Ocean PhysicsOcean Physics

Ocean PhysicsOcean Physics• 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

• 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

• Blubber

• Swim bladder

• Fatty liver

• Buoyancy Compensator Device

(BCD)

Buoyancy Adaptation

Temperature

IsothermsIsotherms

Lines of equal temperature

60o

30o

0o

30o

60o

tropic

temperate

temperate

polar

polar

Sea Surface TemperatureSea 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

~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.

Density

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

64 lbs

64 lbs

Water doesn’t change density under pressure

Temperature Salinity DensityLow High Low High Low High

surface 0 m

100 m

1000 m

Thermocline + Halocline = Pycnocline

thermocline pycnoclinehalocline

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

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

Dep

th (

m)

0

500

1000

1500

2000

SOFAR Channel

Distance

SOFAR channel

sound rays

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

Dissolved Gasses in Seawater

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 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:Dissolved gasses in seawater:

Seawater AirN2 48% 78% O2 36% 21%CO2 15% 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?