1. CHAPTER 7 Ocean Circulation
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2. © 2011 Pearson Education, Inc.
Chapter Overview
Ocean currents are moving loops of water.
Surface currents are influenced by major wind belts.
Currents redistribute global heat.
Thermohaline circulation affects deep currents.
Currents affect marine life.
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3. Types of Ocean Currents
Surface currents
Wind-driven
Primarily horizontal motion
Deep currents
Driven by differences in density caused by differences in temperature and salinity
Vertical and horizontal motions
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4. Global Surface Current Flow
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Argo
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Surface Currents
Occur above pycnocline
Frictional drag between wind and ocean
Generally follow wind belt pattern
Other factors:
Distribution of continents
Gravity
Friction
Coriolis effect
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Subtropical Gyres
Large, circular loops of moving water
Bounded by:
Equatorial current
Western Boundary currents
Northern or Southern Boundary currents
Eastern Boundary currents
Centered around 30 degrees latitude
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8. Five Subtropical Gyres
North Atlantic – Columbus Gyre
South Atlantic – Navigator Gyre
North Pacific – Turtle Gyre
South Pacific – Heyerdahl Gyre
Indian Ocean – Majid Gyre
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9. Subtropical Gyres and Currents
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10. Subtropical Gyre Currents
Four main currents flowing into one another:
Equatorial Currents
North or south
Travel westward along equator
Western Boundary Currents – warm waters
Northern or Southern Boundary Currents – easterly water flow across ocean basin
Eastern Boundary Currents – cool waters
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11. Gyres and Boundary Currents
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12. Other Surface Currents
Equatorial Countercurrents – eastward flow between North and South Equatorial Currents
Subpolar Gyres
Rotate opposite subtropical gyres
Smaller and fewer than subtropical gyres
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Activity:
How do we measure both surface and deep water currents? List and explain each
What is ARGO? Give details, and why it is important. Who will be interested in the data
Diagram the Earth; label the prevailing wind patterns, and then label the major surface gyres. Explain the correlation. How different would it look without the continents?
Make a table similar to 7.1. just label the 5 major gyres, and include the 4 major currents
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Ekman Spiral
Surface currents move at an angle to the wind.
The Ekman spiral describes speed and direction of seawater flow at different depths.
Each successive layer moves increasingly to the right in the Northern Hemisphere
Coriolis effect
Ekman Spiral Animation
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Ekman Transport
Average movement of seawater under influence of wind
90 degrees to right of wind in Northern hemisphere
90 degrees to left of wind in Southern hemisphere
Ekman Transport Animation
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16. Ocean Currents and Climate
Warm ocean currents warm the air at the coast.
Warm, humid air
Humid climate on adjoining landmass
Cool ocean currents cool the air at the coast.
Cool, dry air
Dry climate on adjoining landmass
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17. Ocean Currents and Climate
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18. Upwelling and Downwelling
Upwelling – Vertical movement of cold, nutrient-rich water to surface
High biological productivity
Downwelling – Vertical movement of surface water downward in water column
Ekman Spiral Animation
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Coastal Upwelling
Ekman transport moves surface seawater offshore.
Cool, nutrient-rich deep water comes up to replace displaced surface waters.
Example: U.S. West Coast
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20. Other Types of Upwelling
Offshore winds
Seafloor obstruction
Coastal geometry change
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21. Converging Surface Water
Surface waters move toward each other.
Water piles up.
Low biological productivity
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Coastal Downwelling
Ekman transport moves surface seawater toward shore.
Water piles up, moves downward in water column
Lack of marine life
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Activity:
Explain, “Western Intensification”. How does coriolis factor into this
Explain the effects of: western vs eastern boundary currents
Look at table 7.2; what is the main function of each (big picture here) boundary current.
Define the terms Upwelling & Downwelling. Which one is more biologically productive and why?
List the 3 other causes of upwelling, and how they work
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24. Pacific Ocean Circulation
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25. Atmospheric-Ocean Connections in the Pacific Ocean
Walker Circulation Cell – normal conditions
High pressure in Eastern Pacific
Strong SE trade winds
Pacific warm pool on western side of ocean
Thermocline deeper on western side
Upwelling off the coast of Peru
HUGE FISHING INDUSTRY HERE!!!
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26. Normal Conditions, Walker Circulation
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27. El Niño – Southern Oscillation (ENSO)
Walker Cell Circulation disrupted
High pressure in E Pacific weakens
Weaker trade winds
Warm pool migrates eastward
Thermocline deeper in eastern Pacific
Downwelling
Lower biological productivity
Peruvian fishing suffers
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Normal vs El Nino
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29. ENSO Conditions in the Pacific Ocean
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30. La Niña – ENSO Cool Phase
Increased pressure difference across equatorial Pacific
Stronger trade winds
Stronger upwelling in eastern Pacific
Shallower thermocline
Cooler than normal seawater
Higher biological productivity
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Normal vs. La Nina
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La Niña Conditions
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ENSO Occurrences
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34. ENSO has Global Impacts
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Activity:
Compare El Nino to La Nina; major differences and expected outcomes
List the events that occurred in 1982/83 and 1997/98
How often do these events occur?
How long do the phases last?
How has science proven these events have always occurred?
What is PDO?
How has this affected climate change?
How long do they occur?
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Deep-Ocean Currents
Thermohaline Circulation – deep ocean circulation driven by temperature and density differences in water
Below the pycnocline
90% of all ocean water
Slow velocity
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37. Thermohaline Circulation
Originates in high latitude surface ocean
Surface waters sink
Identifies deep water masses based on temperature, salinity, and resulting density
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38. Thermohaline Circulation
Deep-water masses include:
Antarctic Bottom Water
North Atlantic Deep Water
Antarctic Intermediate Water
Oceanic Common Water
Cold surface seawater sinks at polar regions and moves equatorward
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39. Conveyor Belt Circulation
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Power From Currents
Currents carry more energy than winds
Florida–Gulf Stream Current System
Underwater turbines
Expensive
Difficult to maintain
Hazard to boating
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Activity:
Complete Worksheet in class
Becomes study guide
Exam ??????
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42. End of CHAPTER 7 Ocean Circulation
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