1. Physical Oceanography Section 2: Seawater
Chapter 15
Physical Oceanography
Section 2: Seawater

2. Chapter Objectives
I will:
Compare and contrast the physical and chemical properties of seawater.
Explain ocean layering.
Describe the formation of deep water masses.

3. Seawater is a solution Solution is a homogeneous mixture 96.5% water
3.5% dissolved salts.
Most abundant salt is (NaCl)
Other salts: elements
chlorides & sulfates of magnesium
Potassium
Calcium

4. Salinity Measure of the amount of dissolved salts in seawater.
Expressed in grams of salt per kilogram of water or parts per thousand (ppt)
Total salt in seawater: avg 35 ppt or 3.5%

5. Seawater composition
Salt Ions (ion is an atom that gains or loses an electron)
Dissolved gases (oxygen, nitrogen, carbon dioxide
Dissolved nutrients (nitrates, phosphates, silicates)
These nutrients
and gases greatly
affect life in the
oceans.

6. Major Ions in Seawater

7. Variations in Salinity
High salinity- areas with high rates of evaporation.
Low salinity – areas where rivers empty into oceans.

8. Sources of Sea Salt
Salinity of ancient seas not much different than today.
Magnesium in calcium-carbonate shells of marine organisms.
Volcanoes- water vapor, gases (chlorine and sulfur dioxide)
Weathering of Feldspar - Na, Ca, K
Weathering of mineral and rocks - Fe, Mg
These ions are flushed into rivers and
transported in the oceans!

9. Removal of Sea Salts
Salinity does not increase although salt ions continuously are added to seawater.
WHY? Salts are removed at same rate as added
Process to remove salts:
Precipitate – forms deposits
Marine Organisms- to
build their shells, bones,
teeth.
Organism die – solid parts
drift to the ocean floor

10. Remember the water cycle?

11. Physical Properties of Seawater
Density - Salt ions are heavier than water molecules
Temperature
Salinity
Absorption of Light

12. Seawater vs. Freshwater
More denser
Density 1.02 g/cm3 to 1.03 g/cm3
This density affects oceanic processes
Freezing point -20C
FRESHWATER:
Less denser
Max density 1.oo g/cm3
Freezing point 00C
Calculation:
d= m/V

13. Absorption of Light Water absorbs light
Light penetrates only upper 100m of seawater
Below is darkness
Photosynthesis exists top 100m

14. Ocean Layers – caused by density differences
Warm, sunlit
Rapid temp. decrease
Cold, dark, freezing temps.

15. Where does all the cold water come from?
Polar seas
Cold temp. causes seawater to become more dense
Seawater freezes, sea ice forms
Salt ions form beneath the ice
Saltwater sinks, it migrates toward equator as cold, deep water mass

16. Deep Water Masses
Antarctic Bottom Water – forms when sea freezes – below 00C
North Atlantic Deep Water –forms off the shore of Greenland
Antarctic Intermediate Water -least dense

17. End of Section 2