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Unit 7 Chapter 25 Movement of the Oceans
Section 1 Ocean Currents
A current is a continuous flow of water along a broad path in the
ocean. It can be at the surface or it can be below the surface.
There are two main categories for ocean currents:
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Factors That Affect Surface Currents
Surface Currents flow in the upper 1000 meters of the ocean. They are
driven by the wind. It is a transfer of energy from the air to the water
and then back again.
Global Wind Belts
___________They are steady winds that always blow from North East
in Northern Hemisphere and South East in the Southern
Hemisphere.
In both hemispheres they push currents
westward across tropical latitudes of all three major oceans. It
is the historical path that the early trade ships sailed; they used
the prevailing winds to help push them along quicker in order to
shorten long trips.
___________ They push ocean currents eastward toward higher
latitudes. They are warm water currents that flow on West side
of the oceans.
Continental Barriers
Continental barriers deflect and divide the currents.
The Coriolis Effect
The Coriolis Effect forms gyres (huge circles of moving water)
Northern Hemisphere the currents flow Clockwise.
Southern Hemisphere the currents flow counter- clockwise.
This difference is due to the spinning (rotation) of the earth on its axis.
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Major Surface Currents
Equatorial Currents
Warm water currents re produced here.
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Currents in the Southern Hemisphere
The Antarctic Circumpolar Current (West Wind Drift)
Currents in the North Atlantic
Gulf Stream
The Gulf Stream is the swift moving, deep, warm Atlantic current that
flows along the Eastern Seaboard. It starts in the Caribbean Sea and
then becomes the North Atlantic Drift traveling all the way to Iceland
and England. This keeps some areas warmer than other locations at
the same latitude. (Palm trees in Ireland)
In the North Atlantic if also forms a gyre that is in the middle of the
ocean, called the Sargasso Sea. It is a warm calm center of the
ocean.
Currents in the North Pacific
Kuroshio Current in North Pacific is similar to our Gulf current.
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Deep Currents
Deep currents are usually cold water currents. Cold Currents flow
toward the equator on the Eastern side of the ocean basins.
The three dense currents are Antarctic Bottom Water, North Atlantic
Deep Water, and the Antarctic Intermediate Water.
________________ flow under the surface due to density differences.
They can stay submerged for 500 – 2000 years and connects with
global surface currents to form circular paths. They are slow moving
and the only source of oxygen for deep-sea life because they retain
what they absorb (salinity, oxygen, temperature and density).
Evaporation can cause them.
Antarctic Bottom Water
The densest water is found in polar-regions due to intense cooling and
freezing. When sea water freezes the salt is left behind, increasing
salinity.
North Atlantic Deep Water
Canary Current
In the North Atlantic
Bengula Current
In the South Atlantic
Labrador Current
Found off the coast of Newfoundland. It can carry icebergs
(remember the Titanic). When it reaches the Gulf Stream (warm)
the mixture produces the thickest fog in the world.
Turbidity Currents
We learned in last chapter, caused by underwater sediment slides.
Counter-Currents
They are currents that flow in the opposite direction of the wind related
currents. They can flow at or beneath the surface. They occur
because steady winds pile water up on either side of an ocean
basin
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Section 2 Ocean Waves
A wave is the periodic disturbance in a solid, liquid or gas as energy is
transmitted through a medium.
Wave Height ______________________________________________
Crest ____________________________________________________
Trough ___________________________________________________
Wavelength i_______________________________________________
Period – is the time it takes a wave to pass a point
Speed = Wavelength
Period
ex.
150 kilometers
12 minutes
= 12.5 km/minute
Wave Energy
Waves form from friction between the wind and the water. The
longer the winds blow, the larger the wave becomes.
Water Movement in a Wave
As a wave moves across the surface of the ocean, only the energy of
the wave, not the water, moves in the direction of the wave. The
water molecules within the wave move in a circular motion. During a
single wave period, each water particle moves in one complete circle.
At the end of the wave period, a circling water particle ends up
almost exactly where it started.
Because waves receive their energy from wind pushing against the
surface of the ocean, the energy received decreases as the depth of
the water increases.
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Wave Size
There are three factors that determine the size of a wave: wind
speed, length of time the wind blows and the fetch.
Fetch is the distance that the wind blows across an area of water.
The larger the fetch, the larger the waves become.
White Caps
A white cap occurs when the wind blows the crest of a wave off.
Wave Swell is when a steady smooth wave comes at regular intervals
up to 10 seconds apart. They are caused by winds and storms far
away.
Waves and the Coastline
In shallow water, the wave bottom will touch the ocean floor and will
cause it to slow down and eventually break.
Breakers
Breakers begin to form as a wave approaches the shore line. The
curl as they slow down and crash on the beach.
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Other actions that a wave takes are Swash and Backwash.
Swash is the motion of water going up the beach. Backwash is the
motion of water going back down the beach.
Refraction
Refraction is the process by which the ocean waves bend directly
toward the coastline as they approach the shallow water.
Undertows and Rip Currents
Undertows are seldom strong and will occur in areas along the
shorelines that have a steep drop-off.
Rip Currents flow perpendicular to the shore and are strong.
Long Shore Currents
A long shore current is a current that flows parallel to the shoreline.
These currents are very strong and can carry large amount of sand,
often forming sandbars.
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Tsunamis
A tsunami is a wave formed from an underwater earthquake.
Tsunamis may travel at speeds of up to 890 km/h (as fast as a jet
airplane).
A Tsunami as a Destructive Force
Near the shore, the height of a tsunami greatly increases as the
tsunami's speed decreases. As a tsunami approaches the shore, it
may reach a height of 30 to 40 m. The arrival of a tsunami may be
signaled by the sudden pulling back of the water along the shore.
This pulling back occurs when the trough of the tsunami arrives
before the crest. If the crest arrives first, a sudden, rapid rise in the
water level occurs.
Section 3 Tides
A tide is the periodic rise and fall of the water level in the oceans.
High Tide – __________________________________________
Low Tide – ___________________________________________
Causes of Tides
In the 1600’s Sir Isaac Newton discovered that gravity pulled on the
water along the coastlines. The gravitational pull of the moon on the
Earth’s water caused the tides.
Behavior of Tides
Earth’s rotational period is 24 hours and the moon’s orbit around the
earth is approximately 29 days. Because the Earth and the moon
orbit in the same direction that the Earth rotates, all areas of the
ocean pass under the moon every _______________________. This
makes the tides change every ________________________. Each
high tide gradually turns into a low tide, and each low tide turns into a
high tide. The time of the high and low tides change each day.
Spring Tides
Spring tides are when the sun is at a 0o or 180o to the moon (New
and Full). The pull is stronger which makes high tides higher and low
tides lower.
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Neap Tides
Neap tides are when the sun and the moon pull against each other at
90o during the quarter moon phases the high tide is not very high and
the low tide is not very low. This occurs at the quarter and ¾ phases.
Tidal Variations
Atlantic Coast has two high tides and two low tides each day
Gulf of Mexico has one high and one low tide each day
Pacific Coast has a mixed pattern. They have Very High tides
followed by very low tides and lower high tides followed by higher
low tides.
Tidal Oscillations
Tidal oscillations are the slow rocking motion of the ocean water that
occurs as the tidal bulges move around the ocean basin.
Tidal Currents
Tidal currents are the movement of water toward and away from the
coast as a result of the rise and fall of the tides.
Ebb Tide when the water moves toward the oceans
Flood Tide is when the water moves toward the coast
Slack Tide is when there are no currents