| 1. The Gases: |
| Learning Objectives: |
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Understanding of gas dissolution in the ocean and their role in sustaining
life
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Nature of oceanographic controls on gas concentrations
|
| Dissolved Gases in Seawater: |
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Gases dissolve and exsolve at air-water interface
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Water becomes saturated with atmospheric gases
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gases present in equilibrium concentrations
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Important gases are N2, CO2 and
O2
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saturation is affected by temperature, salinity and pressure.
|
| Influences on Distribution of Gases with Depth: |
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Plant photosynthesis:
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uses CO2 and produces O2 and
organic matter
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it requires light and therefore occurs in surface waters
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Respiration is the reverse process:
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use of O2 and organics to produce CO2.
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also decomposition uses O2
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respiration occurs throughout water column
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Compensation depth where rate of production = rate of respiration
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No dissolved O2 waters become anoxic
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support anaerobic organisms
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Supersaturation from high productivity (abundant plant populations)
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Partial removal creates mid-water O2 minimum.
|
| CO2 Effects, Oxygen and Measurements: |
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CO2 as a Buffer:
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CO2 + H2O yields H2CO3
(carbonic acid)
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H2CO3 forms H+
+ HCO3-
(bicarbonate)
-
HCO3- forms H+
+ CO32- (carbonate)
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dissolved CO2 buffers seawater.
-
pH, a scale measuring the abundance of H+
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neutral, pH = 7
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acidity ranges down to pH = 0
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alkalinity up to pH = 14
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seawater pH = 7.5 - 8.5, ave. 7.8
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CO2 cycle:
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biological pump contributes CO2 to deep ocean as organic
matter
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calcareous organisms sink
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Oxygen balance:
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excess O2 (production > consumption) released to atmosphere
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used in weathering and oxidation processes on land
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Measuring gases:
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by specialized probes (O2) or determined from pH (CO2).
|
| 3. Other Substances, Practical Considerations: |
| Learning Objectives: |
-
Recognition of roles of components of seawater in life processes
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Understanding of viable methods foe desalination of seawater
|
| Components of Seawater and Desalination: |
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Nutrients:
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nitrate (NO3-) and phosphate (PO43-)
ions required by all organisms
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silicate (SiO4-) needed by siliceous organisms
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ions removed from seawater during growth, recycled by decay.
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non-conservative: concentrations vary greatly
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Organics:
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Proteins, carbohydrates, lipids, etc.
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Chemical resources:
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salt from seawater, also Mg and Br
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Desalination (fresh water from salt water):
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freezing or evaporation (salts remain in solution)
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ion exchange (removes ions)
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electrodialysis
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reverse osmosis (semi-permeable membrane excludes salts)
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reverse osmosis uses pressure to force water through the membrane.
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