Argo project

Did you know that today there are 2,917 Argo floats bobbing around the world's oceans? I didn't, but exploring the Web site devoted to the Argo project had me gripped.

An Argo float is a 25kg free-drifting profiling float that measures the temperature and salinity of the upper 2000m of the ocean. This allows, for the first time, continuous monitoring of the temperature, salinity and velocity of the upper ocean, with all data being relayed and made publicly available within hours after collection. The power of the Internet!

The battery-powered autonomous floats spend most of their life drifting at a depth where they're stabilised by being neutrally buoyant, usually 1000m to 2000m. This "parking depth" pressure means they have a density equal to the ambient pressure and a compressibility that is less than that of sea water. A typical model operates at about 10-day intervals - the floats pump fluid into an external bladder and rise to the surface over about six to 12 hours while measuring temperature and salinity. Satellites determine the position of the floats when they surface, and receive the data transmitted by the floats. The bladder then deflates and the float returns to its original density and sinks to drift until the cycle is repeated. Ingenious! Floats are designed to make about 150 such cycles, so they typically last about 3.5 to four years.

Another factor that picked up my interest, is that New Zealand has a role to play in the Argo project. The R/V Kaharoa, based out of Wellington, has recently returned from its seventh Argo mission since beginning the program in 2004, and has now deployed 439 active floats. Altogether, the 28m Kaharoa has spent nearly a year at sea for Argo.

UPDATE: October 2nd: The 3,000th Argo was launched today!