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When Arctic 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 percent of the total sea ice algal biomass in the Arctic. That was far more than we expected. That means that most of the life in the sea ice could be linked to these ridges. And yet they are one of the least investigated environments in the Arctic,” microbial ecologist at The University of Bergen, Oliver Müller �������.��

Müller’s study is based on fieldwork from the 2020 Arctic drift expedition (MOSAiC), where the German research icebreaker Polarstern was frozen into sea ice near the Siberian shelf and drifted across the Arctic Ocean.

Because sea ice algae form the very base of the ice associated Arctic food web, the findings could reshape how scientists understand life in the far north.

The Hidden Architecture of 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 meters downward into the ocean.

Above the surface, they look like small, rough ice hills. Below, they are like 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 of up to 9 m total thickness, they found not only high biomass, but extraordinary diversity in a relatively small area.

From microscopic algae to zooplankton and small fish seeking shelter, the ridges function as compact ecosystems.

Why Algae Matter for Polar Bears

Sea ice algae are not visible to the naked eye unless they are found in dense concentrations, and they are the foundation of Arctic marine life.

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 base is disrupted, the effects can ripple upwards.

“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 percent of sea ice algal biomass is concentrated in ridges, those structures may play a far larger ecological role than previously understood.

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 two decades 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 Mørk 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 lightless winter.

The Arctic is warming rapidly, and summer sea ice is expected to decline dramatically in coming decades. Understanding where life is concentrated, and how it responds to structural changes in sea ice is crucial for predicting future ecosystem shifts.

References:

Oliver Müller et.al: Arctic sea-ice ridges are biomass hotspots harboring diverse microbial communities. Commun Earth Environ��(2026).��

And

Olsen, L.M., Salganik, E., Müller, O.��et al.��Sea-ice ridge formation fuels Arctic pelagic food webs during the polar night.��Commun Earth Environ��(2026).
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