Water Cycle - Oceans (3)
Post Lab 

   
OBJECTIVES:
  • Distinguishing bodies of salt and fresh water.
  • Comparing bodies of salt and fresh water.
VOCABULARY:
  • lake
  • marine
  • ocean
  • sea
MATERIALS:

Students use a globe and worksheet to find fresh and salt water sources.

BACKGROUND:

A globe or atlas shows fresh and salt water masses as being the same.  However, one infers that the large bodies of water are usually salty while the smaller bodies of water are usually fresh. 

Point out that not all salt water is the same.  The amount of salt is measured by its salinity which is measured by parts per thousand of that salt in water.  For instance normal salinity of the major oceans is around 35-36 o/oo (read parts per thousand), but some bodies of water like Great Salt Lake in Utah has a salinity much higher than seawater.  You may want to discuss with students where there  may be more salinity than others.  In places where evaporation is high there is a higher salinity. If there is a lot of precipitation the salinity would be less because rain water is fresh water.  In waters where there are icebergs, the salinity would be higher because the icebergs are fresh water and the salt gets concentrated.  But if the icebergs melt, it adds fresh water and the salinity goes down.  The oceans are a complicated place!

PROCEDURE:
  1. You might want to make a list of the bodies of water that are fresh and salty.  You should introduce the term "marine" which is the correct way of referring to salty water.  Salt water examples include Pacific Ocean, Indian Ocean, Great Salt Lake, Salton Sea in southern California, and Mediterranean Sea to name a few.  Fresh water examples include the Great Lakes, Lake Tahoe, Mississippi River, and local reservoirs.  Potential fresh water is tied up in icebergs, ice sheets, and glaciers.  Antarctica is a large source of fresh water. 
      
  2. Students can color the different parts of the globes and label the different parts.  You might want them to use a lighter blue for fresh water.  So, for instance around Antarctica (D) you might want another shade of blue that is between fresh and normal salinity.  This would also hold true for the Arctic Ocean (C).  Since there are polar caps there, you might suggest that student color it gray to represent ice sheets.
          
  3. Main areas students  should identify is the following: 
  1. Africa, Eurasia, Indian Ocean, Atlantic Ocean, Caspian Sea (salt), Black Sea (salt), Red Sea (salt), Mediterranean Sea (salt)
  2. Atlantic Ocean, Pacific Ocean, South American, North America, Great Lakes (fresh)
  3. Arctic Ocean, ice caps (fresh), Eurasia, North America, Pacific Ocean, Atlantic Ocean
  4. Antarctica, ice sheets (fresh), Indian Ocean, Atlantic Ocean, Pacific Ocean.

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