Arctic Ocean chemical shift from sea-ice loss threatens marine food chain and carbon sink

A 20-year study of the Fram Strait shows an irreversible decline in nitrate levels in the Arctic Ocean, driven by accelerating sea-ice loss. Without ice cover, sunlight hits shallow continental shelves and triggers benthic denitrification, converting nitrate into nitrogen gas and permanently removing it from seawater. This nutrient depletion has pushed the ecosystem past a tipping point, limiting phytoplankton growth and reducing the total biomass the food web can support. The shift means the Arctic Ocean will likely support smaller plankton species, which reduces food for fish, seabirds, and marine mammals. It also weakens the ocean's ability to absorb atmospheric carbon, since plankton capture CO2 through photosynthesis. The change is tied directly to ongoing global sea-ice loss and is not expected to reverse, with implications for commercial fishing and the global carbon cycle.