Terrawatch: unearthing snow's 'Fukushima layer'

Kate Ravilious
Photograph: TPG/Getty Images

The Fukushima nuclear accident has added a distinctive signature to snow and ice across the northern hemisphere, new research published in Environmental Research Letters shows. Triggered by the Tōhoku earthquake and tsunami off the coast of Japan on 11 March 2011, the disaster resulted in a month-long discharge of radioactive material into the atmosphere, ocean and soil.

Feiteng Wang from the Tian Shan glaciological station in Lanzhou, China, and colleagues collected snow samples in 2011 and 2018 from a number of glaciers (spanning a distance of more than 1,200 miles (2,000km) in north-western China. They expected the Fukushima signature to have faded away by 2018, but to their surprise the freeze-thaw processing had made it more concentrated, creating a strong and lasting reference layer in the ice.

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Many reference layers from the last 50 years (such as the Chernobyl nuclear disaster) have melted away in recent warming events, making it difficult to date the upper layers of ice cores. “Reference layers are crucial and a prerequisite for telling the story of the ice core,” says co-author Jing Ming. “The Fukushima layer will be useful for dating ice in one or two decades when the snow transforms to ice,” he adds.