Download Surface Currents

Lesson 8:
Currents
Physical Oceanography
Last class we learned about ocean layers
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
What are the three main ocean layers?

How does temperature change with depth in the
thermocline?

How does it change below the thermocline?
Today we’re going to explore ocean
currents
1.
An ocean current is a regular movement of large amounts of
water along defined paths.
2.
There are two primary types of ocean currents:
–
Surface Currents (to a depth of about 400 m)

–
Deep Currents (entirely below the effect of wind)

3.
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Driving factor: Wind
Driving factor: Density differences
Thermohaline circulation: Ocean circulation driven by
differences in density caused by temperature (“thermo”) and
salinity (“haline”) variations
Why are currents so important?
Photo: NOAA
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
Influence world climate and
weather

Ocean navigation and
transportation

Support marine life (transport
mechanism, food source)

Transport of materials (both
helpful and harmful) and energy
to different regions and depths
of the ocean
Marine organisms like the Southern
right whale (above) depend upon currents
to circulate the nutrients that support
their food sources
What drives ocean currents?
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
Density gradients (differences) drive deep ocean
currents

Upwelling brings cold, nutrient-rich water from the
depths up to the surface

Wind is one of the primary drivers of surface
currents
Density Currents

Density Currents are a type of vertical current that
carries water from the surface to deeper parts of the
ocean.
 Density currents
circulate thermal
energy, nutrients
and gases.
Upwelling




Upwelling is the vertical movement of water
toward the ocean’s surface.
occurs when wind blows across the ocean’s
surface and pushes water away from an
area. Deeper colder water then rises to
replace it.
often occurs along coastlines.
brings cold, nutrient-rich water from deep in
the ocean to the ocean’s surface.
Major Ocean Currents

Surface currents extend
to about 400 m below
the surface, and they
move as fast as 100
km/day.

Earth’s major wind
belts, called prevailing
winds, influence the
formation of ocean
currents and the
direction they move.
Coriolis Effect
 The Coriolis Effect is the movement
of wind and water to the right or left
that is caused by Earth’s rotation.
 It causes fluids such as air and water
to curve to the right in the Northern
hemisphere, in a clockwise direction.

The Coriolis effect also cases fluids
to curve to the left in the southern
hemisphere, in a counterclockwise
direction.
Other Impacts


The shapes of continents and other land
masses affect the flow and speed of currents.
Currents form small or large loops and move
at different speeds, depending on the land
masses they contact.
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An important ‘current’ event:
Thermohaline Circulation (THC)


THC creates a world wide current system called the
“global conveyor belt"
The global conveyor belt begins with sinking of cold,
dense water near the North Pole in North Atlantic
–



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Cold temps + Sea ice = cold, salty, dense water that sinks
Then water moves south and circulates around
Antarctica, where cold salty conditions “recharge” it
The water then moves northward to the Indian, Pacific
and Atlantic ocean basins
It can take around 1,000 years for water to complete
one cycle of the entire global conveyor belt!
A map of the global conveyor belt
Photo: NASA
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Student activity
In today’s activity, we will play a game to learn the
names and locations of the ocean’s currents
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