|December 27, 2013|
Giant Aquifer Discovered Beneath Greenland
|In April 2011, researchers on the Greenland ice sheet were drilling an ice core, trying to understand how much snow accumulates on the sheet each year.|
About 30 feet down, though, they hit water.
"There was just water gushing out of the core itself," said Richard Forster, a glaciologist at the University of Utah whose students were among those drilling the core. "So that was a complete surprise---we weren't expecting anything like that at all."
It turns out the team had happened upon a giant aquifer. At 27,000 square miles, it's larger than the state of West Virginia---buried underneath the snow covering the ice sheet. Their finding was published yesterday in the journal Nature Geoscience.
Prior to this discovery, scientists had no idea this aquifer existed, Forster said. The Greenland ice sheet is incredibly large, covering a land area the size of Arizona, California, Colorado, New Mexico, Nevada and Utah combined.
"This is a feature that hadn't been known about before at all," he said.
The discovery has the potential to change researchers' understanding of how ice melt from the Greenland ice sheet contributes to sea-level rise.
Water, water everywhere
The aquifer is located in a type of snow called firn. Firn, a name originating from a Swiss German word meaning "last year's," is snow from years past that has compacted but not yet turned into glacier ice.
The original goal of the research project, which took place in the southeastern part of the ice sheet, where snowfall is very high, was to use the layers of firn accumulated in the ice core to measure how much snowfall occurs there each year.
When the scientists encountered water, they had to move to a new site, because their drill, which has an external motor, was not equipped to run in water.
Yet in the new site, after drilling 80 feet down into the firn, they came upon water yet again, even though air temperatures at the time were 4 degrees below zero Fahrenheit.
After some satellite phone calls from the ice sheet back to Forster, the drill team started to form a hypothesis about the water. They guessed there might be a significant amount of water that melted in the summer and was then insulated by winter snowfall so that it remained in liquid form.
"As we talked about it more, it kind of made sense that in a high accumulation layer, you could start to insulate the water very quickly," said Forster.
The researchers then took some ground-penetrating radar measurements in the area and mapped part of the aquifer.
At the same time, NASA's IceBridge campaign was conducting aerial flights over Greenland, part of an effort to map the ice sheet. That plane was equipped with different types of radar, some of which could see into the ice sheet.
Forster and his fellow researchers were able to use that data to map what they believe is the full extent of the aquifer. Although they are still trying to determine exactly how deep it is, their preliminary estimate, which is being published in the journal Geophysical Research Letters, puts the amount of water in the aquifer at 150 trillion tons.
That's enough water to raise global sea levels by 0.4 millimeter, if it all flowed into the sea at once. Currently, Greenland's ice sheet melt contributes to about 0.7 millimeter of sea-level rise each year.
"So that ends up being a significant volume of water," Forster noted.
Although the Greenland ice sheet experienced record-breaking melt in 2012, which may have slightly increased the aquifer's size, based on model results the researchers believe it has been in existence at least since the 1970s.
Aiding ice melt estimates
Scientists studying how ice melt from Greenland affects sea-level rise will now need to learn more about the role the newly discovered aquifer plays in transporting water to the sea, or lubricating ice sheets on their way out to the ocean.
Richard Alley, a glaciologist at Pennsylvania State University and an authority on ice sheet melt and sea-level rise who was not affiliated with the research, called the paper a "fascinating piece."
Alley likened the water found underneath the ice to the liquid flavoring of a snow cone that flows between the ice crystals that make up the cone.
"The existence of this rather flavorless natural snow cone has many implications for the future of the ice sheet, some that may make the ice go away faster, and others that help keep the ice a little longer," he wrote in an email.
"This doesn't change our knowledge that too much CO2 in the air will melt Greenland's ice, but it will help us make better estimates of how much and how fast," Alley added.
It's possible, said Forster, that the water in the aquifer is connected to a network of crevasses and streams and it already flows down to ice sheets and speeds their path to the sea. But there's also a chance that the aquifer is more like a giant storage area for water that might one day burst like a broken dam, pushing a large amount of water out of the ice sheet.
"Those are kind of the two extreme possibilities," Forster said. In reality, a little of both might be happening.
That's the next step in learning more about the aquifer. Forster has applied for additional funding to return to the aquifer and learn more about how this giant, underground water pocket might affect ocean levels in the future.
"We need to understand this better to really assess what it means for current sea-level rise and future sea-level rise from Greenland," he said.