Abiotic Factors Controlling Marine Organisms, Part II

I. Thermohaline circulation
    A. Gradients caused by differences in density of the water masses generate slow currents
         -sinking of cold and dense water produced in the high latitudes

    B. Well defined water masses are identifiable in the water column
    C. "Great Ocean Conveyor"

II. ENSO – El Niño/Southern Oscillation (not in book, so more detail here)
    A. Normal conditions
        1. trade winds blow from east to west across Pacific
        2. sea surface level
        3. sea surface temperature is 8o C higher in the W. Pacific than in the E.
        4. upwelling off the coast of S. America
            a. nutrient rich water
            b. high production, diverse ecosystems, major fisheries
    B. El Niño conditions
        1. originally recognized and named by fisherman off the coast of South America
        2. appearance of unusually warm water in the Pacific ocean off the coast of S. America; El Niño conditions often begin to occur in Dec./Jan.

        3. upwelling is stopped
        4. fish and bird populations are disrupted
        5.disruption of ocean-atmosphere system in the tropical Pacific that affects weather around the globe -- due
            to the 'Southern Oscillation' (Gilbert Walker in 1928) -- an inter-annual switch in tropical sea level pressure
            between W and E Pacific

        6. 1957 - large El Niño; scientists first realized that El Niño affects not only Peru and Ecuador on the S. American coast,
            but the entire Pacific Ocean and is tied to the Southern Oscillation.

        7. El Niño occurs when there is a large scale weakening of the trade winds -- warming of
            the surface layers in the eastern and central equatorial Pacific Ocean.  Thermocline increases in depth in the eastern Pacific and is closer
            to the surface in the West.
        8. Rain follows the warm water eastward, leading to flooding in Peru and drought in Indonesia and Australia.
        9. El Niños occur irregularly at intervals of 2-7 years (average 3-4 years) and last 12-18 months (typically)
        10. Severe El Niños have recently resulted in a few thousand deaths worldwide (mudslides, floods, droughts-fires), left thousands of
            people homeless, and caused billions of $ worth of damage. 
        11. Changes the distribution of organisms in the ocean -- anchovy, warm water species
 
        12. Some positives as well as negatives
                rain in Chile and SW US -- may be vital for desert ecosystems
                heavy snowfall increased tourism in the West
                mild winter in much of N. US and Europe -- saved heating dollars

    C. La Niña -- other extreme of the ENSO cycle where sea surface temperatures in the tropical Pacific drop below normal.  Also has
            global consequences (currently developing La Niña)
    D. ENSO is illustrative of the major effects of ocean circulation on ocean systems and global climate

III. Tides (see textbook pp. 267-270 for more information)
    A. Definition -- predictable rise and fall of sea level
    B. Important for organisms; especially in intertidal zone
    C. Balance of gravitational and centripetal forces controlled by:
        1. positions of moon and earth
        2. earth's tilt (23.5 degrees from vertical)
        3. moon's elliptical orbit -- sometimes closer to earth than others
        4. full tidal cycle is 24 hours and 50 minutes
    D. Spring tides versus neap tides
        1. spring -- greatest range (height of tides); moon and sun are directly aligned with earth
        2. neap -- minimum range; moon and sun at right angles relative to earth
    E. Semidiurnal, diurnal and mixed tides
        1. semidiurnal
        2. diurnal
        3. mixed
    F. Bay of Fundy (Nova Scotia); Cook Inlet (Alaska); geometry of basin contributes to huge tides 

IV. Properties of Water
    A. H2O
    B. Polar molecule
    C. Hydrogen bonds
 
    D. Only substance on earth that naturally occurs in all three states (solid, liquid, gas)
    E. Special properties of water
        1. cohesion --
            a. water 'sticks to itself'
            b. cohesion causes there to be surface tension
                i. highest surface tension of all common liquids
                ii. specialized organisms live on ocean surface or suspended below it
            c. cohesion also influences the viscosity of water
                i. viscosity affected by temperature -- increases as it gets colder
                ii. viscosity affected by salinity -- increases as it gets more saline
                iii. important in sinking rates of organisms
                iv. important in movement of organisms -- for very small organisms, life in water is like living in Karo Syrup
        2. heat of vaporization/evaporation
           

        3. latent heat of fusion/melting
            

        4. heat capacity
            a. quantity of heat needed to raise the temp. of 1 g of substance 1 degree C
            b. highest of all common solids and liquids
            c. temperature buffer for organisms --
              
