 |
The Northeast Greenland Ice Stream fans out and terminates at several outlet glaciers. Photo by Nicolaj Krog Larsen |
By Brooks Hays, UPI
Over the last 45,000 years, a thin drainage stream, stretching more than 370 miles through Greenland's ice sheet and glaciers, has been narrower than it is today more than half the time.
New analysis of the ultra sensitive ice stream, the Northeast Greenland Ice Stream, suggests the long, narrow ribbon drains as much as 12 percent of the massive Greenland Ice Sheet.
The new research -- conducted by scientists at Oregon State University and published in the journal Nature Communications -- showed the ice stream continued to drain the ice sheet during the glacial maximum, a prolonged period of extreme cold, suggesting the stream is especially sensitive to environmental change.
"There are some parts of the ice sheet that are relatively stable and others that show evidence of very rapid retreating -- a pattern we're seeing today as well as thousands of years ago," Oregon State geologist Anders Carlson said in a news release. "Some of it relates to bed topography -- when the bed is below sea level, it stabilizes that part of the ice sheet. In low spots, it is unstable."
Carlson and his colleagues suggest the stream is especially sensitive to warm summer temperatures. Scientists also believe a period of accelerated drainage flow, beginning 9,000 years ago, may have been triggered by the Earth's orbit, which inched slightly closer to the sun.
Researchers sampled and studied ice cores to estimate shifts in air temperature over the last 45,000 years. Their analysis showed that even during the glacial maximum, summer temperatures remained relatively warm, causing the stream to continue draining the ice sheet throughout the cold spell.
"That period was also quite dry and there wasn't nearly as much snowfall," Carlson said, "which may have driven the ice margin to be smaller."
Scientists were able to estimate glacial retreat by measuring the amounts of beryllium-10 in rocks. When retreating glaciers expose rocks, cosmic rays react with the quartz to produce the isotope.
Though the stream has been draining the Greenland Ice Sheet consistently for 45,000 years, the evidence suggests it is in a period of accelerated flow.
"Modern observations have shown that the NEGIS is very susceptible to changes in both air and ocean temperatures and is presently in a phase of rapid ice retreat," said Nicolaj Larsen of Aarhus University in Denmark.
