Argo float : a platform of the IMOS Argo Australia Facility

Argo floats have revolutionised our understanding of the broad scale structure of the oceans to 2000 m depth. In the past 10 years more high resolution hydrographic profiles have been provided by Argo floats then from the rest of the observing system put together.

Each Argo float is identified by a unique identification number called a WMO ID. WMO (World Meteorological Organisation) ID Numbers are assigned to measurement stations and observing platforms to enable researchers to keep track of, and uniquely identify their floats.

Argo floats alter their buoyancy by using a battery pack and motor to drive oil from inside the float to an external bladder. This changes the floats volume and thus its density relative to the surrounding seawater allowing it to move up and down through the water column.

A typical Argo float mission is to profile from 2000 m depth to the sea surface every 10 days. On deployment, the float sinks to a depth of 1000 m and drifts with the ocean currents for 9 days. Then the float sinks deeper to its profile depth (usually 2000 m) before starting to ascend through the water column measuring temperature, salinity and pressure as it rises. Once at the surface it transmits location and profile data via satellite to land-based Argo data centres. After transmission the float sinks again and repeats the cycle.

The average life of the latest model APEX Argo floats are around 3.7 years or approximately 135 cycles. These statistics are for floats with the standard alkaline battery configuration from an analysis by Kobayashi et al (2009).In the Australian Argo program, the floats are deployed with a combination of lithium and alkaline battery packs which extends float lifetime. Argo Australia floats usually last 7 years and several floats are approaching their 9th birthday and are still returning good data.