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Below the surface
Glider fleet will survey water around Antarctic Peninsula
Posted May 2, 2008
Oscar Schofield pauses the phone conversation for a moment, as he pulls up a Web page that tracks the location of two underwater gliders operated by Rutgers University’s Coastal Ocean Observation Lab.
He reports to his caller that one of the sleek robots has covered more than 2,000 kilometers since it left the New Jersey coast on March 7. It has made some 1,500 profiles of the water column, as it slowly bobs up and down in a sawtooth pattern below the surface, measuring physical ocean properties like salinity and temperature.
An associate professor at Rutgers whose research interests focus on phytoplankton, Schofield envisions a small fleet of these autonomous robots, known as Slocum gliders, swimming and prowling the cold waters off the Antarctic Peninsula to collect information about the rapidly changing marine ecosystem there.
“It’s just another tool, but it’s a real powerful tool, for filling in the picture” of climate change, said Schofield, now a principal investigator with the Palmer Long Term Ecological Research (PAL LTER) program.
The PAL LTER is a multi-disciplinary program to study the West Antarctic marine ecosystem over a long time scale, as typical National Science Foundation (NSF) grants last three to five years. The NSF established the PAL LTER, part of a larger network of LTER sites, mostly in and around the United States, in 1990.
In the last 18 years, the PAL LTER scientists have watched a warmer, moister climate migrate into the area around the U.S. Antarctic Program’s Palmer Station. This new subantarctic climate has driven the local Adélie penguin population to near extinction, and the researchers believe the upwelling of warmer ocean water plays a key role in accelerating melting along the icy edges of West Antarctica.
Much of the data collection over the last two decades has been from a science vessel during the month of January, the middle of the Antarctic summer. Now, with the Rutgers gliders, the researchers will cover more of the marine environment than ever before — and in new ways and at different times of the year.
The glider proved its worth during a test run in 2007, confirming what the PAL LTER researchers had suspected: that warm, deep ocean water was coming on to the continental shelf, bringing an enormous amount of heat to bear against the peninsula’s ice sheet and ice shelves.
“Just from throwing one glider out for three weeks, we got this tremendous new knowledge that there’s circulation all over the shelf of our region,” said Hugh Ducklow, the lead investigator for the PAL LTER.
Conceived by former Woods Hole Oceanographic Institution engineer Douglas Webb and named after the first man to sail solo around the world, the Slocum glider looks like a torpedo with wings.
It moves through the water by varying its buoyancy, sucking in about a coffee cup worth of water through its nose to dive and then expelling water to float back up, running horizontally in a sawtooth pattern. The relatively low energy requirements of the buoyancy pump allow most of the battery power to be devoted to scientific sensors.
Schofield said the latest robots, with extended bodies to carry additional batteries or instruments, can “fly” through the water for more than a month at a time, covering incredible distances, such as the glider winging its way toward Canada — 2,000 kilometers and counting.
“That’s enough distance that we can really start thinking about these things being networks,” Schofield said. He noted that the PAL LTER cruises have collected about 2,400 vertical profiles of the ocean over the last 18 years, one of the world’s most extensive regional marine records.
“That’s a huge amount of work,” he noted, but added, “The glider that flew last January [in 2007 on the LTER cruise] was a single system … it collected 1,200 profiles off of one battery pack.”
The glider remains submerged for several hours before surfacing to phone home through the iridium satellite system. It relays their data back to the Coastal Ocean Observation Lab, checks its e-mail for any new instructions, and then dives underwater again toward the next waypoint on its mission.Each glider weighs about 50 kilograms, and can easily be launched and retrieved from a small boat like a Zodiac. Scientists at the Coastal Ocean Observation Lab can track its movements and send commands remotely.