Research published Thursday in the journal Science says that even slightly warmer temperatures could start melting permafrost, which in turn threatens to trigger the release of huge amounts of greenhouse gases trapped in ice.
The frosty dungeon hides a dark secret. At least a quarter of the Northern Hemisphere's landmass is frozen and, like a vault, it holds 1,700 gigatonnes of carbon. This unimaginably high quantity of carbon comes from countless generations of creatures that have lived and died in the area over millions of years.
A portion of those dead plants and animals weren't decomposed by microorganisms because, at a certain point, it was simply too cold for that. But the permafrost is slowly melting. If large areas of ground underneath were to thaw one day, the bacterial decomposition process would pick up where it left off, releasing huge amounts of greenhouse gases. In total, permafrost contains twice as much carbon as what is currently billowing through the Earth's atmosphere.
If major portions of that carbon become released, the world's climate would suffer fatal consequences. For this reason, scientists have for some time now been asking the frightening question of just how strongly global warming affects permafrost areas. Using ingenious measuring methods, they are meticulously monitoring the fate of the planet. A new study, published in the professional journal Science on Thursday, suggests that it's possible that even slightly higher temperatures could thaw out significant portions of the region's permafrost areas.
A team of researchers led by Anton Vaks at the University of Oxford examined calcareous deposits from a total of six Siberian caves. Specifically, they looked at so called speleothems, which are mineral deposits -- including stalactites and stalagmites -- that form in limestone and other caves. "Speleothems only grow when rain and meltwater can seep through cracks into the caves," Vaks told SPIEGEL ONLINE. "And that process only occurs when temperatures are above the freezing point." Precise Climate Records
Since water from the frozen earth can't reach cracks deep within the caves, the mineral deposits are precise records of the climate. In warmer times, the so-called interglacial periods, stalactites and stalagmites form. In colder phases, so called glacial periods, they don't. So there is a pattern similar to how tree rings can be used to tell their age.
A total of 36 speleothems were dated using the uranium-thorium method. Over time, uranium decays into thorium. The uranium isotopes dissolve in water that penetrates into the speleothems, while thorium does not and thus remains in the deposits.
Researchers can look back about 500,000 years in the past using this method. Speleothems in today's permafrost areas must have come from a significantly warmer period in which water was flowing. Vaks and his colleagues have been able to show that stalactites in the northern-most Lenskaya Ledyanaya Cave only grew in a very warm part of an interglacial period about 400,000 years ago.
At that time, average temperatures were about 1.5 degrees Celsius higher than they are today. Traces of this particularly warm period were also proven with pollen deposits and residue of algae found in the sediment of Elgygytgyn Lake, in northeastern Siberia, as well as from other sources of evidence. During this time, there were probably even numerous trees in southern Greenland.
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