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Deploying an Argo float
These floats are battery-powered and neutrally buoyant so they can drift at depth. Every 10 days, the floats rise to the surface while measuring temperature and salinity. When they reach the surface, the floats transmit the data to satellites, which determine the floats' position. One recently sent the one-millionth Argo data transmission. Credit: California Polytechnic State University
Like a bunch of fussy nurses, a fleet of five-foot-tall devices has been constantly taking the ocean’s temperature, measuring its saltiness, and gathering other information to monitor the health of the body of water that covers more than 70 percent of the planet.
One of those autonomous devices recently collected the one millionth profile.
To put this achievement in perspective, it took oceanographers more than 100 years to collect half a million profiles in the upper 3,000 feet of the ocean. The Argo fleet, now more than 3,000 floats strong, is expected to report its second millionth profile just eight years from now.
Scientists have been quick to use the data. Since the program began in 1999, scientists have published more than 1100 studies based on the data collected from the Argo fleet.
Gregory Johnson, Ph.D., an oceanographer in Seattle, Wash., at NOAA’s Pacific Marine Environmental Laboratory which deploys Argo floats and develops data quality control methods, used the data for his work which includes new insights into heat gains in Antarctic waters and how deep ocean waves move in the Indian Ocean.
"The year-round, globally distributed Argo data not only revolutionize our ability to study modern ocean temperature, salinity, and currents; they also greatly improve our ability to analyze ocean changes over decades, even a century, by facilitating comparisons with historical data," Johnson said.
It was well known that the ocean absorbs heat, but scientists needed more details, especially as they better understood the interaction between the ocean and the atmosphere and that role in regulating climate.
Sydney Levitus, director of the NOAA World Data Center for Oceanography in Silver Spring, Md., is known for his seminal work on ocean heat content.
“Argo data allows us to generate much better estimates of changes of quantities such as ocean heat content and salinity changes that are critical for understanding the role of the ocean as part of earth's climate system,” Levitus said. “The Argo project has already dramatically changed our ocean observing system for the world ocean and will continue to do so as the technology on which Argo is based continues to advance.”
Argo floats create an ocean-wide monitoring network
This Science on a Sphere® visualization shows the coverage buoys in the Pacific region - each dot in the ocean represents one of the Argo buoys.
The data from more than half of the floats – about 1,800 of them – come into the only U.S. Argo data center, at NOAA’s Atlantic Oceanographic and Meteorological Laboratory in Miami, Fla. Here a small team of about four gather the incoming data, translate it into real physical units – such as pressure, temperature and salinity – and then pass it through an automatic quality control. Within 24 hours, about 90 percent of the data are ready to be shared with users worldwide.
Claudia Schmid, Ph.D., the Argo data manager, is also a scientist who studies ocean circulation and ocean/atmosphere interaction. She’s written papers on the circulation of the Antarctic Intermediate Water based on Argo data.
“We can now derive the three dimensional flow field in high resolution without using numerical models thanks to the data collected by Argo floats,” she said. “It’s a dream come true.”
Scientists were also quick to see the usefulness of the free-floating instruments and are adding new sensors, such as those to measure oxygen and nitrate. By using a different transmitting system, floats can stay under the ice in the polar regions and store and send more data than the original floats could.
In addition to new uses, the floats are also lasting longer. The floats that first went into the water in 2000 were expected to last about three to four years – the newer ones can last about twice as long.
In partnership with the Scripps Institution of Oceanography, Woods Hole Oceanographic Institution and the University of Washington, NOAA is committed to maintaining one-half of the worldwide Argo network and supports the U.S. component of the international program.
Argo maintains a bibliography of journal articles as well as submitted and in-press journal articles.
NOAA's mission is to understand and predict changes in the Earth's environment, from the depths of the ocean to the surface of the sun, and to conserve and manage our coastal and marine resources. Join us on Facebook, Twitter and our other social media channels.