Extensive groundwater system helps feed Antarctic glaciers

Lake Whillans is a strange body of water, starting with the fact that there is liquid to fill it. Although buried under more than 2,000 feet of Antarctic ice, its temperatures soar to just under 0 degrees Celsius, thanks to a combination of geothermal heat, intense friction of ice scraping rock, and this thick ice cover the protection from polar air. Considering the immense pressure there, it’s just mild enough to keep the lake water watery. Stranger still, Lake Whillans is also teeming with life. Investigation a decade ago found thousands of varieties of microscopic creatures, thought to feed on nutrients left behind by seawater that poured into the basin several millennia ago, when the glaciers last retreated.

More recently, Chloe Gustafson, a geophysicist at the Scripps Institution of Oceanography, arrived at the isolated expanse of ice above Lake Whillans with another mystery in mind: what’s going on beneath this lake? Antarctic researchers had long suspected that the plumbing under the glacier was much deeper than they could see. Any groundwater below the lake would have implications for how the ice above moves toward the ocean, and therefore how quickly it could contribute to rising seas. But they couldn’t definitively prove what groundwater was there. It was too deep, too covered in ice, to map with the traditional tools of glaciology, like bouncing radar signals off the ice or setting off explosives and listening for shock waves.

In a published study in the review Science, Gustafson’s team offers a long-awaited diagram of the aquatic world under the ice. A vast reservoir of groundwater extends over a kilometer below subglacial water bodies like Lake Whillans, holding 10 times as much water. To see this, the researchers turned to a technique called magnetotellurics, or MT, which harnesses natural variations in the Earth’s electromagnetic field to sketch a broad picture of the sediments below. They expect similar groundwater systems to underlie other areas of fast-flowing ice – the so-called ice streams that account for about 90% of ice flowing from the interior of the continent towards the ocean. “It’s a piece of the puzzle asking why this ice is flowing the way it does,” says Gustafson. “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 above it moves. One factor is how it alters the sediment below, creating ruts and planes on the ground. Another is to lubricate the floor, which allows the ice to slide off faster. “If you have water on a Slip ‘n Slide, you’re going to slip pretty quickly,” says Gustafson. “If you don’t have water, you won’t get very far.” Understanding this subglacial hydrology is particularly important for researchers rushing to model particularly precarious regions of ice, 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 enough ice to raise global sea levels by 2ft – could collapse within five years.

But without groundwater, these models are incomplete. Researchers have long observed that more water is pouring under the Whillans Ice Stream than expected, says Slawek Tulaczyk, an earth science professor at UC Santa Cruz who studies the area but was not involved in the study. the research. It was strange. As the ice sheets approach the ocean, they tend to thin out and therefore less well insulate the ground from the frigid Antarctic air. On these edges, the water should tend to freeze, slowing the movement of the ice. But that was not what glaciologists saw. “That was the enigma,” he says. Somehow, the patterns they observed “counteracted thermodynamics.” The researchers speculated that nearly half of this water must come from unmapped underground sources.

Gustafson’s team set out to map it. The ice above Lake Whillans is in the western part of Antarctica, at the foot of the Transantarctic Peaks that divide the continent. The area gained favor with scientists conducting research in the pre-GPS era because these mountains served as navigational aids. But it is far. “It was the longest, most exhausting camping trip of my life,” Gustafson says of weeks spent trudging through snow and ice, digging holes where the team would leave devices that passively listen to people. electromagnetic signals. The instruments sat there for 24 hours before researchers dug them up and moved them to the next site two kilometers away.

About Lucille Thompson

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