CHAPTER 7 Ocean Circulation © 2011 Pearson Education, Inc.

© 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. © 2011 Pearson Education, Inc.

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 © 2011 Pearson Education, Inc.

Global Surface Current Flow © 2011 Pearson Education, Inc.

© 2011 Pearson Education, Inc. Argo © 2011 Pearson Education, Inc.

© 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc.

© 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc.

Five Subtropical Gyres North Atlantic – Columbus Gyre South Atlantic – Navigator Gyre North Pacific – Turtle Gyre South Pacific – Heyerdahl Gyre Indian Ocean – Majid Gyre © 2011 Pearson Education, Inc.

Subtropical Gyres and Currents © 2011 Pearson Education, Inc.

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 © 2011 Pearson Education, Inc.

Gyres and Boundary Currents © 2011 Pearson Education, Inc.

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 © 2011 Pearson Education, Inc.

© 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc.

© 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc.

© 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc.

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 © 2011 Pearson Education, Inc.

Ocean Currents and Climate © 2011 Pearson Education, Inc.

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 © 2011 Pearson Education, Inc.

© 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc.

Other Types of Upwelling Offshore winds Seafloor obstruction Coastal geometry change © 2011 Pearson Education, Inc.

Converging Surface Water Surface waters move toward each other. Water piles up. Low biological productivity © 2011 Pearson Education, Inc.

© 2011 Pearson Education, Inc. Coastal Downwelling Ekman transport moves surface seawater toward shore. Water piles up, moves downward in water column Lack of marine life © 2011 Pearson Education, Inc.

© 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc.

Pacific Ocean Circulation © 2011 Pearson Education, Inc.

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!!! © 2011 Pearson Education, Inc.

Normal Conditions, Walker Circulation © 2011 Pearson Education, Inc.

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 © 2011 Pearson Education, Inc.

© 2011 Pearson Education, Inc. Normal vs El Nino © 2011 Pearson Education, Inc.

ENSO Conditions in the Pacific Ocean © 2011 Pearson Education, Inc.

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 © 2011 Pearson Education, Inc.

© 2011 Pearson Education, Inc. Normal vs. La Nina © 2011 Pearson Education, Inc.

© 2011 Pearson Education, Inc. La Niña Conditions © 2011 Pearson Education, Inc.

© 2011 Pearson Education, Inc. ENSO Occurrences © 2011 Pearson Education, Inc.

ENSO has Global Impacts © 2011 Pearson Education, Inc.

© 2011 Pearson Education, Inc. 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? © 2011 Pearson Education, Inc.

© 2011 Pearson Education, Inc. 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 © 2011 Pearson Education, Inc.

Thermohaline Circulation Originates in high latitude surface ocean Surface waters sink Identifies deep water masses based on temperature, salinity, and resulting density © 2011 Pearson Education, Inc.

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 © 2011 Pearson Education, Inc.

Conveyor Belt Circulation © 2011 Pearson Education, Inc.

© 2011 Pearson Education, Inc. Power From Currents Currents carry more energy than winds Florida–Gulf Stream Current System Underwater turbines Expensive Difficult to maintain Hazard to boating © 2011 Pearson Education, Inc.

© 2011 Pearson Education, Inc. Activity: Complete Worksheet in class Becomes study guide Exam ?????? © 2011 Pearson Education, Inc.

End of CHAPTER 7 Ocean Circulation © 2011 Pearson Education, Inc.