A: Yes, a motor is needed to make Argo floats travel up and down in the ocean, but not in the way you’d think. Here’s how it all works:
Thousands of years ago, a Greek mathematician named Archimedes discovered that an object underwater experiences an upward push equal to the weight of the water it moves aside or displaces. The displacement is the volume of the object.
Most components of the floats used in the Argo program are housed in a big tube called the pressure case. The weight of a float never changes when it’s in the water. What does change, however, is its volume. When a float is big, it floats up; when it is small, it sinks.
How do we do this? Here’s where that motor comes in. A battery-powered motor inside the float pushes oil in and out of a small, flexible, and inflatable bladder outside, making the float bigger or smaller. When the oil inflates the bladder, the float rises. It sinks when the oil is drained back inside. Then it’s ready for another cycle!
We can control how deep or high it goes because of density, or the weight of the water per the volume of water around it. Because the ocean's density increases with depth, once a float's volume is set, it sinks or rises until its density matches the water density.
— Russ Davis, Research Oceanographer, Physical Oceanography Research Division