1. Chemical Oceanography:
Salinity

2. What is Salinity?
A measure of the amount of salt in seawater, measured in parts per thousand (ppt) or (%o).
Seawater has an average salinity of about 35 ppt. or 3.5 %o.

3. Salinity Varies by Latitude and Across the Different Oceans

4. Salts Dissolved in Seawater:
Cations:
Sodium (Na+) – 31% by weight
Magnesium (Mg2+) – 4 % by weight
Calcium (Ca2+) – 1% by weight
Potassium (K+) – 1% by weight
Anions
Chloride (Cl-) – 55% by weight
Sulfate (SO4-) – 8 % by weight

5. That’s a lot of salt!!!
It has been calculated that if all the salts in the oceans of the world were dried up they would yield approximately 4.4 million cubic miles of rock salt. That's enough salt to cover all the landmasses of the world to a depth of 150 feet.

6. Where does the salt come from?
Weathering of Rocks on Land
Volcanic Gases
Circulation at Deep Sea Hyrdothermal Vents

7. Weathering of Rocks
Rain is slightly acidic and dissolves rocks and sediments in a slow process called weathering.
Calcium carbonate is particularly vulnerable to weathering.
Runoff and rivers carry the dissolved minerals from the land to the sea.
Sphinx

8. Volcanic Gases
Volcanoes spew gas rich in chlorine and sulfate from the Earth’s interior.

9. Deep Sea Hydrothermal Vents
Occur along mid-ocean ridges where clouds of mineral-rich superheated water erupt from fissures in the seafloor.
VIDEO CLIP: CLICK TO WATCH

10. Why doesn’t salinity increase with time?
There is a Constant inflow and outflow of water and salts.
Inflow:
Dissolved minerals from the land and fresh rain/runoff
Outflow:
Water evaporation and Sea Spray depositing salt on coastlines

11. Ocean Salt Content

12. Why is the salinity lower at the poles?
Why is the Salinity higher near the Equator?
Salinity can change near the shore. What can make it higher? What can make it lower?
Why does the salinity stay near constant in the Ocean Basins?

13. Less volcanic activity there to add salts, melting icecaps may dilute the water
Warmer near equator and therefore more evaporation: water leaves, leaving salt behind
Higher: shallow water heats up faster -> evaporation occurs -> lose water & leaves salt
Lower: people could harvest the salt or there might be freshwater runoff from a river or sea spray may wash the salt up on the shore.

14. Resources in the Oceans
Chemical Resources:
About 30% of the world’s table salt is extracted from sea water.

15. Salt Recovery – Warm Climate
In warm dry climates seawater is allowed to flow into shallow ponds and evaporate down to a concentrated brine solution.
More seawater is added and evaporated and the process is repeated several times until a thick brine is produced.
Full evaporation is then allowed to take place so that a thick white salt deposit is left on the bottom of the pond.
This salt is then collected and refined to produce table salt

16. Salt Recovery - Cold Climate
In cold climate areas salt can also be recovered. This occurs in freezing ponds.
The ice that forms on the surface of the seawater is nearly fresh (very little salt)
The salts are concentrated in a brine solution below.
The cold brine is then collected, removed and heated so that the last of the water can be removed and only the salt remains.

17. Other Minerals in Seawater
- 60% of the world’s magnesium comes from the sea
- 70% of the world’s bromine
- 10 million tons of gold and 4 billion tons of uranium are dissolved in the world’s seawater, however, the concentration is so low (one part per billion or less) that there is no economic way to recover these minerals.

18. Resources continued… Fresh Water
DESALINATION
the process of obtaining fresh water from salt water
There are three main desalination methods:
1- processes involving a change of state of water (liquid to solid, or liquid to vapor)
2- processes requiring ion exchange columns
3- processes using a semi-permeable membrane, such as electrodialysis and reverse osmosis