Download Absolute Pressure

Ocean Physics
Ocean Physics
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Buoyancy
Temperature
Light
Density
Pressure
Depth
Salinity
Sound
Dissolved Gasses
Buoyancy
Archimedes Principle of Buoyancy
A floating object displaces a volume of fluid
equal in mass to the floating object
empty
loaded with fish
Displaced water
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Objects that are more dense than water will sink.
Objects that are less dense than water will float.
Objects that are the same density as water will neither
sink nor float.
float
Neutrally
buoyant
sink
Buoyancy Adaptation
• Blubber
• Swim bladder
• Fatty liver
• Buoyancy Compensator Device
(BCD)
Temperature
Isotherms
polar
temperate
60o
30o
0o
30o
tropic
temperate
polar
Lines of equal temperature
60o
Sea Surface Temperature
July 2005
Properties of Light in the Ocean
The Electromagnetic Radiation
Spectrum
Only green and blue wavelengths pass through water a great
distance.
Light Absorption in the Ocean
• Light Intensity
–decreases with depth
–0-100 m (photic zone)
–100-1000m (dysphotic zone)
–>1000 (aphotic zone)
Light Penetration in the Ocean
Wavelength (nm)
400
500
600
700
0m
Photic Zone
Photosynthesis
100m
No Photosynthesis
Dysphotic Zone
1000m
Aphotic Zone
~65% of visible light is absorbed in the 1st m
Light Absorption in the Ocean
• Spectral Characteristics
– red wavelengths absorbed more readily by
water than blue wavelengths
– blue light penetrates deepest in the oceans
Light effects organisms residing in the
photic and aphotic zone.
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Phytoplankton productivity
Algae- green, brown, red
Predator/Prey relationships
Diurnal vertical migration
Bioluminescence- luminescent organs on
underside mimic downwelling light
Refraction- as light enters the water, it bends; this is
due to light traveling through different densities
Light entering the ocean is weakened by
scattering and absorption.
Density
Density
1 ft
1 ft
1 ft
Air
0.08 lbs
fw
62.4 lbs
sw
64 lbs
1 ft
1 ft
1 ft
Piston example:
Air is compressible
Water is incompressible
64 lbs
64 lbs
Water doesn’t change
density under pressure
Temperature
Salinity
Low
High Low
Density
Low
High
High
surface 0 m
100 m
thermocline
halocline
pycnocline
1000 m
Thermocline
+ Halocline
=
Pycnocline
Sound in Water
Sound in Water
Speed of sound- faster in ocean (higher
density)
1500 m/sec, which is 4x faster than in air
Difficult to determine direction of sound
source of noise
Can hear many things such as ships miles
away, shrimp eating, helicopters overhead, and
whales communicating.
Speed of Sound (m/sec)
1,475
1,500
0
high speed
Depth (m)
1000
min speed
2000
3000
4000
high speed
sofar layer
SOFAR Channel
Distance
0
Depth (m)
500
sound rays
1000
1500
2000
SOFAR channel
Sofar Layer
The depth at which the speed of sound is
minimum; Thus, loud noises can be heard for
thousands of km
Sound generated by Navy test in Indian Ocean
at sofar layer was heard as far away as the
Oregon coast. May affect behavior and
anatomy of marine organisms
Dissolved Gasses in Seawater
Solubility of Gases in Seawater as a
Function of Temperature (salinity @ 33o/oo)
Temperature
(oC)
0
10
20
30
Solubility
(ml/l at atmospheric pressure)
N2
O2
CO2
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14.47
11.59
9.65
8.26
8.14
6.42
5.26
4.41
8,700
8,030
7,350
6,660
Relationship between water depth, pressure,
and volume
Air weighs 14 lbs/in2 (psi)
Absolute pressure is the combined pressure of water and air
Depth
0 ft
33 ft
66 ft
99 ft
Absolute Pressure
1 atm 14.7 psi
2 atm 29.4 psi
3 atm 44.1 psi
4 atm 58.8 psi
Volume
x1
x 1/2
x 1/3
x 1/4
Boyle’s Law
For any gas at a constant temperature,
the volume will vary inversely with
absolute pressure while the density will
vary with absolute pressure.
I.e., volume  with  pressure
 pressure  density
Daltons Law of Partial
Pressure
The total pressure of a gas exerted by a mixture of gas is
the sum of the gases exerted independently.
Air
N2
O2
CO2
H2O
Total
%
78.6
21.0
0.04
0.46
100
partial pressure (mm Hg)
597
159
0.3
3.7
760
Partial pressure is directly related to its % in the total gas
mixture. E.g., at 1 atm PO2 = 159 mm Hg
Henry’s Law
When a mixture of gas is in contact w/a liquid,
each gas will dissolve in the liquid in proportion
to its partial pressure.
Gasses can go in and out of solution
e.g., open soda, get CO2 bubbles (CO2
is under pressure)
Dissolved gasses in seawater:
Seawater
N2 48%
O2 36%
CO2 15%
Air
78%
21%
0.04%
Gasses dissolve most readily in cold
water
Decompression sickness
It is caused when N2 enters the blood circulation
and the tissues.
When extra N2 leaves the tissues, large bubbles
form. N2 bubbles can travel throughout the
system and into the lungs and blood routes.
Treatment: hyperbaric chamber
Inquiry
1. What is isostacy?
2. Why do objects in water seen from the surface
appear to bend?
3. Which gas is responsible for decompression
sickness?
4. If a balloon is brought to 6 atm, what would it’s
volume be?
5. Which wavelength of light penetrates the
ocean the deepest?