1. Physical and Chemical Oceanography
Part II: Tides, Currents and Upwelling

2. Tide Regular rise and fall of sea level
Due to gravity of Sun, Moon, Earth and rotation of Earth
Cycle of 24 hours and 50 minutes
Most coasts: 2 high and 2 low tides daily
(e) Describe how tides are produced, and how the alignment of the Moon and Sun, coastal geomorphology, wind, air pressure and size of water body affect tidal range.

3. To understand…
3rd QUARTER
NEW Moon
FULL Moon
1st QUARTER

4. Spring Tide New Moon Earth, Moon and Sun are aligned Full Moon
Amplitude is greatest

5. Neap Tide Tidal range is smaller
Due to Moon being perpendicular to Earth/Sun

6. Conclusion
Spring Tide vs. Neap Tide (Moon has about 70% effect on tides)

7. Tidal Amplitude Tidal range Varies considerably
Difference in height between low and high water
Varies considerably
12 m tall to 0.1 m

9. Influences on Tides Shape of coastline Wind and air pressure changes
Tide enters tapering river mouth or bay  tide increased by opposite sides of channel
Wind and air pressure changes
Strong onshore wind and low pressure  tidal surge (exceptionally high tide)

10. Tidal Amplitude Ocean TA Average = 0.6 m
Increases as tide enters shallow continental margins
Lowest TA: small bodies of water
Ex: Mediterranean Sea, Red Sea, Baltic Sea
Small tidal ranges in large lakes, but often masked

11. Ocean Currents Continuous movement of water
Forces like waves, wind, Coriolis effect, temperature, salinity, tides
Sea bed contours influence direction and strength
Warm, less dense, less salinity
(f) Explain how wind, temperature, density, the Coriolis effect and the shape of the sea bed produce ocean currents and upwelling
Cold, more dense, more salinity

12. Surface Ocean Currents
Driven by wind
Clockwise spiral in N. hemisphere and vice-versa in S.

13. Coriolis Effect Earth rotates, causes water to move to the right
Vice versa in S. hemisphere
Surface currents not entirely driven by wind direction (deflected by the Coriolis effect)

14. Deep Ocean Currents Driven by temperature and density gradients
Recall: upwelling – significant vertical movement of water occurs
Mid-ocean ridge: deflects deep water currents upward