Chapter 21 Section 1

1. Chapter 21 Section 1

2. Ocean Currents Objectives • Describe how wind patterns, the rotation of the Earth, and continental barriers affect surface currents in the ocean • Identify the major factor that determines the direction in which a surface current circulates • Explain how differences in the density of ocean waters affect the flow of deep currents

3. Ocean Currents • The water in the ocean moves in giant streams called currents • Oceanographers study currents by examining the physical and chemical characteristics of ocean water • They also identify currents by mapping the paths of debris that is dumped or washed overboard from ships • Scientists place currents into two main categories, surface and deep currents

4. Ocean Currents • Currents that move on or near the surface of the ocean, and are driven by winds are called surface currents • These are controlled by three factors, winds, Earth’s rotation, and location of the continents • Winds are caused by uneven heating of the atmosphere

5. Ocean Currents • Global wind belts, such as trade winds and the westerlies are major factors affecting the flow of ocean surface waters • Trade winds are located just north and south of the equator • In the Northern Hemisphere they blow from the north east • In the Southern Hemisphere they blow from the south east

6. Ocean Currents • Continents are another major influence on surface currents • They act as barriers to surface currents • When surface currents flow against the continents the current is deflected and divided

7. Ocean Currents • Global wind belts and ocean currents do not flow in straight lines, the follow a curve or circular pattern that is caused by Earth’s rotation • The Coriolis Effect cause huge circles of moving water called gyres, to form

8. Ocean Currents • Warm equatorial currents move in a western direction in the oceans • Between these westward flowing currents lies a weaker, eastward flowing current called the Equatorial Countercurrent

9. Ocean Currents • In the Southern Hemisphere the currents in gyres move counterclockwise • In the most southerly region of the oceans constant westward winds produce the world’s largest current, the Antarctic Circumpolar Current also known as West Wind Drift • No continents interrupt the movement of the current that completely circles Antarctica

10. Ocean Currents • The Indian Ocean surface currents follow two patterns, in the south they follow a circular counter clockwise gyre • In the north they are governed by monsoons and change seasonally

11. Ocean Currents • In the North Atlantic warm ocean water moves through the Caribbean Sea and the Gulf of Mexico and north along the east coast of North America in a swift long current called the Gulf Stream • Further north the Labrador Current flows south and joins the Gulf Stream

12. Ocean Currents • At the poles water cools and freezes making the water saltier and denser • The denser water sinks and begins to flow toward the equator • The journey of this cold dense water takes hundreds of years to complete

13. Ocean Currents • The temperature of water near Antarctica is very cold and the water salinity is high • This makes the water of Antarctica the densest and coldest water in the ocean • This forms a deep current called Antarctic Bottom Water

14. Ocean Currents • A strong current caused by an underwater landslide is a turbidity current • This occurs along the continental shelf or the continental slope, and a large amount of sediment breaks loose • The cloudy water gets denser than the surrounding water, moves beneath the clear, less dense water