Yeah Baby, Yeah!
Oceanography
Lecture 9
Filling up the Oceans:
Physical Properties of water
a. Physical Notions
Density
Phases (States) of Matter
b. The Water Molecule (“
(“Mickey Mouse”
Mouse” Molecule)
c. Heat Capacity – Change of Phases
d. Pressure, Density, and Temperature
e. Sound
f. Light
Physical Notions
1) Kinetic energy and temperature:
temperature: Heat is a measure of the physical
motion (vibration) of atoms and molecules in a medium. Physical
vibrations represent energy motion, called kinetic energy.
energy. The
more heat in a system, the greater the agitation of its atoms and
molecules.
2) Density:
Density: The amount of mass of (any material) in a unit volume
(usually g/cm3).
3) Phases:
Phases:
o Solids - Characterized by resistance to any change in shape,
caused by a strong attraction between the molecules of which
it is composed
definite volume and definite shape
o Liquids - Matter does not resist forces that act to change its
shape, because the molecules are free to move with respect to
each other
definite volume but indefinite shape
o Gases - Molecules are widely dispersed and move freely,
offers no resistance to change of shape and little resistance
to change of volume
neither definite volume or definite
shape
The Water (“
(“Mickey Mouse”
Mouse”) Molecule
Water: H2O! How simple can that be?
The two hydrogen bonds are not symmetrically attached to the Oxygen
atom. They form an angle of 105°
The sharing of electrons and
105°C
asymmetry creates a dipolar electrical field (slightly charged at each
end!)
The Water (“
(“Mickey Mouse”
Mouse”) Molecule
Water: H2O! How simple can that be?
Dipole
Uneven charge
Hydrogen bonds! (DNA anyone?)
Higher energy requirement for change of state (i.e. to “separate”
separate”
Mickey and Minnie!)
Heat Capacity – Change of Phase
Heat Capacity:
Capacity: Defined as the quantity of heat required to raise the
temperature of 1 gram of a substance by 1°
1°C.
• More energy is require to raise the temperature of a substance with
high heat capacity
• At constant energy inputs, the substance with lower heat capacity will
show a higher increase in temperature
• High heat capacity substances can store large amount of energy.
energy.
Substance
Lead
Mercury
Silver
Copper
Aluminium
Acetone
Ice
Water
Ammonia
Heat Capacity
Substance
Heat Capacity
(Calorie/g.°C)
Water
1.00
Sea water
0.94
Air
0.25
Granite
0.20
Change in amount of heat (Q): ! Q
! Q = M x Cp x ! T
But
Mass = !w x Volume
! Q = !w x V x Cp x ! T
Heat Capacity
(Calorie/g/°C)
0.03
0.03
0.06
0.09
0.22
0.51
0.50
1.00
1.13
Heat Capacity – Specific Heat
Throughout most of the Ocean, day and night temperature vary by less
than 1°
1°C because the high heat of water easily absorbs the daily gains
and minimizes the the daily losses of heat energy.
How about Continents?
- Deserts?
- Forested Areas?
Substance
Heat Capacity
(Calorie/g/°C)
Water
Sea water
Air
Granite
1.00
0.94
0.25
0.20
Heat Capacity – Specific Heat
Land vs Ocean breeze
Latent Heat–
Heat– Change of Phase
Liquid
Liquid
Solid
Gas
±80 calories per each gram
±540 calories per each gram
© The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Changes of State
Example 2:
2: Change in Heat but not in Temperature
Latent Heat - Change of phase
Liquid
Liquid
Solid = ±80 calories per gram
Gas = ±540 calories per gram
! Q = !w x V x CL
Change of Phase - Density
During the transition from liquid to solid state, at the freezing point,
the bond angle between oxygen and hydrogen atoms expands from about
105°
105° to about 109°
109°. This change allows ice to for a hexagonal crystal
lattice. The space taken by 24 molecules in solid state could be occupied
by 27 in the liquid state Water expands about 9%!
Ice has a density of 0.917 vs. ~1.000 g/cm3. Maximum density at ~4°
~4°C
Heat – Density
Fresh water maximum density at ~4°
~4°C
stratification
Seasonal inversion and
Pressure, Density and Temperature
The hydrostatic equation describes the way in which pressure P is
related to the depth (z) in a column of fluid.
fluid.
