Sea Water Chemistry

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Sea Water Chemistry

• Chapter 7

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Major Ions in Typical Seawater

• Ion Parts per thousand by weight (ppt)(Table
  7.1)
• Cl- 18.98
• SO4-2 2.649
• HCO3- 0.140
• Na 10.556
• Mg2 1.272
• Ca 0.400
• K 0.380

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• On average, concentration of dissolved salts,
  i.e., the salinity, in seawater is 3.5 or 35.
• The relative abundances of the ions listed above
  does not change, even though salinity does are
  said to be conservative.
• Relative abundances of minor and trace
  constituents do vary

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Determining Salinity

• Evaporation of water to weight the salt is an
  imprecise method
• Because of the constancy of composition if we
  measure one component we can get a more precise
  measurement
• Salinity ppt 1.80655 x Chlorinity in ppt
• If chlorinity is 19.2 ppt, what is the salinity
  of sea water?
• 34.7 ppt 35 ppt

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• Density - mass per unit volume (grams/cm3)
• density of water phases (ice, liquid, vapor) due
  to structural changes at molecular level
• density maximum at 4C in pure water
• Major role in deep ocean circulation and water
  column structure and stability

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Water Density

• Influenced by three factors
• Salinity - proportional
• Pressure - proportional
• Temperature inversely proportional

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Ocean Structure

• Upper 100-500 m to have uniform temperature and
  salinity because of mixing by waves.(6.13)
• Below this, to a depth of 1000 m, Temp.,
  Salinity, and density change ( Thermocline,
  Halocline, Pycnocline) (6.12)

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• In deep water, temperature, salinity and density
  are relatively uniform
• This structure varies latitudinally. At
  mid-latitudes, it also varies seasonally upper
  mixed layer will deepen in summer
• thermocline might largely disappear in winter

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