A massive rift valley that lies under a portion of the West Antarctic ice sheet could be speeding its melt, according to scientists who compared their discovery to a frozen Grand Canyon.
The subglacial basin underneath the Ferrigno Ice Stream is up to a mile deep in places. It lies in West Antarctica, a region where thinning glaciers shed so much ice they contribute 10 percent of global sea-level rise.
For scientists, news of the ice-filled rift valley goes beyond novelty. They hope the discovery will help them understand how the contours of the bedrock that underlies most of Antarctica's ice affects where, and how quickly, that ice will melt as the climate changes.
Rob Bingham, the University of Aberdeen glaciologist who led the new study, said the rift appears to connect inland portions of the Antarctic ice sheet to the ocean.
That is significant because a recent British Antarctic Survey study concluded that influxes of warm ocean water are driving ice loss in West Antarctica. The warm currents eat at the floating tongues of ice that help slow the seaward flow of glaciers sitting on Antarctic bedrock.
When those ice tongues disappear, the ice on land speeds up and thins as it slides to the coast and calves icebergs.
The discovery of the new rift "ties in so well with the signal of ice thinning," Bingham said. "There is a clear correspondence with this feature that was created over thousands of years and this phenomenon that has been happening over 20 years."
He and several colleagues from the British Antarctic Survey published the new findings yesterday in the journal Nature.
Studying the two extremes
Bingham said the topography in and around the Ferrigno Ice Stream appears to be similar to bedrock configurations that underlie two much-studied and rapidly thinning glaciers in West Antarctica, Pine Island and Thwaites.
"Pine Island and Thwaites are the absolute extremes," he said. "They are the ones experiencing the most thinning, whose loss would cause the greatest impact on sea level." (Pine Island Glacier, Antarctica's speediest, sheds 46 billion metric tons of ice per year.)
Though the Ferrigno Ice Stream isn't moving as quickly or shedding as much ice as Pine Island, its melting may still be at a more advanced stage.
"It doesn't have an ice shelf in front of it," Bingham said of the ice stream. "We think there was an ice shelf there, and it has been removed by a warm sea. ... It has potentially experienced warming before Pine Island and Thwaites did."
The new study marks the first time scientists have visited Ferrigno since the early 1960s, when the U.S. government sponsored a series of overland traverses to explore Antarctica's vast expanse of ice. Today, the Ferrigno Ice Stream lies hundreds of miles from the nearest science base.
"When you mount a mission anywhere in this region of West Antarctica, you're talking very serious logistics," Bingham said. "It's hard to get planes into this area. The weather is not hospitable."
But satellite data showing that the ice stream is one of the areas where the edges of the Antarctic ice sheet is thinning drew his attention.
An ancient network
Bingham, with help from the British Antarctic Survey, traveled south during the Antarctic summer of 2009-2010 to survey the area. He and an assistant spent 10 weeks mapping the hidden world beneath the ice stream using a Ski-Doo pulling ground-penetrating radar.
They supplemented that data with additional ice-thickness measurements gathered by NASA's Operation IceBridge project, which uses specially outfitted aircraft to monitor polar ice.
The magnitude of what lay under the Ferrigno Ice Stream's smooth surface soon became apparent.
"We knew next to nothing about the subglacial topography. It was kind of a blank canvas," Bingham said. "After one of the first traverses, I was back in the tent looking at data on my laptop, and I saw that this bed dropped away in a spectacular manner."
At one point near the edge of the hidden rift valley, the ice is about three-tenths of a mile thick. But about 20 miles away, over the ice-filled rift, it is about a mile thick.
The newly discovered rift is part of an ancient network, the West Antarctic Rift System, that lies between eastern and western Antarctica. The most explored sections of the rift system are near the Ross Sea, close to the United States' McMurdo Station and the Transantarctic Mountains.
Bingham plans to return to Antarctica in 18 months to work on a study investigating the stability of the West Antarctic Ice Sheet, with a particular focus on Pine Island Glacier. But he hopes the news about Ferrigno Ice Stream's dramatic topography will spur further research there, he said.
Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500