P=g z
Where:
-) P: Pressure
-) g: acceleration due to gravity
-) : density of the fluid
-) z: the depth of the water column
Assuming remains “virtually”
virtually” constant, then there is a proportional
relationship between pressure and depth! Water is only slightly
compressible and density remains within ±2% of its mean value in deep
ocean basins!
Pressure
Pressure
Example 3:
3: Change in Temperature but not in Heat
Example 3:
3: Change in Temperature but not in Heat
Adiabatic change
Water is compressible which induces
friction and thus higher kinetic energy
increase in
temperature
Adiabatic change
Water is compressible which induces
friction and thus higher kinetic energy
increase in
temperature
In situ temperature: Instability?
Potential is in situ temperature – adiabatic effect
Depth
(m)
1455
In situ T
(°C)
3.20
Depth
(m)
1455
In situ T
(°C)
3.20
Potential T
(°C)
3.09
2470
1.82
2470
1.82
1.65
3470
1.59
3470
1.59
1.31
4450
1.65
4450
1.65
1.25
6450
8450
1.93
6450
1.93
1.25
2.23
8450
2.23
1.22
10035
2.48
10035
2.48
1.16
Density and Temperature
The inclusion of salts (dissolved) in the water also
contributes to the total weight but not volume
increased density with decreasing temperature and
increased salt content.
-1
Fresh
Water
0.917
Salt
20 g/kg
1.01606
Salt
25 g/kg
1.02010
0
0.99984
1.01607
1.02008
1.02813
1
0.99990
1.01605
1.02005
1.02807
2
0.99994
1.01603
1.02001
1.02799
4
0.99997
1.01593
1.01988
1.02781
°C
At a salt content of 24.7 g/kg, the freezing point and the temperature
of maximum density of seawater coincide at –1.332°
1.332°C.
The temperature of maximum-density of average seawater (~35‰
(~35‰) is
well below its freezing point
Seawater of average salinity will
freeze before it will sink.
Salt
35 g/kg
1.02817
5
0.99996
1.01586
1.01980
1.02770
10
0.99970
1.01532
1.01920
1.02697
20
0.99820
1.01342
1.01720
1.02478
30
0.99565
1.01057
1.01428
1.02175
Light
Life – with a few exceptions – depends on energy from sunlight. As do
land plants, marine plants use chlorophyll and other pigment to capture
the visible light from the sun to perform photosynthesis.
As solar radiation strikes the
surface of the Ocean, a large
fraction of it is reflected back to
the atmosphere (dependent on the
angle of the sun’
sun’s rays and the
smoothness of the water surface).
The amount that enters is
ultimately absorbed by water
molecules (~65% of visible light is
absorbed within 1 m depth!):
depth!):
Absorbed energy manifests
itself as heat (elevating the
temperature of the surface water)
Density: Temperature and Salinity
Absorption: Greatest
at longer wavelength
At 100 m, only ~1% of
surface energy remains
Light
In very clear water, only 1% of the light reaches >100m depth (only
in the Blue: “Blue Waters”
Waters”)
On continental margins and in coastal waters there is a high load of
particles (remember sediments?). Light, in these turbid waters
cannot penetrate more that 20 m and is scattered in the greenyellow (“
(“Green or Brown Waters”
Waters”)
Sound
Sound is transmitted more rapidly and efficiently in water than in
air. (1445 m/s vs. 334 m/s). Additionally, it increases:
~1.3 m/s for every ‰ increase in salinity
~4.5 m/s for every 1°
1°C increase
1.7 m/s for every 100 meters in water depth (increased pressure)
Because salinities varies only slightly with depth, the speed of
sound in the Ocean is mostly affected by temperature and
pressure.
Sound
SOFAR (SOund
(SOund Fixing And Ranging) channel
Sound generated in this channel is refracted
(bent) and focused (Large-scale fiber-optic!).
Sound is not dispersed (trapped and confined):
tests have transmitted sounds over 18,000 km!
It has also been used to test the hypothesis of
Global Warming!