WASHINGTON (AP) — Rebounding from the weight of ice sheets that depressed the land during the ice age, Scandinavia has risen more than a half-mile in the past 20,000 years, according to new satellite measurements.
In a study appearing today in the journal Science, researchers report that Sweden, Norway, Finland and Denmark are moving upward at almost a half inch a year as a rebound from the melting of two-mile-thick ice mountains.
"There is not one place in Scandinavia that was not covered with ice," said Jerry X. Mitrovica of the University of Toronto. "The land was pressed down about a kilometer (five-eighths of a mile), and when the ice melted, the land started going up in a process that continues even today."
Mitrovica, co-author of the study, said the weight of the ice was equal to about 6.6 million pounds per square yard of land surface in Scandinavia.
Scientists have long known that Scandinavia, Canada and other places buried under frozen mountains during the last ice age have been rebounding. Until now, however, researchers were not sure how fast the land was rising.
Mitrovica and his co-authors used data from 33 sensors placed strategically around Scandinavia to pick up signals from the Global Positioning Satellite system. Combining this data and correcting it for atmospheric distortion enabled them to measure the land movement to a scale of about 1 millimeter, a fraction of an inch, per year.
They found that, on average, the land under the ancient ice burden is rising annually by about 9 millimeters. An inch is about 25 millimeters.
Knowing this amount of rise, Mitrovica said, makes it possible for the first time to use two centuries of sea level measurements from Scandinavia.
"The best-kept records for sea level change in the world is in the Scandinavian region," said Mitrovica. But scientists have not been able to trust the records because they knew the land rebounding from the ice age was affecting sea levels in the area.
For instance, Mitrovica said, the ocean could be rising at 7 millimeters a year in Scandinavia, but because the land was rising at 9 millimeters a year, it would appear that sea level was dropping.
"Our study confirms that the sea level in Scandinavia is doing what others have seen in other parts of the globe," said Mitrovica. "This is one of the important confirmations of sea level rising. Sea level is going up worldwide about 2 millimeters a year."
Besides rising, Scandinavia's rebound is also moving horizontally, he said.
Mitrovica compares this type of expansion to what would happen if someone turned over a bowl and stepped on it. While the bowl center is flattened, the edges of the bowl move outward. The same thing is happening in Scandinavia, he said.
"We measure a horizontal change in the land of 2 to 3 millimeters a year," said Mitrovica.
This means that Scandinavia, in its 20,000-year recovery from the last ice age, is growing both upward and outward, he said.
Mitrovica said that all the ice from the last ice age is gone from Scandinavia, but traces still exist of ancient ice in Canada. The North American ice sheet once extended from the Canadian Arctic deep into the northern United States.
On the Net: Science magazine: www.eurekalert.com