Ocean currents
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Ocean Currents . Earth Science . Ocean Currents . Currents- water in a stream Surface currents- currents that move on or near the surface & are caused by wind Deep current- move very slowly beneath the surface of the ocean & are caused by density differences in water .

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Ocean Currents

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Ocean currents

Ocean Currents

Earth Science

Ocean currents1

Ocean Currents

  • Currents- water in a stream

    • Surface currents- currents that move on or near the surface & are caused by wind

    • Deep current- move very slowly beneath the surface of the ocean & are caused by density differences in water

Ocean currents surface currents

Ocean Currents: Surface Currents

  • Driving energy source for surface currents is wind

  • Surface currents extend down to a depth of 100m

  • 3 controlling factors in surface currents

    • Wind belts

    • Earth’s rotational effects

    • Location of the continents

Ocean currents surface currents1

Ocean Currents: Surface Currents

  • Wind belts

    • Most directly affect the surface currents

    • Trade winds & westerlies

      • Trade winds at latitudes north & south of the equator

      • Westerlies are located in the middle latitudes

      • North of the equator the trade winds blow from the northeast (Northern Hemisphere) & are usually warm

      • Southern Hemisphere trade winds blow from the south east

        • In both hemispheres they push water to the west

Ocean currents

  • Wind Belts

    • Northern Hemisphere westerlies blow from the southwest…moves currents eastward across the Atlantic & Pacific Oceans

    • Southern Hemisphere westerlies blow from the northwest…moves currents eastward

      • Produce the largest current on earth…West Wind Drift

        • Travels the entire circumference of the earth and is located in the southern part of all 3 major oceans

Ocean currents surface currents2

Ocean Currents: Surface Currents

  • Coriolis Effect

    • Deflection of the earth’s winds and ocean currents based on the rotation of earth

    • Coriolis effect along with the earth’s winds cause gyres

      • Gyres- huge circle of moving water

      • Northern hemisphere- gyre moves clockwise

      • Southern hemisphere- gyre moves counterclockwise

Ocean currents surface currents3

Ocean Currents: Surface Currents

  • Continents

    • The surface current flows against a landmass and is divided and deflected

  • Equatorial Current

    • Warm currents

    • 2 of them both move in a westward direction

Ocean currents surface currents4

Ocean Currents: Surface Currents

  • North Pacific & Atlantic Currents

    • North Atlantic

      • North Atlantic Equatorial Current

        • Warm current that moves water north along the east coast of North America called the Gulf Stream

        • Gulf Stream widens & slows and becomes the North Atlantic Drift

          • Drift- weak current

        • All of those currents form the North Atlantic Gyre

Ocean current surface currents

Ocean Current: Surface Currents

  • North Pacific

    • Similar to the North Atlantic

    • Japan Current is equivalent to the Gulf Stream

      • Flows northward & turns into the North Pacific Drift when it spreads out & slows down as it flows towards North America

Ocean currents surface currents5

Ocean Currents: Surface Currents

  • Currents in the Southern Hemisphere

    • Currents here also flow in gyres but in a counterclockwise direction

    • Southern regions of all three major oceans constant westward winds produce the West Wind Drift

      • West Wind Drift is the largest current in the world

      • Because there is no continents to stop it the West wind drift completely circles Antarctica

Ocean currents surface currents6

Ocean Currents: Surface Currents

  • Currents in the Southern Hemisphere cont…

    • Indian Ocean currents follow 2 patterns

      • Southern part the currents follow a counterclockwise gyre

      • Northern part the currents are governed by monsoons

        • Monsoons change directions with the seasons

Ocean currents deep currents

Ocean Currents: Deep Currents

  • Cold, dense currents that flow beneath the surface of the ocean

    • Much slower moving than surface currents

  • Produced as cold, dense water of the polar regions sinks & flows beneath warmer ocean water toward the equator

    • Movements are the result of density differences

    • Higher density of polar waters is also a result of an increase in salinity

  • Deep-current layer rises only when winds blow the surface water out of the way

Ocean currents deep currents1

Ocean Currents: Deep Currents

  • Antarctic Bottom Water

    • The densest & coldest ocean water in the world

    • Dense, cold water sinks to the bottom & very slowly move north forming the Antarctic Bottom Water current

      • Moves to north to about 40 degrees & takes several hundred years to make the trip

Ocean currents deep currents2

Ocean Currents: Deep Currents

  • North Atlantic Deep Water

    • South of Greenland the water is exceptionally cold & has high salinity causing it to sink

      • Forms a current that travels south underneath the Gulf Stream

      • Flows southward all the way to the Antarctic & over the Antarctic Bottom Water

    • Deep Atlantic currents also are found near the Mediterranean Sea

Ocean currents deep currents3

Ocean Currents: Deep Currents

  • Turbidity Currents

    • Occur when large masses of sediment that have accumulated along a continental shelf or continental slope suddenly break loose and slide downward

      • Causes the water to become more dense than the surrounding water

      • Believed to cause submarine canyons to deepen

Ocean waves

Ocean Waves

  • Wave- periodic up and down movement of water

    • Transfer energy

  • 2 basic parts of a wave:

