Spatial distribution of soil organic carbon in northwest Greenland and underestimates of high Arctic carbon stores

The amount of soil organic carbon (SOC) in the high Arctic is generally poorly constrained. Because of periglacial processes such as frost churning and sequestration in frozen soils, a substantial amount of SOC is typically not inventoried. This study provides a detailed study of SOC content by depth in 55 soil pits in a high Arctic ecosystem of northwest Greenland. Sampling sites spanned ecosystems from mires to polar deserts, from sea level to the margins of the Greenland Ice Sheet, and across various periglacial features. The amount of SOC in the various ecosystems was mapped using a correlation of SOC with high-resolution ASTER satellite imagery and the normalized difference vegetation index (NDVI) classes from the Circumpolar Arctic Vegetation Map. On the basis of this correlation, the total carbon was extrapolated to greater areas of the high Arctic. Our study found the amount of SOC in the high Arctic has typically been grossly underestimated, remarkably by the greatest amount in the most barren environments of the polar desert. We estimate that the high Arctic contains about 12 Pg SOC, a factor of over 5 times greater the most cited values previously reported. Since our estimate was only assessed in seasonally frozen ground, additional carbon frozen in the permafrost is likely present and potentially available in the event of permafrost thawing due to warming of the Arctic.