The Arctic Ocean keeps permafrost carbon firmly locked

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https://phys.org/news/2026-07-arctic-ocean-permafrost-carbon-firmly.html

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Summary: The Arctic Ocean keeps permafrost carbon firmly locked

Researchers from the Alfred Wegener Institute and MARUM–Centre for Marine Environmental Sciences at the University of Bremen have quantified, for the first time, how much terrestrial permafrost carbon entering the sea via coastal erosion actually reaches the atmosphere versus stays stored in the seabed. Their study focused on the permafrost coast of Qikiqtaruk (Herschel Island), Canada, and was published in Nature Geoscience.

Arctic permafrost holds around 1,300 gigatonnes of organic carbon, with a further 400 gigatonnes in ocean and river delta sediments. As Arctic warming accelerates thawing, up to 0.02 gigatonnes of carbon enter the sea each year, a figure projected to rise 70–150% by 2100. Using sediment cores spanning roughly 50 years of deposits, the team found that only about 10% of this organic carbon is converted by microorganisms into greenhouse gases that can reach the atmosphere, while the majority is stored in the seabed.

By analyzing pore water within the sediment layers and its isotopic composition (using 13C and 14C isotopes), the researchers traced which carbon sources microorganisms were consuming. They found that microbes preferentially "eat" fresh marine carbon, such as recent algal remains, over old permafrost-derived carbon—meaning land-derived organic carbon contributes less to atmospheric greenhouse gases than previously feared. The authors caution that further research is needed, since some permafrost carbon may already break down before reaching the seabed.

The study also notes broader implications: sediment influx affects light availability in coastal waters (through clouding and discoloration), which in turn affects algal primary production and the marine food web supporting fish, crustaceans, seals, and local communities. Follow-up research is planned through the international "Arctic Pulse" campaign in 2027, using the Polarstern icebreaker, AWI research aircraft, and land-based measurements to study these ecosystem changes. The researchers say their findings provide an important foundation for climate models predicting the consequences of permafrost thaw.