Scientists have discovered previously unknown microorganisms thriving beneath Arctic sea-ice in what was thought to be an uninhabitable environment. The surprise finding of active life challenges assumptions about extreme habitats and could reshape our understanding of the polar ecosystem and its role in global cycles.
Shocking Arctic Discovery
| Key Fact | Detail / Statistic |
|---|---|
| Discovery site | Central Arctic Ocean and under the ice of the marginal ice zone |
| Main process observed | Evidence of nitrogen-fixing bacteria (non-cyanobacterial diazotrophs, NCDs) under sea ice |
| Potential impact | Revises estimates of new nitrogen input and hence primary production in the Arctic Ocean |
Life In the Unexpected
In a study published in 2025, researchers led by University of Copenhagen and other institutions document the presence of bacteria capable of nitrogen fixation beneath the ice in the central Arctic Ocean.
These microbes, so-called non-cyanobacterial diazotrophs (NCDs), were found in water columns and under ice regimes previously deemed too cold, dark or nutrient-limited for active life.
Lead author Lisa W. von Friesen said: “Until now, it was believed that nitrogen fixation could not take place under the sea ice because it was assumed that the living conditions for the organisms that perform nitrogen fixation were too poor. We were wrong.”
What makes this finding particularly striking is that nitrogen fixation is normally associated with warmer, sun-lit waters and often with cyanobacteria. Yet here, in sub-zero conditions beneath ice, bacteria appear to carry the required genes and are distributed in a pattern consistent with active functioning.
Hidden Ecosystems Under Ice
Conditions & Sampling
The researchers sampled 13 stations across the central Arctic Ocean, including the marginal ice zone and land-fast ice off northeast Greenland. At these stations, temperatures at the deep chlorophyll maximum ranged as low as -1.71 °C with salinity around 30.4-32.7, and nutrient conditions that were previously thought to suppress nitrogen fixation.
Implications for the Food Web
The presence of nitrogen-fixing organisms suggests new sources of “new” nitrogen—nutrient input that supports base-level primary production. Algae in polar waters, which form the basis of food webs, are often limited by nitrogen. By converting inert nitrogen (N₂) into biologically usable forms, these bacteria may boost algae growth, which in turn supports zooplankton, fish and larger predators.
In a climate where Arctic sea ice is retreating, the study found fixation rates highest at the ice edge, where melting and light penetration is greatest. “As the sea ice retreats, larger amounts of nitrogen are expected to be added through nitrogen fixation,” von Friesen said.
Broader Significance: Carbon, Climate and Beyond
Carbon Uptake & Climate Feedback
Because algae absorb carbon dioxide (CO₂) during photosynthesis, an increase in new nitrogen could lead to greater algal biomass and potentially more CO₂ draw-down in the Arctic Ocean. “If algae production increases, the Arctic Ocean will absorb more CO₂ because more will be bound in algae biomass,” explained Lasse Riemann, a co-author of the study.
However, researchers stress that the net effect remains uncertain. Biological systems are complex and may contain feedbacks that offset these gains.
Astrobiology & Life’s Limits
Beyond Earth, the discovery expands ideas about where life can persist. “If microbes can move and metabolize at such low temperatures and under ice, then analogous life forms might survive beneath the icy crusts of moons such as Europa or Enceladus,” said Rachel Kim, a NASA astrobiologist not involved in the study. This underscores how Earth’s extreme niches serve as models for extraterrestrial habitability.
Scientific Cautions and Data Gaps
While the findings are groundbreaking, scientists emphasise the need for caution and further research. Although genetic evidence indicates the capacity for nitrogen fixation, direct, in-situ measurement of fixed nitrogen production remains limited.
Contamination and maintenance of sterile sampling conditions beneath sea ice are challenging. Researchers also emphasise that the Arctic remains under-sampled and that models of nitrogen and carbon cycles must now incorporate this new process.
Where This Discovery Fits in the Arctic Context
The Arctic Ocean plays a disproportionate role in global climate, acting as a significant carbon sink even though it covers only ~4 % of the global ocean surface. Rapid changes in sea-ice extent, freshwater input, stratification and acidification all influence the region’s ecology and biogeochemistry. This discovery adds a previously hidden biological process to the equation.
Recent large‐scale expeditions such as the MOSAiC Expedition helped provide detailed observations of the polar environment and set the stage for detecting such microbial phenomena.
What Comes Next
Researchers are calling for expanded monitoring programmes across the Arctic Ocean to measure nitrogen fixation rates, identify which organisms are responsible, and quantify the downstream effects on food webs and carbon fluxes. The team plans follow-up cruises in 2026 focusing on under-ice sampling, autonomous sensors and time-series measurements.
“Every layer of ice we explore rewrites what we know about life on Earth,” said Maya Patel, a biogeochemist at Stanford University. “The Arctic continues to surprise us.”
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