
sea which the surface sea water evaporates
a lot , the density of water rises and as
a result it moves downward to the bottom of
the sea.This water is replaced by the lighter
water entering the Mediterranean sea from
Gibraltar strait;and the hevier water at
the bottom of the Mediterranean sea passes
the mouth of Gibraltar strait and enters
the lower level of the Atlantic ocean waters;
the same phenomenon occurs in the Baltic Sea
too.
7 - Waves :
Sea waves themselves cause water currents.
As waves approach seashores , they deviate
move until they become parallel to the shore.
These waves are convergent at the two ends of
the shore and divergent in the middle.
Therefore ,it is expected that the waves be
more intense and higher at the convergent
site,and at the divergent site they be less
intense and shorter . The difference in the
intensity of these waves becomes a current
towards the divergent site . Such currents
are called wave made currents.
Types of water currents :
1 - Warm currents : These currents come about as a result of the
movement of warm waters to higher latitudes,
like Gulf stream current in the North
Atlantic ocean and the Kuroshio current in
the North Pacific ocean.
2 - Cold currents :
A These currents come about following
the movement of cold waters to colder
latitudes like the Falkland current in
the South Atlantic ocean.
B Currents which are formed following the
upward movement of deep waters to the surface
of the sea , such as the Peruvian current in
the current of California in the West Coast
of the North America.
C Deep currents are among slow currents
about which there exists little information.
