Download - Ocean Currents
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Ocean Currents
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Why is Ocean Circulation Important?
• Transport nutrients and organisms
• Influences weather and climate
• Influences commerce
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Density of air
• Warm, low density air rises
• Cool, high density air sinks
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ITCZ intertropical convergence zone= doldrumsLow pressure, wet climate
High pressure, dry climate
Low pressure, wet climate
30o
30o
60o
60o
90o
90o
0o
High pressure, dry climate
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The Coriolis effect• The Coriolis effect
– Is a result of Earth’s rotation– Causes moving objects to follow
curved paths:• In Northern Hemisphere, curvature
is to right• In Southern Hemisphere, curvature
is to left
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Surface Currents
The upper 400 meters of the ocean (10%).
Deep Water Currents
Thermal currents (90%)
Ocean Currents
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Wind-driven surface currents
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Wind-Driven and Density-Driven Currents
• Wind-driven currents occur in the uppermost 100 m or less
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Sailors have know about ocean currents for centuries
Sailors have know that “rivers” flow in the seas since ancient times. They used them to shorten voyages, or were delayed by trying to stem them.
If navigators do not correct to deflection by currents, they may be far away from where they think they are and meet disaster.
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Ben Franklin and the Gulf Stream
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Matthew Fontaine MauryThe first systematic study
of currents was done by Maury based on logbooks in the US Navy’s Depot of Charts and Instruments.
His charts and “Physical Geography of the Sea” assisted navigators worldwide.
http://www.npg.si.edu/exh/brady/gallery/97gal.html
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Gyres are large circular-moving loops of waterFive main gyres (one in each ocean
basin):• North Pacific• South Pacific• North Atlantic• South Atlantic• Indian
• Generally 4 currents in each gyre• Centered about 30o north or south
latitude
Current Gyres
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Pacific Ocean surface currents
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What do Nike shoes, rubber ducks, and hockey gloves have to do with currents?
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Lost at Sea
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• January 1992 - shipwrecked in the Pacific Ocean, off the coast of China
• November 1992 - half had drifted north to the Bering Sea and Alaska; the other half went south to Indonesia and Australia
• 1995 to 2000 - spent five years in the Arctic ice floes, slowly working their way through the glaciers2001 - the duckies bobbed over the place where the Titanic had sunk
• 2003 - they were predicted to begin washing up onshore in New England, but only one was spotted in Maine
• 2007 - a couple duckies and frogs were found on the beaches of Scotland and southwest England.
Duckie Progress
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2004-2007 Barber’s Point
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• “Great Pacific Garbage Patch”
• Estimate: 46,000 pieces of floating garbage/mi2.
North Pacific Subtropical Gyre
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North Pacific Subtropical Gyre
135° to 155°W and 35° to 42°N
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North Pacific Subtropical Gyre
http://marinedebris.noaa.gov/info/patch.html#6
Great Pacific Garbage Patch- Good Morning America 2010 http://www.youtube.com/watch?v=uLrVCI4N67M&feature=player_embedded
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Upwelling and downwellingVertical movement of water ()
– Upwelling = movement of deep water to surface• Hoists cold, nutrient-rich water to surface• Produces high productivities and abundant
marine life– Downwelling = movement of surface water
down• Moves warm, nutrient-depleted surface water
down• Not associated with high productivities or
abundant marine life
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El Niño
• El Niño = warm surface current in equatorial eastern Pacific that occurs periodically around Christmastime
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El Niño
• Oceanic and atmospheric phenomenon in the Pacific Ocean
• Occurs during December• 2 to 7 year cycle
Sea Surface Temperature
Atmospheric Winds
Upwelling
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Normal conditions in the Pacific Ocean
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El Niño conditions (ENSO warm phase)
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La Niña conditions (ENSO cool phase; opposite of El
Niño)
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El NiñoNon El Niño
1997
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Non El Niño
El Niño
thermocline
upwelling
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Surface and Deep-Sea Current Interactions
Unifying concept: “Global Ocean Conveyor Belt”
http://seis.natsci.csulb.edu/rbehl/ConvBelt.htm
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Matter Transport and Surface Currents
• Currents also involved with gas exchanges, especially O2 and CO2
• Nutrient exchanges important within surface waters (including outflow from continents) and deeper waters (upwelling and downwelling)
• Pollution dispersal• Impact on fisheries and other resources
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Global ocean circulation that is driven by differences in the density of the sea water which is controlled by temperature and salinity.
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White sections represent warm surface currents. Purple sections represent deep cold currents
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What effect does global warming play in
thermohaline circulation?
http://www.youtube.com/v/MZbsMlr9WRI?version=3
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North Atlantic regional cooling
Global climate interconnections
CO2 fossil fuel combustion
Atmospheric and ocean temp
1 2 3 4
6 5
Subtropical evaporation
High latitude precipitation & runoff
Deep water formation & thermohaline circulation
Nordic seas salinity & deep convection
Potential feedback of increased
tropical salinity
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1. What is a convection cell?2. Which direction do currents get deflected in
the Southern Hemisphere?3. What depth should the water be for an Ekman
spiral to occur?4. How are surface currents created?5. What is a gyre?6. How can an El Nino impact upwelling?7. Coriolis Effect is strongest near the _____?
Conclusion