Around the planet’s oceans, nearly 4,000 floats - many of them built at the University of Washington - are plunging up and down, collecting and transmitting observations of the world’s oceans.
This fall, one of these diving robots made the program’s 2 millionth measurement , reporting temperature and salinity recorded to a depth of about a mile.
" Argo program achieves milestone with 2 million ocean measurements ” -NOAA
" ’Silent sentinels’ deliver their 2 millionth snapshot of our changing oceans ” - Intergovernmental Oceanographic Commission
" Fifteen years of ocean observations with the global Argo array ” by Stephen Riser et al.
The Argo Program áis a 20-year-old project to gather 3D data on the oceans. The U.S. program is part of an international observing effort with 26 countries that operate floats throughout the planet’s waters.
"When we started in 1999, no one would have even considered the 2 million profile milestone,” said Stephen Riser , a UW professor of oceanography. "In the beginning there was some question about whether the instruments would even work well enough to do this. We were just hoping it would work for the first few years.”
The UW has manufactured between one third and one half of the U.S. floats now in use, Riser said, which account for about half the international total. So the UW has manufactured about a fifth or a sixth of the world’s supply.
The UW manufactures roughly 110 floats per year that get deployed around the planet. Two undergraduates work in the lab and three graduate students are working with the data. Of this year’s UW floats, two-thirds were destined for the South Pacific and the other third are going to Antarctica.
Scientists say the nearly 20-year-old robotic fleet has transformed oceanography: Satellites track information only from the ocean’s surface, while ship-based observations are expensive and see only a small snapshot.
"Not to be too hyperbolic, but Argo has really revolutionized physical oceanography,” said Alison Gray , an assistant professor of oceanography. "I think it’s been one of the largest successes of any observational program of its kind.”
The cylindrical robots, about the size of a large rolled-up poster, dive down to a depth of 1 kilometer (0.6 miles) to drift with currents, then later sink down to 2 kilometers. After 10 days below the surface they adjust their buoyancy and gather data on the upward trip. Once at the surface, an antenna beams data back to computers onshore. A single battery lets the robot explore unaided for four to five years.
"One of the most important practical uses for the data is in weather forecasting, in that the data that we get from Argo have significantly improved weather forecasts and marine forecasting around the world,” Gray said. "But scientists are interested in the data to understand the processes that are controlling the ocean, and how the ocean impacts the climate system.”
More than 4,000 scientific papers and 275 doctoral theses have been written using Argo data. Observations are uploaded to the internet every three hours and are then available for free for anyone to use.
"That’s become the norm, the real-time availability of data,” Riser said. "But that was not the norm when we started in 2000.”
In the future, Deep Argo and Biogeochemical Argo floats will travel deeper and measure more things than the original devices. Both are in small-scale prototype mode now, Riser said, and researchers hope to secure funding for a larger-scale deployment. In addition to temperature and salinity these can measure ocean pH, oxygen, nitrate, chlorophyll that results from photosynthesis, and light penetration.
While the existing Argo array helps to understand the movement of heat in the oceans, the newer technology will explore the deep ocean and help track the movement of carbon, which is the other half of the climate puzzle, Riser said.
"In coming years, it will be really important to maintain the core array, the high-quality data that’s coming in, but also to expand into these new areas: sensors that can measure new variables, and technology that lets us go into deeper water or even into coastal regions,” Gray said.
The UW has already been building biogeochemical floats as part of a dedicated project to study the ocean around Antarctica. A global Argo version would be similar, Riser said, but without the ice-avoidance capabilities.
"The biogeochemical floats will be a whole different set of results that we can’t even imagine right now,” Riser said. "It won’t just be the heat part of the ocean cycle, it will be the carbon cycle. There’s a tremendous amount to learn.”