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Over 80% of Greenland’s surface is covered with ice, which features vast crystal blue rivers of meltwater. As gorgeous as the scenery is, a new study has indicated that meltwater from this ice sheet is the largest contributor to rising sea levels. The water from the streams drains more water into the ocean than the combination of Greenland’s meltwater lakes and chunks of ice that break off and fall in, which were previously believed to play the biggest role in rising sea levels. Laurence Smith of UCLA served as the lead author of the paper, which was published in the Proceedings of the National Academy of Sciences.
“It’s the world’s biggest water park, with magnificent and beautiful — but deadly — rushing blue rivers cutting canyons into the ice,” Smith said in a press release, describing Greenland’s topography.
During a six-day-long expedition in July of 2012, the research team studied these streams using a variety of equipment, including GPS-buoys, a drone boat, and extensive satellite imaging. These measured the location, length, and depth of the streams, as well as how much light was reflected off the water. The expedition was well-timed, as the amount of meltwater in 2012 was one of the highest of the last 700 years.
“It was a real preview of just how quickly that ice sheet can melt and the meltwater can escape,” Smith said.
They found that as the ice melts on the surface, it forms swift-moving rivers that quickly ferry the water away. The water then drains into an opening in the ice called a moulin, travels through the inside of the ice sheet, and emerges underneath, where it can then flow out into the ocean at a rate of 55,000 to 61,000 cubic feet per second. Before this study, not much was known about the ultimate fate of the meltwater rivers. It hadn’t been clear whether all of the meltwater drained into the ocean, or if some remained inside the ice. Though nearly all of the water in the 523 streams drained off of the surface, there does seem to be an unspecified amount getting hung up within the ice.
This study also examined the Isortoq River, which is an integral component of the IPCC’s MAR climate model and drains 20% of all Greenland’s meltwater. The river’s output was over 25% lower than previously believed, indicating that some gets held within the ice. Having a better understanding of the river’s true output and contribution to sea level will improve future climate models, though further research is necessary to determine exactly how much water stays inside the ice.
“If we can get better estimates, then we can have better projections for the extent and the impact of global warming,” added co-author Marco Tedesco of City College of New York. “Greenland is really the big player for sea level rise in the future, so improving climate models is extremely crucial.”
The team has dedicated the research to the memory of co-author Alberto Behar, who was a researcher at Jet Propulsion Laboratory and Arizona State University. He designed the drone boat used by the research team for data collection. Behar died on January 9 in a small plane crash in Los Angeles.
"The measurements we collected would not have been possible without the truly innovative instruments designed by Alberto Behar, and his steady hand during some very trying conditions in the field. The scientific outcomes of this study can be traced directly to him," Smith told NASA.
