Carbon storage in permafrost and soils of the mammoth tundra-steppe biome: Role in the global carbon budget

During the Last Glacial Maximum (LGM), atmospheric CO2 concentration was 80–100 ppmv lower than in pre‐industrial times. At that time steppe‐tundra was the most extensive biome on Earth. Some authors assume that C storage in that biome was very small, similar to today's deserts, and that the terrestrial carbon (C) reservoir increased at the Pleistocene‐Holocene transition (PHT) by 400–1300 Gt. To estimate C storage in the entire steppe‐tundra biome we used data of C storage in soils of this biome that persisted in permafrost of Siberia and Alaska and developed a model that describes C accumulation in soils and in permafrost. The model shows a slow but consistent C increase in soil when permafrost appears. At the PHT, C‐rich frozen loess of Europe and South of Siberia thawed and lost most of its carbon. Soil carbon decreases as tundra‐steppe changes to forest, steppes and tundra. As a result, over 1000 Gt C was released to the atmosphere, oceans, and other terrestrial ecosystems. The model results also show that restoring the tundra‐steppe ecosystem would enhance soil C storage, while providing other important ecosystem services.