Ocean Ocean Physics Physics
Dec 20, 2015
Ocean PhysicsOcean Physics• Buoyancy• Temperature• Light• Density• Pressure• Depth• Salinity• Sound • Dissolved Gasses
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
• 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
• Air chambers
• Large liver & heterocercal tail
• Buoyancy Compensator Device
(BCD)
Organisms adaptation to buoyancy in water
IsothermsIsotherms
Lines of equal temperature
60o
30o
0o
30o
60o
tropic
temperate
temperate
polar
polar
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
~65% of visible light is absorbed in the 1st m
Photic Zone
Aphotic Zone
No Photosynthesis
100m
0 m
Wavelength (nm)400 700600500
Photosynthesis
Dysphotic Zone
1000m
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.
• 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.
DensityDensity
Air0.08 lbs
1 ft
1 ftfw
62.4 lbs
1 ft
1 ftsw
64 lbs
1 ft
1 ft
Piston example:
Air is compressible Water is incompressible
Temperature Salinity DensityLow High Low High Low High
surface 0 m
100 m
1000 m
Thermocline + Halocline = Pycnocline
thermocline pycnoclinehalocline
Speed of sound- faster in ocean (higher density)
1500 m/sec, which is 4x faster than in air
Difficult to determine direction of sound
Can hear many things such as ships miles away, shrimp eating, helicopters overhead, and whales communicating.
Sound in Water
source of noise
Dep
th (
m)
0
1000
2000
3000
4000
Speed of Sound (m/sec)
1,475 1,500
sofar layermin speed
high speed
high speed
• 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
Sofar LayerSofar Layer
Solubility of Gases in Seawater as a Function of Temperature (salinity @ 33o/oo)
Solubility(ml/l at atmospheric pressure)
Temperature N2 O2 CO2
(oC) .
0 14.47 8.14 8,700 10 11.59 6.42 8,030 20 9.65 5.26 7,350 30 8.26 4.41 6,660
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
Relationship between water depth, pressure, and volume
Volume
x1
x 1/2
x 1/3
x 1/4
Boyle’s LawBoyle’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 Daltons Law of Partial PressurePressure
The total pressure of a gas exerted by a mixture of gas is the sum of the gases exerted independently.
Air % partial pressure (mm Hg)N2 78.6 597O2 21.0 159CO2 0.04 0.3H2O 0.46 3.7Total 100 760
Partial pressure is directly related to its % in the total gas mixture. E.g., at 1 atm PO2 = 159 mm Hg
Henry’s LawHenry’s LawWhen 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)
Increase pressure, increase concentration
Seawater AirN2 48% 78% O2 36% 21%CO2 15% 0.04%
Dissolved gasses in Dissolved gasses in seawater:seawater:
Gas Solubility vs TemperatureGas Solubility vs Temperature
Gasses dissolve most readily in cold water
Honaunau Tide Pool
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