Ocean Chemistry

1
Ocean Chemistry

• Unit 5

2
Ocean Chemistry

• The chemical properties of the ocean are
  important to understand because the marine
  environment supports the greatest abundance of
  life on earth.
• This life is largely made up of the same
  chemicals that comprise the oceanwater and
  salts.

3
Reflection

• 1. Why is it important to understand the
  chemistry of the ocean?
• 2. What is the chemical make-up of the life in
  the oceans? What is it similar to?

4
Properties of Water

• H20 is a compound of 2 hydrogen atoms
• and one oxygen atom in a fixed proportion.
• Held together by covalent bonds
• (sharing of e-)
• Molecular shape is bent into a 105 angle
• Electrically unbalanced because of the angle and
  thus considered polar because of the () and (-)
  end
• H bonds form between water molecules and other
  charged substances due to the polarity.
• This allows water to stick to itself, a process
  known as cohesion
• Adhesion is when water H bonds to other materials
• Universal solvent it will dissolve almost
  anything

5
Reflection

• 3. What makes up a water molecule?
• 4. How is it bonded? Give details.
• 5. Discuss the polarity of water.
• 6. Write about its adhesive, cohesive and solvent
  properties.

6
Seawater

• NaCl dissolves in water because of its polarity
• 97.2 of Earths surface water is marine
• Seawater is 96.5 water and 3.5 dissolved
  substances (mostly salts)
• Earth has 5.5 trillion tons of salt
• Nearly every element found in the crust and
  atmosphere is also present in the ocean
• Major constituents of seawater
• H, O, Cl, Na, Mg, Ca, K, SO43-, and HCO3-
• Elements lt1 ppm are called trace elements

7
Reflection

• 7. Use the previous slide to describe marine
  water (saltwater) in detail. Include in your
  description all of the properties and composition
  that is given.

8
Sources of Ocean Salts

• Weathering
• running water dissolves crustal rock
• Excess volatiles
• hydrothermal vents (underwater volcanoes) on the
  ocean floor leak chemicals (C02,Cl, S, H, F, N)
  into the water

9
Chemical Equilibrium

• The ocean is in chemical equilibrium
• For the most part, ions are added to the ocean at
  the same rate they are subtracted
• Certain ions have longer residency times then
  others
• Addition of salts from the mantle and weathering
  are balanced by the subtraction of minerals bound
  into sediments

10
Reflection

• 8. Where do the salts and other minerals in the
  ocean come from?
• 9. What is meant by equilibrium? How does the
  ocean maintain equilibrium?

11
Water and Heat

• Heat is energy produced by random vibrations of
  atoms or molecules.
• Four sources of heat in the ocean
• solar energy
• radioactive decay
• heat from Earth formation
• artificial heat from humans
• Temperature is an objects response to input or
  removal of heat.
• 1C 1.8F
• OC is freezing
• 100C is boiling
• About 1m (3.3 ft) evaporates from the surface of
  the ocean every year.

12
Reflection

• 10. Define heat.
• 11. What are four sources of heat in the ocean?
• 12. Define temperature and note the freezing and
  boiling points for water.
• 13. How much water evaporates from the ocean each
  year?

13
Colligative Properties of Seawater

• Heat Capacity
• heat required to raise 1 g of substance 1C
• Heat capacity of water is among the highest of
  all known substances.
• Water can absorb (or release) large amounts of
  heat with little change in temp.
• The heat capacity of seawater decreases with
  increasing salinity (saltwater is less able to
  hang on to heat)

14
Colligative Properties of Seawater

• Salinity
• total quantity of dissolved inorganic solids in
  water (NOT just salt!)
• Salinity is usually 3.3-3.7 depending on
  evaporation, precipitation, and freshwater runoff
• Proportion of Cl to salinity is constant
• Salinity in 1.81 x Cl
• As salinity increases, freezing point decreases
• Gives seawater a natural antifreeze property
  (saltwater freezes at a lower temp than fw)
• Salt water evaporates more slowly than fw (salt
  hangs onto water)

15
Colligative Properties of Seawater

• Osmotic Pressure
• O.P. of organisms increases with increasing
  salinity (organisms lose more water when salinity
  is higher)

16
Reflection

• 14. What are the 3 given colligative properties
  of seawater?
• 15. Describe, in detail, the heat capacity of
  water.
• 16. Describe, in detail, the salinity of sea
  water.
• 17. How is the osmotic pressure of organisms
  affected by salinity?

17
Water Density

• Density of water is a function of salinity and
  temperature.
• Seawater density increases with increasing
  salinity, increasing pressure, and decreasing
  temperature.

18
Water Density

• Freezing Density
• During the transition from liquid to solid, water
  expands
• This makes ice less dense than liquid water, and
  thus floats.
• Density of ice is .917 g/cm3
• Density of liquid water is .999 g/cm3.
• Density of water increases as seawater freezes.
• Ice crystals are pure water because they exclude
  the salt.
• The left over cold, salty water is very dense.

19
Water Density

• Ocean Layers
• The ocean layers by density stratification.
• Surface (mixing) zone
• 2
• least dense zone
• Top of the sea can actually be fw
• Pycnocline
• 18
• density increases with depth
• Deep zone
• 80
• below 1000m, densest layer

20
Reflection

• 18. How does salinity and temperature affect the
  density of the ocean?
• 19. Describe in detail, the relationship of
  freezing temperatures and water.
• 20. Describe the result of density stratification
  and the three layers of the ocean associated with
  it.

21
Pycnocline

• Thermocline Halocline Pycnocline
• Halocline - the area where the salinity changes
  rapidly.
• Thermocline - the layer that changes in temp
  rapidly.
• Can range in temp from 30.5-37.5F
• Average temp of ocean being 38F.
• Water masses (having characteristic temp and
  salinity, density) get trapped at great depths.
• The pycnocline isolates 80 of the ocean from the
  20 circulating on the surface.

22
Reflection

• 21. What are the two layers that make up the
  pycnocline?
• 22. What is special about each of these two
  layers?
• 23. How does the pycnocline isolate 80 of the
  water in the ocean?

23
Dissolved Gases

• Gases dissolve most readily in cold seawater
• Plants and animals in the ocean require dissolved
  gases in order to survive
• Nitrogen
• 48 of gas in ocean (atmosphere 78)
• living organisms require N to build proteins, but
  bottom dwelling bacteria must fix the N into a
  useable form for them
• Oxygen
• 36 of gas in ocean (atmosphere has 100x more)
• Primary source of O2 in ocean is from plants
• most of the oxygen is near the surface and
  diffuses into the atmosphere
• Carbon dioxide
• 15 of gas in ocean (60x more in ocean than
  atmosphere)
• used by phytoplankton- low at surface

24
Reflection

• 24. Where does gas most readily diffuse in the
  ocean?
• 25. What are three major gasses found in the
  ocean? In what quantity is each found? How are
  they each used in the ocean?

25
pH

• Acidity (release of H) and alkalinity (release
  of OH-) is measured by pH
• The ocean contains buffers to prevent large
  swings in pH when acids or bases are introduced
• pH scale
• 0-----------------------------7------------------
  ----------14
• acid neutral base
• (alkaline)

Pure water
Seawater 7.8
26
Reflection

• 26. Explain how pH works and in specific, the pH
  of the ocean.
• The End