Polar vs Tropical Water

Yet another experiment from All Things Beautiful. (http://homeschooljournal-bergblog.blogspot.com/2011/02/ocean-currents-part-iv-polar-vs.html)

Materials:
   2 plastic cups
   20-30 marbles
   clear plastic tub
   2 push pins
   red & blue food coloring
   ice water
   hot water
   2 jars
   room temp water
   white paper (back ground for tub)

First I filled one jar with hot water and colored it with red food dye. Then I filled another jar with ice water and colored it with blue food dye. I put the marbles in the two plastic cups and put hot water in one cup and cold water in the other. We put push pins in the cups about 1 cm below the level of the water. We set the cups in the clear tub with the push pins facing the outer edges of the tub, not each other. We taped white paper to one side of the tub so it was easier to see what happened.

We filled the tub most of the way with room temperature water, but kept this level below the lips of the two cups. Then we took out the push pins and watched. 

The hot water hit the wall of the tub and rose to the top. 

The cold water hit the wall of the tub and sank to the bottom. It appeared there was a thin layer of cool water in between. (Ignore the Mama oops, it was completely accidental.) Warm water rises to the top and cold water goes to the bottom. So it will generally be warmer on the surface of the water and cooler down low. 

After waiting a while, upwelling was visible where the blue water hit the opposite side of the tub and went upwards.

 Upwelling brings nutrient rich cold water up to the surface. This makes these areas a favorite place for creatures to come eat.