13-1    Surface current:

1. Ocean circulation: regular patterns followed. Mainly clockwise in Northern Hemisphere and counterclockwise in Southern Hemisphere, due to Coriolis effect.

   • Centrifugal force due to Earth's rotation is counteracted by water near the equator. Thus, water rotates slower compared to rigid rocks ==> moving west near the Antarctica, west wind drift.

2. Upwelling: vertical circulation. Cold water rises and hot water sinks. Why? As wind blow parallel to coast on west coast, warm surface water is blown away south, deeper cold water from north compensate. On East coast? Wind direction opposite. Warm water from south going north and up.

3. Role of ocean current:

   • Affect navigation: against current need more energy or longer time.

   • Affect climate: latitude: London high in latitude, not too cold. Why? North Atlantic drift bring warm water, then westerly wind carry it inland to Europe.

4. Deep-ocean circulation:

   • Affected by density difference due to salinity difference. Also temperature difference. Near pole, temperature low, thus sink. Then bottom water upwell. A cycle last ~ 2000 years Therefore, long slow precess.

13-2    Tides:

Sea level ride or fall with respect to date

1. Cause: gravitational forces by the Moon and the Sun. The force is reversely  proportional to the distance². As the distance increases, the force decreases. Fig. 13.8 shows the tidal budge facing the Moon and directly opposite of the Moon. The Earth rotates one full circle every 24 hours. Therefore, 2 high tides and 2 low tides each day.

2. Types of tides:

   • Semidiurnal: 2 high tides and 2 low tides daily.

   • Diurnal: 1 high tide and 1 low tide daily.

   • Mixed: 2 high and 2 low tides each day, but not equal in heights.

3. Tidal current:

   • Flood current: when current advance to land.

   • Ebb current: when current retreat to sea.

   • Area sitting between is called tidal flats.

   • Tidal deposits - tidal delta.

13-3    Waves:

1. Characters of waves:

   

   • Wavelength: distance between 2 waves. Horizontal.

   • Wave height: vertical distance between a crest and a trough.

   • Wave period: time for a wave to pass form one crest to another.

   • These 3 characters are affected by:

     1. Wind speed.

     2. Duration of wind blowing.

     3. Distance wind travels.

   • Waves move in oscillating fashion, i.e., objects do not move horizontally. Fig.13.13. Only circular motion.

   • As depth increases circular motion decreases until depth = 1/2 of wavelength, in which no motion any more. Fig. 13.12.

   • As the wave depth > the water depth, the waves feel the bottom. Due to friction bottom of the waves travels slower while top of the wave travel at the normal speed, resulting wave breaks ==> surf. Fig. 13.14.

2. Wave erosion:

   • by impact of water against rocks. Fig. 13.15.

   • by abrasion: grinding by sand.

3. Wave refraction:

   • When waves approach shore, bend to parallel the shore. thus, the headland is impacted more and experienced more erosion.

   • In bay area deposit. Fig. 13.17. 

   • Overall, for a long run the shore line straightened.

   • Sands are carried by waves at the shore. they move parallel to longshore current.

   

13-4    Shoreline features:

1. By wave cutting:

   • Wave cutting cliffs and platforms: Fig.13.19.

   • Arches and stacks: Fig. 13.20.

2. By drift sand deposits:

   • Bay mouth bar or spit: Fig. 13.21. 

3. Barrier islnads:

   • Sand ridge parallel to the coast, often found in flat coast.

13-5    Atlantic coast vs. Pacific coast:

Atlantic	Pacific
Wider beaches	Narrow beaches
Submerging	Emerging
Tectonic stable	Tectonic active

Homework:

• Read chapter summary on p.372.

• Use your own word to explain the key terms on page 373.

• Answer the review questions on page 373.