Scientists at the University of Colorado Boulder reported that they re-awakened microbes frozen in Alaskan permafrost for about 40,000 years, documenting the work in the Journal of Geophysical Research: Biogeosciences. Once thawed, the organisms resumed metabolism, raising concern about what rising Arctic temperatures might release.
The team collected samples in the U.S. Army Corps of Engineers Permafrost Tunnel near Fairbanks, a facility that extends more than 350 feet into frozen ground. “The first thing you notice when you walk in there is that it smells really bad… like a musty basement that’s been left to sit for way too long,” said geological scientist Tristan Caro, according to Phys.org. “To a microbiologist, that’s very exciting because interesting smells are often microbial.”
In Boulder, Caro and colleague Sebastian Kopf simulated future Arctic summers by moistening the samples with deuterium-labeled water and incubating them at 4 °C and 12 °C. Those temperatures are warm for soil that had remained below freezing for millennia.
“These are not dead samples by any means. They're still very much capable of hosting life that can break down organic matter and release it as carbon dioxide,” said Caro, according to Phys.org. For several months only a few cells divided each day, but around the six-month mark the populations surged, covering culture slides with biofilm large enough to see without a microscope, Popular Science reported.
The revived microbes consumed buried organic material and emitted methane and carbon dioxide inside their sealed chambers. Short heat spikes mattered little, yet an extended warm season proved critical. “The lengthening of the summer season, where these warm temperatures extend into the autumn and spring, is more worrisome than a single hot day,” said Caro.
After a year of monitoring, the researchers found that several months of sustained warmth were required before large volumes of greenhouse gases escaped, suggesting a delayed yet powerful climate feedback. Kopf called the awakening of frozen life “one of the biggest unknowns in climate responses.”
Permafrost stores an estimated 1,500 billion tons of carbon—nearly double the amount in today’s atmosphere—and covers nearly one-quarter of the Northern Hemisphere. The European Space Agency warned that up to two-thirds of its upper layer could vanish by 2100, potentially accelerating a cycle of thawing and emissions.
The Colorado team kept all cultures in sealed vessels and noted that most revived microbes are unlikely to harm humans directly. Even so, the 2016 anthrax outbreak on Siberia’s Yamal Peninsula, traced to spores released from thawing reindeer carcasses, demonstrated that spillovers can occur.
Studying long-dormant organisms may also yield benefits; one Arctic bacterium has already shown potential for cleaning up oil spills. “There are reasons for concern,” said Andrea Hinwood, chief scientist of the United Nations Environment Programme.
“There’s so much permafrost in the world—in Alaska, Siberia and other northern regions. We've only sampled one tiny slice of that,” said Caro.
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