Scientists working in Greenland have discovered an extensive aquifer of meltwater that sits under the Greenland ice sheet all year round — but it's not known if this reservoir, which is about the size of Ireland, will ever make its way to the ocean.
Meltwater pouring off from Greenland's extensive ice sheets is a known contributor to rising sea levels. And in fact, high meltwater runoff is responsible for half of Greenland's mass loss — and it's a phenomenon that's progressively getting worse. It now appears, however, that much of Greenland's meltwater isn't getting to the ocean, which may help explain disparities seen between climate models and satellite observations.
The discovery came as a complete surprise to a team of geoscientists who were expecting to find layers of dry snow. In a new study published in Nature Geoscience, they describe how the water, instead of being stored in the air space between subsurface rock particles, sits in the air space between the ice particles. It's similar to the way fruit juice stays liquid in a slushie.
Image: Beeld: Universiteit Utrecht.
The team, led by the University of Utah's Richard Forster, had been drilling in Greenland in early spring — a time before the annual melt. As they brought up a core sample, water started gushing out of it. The new observations suggest that a significant amount of water is stored in this partially compacted snow, which is called firn. This water remains in liquid form all year round — even when freezing air temperatures reach -5ºF (-15ºC). The water is insulated by the large amounts of snow that fall on the surface of the ice sheet in late summer.
Unsure of just how much water was below the ice, the researchers used ice penetrating radar to identify the top of reservoir near the watery cores. The resulting data was used to search for and map how much more water sat below. The survey revealed a gigantic area — about 27,000 square miles (70,000 square km). But what the scans did not reveal was the depth of the aquifer, the top layer of which just sits a few dozen feet below the icy surface. The geoscientists think the depth of the reservoir is about 16 to 165 feet (5-50 meters).
Should this be the case, that's about 140 billion tonnes of water. That's equal to 0.4 mm of sea level rise per year, which is about half of Greenland's contribution to the sea each year. The researchers don't know if the water will ever make its way to the ocean.
"It depends on whether it is currently connected to a system that is draining into the ocean or if it is a bit isolated and completely acting as a storage source without a current connection," said Forster. "We don't know the answer to this right now. It's massive, it's a new system we haven't seen before — we need to understand it more completely if we are to predict sea level rise."
Read the entire study at Nature Geoscience: "Extensive liquid meltwater storage in firn within the Greenland ice sheet."
Top image: Surface melt water rushed along the surface of the Greenland Ice Sheet through a supra-glacial stream channel, southwest of Ilulissat. via. Ian Joughlin/Associated Press.