Study Finds Arctic Wildfires Release Carbon Up to 5,000 Years Old

A study of soil cores collected from areas affected by recent wildfires found that fires are releasing carbon stored for centuries to millennia. Researchers reported that surface vegetation burns rapidly and triggers slower smouldering of deeper organic layers, releasing both carbon dioxide and black carbon.

Meri Ruppel at the Finnish Meteorological Institute led the team that sampled sites across the Arctic and boreal zones. The cores showed combustion reaching several centimetres into the soil, with carbon ages varying by location and soil depth.

In the Northwest Territories of Canada, fires released carbon up to 400 years old. In Greenland, average burn depths of 10 centimetres released material up to 560 years old, while some spots reached 15 centimetres and 1,000-year-old carbon. In boreal forest sites in Quebec, isolated locations yielded carbon dated to 5,000 years.

Ruppel stated that Arctic soils tend to hold older carbon closer to the surface because they are shallower. The same statement noted that boreal forest soils can store older carbon at greater depths, but such deep burns were not widespread.

Current climate models do not account for the release of this ancient carbon. Ruppel said further measurements are required to estimate total quantities now entering the atmosphere. Sandy Harrison of the University of Reading, who attended the presentation at the European Geosciences Union meeting in Vienna, said the findings highlight that high-latitude soils and peatlands contain substantial old carbon that new fire patterns can release.