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80 per cent of life in Arctic sea ice may be hidden here
Researchers drilled and took samples from ice ridges in the Arctic and found large amounts of living organisms and many different species.
When marine researchers talk about life in sea ice, they normally mean the organisms living in the thin, flat ice that covers most of the frozen ocean.
But a new study suggests that the real biological hotspots lie somewhere else: inside the chaotic, broken structures where ice floes crash together.
"These sea‑ice ridges may hold up to 80 per cent of the total algal biomass in Arctic sea ice. That was far more than we expected. It means that most life in sea ice could be linked to these ridges. Yet they are one of the least investigated environments in the Arctic,” says Oliver Müller, a researcher at the University of Bergen.
Müller’s study is based on fieldwork from the 2020 Arctic drift expedition called MOSAiC. The German research icebreaker Polarstern froze into the sea ice near the Siberian shelf and drifted across the Arctic Ocean.
Because sea ice algae form the very foundation of the food chain associated with Arctic sea ice, the findings could change how researchers understand life in the far north.
Pockets of water inside the ice
Sea ice ridges are common across the Arctic. They form when large ice floes crash into each other.
Ice slabs break, tilt, and pile up, forming structures that may stretch eight or nine metres downwards into the ocean.
Above the surface, they look like small, rough ice hills. Underwater, they resemble labyrinths.
Inside the ridges are cavities: water-filled pockets between crushed ice blocks. The researchers discovered that these cavities are biological gold mines.
“On level ice, algae can only grow on a single surface. Inside ridges, they can grow on multiple surfaces, in all directions. That creates much more habitat space,” Müller explains.
When the team drilled and sampled the ridges that are up to nine metres thick, they found large amounts of life and extraordinary diversity in a relatively small area: microscopic algae, zooplankton, and small fish seeking shelter.
The ridges function as compact ecosystems.
Why algae are important for polar bears
Sea ice algae are not visible to the naked eye unless they are found in large quantities.
They use sunlight and nutrients to grow along the ice. Zooplankton eat the algae. Fish eat the zooplankton. Seals eat the fish. And polar bears hunt the seals and fish.
If the foundation of life is disrupted, the effects can ripple upwards through the food chain.
“What people often associate with the Arctic are polar bears. But even polar bears ultimately depend on these microscopic algae,” Müller says.
If as much as 80 per cent of sea ice algal biomass is concentrated in ridges, these structures may play a far larger ecological role than previously thought.
A changing and uncertain future
Studying ridges is notoriously difficult, which partly explains why they have received relatively little attention.
They form and break apart continuously as sea ice drifts.
“During the expedition, we originally planned to study one ridge over an entire season. Instead, we ended up studying three, because the first ones vanished,” Müller says.
Climate change is reshaping the Arctic ice landscape. Today’s sea ice is generally younger and more dynamic than it was 20 years ago.
In the past, thick multi-year ice could support ridges that lasted several seasons. Now, many ridges form and melt within a single year.
Winter life in the dark
A companion study led by Müller’s colleague Lasse Mork Olsen reveals another surprising process.
During the polar night, when the sun does not rise and algae cannot grow, researchers still observed high concentrations of active zooplankton in the water beneath the ice.
The explanation appears to lie in ridge formation.
When ice floes collide and ridges form, previously frozen organic material from earlier seasons can be released into the surrounding water. That material may provide enough energy to sustain parts of the ecosystem through the dark winter months.
Together, the findings suggest that ice ridges influence Arctic ecosystems year-round, both in the bright summer and the dark winter.
References:
Müller et al. Arctic sea-ice ridges are biomass hotspots harboring diverse microbial communities, Communications Earth & Environment, 2026. DOI: 10.1038/s43247-026-03364-8
Olsen et al. Sea-ice ridge formation fuels Arctic pelagic food webs during the polar night, Communications Earth & Environment, 2026. DOI: 10.1038/s43247-026-03486-z
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