71% of the Earth’s surface is covered by oceans. The oceans contain more than 97% of the planets water Only 10% has been explored by humans. The average temperature of the oceans is 2˚C or 39˚F. The deepest point in the ocean is the Challenger Deep in the Mariana’s Trench it is 6.86 miles deep. The Blue Whale is the largest animal in the ocean, it is the largest animals ever to live on earth. The average salinity of the world’s oceans is 35‰. The most common salt is sodium chloride.

 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‰.

 Freshwater: less than.5 ‰  Brackish:.5 to 17 ‰  Seawater: 17 – 40 ‰  Brine (hypersaline): greater than 40 ‰

 Lack of Rainfall and a high evaporation rate (increases salinity) -Red Sea- 40‰-Mediterranean Sea- 38‰ -Dead Sea ‰  High influx of fresh water and low evaporation rate. (decreases salinity) -Black Sea- 18 ‰-Baltic Sea- 8 ‰

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.

 Mainly composed of six different ions (99%)  Chloride (Cl - ): 55.03%  Sodium (Na + ): 30.59%  Sulfate (SO 4 -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).

 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.

 Freshwater –1.001  Brackish  Seawater  Hypersaline (Brine): > 1.030

 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.