The amount of melt per square foot is not huge. But in an area the size of two European powers, the scale has grown. “We came to the conclusion that the amount of melt was very small — about a millimeter per year,” Siegert said. “But the catchment area is huge, so you don’t need much melting. All of this feeds into the hundreds of kilometres of river, which flows three times as fast as the Thames in London. “
Water is under extreme pressure, both because there is a lot of ice pressing down from above and because there isn’t much space between the ice and the bedrock for the liquid to move around. “And because it’s at high pressure, it lifts the ice off the bed, which reduces friction,” Siegert said. “If you reduce this underlying friction, the ice will flow much faster than it would otherwise.” Think of ice as a puck sliding across an air hockey table, except instead of riding on air, the ice rides on pressurized water .
University of Waterloo glaciologist Kristin Dow, lead author of the new paper, said the huge hidden river “can pump a lot of fresh water into the ocean.” That could be bad news for the connection of glacial ice sheets to floating ice shelves . “Where the ice starts to float is the most sensitive area,” she continued. “So anything that changes where the grounding line is located will have a big impact on how much sea level rise we have going forward.”
What holds back the ice sheets — and keeps sea levels from rising a few feet — is the ice shelf, which acts like a big, heavy cork that slows the flow of glaciers into the sea. But in Antarctica, those corks are crumbling as warming waters eat away at their bottoms. For example, recent research suggests that the ice shelves of Thwaites Glacier (aka Doomsday Glacier) in Antarctica could collapse within three to five years. If we lose Thwaites altogether, that alone would cause sea levels to rise by two feet.
Not just Thwaites. The researchers found that many grounding lines in Antarctica were receding, like hairlines. However, models that predict the future state of these glaciers assume that the grounding line is static. Scientists already knew that the models were missing another key factor that could affect how well the lines hold: an effect called tidal pumping. As tides come in and out, they lift the ice shelves up and down, allowing warm water to flood inland and melt the bottom of the ice. The new study now shows that pressurized meltwater is also coming from the other direction, flowing from inland to the grounding line.
“The problem is, if you have a lot of fresh water being pumped into the ocean, it’s going to buoyantly move up to the bottom of the ice and drag the warmer water up and melt the ice,” Dow said. “That caused that grounding line to retreat. Then all the ice that was stranded before is now floating to immediately Exacerbating sea level rise and destabilizing the entire system. In other words, the ice doesn’t need to melt to raise the water level, because its enormous volume also displaces the liquid.
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