Effects of climatic variability on the active layer and permafrost

Dissertation (Ph.D.) University of Alaska Fairbanks, 1996This thesis represents a collection of papers on the response of the active layer and permafrost to climatic variations on different time scales. Quantitative estimates of the amplitudes of the Milankovich rhythms in several regions of the Russian permafrost zone were used in numerical simulations of permafiost dynamics. The results of modeling explained many aspects of the permafrost distribution and its vertical structure within Russia. Spatial and temporal variability of the air, ground surface and permafrost temperatures were also analyzed using daily temperature data (upper 0.9 m) from 1986-1993 and results of annual temperature measurements in boreholes (nominally 60 m) from 1983-1995 at three sites in the Prudhoe Bay region of Alaska. Three numerical models which are based on different numerical methods and are used for calculations of the ground thermal regime were compared with each other, with analytical solutions, and with temperature data. Several approximate analytical solutions for the temperature regime and thickness of the active layer were introduced. The calculations were used to estimate the interannual variability of the thermal properties of soils which appear to be a result of interannual variations of the average water content during the summer in the upper part of the active layer. Precise temperature data together with computer modeling provided essential new information on dynamics of unfrozen water content in the ground in natural undisturbed conditions during freezing and the subsequent cooling of the active layer. A layer with unusually large unfrozen water content was found to exist at the depth of freeze-up. The same set of data was used to reconstruct daily permafrost temperatures from 1986-1993 for all depths down to 55 m. Mean annual temperature profiles for each year of 1987-1992 show significant interannual variations within the upper 40 m in a good agreement with published data. A numerical model of the temperature field in permafrost near its southern limits was developed to study the influence of short-term climatic variations (with periods of 300 and 90 years) on permafrost dynamics