1. Water – The Universal Solvent
Water is often called the universal solvent because …?
Why do so many substances readily dissolve in water?

2. Solubility
Solubility is the ability of a substance to dissolve in a liquid. This is determined by the molecular arrangement of the liquid and the substance.
Solvent = does the dissolving
Solute = is the substance dissolved

3. Water is polar. Substances with (+) and (-) surface charges are attracted to the (+) and (-) ends of the water molecule.
Hydrogen bonding of these electrically polarized molecules gives water the properties of cohesion, adhesion and dissolving power.

4. Composition of Seawater
Seawater consists of about 3.5% (by weight) of dissolved minerals; typically expressed in parts-per-thousand (‰)
Salinity (NaCl)
Average salinity is 35‰

5. Relative proportions of water and dissolved components in seawater

6. Ions in Seawater
HMS Challenger: 1884 Dittmar found that the relative concentration of ions is the same all over the world (took over 77 samples from various depths and locations).
Sources:
Chlorine, sulfates from volcanic activity
Na, Mg, K, Ca ions come from the weathering of feldspar-rich rocks (granites and other igneous rocks).

7. Sulfur – hydrothermal vents

8. Salinity Sources of sea salts Chemical weathering of rocks
Outgassing – gases from volcanic eruptions
Surface salinity in the open ocean ranges from 33‰ to 38‰
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

10. Ocean temperature variation with depth
Low-latitudes
High temperature at the surface
Rapid decrease in temperature with depth
Called the thermocline
High-latitudes
Cooler surface temperatures
No rapid change in temperature with depth

11. Variations in ocean water temperature with depth

12. Variations in the ocean’s surface temperature and salinity with latitude

13. Ocean Density
Density is mass per unit volume – how heavy something is for its size (g/cm3) Determines the water’s vertical position in the ocean
Factors affecting seawater density: Temperature - the greatest influence Salinity

14. Variations in ocean water density with depth

15. Ocean Layering Three-layered structure Shallow zone(300 – 450 m)
Surface mixed zone
Sun-warmed zone
Zone of mixing
~2% of ocean water
Transition zone
Between surface layer and deep zone
Thermocline and pycnocline
~18% of ocean water
Deep zone
Sunlight never reaches this zone
Temperatures are just a few degrees above freezing
Constant high-density water
~80% of ocean water

16. Layering in the ocean

17. Thermohaline Oceanic Circulation