Why Doesn't the Ocean Freeze?
In many parts of the world, winter temperatures drop low enough to make rivers and lakes freeze. And in those same parts of the world, where even those waters freeze, the ocean waters will not. Think about the pictures you’ve seen of the Arctic region. Most of the earth’s Arctic region is a frozen tundra, except the ocean. Why?
Is it because the water is always moving? Rivers move, yet they can still freeze (at least at the surface!). So what makes the ocean waters so different that at the subzero temperatures, they remain unfrozen?
Problem:
Why doesn’t the ocean freeze?
Materials:
- 8 cups water
- 2 tablespoons salt
- 2 large plastic bowls
- Freezer
- Spoon
- Dry-erase marker
Procedure
- Label the bowls “Bowl 1” and “Bowl 2.”
- Measure out 4 cups of water.
- Pour the water into Bowl 1.
- Pour 4 more cups of water into Bowl 2.
- Add 2 tablespoons of salt to Bowl 2 a little at the time, stirring until the salt is completely dissolved.
- Leave both bowls in the freezer overnight.
- Check to see if both bowls are frozen.
- Record your results.
Results:
The water in Bowl 1 should have frozen. Bowl 2’s water should still be liquid.
Why?
The water in Bowl 2 approximates the same concentration of salt found in the ocean’s water. Salt is the key to understanding our experiment’s results! Here’s why: The more salt in the water, the lower the temperature has to be for the water to freeze.
This is why the ocean doesn’t freeze: There’s too much salt in it. Bodies of water located farther inland like islands and rivers have less salt in them, allowing them to freeze when the temperature drops to 0 degrees Celsius.
Digging Deeper
The beauty of science is that we never run out of opportunities to learn. Try repeating this experiment with several bowls of water of varying salt concentrations. Which ones freeze? Which ones remain liquid?
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