Movements of the Ocean

Chapter 22

22.1: Ocean Currents

• Current: Giant streams of water that move through the ocean

• Examples: Gulf Stream, El Niño• Surface currents: move on or near the

surface of the ocean and are driven by winds

• Deep currents: move slowly beneath the surface due to differences in water density

Factors that affect surface currents

1. Winds—movement from high pressure air towards low pressure air

• Trade winds: found in tropics, blow from east to west (called easterlies)– North of the equator they blow from northeast– South of the equator they blow from southeast

• Westerlies: blow from west to east in middle latitudes

Moisture/Pressure Zones

Low Pressure: WetHigh Pressure: Dry

High Pressure: Dry

Low Pressure: Wet

Low Pressure: Wet

High Pressure: Dry

High Pressure: Dry

Factors that affect surface currents

2. Earth’s rotation: as air moves up and down, the earth rotates below it. Therefore, the air comes down west of where it went up.

• Coriolis effect: the deflection of the earth’s winds and currents due to the earth’s rotation

• Gyre: huge circular currents that are driven by wind and coriolis effect– Clockwise in north, counter-clockwise in south

Factors that affect surface currents

• Continents: water is deflected and divided when it hits continents.

Equatorial Currents

• Equatorial currents: north and south of the equator in each ocean are warm currents flowing westward

• Equatorial countercurrent: warm, weak current between the equatorial currents that flows eastward.

North Atlantic Gyre

• Gyres typically consist of four currents• Weaker currents are called “drifts”• Gulf stream (5000X bigger than the

Mississippi) to North Atlantic Drift to Canary Current to North Atlantic equatorial current

• Sargasso Sea: relatively still water in the middle.

North Pacific Gyre

• Japan current to North Pacific current to California Current to North Pacific equatorial current

Southern Hemisphere Currents

• West wind drift: world’s largest current, goes through all three oceans around Antarctica

Deep Currents

• Antarctic bottom water: coldest, saltiest, densest water is near Antarctica, it flows slowly north to about 40° latitude. Takes 100s of years

• North Atlantic deep water: flows south from Greenland, below the Gulf Stream but on top of Antarctic bottom water

22.2: Ocean Waves

• Wave: periodic up and down movement of water

• Crest: highest point of the wave

• Trough: lowest point of the wave

• Wave height: vertical distance between crest and trough

Ocean Waves

• Wave length: horizontal distance between two consecutive troughs or crests

• Wave period: Time in seconds it takes for one complete wavelength to pass a given point.

• Wave speed: wave length divided by wave period

Wave energy

1. Energy from the wind is transferred to the surface of the water by friction

2. Small ripples form3. As ripple receives more energy from

wind, it grows into wave4. Longer the wind blows, more energy is

transferred and the bigger the wave becomes

Wave energy

• Swell: one of a group of long rolling waves that are all the same size

Water movement in waves

1. Energy in waves moves forward, water does not

2. Water molecules move in a circular pattern

3. The diameter of the circle is equal to wave height

4. Very little movement of water at a depth equal to half the wavelength

Factors Affecting Wave Size

1. Speed of the wind

2. Length of time wind blows

3. Fetch: the distance the wind can blow across open ocean

• Biggest waves: strong, steady winds over a long fetch—typical in storms

Wave Size

• Limit to wave size: if the wave gets too high compared to the length (height of about ½ length), the wave collapses

• Whitecaps: when high winds blow crest off the top of the wave

Breakers

1. When the depth of the water is about ½ wavelength, the wave touches bottom

2. This slows the bottom of the wave while the top keeps going

3. The top gets so far ahead that it falls over, forming a breaker

4. Height of wave when it falls is usually 1-2 times original wave height

Breakers

5. Steep slopes lead to bigger breakers, common on Pacific Coast

6. Gentle slopes, waves break with a rolling motion, common on sissy Atlantic Coast

Other waves

• Refraction: most waves approach shore at an angle then bend and approach parallel

• Undertow: water that breaks on beach is pulled back to sea, usually only strong on steep beaches

• Rip current: occur when water from large breakers flows through channels in sandbars—detected by a gap in breakers

22.3: Tides

• Tide: daily changes in the level of the ocean surface, caused by moon’s gravitational pull on the oceans.

NorthPole

High Tide

High Tide

Low Tide

Low Tide

Moon/earth relationship

1. Earth rotates once every 24 hours

2. Moon travels 1/27th of its orbit every day

3. Therefore, the moon is over one part of the earth every 24 hours and 50 minutes.

4. Therefore, tides are 50 minutes later each day.

Tides

• Daily Tidal Range: difference in height between high and low tide.

• Sun: also affects tides, but is not as strongly as moon (it’s bigger but farther away)

Full Moon

New Moon

Spring tides: occur during full/new moon when earth, sun, and moon are all in a line, increases the daily tidal range because gravitational pull of moon and sun are combined.

¼ Moon

¾ Moon

Neap Tides: occur during first and third quarter moons, pull of sun and moon tend to cancel each other out so that the daily tidal range is less.

Tides

• Tidal currents: as ocean rises and falls with tides, it flows towards or away from the coast

• Flood tide: tidal current towards coast

• Ebb tide: tidal current away from coast

• Slack water: time between flood and ebb tides