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Physical and Chemical Oceanography

Physical and Chemical Oceanography. Section 7 Part II: Tides, Currents and Upwelling. Tide. Regular rise and fall of sea level Due to gravity of Sun, Moon, Earth and rotation of Earth Cycle of 12.5 hours Most coasts: 2 high and 2 low tides daily. To understand…. 3 rd QUARTER.

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Physical and Chemical Oceanography

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  1. Physical and Chemical Oceanography Section 7 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 12.5 hours • Most coasts: 2 high and 2 low tides daily

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

  4. Spring Tide • New Moon • Full Moon • Earth, Moon and Sun are aligned • 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 • Difference in height between low and high water • Varies considerably • 12 m tall to 0.1 m

  8. Influences on Tides • Shape of coastline • 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)

  9. 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

  10. 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 Cold, more dense, more salinity

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

  12. 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 Corioliseffect)

  13. 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

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