Beneath a frozen expanse in Alaska, tiny organisms survive in a dormant state, witnesses to bygone eras when mammoths still roamed the Earth. Their gradual awakening, triggered by the thawing of Arctic soils, could fundamentally alter our planet's balance.
Scientists have successfully revived these ancient microbial communities, some over 40,000 years old. Their work reveals the biological mechanisms that activate when ice gives way to liquid water. This microbial resurrection offers a unique window into ecological processes likely to intensify with current global warming.
The gradual awakening of ancestral microbes
The research team collected permafrost cores from the Fox Tunnel in Alaska, a unique military facility providing access to layers frozen since the Pleistocene. The samples, carefully transported to the laboratory, were maintained under strict anaerobic conditions to preserve their integrity. Scientists then initiated controlled thawing at different temperatures, simulating Arctic summer conditions.
During the first weeks, microbial activity remained almost undetectable. Cellular turnover reached barely one hundred-thousandth of cells per day, an extremely slow pace compared to modern strains. This latency period would correspond to a phase of gradual metabolic reactivation after millennia of dormancy.
It was only after six months of incubation that the microbial communities showed significant activity. Some developed biofilms visible to the naked eye, protective structures indicating full reactivation. The incubation temperature proved less decisive than the duration of exposure to unfrozen conditions in triggering this awakening.
Implications for the carbon cycle
The restored activity of these ancient microorganisms directly influences greenhouse gas emissions. By decomposing organic matter preserved in the permafrost, they release carbon dioxide and methane into the atmosphere. This process transforms Arctic soils, traditionally carbon sinks, into potential emission sources. The amount of carbon stored in these frozen soils is estimated at approximately 1,500 billion tons, nearly double the carbon present in the atmosphere.
Methane production, a gas with a warming power thirty times greater than CO2 over a century, occurs particularly in water-saturated areas. Methanogenic microbes, belonging to the archaea group, thrive in these oxygen-deprived environments. Their awakening could significantly amplify the greenhouse effect, creating a positive feedback loop. Climate models still struggle to precisely quantify this biological contribution.
The observed delay between thawing and significant microbial activity offers a temporary but limited respite. The lengthening of warm seasons in the Arctic gradually reduces the freezing duration, allowing microbial communities to reach their full metabolic potential. This gradual activation explains why observed emissions don't immediately follow heat episodes but intensify with persistent positive temperatures.
Going further: How do microbes survive for so long?
Cryopreserved microorganisms employ different strategies to survive millennia of freezing. Some enter a state of deep dormancy, slowing their metabolism to almost undetectable levels. Others produce cryoprotective compounds that preserve the integrity of their cellular structures.
Natural freezing in permafrost occurs gradually, allowing cells to adapt to osmotic changes. The absence of oxygen in deep layers also limits oxidative damage. These particular conditions explain the exceptionally long survival.
The reactivation process requires gradual reconstruction of cellular functions. Membranes must regain their fluidity, ribosomes their activity, and metabolism its normal rhythm. This startup process explains the observed delay before activity resumes.
Article author: Cédric DEPOND