Argo: a revolution in ocean observations

The world’s oceans are being taken over by a fleet of robots with an ambitious mission: to measure ocean temperature and salinity throughout the globe, providing the information needed to understand and predict climate change.

The Argo ‘robots’ are autonomous floats that drift with the ocean currents, usually at a depth of 2000m. Every ten days, a small pump inflates a bladder with oil, increasing the buoyancy of the float. As the float rises, it records the water temperature and salinity. Once the float reaches the sea surface, the information is relayed via satellite to researchers on land. The pump then deflates the bladder and the float sinks back to its ‘park depth’ to begin another cycle. Each float lasts for about four or five years, sending back up to 150 vertical profiles of ocean conditions.

Argo floats will completely revolutionise our ability to measure — and understand — the oceans. For the first time, we can measure the global-scale ocean circulation in real time. Because the floats drift with the currents, they are ideal for obtaining measurements in remote regions away from shipping routes (like the Southern Ocean). Argo floats are also extremely cost-effective: for the cost of a single day on a ship, during which up to four or five profiles might be made, two or three floats could be purchased, capable of providing 300 to 450 profiles.

The Argo data will be used for a wide range of studies. The drift of the floats will provide a direct measurement of deep ocean currents. The temperature and salinity profiles will allow us to measure how rapidly the ocean is changing and to relate these changes to climate variability experienced on land. The floats also provide essential data for testing climate models, leading to improved climate predictions. Measurements of ocean variability obtained from Argo will help scientists understand how variations in the physical environment are linked to changes in biological populations and hence contribute to conservation and sustainable management of marine resources.

About 500 floats are currently in the water. When fully implemented in 2005, 3,000 floats will form a global network covering all the world's oceans. While Australia is so far a small participant in Argo, we are seeking support to expand our contribution (e.g. through the proposed Antarctic Climate and Ecosystems Cooperative Research Centre). The likely pay-off to Australia from participating in Argo is huge. For the first time, we would be able to obtain the ocean measurements we need in order to understand, predict, and respond to future changes in the marine and terrestrial environment.

Stephen Rintoul,
CSIRO Marine Research