PARIS (AFP) ― A vast store of water equivalent in area to Ireland lies beneath Greenland’s icesheet, and it may provide answers to one of the big riddles of climate change, scientists reported on Sunday.

In 2011, U.S. scientists crossed the southern Greenland icesheet on an expedition to drill ice cores, a benchmark of annual snowfall.

They were stunned when they drilled into a layer of compressed snow called firn ― for instead of piercing an icy sponge at a depth of 10 meters as expected, they encountered liquid water and ice granules instead.

They carried out another drilling a few kilometers away, and got the same result when they reached the firn layer at 25 meters.

Seeking an answer to the liquid mystery, a NASA plane with terrain-mapping radar was brought in to fly over the zone, as well as ground-penetrating radar towed by a snowmobile.

Radar returned bright reflections pointing to the presence of a vast reservoir of water beneath the ice.

Extending down Greenland’s southeastern flank, the hidden water covers a whopping 70,000 square kilometers. It is found at depths beneath the ice that range from 5 to 50 meters.

The store is believed to hold melted snow from the previous summer, according to the paper published in the journal Nature Geoscience.

It works similarly to an aquifer below the ground, which is a spongy rock that holds water in its air spaces.

In this case, the air spaces in the firn are occupied by water, resulting in something akin to the crushed-ice soft drink called a snow cone.

“The surprising fact is the juice in this snow cone never freezes, even in the dark Greenland winter,” said Rick Forster, a professor of geography at the University of Utah, who led the mission.

“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.”

The secret store appears to have been around for some time and was not initiated by man-made global warming, the scientists believe.

But, they add, it could provide insights into the fate of the icesheet, a key question in climate science.