Soil Organic Carbon Pools in the Northern Circumpolar Region

During the last decade there has been a remarkable increase in soil carbon studies in the northern circumpolar permafrost region. With the development of large soil databases, it has been possible to obtain new estimates of the amount of soil organic carbon occurring in this region. These estimates include the near-surface organic carbon (0-30 cm), the carbon in the deeper soil layer (0–3 m) and the carbon in some high-carbon-content deposits that are deeper than 3 m and were not accounted for in previous estimates.

This vast region has a soil area of approximately 18,782 x 10³ km², which is approximately 16% of the global soil area. The new carbon pool estimates are 191.29 Gt for the 0–30 cm depth, 498.80 Gt for the 0–1 m depth and 1024.00 Gt for the 0–3 m depth. Carbon pools in layers deeper than 3 m were estimated for two types of high-carbon-content deposits, the yedoma deposits (407 Gt) and the deltaic deposits (241 Gt). In total, the northern permafrost region contains approximately 1672 Gt of organic carbon, of which approximately 1466 Gt, or 88%, occurs in perennially frozen soils and deposits. This 1672 Gt of organic carbon accounts for approximately 50% of the currently-estimated global belowground organic carbon pool.

Data used in this study were derived from a number of sources with different rates of accuracy and uncertainty. Thus, North American carbon estimates (0–30 cm and 0–1 m) were given a medium to high confidence levels (66–80%). Eurasian carbon estimates were given a low to medium confidence levels (33–66%) based on the smaller dataset. Carbon estimates for deeper layers and other deposits were given very low to low confidence levels (<33%) since the dataset was very small.

Soils in the northern circumpolar permafrost region contain approximately three times more carbon than is stored in the aboveground biomass, two times more than the anthropogenic carbon in the ocean and many times more than the annual carbon input into the atmosphere by human sources. Since the greatest global warming is predicted to occur in this region, it could ultimately be exposed to new environmental conditions more amenable to decomposition of organic matter. As a result, high amounts of carbon dioxide and methane could be released with the potential for carbon-climate feedbacks, which would further increase climate warming.