Argo is an international program that uses autonomous (self-controlled) floats to collect temperature, salinity and current data from the oceans. These floats gather information about the surrounding ocean as they sink, drift and rise. This process is called a cycle. Each float takes about ten days to complete a cycle. After the cycle is complete and an Argo float has risen to the surface of the ocean, it transmits its data to a satellite. The satellite sends its information to scientists around the world who use it to monitor the world's oceans and climate.

Argo is able to sink and rise because of a special bladder on the outside of the floats' casing. When oil is pumped into the bladder, it causes the volume of the float to increase and the float rises to the surface. When oil is drained from the external bladder, it sinks again.

Adding and removing the oil causes the float to match the density of the water around it. Density is the amount of particles in a specific amount of space or liquid. For example, you can increase the density of tap water by adding particles or grains of salt. You can see this principle in action by trying the activity below.

Build Your Own Ocean Float

MATERIALS

  • Clear 16- or 25-ounce water bottle with lid
  • Plastic pen cap (cap must not have any holes in the top). Bic pens work well
  • Modeling clay

DIRECTIONS

Remove labels and glue from water bottle. Fill the water bottle to the very top with water. Place a small amount of clay (pea size) at the end of the point on the pen cap. See diagram. Carefully place the pen cap, clay end first, into the water bottle. Some water will spill over, but that is OK. The pen cap should barely float. If your cap sinks, pull it out and remove some clay. If it floats too much, add some clay.

Once your cap is barely floating, screw the bottle cap on tightly. Remember to have the bottle completely filled with water.

Now you can control the sinking and rising of your float by squeezing the bottle. Squeezing the bottle changes the size (density) of the air bubble inside the pen cap. As the bubble gets smaller, more water can fill in the cap, making it heavier and it sinks. Releasing your squeeze allows the cap's air bubble to expand and water to be pushed out of the cap. The cap is less heavy and rises towards the surface. Practice stopping your float at different depths within the bottle by changing the way you squeeze.


argo cutaway

A cutaway of the Argo float.

activity diagram

Practice stopping your float at different depths within the bottle by changing the way you squeeze.