Motions of the Ocean

Waves, Currents and Tides

I. General Info.

A. The ocean is in constant motion

1. motion is needed for “mixing”

2. replenishing of O2

3. “moving” of food

4. change in our weather

B. The three major motions are

1. Waves

2. Currents

3. Tides

II. Waves

A. Waves – pulses of energy through the water = the water does NOT move*water usually moves in a

circular motionB. Causes:

1. Wind = most waves are created from winds

2. Earthquakes3. Volcanoes

4. Underwater landslides

5. These create tsunamis = large waves of 35m =

75ft

WAVES

C. Size of a wave determined by:

1. The wind’s speed

2. Duration of wind = length of time wind

blows

3. Fetch = distance wind blows without interruption

D. Sizes of wave

1. ripples = 0 - .3m, clam waters

2. moderate = .6 – 1m (1 – 3ft.); mild seas

3. medium = 1 – 2m (3 – 8ft.), rough seas or whitecaps

4. high = 4 – 9m (13-30ft.), high seas

5. towering waves = 35m +, hurricane (typhoon)

E. Parts of a Wave1. Crest – highest point of wave2. Trough – lowest point of a

wave3. Wave length – distance

between two consecutive crests

4. Wave height – distance between a crest & a trough

5. Wave period – time it takes for two consecutive crest to pass a fixed point

Crest

Trough

Wavelength

Wave height

6. Can calculate speed of the wave:

a. wave length/wave period = wave speed or L/T = C

b. wave length of 20m & wave period of 4sec = 5m/sec

c. so, can also calculate length & period

7. This helps to determine navigation, hurricane power, etc

F. Life of a Wave

1. Energy is transferred from the wind to the water (earthquakes, etc)

2. A constant wave is generated, not very high, but very long = swell

*the water doesn’t move forward, the energy does

*creating wave after wave

3. Wave moves closer to shore*waves also move downward,

but loses energy the deeper it goes

4. L (wave length) decreases; H (wave height) increases

5. Wave crashes forwards = breaker

* waves break about 1.3 X H (wave height)

6. Wave surges onto shore = surf

7. Water flows back into ocean = undertow; carrying pebbles & sand with it

*undertows can be very dangerous; very strong retreating water,

lasting several km

G. Types of Breakers1. Plunging breaker – form tubes or

curlsa. high speedb. need steep, sloping bottomc. can be dangerous = pounds

downward, trapping people

2. Spilling breakers – has line of tumbling foam

a. longest ride for surfer

b. needs a gentle sloping bottom

3. Surging breakers – walls of white watera. large wave suddenly hits

bottomb. causes great damage;

tsunami

H. Importance of waves

1. Replenishes O2

2. Brings in food

3. Erodes beaches

4. Depositional activity (deposits sand)

III. CurrentsA. Currents = streams of moving water

B. History

1. 1st studied in detail by Benjamin Franklin in 1777

2. In 1855, Maury made accurate charts of the major currents

3. Today, 100s of currents now known

4. Many currents are constant

C. Causes

1. Wind patterns – set wind patterns create set

currents

2. Rotation of Earth & Coriolis Force

3. Differences in water densities & T0

4. Drag of Earth’s rotation

D. Wind Patterns

1. Creates surface currents – depth of several 100m

a. T0 of current depends on origin

b. Types of surface currents

1) long distance surface currents – travel for 1000’s of km

a) very constant & predictable

b) Ex. Gulf Stream Current – 150km wide, from Gulf

of Mexico to the top of Canada

2)Short distance surface current – travels short distances

a) usually travels close to shore

b) narrow, but can be very strong

3. Longshore currents – runs parallel to the shoreline

a. current of fast moving water

b. creates rip currents – acts as an undertow

1) not usually dangerous

2) short lived

3) 2 longshore currents run into each other

4) look for area with no breaking waves or

5) lighter waters

4. Eddies – circular motion of water on surface

a. can be dangerous

b. drags downward

E. Earth’s Rotation and Coriolis Force

1. Creates surfaces and deep sea currents

2. Also causes surface currents to move faster

3. And deep currents to move slower

2. Coriolis force – forces that deflect water masses

a. In Northern Hemisphere – currents deflected to the right

b. In Southern Hemisphere – currents deflected to left

c. This allows for a predictable motion – giving us “current patterns”

3. These two causes allow for a “well-mixed” ocean.

a. surface currents flow in opposite direction of deep currents

b. causes a change in T0

c. mixes ocean from top to bottom

F. Differences in Water Density

1. Causes deep currents

2. Cold water is more dense = sinks

3. Warm water is less dense = rises

4. High salinity water is more dense = sinks

5. Deep currents flow in opposite directions of surface currents

6. Helps mix ocean from top to bottom

Agulhas Current Indian Warm

Alaska Current North Pacific

Warm

Benguela Current South Atlantic

Warm/Cool

Brazil Current South Atlantic

Warm

California Current North Pacific

Cool

Canaries Current N. Atlantic Cool

Gulf Stream North Altantic

Warm

Humboldt (Peru) Current

South Pacific

Cool

Kuroshio (Japan) Current

North Pacific

Warm

Labrador Current North Atlantic

Cool

East Australian Current

South Pacific

Warm

Equitorial Current Pacific Warm

North Atlantic Drift

North Atlantic

Warm

North Pacific Drift

North Pacific

Warm

Oyashio (Kamchatka) Current

North Pacific

Cool

West Australian Current

Indian Cool

West Wind Drift South Pacific

Cool

G. Upwelling

1. Most important current in the ocean

2. upwelling – a nutrient rich deep current that is forced to the surface

3. brings all kinds of food, nutrients, etc

4. makes for very rich fishing ground

5. Created when a deep current is forced to surface

H. Importance of Currents

1. Alters Earth’s surface T0

2. Circulates ocean

3. Helps shape our shoreline by erosional & depositional activity

4. Creates upwellings = very important to organisms

IV. TidesA. Tides = Periodic rise and fall of the

level of the ocean

B. Causes

1. Alignment of the sun, moon, & earth

2. Gravitational pull of sun & moon

3. Centrifugal force – force that pushes “objects” away from

center of rotation

C. Types of Tides

1. High tide – when sea level has risen

2. Low tide – when sea level is low

3. Ebb tide – outgoing tide, between the high & low tides

4. Flood tide – incoming water, between low & high tide

5. Spring tides – very strong tides; very high & very low tides

a. Last 7 daysb. Occur every 14 days

6. Neap tides – very weak tides; not very high or low

a. Last 7 daysb. Occur every 14 days

7. Mixed tides – not as strong or as weak as others

a. occur between spring & neap tidesb. occur every 14 daysc. last 7 days

D. When Tides Occur

1. Diurnal tides – have one low tide & one high tide in 24 hr.

2. Semidiurnal tides – two high tides & two low tides in 24

hr.

E. What Determines Type of Tides1. Sun, Moon & Earth in a straight

line causes spring tidesa. gravitational pull on Earth

created by Sun & Moon causes a “bulge”b. centrifugal force creates a

“bulge” on the other sidesc. Full Moon & New Moon gives us

the highest tides

F. Sun, Moon & Earth in a 90 causes neap tides

a. gravitational pull is balanced

b. centrifugal force is cancelled out by places of Sun &

Moon

G. Importance of Tides

1. Tides shape the shoreline by erosion

2. Tides create completely new ecosystems

3. Tides are a good source for generating electricity

4. Some areas have extremely forceful tides