Hidden Nitrogen Fixation Beneath Melting Arctic Ice May Boost Algae and Carbon Uptake

Environment By Mattias Risberg
Hidden Nitrogen Fixation Beneath Melting Arctic Ice May Boost Algae and Carbon Uptake
Researchers report nitrogen fixation occurring under Arctic sea ice—primarily by non-cyanobacterial microbes—concentrated at melting ice edges. Rising ammonia availability as ice retreats could fertilize algal growth and influence carbon uptake, but net climate effects remain uncertain.

New observations under the ice

A study published on October 20, 2025 in Communications Earth & Environment reports the first detections of nitrogen fixation beneath central Arctic sea ice. In this process, microbes convert atmospheric dinitrogen gas into ammonia, a biologically available form of nitrogen that supports algae and other marine life.

Scientists had long assumed conditions beneath Arctic ice were too harsh for nitrogen-fixing organisms. The new work shows those assumptions were incomplete: nitrogen fixation does occur under the ice, and rates rise sharply along the edges of melting sea ice where conditions are most dynamic.

Different microbes, similar function

Potential ecological and climate implications

As sea ice retreats, the researchers conclude ammonia availability in the Arctic Ocean is likely to increase substantially. Greater nitrogen supply could fertilize algal production, with cascading effects through the food web: more algae can support larger populations of small animals such as planktonic crustaceans and, ultimately, fish.

An increase in algal biomass also has climate implications. Growing algae take up carbon dioxide from the atmosphere; if a larger portion of that carbon is retained in Arctic waters or exported to the deep ocean, it could represent an additional sink for CO2. However, the net climate effect depends on multiple interacting processes and is not yet known.

Gaps for models and future research

Summary

Tags

Arctic carbon sequestration climate mitigation ice melt
Mattias Risberg

Mattias Risberg

Cologne-based science & technology reporter tracking semiconductors, space policy and data-driven investigations.

University of Cologne (Universität zu Köln) • Cologne, Germany

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Readers Questions Answered

Q What did the study detect under central Arctic sea ice, and which microbes are primarily responsible?
A The study reports the first detections of nitrogen fixation beneath central Arctic sea ice, showing microbes convert atmospheric dinitrogen into ammonia to feed marine life. The process is primarily carried out by non-cyanobacterial microbes and is most concentrated along melting ice edges where conditions are most dynamic.
Q How does nitrogen fixation change as sea ice melts?
A As sea ice retreats, ammonia availability in the Arctic Ocean is likely to rise substantially, with nitrogen fixation rates increasing sharply at the edges of melting ice where conditions are most dynamic, signaling more nitrogen to support algal production and linked ecosystem processes.
Q What ecological and carbon-cycle implications are discussed?
A Greater nitrogen supply could fertilize algal production, supporting larger populations of small animals such as planktonic crustaceans and, ultimately, fish. Growing algae take up carbon dioxide from the atmosphere, and if more carbon is retained in Arctic waters or exported to the deep ocean, it could represent an additional sink for CO2.
Q What does the article say about the net climate effect of this process?
A The net climate effect remains uncertain and is not yet known because it depends on multiple interacting processes, requiring further study and modeling to determine whether increased nitrogen fixation and algal growth will enhance or reduce atmospheric CO2 in the long term.

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