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 Frank lin Bluffs and varied systematically from 1986 to 1992 by factors up t o 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 1 992 through 1995. Since trace gas emissions from tundra depend on acti ve layer thicknesses, these results indicate potential systematic chan ges in trace gas emissions. A modified Kudryavtsev equation has advant ages over other analytical models and accurately estimates active laye r thicknesses in the Prudhoe Bay region. Stefan-type equations for pre dicting active layer thicknesses can lead to systematic errors of up t o 71%. Temperatures at the ground surface when thawing ceases were est imated to be about 2 degrees C. The active layer typically reached its maximum thickness and began freezing upward from the bottom one to tw o weeks earlier than the beginning of freezing from the surface. Devia tions (RMS) between calculated (using a calibrated finite element mode l) and measured temperatures were in the range 0.2-0.3 K indicating th at a purely conductive heat flow model can be used for accurate predic tions of active layer and permafrost temperatures. Previously estimate d values of thermal offset were improved using adjusted thermal conduc tivity values indicated by the thermal modelling. (C) 1997 by John Wil ey & Sons, Ltd.