By Sid Perkins
Scientists recently found that Greenland’s central ice sheet isn’t getting any thinner overall, although particular areas show significant gains or losses (SN: 7/22/00, p. 54: Available to subscribers at Greenland’s ice is thinner at the margins). Other researchers report in the Aug. 24 Nature that these changes are no larger than those that have occurred during the past 4 centuries.
Space-based radar showed substantial changes in elevation for southern portions of the ice sheet between 1978 and 1988. A team of scientists recently looked at shallow ice cores collected at 12 different locations in that part of Greenland. At 11 of the sites, they were able to match yearly snow accumulations to the satellite measurements.
The researchers then looked at variations in the snowfall during that period and compared them with changes in precipitation recorded in deeper core samples spanning as many as 400 years.
The team found that the recent changes in snowfall were similar to those recorded within the older ice cores, says Joseph R. McConnell, hydrologist at the Desert Research Institute in Reno, Nev., and lead author of the report.
Some scientists, including William B. Krabill, a researcher at NASA’s Wallops Island (Va.) Facility, question whether a sample of 12 shallow ice cores can represent changes that are taking place over the entire central ice sheet.
“It makes a big difference where you take the ice cores,” Krabill says. A natural next step, he adds, would be to develop techniques for using isolated measurements of precipitation to discern trends in snow accumulation over larger regions.
