An international team of researchers has now dated the oldest known permafrost in Siberia. The permafrost layer, located near the eastern Siberian village of Batagay, has been frozen in a depth of ca. 50 metres for the past 650,000 years – a record.
The team, which included German, Russian and English researchers and was led by Prof Julian Murton from the University of Sussex.
Dr Thomas Opel from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) in Potsdam, told The Polar journal that the finding is relevant because it shows that, even during warmer periods, permafrost doesn’t necessarily have to thaw entirely.
For example, the permafrost in Batagay apparently survived a particularly warm phase roughly 130,000 years ago, when it was four to five degrees Celsius warmer in the Arctic summer than today.
Permafrost is defined as ground (soil or rock and included ice or organic material) that remains at or below 0°C for at least two consecutive years.
When permafrost thaws, it activates bacteria that begin breaking down the ancient biomass and, through their metabolic processes, release the climate-relevant gases carbon dioxide and methane; the more intensive the thawing, the more gas is released. With regard to the on-going climate change, experts fear that this aspect could worsen the greenhouse effect.
The situation near Batagay demonstrates how sensitive permafrost is to anthropogenic disturbances. The 650,000-year-old permafrost is located on a hillslope at a depth of ca. 50 metres, where the temperature remains stable at minus 10 degrees Celsius. But, from the 1940s to the 1960s, the slope was partly cleared, and used by heavy tracked vehicles as a road to reach a nearby mine.
In the process, it lost its protective and insulating plant cover. As a result, the younger permafrost began thawing near the surface in summer, until the ground finally began sliding away, uncovering the older permafrost. For years, meltwater has transported the thawed material downhill, forming a large crater.
Once the damage is done, it’s irreparable, because the exposed permafrost thaws even more with every summer. Over the past 50 years, the ‘megaslump’ has grown to a width of ca. 900 metres.