A Field Examination of Climate-Permafrost Relations in Continuous and Discontinuous Permafrost of the Slave Geological Province.

摘要

Climate-permafrost relations were examined across treeline using field data from the Slave Geological Province. The surface and thermal offsets, parameterized in the TTOP model, were used as a framework for the investigation. Air, ground surface, and permafrost temperatures were measured for two years (2004-06) at 24 peatlands in three study areas near Yellowknife, Colomac, and Ekati, Northwest Territories. The Yellowknife and Colomac study areas lie south of treeline in the discontinuous permafrost zone, but Ekati lies north of treeline in the continuous permafrost zone. Surveys of vegetation, snow, and soil were conducted to assess the role of microclimate on the climate-permafrost relation. Air temperatures across the Slave Province were near climate normals (1971-2000) in the first year, and were 4 °C higher on an annual basis in the second year.;The thermal offset was controlled locally by changes in the thermal conductivity ratio (rk), and regionally by climate. To evaluate the thermal offset model, values of rk determined from soil samples were compared with values obtained directly from field temperature measurements. The model performed well under normal climate conditions, but only to the north where freezeback was short. The thermal offset model did not calculate ground temperatures accurately for wet active layers under thick snow covers, or for transient conditions regardless of moisture regime or permafrost temperature.;South of treeline, the ground thermal regime was similar and did not respond to spatial or temporal changes in air temperature. North of treeline, surface and ground temperatures were considerably lower, and the climate-permafrost relation was stronger. Differences in climate-permafrost relations within the discontinuous permafrost zone, across treeline, and interannually resulted from differences in the duration of active-layer freezeback, when release of latent heat prevents substantial ground cooling. South of treeline, freezeback of the active layer was prolonged by thick snow covers, while north of treeline, where snow covers were thinner, freezeback was shorter and allowed the ground to cool for the majority of the winter. The variability of the surface offset south of treeline was controlled by total active-layer water, which is not easily estimated remotely, rather than snow.