Topic 9 Salt Water

1
Topic 9 Salt Water

• GEOL 2503
• Introduction to Oceanography

2
What is in seawater?

• Hydrogen Oxygen make up only 96.5
• Not 100 as in pure water
• In 1,000 grams of seawater
• 965 grams water
• 35 grams salt

3
Salinity

• Salt content of water is called salinity
• Measured in units of
• grams salt per kilogram of seawater (g/kg)
• parts per thousand ()
• A typical open ocean salinity is around 35 or 35
  g/kg

4
Major Constituents(not just salt, which is NaCl)

• Sodium (Na) Chlorine (Cl) 86
• Sulfur (S)
• Magnesium (Mg)
• Calcium (Ca)
• Potassium (K)
• Bring total to 99.36
• Everything elsetrace elements

5
(No Transcript)
6
Major Constituents
7
Table Salt

• Table salt is sodium and chlorine
• Each salt molecule Na Cl- (ions)
• Water forms spheres around ions
• Salt ions are surrounded and separated by water
  molecules
• Sodium Chloride is the chemical name
• Halite is the mineral name

8
Atoms arranged in a crystal lattice (framework)
9
NaCl molecule dissociates in water into
individual atoms of Na and Cl-
10
Dissolving Ability of Water

• Substances dissolved from land are carried to sea
  by rivers, streams, underground water
• Supply salt to oceans
• That is why oceans are salty

11
But why arent oceans getting saltier?

• Salt Inputs
• Volcanoes
• Rivers
• Rainfall
• Hydrothermal vents

• Salt Outputs
• Seaspray
• Bottom sediments
• Biologic processes
• Adsorption
• Chemical precipitation

12
Principle of Constant Proportions

• William Dittmar analyzed the 77 water samples
  from the Challenger Expedition
• He found that, regardless of the actual salinity,
  the ratios of the major constituents remained
  constant
• Applies to major constituents in open-ocean water
  only

13
Determining Salinity

• Salinometer
• Measures electrical conductivity, which reflects
  dissolved material

14
Gases in Seawater
Numbers are percents of total gases
15
Dissolving Gases in Water

• Cold water holds more gases than warm
• Water under pressure holds more gases than water
  under less pressure

16
Oxygen

• Produced by plants (photosynthesis)
• Plants only live in upper 100 meters (more or
  less) of ocean
• Also mixed into ocean from atmosphere at surface
• Used by animals and plants at night for
  respiration, and in decomposition

17
Carbon Dioxide (CO2)

• Used by plants in photosynthesis
• Produced by respiration and decomposition
• Also enters oceans from atmosphere at surface,
  but produced and available at all depths

18
(No Transcript)
19
Oxygen Concentrations

• Surfacehigh concentration because of
  photosynthesis plus mixing from atmosphere
• Below surface layerconcentration decreases
  because of respiration and decomposition
• Oxygen minimum layeraround 800 meters

20
Why does Oxygen increase below 800 meters?
21
Why does Oxygen increase below 800 meters?

• Oxygen falls from the surface layer in sinking
  water
• Rate of removal decreases because there are fewer
  animals, less matter to decompose

22
Carbon Dioxide Concentrations

• Opposite of Oxygen
• Low in surfaceused in photosynthesis
• Increases throughout the rest of the water
  columnanimal respiration and decomposition

23
Salt as a Resource

• 30 of worlds salt is extracted from seawater
  (here we mean NaCl)
• Primarily in evaporating ponds in warm, dry
  climates
• Southern France, Puerto Rico, Mexico, California

24
Desalinization

• Any of several methods of obtaining fresh water
  from salt water

25
Why Desalinate?

• There is no absolute shortage of fresh water in
  terms of overall supply, but mostly its not
  where the people are. Why?
• Distributionnot where we need it
• Mismanagementpollution, unwise use
• Population increasemore users
• Increased usageper person per day

26
Solar Still

• Simplest method of desalinization
• Use Suns energy to evaporate water
• Evaporated water is fresh
• Trap water on plastic dome cap
• Water condenses, rolls along cap to collectors
• Slow production

27
(No Transcript)
28
Osmosis

• Water molecules move across a semipermeable
  membrane from region of high concentration of
  water to region of low concentration
  (gradient-driven)
• Well see this again in biological oceanography
• Creates pressure

29
Reverse Osmosis

• We supply the pressure
• Force salt water through a semi-permeable
  membrane
• Dissolved substances cant pass
• Fresh water is produced

30
(No Transcript)
31
(No Transcript)
32
(No Transcript)