Scientists Discover Ominous Waters Under Antarctic Ice
It’s not a huge amount of melt per square foot. But over an area as large as two major European countries, that is scaling up. “What we concluded is that the melting is very small — it’s about a millimeter per year,” Siegert says. “But the catchment area is enormous, so you don’t have to melt much. It all flows into this river, which is several hundred miles long, and it is three times the flow rate of the River Thames in London.”
That water is under extreme pressure, both because there is a lot of ice pushing down from above, and because there isn’t much space between the ice and the rock for the liquid to move. “And because it’s under high pressure, it can lift the ice off its bed, which can reduce friction,” Siegert says. “And if you reduce that basal friction, the ice can flow much faster than it would otherwise.” Think of that ice as a puck sliding across an air hockey table, only instead of riding on air, the ice rides on pressurized water.
This huge hidden river, says University of Waterloo glaciologist Christine Dow, lead author of the new paper, “can pump an enormous amount of freshwater into the ocean.” And that could be bad news for the glacial ice’s connection to the floating ice shelf. “Where the ice starts to float is the most sensitive region,” she continues. “So anything that’s going to change where that ground line rests is going to have significant control over how much sea level rise we’re going to have going forward.”
What holds back the ice sheet — and keeps sea levels from jumping many feet — is the ice shelf, which acts like a large, heavy cork to slow the flow of a glacier into the sea. But in Antarctica, these corks are fragmenting as warming water eats away at the bottom of them. For example, the ice shelf of Antarctica’s Thwaites Glacier (aka the Doomsday Glacier) could collapse three to five years, recent research suggests. If we lost Thwaites completely, it alone would contribute 60 centimeters to sea level.
It’s not just Thwaites. Researchers find that many of Antarctica’s ground lines are receding, such as hairlines. But models predicting the future condition of these glaciers assume that grounding lines are static. Scientists already know that those models are missing another key factor that could affect how well these lines hold: an effect known as tide pumps. When the tides go in and out, they lift the ice shelf up and down, allowing warm seawater to flow inland and melt the underside of the ice. This new research now shows that meltwater under pressure also comes from the other direction, from the interior to the earth pipe.
“The problem is that when a lot of fresh water is pumped into the ocean, it floats up to the base of the ice, and it drags the warm ocean water along, melting that ice,” Dow says. “That causes the grounding line to retreat. And then all the ice that used to be on the ground now floats to immediately add to sea level rise and destabilize the whole system.” In other words, the ice doesn’t have to melt to raise the water level, because the massive volume also displaces liquid.
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