Thawing Arctic permafrost is releasing vast amounts of ancient carbon into the ocean, but most of it is being locked away in seabed sediments instead of returning to the atmosphere as greenhouse gases, according to a study published in Nature Geoscience.
Researchers from the Alfred Wegener Institute (AWI) and MARUM Centre for Marine Environmental Sciences studied sediment cores collected off Canada’s Herschel Island (Qikiqtaruk) to understand the fate of carbon released from thawing permafrost.
The Arctic’s permafrost stores around 1,300 gigatonnes of organic carbon on land, while another 400 gigatonnes are trapped in marine sediments and river deltas. As rising temperatures accelerate permafrost thaw and coastal erosion, scientists estimate that up to 0.02 gigatonnes of carbon currently enter the Arctic Ocean every year, with projections suggesting this could increase by 70 to 150 per cent by 2100.
The study found that only about 10 per cent of the organic carbon reaching the seabed is broken down by microorganisms into gases that can eventually escape into the atmosphere. The remaining carbon becomes buried in marine sediments, limiting its immediate contribution to climate change.
Researchers also discovered that seabed microorganisms preferentially consume fresh organic matter from marine algae instead of the much older carbon released from thawing permafrost. This selective feeding behaviour helps preserve a large share of ancient carbon within the seabed.
However, the scientists cautioned that some permafrost derived carbon may already decompose before reaching the ocean floor, and further research is needed to fully understand its long term climate impact.
The findings provide new insights for improving climate models and suggest that Arctic seabeds may play a more significant role in storing ancient carbon than previously understood, even as warming continues to accelerate permafrost thaw.