Abiotic Factors Affecting Marine Organisms:
Physical and Geological Processes


I. Geography and Geomorphology of the Oceans
    world ocean

   -uneven distribution of water on earth
   -divided for convenience (order of decreasing size):
        -Pacific
            -largest
            -deep trenches
        -Atlantic
            -longer coastline
            -many major river inputs
                Amazon
                Zaire
                Mississippi
       -Indian
            -Brahmaputra/Ganges river
        -Arctic
            -shallowest and smallest ocean
        -Southern Ocean

                                  world ocean                                   continents
total area                    362 X 106 km2                              155 X 106 km2
average depth              3,729 m                                         840 m
max. depth/height       11,022 m (Marianas trench)          8,848 m (Mt. Everest)

II. Cross section of the ocean basin
    -continental shelf
        shallow areas at margins of the continent
        ~7-8% of the total ocean area
        biologically very rich
    -continental slope

       sometimes followed by a continental rise
    -abyssal plain
        -more flat, sediment covered
        -4,000-5,000 m

    -submarine ridges
        -continuous chain
        -found in all oceans (e.g., mid Atlantic ridge)

    -trenches
        -7,000-11,022 m deep (Challenger deep in the Marianas trench)

    -seamounts
        -isolated islands formed by volcanic action

III. Plate Tectonics
    -Alfred Wegener, 1912
        -His ideas were rejected because he lacked a mechanism
    -Major plates of the world
        -earth’s crust divided into a number of large plates bounded by ridges and trenches
        -7 major plates
    -Difference between continental and oceanic crust (earth surface)
 
Continental crust
            granite
            35 km thick on average
            density 2.7 g cm-3
            oldest rocks are 3.8 billion years old
Oceanic crust
            basalt
            5-7 km thick on average
            density 3.0 g cm-3
            oldest rocks are <200 million years old
   
    -Plates float on upper mantle

    -When plates meet they may:
        (1) Spread (diverging) – oceanic ridges

            seafloor spreading

        (2) Collide (subduction or mountain building)
            a. trenches –
                ocean-ocean
                ocean-continent
            b. continent-continent -- mountains

        (3) Slide – transverse faults (transform faulting); e.g., California fault
          
     -‘ring of fire’ – volcanic and geothermal activity
     -seismic activity

    -Hotspots – weak points in crust, e.g., Hawaiian islands

    -Coasts – parts of the continental margin may be classified as
        -active margin
        -passive margin

IV. Physical Environment – wind, waves, tides, currents, temperature

    A. Temperature and Vertical Stratification

        -4 major biogeographical zones: polar, cold temperate, warm temperate (subtropical), tropical (equatorial)

        -metabolic reactions of different organisms are often optimized for particular temperatures
            -metabolism often increases by a factor of two for each 10 degree C rise in temperature
            -most marine organims  are poikilothermic (ectothermic)

    -temperature varies with depth
            -less dense water floats on more dense water
                -thermocline – depth of most rapid temperature decline
                -pycnocline – depth of rapid density change (caused by either temperature or salinity)
            -what affects water density?
                -density versus temperature
                    -for freshwater the most dense water is at 4 C
                    -ice is lighter and floats
                    -warmer water is lighter and floats                   
            -density versus salinity
               -freezing point depression
               -for seawater the colder the water gets, the denser it gets
               -if you increase salt content, then water is denser also

    B. Water Masses
        -Upper water mass – mixes due to wind
        -Deep water masses – often several different layers

    C. Circulation
        -waves - little net horizontal motion
            -wave height –distance between crest and trough
                -wind speed
                -fetch – distance over which the wind blows
                -length of time the wind blows
            -wavelength – horizontal distance between the crests of waves
            -period – time for wave to pass by (for two crests to pass a fixed point)
            -wave energy mostly dissipated at a depth of ½ the wavelength
                -when water depth is 1.3 times the wave height --  breaking waves
           -water molecules remain in one place horizontally, just move up and down           
           -internal waves on pycnocline - high amplitude
 
        -currents – water movements that result in horizontal water movement
            -Influenced by winds, uneven solar radiation, land masses, earth's rotation
            -Winds -- caused by sun
            -Coriolis Effect (not a force)
                -due to earth's rotation on its axis
                -spin imparts a deflection to the water
 
               -causes huge circular current patterns called gyres

    -How do currents affect the deeper water column?
        -Ekman spirals
            -wind energy is passed through the water column
                -friction dissipates energy
                -Coriolis effect deflects each layer with respect to the layer above it
                -limit of the spiral is generally ~100 m

        -Currents may also cause vertical motion when they interact with land masses
            -If water is blown offshore (due to winds or Coriolis effects), then you can get upwelling
                -deep water replaces the surface waters that were pushed offshore
                -consequences for organisms (nutrients, temperature)
            -Upwelling at equator

        -Water also can sink if it increases in density:
                (1) can get more salty –
                    -evaporation
                    -freezing of ice
                (2) can get colder – at the poles
                    North Atlantic deep water

            -causes deep global water circulation patterns - thermohaline circulation
                -refreshes oxygen in deep waters
                -replenishes nutrients in surface waters
                -hundreds of years are required for circulation of these major water masses throughout the oceans
 

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