Arctic seabed traps 90% of carbon from thawing permafrost

Only about ten percent of organic carbon in coastal sediments from thawing permafrost is converted into greenhouse gases that can enter the atmosphere, with the rest remaining buried in the seabed, according to a study published in Nature Geoscience on August 3, 2026.

The Arctic’s permafrost holds roughly 1,300 gigatonnes of organic carbon, with another 400 gigatonnes stored in ocean sediments and river deltas. Warming is causing coastlines to erode, releasing up to 0.02 gigatonnes of carbon into the sea each year, a figure that could rise by 70 to 150 percent by 2100, said lead author Dr. Manuel Ruben of the Alfred Wegener Institute (AWI).

Researchers analysed sediment cores collected off the coast of Qikiqtaruk (Herschel Island) in Canada, representing roughly 50 years of deposition. Using carbon isotopes, they found that marine microorganisms preferentially consume fresh carbon from ocean algae, leaving most permafrost-derived carbon buried.

Prof. Gesine Mollenhauer, a geochemist at AWI and co-spokesperson for the Cluster of Excellence ‘The Ocean Floor – Earth’s Unexplored Interface’, described the sediment-dwelling microbes as ‘gourmet’ bacteria that favour fresh carbon from recent algal remains over ancient permafrost deposits.

The findings suggest that carbon from thawing permafrost may contribute less to atmospheric greenhouse gas levels than previously feared. However, the researchers caution that some permafrost carbon may break down before reaching the seabed, and further research is needed.

This study provides a more precise foundation for climate models predicting the global impact of permafrost thaw. The international ‘Arctic Pulse’ campaign, planned for 2027, will use the research icebreaker Polarstern, AWI aircraft and land sites to further explore how permafrost carbon affects coastal ecosystems, including light penetration and the food web.