        5. density-temperature relationship - ice
           
        6. Excellent solvent ('universal solvent')

V. Chemical composition of seawater

    1. salinity
        a. total amount of dissolved material in water
        b. 1,000 g of average seawater contains ~35 g of dissolved salts (96.5% water; 3.5% dissolved substances)
        c. units - parts per thousand (o/oo)  or practical salinity units (psu)
        d. away from coastal areas, salinity varies within a narrow range 34-37 psu
        e. near shore salinity can be more variable

        f. salinity is determined by a balance of precipitation (rain and snow; and river input from precipitation on land), evaporation and
           freezing
        g. salinity strongly affects what organisms are in seawater

    2. what are the dissolved substances?
        a. inorganic salts
        b. organic compounds (originally from organisms)
        c. dissolved gases
    3. source of dissolved solids
        a. chemical weathering of rocks on land, carried to sea by runoff & rivers (e.g., Na, Mg)
        b. earth's interior; released through hydrothermal vents (e.g., Cl, S)
        c. atmosphere (volcanoes, other sources) -- enter in rain or snow
    4. The inorganic salts
        a. major ions -- 99.28% of the solid matter in seawater
               ION                     % by weight
            i. chloride (Cl-)                  55.04%
            ii. sodium (Na+)                 30.61%
            iii. sulfate (SO42-)               7.68%
            iv. magnesium (Mg2+)         3.69%
            v. calcium (Ca2+)                1.16%
            vi. potassium (K+)               1.10%

        b. minor ions -- bring total up to 99.99% of the dissolved substances
               bicarbonate (HCO3-), bromide (Br-), boric acid (H3BO3), strontium (Sr2+), fluoride (F-)                       0.003%

        c. ratios among these salt ions remains virtually constant -- rule of constant proportions
 
    5. dissolved gases
        a. oxygen (O2), carbon dioxide (CO2) and nitrogen (N2)
        b. the lower the temperature, the greater the solubility of gases (cold water has more oxygen)
        c. much lower solubilities of gases in water than in air
        d. oxygen profiles
            i. maximum in the upper 10-20 m
                a) photosynthesis by plants releases oxygen
                b) diffusion of oxygen from the atmosphere
            ii. oxygen declines below this -- used by respiration
            iii. oxygen minimum zone -- generally between 200 and 1,000 m in the open ocean

            iv. below this oxygen increases to some extent -- colder water formed at the poles

        e. carbon dioxide
            i. increasing concentrations in atmosphere
            ii. photosynthesis and respiration

            iii. reacts with seawater to form bicarbonate and carbonate ions
                  1.
                  2.
                  3.

            iv. bicarbonate is one of the minor ions -- is relatively abundant
            v. more CO2 stores in the ocean than in on land -- carbon doesn’t generally limit photosynthesis in the ocean
            vi. pH; buffering system
            vii. seawater slightly alkaline due to the bicarbonate buffering system and to sodium, calcium and potassium -- pH typically
                    7.5-8.4 and fairly constant

VI. Nutrient cycling

    A. Carbon Cycle
        1. global increase with fossil fuel burning; global warming
        2. reservoir (pool) in ocean is carbonic acid-bicarbonate-carbonate system
        3. taken up by photosynthetic organisms
        4. these are eaten by animals and decomposed by bacteria; respiration returns carbon dioxide to the water
        5. one carbon sink (loss) is inorganic minerals -- e.g., calcium carbonate, CaCO3 (example in shells)

    B. Phosphorus Cycle
        1. Phosphorus rock on land is the major reservoir
        2. Erosion/weathering brings it to water
        3. Plants/phytoplankton take it up
        4. Returned by decomposition
        5. Lost when dead organisms sink to the bottom and are buried

    C. Nitrogen Cycle
        1. Air is the major reservoir
        2. Only a few organisms can take up atmospheric N (N fixing bacteria and algae)
        3. Useful N is also produced by volcanoes
        4. Taken up by organisms
        5. Released by decomposition
        6. Some loss to burial in sediments

VII. Light in Water
    A. transparency of water is vital -- photosynthesis and temperature
    B. sunlight contains all of the colors of the spectrum (rainbow), but not all colors penetrate equally well
    C. open ocean is most transparent to blue light
    D. red light penetrates least

    E. eventually all light is absorbed by the water and there is total darkness
    F. near the coasts lots of sediment may be brought in from rivers that reduces the light penetration
    G. this suspended material near shore can give the coastal waters a greenish tint
   
 

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