Thawing Arctic Soil Awakens Only Half of Soil Microbes

As Arctic temperatures rise, frozen soils are thawing for longer periods-but new research shows this doesn’t fully activate the life hidden underground. Instead, only about half of soil microbes “wake up,” meaning greenhouse gas release depends on which microbes respond, and how quickly, rather than warming alone.

As the Arctic warms at an unprecedented rate, frozen soils that have remained locked in ice for most of the year are now thawing for longer periods. Yet new research led by an international team including scientists from Queen Mary University of London has found that these seasonal thaws only partially revive the hidden ecosystem beneath the surface. The study, published in mSystems, shows that even after months of thawing, around half of the microorganisms in High Arctic soils remain dormant. This challenges the assumption that warming uniformly boosts microbial activity and carbon release from thawing permafrost. 

Tracking life as frozen soils thaw 

Despite their barren appearance, Arctic soils host diverse microbial communities that play a crucial role in the global carbon cycle. When ice melts, liquid water becomes available, allowing some microbes to resume activity and begin breaking down organic matter – a process that releases greenhouse gases such as carbon dioxide and methane. 

To understand which microbes “wake up” after thaw, researchers incubated soil samples from Svalbard, a remote archipelago between mainland Norway and the North Pole, and used DNA stable isotope probing to directly track microbial growth. This advanced method enabled the team to distinguish active organisms from those remaining dormant. 

The results revealed striking differences: 

• Some microbes grew rapidly within days, 

• Others only began to grow after several weeks, 

• And a large proportion stayed inactive throughout the 98‑day experiment. 

More than just decomposition 

Unexpectedly, the team also identified predatory and epibiotic bacteria, microbes that feed on or grow attached to other microorganisms, as part of the active community. Their presence indicates that thawing soil triggers not only decomposition but also complex microbial food webs. 

The researchers also detected methane‑oxidising microbes that became active only after prolonged thaw, suggesting that the later stages of the thaw season may play a bigger role in regulating methane fluxes than previously recognised. 

Implications for climate change 

Arctic soils store nearly one‑third of the world’s soil carbon. As thaw seasons lengthen, understanding the timing and identity of active microbes becomes critical for predicting the release, or consumption, of greenhouse gases. 

The study shows that carbon release from thawing soils is not simply controlled by temperature, but by the complex dynamics of which microbial groups switch on, and when. Current climate models often assume uniform microbial responses to warming, but these new findings suggest a need for greater nuance to accurately project future carbon emissions from the Arctic. 

Dr James Bradley, Honorary Reader at Queen Mary University of London and CNRS researcher at the Mediterranean Institute of Oceanography in Marseille, said: 

“The thawing of soils in the Arctic doesn’t simply switch on microbial activity. We found that only part of the community responds, and that response develops over time. This has important implications for how we predict carbon release in a warming Arctic.” 

Dr Margaret Cramm, lead author of the study, who completed her PhD and postdoctoral research at Queen Mary and is now a Research Fellow at University College London, said: 

“We found that some methane‑consuming microbes only become active after longer periods of thaw. This suggests that the impact of Arctic soils on greenhouse gas fluxes may increase over time as thaw seasons lengthen.”