GEOG101: Physical Geography

Lecture 19: Monday, April 20, 2009

Topics
1. Global Oceans and Seas
2. Coastal System Actions
3. Coastal System Outputs
4. Wetlands, Salt Marshes, and Mangrove Swamps
5. Human Impact on Coastal Environments

Global Oceans and Seas
• Chemical Composition of Seawater: Salinity
      • 57 of the 92 natural elements dissolves in seawater
      • The concentration of dissolved solids is called Salinity
      • The ocean remains a remarkably homogeneous mixture
      • Therefore marine precipitates record information of the past
      • Seven elements accounts for > 99% of the dissolved solids in seawater:
            Chlorine (CL^- )
            Sodium (Na⁺ )
            Magnesium (Mg²⁺ )
            Sulfur (as sulfate, SO4^2- )
            Calcium (Ca²⁺ )
            Potassium (K⁺ )
            Bromine (Br^- )
• Average Salinity of seawater: 35‰
      • Expressions:
      3.5% (percent); 35 ‰ (per thousand; most popular notation);
      35,000 ppm (parts per million; commonly used for low concentrations);
      35,000 mg/l; 35g/Kg;
• Brine seawater: > 35‰ salinity
• Brackish seawater: < 35‰ salinity
• Salinity change with latitudes:
             Equatorial seawater: higher precipitation --> lower salinity (~34.5‰)
            Subtropical oceans: higher evaporation --> higher salinity (~36‰)
            Restricted areas (enclosed areas) has unusual salinity: Persian Gulf (40‰); Red sea and Mediterranean sea (225‰)

• Ocean's Physical Structure
             Mixing zone (2%);
             Thermocline transition zone (18%)
             Deep cold zone (80%)
• Seawater freezes at about -2°C because of the salinity
• The salinity and intense pressure at depth decrease the freezing point even more

Coastal System Actions
• Tides
       Spring tides: Moon and sun stay in the same line or conjunction:
             Gravitational pull and inertia
            Not a seasonal term
       Neap tides: Moon-Earth and sun-Earth at ~90° angle
       Every 24 hours and 50 minutes: a point experience two flood (rising) tides and two ebb (falling) tides
       Every month, a point on earth experiences two spring tides and two neap tides

• Waves
       Wave refraction and coastal straightening
       Longshore Current and Beach Drift

Coastal System Outputs
• Erosional Coastal Processes and Landforms
        Sea cave
        Sea arch
        Sea atack
        Sea cliff
        Wave-cut platform (terrace)

• Depositional Coastal Processes and Landforms
        Barrier spit
        lagoon
        Bay barrier
        Tombolo
        Beach
• Biological Processes: Coral Formations
        Fringing coral reefs
        Barrier coral reefs
        Atoll
• Coral Bleaching: Colorful Corals turn stark white by expelling their own nutrient supply (colorful alage -- Red-brown to green): A type of suicide?
        Unknown reason, possibly pollution, disease, or change in salinity. By 2000, 30% of coral s were lost

Wetlands, Salt Marshes, and Mangrove Swamps
• Wetlands: areas saturated with water long enough to support hydrophytic vegetation.
• Two types:
        Salt marshes: North of 30° latitudes in N. Hemisphere or south of 30° latitude in S. Hemisphere
        Mangrove swamps: From 30° N and 30° S to equatorial areas
        The different types occur mainly because of the freezing conditional in higher latitudes controls the survival of mangrove seedlings.

Human Impact on Coastal Environments
• About 40% of the world population live within 200 km of coastlines
• About 50% of the US population live along coastal lines (including lakes)
• Catutions have to be taken for long term planning, infrastructure, pollution, etc.