Currents

1. Currents Pgs. 70 - 77

2. Exploring Currents • Thor Heyerdahl – theorized that the inhabitants of Polynesia originally sailed from Peru on rafts powered only by the wind and ocean currents. • 1947, Heyerdahl sets out to prove his theory by setting sail from Peru on a man-made raft. • By day 97, Thor and his crew made it to Polynesia. • Ocean currents sent their raft 6,000km west across the Pacific ocean. • So if currents carried Thor over the Pacific, what is driving these currents?

3. Surface Currents • Streamlike movements of water that occur at or near the surface of the ocean are called surface currents. • Currents can be thousands of kilometers in length. • The Gulf Stream is one of the longer currents transporting more than 25 times more water than all the world’s rivers. • What controls these currents? • Global winds, Coriolis effect, and continental deflections.

4. Global Winds • The best way to visualize what global winds do, is to imagine you are blowing on a cup of hot chocolate. • The ripples created from you are the same way the winds blowing across the Earth’s surface create surface currents in the ocean. • Surface currents can go down to several hundred kilometers deep and several thousand kilometers long. • Certain areas on the world have different patterns of global winds creating currents in the oceans.

5. Coriolis Effect • The Earth’s rotation causes surface currents to move in curved paths rather than in straight lines. • The curving of moving objects from a straight path due to the Earth’s rotation is the Coriolis Effects. • To better understand the coriolis effect, imagine trying to roll a ball straight across a moving merry-go-round.

6. Continental Deflections • If the Earth’s surface were covered only with water, the surface currents would travel freely across the globe in a very uniform pattern. • The continents rise above sea level and when surface currents meet continents, they deflect, or change direction. • Think of it like when a bouncy ball hits a wall and changes direction.

7. Taking Temperatures • All three, global winds, Coriolis effect, and continental deflections, work together to form a pattern of surface currents on Earth. • Warm currents begin near the equator. • Cold water currents begin near the poles. • Cold and warm water currents mix and share in all the oceans.

8. Deep Currents • Streamlike movements of ocean water far below the surface are known as a deep current. • Deep currents form in parts of the ocean where water density increases. • Temperature and salinity combine to affect the density of ocean water.

9. Deep Current Formation • At the poles of the Earth, the cold air cools the water and the cold water sinks down and travels toward the equator. • If the ocean water freezes, ice will float on top of water because ice is just water while the ocean has many dissolved materials in it. • It is denser with more dissolved particles in it. • Also, in warm, tropical climates, much water is evaporated, making the water around it more dense and sink toward the bottom of the ocean.

10. Movement of Deep Currents • Deep current movement is complex. • Due to differences in temperature and salinity, the North Atlantic Deep Water flows on top of the denser Antarctic Bottom Water. • The Antarctic Bottom Water is so dense that it takes 750 years for the water to make it to the equator.

11. Currents Trading Places • The surface and deep currents exchange places where they meet. • Warm water from the equator will push cold Arctic water down to the ocean floor. • The cold water travels the ocean floor until it meets more cold water from the other pole and gets force to the surface to warm in temperature again.

12. Surface Currents and Climate • Currents affect climate because they bring the temperature with it. • Warm waters will bring warm weather and cool waters will bring cool weather. • The Gulf Stream keeps the east coast warm, while the California current keeps the west coast cool.

13. El Nino • Surface currents in the tropical region of the Pacific Ocean usually travel with the trade winds from east to west. • This causes upwelling in the eastern Pacific ocean • Upwelling is a process in which cold, nutrient-rich water from the deep ocean to rise and replace surface water. • As a result the coastal waters in South America rise and affects the interactions of global weather patterns and sea-life.

14. El Nino Effects • This phenomenon can cause floods, mudslides, and millions of dollar of damage to areas affected by it.