Extent of Permafrost
The extent of permafrost varies with the climate. Today, a considerable area of the Arctic is covered by permafrost (including discontinuous permafrost). Overlying permafrost is a thin active layer that seasonally thaws during the summer. Plant life can be supported only within the active layer since growth can occur only in soil that is fully thawed for some part of the year. Thickness of the active layer varies by year and location, but is typically 0.6–4 m (2.0–13 ft) thick. In areas of continuous permafrost and harsh winters the depth of the permafrost can be as much as 1,493 m (4,898 ft) in the northern Lena and Yana River basins in Siberia. Permafrost can also store carbon, both as peat and as methane. The most recent work investigating the permafrost carbon pool size estimates that 1400–1700 Gt of carbon is stored in permafrost soils worldwide. This large carbon pool represents more carbon than currently exists in all living things and twice as much carbon as exists in the atmosphere.
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