Using a new approach to ice-penetrating radar data, researchers show that this melting left behind a contiguous layer of refrozen ice inside the snowpack, including near the middle of the ice sheet where surface melting is usually minimal. Most importantly, the formation of the melt layer changed the ice sheet's behavior by reducing its ability to store future meltwater. The research appears in Nature Communications.
"When you have these extreme, one-off melt years, it's not just adding more to Greenland's contribution to sea-level rise in that year – it's also creating these persistent structural changes in the ice sheet itself," said lead author Riley Culberg, EE PhD candidate. "This continental-scale picture helps us understand what kind of melt and snow conditions allowed this layer to form."
Airborne radar data, a major expansion to single-site field observations on the icy poles, is typically used to study the bottom of the ice sheet. But by pushing past technical and computational limitations through advanced modeling, the team was able to reanalyze radar data collected by flights from NASA's Operation IceBridge from 2012 to 2017 to interpret melt near the surface of the ice sheet, at a depth up to about 50 feet.
"Once those challenges were overcome, all of a sudden, we started seeing meltwater ice layers near the surface of the ice sheet," EE courtesy professor, Dustin Schroeder said. "It turns out we've been building records that, as a community, we didn't fully realize we were making."
Melting ice sheets and glaciers are the biggest contributors to sea-level rise – and the most complex elements to incorporate into climate model projections. Ice sheet regions that haven't experienced extreme melt can store meltwater in the upper 150 feet, thereby preventing it from flowing into the ocean. A melt layer like the one from 2012 can reduce the storage capacity to about 15 feet in some parts of the Greenland Ice Sheet, according to the research.
Excerpted from "Stanford researchers reveal the long-term impacts of extreme melt on Greenland Ice Sheet", Stanford News, April 20, 2021