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Currents
Oceans 11
Essential Questions
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What are ocean currents?
What is the purpose / role of
ocean currents?
What is the Coriolis Effect?
What are thermohaline
currents?
What are the major global
gyres?
What are the major currents
affecting Atlantic Canada?
What are ocean currents?
What is a current?
• A continuous, directed
movement of ocean water
generated by the forces acting
upon this mean flow, such as:
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breaking waves,
wind,
Coriolis force,
Temperature,
salinity differences, and
tides caused by the gravitational
pull of the Moon and the Sun.
What is a gyre?
• Gyres are any large system
of rotating ocean currents,
particularly those involved
with large wind movements.
• Gyres are caused by the
Coriolis Effect; planetary
vorticity (tendency for
elements of fluid to spin)
along with horizontal and
vertical friction.
What is the purpose / role of
ocean currents?
Purpose…
• to carry heat from place to
place in the Earth system
• affects regional climates
• they transport creatures
around the world and affect
the water temperature in
ecosystems
Anomalies of Surface Currents
• Ocean Eddies
– form when a bend in a surface ocean current
lengthens and eventually makes a loop, which
separates from the main current.
– the swirling waters last for at least a few months
– Warm water eddies are sparse in marine life because
the water does not have many nutrients
– Cold water eddies are usually full of nutrients and
marine life.
• Upwelling
– where water from the deep sea travels up to the
surface
– often happens where wind blows along a coastline
– upwelling areas are full of marine life
What is the
Coriolis Effect?
Who discovered the
Coriolis Effect?
• Gustave-Gaspard Coriolis
– in 1835
– he was a French engineermathematician
Coriolis Effect explained…
• The rotation of the Earth causes an
interesting phenomena on free moving
objects on the Earth.
• Objects in the Northern Hemisphere are
deflected to the right, while objects in the
Southern Hemisphere are deflected to the
left.
• The Coriolis effect, thus tries to force
winds to shift towards the right or left. The
Coriolis effect can at times cause winds to
blow back up the pressure gradient.
Why does this happen?
• There are two reasons for
this phenomenon:
– the Earth rotates eastward
– the tangential velocity
(speed along a curve) of a
point on the Earth is a
function of latitude (the
velocity is essentially zero
at the poles and it attains a
maximum value at the
Equator)
What does the
Coriolis Effect affect?
• it affects the rotation of
the oceanic currents
• it affects prevailing winds
and the rotation of storms
What are thermohaline
currents?
How does it work?
• Thermohaline currents are driven
by density differences in the water
– density depends on its temperature
(thermo) and salinity (haline)
• At the earth's poles, when water
freezes, the salt doesn't
necessarily freeze with it, so a
large volume of dense cold, salt
water is left behind.
• When this dense water sinks to
the ocean floor, more water moves
in to replace it, creating a current.
• This current begins with the cold water near
the North Pole and heads south between
South America and Africa toward Antarctica,
partly directed by the landmasses it
encounters.
• In Antarctica, it gets recharged with more
cold water and then splits in two directions -one section heads to the Indian Ocean and
the other to the Pacific Ocean.
• As the two sections near the equator, they
warm up and rise to the surface as an
upwelling.
• When they can't go any farther, the two
sections loop back to the South Atlantic
Ocean and finally back to the North Atlantic
Ocean, where the cycle starts again.
Interesting details
• An underwater current
circles the globe with a force
16 times as strong as all the
world's rivers combined
• Moves much more slowly
than surface currents -- a few
centimeters per second,
compared to tens or
hundreds of centimeters per
second.
Purpose…
• It is crucial to the base of the world's
food chain:
– transports water around the globe
– enriches carbon dioxide-poor, nutrientdepleted surface waters by carrying them
through the ocean's deeper layers where
those elements are abundant
– nutrients and carbon dioxide from the
bottom layers are brought up to the
surface
– allows algae and seaweed to grow
• also helps to regulate temperatures.
The Endless Voyage Series
- Deep Connections -
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http://learning.aliant.net/Player/ALC_Player.asp?ProgID=INT_
ENDVOY08
What are the
major global gyres?
Major gyres
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North Atlantic Gyre
South Atlantic Gyre
Indian Ocean Gyre
North Pacific Gyre
South Pacific Gyre
North Atlantic Gyre
• located in the Atlantic
Ocean
• contains the Sargasso Sea
• circulates clockwise
• traps man-made ocean
debris in the North Atlantic
Garbage Patch
South Atlantic Gyre
• the southern branch of the
subtropical gyre in the
south Atlantic
• circulates counterclockwise
• this current allows
Antarctica to maintain its
huge ice sheet by keeping
warm ocean waters away
• is the largest ocean current
Indian Ocean Gyre
• is located in the Indian
Ocean
• circulates counterclockwise
North Pacific Gyre
• located in the northern Pacific
Ocean
• comprises most of the northern
Pacific Ocean
• circulates clockwise
• is the largest ecosystem on our
planet
• an accumulation of man-made
marine debris, known as the
Great Pacific Garbage Patch
South Pacific Gyre
• located south of the equator
between South America
and Australia
• circulates counterclockwise
• is the Earth's biggest
system of ocean currents
• it is mostly inactive and
contains little marine life
What are the major currents
affecting Atlantic Canada?
The currents of the North Atlantic
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The Gulf Stream
The North Atlantic Current
The Irminger Current
The Labrador Current
The Greenland Current
The Gulf Stream
• is a powerful, warm, and swift
Atlantic ocean current
• it originates at the tip of Florida, and
follows the eastern coastlines of the
United States and Newfoundland
before crossing the Atlantic Ocean
• The Gulf Stream influences the
climate of the east coast of North
America from Florida to
Newfoundland, and the west coast of
Europe
• is also a significant potential source
of renewable power generation
The North Atlantic Current
• is a powerful warm ocean
current
• it continues the Gulf Stream
northeast.
• West of Ireland it splits in two.
– one branch (the Canary Current)
goes south
– the other continues north along
the coast of northwestern Europe
where it has a considerable
warming influence on the climate.
The Irminger Current
• is a north Atlantic ocean
current setting westward off
the southwest coast of
Iceland
The Labrador Current
• is a cold current in the North Atlantic
Ocean
• it flows from the Arctic Ocean south
along the coast of Labrador and
passes around Newfoundland,
continuing south along the east coast
of Nova Scotia
• It meets the warm Gulf Stream at the
Grand Banks southeast of
Newfoundland and again north of the
Outer Banks of North Carolina. The
combination of these two currents
produces heavy fogs and also
created one of the richest fishing
grounds in the world.
The Greenland Current
• is a weak cold water current
that flows to the north along
the west coast of
Greenland