Physics

003b

Seawater PhysicsSeawater Physics

                                                       

• Temperature• Light• Sound• Buoyancy• Dissolved gasses• Waves• Tides

Temperature

IsothermsIsotherms

Lines of equal temperature

60o

30o

0o

30o

60o

polar

polar

temperate

tropic

temperate

Sea Surface TemperatureSea Surface Temperature

Oct. 2010

Sea Surface TemperatureSea Surface Temperature

Sea Surface TemperatureSea Surface Temperature

10-24-10 to 10-27-2010

Temperature Salinity DensityLow High Low High Low High

surface 0 m

200 m

1000 m

Thermocline + Halocline = Pycnocline

thermocline pycnoclinehalocline

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

–0-200 m (photic zone)

–200-1000m (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

200m

0 m

Wavelength (nm)400 700600500

Photosynthesis

Dysphotic Zone

1000m

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

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

• Blubber

• Swim bladder

• Pneumatophore

Organisms adaptation to buoyancy in water

             

                        

• Air chambers

• Large liver & heterocercal tail

• Buoyancy Compensator Device

(BCD)

Organisms adaptation to buoyancy in water

             

                        

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

Zebra ‘Tidepool’ Blenny

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

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

O2 Minimum Zone (OMZ)

O2 Content (ml/L)

Wat

er d

epth

(m

)

What causes the O2 minimum layer?

Marine snow

Why are there high levels of O2 at depth?

O2 Dead Zones

Surface currents are wind driven currents

Ekman Transport

Water flow in the Northern hemisphere- 90o to the right of the wind directionDepth is important

Upwelling and downwelling• Vertical movement of water ()

– Upwelling = movement of deep water to surface• Hoists cold, nutrient-rich water to surface• Produces high productivities and abundant marine life

– Downwelling = movement of surface water down• Moves warm, nutrient-depleted surface water down• Not associated with high productivities or abundant

marine life

upwelling

downwelling

Langmuir Circulation

1.Gravitational pull of the moon and sun

2.Centripetal force of the rotating Earth

Tides are generated by:

Tides are generated by:• the gravitational pull of the moon and sun

- moon has 2x greater gravitational pull than the sun - sun is 10 million x more massive than the

moon and is 390 times farther away

Centripetal force

CENTRIPETAL

GRAVITATIONAL FORCE

GRAVITATIONAL & CENTRIPETAL

• Diurnal Tide: 24 hr 50 min cycle

• Semi Diurnal Tide: 12 hr 25 min cycle

• Mixed Tide: 12 hr 25 min cycle

Tidal Cycles

• High water: a water level maximum ("high tide") • Low water: a water level minimum ("low tide") • Tidal range: the difference between high and low

tide• Spring Tide: full moon and new moon (14.77 days)• Neap Tide: 1st quarter and 3rd quarter (14.77 days)

Description of tides

Intertidal zoneHigh tide

Low tide

The monthly tidal cycle(29½ days)

• About every 7 days, Earth alternates between:– Spring tide

• Alignment of Earth-Moon-Sun system • Lunar and solar bulges constructively interfere• Large tidal range

– Neap tide• Earth-Moon-Sun system at right angles • Lunar and solar bulges destructively interfere• Small tidal range

Earth-Moon-Sun positions and the monthly tidal cycle

Spring TideHighest high tide and lowest low tide

Neap TideModerate tidal range

6 ft

Tidal Range

56 ft

The Bay of Fundy: Site of the world’s largest tidal range

• Tidal energy is focused by shape and shallowness of bay

• Maximum spring tidal range in Minas Basin = 17 meters (56 feet)

Alma at High Tide

Alma at Low Tide

http://life.bio.sunysb.edu/marinebio/mbweb.html

Tidal Information

HAWAIIAN ISLANDSMean Spring Mean Tide        Station Latitude Longitude Range Range Level Predictions SAND ISLAND, MIDWAY ISLANDS 28° 12.7' 177° 21.6' 0.8 1.2 0.6 Predictions

Laysan Island 25° 46' 171° 45' 0.7 1.0 0.4 Predictions East Island, French Frigate Shoals 23° 47' 166° 13' 0.9 1.4 0.6 Predictions Nonopapa, Niihau Island 21° 52' 160° 14' 1.0 1.6 0.7 Predictions

Kauai Island Waimea Bay 21° 57' 159° 40' 1.0 1.6 0.7 Predictions Port Allen, Hanapepe Bay 21° 54' 159° 35' 1.1 1.7 0.7 Predictions NAWILIWILI 21° 57.4' 159° 21.6' Predictions Hanamaulu Bay 22° 00' 159° 20' 0.0 1.2 1.8 Predictions Hanalei Bay 22° 13' 159° 30' 1.3 1.8 0.8 Predictions

Oahu Island Haleiwa, Waialua Bay 21° 36' 158° 07' - - 1.6 0.7 Predictions Waianae 21° 27' 158° 12' 1.2 1.8 0.8 Predictions

HONOLULU 21° 18' 157° 52' 1.3 2.0 0.8 Predictions Hanauma Bay 21° 17' 157° 42' 1.3 1.9 0.8 Predictions Waimanalo 21° 20' 157° 42' 1.1 1.8 0.8 Predictions MOKUOLOE 21° 26.2' 157° 47.6' 1.2 2.0 1.0 Predictions Waikane, Kaneohe Bay 21° 30' 157° 51' 1.4 2.2 1.1 Predictions

100m

dysphotic

aphotic

photic

Inquiry1. What zone does photosynthesis occur?2. Why does light appear to bend when it enters

water?3. Which wavelength of light penetrates the

ocean the deepest?4. What is SOFAR?5. It’s high tide at 9am with a diurnal tidal cycle.

When is the next high tide?6. What causes the OMZ?7. How do sharks maintain buoyancy?8. What areas in the ocean are the most

productive?9. Why is the open ocean considered a biological

desert?