The Motion of the Ocean

1. The Motion of the Ocean An overview of… Waves Currents & Tides

2. Regular ocean waves are the main reason behind re-shaping the shore. What is the driving force for these waves? • The Earth’s gravity • The Moon’s gravity • The Wind • Underwater earthquakes • None of these

3. How do ocean waves happen? • Wind has friction with the water surface which makes it move in an orbital like this. • When the bottom orbital makes contact with the ocean floor the wavelength decreases, and the wave height increases. • The friction with the bottom slows the bottom orbitals, but the top ones keep moving at the same speed, so the wave topples over onto the beach sand—so the waves ‘break’ on the beach.

4. Waves can ADD sediment TO the beach Waves can TAKE sediment FROM the beach

5. What factor DOES NOT cause different ocean wave heights? • Wind Speed • Wind Duration • Water Depth • Fetch—the area over which the wind can build up the waves. • Ocean water salinity • All of these can affect ocean wave height

6. These factors affect ocean wave height: • Wind Speed • Wind Duration • Water Depth • Fetch—the area over which the wind can build up the waves. This is why people go to Hawaii to surf—not Long Island Sound.

7. Which location will receive the MOST wave energy if the waves are moving from the bottom of the picture to the top? 1 3 2

8. This is explained by Wave Refraction Waves bend when they encounter a shallow depth in one spot because the will slow down in the shallow location—but not the deeper places.

9. http://piru.alexandria.ucsb.edu/collections/geography3b/p-s/ps17-07.jpghttp://piru.alexandria.ucsb.edu/collections/geography3b/p-s/ps17-07.jpg

10. If wind is what drives ocean waves, does that mean that only one side of an island experiences ocean waves? • Yes • No, all sides of the island will receive waves because wind direction constantly changes. • No, all sides of the island will receive waves because of wave refraction.

11. Waves refract around an island, causing waves on all sides

12. Ocean Currents Notice how the 5 major ocean basins seem to move in large circles. These are referred to as “Gyres”.

13. What did you notice about gyres in the different hemispheres? • They move in opposite directions • They move in the same direction • Hey, what do you think, I have a photographic memory?

14. Ocean Currents Northern Hemisphere Gyres move CW while Southern Hemisphere Gyres move CCW.

15. The ocean current map showed warm currents in red and cold currents in blue.Based upon the Gyre circulation patterns seen on earth, where will you find warm ocean currents? • Always on the Eastern side of the Gyre • Always on the Western side of the Gyre • On the Eastern side in the NH, but Western side in the SH • On the Western side in the NH, but Eastern side in the SH

16. Warm Currents are always on the WESTERN SIDE of the Gyre • Warm currents result when water flows FROM the equator

17. Which of the following DOES NOT cause the currents go this way? • Global Wind Patterns • Ocean Temperatures • Coriolis Effect • Continent positions • All of these factors cause the currents to go this way.

18. Ocean current directions are caused by… • Global Wind Patterns • Coriolis Effect • Continent positions

19. Compare wind and ocean currents Wind makes ocean water start moving, but the continents and Coriolis effect shift their directions.

20. Tides How many tides does a typical beach location experience in a day (on average)? • One (either high or low) • Two (one high and one low) • Three (two of one type and one of the other) • Four (two high and two low) • None of these

21. 2 high & 2 Low tides per day as your location rotates into and out of the high tide bulges every 24 hours. Earth Moon The places on earth that face toward the moon AND exactly opposite the moon experience a high tide. Key: = force of moon’s gravity = inertial force

22. So how much time passes between a high tide and a low tide (on average?) • Exactly 6 hours • A little more than 6 hours • A little less than 6 hours

23. Why a little more than 6 hours? • The moon is orbiting around the earth in the same direction that we rotate (CCW). That means that a location on earth must rotate more than 360° (which takes 24 hrs) in order to line up with the moon the next day. • The average time between tides is about 6 hours and 12.5 minutes. • That means the tides happen about 50 minutes later each day.

24. Why does the height of the tide shift in a cycle? Spring Tide --More extreme tides Neap Tide --Less extreme tides These happen about every 7 days since 1 full cycle of moon phases takes 29.5 days.