Thawing of the Active Layer on the Coastal Plain of the Alaskan Arctic

Maximum active layer thicknesses increased from the coast inland with means of 0.36 m at West Dock, 0.53 m at Deadhorse, and 0.62 m at Franklin Bluffs and varied systematically from 1986 to 1992 by factors up to two (0.21 m to 0.45 m at West Dock). Maximum thicknesses occurred at all sites in 1989 and the recent data indicate a broad minimum from 1992 through 1995. Since trace gas emissions from tundra depend on active layer thicknesses, these results indicate potential systematic changes in trace gas emissions. A modified Kudryavtsev equation has advantages over other analytical models and accurately estimates active layer thicknesses in the Prudhoe Bay region. Stefan-type equations for predicting active layer thicknesses can lead to systematic errors of up to 71%. Temperatures at the ground surface when thawing ceases were estimated to be about 2°C. The active layer typically reached its maximum thickness and began freezing upward from the bottom one to two weeks earlier than the beginning of freezing from the surface. Deviations (RMS) between calculated (using a calibrated finite element model) and measured temperatures were in the range 0.2-0.3 K indicating that a purely conductive heat flow model can be used for accurate predictions of active layer and permafrost temperatures. Previously estimated values of thermal offset were improved using adjusted thermal conductivity values indicated by the thermal modelling. © 1997 John Wiley & Sons, Ltd.