Argo is now the dominant source of subsurface ocean data and has a critical role in the Global Ocean Observing System

The Argo Program was developed in 1999 and today supports a global array of almost 4,000 robotic profiling floats that measure the temperature and salinity of the upper 2,000 meters (1.2 miles) of the ocean. The Argo Program has an international reach with participation from close to 30 countries. This partnership allows, for the first time, constant monitoring of the temperature, salinity, and currents of the upper ocean.

Two new types of Argo floats are now being tested to dive down to a depth of 6,000 meters (3.7 miles) and to have additional sensors on them to collect information about the biology and the chemistry (oxygen, pH, nitrate, suspended particles, and downwelling irradiance) of the global ocean. Argo floats work on a 10-day cycle (see diagram). After 10 days, the floats rise to the ocean surface and send their data to satellites. This data is publicly available within hours after collection and used in research and forecasting across the globe.

Fun Fact: The Argo Program is named after the Greek mythical ship Argo (captained by Jason) to emphasize the complementary relationship of Argo with the Jason satellite altimeters.