1. The Composition of Seawater
15.1

2. Salinity
• The proportion of dissolved salts to pure
water, usually expressed in parts per
thousand.

3. Thermocline
• A layer of water in which there is a rapid
change in temperature with depth.

4. Density
• Mass per unit volume of a substance, usually
expressed as grams per cubic centimeters.

5. Pycnocline
• A layer of water in which there is a rapid
change of density with depth.

6. Mixed Zone
• An area of the ocean surface with uniform
temperatures created by the mixing of water
by waves, currents, and tides.

7. Key Concept
• What units are used to express the
salinity of ocean water?
–Oceanographers typically express
salinity in parts per thousand.

8. Key Concept
• What are the sources of salt in Ocean
Water?
–Most of the salt in seawater is sodium
chloride, common table salt. Chemical
weathering of rocks on the continents
is one source of elements found in
seawater.

9. Key Concept
• What factors affect the density of
ocean water?
–Seawater density is influenced by two
main factors: salinity and temperature.

10. Key Concept
• What are the three main zones of
the open ocean?
–Oceanographers generally recognize a
three-layered structure in most parts
of the open ocean: a shallow surface
mixed zone, a transition zone, and a
deep zone.