New seagoing robots read oceans' vital signs

WASHINGTON — Scientists have just finished deploying a worldwide network of 3,000 automated floating sensors that will provide unprecedented information about the oceans' powerful impact on the world's climate.

The Argo network, named for the ship that carried the fabled Greek sailors, the Argonauts, covers the seas in unmatched scope and detail. Because water covers 75 percent of the Earth's surface, what happens in the oceans affects rising sea levels, the warming of the atmosphere, the birth of tropical storms and hurricanes, and much of the world's food supply. The sea also absorbs half of the excess carbon that's blamed for global warming.

"Now we can accurately measure changing ocean temperature globally for the first time," said Dean Roemmich, a marine scientist at the Scripps Institution of Oceanography in San Diego.

Before Argo, oceanographers depended mainly on measurements taken for short periods in scattered locations. The new network is designed to produce a continuous stream of data from various ocean depths for decades.

"The climate science objectives that drive the Argo array require that we observe the global oceans indefinitely," said Roemmich, the co-chairman of the Argo steering committee. "Achieving the global array is merely the beginning."

A New Zealand research vessel dropped the last two units in the Argo fleet into the southern Pacific Ocean on Thursday. More than 30 countries have participated in the program since the first floats were deployed seven years ago.

The torpedo-shaped robots, each 5 feet long plus a 3-foot antenna, drift with the currents, rising and sinking to a depth of more than a mile. Every 10 days they bob to the surface and transmit their data to passing satellites.

As the robots rise and fall, their sensors record the temperature and salinity (saltiness) of the water at each depth, the ocean's so-called "vital signs." This is important, for example, because warmer water expands, causing sea levels to rise and threatening low-lying coastal areas.

The robots' movements also provide valuable information about the speed and direction of ocean currents.

The Argo floats will provide about 100,000 observations a year. Some 800 new instruments will have to be put in the water annually to replace ones that are no longer active.

Each float costs about $15,000, plus another $15,000 in operating costs over four years. The United States has paid about half the cost of the network.


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An animation of an Argo robot at work: