Physical and Chemical Oceanography 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 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.

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

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

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

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

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

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)

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

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

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

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)

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