Researchers said they discovered a large reservoir of more than 100 billion tons of liquid water underneath Greenland's ice sheet, BBC News reported.
While drilling into the country's frozen surface in spring 2011, scientists unexpectedly struck more than 27,000 square miles of water - an area about the size of Iceland.
The discovery, they said in a study published in the journal Nature Geoscience, could provide important clues about sea level rise.
"We thought we had an understanding of how things work in Greenland, but here is this entire storage system of water we didn't realize was there," Richard Forster, lead study author and a glaciologist at the University of Utah, said in a statement. "The discovery was a surprise."
They said the water is stored in partially compacted snow or the air space between particles of ice, called firn. Its storage is similar to juice in a snow cone, BBC News reported.
"The surprising fact is the juice in this snow cone never freezes, even in the dark Greenland winter," Forster said. "Large amounts of snow fall on the surface later in the summer and quickly insulates the water from the sub-freezing air temperatures above, allowing the water to persist all year long."
Researchers found that the melting of the Greenland ice sheet has been a bigger contributor than they thought to sea level rise in the past century.
LiveScience, a science news Website, reported that scientists originally thought melted ice in Greenland went to the ocean or refroze on the ice.
The large slab of ice in Greenland, averaging 5,000 feet in thickness, is suffering "unprecedented melt" as global warming accelerates, Agence France Presse reported.
In 2012, the ice sheet lost a record 60 cubic miles in volume, making it the biggest single contributor to the rise in world sea levels, said Forster.
If the ice sheet completely melted, it would drive up sea levels by around 21 feet.
"Of the current sea level rise, the Greenland Ice Sheet is the largest contributor - and it is melting at record levels," Forster said. "So understanding the aquifer's capacity to store water from year to year is important because it fills a major gap in the overall equation of melt water runoff and sea levels."
Scientists say the next step is to determine whether the reservoir helps or hinders the survival of Greenland's ice sheet.
"It might conserve the melt water flow and thus help slow down the effects of climate change," said Forster. "But it may also have the opposite effect, providing lubrication to moving glaciers and exacerbating ice velocity and (iceberg) calving, increasing the mass of ice loss to the global ocean."
