Dec. 26, 2013 -- A large liquid water reservoir buried underneath compacted snow and ice in Greenland has recently been mapped by researchers using data from NASA's Operation IceBridge airborne campaign.
A team of glaciologists found the aquifer while drilling in southeast Greenland in 2011 to study snow accumulation. Two of their ice cores were dripping water when the scientists lifted them to the surface, despite air temperatures of -4˚F (-20˚C). The researchers later used the data to confine the limits of the water reservoir, which spreads over 27,000 square miles (69,930 square km) -- an area larger than the state of West Virginia. The water in the aquifer has the potential to raise global sea level by 0.016 inches (0.4 mm).
Southeast Greenland is a region of high snow accumulation. Researchers now believe that the thick snow cover insulates the aquifer from cold winter surface temperatures, allowing it to remain liquid throughout the year. The aquifer is fed by meltwater that percolates from the surface during the summer.
The new research is being presented in two papers: one led by University of Utah's Rick Forster that was published on Dec. 22 in the journal Nature Geoscience and one led by NASA's Lora Koenig that has been accepted for publication in the journal Geophysical Research Letters. The findings will significantly advance the understanding of how meltwater flows through the ice sheet and contributes to sea level rise.
Koenig, a glaciologist with NASA's Goddard Space Flight Center in Greenbelt, Md., co-led another expedition to southeast Greenland with Forster in April 2013 specifically designed to study the physical characteristics of the newly discovered water reservoir. Koenig's team extracted two cores of firn (aged snow) that were saturated with water. They used a water-resistant thermoelectric drill to study the density of the ice and lowered strings packed with temperature sensors down the holes, and found that the temperature of the aquifer hovers around 32˚F (0˚C), warmer than they had expected it to be.
Koenig and her team measured the top of the aquifer at around 39 feet (12 meters) under the surface. This was the depth at which the boreholes filled with water after extracting the ice cores. They then determined the amount of water in the water-saturated firn cores by comparing them to dry cores extracted nearby. The researchers determined the depth at which the pores in the firn close, trapping the water inside the bubbles -- at this point, there is a change in the density of the ice that the scientists can measure. This depth is about 121 feet (37 meters) and corresponds to the bottom of the aquifer. Once Koenig's team had the density, depth and spatial extent of the aquifer, they were able to come up with an estimated water volume of about 154 billion tons (140 metric gigatons). If this water was to suddenly discharge to the ocean, this would correspond to 0.016 inches (0.4 mm) of sea level rise.
Researchers think that the perennial aquifer is a heat reservoir for the ice sheet in two ways: melt water carries heat when it percolates from the surface down the ice to reach the aquifer. And if the trapped water were to refreeze, it would release latent heat. Altogether, this makes the ice in the vicinity of the aquifer warmer, and warmer ice flows faster toward the sea.
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