1. The Restless Ocean
Chapter 13

2. Surface Currents
Surface Currents – movement of surface waters closely related to atmospheric circulation and driven by unequal heating of the Earth by the Sun

3. Ocean Circulation Patterns
Winds are the driving force of surface currents. When winds change direction, the surface currents also change direction.

5. Ocean Circulation Patterns
The Earth’s rotation causes currents to deflect to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This is called the Coriolis Effect.

6. Ocean Circulation Patterns
Surface currents form a “gyre”, or circular vortex, with currents moving west at the equator, deflecting off land towards the poles and circling back down.

9. Ocean Circulation Patterns
Large central area in the middle of the gyre is a zone of calmer waters. Around the Antarctic there are no continents to deflect the current so it is a continuous circulation.

11. Ocean Currents and Upwelling
Winds may cause vertical movements called upwellings, where colder deeper water is force to the surface.

12. Ocean Currents and Upwelling
Usually occurs in areas where the wind blows towards the equator and parallel to the coast (Ex. California, South America, West Africa)

13. Ocean Currents and Upwelling
Due to the Coriolis Effect the warmer surface waters are deflected away from the shore and are replaced by cold “upwells”.

14. The Importance of Ocean Currents
Navigation – ships could use currents to make quicker ocean crossings and trying to move against the current would cause slower passages.

16. The Importance of Ocean Currents
Climate – warm water from the poles moves north and cool water from the poles is circulated towards the equator, moderating climates along the way.

18. The Importance of Ocean Currents
Maintains Earth’s Heat Balance

19. Deep Ocean Circulation
Controlled by gravity and density differences.
Also called thermo-haline circulation (thermo – heat, haline – salt)

21. Deep Ocean Circulation
Water at the surface can become colder and more salty which will make it denser.
The dense water sinks toward the ocean bottom, displacing lighter water.

22. Deep Ocean Circulation
This mainly occurs in the Arctic and Antarctic, where temperatures are low enough sea ice forms. Salts don’t get frozen in the ice making the surrounding water saltier.
Deep ocean currents are difficult to measure and so little is known about them.

23. Tides
Daily change in the elevation of the ocean surface.

24. Causes of Tides
Ocean tides result from the gravitational attraction exerted upon the Earth by the moon and to a lesser extent by the sun.

26. Causes of Tides
Tidal bulges remain in place while Earth “rotates” through them. In one day the Earth experiences one high tide and one low tide. The tides migrate as the moon revolves around the Earth, shifting about 50 minutes a day.
The tide generating power of the Sun is less than half that of the moon

28. Causes of Tides
At times of the new and full moons the sun and moon are aligned together and produce higher high tides and lower low tides. These are called the spring tides.

31. Causes of Tides
During the first and third quarters the sun and moon act at right angles and offset the influence of each other. These are called neap tides.

32. Types of Tides
Semidinural - Two high and two low tides daily, with small differences in the high and low water heights
Dinural - one high and one low tide
Mixed – usually two high and two low with a large inequality between high water heights and low water heights

33. Semidiurnal

34. Diurnal Tide

35. Mixed Semidiurnal

37. Tidal Currents
Horizontal flow of water accompanying the rise and fall of the tides
Flood currents – tidal currents that advance into the coastal zone
Ebb currents – currents generated by seaward moving water
Slack water – periods of little or no current

38. Flood Current and Ebb Current

39. Resources