Uranium recorded in high-altitude ice

A team of scientists seeking to develop a historical database of uranium concentrations in the environment has analyzed a long core of ice and snow drilled from atop Europe’s tallest mountain. From the data, they’ve assembled the first century-long record of uranium lofted to a high altitude.

The researchers collected the 140-meter-long ice core in 1994 at an altitude of about 4,250 m, near the summit of France’s Mont Blanc. The concentrations of uranium deposited on the mountaintop before 1940 were a nearly constant 2.1 picograms (or trillionths of a gram) per gram of ice, says Claude Boutron, a geochemist at Joseph Fourier University in Grenoble, France. After World War II, uranium concentrations in the ice climbed and then fell, generally correlating with uranium production at sites in France and the former East Germany, about 500 and 700 km away, respectively. Boutron and his colleagues report their data in the Oct. 15 Environmental Science & Technology.

The highest concentrations of uranium, almost 20 picograms per gram of ice, appeared in the snow and ice that fell in 1980. Records that came to light after the fall of the Berlin Wall show that uranium production in East Germany dropped sharply after that year. The most recent layer of the ice core, from 1994, contains about 8 pg of uranium per gram of ice, around 4 times the pre-World War II concentrations.

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