Transcript Ocean Currents - Hrsbstaff.ednet.ns.ca

Ocean Currents
• The water in the ocean is constantly
moving
• Broad bands of ocean water that flow in
one direction and connect one place to
another are known as currents
• There are two main types of currents:
• a) horizontal and
• b) vertical
A) Horizontal Currents
• Also known as surface currents
• Flow in the top 100 to 200m of water
• Primarily driven by winds
• Three factors influence the direction of
winds and surface currents:
– 1.Uneven heating of the atmosphere
– 2.Rotation of the earth
– 3.continents
1. Uneven Heating of the
Atmosphere
• All winds begin as a result of uneven
heating of the atmosphere
• Warm air expands and rises, producing an
area of low pressure
• Cooler air will move into the area (higher
pressure)
• These moving masses of air create winds
http://www.trewern.bardaglea.org.uk/trewernnew/weather/Understand-a-pressure-map.htm
2. Rotation of the Earth
• This produces a bending of moving
currents called the Coriolis effect
• Wind and water current flow over the
Earth’s surface, and the planet is turning
beneath them from west to east
• This motion causes current in the
Northern hemisphere to turn to their right
relative to the Earth’s surface
• Currents in the southern hemisphere turn to
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their left
The overall result is that winds along the
equator blow from the east
these are called trade winds
Trade winds push ocean currents near the
equator to the west (so from east to west)
Near the polar regions, westerly winds drive
currents from west to east
http://www.simplyasolution.com/docs/wind_diagram.jpg
http://www.frontiernet.net/~docbob/weather.htm#wind
3. Continents
• Moving ocean currents are forced to turn
when they meet a continent
• Continents deflect east-west currents to
either the north or south
• The combined influence of winds, the
Coriolis effect, and the continents keeps
ocean currents circulating clockwise in the
northern hemisphere and
counterclockwise in the southern
hemisphere
Gyres
http://web.deu.edu.tr/atiksu/toprak/den07.gif
B) Vertical Currents
• Flow beneath the surface waters and result in
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either the downward or upward movement of
water
Density currents are downward moving currents
and are caused by differences in density and
salinity
Cold water is denser than warm water, and
tends to sink
In the oceans, sinking masses of cold water flow
downward and move along the sea floor
• Saltier water is denser than less salty
water, and will tend to sink
• The sinking masses of saltier water flow
downward and move along the sea floor
• Both evaporation and freezing of water
will cause increases in salinity, and lead to
the formation of density currents
http://www.anl.gov/Media_Center/Frontiers/2003/images/d8ee2.jpg
Upwelling
• Occurs when the current flows from the sea
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floor up to the ocean surface
Most common along coastlines where strong
winds blow offshore
Winds will blow the surface water away from the
land
Cold, deep water then rises from below to
replace the surface water that has been moved
out to sea
• Upwellings have an important effect on the
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ecology of the sea and on human fisheries
Upwelling water contains a large amount of
nutrients from the sea floor
Plants living near the surface will use these
nutrients to grow
Plants then attract fish to areas of upwelling
• Major fishing industries are based on
upwellings along the coast
• Fishing industries along the west coast of
the US and Peru are based on the
upwelling that occurs there
http://www.galapagosonline.com/Galapagos_Natural_History/Oceanography
/Oceanography.html
http://hypnea.botany.uwc.ac.za/marbot/im
ages/upwell.gif