Active-layer thickness in the Kuparuk region, north-central Alaska: Spatial time series analysis and stochastic modeling

The uppermost layer of seasonal thawing above permafrost (the active layer) is an important regulator of energy and mass fluxes between the surface and the atmosphere in the polar regions. The major difficulty in predicting the current state of active-layer thickness is associated with the extremely high spatial variability of thaw depth over a wide range of scales, in response to the large number of interacting climatic and terrestrial factors. This dissertation addresses the problem of spatial and temporal variability of active-layer thickness at a regional scale, and the landscape-specific effects of this variability in a contemporary environmental setting. Extensive, spatially oriented field investigations conducted in the Kuparuk River region of north-central Alaska were used to analyze spatial and temporal regularities in the active layer and to develop an analytical technique for regional active-layer mapping. Validation of an analytically derived active-layer field, conducted using data obtained from an extensive, helicopter supported survey, demonstrate that it is feasible to map active-layer thickness over large areas. To evaluate the effect of interannual climatic variability on regional thaw depth estimates, a 13-year series of regional thawing degree-day fields was constructed using topographically and climatologically aided interpolation of available air temperature records. The problem of uncertainties associated with regional quantitative estimates of the total volume of thawed soil was addressed by developing a stochastic model based on analytic techniques for thaw-depth mapping, in conjunction with a Monte Carlo simulation of observed variations in active-layer thickness. The stochastic modeling approach captures the distribution of active-layer thickness at the regional scale, and produces regional estimates of the volume of thawed soil with corresponding confidence intervals. A series of probability maps is used to communicate information about active-layer thickness in the Kuparuk region.