Standard 5.6
b) physical characteristics
- Ocean currents, including the Gulf Stream, are caused by wind patterns and the differences in water densities (due to salinity and temperature differences). Ocean currents affect the mixing of ocean waters. This can affect plant and animal populations. Currents also affect navigation routes.
- As the depth of the ocean water increases, the temperature decreases, the pressure increases, and the amount of light decreases. These factors influence the type of life forms that are present at a given depth.
This webpage outlines the purpose, materials, background information, and procedure for a whole class experiment illustrating the differences in density between room temperature water, ice water, hot water, and saline water. Using just a few materials, including a fish tank or bowl, water at different temperatures, and food coloring, the students will observe how ocean water moves as cold, salty water sinks and warm, fresh water floats.
Adaptation
What follows is a slightly more challenging adaptation of the original Oceans Alive! experiment, designed for the fifth grade classroom.
Time: 20 Minutes.
Materials
- Fish Tank
- Something sturdy to prop one end of the tank on
- Four cups
- 1 cup with hot, salty water (1/2 teaspoon salt)
- 1 cup with cold, salty water (1/2 teaspoon salt)
- 1 cup with hot, fresh water
- 1 cup with cold, fresh water
- Room temperature water (enough to fill 1/4 tank)
- 1 teaspoon salt
- Food coloring (red, blue, green, yellow)
Procedure
- Have students make predictions regarding the order in which the colors will become layered based upon the temperature and salinity of each colored cup of water.
- Fill the tank 1/4 of the way with room temperature water.
- Set one end of the tank on something tall to prop it up.
- Gently pour each cup of water into the tank, begining at the raised end. Make sure to allow time for the water from each cup to settle. Use this time to have students write down their observations.
Result
Students should be able to identify that the blue, cold, salty water is the most dense; the red, hot, salty water is a little less dense; the green, cold, fresh water is even less dense; and the yellow, hot, fresh water is the least dense.
Click to view the outline for the original experiment at Oceans Alive!
Link/File Type: Website