Estimating the Stocks and Uncertainty of Seasonally-thawed Soil Organic Carbon and Nitrogen Overlying Permafrost in the Arctic Foothills of Alaska

The vast amounts of organic carbon (C) and nitrogen (N) in permafrost landscapes strongly influence climate warming because once thawed they can be released as greenhouse gases. An imminent driver of environmental change is the C and N in soils above permafrost within the seasonally-thawed active layer. We produced a new dataset of active-layer soil organic C and N by sampling based on stratigraphic horizon and vegetation type across the North Slope foothills. Our active-layer soil C stock estimate of 40.3 kg C/m<sup>2</sup> (interquartile range of 29.9 - 47.8 kg C/m<sup>2</sup>) and N estimate of 3.12 kg N/m<sup>2</sup> (interquartile range of 2.07- 3.80 kg N/m<sup>2</sup>) are similar to or higher than previously reported values from sparse published measurements over the same region. Monte Carlo-based uncertainty analyses show that previous estimates are likely a low-biased subset of the distributions we derived for the active layer C and N stocks of the North Slope foothills. The high stocks reported here imply that substantial C and N are vulnerable to loss during pulse-disturbances such as fire or thermal erosion, and are available to sustain long-term C and N processing and losses from land to the atmosphere or surface waters.