1. Ocean Currents Chapter 16

2. Surface Currents  A current is the flow of water moving through the ocean.  Surface currents (flow in the upper 1000 m) are caused by wind.

3. Surface Currents in the Ocean  Warm currents flow from the equator to the poles, and cold currents flow from the poles to the equator  Surface currents form a circularpatterncalled a gyre.

4. Surface Currents in the Ocean  Gyres in the Northern Hemisphere flow clockwise, gyres in the Southern Hemisphere flow counterclockwise.

5. Surface Currents in the Ocean  West sides of oceans have warm ocean currents that flow away from the equator.  East sides of oceans have cold ocean currents that flow to the equator.

6. Surface Currents & Wind  The earth rotates in an easterly direction.  This makes the winds blowing toward the equator curve westward, and the winds blowing toward the poles curve eastward.

7. Surface Currents and Winds  Trade winds drive the equatorial part of the ocean currents.  They blow from the east, towards the west.  The westerly winds drive the polar part of the ocean currents.  They blow from the west, towards the east.

8. Surface Currents and Winds

9. Deep Currents  Because the warm surface water and cold deep waters don’t mix, surface currents have little effect on the deep ocean water.  Deep currents are caused by density differences. Remember, cold water is more dense than warm water! Remember, cold water is more dense than warm water!

10. Deep Current Movement  The densest water is at the poles.  As ice forms, the salt is left behind, leading to high-salinity, dense water.  This water sinks to the deep ocean (deep water masses).  Water flows from high density to low density, and moves from the poles toward the equator.

11. Upwelling  When wind blows parallel to a shoreline, surface currents and deep currents can mix.  The wind pushes the warm water away from the coast, and cold deep water takes its place.  This upward movement of cold water is called upwelling.  Where upwelling occurs, the water is rich with nutrients that it brings up from the ocean floor.

12. Upwelling

13. Shoreline Currents  A longshore current forms when waves approach a shore at an angle.

14. Rip Currents  A rip current forms when water that is built up behind a sandbar due to a longshore current finally breaks through.