Huge underground water system helps float Antarctica’s glaciers

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Lake Whillans is a strange body of water, starting with the fact that there is liquid to fill it at all. Though buried under more than 2,000 feet of Antarctic ice, temperatures soar to just 0 degrees Celsius, thanks to a combination of geothermal heat, intense friction from ice-scraping rocks, and that thick glacial blanket that protects it from the Arctic air. Given the immense pressure down there, that’s just soft enough to keep the lake waters watery. Stranger still, Lake Whillans is also teeming with life. A decade ago, a study found thousands of varieties of microscopic critters, thought to have fed on nutrients left behind by seawater sloshing into the basin several millennia ago, when the glaciers last retreated.

More recently, Chloe Gustafson, a geophysicist at Scripps Institution of Oceanography, arrived at the remote patch of ice above Lake Whillans with another mystery in mind: What’s going on beneath that lake? Antarctic researchers had long suspected that the pipes beneath the glacier ran much deeper than they could see. Any groundwater under the lake would affect how the ice above moves oceanward, and thus how quickly it could contribute to rising seas. But they couldn’t definitively prove what groundwater was there. It was too deep, too icy to be mapped with the traditional tools of glaciology, such as reflecting radar signals off the ice or setting off explosives and listening to the shock waves.

In a study published in the journal Science, Gustafson’s team provides a long-awaited map of the watery world beneath the ice. A huge reservoir of groundwater reaches more than a kilometer below subglacial bodies of water such as Lake Whillans, which contains 10 times as much water. To see it, the researchers turned to a technique called magnetotellurics, or MT, which uses natural variations in Earth’s electromagnetic field to paint a broad picture of the sediment beneath. They expect similar groundwater systems to support other areas where the ice flows quickly — so-called ice flows that represent about 90 percent of the ice that makes its way from the continent’s interior to the ocean. “This is one piece of the puzzle wondering why this ice flows the way it flows,” Gustafson says. “So it’s very important to understand what’s going to happen to Antarctica.”

Scientists have long understood that subglacial water plays a role in how the ice moves above it. One factor is how it changes the sediment below, creating ruts and flats on the terrain. Another is by smearing the ground, which allows the ice to slide faster. “If you have water on a Slip ‘n Slide, you’re going to slide pretty quickly,” Gustafson says. “If you don’t have water, you won’t get very far.” Understanding that subglacial hydrology is especially important for researchers racing to model particularly precarious ice regions, such as Thwaites Glacier, a few hundred miles from Whillans. In January, a group of researchers reported that Thwaites — the so-called Doomsday Glacier, which holds back enough ice to raise sea levels globally by 2 feet — could collapse within five years.

But those models are not complete without groundwater. Researchers had long noticed that more water flowed from the Whillans ice stream than expected, said Slawek Tulaczyk, a professor of earth sciences at UC Santa Cruz who studies the region but was not involved in the study. This was strange. As ice sheets approach the ocean, they tend to get thinner and thus less good at insulating the ground from the frigid Antarctic air. At these edges, the water should tend to freeze, slowing the movement of the ice. But that was not what glaciologists saw. “This was the riddle,” he says. Somehow the patterns they observed were “thwarting thermodynamics.” The researchers hypothesized that nearly half of that water must be rising from unmapped underground sources.

Gustafson’s team was going to map it out. The ice above Lake Whillans is located in the western part of Antarctica, at the base of the craggy Transantarctic peaks that divide the continent. The area gained favor with scientists conducting research in the pre-GPS era because those mountains served as aids to navigation. But it is remote. “It was the longest, most grueling camping trip of my life,” Gustafson says of weeks of trudging through the snow and ice, digging holes where the team would leave devices that passively listen for electromagnetic signals. The instruments would remain there for 24 hours before the researchers dug them up and moved them to the next location, two kilometers away.

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