Ocean 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

Isotherms Lines of equal temperature 60 o 30 o 0o0o 60 o tropic temperate polar

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) – m (dysphotic zone) –>1000 (aphotic zone)

Light Penetration in the Ocean ~65% of visible light is absorbed in the 1 st m Photic Zone Aphotic Zone No Photosynthesis 100m 0 m Wavelength (nm) 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

Density Air 0.08 lbs 1 ft fw 62.4 lbs 1 ft sw 64 lbs 1 ft Piston example: Air is compressibleWater is incompressible

64 lbs Water doesn’t change density under pressure

TemperatureSalinityDensity Low High Low High LowHigh surface 0 m 100 m 1000 m Thermocline + Halocline = Pycnocline thermoclinepycnoclinehalocline

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

Depth (m) Speed of Sound (m/sec) 1,475 1,500 sofar layer min speed high speed

Depth (m) 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 Layer

Dissolved Gasses in Seawater

Solubility of Gases in Seawater as a Function of Temperature 33 o / oo ) Solubility (ml/l at atmospheric pressure) TemperatureN 2 O 2 CO 2 ( o C) , , , ,660

Air weighs 14 lbs/in 2 (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 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% partial pressure (mm Hg) N O CO H 2 O Total Partial pressure is directly related to its % in the total gas mixture. E.g., at 1 atm PO 2 = 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 CO 2 bubbles (CO 2 is under pressure)

Dissolved gasses in seawater: SeawaterAir N 2 48%78% O 2 36%21% CO 2 15%0.04% Gasses dissolve most readily in cold water

Decompression sickness It is caused when N 2 enters the blood circulation and the tissues. When extra N 2 leaves the tissues, large bubbles form. N 2 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?