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  the Barne glacier  
The Barne glacier soars 150 feet (50m) above the sea and extends 1500 feet (500m) below. Click to enlarge.
   

Iron Science Teacher

Science Teaching from Antarctica
by Paul Doherty

December 15, 2001

Our video link to the Exploratorium allowed me to compete in the special holiday edition of Iron Science Teacher. Host Linda Shore opened the program by introducing the contestants: Eric Muller, Ken Finn, and me. Linda explained the rules: we would be given a secret ingredient then have to create and present a science lesson using that ingredient. The secret ingredient was....ice! How appropriate for an Antarctic science lesson.

Eric Muller went first. He put on protective goggles, then boiled water in a flask. He took the flask off the heat, and as it cooled, he plugged it with a stopper. As the gas cooled, a vacuum was created in the flask. The lowered pressure allowed water to boil at lower temperatures. He was then able to place ice cubes against the bottom of the flask and start it boiling again. A great and surprising experiment!

Ken Finn soaked his hand in ice water for 20 minutes and then tried to write his name. He had great difficulty. When you cool the nerves in your hand, they do not send electrical signals as well as when they are warm. In addition, the cooled muscles in his hand did not work as well. I mentioned that I had done a similar experiment in Antarctica when I tried to erect my tent with cold hands.

   
 
© Henry Kaiser
 
View movie (1.3 MB) of a diver freeing ice crystals from ocean floor. (Get QuickTime)
   

For my experiment, I placed ice cubes in a tall glass beaker full of water. They floated, just as icebergs or glaciers would float, with 10% out of the water and 90% underwater. I then replaced the ice cube with frozen milk. As the frozen milk cube melted, streamers of white milk settled to the bottom of the beaker. The cold milk liquid is denser than the warm water, and so the milk liquid sank to the bottom of the beaker. This is the same thing that happens in Antarctica when cold icebergs, with temperatures below freezing hit the sea ice. The sea ice freezes around the berg. But when the sea ice freezes, the salt in the sea ice is left behind as pure fresh water crystallizes onto the berg. The salt creates a cold dense solution that sinks down toward the ocean floor. The sunken cold salt water freezes the water at the bottom of the sea and creates strange ice structures.

  An ice cbe floats inside a solution  
An ice cube floats above a water layer and beneath a layer of rubbing alcohol. Click to enlarge.
   

In the second part of my experiment, I half-filled a beaker with a 90% solution of rubbing alcohol, or isopropanol, and dropped an ice cube in it. The ice cube sank to the bottom, since ice is denser than isopropanol. I added many ice cubes and waited for them to melt on the bottom of the beaker. This created a dense layer of water beneath the alcohol. When I added another ice cube, it hovered in the middle of the beaker, floating at the boundary between the alcohol and the water. As the ice cube melted, air bubbles trapped in the ice rose toward the surface.

Antarctic glacier ice also has trapped air bubbles. These bubbles are squeezed beneath hundreds of feet of ice and so are under high pressure. When you add ice cubes carved from a glacier to your drink, they rupture and make a loud musical ping.

Then it was time for the audience to vote. All of the contestants got applause, but I narrowly squeezed out a victory. Now I can call myself the Iron Science Teacher of Antarctica!

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