Reduced Arctic Sea Ice Threatens Polar Cod, Restructuring Food Webs

Nature Communications, 6 November 2025

The amount of sunlight entering the Arctic Ocean will likely increase by 50-77% over coming decades as sea ice cover declines, but a high emissions scenario could push this system even further, past a threshold after 2050 if sea ice levels collapse. With such extreme sea ice loss, increased light reaching greater depths would further speed up both additional ice loss and ocean warming. These changes would affect the timing and growth of microscopic plants, leading to an earlier spring surge of microscopic algae under very high emissions. Today, warming and reduced ice are already reshaping Arctic food webs by altering prey availability and sharply reducing polar cod egg survival. Species like Atlantic cod and walleye pollock are already beginning to expand northward, and there is potential for them to soon outcompete polar cod, leading to shifts from cold Arctic ecosystems to warmer-water species. However, this study does not factor in ocean acidification, which might limit the expansion of cod and other species further northwards, as these cold waters draw down high levels of carbon dioxide from the atmosphere.

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