Transcript Slide 1

Mass movements of water in the ocean
Formation of Surface Currents
• Currents = The forces that move water to
produce ocean currents are caused by:
▫ Rotation of the earth
▫ Winds
▫ Water density Differences
Effect of a Rotating Earth
• Turns from west to
east.
• Velocity of rotation at
its surface is greatest
at the equator and
least at the poles.
• This is called the
Coriolis effect.
• Click here
• In the Northern Hemisphere, ocean currents
are deflected to the right, in a clockwise motion.
In the Southern Hemisphere, ocean currents
are pushed to the left, in a counterclockwise
motion.
Click here –VIDEO
Caution, this video
might make you dizzy.
CLICK HERE
Gyres – circular flow of water
• Flow clockwise in the
northern hemisphere
Gyres = A natural phenomenon
• Flow counterclockwise of a rotating current system.
in the southern
hemisphere
• There are 5 Major Gyres
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North Atlantic
South Atlantic
South Pacific
North Pacific
Indian
What is stuck in the Gyres?
• Click here- Video
• Click here- Video
• If you were to take a
trip out to a Gyre,
what do you think
(specifically) you
would you find?
• Take 3 min and
discuss this with your
neighbor.
Coriolis Effect Recap
• Simply is the Earth rotation causes a phenomena
on free moving objects.
Video
Recap Gyres – circular flow of water
There are 5 Major Gyres
North Atlantic
South Atlantic
South Pacific
North Pacific
Indian
Ekman Transport
• Coriolis effect – spinning
of the earth
• Water flows to the
right of the direction
of the wind
• Water in each water
column flows a little
more to the right as you
go down
• A down flowing spiral
occurs
Western and
Eastern
Boundary Currents
• 5 major ocean gyres flow in relation to the spin
of the earth – geostrophic currents.
• Currents on the western boundary of the ocean
flow from the equator to the poles
• Currents on the eastern boundary of the ocean
flow from the poles to the equator
• Western boundary currents are narrower, faster
and deeper than other currents.
Western Boundary Currents
• Western boundary currents are:
▫ faster than their eastern counterparts
▫ fastest surface currents in the ocean
• The Coriolis effect is stronger in the latitudes of
the westerlies than the trade winds.
Western Boundary Currents Cont.
• Water moving toward the western boundary of
the ocean basins causes the ocean-surface slope
to be steeper on the western side (versus eastern
side) of a gyre (in either hemisphere).
• A steeper ocean-surface slope translates into a
faster geostrophic flow on that side of the gyre.
Eastern Boundary Currents
• Are relatively shallow, broad and slow-flowing.
• Found on the eastern side of oceanic basins.
• Subtropical eastern boundary currents flow
equatorward, transporting cold water from
higher latitudes to lower latitudes;
• examples include the:
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Benguela Current
Canary Current
Humboldt Current
California Current
Stop Here
• Each person will be completing the Surface
Current Map.
• With one partner you will match the correct
number for the corresponding location of the
current on your map, as well as record whether
the current in warm by placing a (W) or Warm
and a (C) for Cold.
Countercurrents and Undercurrents
• Countercurrent - water at the equator where lack
of wind allows them to flow in the opposite
direction of the current next to it.
• Undercurrent – water flows beneath and
opposite of the current over it.
• Both return excess water to their source
Upwellings and Downwellings
• Upwellings
▫ Form when winds parallel to shore force water
away from shore; west coast of continents.
▫ Water from the bottom (max depth of a few 100
meters deep) is brought up to replace the moved
water
▫ Water brings with it nutrients from the ocean
bottom
• Downwellings
▫ Form when winds parallel to shore force water
into shore; east coast of continents
▫ Extra water is forced down towards the bottom
Heat transport and Climate
• Currents redistribute heat throughout the globe
• Without these, Earth would have more extreme
weather.
• Cold water from the poles keeps the Galapogos
Islands cool even though they are in the tropics
• Warm water from Gulf Stream, warms the air
above and keeps much of Europe warmer than
other places at similar latitudes.
** This phenomena is called Thermohaline
Circulation.
Gravitational Currents
• Two forces that explain vertical movement in the
ocean:
▫ Gravitational Force (G)
▫ Buoyant Force (B)
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G > B – downward movement = sinking
B >G – upward movement = rising
G = B – no movement = floating at surface
G = B – no movement = floating neutrally
buoyant
Thermohaline Circulation and how it
works:
Deep Ocean Currents
• Thermohaline circulation, also known as the
ocean's “conveyor belt”, refers to the deep
ocean density-driven ocean basin currents.
• Video
• These currents, which flow under the surface of
the ocean and are thus hidden from immediate
detection, are called submarine rivers.
• Thermo = tempretaure
• Haline = salinity
Density Current
• Cold water molecules are packed more tightly
together then warm water molecules making
cold water more dense.
• Density currents form at the North and South
poles:
▫ Cold air at the poles makes the surface water
temperature cooler making the dense water
molecules sink.
Density Current cont.
• When ice forms in saltwater it leaves behind salt,
increasing the salinity making the water salter.
• Evaporation also increase salinity.
▫ For example: In the Mediterranean sea, where
there is little rainfall and lots of heat, the water
becomes more dense and sinks to the bottom.
• Deep water only forms in 2 places:
▫ NADW = North Atlantic Deep Water (off
Greenland)
▫ AABW = Antarctic Bottom Water
What causes Thermohaline
Circulation?
• Denser water sinks
causing a downward
flow.
• Other water must then
rise to replace it causing
an upward flow.
• Water density differences
drive the slow circulation
of deep water.
Deep Water Flow Patterns
• Dense water descends quickly into deep areas
• As deep or bottom water is mixed upward, it
warms
• Rises to surface and is carried by surface
currents to poles where it cools and sinks
repeating the process
• Takes about 1,000 years for a water mass to
complete the cycle
Thermohaline Circulation
• Water movement caused by differences in
temperature and salinity.
• Processes that decrease salinity:
▫ Precipitation
▫ Freshwater run-off
• Processes that increase salinity:
▫ Evaporation
▫ Freezing
The interconnected flow of currents that
redistribute heat is called the “Ocean
Conveyor Belt” or the Earth’s “Air Conditioner”
Deep ocean currents are driven by
density and temperature
gradients.
• These deep currents are currently being
researched by a fleet of underwater robots called
Argo.
ARGO
• A system for observing temperature, salinity,
and currents in the Earth's oceans for climate
and oceanographic research.
• Consists of a fleet of approximately 3700 drifting
profiling floats deployed worldwide
• How it works:
▫ Probes drift at a depth of 1000 metres and every
10 days they change their buoyancy and dive to
2000 metres. Then they move to the sea-surface,
measuring conductivity and temperature profiles
as well as pressure.
ARGO at work
Deep Ocean Currents
Remember:
• Deep ocean currents are driven by density and
temperature gradients.