Arctic sea-ice ridges are hidden biological hotspots – new research

During the Arctic winter, the sun disappears below the horizon for months. The ocean surface freezes, temperatures plunge, and the landscape appears almost lifeless. Yet beneath the darkness, a hidden ecosystem remains active. New research reveals that sea-ice ridges — towering, chaotic structures created when ice floes collide — play a crucial role in keeping Arctic food webs alive throughout the year.

Two recent studies published in Nature Communications Earth & Environment [1 and 2] reveal that sea-ice ridges are much more than frozen obstacles drifting through the Arctic Ocean. They are biological hotspots during summer and seasonal “larder” that release stored food during the polar night. Together, the studies uncover a previously overlooked link between summer productivity and winter survival in one of Earth’s most rapidly changing environments.

Figure: Chlorophyll a and particulate organic carbon in different ice types. Credit: Müller et al. (2026), Nature Communications Earth & Environment.

Sea-ice ridges: oases in the frozen ocean

Sea ice is often imagined as a uniform white blanket. In reality, it is a complex three-dimensional habitat filled with cracks, channels and pockets of salty water where microorganisms can live. Among the most extreme examples are sea-ice ridges, formed when drifting ice floes collide and pile up on top of each other.

The first new study shows that these ridges can become extraordinary biological hotspots during the summer melt season. Compared with surrounding sea-ice and open-water environments, ridges contain much larger amounts of biomass, such as ice algae.

This biomass forms the foundation of Arctic marine ecosystems. Through photosynthesis, ice algae capture carbon dioxide and produce organic matter that supports food webs extending from microscopic grazers to larger animals. By concentrating biological material, ridges create productive ‘islands’ within the frozen ocean.

Co-author of the study Philip Assmy from the iC3 Polar Research Hub says:

“Sea-ice ridges are often seen as physical features of the ice landscape, but our results show that they are living structures. Their complex internal spaces create habitats where microscopic organisms can thrive and accumulate biomass.”

Opening the sea-ice larder in the polar night

But what happens when summer ends? The Arctic winter brings months of darkness, stopping photosynthesis and cutting off the main source of new food production. How can organisms remain active during this challenging period?

The second study provides an important piece of the puzzle. It shows that sea-ice ridges act as storage systems, preserving organic material produced during the productive season. When ridges form, the physical disturbance of the ice can release this stored material into the surrounding seawater.

This process effectively unlocks a hidden ‘sea-ice larder’. The released organic matter fuels microbial communities and provides energy for organisms living in the water column during the polar night, when fresh production is almost absent.

In other words, ridges help life to bridge the Arctic seasons. They capture biological production during the bright months and redistribute it during the darkest time of the year.

Why this matters in a changing Arctic

The Arctic is warming several times faster than the global average, causing profound changes in sea-ice extent, thickness and dynamics. While much attention has focused on how much ice is disappearing, these studies show that how ice moves and deforms may be equally important.

If changes in climate alter the formation of sea-ice ridges, they could affect where biological material accumulates and how it is transferred through Arctic food webs. This may influence everything from microbial communities and carbon cycling to the productivity of larger marine organisms.

Philipp concludes that:

“As the Arctic sea-ice environment changes, we need to understand not only how much ice remains, but also what kind of ice remains. The structure and dynamics of sea ice can determine how energy moves through the ecosystem.”

Find out more

The first paper “Arctic sea-ice ridges are biomass hotspots harboring diverse microbial communities” is available open access in Nature Communications Earth & Environment. It has two lead authors: Jessie Gardner from the Department of Arctic and Marine Biology at the UiT The Arctic University of Norway (iC3’s host university) and Oliver Müller.

The second paper “Sea-ice ridge formation fuels Arctic pelagic food webs during the polar night” is available open access in Nature Communications Earth & Environment. Lead author is Lasse Mork Olsen.

Co-author of both papers Philipp Assmy is a researcher at the iC3 Polar Research Hub and the Norwegian Polar Institutein Tromsø. His work focuses on understanding the complex interactions between ice and ocean systems and their impact on marine ecosystems, particularly in the rapidly changing Arctic and Antarctic regions.