A new study looked at rivers and streams flowing on the top of Greenland's ice sheet that have not been accounted for in previous models, predicting the object's ability to cause devastating rises in sea level.
The findings suggests this "missing water" could be responsible for even more sea level rise that the ice sheet's aquamarine lakes and ice that slides into the water to form icebergs combined, the University of California, Los Angeles, reported. The findings show in the summer months when the ice thaws these waterways cause a complex drainage system that captures almost all of the surface runoff.
"It's the world's biggest water park, with magnificent and beautiful -- but deadly -- rushing blue rivers cutting canyons into the ice," said Laurence C. Smith, the study's lead author and the chair of UCLA's geography department.
To make their findings a team of researchers spent six days in July 2012 gathering measurements in the region, which is so dangerous that this type of study has never been conducted in the past. They mapped the river networks and computed the rivers' flow rates using a helicopter as well as military-grade satellite imagery, buoys outfitted with GPS technology and a drone boat. The study happened to coincide with an unusually drastic melt season which has only been seen once before in the past 700 years.
The team was hoping to determine how much meltwater was restrained by the system and how much of it was released into the ocean.
"The question was whether the ice sheet acts like a sponge or like Swiss cheese," Smith said.
The researchers determined the answer was "a little bit of both." The sheet's surface acted more like "Swiss cheese" because all 523 actively flowing streams and rivers across a 2,000-square-mile area of the ice sheet drained into sinkholes that carried the water into the ocean.
On the other hand, a "sponge effect" was found to occur somewhere below the ice's surface. Here the ice drained at a rate between 55,000 and 61,000 cubic feet per second, which is double the rate of flow of the Colorado River.
The findings also suggest the Isortoq River, which is a key element of the Modele Atmospherique Regional (MAR) used by the Intergovernmental Panel on Climate Change, has a rate of discharge more than 25 percent higher than the model predicted.
"There's a lot of water coming out of the ice sheet but a certain amount can't be accounted for," said study co-author Vena Chu, a UCLA doctoral candidate in geography.
The research could allow scholars to create more accurate climate models.
"If we can get better estimates, then we can have better projections for the extent and the impact of global warming," said Marco Tedesco, a co-author and head of City College of New York's Cryospheric Processes Laboratory. "Greenland is really the big player for sea level rise in the future, so improving climate models is extremely crucial."
The findings were published in a recent edition of the Proceedings of the National Academy of Sciences.
