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Do an experiment to learn how water temperature and salinity affect ocean currents and, in turn, weather and ocean life.
Academic Areas: | Science |
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Grade Levels: | Grades 4–6
Activity extension for older students included. |
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Learning Objectives: |
After participating in the activity that follows, students will be able to do the following:
- Explain how temperature and salinity affect the movement of ocean water.
- List ways ocean currents are important.
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Science Standards Met: |
- Gains abilities necessary to do scientific inquiry
- Learns properties and changes of properties in matter
- Understands transfer of energy
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Materials for each team of two students: |
Water, salt, measuring cup, spoon, food coloring, glass or plastic jar (You'll also need a gallon jug or pitcher, water, salt, and a spoon to prepare a saltwater mixture ahead of time.)
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Background:
To learn about the ocean, you must learn about water and its properties. Water temperature and salinity affect ocean currents and global weather systems. For example, ocean currents carry heat and cold thousands of miles. Cold-water currents begin at Earth's poles and make their way through the ocean depths toward the equator. Warm-water currents originate at the equator and flow along the ocean's surface toward the poles. Such currents are crucial to the health of the ocean and global weather patterns. Cold, saltier water sinks, taking oxygen from the surface with it to the ocean depths. Without the constant motion of rising and sinking currents, there would be no oxygen—and no life—on the ocean floor.
Life on land also relies on ocean currents. Warm, less salty water rises and heats air masses above it. The Gulf Stream is a current that carries warm water from the Caribbean up the East Coast of the United States and then eastward toward Northern Europe. This flow of warm water means the British Isles and Norway enjoy a milder climate than other northwestern European countries. Winds blowing over the stream are warmed, affecting weather in North America as well.
The following activity allows students to see for themselves how temperature and salinity affect the movement of seawater.
What to Do: |
- The day before the experiment, add 2/3 cup of salt to a gallon of cold water, and stir until well mixed. Put the water in the refrigerator until needed for the experiment. When ready to begin the experiment, stir the mixture again, and portion it out, 1 cup per team. You should have enough cold saltwater mixture for 16 teams.
- Divide the class into teams of two, and give each pair the materials listed above. Direct the students to follow these instructions in carrying out the experiment:
- Put 1 spoon of salt into the measuring cup, and add 1 cup of very hot tap water. Stir to mix the salt into the water.
- Pour the cold saltwater mixture into the glass or plastic jar.
- Stir several drops of food coloring into the warm-water mixture.
- Write down what you think will happen when you add the warm-water mixture to the cold.
- Use the spoon to slowly pour small amounts of the warm-water mixture down the side of the jar and into the cold water. Add several spoonfuls. Observe what happens, and write it down.
- Have the class answer these questions: Which is heavier, cold or warm water? The cold water contains about twice as much salt as the warm water. What conclusions can you draw from that fact? Using the results of this experiment, where in the ocean would you find warm currents and cold currents? Where would you find water that is very salty? Less salty?
- Discuss the experiment and the students' answers to the questions. Explain that the cold water sinks to the bottom of the jar because the colder, saltier water is heavier than the warm, less salty water. That's why warm ocean currents flow along the surface and cold currents flow in the ocean depths. Explain that ocean water is constantly warming up and cooling off, and that is why ocean currents are always on the move. Ask students why this constant mixing is important. Explain that this process helps to even out global temperatures and to carry oxygen from the surface to the ocean depths.
An extension of this activity for older students is to let them devise additional water experiments to answer questions they have about the sea and how it "works." Some experiments to try might include water pressure tests, wave experiments, or investigations into shore erosion. See the resources below for materials that can guide you and your students in conducting these experiments.
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Resources
Diving into Oceans by National Wildlife Federation (Learning Triangle Press, 1997)
Janice VanCleave’s Oceans for Every Kid: Easy Activities that Make Learning Science Fun by Janice VanCleave (Wiley, 1996)
Oceans by Andrew Haslam (Two-Can Publishing, 1997). This book contains hands-on activities focusing on ocean geography.
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Listen to More?
Click on these links to hear more about ocean currents, how they move, and in what ways the ocean affects Earth's weather.
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![Ocean Climate Change [4/14/99]](images/audio.gif){kind=small}