Wind-driven surface currents
Ocean Circulation
Animation
Figure 7-4
Ocean Currents
 Ocean currents- are stream-like movements of water
 Ocean currents affect our weather and climate
 2 Types:
 1) Surface Currents
 2) Deep (or Density) Currents
Surface Currents
 Are at or near the surface of the ocean
 Some can travel across entire oceans (Ex: Gulf
Stream—NEMO)
 Created and controlled by 4 things:
 1) Global Winds
 2) Coriolis Effect
 3) Continents deflecting ocean water
 4) Temperature of the water where they form
 These four factors create a pattern of surface currents
on the Earth
Surface Currents-Global Winds
 Winds blowing across the Earth’s surface create
surface currents in the ocean
 Different global winds can cause currents to flow in
different directions-Earth rotation
Coriolis Effect
 The Earth’s rotation causes surface currents to move in
curved paths rather than straight lines.
 This is called the Coriolis Effect
 Ocean currents turn clockwise (to the right) in the
Northern Hemisphere
 Ocean currents turn counterclockwise (to the left) in
the Southern Hemisphere
https://www.youtube.com/watch?v=BPNLZ
yBNPTE&NR=1
Coriolis Effect
 Since the Earth is rotating;
anything that moves over
its surface tends to turn a
little to one side rather
than moving in a straight
line
 Deflects large scale motion
in the Northern
Hemisphere to the right
 Deflects motion to the left
in Southern Hemisphere
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.
Rip Currents
 A rip current is a narrow,
powerful surface current which
flows away from the shore.
 It is caused by pressure building
up from uneven buildup of
water from waves.
 They can flow very quickly and
can be difficult to detect until
you are in one.
Rip Currents are Dangerous!
 Rip currents are responsible
for about 150 deaths every
year in the United States.
 About 80 percent of all
beach rescues are related to
rip currents.
 Rip currents don’t pull swimmers under, they flow out for
several miles.
 If you get caught in a rip current, swim parallel to the
shore until you are out of the current.
Coriolis Effect
 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.
Surface Currents
 Major wind fields of atmosphere that push sea surface
creating currents
 All major currents of the open ocean are driven by
wind
 Equatorial currents are driven by the trade winds and
move parallel to the equator
 Gyres- large circular system of surface currents
influenced by global wind patterns and the Coriolis
Effect
Wind Patterns
 Affected by density of air molecules (hot air rises, cold
air sinks)
 Driven by heat energy from the sun (convection
currents)
 Air is warmer at the equator and colder at the poles
Trade Winds
 Approach the equator at
about a45o angle
 Lie 30oN and 30oS of the
equator
 Steadiest of all winds
Surface Current Picture
Gulf Stream
 https://www.youtube.com/watch?v=UuGrBhK2c7U
Westerlies
 Move opposite the trade
winds
 From 30o-60o N or S
Polar Easterlies
 At high latitudes above
60oN or below 60oS
 Most variable winds
Upwelling
 Upwelling is the vertical movement of water toward
the ocean’s surface.
 Upwelling occurs when wind blows across the ocean’s
surface and pushes water away from an area. Deeper
colder water then rises to replace it.
 Upwelling often occurs along
coastlines.
 Upwelling brings cold, nutrientrich water from deep in the ocean
to the ocean’s surface.
Density Currents
 Density Currents are a type of vertical current that
carries water from the surface to deeper parts of the
ocean.
 Density Currents are
caused by changes in
density rather than
wind.
 Density currents
circulate thermal
energy, nutrients and
gases.
Impacts of Weather and Climate
 Warm-water currents
and cold-water currents
affect weather and
climate in different
ways
 Regions near warmwater currents are often
warmer and wetter than
regions near cold-water
currents
Impacts on Weather and Climate
 The Gulf Stream is a warm-water current that affects
coastal areas of the southwestern United States by
transferring lots of thermal energy and moisture to the
surrounding air.
 The cold California
Current affects
coastal areas of the
southwestern United
States.
Great Ocean Conveyor Belt
 The Great Ocean conveyor Belt is the name for a
model of the large system of ocean currents that
affects weather and climate by circulating thermal
energy around Earth.
 In this model, high salinity water cools and sinks in the
North Atlantic, and deep water returns to the surface
in the Indian and Pacific Oceans through upwelling
https://www.brainpop.com/science/earthsys
tem/oceancurrents/preview.weml
Great Ocean Conveyor Belt
 Scientists estimate that the Great Ocean Conveyor Belt
model takes about 1,000 years to complete a cycle.
Conveyer-belt circulation: Deep Currents
Figure 7-27