Arctic river deltas hold 63 billion tons of frozen carbon that could accelerate warming as permafrost thaws

New research led by Matthias Fuchs at the University of Colorado and the Alfred Wegener Institute estimates that Arctic river deltas store about 63.4 billion tons of carbon and 4.2 billion tons of nitrogen in frozen soils. That is roughly 5% of all permafrost carbon packed into just 1% of the permafrost area. The study analyzed over 1,600 soil samples from 17 deltas including the Lena and Mackenzie rivers. As permafrost thaws due to warming, microbes break down ancient plant material and release carbon dioxide and methane. Deltas face multiple pressures at once: retreating sea ice, rising sea levels, warmer river water, and longer thaw seasons. Some coastal land is also sinking, which accelerates the process. The carbon stockpile is more than 12 times the annual human-caused increase in atmospheric carbon, though researchers stress it will not all escape at once. The findings give climate models a more realistic baseline for forecasting future warming.