1. Movements of the Ocean 22.1 Ocean Currents How do we track currents? It’s not like we can follow a piece of water... http://www.youtube.com/watch?v=exNYUbY5mAU (40s) http://oceanexplorer.noaa.gov/edu/learning/player/lesson08.html Ocean explorer: Ocean Currents

2. Surface Currents Surface currents – move on or near the surface of the ocean and are driven by winds Winds determine the direction and speed of the current and the height of the waves. (Surface currents are undetectable <100m down) Factors affecting ocean surface currents: 1.Wind belts 2.Earth’s rotation 3.Location of continents http://www.youtube.com/watch?v=Hu_Ga0JYFNg (1:19)

3. 1. Wind belts Surface currents created by the wind; move the fastest Trade winds – N & S of the equator Westerlies – between trade and polar regions Northern hemisphere: trade winds blow from NE Southern hemisphere: trade winds blow from the SE Trade winds push currents west across the tropical latitudes of all 3 major oceans http://www.youtube.com/watch?v=qh011eAYjAA (4:51)

4. 1. Wind belts Surface currents created by the wind; move the fastest Trade winds – N & S of the equator Westerlies – between trade and polar regions Northern hemisphere: Westerlies blow from the SW, pushing currents eastward across the Atlantic and Pacific Southern hemisphere: Westerlies blow from the NW, pushing earth’s largest current around the world (called the West Wind Drift)

5. 2. Earth’s Rotation Northern Hemisphere – the flow is to the right (clock-wise) Southern Hemisphere – the flow is to the left (counter-clockwise) Coriolis effect – deflection of the earth’s winds and ocean currents caused by earth’s rotation http://en.wikipedia.org/wiki/Coriolis_effect

6. 3. Earth’s Continents Earth continents are barriers to the surface currents. Currents are deflected. Gulf Stream – Gulf of Mexico, around Florida and up the east coast - North Atlantic Drift (weak current) - Gulf Stream slows down when it hits Greenland & cold water - Splits, creating the Sargasso Sea, where water is relatively warm and calm (floating pollution gathers here) Page 429

7. Deep Currents Deep Currents – cold, dense currents that move very slowly beneath the surface and are caused by the differences in the water’s density Dense water is from the polar regions. Antarctic bottom water – cold, salty, water sinks and forms deep current that moves south, beneath the Gulf Stream Most deep currents flow in the opposite direction of surface currents. AABW – Antarctic bottom water NADW – North Atlantic Deep Water See p. 431

8. Turbidity Currents – a strong current caused by an underwater landslide, or shallow. Sediment from a continental shelf or slope, breaks loose. Water becomes cloudy (turbid) and dense, sinking down. Text p. 432

9. 22.2 Ocean Waves Waves – a periodic up and down movement; transfer of energy Crest – highest point of the wave Trough – lowest point of the wave Wave height – vertical distance between crest and trough Wavelength (λ – lambda) – distance from crest to crest Wave period (T)- time between passage of crests Wave speed (v) – time between the crests of a wave Wave speed = wavelength ÷ period or, v = λ ÷ T See example: page 433

10. Wave Energy Waves are formed from a transfer of energy. The wind transfers energy to the water, so the stronger the wind, the higher the wave. Larger waves tend to receive more energy than smaller waves (more surface area) What happens to larger waves? Swell – a group of long, rolling waves...

11. Water movement in a Wave Energy is transferred from molecule to molecule, but the water itself moves very little. http://www.youtube.com/watch?v=7yPTa8qi5X8 http://www.reefnews.com/reefnews/infopag e/waves/waveinfo.html Water waves are a combination of Longitudinal and Transverse waves http://www.acs.psu.edu/drussell/demos/waves/wavemotion.html

12. Wave size Fetch – distance that the wind can blow across open water Factors in wave size: 1. speed of the wind 2. length of time the wind blows 3. fetch of the wave

13. Waves and the Shore When depth decreases, wave height increases. When a wave topples over, it is called a “breaker” Shells on the shore mark the Farthest point reached by the wave.

14. Rip Currents Please pay attention! Over 100 people drown/year from Rip Currents Rip current – waves break near the shoreline. When waves break strongly in some locations and weakly in others, this can cause circulation cells which are seen as “rip currents”, narrow, fast-moving belts of water travelling offshore. Undertow is a term that is no longer used in oceanography.

15. 22.3 Tides Tides – the daily changes in the level of the ocean surface The gravitational pull of the moon on the earth is the major cause of tides. Gravity is strongest when objects are close

16. Types of tides Spring tides – highest tides at new moon and full moon Neap tides – lowest tides at ¼ and ¾ moon The difference between high tide And low tide is the tidal range

17. Tidal Currents Flood tides – water coming on shore; water getting higher Ebb tides – water into the ocean; water getting lower

18. Spring & Neap tides Spring tides are highest. The sun, moon and earth are all in line. Neap tides are lowest. The moon is at right angles from the sun.

19. Tidal bore Bay of Fundy Tide that occurs when a river enters the ocean through a long bay http://www.youtube.com/watch?v=qfhNjpu_IU4 http://www.youtube.com/watch?v=OP0cpXpw8yk