Sun Feb 24, 2013, 03:32 PM
WillyT (68,560 posts)
Siberian Caves Reveal Advancing Permafrost Thaw - ScientificAmerican
Siberian Caves Reveal Advancing Permafrost Thaw
Melting of significant portions of Arctic permafrost could accelerate climate change into a catastrophe
By David Biello - ScientificAmerican
PERMAFROST CAVE: The frost crystals at the entrance to the Ledyanaya Lenskaya cave in Russia denote the region's permafrost, which has been in place for roughly 400,000 years, according to the cave's speleothems.
Image: Vladimir V Alexioglo
Permafrost is not so permanent. Across the Arctic, swathes of once-frozen-solid ground have begun to thaw. If the records preserved in Siberian caves are accurate, much more of the region could melt if temperatures continue to warm.
Geoscientist Anton Vaks of the University of Oxford led an international team of experts—including the Arabica Caving Club in Irkutsk—in sampling the spindly cave growths known as stalagmites and stalactites across Siberia and down into the Gobi Desert of China. Taking samples of such speleothems from six caves, the researchers then reconstructed the last roughly 500,000 years of climate via the decay of radioactive particles in the stone. When the ground is frozen above a cave no water seeps into it, making such formations "relicts from warmer periods before permafrost formed," the researchers wrote in a study published online in Science on 21 February.
The details of the study reveal that conditions were warm enough even in Siberia for these mineral deposits to form roughly 400,000 years ago, when the global average temperature was 1.5 degrees Celsius higher than present. It also suggests that there was no permafrost in the Lena River region at that time, because enough water seeped into the northernmost cave to enable roughly eight centimeters of growth in the formations.
That was, in fact, the last time the formations in the Ledyanaya Lenskaya Cave grew, although other caves further south showed multiple periods of growth coinciding with other warmer periods. "That boundary area of continuous permafrost starts to degrade when the mean global temperature is 1.5 degrees C higher than present," Vaks explains. "Such a warming is a threshold after which continuous permafrost zone starts to be vulnerable to global warming."
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