The current estimate for soil organic carbon (SOC) quantity in the northern circumpolar permafrost region (Tarnocai et al., 2009) is 191 Pg for topsoil (0–30 cm depth), 496 Pg for the upper 100 cm of soil and SOC mass to 300 cm soil depth is estimated to be 1024 Pg. In addition, storage in deeper (〉 300 cm) Yedoma deposits (407 Pg) and deltaic deposits (241 Pg) brings the total estimate to 1672 Pg, of which 1466 Pg is stored in perennially frozen ground.
The estimate for 0–1 m depth SOC mass is based on the Northern Circumpolar Soil Carbon Database (NCSCD), a geospatial database which links 1647 pedons from the northern permafrost regions to several digitized regional/national soil maps with a combined circumpolar coverage. This database has recently been published online and the data is available in several different file formats, including gridded files with different spatial resolutions. Files adapted for use in GIS or modeling applications (shape-files, TIFF-rasters and NetCDF files) are available for separate regions or with merged circumpolar coverage.
Estimates for the 0–30 cm and 0–100 cm depth ranges based on the NCSCD are unlikely to be significantly changed or refined in the coming years. However, the emergence of high quality geospatial datasets with circumpolar coverage as well as applications of spatially distributed regression/kriging techniques in periglacial environments (e.g. Mishra and Riley, 2012) point towards complementary approaches that may significantly increase our knowledge of circumpolar SOC distribution.
The present estimates of SOC mass in the 0–300 cm depth range is based on very limited field data (46 Canadian pedons), is accorded low to very low confidence and is not included in the spatially distributed NCSCD (Tarnocai et al., 2009). However, a compilation of additional pedon data is underway and an updated version of the NCSCD will be complemented with spatially distributed estimates of 100–200 cm and 200–300 cm depth SOCM based on 〉 200 deep pedons from around the circumpolar region. This estimate is also planned to include quantification of upscaling uncertainties caused by insufficient field sampling of naturally variable soils and areal misrepresentation of soil types in the maps used for upscaling (following Hugelius, 2012).
Hugelius, G. (2012), Spatial upscaling using thematic maps: An analysis of uncertainties in permafrost soil carbon estimates, Global Biogeochem. Cycles, 26, GB2026, doi:10.1029/2011GB004154
Mishra U. and Riley W.J. (2012) Alaskan soil carbon stocks: spatial variability and dependence on environmental factors, Biogeosciences Discuss, 9, 5695–5718
EPIC Alfred Wegener Institut