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Three thousand research buoys in all our oceans

Miniature buoys, drifting in all our oceans at depths of more than 1000 m, are recording data for scientists from all over the world. Every ten days, each of these Argo buoys rises to the surface to transmit information about its own position and the sea’s temperature, salinity and pressure to a satellite that re-transmits the information to data centres that make it available to anyone interested.

By Beate Hoddevik Sunnset

Deployment of the Argo buoys is an international project with participants from more than 30 countries. The project was launched after scientists from several countries realised that there was a need for systematic real-time measurements from the uppermost 2000 m of the sea, and the aim of setting out 3000 buoys has now been achieved. The projects offers scientists the climatic status of the sea, which allows them to see whether there are changes in the course of time.

Drifting with the currents

One of the advantages of using the Argo buoys is that they provide records from the whole of the ocean rather than just individual points, and that the measurement are made in both winter and summer.

- The buoys live their own lives once they have been deployed. They drift with the current at whatever depth they have been programmed to be at, and only come to the surface every ten days. On the way up, they make a continuous series of measurements, which are sent ashore when the buoy reaches the surface, together with its position. The tracks of the buoys also provide completely new knowledge of deep ocean currents. The buoys remain floating on the surface until all their data have been sent, before sinking again to drift further with the current, says Kjell Arne Mork, one of the Institute of Marine Research scientists who is involved in the project and utilises the data from the buoys.

More measurements than before

Scientists used to be dependent on measurements of temperature, salinity and pressure being made from ships, a method that left them with fewer measurements than they can obtain now, because in many regions, particularly in winter, weather conditions permitted fewer measurements to be made. Another problem was that it often took a long time to make the measurements available to everyone who needed them.

- Now, the data are sent to shore-based centres via satellite, and these make them available to all interested parties as rapidly as possible, says Mork.

Today, these data are extremely useful for operational ocean weather forecasting; a number of climate centres all over the world use them for instance, to help them understand how the oceans affect the climate. For example, the data are used in climate models for seasonal and interannual forecasts and to improve forecasts of major cyclical climate changes, such as El Niño.

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Buoys need to be renewed

The aim of the Argo project is to have 3000 Argo buoys in operation, and this goal is expected to be reached by the end of the year. The Institute of Marine Research has launched 11 buoys in the Norwegian Sea, and six of them are still sending information ashore. Each buoy has an operational lifetime of about four years. The scientists aim to set out new buoys as the old ones stop sending information. In order to put this programme of renewal into effect, the EU has launched a new project called EuroArgo, of which the Institute of Marine Research is a member, together with other European countries. The aim of this project is to gain acceptance for the idea that it will be necessary to renew the buoys as they gradually stop working, so that the number of buoys remains constant. The project will also attempt to improve data-flow and quality assurance, to incorporate a wider range of sensors in the buoys, and to improve the ways in which the information is utilised.

- The last two buoys that we deployed last year we also fitted with oxygen and chlorophyll sensors. The ability to measure biological parameters of this sort makes the buoys even more useful, and more interesting for a wider range of users, says Kjell Arne Mork.