Scientists just found hidden life thriving beneath the Arctic ice

Algae form the base of most ocean ecosystems, but they depend on nitrogen to grow -- and nitrogen is scarce in Arctic waters. Now, an international team led by the University of Copenhagen has discovered that more nitrogen may become available than scientists once believed. This shift could reshape the future of marine life in the region and influence how much carbon the ocean can absorb.

A Hidden Source of Nitrogen Beneath the Ice

The study is the first to confirm that nitrogen fixation -- a process in which certain bacteria transform nitrogen gas (N₂) dissolved in seawater into ammonium -- occurs beneath Arctic sea ice, even in its most remote and central areas. Ammonium not only helps these bacteria thrive but also nourishes algae and, by extension, the creatures that depend on them.

"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," says Lisa W. von Friesen, lead author of the study and former PhD student at the Department of Biology.

Less Ice, More Life

Unlike most other oceans where cyanobacteria dominate nitrogen fixation, the Arctic Ocean relies on an entirely different group of bacteria known as non-cyanobacteria. The researchers found the highest nitrogen fixation rates along the ice edge -- where melting is most intense. While these bacteria can operate beneath the ice, they flourish along the melting boundary. As climate change accelerates ice retreat, this expanding melt zone could allow more nitrogen to enter the ecosystem.

"In other words, the amount of available nitrogen in the Arctic Ocean has likely been underestimated, both today and for future projections. This could mean that the potential for algae production has also been underestimated as climate change continues to reduce the sea ice cover," says von Friesen.

"Because algae are the primary food source for small animals such as planktonic crustaceans, which in turn are eaten by small fish, more algae can end up affecting the entire food chain," she adds.

Could This Help the Planet Absorb More CO₂?

This new nitrogen source could also influence how much carbon dioxide the Arctic Ocean takes in. More algae mean more photosynthesis, which enables the ocean to capture greater amounts of CO₂.

"For the climate and the environment, this is likely good news. If algae production increases, the Arctic Ocean will absorb more CO₂ because more CO₂ will be bound in algae biomass. But biological systems are very complex, so it is hard to make firm predictions, because other mechanisms may pull in the opposite direction," explains Lasse Riemann, professor at the Department of Biology and senior author of the study.

The researchers emphasize that nitrogen fixation should now be considered in models predicting the Arctic's future. "We do not yet know whether the net effect will be beneficial for the climate. But it is clear that we should include an important process such as nitrogen fixation in the equation when we try to predict what will happen to the Arctic Ocean in the coming decades as sea ice declines," adds Riemann.

How Nitrogen Fixation Works

In the Arctic, non-cyanobacteria perform nitrogen fixation. These microorganisms consume dissolved organic matter -- often released by algae -- and in turn, produce fixed nitrogen that promotes further algal growth. This exchange creates a small but vital nutrient loop beneath the ice.

Algae play a double role in the ecosystem: they are both the starting point of the marine food chain and natural absorbers of CO₂. As they grow, they pull carbon dioxide from the air, which can later sink to the ocean floor as part of their biomass.

Behind the Discovery

The study, published in Communications Earth & Environment, involved scientists from the University of Copenhagen (Denmark), Linnaeus University (Sweden), Alfred Wegener Institute (Germany), Aix Marseille University (France), National Oceanography Centre (United Kingdom), Max Planck Institute for Chemistry (Germany), Stockholm University (Sweden), and the Swedish University of Agricultural Sciences (Sweden).

Their findings are based on two major research expeditions aboard the icebreakers IB Oden and RV Polarstern. Samples and measurements were collected at 13 sites across the central Arctic Ocean, including regions off northeast Greenland and north of Svalbard.