ELEMENTS OF OCEANOGRAPHY

 

TOPIC 7 - THE NATURE AND PROPERTIES OF WATER [Lecture ppt | pdf]

Overheads:

The Earth's Hydrosphere
All water at or near the earth's surface is termed the hydrosphere
It includes atmospheric water vapor, ground water, lakes, rivers, polar icecaps, and the oceans
Water distribution
Oceans- 97.54%
Icecaps- 1.81%
Groundwater- 0.63%
Everything else- 0.02%

Water as a Chemical Compound
Water is a composed simply of two hydrogen atoms and one oxygen atom
Placement of hydrogen atoms is not symmetric - creating a "polar" ionic structure

Three States of Water
Gas (water vapor) - each molecule is energetic and separated ; T>100 degrees C
Liquid - some molecules link into loose groups; 100 degrees C>T< 0 degrees C
Solid (Ice)- all molecules linked in rigid open crystalline structure; T<0 degrees C

Water Properties
High heat capacity
­ latent heat of vaporization
­ latent heat of melting
Density varies as a function of temperature - densest near 4 degrees C
Extremely effective solvent
Colorless (blue) in small (large) volumes
Viscosity varies as a function of temperature
Sound speed ~1500 m/sec; low frequences travel long distances

Dissolved Solids in Seawater
Six major ions compose more than 99% of all dissolved material in seawater: Cl(-), Na(+), SO4(2-), Mg(2+), Ca(2+), K(+)
Salinity is a measure of amount of dissolved material in water after correcting for gases and organic material
Average ocean salinity is 35.0 ppt (3.5%)
All major ions in seawater are conservative - their ratios do not change
All dissolved materials have residence times varying from hours (NO3) to millions of years (Na)

Dissolved Gases in Seawater
At the ocean/atmosphere interface gases are added to seawater by diffusion and wave action
Gas composition at the ocean surface is in equilibrium with atmosphere
Gas composition changes with time and depth in the oceans

 


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