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Published:September 29th, 2007 05:04 EST
European Union, 23 countries contribute instruments to global Argo array

European Union, 23 countries contribute instruments to global Argo array

By SOP newswire

This is the third in a series of articles about U.S. contributions to direct observations of the changing climate.

Washington -- A small but sturdy ocean-going vessel -- the New Zealand National Institute of Water and Atmospheric Research's Kaharoa -- will sail from Wellington October 3, carrying 64 ocean-profiling floats that are headed for remote locations in the Antarctic Ocean.

The floats will become part of Argo, an internationally funded global array of instruments that are placed in the world's oceans at strategic points about every 300 kilometers to measure temperature, salinity and circulation in the upper 2,000 meters of the sea. (See related article.)

This voyage, as were Kaharoa's previous seven voyages, is a collaborative effort of the U.S. and New Zealand Argo programs.

Steve Piotrowicz, an oceanographer in the Office of Oceanic and Atmospheric Research at the U.S. National Oceanic and Atmospheric Administration (NOAA), told USINFO that Argo "is the most significant in situ ocean observing system to date, and probably the most significant one in the history of oceanographic research."

Twenty-three countries and the European Union provide floats to the array, and many more countries contribute by helping deploy floats or devising new ways to use the Argo data, which is freely available to anyone from Argo's Global Data Assembly centers in Brest, France, and Monterey, California.

Five institutions make up the U.S. Argo program -- the Scripps Institution of Oceanography at the University of California-San Diego, Woods Hole Oceanographic Institution, the University of Washington, the NOAA Pacific Marine Environmental Laboratory and the NOAA Atlantic Oceanographic and Meteorological Laboratory.

The U.S. contribution is about half of the global array, funded mainly by NOAA. With the October 3 Kaharoa deployment, Argo will reach its intended size of 3,000 floats.


The battery-powered Argo floats -- about 130 centimeters long, plus a 70-centimeter antenna -- do not just drift around the ocean; they drift under the ocean, gathering data that represent the oceans' vital signs.

When a float first is placed in the sea, Dean Roemmich, professor of oceanography at Scripps in San Diego, told USINFO, it dives to 1,000 meters, then begins rising to the surface by pumping fluid into an external bladder, taking about 70 readings of temperature and salinity as it ascends over several hours.

When it reaches the surface, it transmits its first "profile" to a satellite, along with engineering data that tells the researchers the instrument is working properly. It then descends to 2,000 meters, drifts for about nine days, and rises again to collect and transmit another profile.

A battery lasts four years or five years, and then the float blinks off, gone from the array. To sustain the array, 600 to 800 floats must be deployed around the world every year.

"We first conceived of Argo almost exactly 10 years ago," said Roemmich, who helped design the program. "The first floats were deployed in 2000 after several years of planning and organization," and it has been a global array since 2004, when it had 1,500 floats.

Argo was conceived to monitor temperature, salinity and ocean circulation. Temperature is especially important, Roemmich said, "because the oceans are very critical in the heat balance of the planet. They're the place where most of the heat gets stored, and they take up most of the planet. So there's enormous interest in knowing how the heat content of the ocean is changing and what the patterns are globally of that change."


Researchers use Argo for a range of applications, including measuring climate change, observing rain and snowfall patterns over the oceans and measuring the height of the ocean surface.

But currently Argo is useful only to scientists. Thirteen operational weather and climate centers now use Argo data to understand better climate variations like El Niño and longer-term changes in the world's oceans associated with global warming.

In the future, Argo data will be combined with satellite altimetry (measurements of sea surface height) to improve predictions of hurricane intensity. Technical improvements could give the floats a longer life span, and new sensors could be added to the floats to measure things like dissolved oxygen and biological activity.

"There is huge interest in the climate problem and there will continue to be a strong need to monitor the oceans for their temperature and salinity, so the requirement for something like Argo goes on indefinitely," Roemmich said, "but I can't tell you how the technology might change. Perhaps we'll devise a better instrument to measure temperature and salinity -- or maybe an instrument that comes back after we're done with it."

More information  about the Argo array is available on the Argo Information Centre Web site.

For more stories on scientific innovations related to climate change, see Climate Change and Clean Energy.

(USINFO is produced by the Bureau of International Information Programs, U.S. Department of State. Web site:

By Cheryl Pellerin
USINFO Staff Writer

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