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Learning Lesson: That Sinking Feeling

OBJECTIVE Learn about the origin of the Great Ocean Conveyor.
OVERVIEW Demonstrates how salinity and temperature affect density of water.
TOTAL TIME 10 minutes
SUPPLIES Fish bowl (or large, deep glass container such as fish tank, bowl or pitcher).
Food coloring.
Table salt.
Ice cube tray.
TEACHER PREPARATION Make the ice cubes the evening before. Into one-half of the ice cube tray pour dark food-colored water. Using a different color, pour into the other half of the tray dark-colored salty water. Freeze the solutions.
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The ocean is water is salty and, in general, cold. Differences in the water density associated with temperature and salinity are vital in shaping the Great Ocean Conveyor.

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  1. Fill the fish bowl nearly full with tap water. Allow the water a minute or two to settle.
  2. Gently add one cube of each color into the water.
  3. Have the students describe and explain what occurs.
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In both cases, the colors will be begin to sink to the bottom of the bowl. This is due to the temperature of water from the melting cube is more dense than the surrounding tap water and therefore sinks. However, the colored water from the salty cube should sink faster than the fresh water cube because the addition of salt further increases the density of water.

Each winter, in the far North Atlantic ocean as new sea ice forms, the salt that is left behind in the ocean makes the water very dense. This dense water sinks to the ocean floor and is the "engine" for Great Ocean Conveyor's motion.
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