1. Ocean Chemistry
Unit 5

2. Focus 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?

3. 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 ocean—water and salts.

4. Focus 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.

5. 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

6. Focus
7. Describe marine water (saltwater) in detail. Include in your description all of the properties and composition that are given.

7. Seawater NaCl dissolves in water because of it’s polarity
97.2% of Earth’s 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 <1 ppm are called trace elements

8. Focus 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?

9. Sources of Ocean Salts Weathering Excess volatiles
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

10. 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

11. Focus 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?

12. 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 object’s response to input or removal of heat.
1°C = 1.8°F
O°C is freezing
100°C is boiling
About 1m (3.3 ft) evaporates from the surface of the ocean every year.

13. Focus 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?

14. Colligative Properties of Seawater
Heat Capacity
heat required to raise 1 g of substance 1°C
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)

15. Colligative Properties of Seawater
Salinity
total quantity of dissolved inorganic solids in water (NOT just salt!)
Salinity is usually % 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)

16. Colligative Properties of Seawater
Osmotic Pressure
O.P. of organisms increases with increasing salinity (organisms lose more water when salinity is higher)

17. Focus
18. How do 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.

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

19. 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.

20. 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

21. Focus 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?

22. 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 °F
Average temp of ocean being 38°F.
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.

23. Focus 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?

24. 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 marine plants- low at surface

25. Focus
26. Explain how pH works and in specific, the pH of the ocean.

26. 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
acid neutral base
(alkaline)
Pure water
Seawater 7.8

27. Focus
27. What equipment is used to measure salinity as specific depths?
28. What equipment is used to measure salinity by the degree of light that is bent?
29. What equipment is used to measure pH of the ocean?
31. What equipment is used to measure heat capacity?
32. What equipment is used to measure osmotic pressure?

28. Equipment Hydrometer Calorimeter pH meter/probe Osmometer
ratio of the density of the liquid to the density of water
Calorimeter
measures heat capacity
pH meter/probe
Measures pH
Osmometer
measures osmotic pressure
Nansen bottle
salinity measured at different depths
bottle is sent down upside down on a string, flipped open at a desired depth, and a sample of water is taken
Salinometer
electronic electricity conductor
Refractometer
measures salinity by the degree the light is bent