WHY IS OCEAN CIRCULATION IMPORTANT?
Transport ~ ____% of
latitudinal heat
 Equator to poles
Transport _________ and
_____________
Influences ________ and
___________
Influences commerce
Non-rotating Earth
Convection
cell model
Add rotation
and add
landmasses
unequal
heating and
cooling of the
Earth
The Coriolis effect
• The Coriolis effect
– Is a result of Earth’s rotation
– Causes moving objects to follow curved paths:
• In Northern Hemisphere, curve to _________
• In Southern Hemisphere, curve to _________
– Changes with latitude:
• No Coriolis effect at Equator
• Maximum Coriolis effect at poles
A) Idealized winds generated by pressure gradient and Coriolis Force.
B) Actual wind patterns owing to land mass distribution..
Understanding what causes currents and where they flow is fundamental to all
marine sciences. It helps explain how heat, sediments, nutrients, and organisms
move within the seas.
Chapter 9 Pages 9-3 & 9-4
Surface Currents
Causes of Currents
Three major factors drive ocean currents.
 1. ____________ - Temporary
 If the wind blows long enough in one direction, it will cause a water current to develop. (and
Waves)
 The current continues to flow until internal friction, or friction with the sea floor, dissipates its energy.
(Storms do not affect the entire ocean)
9-6
Causes of Currents
Chapter 9 Pages 9-3 & 9-4
Surface Currents
Three major factors drive ocean currents.
 2. ________________________________________. (Tides and water build up)
 Sea level is the average level of the sea’s surface at its mean
height between high and low tide.
 The ocean’s surface is never flat, ocean circulation cause slopes to develop. The steeper the
“mound” of water, the larger and faster the current. The force that drives this current is the
pressure gradient force.
9-7
Causes of Currents
Chapter 9 Pages 9-3 & 9-4
Surface Currents
Three major factors drive ocean currents.
 3. _______________________________________________.
 Differences in water density also cause horizontal differences in water pressure. When the
density of seawater in one area is greater than another a current flows below the surface
horizontally.
9-8
GYRES
The combination of westerlies, trade winds, and the Coriolis effect results in a
circular flow in each ocean basin. This flow is called a gyre.
There are five major gyres – one in each major ocean basin:
Chapter 9 Pages 9-5 & 9-6
Surface Currents





1. _______________________
2. _______________________
3. _______________________
4. _______________________
5. _______________________
The flow of currents in all parts of the
ocean is a balance of various factors,
including the pressure gradient force,
friction, and the Coriolis effect.
9-9
EKMAN TRANSPORT
The Ekman transport is an interesting phenomenon
discovered in the 1890s by Fridtjof Nansen.
Chapter 9 Pages 9-6 to 9-8
Surface Currents
The wind and the Coriolis effect influences water
well below the surface because water tends to flow
in what can be imagined as layers.
the Ekman transport is a net motion imparted to the water column down to the
friction depth.
9 - 10
9 - 11
WESTERN AND EASTERN BOUNDARY
CURRENTS
Satellite images show that the oceans are really “hilly,” not calm or flat.
 _______________________
 _______________________
Chapter 9 Pages 9-8 to 9-10
Surface Currents
 There is a dynamic balance between the clockwise deflection of the Coriolis effect
(attempting to move water to the right) and the pressure gradient created by gravity
(attempting to move the water to the left).
 The balance keeps the gyre
flowing around the outside of
the ocean basin.
Geostrophic currents
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9 - 13
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WESTERN AND EASTERN BOUNDARY
CURRENTS
(CONTINUED)
Chapter 9 Pages 9-10 to 9-16
Surface urrents
Western boundary currents are found on
the east coasts of the continents and are
stronger and faster than eastern boundary
currents due to western intensification.
Western boundary currents flow through
smaller areas than eastern boundary currents.
9 - 15
COUNTERCURRENTS
Countercurrents and undercurrents are water flows that differ from the
major ocean currents.
_______________________ are associated with equatorial currents –
it runs opposite of its adjacent current.
Chapter 9 Pages 9-16 & 9-17
Surface Currents
 It is hypothesized they develop in equatorial regions because of the doldrums.
Without wind pushing water westward, water driven in from the east enters the basin
more quickly than it exits. This causes a
countercurrent to develop.
_______________________ flow beneath the
adjacent current and are found
beneath most major currents.
.
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UPWELLING AND DOWNWELLING
Upwelling is an upward vertical current that brings deep water to the
surface. _____________________ is a downward vertical current that
pushes surface water to the bottom.
Chapter 9 Pages 9-17 to 9-20
Surface Currents
_____________________occur when the wind blows offshore or
parallel to shore. In the Northern Hemisphere this wind blowing
southward will cause an upwelling only on a west coast.
 These currents have strong
biological effects:
9 - 17
HEAT TRANSPORT AND CLIMATE
Currents play a critical role by transporting heat from warm areas
to cool areas and affects climate by moderating temperatures.
Without currents moving heat, the world’s climates would be more
extreme.
