Greenland Ice Sheet Receding And Is Now Considered Unstable
March 17, 2014

Key Ice Stream In Greenland Is Receding

Brett Smith for - Your Universe Online

According to a new report in the journal Nature Climate Change, the last stable section of the Greenland ice sheet is receding and now considered unstable – a development that could portend even more ice loss in the future and significant sea level rise.

The report focused on a key ice stream in the Greenland ice sheet. Ice streams drain an ice basin from the interior of the sheet, in the same way that regular streams drain water from the Amazon River basin.

The study concluded that the Zachariae ice stream in northeast Greenland has receded about 12 miles throughout the last decade. By comparison, one of the fastest shifting glaciers, the Jakobshavn ice stream in southwest Greenland, has receded almost 22 miles across the last 150 years.

"Northeast Greenland is very cold. It used to be considered the last stable part of the Greenland ice sheet," said study author Michael Bevis of the Greenland GPS Network (GNET) project at The Ohio State University. "This study shows that ice loss in the northeast is now accelerating. So, now it seems that all of the margins of the Greenland ice sheet are unstable."

A bay clogged with floating ice debris has historically kept Zachariae from draining swiftly. Now that the ice is receding, this buffer is significantly decreased, enabling the glacier to speed up and draw more ice from the interior of the basin.

"This suggests a possible positive feedback mechanism whereby retreat of the outlet glacier, in part due to warming of the air and in part due to glacier dynamics, leads to increased dynamic loss of ice upstream," said Bevis, who is also a professor of earth sciences at Ohio State. “This suggests that Greenland's contribution to global sea level rise may be even higher in the future.”

Study author Shfaqat Abbas Khan, a senior researcher at the National Space Institute at the Technical University of Denmark, said his team’s conclusion is fairly troubling.

"The fact that the mass loss of the Greenland Ice Sheet has generally increased over the last decades is well known," Khan said, "but the increasing contribution from the northeastern part of the ice sheet is new and very surprising."

To weigh the ice sheet, researchers at the GNET project used the earth's normal elasticity to gauge the mass of the ice sheet. As previous research has pointed out, ice weighs down bedrock, and when the ice melts, the bedrock rises significantly in response. With over 50 GNET stations along Greenland's coast measuring the ice sheet like a massive bathroom scale, Khan and his colleagues combined this information with ice density measurements taken by four different satellites.

The team discovered that the northeast Greenland ice sheet shed about 10 billion tons of ice per year from April 2003 to April 2012. Khan said this finding is cause for particular concern because the northeast ice stream is connected to the heart of Greenland's ice reservoir.

"This implies that changes at the margin can affect the mass balance deep in the center of the ice sheet,” he said. “Furthermore, due to the huge size of the northeast Greenland ice stream, it has the potential of significantly changing the total mass balance of the ice sheet in the near future.”

"The fact that this ice loss is associated with a major ice stream that channels ice from deep in the interior of the ice sheet does add some additional concern about what might happen,” Bevis agreed.