Greenland has been hiding a lot of melt water that may or may not end up contributing to rising sea levels. The discovery of liquid water hiding inside layers of glacier-top snow in southern Greenland came as a shock to the scientists drilling the ice.
"It was a complete surprise," said Richard Forster of the University of Utah in Salt Lake City. "We brought the core up and the water was just gushing out of it."
Forster's team had expected layers of dry snow, which had been the case in other areas they drilled, because it was early spring and there had not been a chance for the surface ice to melt and seep down into the layers of packed snow beneath the surface, called firn. The liquid water also worried the team because the ice drilling probe they were using had unprotected electronics on it not designed for submersion in water.
To get a better idea how much water was hidden in the packed snow, the team employed ice penetrating radar to identify the top of the ice-cold aquifer near the watery cores, and then used that information to search for and map out how much more water there was tens of meters down in the firn. What they found was evidence of about 70,000 square kilometers of water – almost the area of Ireland. They reported their discovery in the Dec. 22 issue of the journal Nature Geoscience.
What they were not able to determine, because of those exposed electronics in their drill, was the depth of the firn aquifer, which was filling the pore spaces between grains of firn in the same way ground water fills the spaces between grains of rock and dirt in the ground. Nor were they able to determine whether that water eventually freezes and becomes part of the glacier, or makes its way to the sea.
"An important source of uncertainty in determining Greenland's runoff - and how it might change in the future - has been in understanding how much of the melt water from firn-covered regions is partitioned into runoff, and how much is left behind in the ice sheet after infiltrating into underlying firn and refreezing," explains Joel Harper of the University of Montana, who commented on Forster's team's work in a separate article in Nature Geoscience.
"Most models assume water runs off or refreezes," said Forster. This water indicates there is a third possibility as well: liquid melt water stored in the firn. "Is this water buffering sea-level rise? Or is it already connected and passing through and there's just a delay? Right now we don't know. It may be something in between."
The researchers returned in April 2013 to conduct work with water-tight drill probes and will be publishing their findings soon.