'Missing' Water from Greenland Ice Sheet Found by Studying Meltwater Rivers

Scientists are taking a closer look at Greenland's ice sheet, and have discovered just how much meltwater is contributing to rising sea levels. They've found evidence that the rivers and streams flowing on top of the ice sheet could be major contributors to rising seas.

Until now, researchers have mostly focused on the ice sheet's lakes: bodies of meltwater that tend to abruptly drain. They also focused on monster chunks of ice breaking off from the ice sheet and slide into the ocean in order to become icebergs. In fact, very little attention has been given to the rivers and streams on the ice sheet.

When snow and ice thaw during the summer, waterways form an intricate drainage system that captures virtually all surface runoff. These small rivulets are capable of flushing their entire volume in less than two days.

"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 lead author of the new study, in a news release.

The researchers moved over the Greenland ice sheet by helicopter, mapping the river network and computing the rivers' flow rates. They used satellite imagery, buoys outfitted with BPS technology, and a drone boat designed for the project.

They found that the top of the ice sheet's surface was a bit like Swiss cheese; all 523 actively flowing streams and rivers across a 2,000-square-mile area of the ice drained into moulins that promptly carried meltwater under the ice and into the ocean. At the same time, a modest "sponge" effect occurred below the ice sheet; within this area, meltwater drained at a rate of 55,000 to 61,000 cubic feet per second, which is a rate more than double the average flow of the Colorado River.

While there's a lot of water coming out of the ice sheet, though, a certain amount can't be accounted for. This discrepancy suggests that meltwater is being captured in a subterranean manner that hasn't yet been accounted for.

The new research should give scientists the ability to refine existing climate models, which modestly overestimate the direct contribution from runoff to rising sea level. This could help with future predictions when it comes to climate change.

"If we can get better estimates, then we can have better projections for the extent and the impact of global warming," said Marco Tedesco, co-author of the new study. "Greenland is really the big player for sea level rise in the future, so improving climate models is extremely crucial."

The findings are published in the journal Proceedings of the National Academy of Sciences.

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