Resurrecting organisms trapped in Arctic ice for thousands of years may sound like something from a science-fiction novel, but that’s exactly what a team of biologists and geologists has done in central Alaska.
The life forms in question are ancient microbes, some as old as 40,000 years, extracted from the walls of the Permafrost Tunnel Research Facility – a permafrost study site near the city of Fairbanks that extends more than 100 metres into the frozen ground beneath Alaska.
Carefully thawing these frozen microbes, researchers from the University of Colorado Boulder (CU Boulder) noticed that, after a few months, they reawakened and formed active colonies.
“These are not dead samples by any means,” says the study’s lead author, Tristan Caro. “They’re still very much capable of hosting robust life that can break down organic matter and release it as carbon dioxide.”
Published in the journal JGR Biogeosciences, the findings may help us understand more about the impact of the planet’s rapidly thawing permafrost on the Earth’s climate.
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Frozen life
The world’s permafrost – a frozen layer of soil, sand and rock that lies on or under the Earth’s surface – is melting at an unprecedented rate due to human-driven climate change. As this frozen ground thaws, microbes begin decomposing ancient organic matter, releasing carbon dioxide and methane into the atmosphere. These greenhouse gases could in turn drive further warming.
“It’s one of the biggest unknowns in climate responses,” says co-author Sebastian Kopf, professor of geological sciences at CU Boulder. “How will the thawing of all this frozen ground, where we know there’s tons of carbon stored, affect the ecology of these regions and the rate of climate change?”
To learn more about the subject, the team ventured into the US Army Corps of Engineers’ Permafrost Tunnel Research Facility. On their way through the tunnel, they passed bone fragments of ancient fauna, such as bison, mammoths and horses, protruding from the icy walls. But it was the far smaller life forms that they were most interested in.
“The first thing you notice when you walk in there is that it smells really bad. It smells like a musty basement that’s been left to sit for way too long,” says Caro. “To a microbiologist, that’s very exciting because interesting smells are often microbial.”
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The researchers extracted a number of samples from the tunnel walls, ranging in age from a few thousand to tens of thousands of years. They then took the samples back to the lab and thawed them at 4 °C and 12 °C (39 °F and 54 °F) – temperatures that mimic what deeper layers of permafrost might endure during future Arctic summers.
To track microbial activity, the team used deuterium-enriched water (containing heavy hydrogen). This method allowed them to detect how microbes consumed water and incorporated hydrogen into cell membranes.
The results surprised researchers. In the early months, growth was slow: in some cases, only one in 100,000 cells was replaced per day – a rate far slower than typical lab bacterial cultures. But by six months, colonies began to grow, some forming slimy, protective microbial layers known as biofilms that can be seen with the naked eye.
Caro notes that hotter temperatures did not dramatically speed up reactivation, suggesting that even after a warm spell, microbes might need months before releasing significant greenhouse gases. However, longer Arctic summers – rather than isolated hot days – may drive the greatest risk, says Caro: “You might have a single hot day in the Alaskan summer, but what matters much more is the lengthening of the summer season, where these warm temperatures extend into the autumn and spring.”
"The results [of the study] have critical implications for predictions of microbial biogeochemical contributions in a warming Arctic, especially as thaw proceeds into deeper and more ancient permafrost horizons," notes the study.
The team says there is still a lot to learn. Do microbes in Siberia and northern Canada respond similarly? Could ancient viruses also reawaken?
“There’s so much permafrost in the world – in Alaska, Siberia and in other northern cold regions,” Caro says. “We’ve only sampled one tiny slice of that.”
Top image: permafrost landscape. Credit: Getty
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