Salinity is the total amount of dissolved salts in water; grams of salts per kilogram of water (g/kg) or as parts per thousand (ppt).

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Salinity

• Salinity is the total amount of dissolved salts
  in water grams of salts per kilogram of water
  (g/kg) or as parts per thousand (ppt).
• Seawater has 11 major constituents that make up
  more than 99.99 of all dissolved materials.
• Although salinity may vary, the major
  constituents are well mixed and present in the
  same relative proportions.

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Major Constituents of Seawater ( by weight)

• Chloride (Cl-) 55.07
• Sodium (Na) 30.62
• Sulfate (SO42-) 7.72
• Magnesium (Mg 2) 3.68
• Calcium (Ca 2) 1.17
• Potassium (K) 1.10
• Bicarbonate (HCO3 -) 0.40
• Bromide (Br -) 0.19
• Strontium (Sr 2) 0.02
• Boron (B 3) 0.01
• Fluoride (F-) 0.01

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Why Study Salinity

• Determines the distribution of plants and animals
  that live in the ocean.
• Affects other properties of seawater, such as its
  density and the amount of dissolved oxygen.

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Significant Values

• The average salinity of the worlds oceans is 35
  ppt.
• Freshwater has a salinity of lt1 ppt.
• Inshore waters with salinity values between 1 -
  25 ppt are called brackish.
• Waters with salinity greater than 40 ppt are
  called hypersaline.

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Salinity Hydrometer Method

• Addition of salts to pure water causes an
  increase in density. Salinity can be calculated
  by measuring the specific gravity of a water
  sample using a hydrometer, correcting for the
  effect of temperature and converting the readings
  to salinity by using conversion tables.
• Specific Gravity density of sample
• Density of pure water

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Hydrometer Reading

• Be sure hydrometer is clean
• Fill 500 mL graduated cylinder with sample water
• Determine the temperature of your sample
• Place the hydrometer in cylinder and let settle.
  It should not touch the cylinder walls, and
  should be read from the bottom of the meniscus.
• Read the specific gravity from the hydrometer
  scale
• Using the specific gravity and temperature
  values, determine salinity from salinity table in
  Teachers Guide
• Read three times. The values should be within 2
  ppt of the average. Discard outliers.

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Calibration - Hydrometer Method

• 35 ppt standard
• Measure out 17.5 g NaCl (table salt) and pour
  into a 500-mL graduated cylinder.
• Fill the cylinder to the line with distilled
  water and carefully swirl the solution to mix the
  standard, until all salt crystals have dissolved.
• Pour the solution into a 1-quart plastic bottle
  and label.
• Prepare a blank using 500 ml of distilled water.
• Follow the directions for a water sample.
• Check technique every six months.

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Salinity titration method

• The amount of halogens (chloride, bromide,
  iodine, and fluoride) in the water sample
  (chlorinity) is determined using a silver nitrate
  titration method. The salinity of the sample can
  then be calculated using the following formula
• Salinity (ppt) 1.80655 x Chlorinity (ppt)
• Use a test kit that meet specifications described
  in the Tool Kit in the GLOBE Teachers Guide
• Follow the instructions in the test kit to take
  three measurements. Values should be within the
  precision stated in the test kit specifications.
  Discard outliers and retake measurements.

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Calibration - Titration Method

• Concentration of standard reflect composition of
  seawater.
• 38.6 ppt sea water titration standard
• Measure out 17.5 g NaCl (table salt) and pour
  this into a 500-mL graduated cylinder.
• Fill the cylinder to the line with distilled
  water and carefully swirl the solution to mix the
  standard, until all salt crystals have dissolved.
• Pour the solution into a 1-quart plastic bottle
  and label.
• Follow directions for a water sample.
• Calibrate every six months to check technique.