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three types of currents
• surface currents
• thermohaline circulation
(shallow & deep currents)
wind--driven vertical currents
wind
(upwelling)
OCEAN CURRENTS
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surface currents
current
• occur at surface
• horizontal currents
• mass of water moving from
one place to another
• like a river within the ocean
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What causes surface currents?
Why is Ocean Circulation Important?
• WIND! Primarily caused
by friction between wind and
water - wind pushes water
• Thermal Expansion & Gravity
• Transport ~ 20% of latitudinal heat
– Equator to poles
• Transport nutrients and Transport nutrients and
organisms
• Influences weather and climate
• Influences commerce
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Ocean Circulation surface currents
gyre
• massive circular system of wind-driven
surface currents
• cover whole
h l oceans
• clockwise in
Northern hemisphere
• counter-clockwise
in Southern
hemisphere
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surface currents
eddies = warm core rings
surface currents
Coriolis effect
break off of currents and
transport organisms elsewhere
→ Clockwise
→ Counter-clockwise
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Wind
driven surface currents
Wind‐drive ocean surface currents
Current Event: Gulf Oil Spill
• How fast? A few miles/hr (Gulf Stream off of Miami = 4.5 mph)
• How much? Total water in ocean surface circulation = about 100
Amazon Rivers (20 million m3/s).
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• The Gulf Loop Current enters from the Caribbean basin, moves around the Gulf
moves around the Gulf of Mexico and exits out the Florida Strait, where it joins the more powerful Gulf Stream current. (msnbc.com)
• Track it
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thermohaline
circulation (currents)
• causes deep ocean circulation
• vertical currents
• temperature and salinity cause
water density differences
• due to density differences,
water masses rise and fall
Remember that the surface circulation is driven by wind.
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Sea Surface Temperature
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Initiating deep water circulation
• A current runs from the equatorial Atlantic up the coast of the Americas.
• Deflects (bounces) off landmasses.
• Crosses Atlantic to warm the west coast of Europe.
http://www.ldeo.columbia.edu/dees/ees/climate/slides/sst_march.gif
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Ocean Salinity
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How does ocean water change as it moves northward?
• Evaporation
• Cooling
• Freezing
http://www.ldeo.columbia.edu/dees/ees/climate/slides/sal_march.gif
•http://ingrid.ldgo.columbia.edu/
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How do evaporation, cooling, and freezing affect salinity and density?
• Evaporation and freezing increase salinity and
salinity and density.
• Cooling also increases density.
• Water that is more dense SINKS!!!
Major Thermohaline Circulation
The cold, salty, really dense water starts to sink down to the bottom of the ocean in the North Atlantic, where it turns around and flows back south towards the equator of the bottom of the ocean basin. 19
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It’s actually a lot more complicated
with many layers of sinking & rising
thermohaline circulation
(currents)
↑ salinity = ↑ density = water mass sinks
↓ temp. = ↑ density = water mass sinks
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Water that reaches the North Atlantic is very COLD and SALTY so it SINKS!
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Complex Thermohaline Circulation
North Atlantic
Deep Water
(NADW
15 million m3 of near surface water descend into the deep ocean each second.
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There are certain places where the surface water typically sinks.
Global Warming a Problem?
• What happens to the salinity and density of water when melting occurs?
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“Ocean Conveyor Belt”
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Melting Ice a Problem?
• Thermohaline circulation is sometimes called the “Ocean Conveyor Belt” because of it’s constant circulation in the ocean.
• Melting land ice may not only raise sea level but also slow circulation by “d
“damming” water in the i ” t i th
tropics.
• As ice melts, ocean water is diluted and therefore does not sink as fast. 26
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The bottom line:
thermohaline circulation
RESULTS: Heat Subsidy
• Heat from tropics ends up north and south.
When combined with surface
currents, results in conveyor belt
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movement of water around globe
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wind driven vertical
currents = upwelling
• wind blows, moves water
away, causes new water to rise
up to
t replace
l
it
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