1. Guided Notes about Seawater
Chapter 15, Section 2

2. 1. Seawater is a solution of about 96. 5% water and 3
1. Seawater is a solution of about 96.5% water and 3.5% dissolved salts. The most abundant salt in seawater is sodium chloride (NaCl).

3. 2. Most elements on Earth are present in seawater in the form of ions.

4. Define salinity and state how it is expressed :
Salinity is a measure of the amount of dissolved salts in seawater. It is expressed as grams of salt per kilogram of water, or parts per thousand.

5. 4. The sources of salts in seawater are volcanic eruptions and the weathering of crustal rock.

6. 5. Salts are removed from seawater through precipitation near arid, coastal regions. Marine organisms also remove ions from seawater to build their shells, bones, and teeth.

7. 6. Seawater is denser than freshwater because salt ions are heavier than water molecules. The density of seawater varies depending on its salinity and temperature.

8. 7. Variations in salinity also cause the freezing point of seawater to be lower than freshwater. Seawater freezes at -2˚C

9. 8. The average surface temperature of ocean water is 15 degrees Celcius, but temperatures decrease significantly with depth, so that deep ocean water is always cold, even in tropical oceans.

10. 3 layers of the ocean, based upon temperature variations:
Warm, sunlit surface layer, 100 m. thick
A transitional layer, the thermocline, in which temperatures decrease rapidly with depth.
The bottom layer is cold and dark, with near freezing temperatures