Crew members deploy a float from a research vessel. Credit: NOAA

Somewhere in the middle of the ocean, a merchant mariner lowers a cylindrical robotic ocean observing instrument from a ship into the sea to record ocean temperature and salinity. Another instrument is deployed from a plane into the eye of a hurricane to take the pulse of the ocean during the storm. In Antarctic waters, a rounder float is released that will sink far deeper than the others, down to 3.7 miles (6,000 meters) below the sea surface. These three robotic floats are part of a fleet of nearly 4,000 that make up what is known as the global Argo “array.” 

This month marks 25 years since Argo floats began drifting with currents and diving for data. The array has helped scientists to better understand changes in the ocean, improve climate and weather forecasts and ultimately help society prepare for environmental change.