An irreversible shift in the chemical makeup of the Arctic Ocean driven by climate change is disrupting the region's food chain, a study suggests. Widespread loss of Arctic sea ice has led to a sharp fall in levels of a key nutrient, affecting populations of plankton, fish, seabirds and marine mammals, say researchers. Their analysis reveals that exposure to sunlight of vast shallow regions of the ocean previously covered by ice fuels a process that breaks down the nutrient—nitrate—and removes it from seawater. The study appears in Communications Earth & Environment.