Temperature and salinity are the two main influences on the density of ocean water. And differing water density, in turn, is what causes the oceans to circulate in deep-water currents—which are vital in keeping a relatively even temperature on earth’s surface.
So how does it work, exactly? You’ve already looked at maps in class that show the ocean’s temperature and salinity, and you know that water is warmer and saltier at the equator and cooler and less salty at the poles. Since lower temperatures and higher salinity both increase density—what’s going on? How do deep ocean currents change as they move from the equator to the poles and back again?
In this experiment, you will observe the action of temperature and salinity on water individually in order to draw conclusions about the ocean’s currents.
Part I: Temperature Materials:
approximately 9x13x3-inch glass dish hot and cold tap water small waterproof Ziplock bags 2 clothespins (or small clamps) 2 different colors of food coloring 2 eye droppers a rock
ice cubes, or a chemical cold pack Procedure:
1. Fill the glass pan with tap water. Let the pan rest for a few minutes while the water settles.
2. Place a rock in a plastic bag and fill the bag with hot water. Seal the bag, and use the clothespin to clip it to one corner of the glass pan.
3. Fill another bag with ice cubes or the chemical cold pack, and clip this bag to the opposite corner of the pan.
4. Use one of the droppers to add four drops of food coloring to the water next to the ice bag. Use the other dropper to add four drops of a different color of food coloring next to the bag of hot water. Observe the food coloring for several minutes. Where did the water sink? In what direction did the current flow along the bottom? Where did the water rise? Make a drawing of what you observed.
5. Using what you know about temperature and water density, write an explanation of what happened below. How does what happened in your pan relate to the map of global temperatures you observed in class?