total amount of salts dissolved in seawater salinity is expressed as the number of grams of salt...
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Salinity and the Oceans
Salinity
Total amount of salts dissolved in seawater
Salinity is expressed as the number of grams of salt left behind when 1,000 grams of seawater are evaporated.
If 35 grams are left behind then the salinity is 35‰.
‰ = part per thousand
Salinity can be increased by the evaporation and freezing which leave salts behind.
Salinity can be decreased by the addition of freshwater.
The average salinity of the world’s oceans is 35‰.
Salinity Levels
Freshwater: less than .5 ‰ Brackish: .5 to 17 ‰ Seawater: 17 – 40 ‰ Brine (hypersaline): greater than 40
‰
Salinity of Seas
Lack of Rainfall and a high evaporation rate (increases salinity)
-Red Sea- 40‰ -Mediterranean Sea- 38‰
High influx of fresh water and low evaporation rate. (decreases salinity)
-Black Sea- 18 ‰ -Baltic Sea- 8 ‰
Seawater
How did the oceans and seas become salty?
The dissolved salts are produced by weathering of rocks and geothermal activity (undersea volcanoes, hydrothermal vents, etc…).
When the ocean water evaporates it leaves the salts behind and therefore the salinity increased over time.
http://www.palomar.edu/oceanography/salty_ocean.htm
Seawater Composition
Mainly composed of six different ions (99%)
Chloride (Cl-): 55.03% Sodium (Na+): 30.59% Sulfate (SO4
-2): 7.68% Magnesium (Mg+2): 3.68% Calcium (Ca+2): 1.18% Potassium (K+): 1.11% Sodium and Chloride account for nearly
85% of the dissolved ions, that is why seawater tastes like salt (NaCl).
How do you measure salinity?
Hydrometer: instrument that measure the specific gravity of a liquid.
Specific gravity: ratio of the density of one liquid to another.
Water is usually the reference liquid since it is 1 g/ml.
Hydrometer readings.
Freshwater- 1.000 –1.010 Brackish- 1.010-1.020 Seawater- 1.020-1.030 Hypersaline (Brine): > 1.030
Halocline
Salinity is not always even throughout the water column.
There are sometimes differences in salinity due to evaporation or addition of freshwater.
Since different salinities have different densities you have stratification (layering).
Sometimes this causes the layers to remain separate and does not allow mixing to occur.
