Seawater also conducts electricity because of its diluted-salt content. It is a
good sound propagator, which helps us to use sound-propagation to map the ocean
floor and to conduct underwater seismic experiments. Because of the dissolved
salts and mineral contents, seawater freezes at about -4 °C. The composition of
seawater with its major dissolved compounds is: Cl
- (55.05 %), SO
2- (7.68 %),
HCO
- (0.41 %), Na
+ (30.61 %), Mg
2+ ( 3.69 %) and Ca
2+ (1.16 %).
How Deep Can Seawater Penetrate into the Earth’s
Lithosphere?
The penetration of seawater into the solid lithosphere is inferred from seismic data
given during earthquakes generated in the ductile portion of the lithosphere. By
analogy, the solid lithosphere is like a thick piece of wood that dries and breaks.
Under some constraints it can generate fissures through which liquid penetrates.
Generally such depths are \20 km deep in most submarine regions except in the
subducting trench area where the depth of penetration could be several 100 km.
The study of tectonic processes taking place in converging margins, such as
underneath island-arcs and in the active margins bounding oceanic regions, can
help us to understand continental accretion. It is under the modern Oceans that the
internal structure of the Earth can best be studied without taking into consideration
the constraints of the large tectonic events taking place during continental growth.
Hydrosphere-Atmosphere Interaction
The interaction between the ocean and the atmosphere has a direct implication on
the climate changes observed on the Earth’s surface. It is a dynamic process
depending on many factors such as convection currents carrying deep water to
shallow levels, the flow of rivers to the ocean, and the wind carrying various sized
particles. Thus, the gas escaping from the crust and mantle is introduced into
seawater and transported to the surface where it will eventually be discharged into
the atmosphere. Helium, carbon dioxide, hydrogen and methane gas are found in
the water column and then released into the atmosphere above their site of production. When measuring the content of seawater at different depths in the water
column, chemists are able to find the exact source of the gas escaping on the ocean
floor. These sources are multiple. They are due to the alteration of oceanic rocks,
to the circulation of magmatic melts that give rise to volcanic eruptions as well as
to hydrothermal fluid discharge into the seawater.
Between the hydrosphere and the atmosphere, it is necessary to maintain an
equilibrium in order for life to exist. This equilibrium is due to the so-called
carbon cycle, which involves carbon oxide (CO 2 ), the bicarbonates (HCO
3- ) and
Why Seawater is Salty
35
good sound propagator, which helps us to use sound-propagation to map the ocean
floor and to conduct underwater seismic experiments. Because of the dissolved
salts and mineral contents, seawater freezes at about -4 °C. The composition of
seawater with its major dissolved compounds is: Cl
- (55.05 %), SO
2- (7.68 %),
HCO
- (0.41 %), Na
+ (30.61 %), Mg
2+ ( 3.69 %) and Ca
2+ (1.16 %).
How Deep Can Seawater Penetrate into the Earth’s
Lithosphere?
The penetration of seawater into the solid lithosphere is inferred from seismic data
given during earthquakes generated in the ductile portion of the lithosphere. By
analogy, the solid lithosphere is like a thick piece of wood that dries and breaks.
Under some constraints it can generate fissures through which liquid penetrates.
Generally such depths are \20 km deep in most submarine regions except in the
subducting trench area where the depth of penetration could be several 100 km.
The study of tectonic processes taking place in converging margins, such as
underneath island-arcs and in the active margins bounding oceanic regions, can
help us to understand continental accretion. It is under the modern Oceans that the
internal structure of the Earth can best be studied without taking into consideration
the constraints of the large tectonic events taking place during continental growth.
Hydrosphere-Atmosphere Interaction
The interaction between the ocean and the atmosphere has a direct implication on
the climate changes observed on the Earth’s surface. It is a dynamic process
depending on many factors such as convection currents carrying deep water to
shallow levels, the flow of rivers to the ocean, and the wind carrying various sized
particles. Thus, the gas escaping from the crust and mantle is introduced into
seawater and transported to the surface where it will eventually be discharged into
the atmosphere. Helium, carbon dioxide, hydrogen and methane gas are found in
the water column and then released into the atmosphere above their site of production. When measuring the content of seawater at different depths in the water
column, chemists are able to find the exact source of the gas escaping on the ocean
floor. These sources are multiple. They are due to the alteration of oceanic rocks,
to the circulation of magmatic melts that give rise to volcanic eruptions as well as
to hydrothermal fluid discharge into the seawater.
Between the hydrosphere and the atmosphere, it is necessary to maintain an
equilibrium in order for life to exist. This equilibrium is due to the so-called
carbon cycle, which involves carbon oxide (CO 2 ), the bicarbonates (HCO
3- ) and
Why Seawater is Salty
35