MODELS FOR PERMAFROST THICKNESS VARIATION IN RESPONSE TO CHANGES IN PALEOCLIMATE

Three models were developed to determine the permafrost thickness response to changes in paleoclimate. Two models represent approximate numerical and analytical techniques to solve the heat balance equation at the permafrost base. The third model (finite element) numerically integrates the thermal energy equation from the surface, through the phase boundary, to the underlying thawed materials. The amplitude of the permafrost thickness variation, A, depends directly on the amplitude of the surface temperature variation, AT, inversely on the geothermal heat flux, J, and inversely on the frequency of the surface temperature variation. For the thermal parameters and conditions used in the present study. the frnite element model predicted a value of A which was reduced by as much as 30 % from the approximate solutions in which J was assumed constant (from 78m to 51 m). The lag. 8, between surface temperature and permafrost thickness response increases with frequency, soil porosity, and AT, and decreases with increasing J. AU three models predict a lag of about 19 130 years. The permafrost response includes an initial transient which has a time-scale, t, of about 41 186 years which increases with soil porosity and AT, and decreases with increasing J. In response to sinusoidal surface temperature, the phase boundary is displaced asymmetrically wit