Microbes that have been frozen in Arctic permafrost for tens of thousands of years are coming back to life in the lab. When researchers warmed deep soil samples from Alaska, these ancient microorganisms slowly woke up, reorganized, and began turning buried organic matter into carbon dioxide and methane within a few months.
The work, led by geobiologist Tristan Caro at California Institute of Technology, points to a troubling possibility. If longer and warmer Arctic summers reach deeper layers of frozen ground, similar microbes in the real world could switch on and add extra greenhouse gases to the atmosphere, feeding a climate feedback that scientists have warned about for years.
A hidden archive beneath Alaska’s frozen ground
Permafrost is ground that stays frozen for at least two years in a row, often much longer. In the hills just outside Fairbanks, Alaska, a facility called the Permafrost Tunnel Research Facility cuts into that frozen soil and exposes layers that record roughly 45,000 years of Earth history, including plant remains, animal bones, and ancient microbes.
The tunnel, operated by the U.S. Army Corps of Engineers, is kept refrigerated all year so the walls stay frozen. That makes it a kind of time capsule where researchers can drill into deep, ice-rich sediments that would never thaw naturally under current conditions, then bring those samples into the lab to see what happens when the cold finally eases.
How scientists brought frozen life back to activity
For the new study, Caro and colleagues collected permafrost blocks from tunnel walls that had remained frozen since the last ice age, in some cases for up to about 40,000 years. They sealed the samples to keep oxygen levels low, then gently warmed them to about 4 and 12 degrees Celsius, temperatures similar to mild and unusually warm Alaskan summers.
To tell which microbes were truly waking up and growing, the team added water that contained a heavier form of hydrogen called deuterium.
Using a technique known as lipid stable isotope probing, they tracked how microbes drank that water and used the heavy hydrogen to rebuild the fatty outer layers of their cells, proof that the organisms were repairing damage or dividing, not just hanging on.
In the first month, very little seemed to happen. Only about 0.001 to 0.01 percent of the microbial cells turned over each day, a growth rate far slower than typical lab bacteria, which can double in hours. That sluggish start helps explain why a short warm spell at the surface is not enough on its own to unleash big pulses of greenhouse gases from deep permafrost.
From quiet start to carbon releasing communities
By around the six month mark, the picture shifted. The revived microbes began forming visible biofilms, slimy layers where cells cluster together and share resources, and the community changed from a diverse mix into a smaller set of hardier winners that were better adapted to their new, warmer conditions.
At that stage, the reawakened communities started turning more of the ancient organic matter into carbon dioxide and methane. Some gas bubbles trapped in the ice were already present before the experiments, but isotopic tools helped separate that old gas from the new emissions coming from active microbes.
The result suggests that once microbes get enough time to adjust, they can become a steady source of greenhouse gases from very old carbon.
Caro has noted that the microbes did not wake up dramatically faster at the higher test temperature. That hints that time spent thawed matters more than brief spikes in heat, a pattern that matches what many Arctic residents already notice when warm seasons stretch further into the calendar.
Longer Arctic summers push permafrost to its limits
According to the National Oceanic and Atmospheric Administration, northern permafrost soils store roughly 1,460 to 1,600 billion metric tons of organic carbon, about twice as much as the carbon currently in the atmosphere.
Warming conditions encourage microbes to convert that frozen material into carbon dioxide and methane, which then escape into the air and add to global heating.
The Arctic is already warming at about twice the global average, and recent NOAA report cards show record warm summers and longer periods when the ground stays thawed.
Other assessments now indicate that the Arctic has shifted from acting mainly as a carbon sink to acting as a net carbon source, especially in the fall and winter months when decomposition outpaces plant growth.
What Caro’s work adds is a close up look at how long it takes ancient microbes to join that process once the ice around them melts. In everyday terms, it suggests that a string of slightly warmer, slightly longer summers could matter more for carbon release than a single record breaking heat wave that comes and goes.
Why this matters for climate models and everyday life
The new experiments focus on one tunnel in interior Alaska, and researchers stress that frozen soils in Siberia, Greenland, or northern Canada may host different microbial communities with their own behaviors.
Even so, the findings underline a key point for climate models to capture more accurately, which is that microbes in deep permafrost need several months of thaw to get going, then can ramp up their activity within a single warm season.
Groups like the National Snow and Ice Data Center warn that thawing permafrost also threatens local roads, pipelines, and buildings as once solid ground slumps and shifts, with real consequences for Arctic communities, supply routes, and even the prices people pay for food and fuel far away.
At the end of the day, the microbes waking up in these samples are a reminder that hidden processes in frozen soil can ripple outward until they touch everything from summer heat waves to the electric bill.
The main study has been published in the Journal of Geophysical Research, Biogeosciences.
