Argo takes the pulse of the ocean

Covering more than 70 percent of the Earth's surface, the oceans are difficult to observe in their entirety. However, with the help of UW scientists, Argo, a network of ocean-observing instrument packages, is able to do just that. Argo reached its final configuration Nov. 2 when the 3000th float was launched.

Taking its name from the ship that carried Jason and the Argonauts in Greek mythology, the Argo network grew out of the World Ocean Circulation Experiment (WOCE). WOCE ran throughout most of the 1990s, using instruments cast from ships to take measurements similar to the Argo floats.

"Argo is unique among ocean observing systems," said Stephen Riser, a professor of oceanography and the principal investigator on the Argo project at the UW. "Unlike ships, [the network] maintain[s] a constant presence in the ocean on a global scale. The data quality is excellent. ... It's also freely available."

The cylindrical floats that comprise Argo can be deployed from airplanes, research vessels and commercial ships. Once in the water, the autonomous floats descend to 2000 meters, taking temperature, pressure and salinity data. After obtaining this initial profile, the floats rise to a parking depth of about 1000 meters. They then drift for 10 days before slowly rising to the surface to gather and transmit their data. This process continues throughout the lifetime of the floats.

"Argo floats live for about four and a half years," Riser said. "With a fleet of 3000, we have to keep replenishing them at a rate of 700 per year."

That means constructing and deploying the floats. The UW is one of four institutions that does this in the United States. A team of three engineers with Riser's group works to develop, build and test the floats to prepare them for deployment. This year, they built custom floats that can function under the ice in the Antarctic. The engineers often deploy the floats themselves, traveling to locales such as the South Pacific Ocean, the Weddell Sea near Antarctica and the Indian Ocean.

"The UW is one of the top deployers of Argo floats," said Rick Rupan, a research engineer with the group. "We also have probably the best success rate."

The floats run on batteries and are able to move vertically by adjusting their buoyancy. The onboard electronics, design and mechanics are continuously engineered to improve performance and save power, increasing the lifetime of the floats.

"Since we don't get them back, we're always trying to squeeze the engineering behind them," Rupan said. "The longer they last, the better."

Once the data is received by satellites, it is distributed for use by scientists around the world. Riser and his two graduate students analyze the data on a daily basis. One of those students, Li Ren, has used data from floats in the North Pacific Ocean to calculate changes in salinity related to increased rainfall in the past decade. Her results are consistent with precipitation measurements made by satellites, lending credence to those observations.

The Argo program is funded at the UW through 2011. It receives strong support from the international community as well, with 22 countries involved.

"This is a whole new generation of global ocean measurement," Riser said.

[Reach reporter Brian Smoliak at news@thedaily.washington.edu.]