Arctic marine ecosystems under pressure in the Nansen and Amundsen basins

The central Arctic Ocean is changing fast. As sea ice disappears, warmer waters from the Atlantic are making their way further north, altering the delicate balance of Arctic ecosystems.

A new study reveals stark differences in ecosystem structure between the Nansen and Amundsen basins. The findings highlight the need for region-specific management strategies to protect Arctic marine life and resources threatened by rapid climate change.

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Two basins, two very different worlds

The Nansen and Amundsen basins are deep-sea regions of the central Arctic Ocean, separated by the Gakkel Ridge. 

The Nansen Basin, located closer to the Atlantic, is increasingly influenced by warm, salty water flowing in from the south. This process, known as “Atlantification,” has led to thinner sea ice, higher nutrient levels, and more biological activity in the water column.

In contrast, the Amundsen Basin remains more isolated from these changes. It is still dominated by fresher, colder waters from the Transpolar Drift—a current that transports sea ice and nutrients from Siberian rivers across the Arctic Ocean. The result is thicker ice cover, lower nutrient availability, and a less productive ecosystem.

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What does this mean for Arctic life?

A research team including Philipp Assmy from the iC3 Polar Research Hub found significant differences in the structure of biological communities in the two basins. 

The Nansen Basin, with its increased nutrient transport, supports larger populations of bacteria, protists (tiny single-celled organisms), and zooplankton. However, this does not necessarily mean a healthier ecosystem. Some species traditionally found in Arctic waters are being replaced by those more common in the Atlantic, potentially disrupting the food web.

In the Amundsen Basin, primary production is lower due to reduced nutrient availability and less light penetration through the thicker ice. This means fewer food resources for larger marine animals. While some species are extending their range northward, others are becoming less common, likely due to changing ice conditions.

Philipp explains: "The differences we observed between these basins underline the complexity of Arctic ecosystems. We can’t assume that the patterns we see in one region apply to the whole central Arctic Ocean."

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A closer look at Arctic oceanography

To understand these differences, the researchers conducted an extensive field campaign in late summer 2021.

They collected samples from sea ice, the water column, and the seafloor at 15 stations, including 5 key sites for detailed ecosystem analysis. They also measured physical properties such as temperature and salinity, assessed nutrient levels, and studied microbial and faunal communities.

One of the most striking findings was the role of ocean currents in shaping ecosystems.

In the Nansen Basin, turbulence caused by Atlantic water mixing allows nutrients to reach surface waters, fuelling biological activity. In contrast, the Amundsen Basin is more stratified, meaning fewer nutrients rise to the surface, limiting productivity.

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Implications for future Arctic management 

The study cautions against using the productive, Atlantified region of the Nansen Basin as a model for the entire central Arctic. Instead, a regional approach is needed, taking into account the unique characteristics of different basins.

This is particularly important given the increasing interest in commercial activities in the central Arctic Ocean. A fishing moratorium is currently in place until 2037, but as ice-free periods become longer, pressure to open these waters to fishing and shipping will grow.

"If we don’t take regional differences into account, we risk making decisions based on incomplete or misleading information," Philipp concludes. "Long-term monitoring and careful management will be key to protecting Arctic ecosystems in the years to come."

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Discover more

 The full study “Nansen and Amundsen basins: Gradients of physico-chemical properties and biota composition with implications for future resource management of the central Arctic Ocean” was published open access in Elementa: Science of the Anthropocene and is available here.

Philipp Assmy from the Norwegian Polar Institute researches the impact of climate change on Arctic marine ecosystems. He leads iC3’s “ice sheets and the oceans” research unit.

Philipp welcomes enquiries from people who want to join his team as MSCA postdoctoral research fellows.