Ocean

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Ocean Currents and Circulation
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Currents Ocean Circulation
The westerlies and the trade winds are two of the
winds that drive the oceans surface currents.
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Currents
Ocean water circulates in currents. Surface
currents are caused mainly by wind, and affect
the uppermost 10 of the ocean.
Circulation of the other 90 of the ocean is
driven by gravity, as Density dense water
sinks and less dense water rises. Upwelling and
downwelling describe the vertical movement of
water masses. The Coriolis effect modifies the
course of ocean currents.
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Current Notes

• Currents are rivers of water on or below surface
• Cause of currents
• 1. Winds create surface currents ( Trades
  Westerlies)
• 2. Rotation of Earth ( Coriolis Effect) makes
  Gyres
• 3. Density changes causes movement
• More dense water moves to bottom
• More dense water moves less dense water
• Evaporation changes density
• Freezing changes density

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Ocean Currents
What are some effects of ocean currents? Ocean
currents ? transfer heat from tropical to
polar regions ? influence weather and
climate ? distribute nutrients and scatter
organisms
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Surface Currents
Surface currents are driven by wind Most of
Earths surface wind energy is concentrated in
the easterlies and westerlies. Due to the forces
of gravity, the Coriolis effect, solar energy,
and solar winds, water often moves in a circular
pattern called a gyre.
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GYRE MOVEMENT
A Gyre is formed of three ocean currents. Water
moves clockwise in the Northern Hemisphere gyres
Counterclockwise in the Southern Hemisphere
gyres.
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Flow Within a Gyre
Gyres can be further subdivided into distinct
currents. The four interconnected currents in the
North Atlantic Gyre have different flow
characteristics and temperatures.
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Flow Within a Gyre
The energy of the wind especially the Trade winds
and the Prevailing Westerlies is transferred to
the ocean to create a current at a 45 degree
angle to the wind. This energy continues to 100m
where the angle is 90 degrees. This is termed the
Ekman spiral.
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Geostrophic Gyres
Warm currents indicated by red Cool currents
indicated by blue
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Currents Within Gyres
What currents are found within gyres? Western
boundary currents -These are warm, narrow, deep,
fast currents found at the western boundaries of
ocean basins. ? the Gulf Stream ? the Kuroshio
(Japan) Current ? the Brazil Current ? the
Agulhas Current ? the Eastern Australian Current
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Currents Within Gyres
What currents are found within gyres? Eastern
boundary currents These currents are cold,
shallow and broad, and their boundaries are not
well defined. ? the Canary Current ? the
Benguela Current ? the California Current ? the
West Australian Current ? the Peru Current
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Effects of Surface Currents on Climate
Surface currents distribute tropical heat. The
warm ocean currents are shown in red and cold
currents in blue.
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Subsurface currents

• Thermohaline changes cause subsurface currents
• Ocean is high heat reservoir ( convection
  movement)
• High latitude water is more dense and it sinks
• Most movement is horizontal
• Middle of ocean ( 18 ) layering, surface is 2
• Pycnocline Halocline
  Thermocline
• Density Salinity Temperature
• Bottom ocean water formation makes up 80
• At the Weddell Sea in Antarctica
• Polar regions are highly saline
• Bottom water moves incredibly slow due to intense
  pressure

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Upwelling And Downwelling
Upwelling is the upward motion of bottom water.
Winds from shore blow surface waters out to
sea. This motion brings cold, nutrient rich
bottom water towards the surface to replace water
blown out to sea. Downwelling is downward
motion of water. Winds blow from the sea inland
causing an abundance of water at the shore. It
supplies the deeper ocean with dissolved gases.
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El Niño
An El Niño Year
A Non-El Niño Year
In an El Niño year, the trade winds diminish and
reverse. Storms over land may increase in these
years.
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The Temperature-Salinity Diagram
A general temperature-salinity (T-S) diagram.
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The End

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