Chapter 9 Pages 9-20 to 9-22
Surface Currents
El Niño Southern Oscillation (ENSO)
El Niño tremendously affects world
weather patterns.

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EL NIÑO
(CONTINUED)
For reasons still not clear, every 3 to 8 years a rearrangement of the high- and low-pressure systems
occur.
High pressure builds in the Western Pacific and low pressure in the Eastern Pacific. Trade winds weaken
or reverse and blow eastward – the southern oscillation.
Chapter 9 Pages 9-22 to 9-24
Surface Currents
 This causes warm water of the west to migrate east to the coast of South America.
_____________________ _____________________ _____________________ _____________________
_____________________ _____________________ _____________________ _____________________
_____________________ _____________________ _____________________ _____________________
_____________________ _____________________ _____________________
 Over the eastern Pacific, humid air rises causing precipitation in normally arid regions.
_____________________ _____________________ _____________________
_____________________ _____________________ _____________________
_____________________ _____________________
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THERMOHALINE CIRCULATION AND WATER
MASSES
Chapter 9 Pages 9-26 & 9-27
Deep Currents
Thermohaline circulation is water motion caused by differing water
densities and includes surface and deep ocean waters.
 _____________________ _____________________ _____________________
_____________________ _____________________ _____________________
_____________________ _____________________ _____________________
 _____________________ _____________________ _____________________
_____________________ _____________________ _____________________
_____________________ _____________________ _____________________
_____________________ _____________________ _____________________
Thermohaline circulation works because water density increases due to cooling,
increased salinity or both.
 When water becomes dense, it sinks, causing a downward flow.
 This means water in some other place must rise to replace it, causing an upward
flow.
 Density differences drive the slow circulation of deep water.
9 - 20
3 Distinct Ocean Layers
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HOW DEEP WATER FORMS
Chapter 9 Pages 9-28 to 9-30
Deep Currents
The intermediate, deep, and bottom water
masses form primarily, but not entirely, at
high latitudes (around 70° North and South).
 The densest ocean waters, Antarctic
Bottom Waters form in the
Antarctic in winter, sink to the bottom
and spread along the ocean floor to
about 40° north latitude.
 _____________________ _____________________ _____________________
_____________________ _____________________ _____________________
_____________________ _____________________ _____________________
_____________________ _____________________ _____________________
 _____________________ _____________________ _____________________
_____________________ _____________________ _____________________
_____________________ _____________________ _____________________
_____________________ _____________________ _____________________
 Mediterranean Deep Waters form due to evaporation rather than cooling, with a salinity
of 38‰. Flowing out of the Mediterranean they form the intermediate water layer resting
above the bottom layer and deep layer.
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DEEP-WATER FLOW PATTERNS
_____________________ _____________________ _____________________ _____________________
_____________________ _____________________ _____________________ _____________________
_____________________ _____________________ _____________________ _____________________ .
 Dense water descends into low areas and bottom water upwell to compensate.
 The rising warm water enters wind-driven currents and is carried to the poles. There it cools, becomes more dense, and sinks again,
repeating the process.
The Ocean Conveyor Belt
Chapter 9 Pages 9-30 to 9-33
Deep Currents
The interconnected flow of currents that redistribute heat is called the ocean conveyor belt or the Earth’s “air
conditioner.”
 The ocean conveyor belt is important because it moderates the world’s climate. This marriage of
surface and deep water circulation carries heat away from the tropics and, in turn, keeps the tropics from getting too hot.
 _____________________ _____________________ _____________________
_____________________ _____________________ _____________________
_____________________ _____________________ _____________________
_____________________ _____________________ _____________________ .
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TWO DISTINCT APPROACHES
There are two main approaches to study currents:
 1. Lagrangian method, also called the float method.
 _____________________ _____________________ _____________________ _____________________
_____________________ _____________________ _____________________ _____________________
_____________________ _____________________ _____________________ _____________________.
 2. Eulerian method, also called the flow method.
 Studying the current by staying in one place and measuring changes to the velocity of the water as it flows
past. This method uses fixed instruments that meter/sample the current as it passes.
There are five examples of instruments or methods
that scientists apply for studying currents.
Chapter 9 Page 9-34
Studying Ocean Currents
Instrumentation and Methods
For Lagrangian study methods researchers use:
 1. A drogue. The advantage over a simple surface
float is that the “holey sock” ensures that the current and
not the wind determine where it drifts.
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INSTRUMENTATION AND METHODS
(CONTINUED)
 2. The Argo float drifts at depth before periodically rising to the surface to transmit
to a satellite a temperature and salinity profile of the water it rose through.
Chapter 9 Pages 9-35 to 38
Studying Ocean Currents
For Eulerian study methods researchers use:
 3. Various types of flow meters. These devices
use impellors and vanes to measure and record
current speed and direction. The information gathered
is either transmitted immediately or stored for
retrieval later.
 4.
A more sophisticated device is the Doppler Acoustic
Current Meter. This instrument determines current
direction and speed.
 5. Oceanographers can now use satellites to help them.
Although they are primarily used for studying the surface,
these instruments use laser and photography to study currents.
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