Organic Carbon in Arctic Permafrost and Its Impact on Climate

Carbon Reserves in Permafrost

Arctic permafrost holds significant amounts of organic carbon, most of which comes from plant remains. Estimates suggest there are about 1,300 gigatons of organic carbon stored in permafrost, with an additional 400 gigatons found in marine sediments and river deltas.

Carbon Transfer to the Ocean

As the Arctic warms faster than other regions due to climate change, permafrost thaws and coastal erosion increases. This process releases previously trapped soil carbon into the Arctic Ocean via rivers and shoreline erosion. Each year, up to 0.02 gigatons of carbon enter the sea, and projections indicate this flow could rise by 70–150% by 2100.

The Role of Microorganisms in the Carbon Cycle

Once in the ocean, some of this carbon is broken down by marine microorganisms, which convert it into greenhouse gases that contribute to climate change. However, research shows that only a small fraction of this carbon becomes part of the active carbon cycle. Microorganisms transform about 10% of the organic carbon from sediments into gases that can then enter the atmosphere. The majority of the carbon remains buried on the seafloor.

Microorganism Preferences

Isotope analysis of pore water in sediments has revealed that marine microorganisms prefer fresh organic material, such as algae remnants, over ancient carbon from permafrost. This suggests that the contribution of old carbon to atmospheric greenhouse gas levels may be lower than previously thought.

Impact on Coastal Ecosystems

The movement of carbon from land to ocean affects not only greenhouse gas emissions but also the chemistry and biology of coastal waters. Sediments from erosion reduce the amount of sunlight penetrating the water, making it murkier. Dissolved organic carbon further darkens the water, which limits photosynthesis in single-celled algae—organisms essential for producing biomass and oxygen. This primary production supports food chains that include fish, crustaceans, and seals.

Future Research Prospects

To better assess the impact of permafrost thaw on the climate, further studies are needed, as some organic carbon may decompose before reaching the seafloor. In 2027, an international research campaign called "Arctic Pulse" is planned, involving coordinated observations from icebreakers, aircraft, and land stations. The goal is to study how rapid environmental changes are transforming Arctic ecosystems.

Significance for Climate Models

The data obtained will help more accurately determine how much carbon remains on the seafloor and how much decomposes, which is crucial for building climate models and predicting the consequences of permafrost thaw for the global climate.