1. Chemical & Physical Properties of SeaWater
Ocean Water
Chemical & Physical Properties of SeaWater

2. Origins Two hypotheses: Icy comets bombarding Earth (~4 BYA)
Outgassing of water vapor from volcanoes + atmospheric condensation
Evidence exists to support both hypotheses

3. Properties of SeaWater
1) Components
Water
Dissolved matter: solids and gas
Suspended matter
2) Properties:
Cohesion: high surface tension
Adhesion: water "sticks" to things
High capillary action:
Powerful solvent
Polar substance
pH is about 8.1, where 1 is acidic and 14 is basic and 7 is neutral
Carbonate buffering keeps pH stable by precipitation (increase pH) or dissolution (decrease pH) of calcium carbonate CaCO3

4. Composition of SeaWater
Seawater consists of about 3.5% (by
weight) dissolved minerals
Salinity:
Total amount of solid material dissolved inwater
Typically expressed in parts-per-thousand (‰)
Average salinity is 35‰ (Open Oceans range ‰)
Major constituent is sodium chloride
Salinity = Weight (mass) of salt
Weight (mass) of water

5. Constituents of SeaWater

6. Ions in SeaWater Major Na, Mg, Ca, K, Cl, SO4 Minor Fe, S, I, F
Trace: almost everything!
 Sources: chemical weathering of rock & outgassing
Measured by electrical conductance or density

7. Processes Effecting Salinity
Variations in salinity are a consequence of changes in the water content of the solution
Processes that decrease salinity (add water)
• Precipitation
• Runoff from land
• Icebergs melting
• Sea ice melting
• Processes that increase salinity (remove water)
• Evaporation
• Formation of sea ice

8. Residence time and steady state

9. Residence time for dissolved substances
(salts, ions, element,..etc)
Average length of time a substance remains
dissolved in seawater = residence time
Ions with long residence time are in high
concentration in seawater
Ions with short residence time are in low
Steady state condition means…
Inputs balance outputs….the concentration
remains constant

10. A Closer Look at pH
The dissolved ions regulate the ocean acidity and alkalinity
Acid releases H+ when dissolved in water
Alkaline (or base) releases OH-
pH scale measures acidity/alkalinity

11. Carbonate-carbonic acid buffering system
CO2 dissolves in water to make carbonic acid (just carbonic acid alone would make the pH go down)
The ocean is loaded with calcium carbonate (just calcium
carbonate alone would make the pH go up)
Calcium carbonate neutralizes acid, carbonic acid neutralizes base
If acid is added, it dissolves calcium carbonate and the pH is stabilized
If base is added, it is neutralized by carbonic acid so the pH stabilized
pH of ocean is constant at 8.1

12. Oceans depend on carbonate buffering to keep their pH Constant
Feedback between CO2,
Carbonic acid, and calcium
Carbonate (CaCO3)

13. Carbonate buffering Keeps ocean pH about same (8.1)
pH too high, carbonic acid releases H+
pH too low, bicarbonate combines with H+
Precipitation/dissolution of calcium carbonate CaCO3 buffers ocean pH
Oceans can absorb CO2 from atmosphere without much change in pH

14. Physical Properties of SeaWater
Ocean Temperature:
Surface water temperature varies with the amount of solar radiation received
• Lower surface temperatures are found in high-latitude regions
• Higher temperatures found in low-latitude regions

15. Temperature variation with depth
• Low-latitudes:
• High temperature at the surface
• Rapid decrease in temperature with
depth (thermocline)
• High-latitudes:
• Cooler surface temperatures
• No rapid change in temperature with depth

16. Ocean Density
Density is mass per unit volume – how heavy something is for its size
Determines the water’s vertical position in the ocean
Factors affecting seawater density
• Salinity
• Temperature - the greatest influence

17. Variations with depth:
• Low-latitudes
• Low density at the surface
• Density increases rapidly with depth
(pycnocline) because of colder water
• High-latitudes
• High-density (cold) water at the surface
• Little change in density with depth

18. Ocean Layering Layered according to density • Three-layered structure:
• Surface mixed zone
• Sun-warmed zone • Zone of mixing
• Shallow (300 meters)
• Transition zone (Between surface layer and deep zone)
• Thermocline and pycnocline
• Deep zone
• Sunlight never reaches this zone
• Temperatures are just a few degrees above freezing
• Constant high-density water

19. Ocean Layers