A vast aquifer "lake" lies trapped under southeastern Greenland, scientists report, based on ice core results. The finding may help reveal a changing climate's effects on the world's massive, but shrinking, ice sheets. (See "Greenland When It's Hot.")
Greenland's ice sheet, the second largest in the world, covers some 656,000 square miles (1,710,000 square kilometers). Together with Antarctica's even more vast ice sheet, its melting in a warming climate is a big factor in projections of future sea-level rise.
That is why the discovery of an aquifer some 27,000 square miles (70,000 square kilometers) in size underlying the frigid southeastern region of Greenland is a matter of considerable scientific interest. (See also: "Giant Canyon Discovered Under Greenland.")
"Think about it like a giant snow cone or slushie," said Lora Koenig of Cryospheric Sciences Laboratory at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "Or like a sandbox that is filled with water. There is water in the spaces between the ice crystals."
The liquid water is not a continuous body of water, as would be found in a surface lake, but it fills up the tiny spaces between ice crystals, said Koenig. She co-authored a paper published in the peer-reviewed journal Nature Geoscience on December 22 on the water discovery in Greenland.
In April 2011, scientists led by the University of Utah's Rick Forster took a core sample of the southeastern Greenland ice sheet before summer melting had begun. The scientists measured the upper layers of the ice, which is essentially compacted snow called firn.
Forster told National Geographic that the team had expected to find only solid material, given surface temperatures that were well below freezing at 0°F (-18°C).
But instead, they found that the ice they pulled up from a few meters down was wet with liquid water, and was right at freezing temperature (32°F or 0°C). "We were surprised and shocked," said Forster. "Ice doesn't melt in this area typically until June, so we knew it was water that had persisted throughout the winter."
The discovery of the firn aquifer "has uncovered a fundamental, but previously overlooked, component of meltwater runoff processes in Greenland," said geoscientist Joel Harper, of the University of Montana in Missoula, in a commentary accompanying the report.
"It's a surprising find because we know ice melts at the surface and water percolates down, but we thought it would refreeze," said Koenig. She added that the scientists think fresh snow that fell on top of the ice sheet after it melted insulated the water from the cold, keeping it at just the right temperature to stay liquid.
In April 2013, Koenig and a small team of colleagues went to Greenland to take additional core samples, this time with a drill that could better handle liquid water. The scientists also tapped flyover data from NASA's Operation Icebridge radar, which they used to calculate the size of the aquifer, which is larger than the state of West Virginia.
Koenig pointed out that this aquifer exists only in the top column of Greenland's ice sheet, which is an estimated 2,600 feet (800 meters) thick in that region. The liquid water has been found at about 39 to 131 feet (12 to 40 meters) below the surface of the ice, in the firn layer.
In contrast, the liquid lakes that have recently been explored in Antarctica lie at depths of thousands of meters, below the ice and on top of the bedrock. Scientists have been probing those deep lakes looking for life, though Koenig said no one has yet analyzed water from Greenland's aquifer for the presence of living things.
Koenig said the aquifer seems to be limited to southeastern Greenland, where the high level of snow accumulation seems to insulate the water and keep it warm enough to avoid freezing.
Clues to Global Warming and Sea-Level Rise?
Koenig said scientists don't know yet how much the under-ice aquifer might change from year to year.
"We do know the Greenland ice sheet is losing mass because of warming in the Arctic," she added. In fact, 2012 saw the highest amount of surface melt and runoff from Greenland ice ever recorded. Greenland lost 121 billion tons of ice a year from 1993 to 2005 and 229 billion tons a year between 2005 and 2010.
The fact that meltwater can remain in liquid form, trapped in the ice, for some time may provide new insight into how long it takes the water to get to the sea, said Koenig. That can determine how much and how fast sea level will actually rise, something that is of key importance to the millions of people around the world who live on the coasts. (See "Rising Seas" in National Geographic magazine.)
The estimated volume of water in Greenland's ice aquifer is 154 billion tons, which would be enough to raise global sea levels by 0.016 inches (0.04 centimeters) if all of it drained into the ocean at once. That's not a lot compared with Greenland's total ice pack, which is more than a mile thick in some places and would contribute more than 20 feet (6 meters) to sea-level rise if it melted all at once.
For now, the water being trapped in the ice "may delay the time it takes to get to the ocean, but at some point it needs to make its way to the ocean," said Koenig. "It may be coming more in spurts [rather] than coming out continually," she said.
In April 2014, scientists will return to Greenland to take more ice samples. They will attempt to date the water in the aquifer and will try to obtain flow measurements to see how the water is moving around and how long it stays trapped within the ice sheet, before eventually running to the sea.
Forster added that, when it comes to sub-surface melt water, "there are probably large mountain glacial systems that have something similar."