CHAPTER 5 Water and Seawater

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CHAPTER 5 Water and Seawater
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• Types of Bonding
• Water Molecule Formation Configuration
• Unusual Properties
• Hydrogen Bonding
• Heat Capacity
• Phases of Water
• Adding Salts to Water
• Constituents of Seawater
• Sampling Devices
• Effects of Density and Salinity
• Hydrologic Cycle
• Composition of River Water
• Residence Times
• Dissolved Gases
• pH of Seawater

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Covalent Bonding
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Ionic Bonding
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WATERS UNUSUAL PROPERTIES
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Hydrogen bonding
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• Polarity means small negative charge at O end
• Small positive charge at H end
• Attraction between and ends of water
  molecules to each other or other ions

Fig. 5.3
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Hydrogen bonding
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• Hydrogen bonds are weaker than covalent bonds but
  still strong enough to result in
• High surface tension
• High solubility of chemical compounds in water
• Solid, liquid, gas at Earths surface
• Unusual thermal properties
• Unusual density

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Surface tension
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CALORIE
the amount of energy required to raise the
temperature of 1 gm of water 1 degree Centigrade
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HEAT CAPACITY (SPECIFIC HEAT)
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• The amount of energy required to raise the
  temperature of 1 gm of a substance 1 degree
  Centigrade

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Granite 0.19
Quartz 0.19
Soil (average) 0.70

(liquid)

0.5
(ice)
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What does this mean?

• If we had 3 cookie sheets each 1 cm deep
• One filled with water, one with soil and
  one with sand
• The same amount of incoming energy that would
  heat the water 1oC, would heat the soil 1.4oC
  and the sand 5oC

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Unusual thermal properties of H2O
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• Water - high heat capacity
• Amount of heat required to raise the temperature
  of 1 gram of any substance 1o C
• Water can take in/lose lots of heat without
  changing temperature very much
• Rocks - low heat capacity
• Rocks quickly change temperature as they
  gain/lose heat

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Day/Night Temperature Differences Large on land,
small in the ocean
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Global thermostatic effects
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• Moderate temperature on Earths surface
• Equatorial oceans (hot) dont boil
• Polar oceans (cold) dont freeze solid
• Marine effect
• Oceans moderate temperature changes day/night
  different seasons
• Continental effect
• Land areas have greater range of temperatures
  day/night and during different seasons

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Unusual thermal properties of H2O

• H2O has high boiling point
• H2O has high freezing point
• Most H2O is in the form of water (liquid) on
  Earths surface (good for life)
• High latent (hidden) heats of
• Vaporization/condensation
• Melting/freezing
• Evaporation

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Specific Heat 1.0 calories/ gm
Specific Heat 0.5 calories/gm
Fig. 5.6
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Water molecules in different states of matter
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Fig. 5.5
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Show water phase animation
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Changes of state due to adding or subtracting heat
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• Heat is energy of moving molecules
• Temperature is measurement of average kinetic
  energy

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Elements within columns share similar properties
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Ionic bonding, loosely held together
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Dipolar water molecules break ionic bonds
by surrounding sodium and chloride ions
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CONSTITUENTS OF SEAWATER
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Salinity
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• Total amount of solid material dissolved in water
• Typical salinity is 3.5 or 35o/oo
• Six elements make up 99 of dissolved solids in
  seawater

Fig. 5.12
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SALINITY UNITS
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• PERCENT OR PARTS PER HUNDRED (PPH)
• Since open ocean salinity varies from 3.3-3.7,
  we move the decimal one place to the right and
  express it as 0/00 OT PARTS PER THOUSAND (PPT)
• 3.3-3.7 BECOMES 33-37 o/oo

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Measuring salinity
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• Evaporation
• Chemical analysis
• Principle of constant proportions
• Major dissolved constituents in same proportion
  regardless of total salinity
• Measure amount of chlorine (chlorinity)
• Electrical conductivity
• Salinometer
• CTD

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Salinity variations
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• Open ocean salinity 33 to 38 o/oo
• Coastal areas salinity varies more widely
• Influx of freshwater lowers salinity or creates
  brackish conditions
• Greater rate of evaporation raises salinity or
  creates hypersaline conditions
• Salinity may vary with seasons (dry/rain)

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gt 100 ppm
gt1, lt100 ppm
lt 1 ppm
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Forchammers Principle
Although the salinity of seawater may change from
place to place, the ratio of ions to each other
remains constant
Importance You only need to measure one ion to
calculate the concentration of others - this can
be the cheapest or easiest one to measure
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How to change salinity
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• Add water
• Remove water
• Add dissolved substances
• Remove dissolved substances

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Processes that add/subtract water from oceans
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Salinity increases through
Salinity decreases through

• Precipitation (rain or snow)
• Runoff (river flow)
• Melting icebergs
• Melting sea ice

• Evaporation
• Formation of sea ice

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Nansen bottle
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Water-sampling bottles
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Salinity is most commonly measured by
electrical conductivity
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Density of water
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• Density of water increases as temperature
  decreases down to 4oC
• From 4oC to 0oC density of water decreases as
  temperature decreases
• Density of ice is less than density of water

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Density of water
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Fig. 5.10
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