SEASONAL PATTERNS OF COUPLED FLOW IN THE ACTIVE LAYER AT 3 SITES IN NORTHWEST NORTH-AMERICA

Vertical arrays of temperature and electric-potential probes were inst alled in the upper soil at sites along the Mackenzie River valley and on the North Slope of Alaska. Time series were obtained at subdiurnal frequencies throughout the year in the active layer and upper permafro st. If the data acquisition system is properly configured, the time se ries can be used to infer soil physiochemical processes. The electric potential develops primarily in response to soil water solute concentr ation gradients in the soil column, and is a crude surrogate of the so il water electrolytic conductivity. Summer precipitation can cause rap id penetration of the thaw front when percolating rainwater, warmed at the ground surface, carries sensible heat downward to the thawing fro nt. Rates of warming at depth occur significantly faster than those ty pical of conductive heat transfer. In early winter, as the freezing fr ont penetrates downward toward the permafrost table, ions are excluded from the ice and concentrated in the intermediate unfrozen zone. Near ly instantaneous warming of the active layer is triggered by spring sn owmelt. At Happy Valley in northern Alaska, temperatures at the 29 cm depth rise from -7 to -3 degrees C in 1 h. For several hours during th is event, the temperature at 29 cm is warmer than that at regions both above and below, producing a strong thermal inversion. Time series of electric potential, or a surrogate derived from electric potential, s uggest rapid transport of meltwater from the snowpack to depth, probab ly through soil cracks. Serial events hasten active-layer warming by 1 -2 weeks.