“We were wrong”: Scientists find hidden phenomenon that could trigger a boom in marine life

As Arctic sea ice melts, new life may emerge from the melt. Researchers have discovered that bacteria beneath and along the melting ice are converting nitrogen gas into a form that feeds algae.

The rapid loss of sea ice in the Arctic is considered a catastrophe. However, in an unexpected twist, melting ice may actually power the foundation of Arctic marine ecosystems: algae.

Algae serve as an essential food source for most ocean life, but their growth depends on nitrogen, a nutrient that is scarce in the frigid Arctic waters. Now, a new international study led by the University of Copenhagen suggests that future nitrogen levels in the Arctic Ocean may be higher than previously estimated. This finding could have important implications for marine ecosystems in the High North and for the global carbon balance.

For the first time, scientists have identified nitrogen fixation occurring beneath Arctic sea ice, even in its most central regions. Certain bacteria intervene in this process and transform the nitrogen gas (N2) dissolved in seawater into ammonium. Ammonium promotes bacterial growth while nourishing algae and the many organisms that depend on them throughout the marine food web.

“Until now it was believed that nitrogen fixation could not take place under sea ice because it was assumed that the living conditions of the organisms that carry out nitrogen fixation were too bad. We were wrong,” says Lisa W. von Friesen, lead author of the study and former doctoral student in the Department of Biology.

Less ice could mean more algae

While in most other oceans it is cyanobacteria that fix nitrogen, the study shows that in the central Arctic Ocean it is a completely different type of bacteria that converts nitrogen: the so-called non-cyanobacteria.

The researchers measured the highest rates of nitrogen fixation at the edge of the ice, where the ice melts most actively. Although bacteria can fix nitrogen beneath the ice, they find it easier to do so along the edge of the ice. So, as sea ice recedes and the melt area expands, greater amounts of nitrogen are expected to be added through nitrogen fixation.

“In other words, the amount of nitrogen available 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 sea ice cover,” says Lisa W. von Friesen.

“Because algae are the main 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,” adds Lisa W. von Friesen.

Can affect ocean CO₂ consumption

Additionally, the newly discovered nitrogen source could also be beneficial for CO uptake.₂ – at least at the regional level. More algae makes the ocean absorb CO better₂.

“For the climate and the environment, this is probably good news. If algae production increases, the Arctic Ocean will absorb more CO₂ because more CO₂ will be linked to the algae biomass. But biological systems are very complex, so it is difficult to make firm predictions, because other mechanisms can act in the opposite direction,” says Lasse Riemann, professor in the Department of Biology and lead author of the study.

However, the researchers believe that nitrogen fixation should be included in forecasts for the Arctic Ocean.

“We don’t yet know whether the net effect will be beneficial for the climate, but it is clear that we should include an important process like nitrogen fixation in the equation when we try to predict what will happen in the Arctic Ocean in the coming decades as sea ice decreases,” says Lasse Riemann.

Reference: “Nitrogen fixation under declining Arctic sea ice” by Lisa W. von Friesen, Hanna Farnelid, Wilken-Jon von Appen, Mar Benavides, Olivier Grosso, Christien P. Laber, Johanna Schüttler, Marcus Sundbom, Sinhué Torres-Valdés, Stefan Bertilsson, Ilka Peeken, Pauline Snoeijs-Leijonmalm and Lasse Riemann, October 20, 2025, Earth and Environment Communications.
DOI: 10.1038/s43247-025-02782-4

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