    • Crest- highest point of a wave

    • Trough- lowest point of a wave

  • Wave characteristics

    • Wave height- vertical distance between a crest & a trough of a wave

    • Wavelength- horizontal distance between 2 crests of a wave

    • Wave period- time it takes for one complete wavelength

    • Wave speed= wavelength/period

Ocean waves1

Ocean Waves

  • Wave Energy

    • Main source of energy for waves is wind

      • The more energy that is transferred the larger the wave becomes

    • Because of surface area…

      • Large waves tend to become larger because the wind has more area to push on

      • Smaller waves tend to die out because there is a very small surface area for the wind to push on

    • Swell- group of long, rolling waves that are the same size

Ocean waves2

Ocean Waves

  • Water Movement in A Wave

    • Only the energy of wave moves forward, the water itself moves very little

      • The water particles within the wave move in a circular motion

        • Circle traced by each water particle in a wave has a diameter equal to the height of the wave

    • Energy received by a wave decreases as depth increases because the waves receive their energy from the wind

      • Diameter of the circle traced by each water particle decreases as depth increases

Ocean waves3

Ocean Waves

  • Wave Size

    • 3 factors that affect wave size:

      • Speed of the wind

      • Length of time the wind blows

      • Fetch of a wave

        • Distance that the wind can blow across open water

        • Long fetch produces very large waves

          • Likely to occur during storms

    • Size of a wave will only increase to a certain height to length ratio before it collapses

    • Whitecaps- occur when high wind speeds blow the crest off of a wave

Ocean waves waves the shore

Ocean Waves: Waves & the Shore

  • Breakers

    • Height of a wave changes as the wave approaches the shore

    • As a wave moves into shallow water, the bottom of the wave is slowed by friction but the top of the wave continues to move at its original speed

    • The top of wave gets farther & farther ahead of the bottom & eventually it topples over & forms a breaker.

      • Height of the wave when it topples over is one to two time the height of the original wave

Ocean waves waves the shore1

Ocean Waves: Waves & the Shore

  • Breakers cont…

    • Size & force of breakers are determined:

      • Original wave height

      • Wavelength

      • Steepness of the ocean floor close to shore

        • More steep = rapid increase of wave height = breaker with greater force

          • Pacific Coast

        • Less steep = slower increase of wave height = breaker with less force

          • Atlantic Coast

Ocean waves waves the shore2

Ocean Waves: Waves & the Shore

  • Undertows & Rip Currents

    • Undertow- water carried onto a beach is pulled back into deeper water by an irregular current

      • Create problems only along shores with steep drop-offs

    • Rip current- form when water from large breakers returns to the ocean through channels in underwater sand bars that are parallel to the beach

      • Flow perpendicular to shore

Ocean waves waves the shore3

Ocean Waves: Waves & the Shore

  • Longshore Currents

    • Form sandbars

    • Forms as waves approach the beach at an angle

    • Flow parallel to the shore

Ocean waves wave the shore

Ocean Waves: Wave & the Shore

  • Tsunamis

    • Most destructive waves in the ocean

    • Energy that forms them comes from seismic sea waves not the wind

      • Usually caused by earthquakes on the ocean floor, but also by volcanic eruptions & underwater landslides

    • Have very long wavelength, wave period is about 15 minutes, and speed of 725 km/hr

    • Entire depth of the water is involved in wave motion

    • Height increase greatly as they approach shore



  • Tides- daily changes in the level of the ocean surface

    • The gravitational pull of the moon on the earth and its waters is the major cause of tides

    • Low tides are formed halfway between two high tides

Tides behavior

Tides: Behavior

  • Tidal movement is due to the rotation of the earth and the pull of the moon.

    • Earth rotates from west to east, so tidal bulges appear to move westward around the earth.

      • Because there are two tidal bulges most locations on the ocean have two high tides & two low tides

    • Tidal range- difference in the level of high tide and low tide at specific locations

      • Can vary widely from place to place

Tides behavior1

Tides: Behavior

  • During period of new moon & full moon the high tides are the highest and the low tides the lowest

    • This is because the sun, moon, & earth are all aligned

    • These are called spring tides

  • During 1st quarter & 3rd quarter phases the daily tidal range is the smallest

    • This is because the moon & the sun are at right angles to each other in relation to the earth

    • These tides are called neap tides

Tides variations

Tides: Variations

  • Tidal patterns are greatly influenced by the size, shape, depth, & location.

    • Atlantic Coast: tides are semidiurnal, which means twice a day

      • Have a fairly regular tidal range

    • Gulf of Mexico: diurnal, which means once a daily

    • Pacific Coast: follow a mixed pattern & have an irregular tidal range

      • Very high followed by very low, then a lower high tide followed by a higher low tide

Tides variations1

Tides: Variations

  • Tidal oscillations- caused by the slow rocking motions of ocean water that occur as the tidal bulges move around the ocean basins

    • Produce the world’s greatest tidal range in the Bay of Fundy (tidal ranges is larger than 15m)

Tides tidal currents

Tides: Tidal Currents

  • Tidal current- occurs as the ocean water rises and falls with the tides, it flows toward & away from the coast.

    • Flood tide- when tidal current flows toward the coast

    • Ebb tide- when tidal current flows away from the coast

    • Slack water- time between flood tide and ebb tide with no tidal currents.

  • Tidal bore- surge of water that rushes upstream where a river meets an ocean

Tide videos

Tide Videos

  • http://youtu.be/kJOvxQElfLc

  • http://youtu.be/5W2sM1Ma7YA

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