TEMPERATURE CONTROL ON POLYGONAL GROUND, TABLE MOUNTAIN, ANTARCTICA

We present the results of 14 months high-precision ground temperature measurements at two sites in cold, dry permafrost at Table Mountain in the McMurdo Dry Valleys, Antarctica. The scale of polygonal ground differed by a factor of 3 at each site and sediment composition was significantly different. Temperature was recorded with thermistor arrays at depth intervals of 13.5cm and time intervals of 4 hours from the surface to a depth of 2 meters. We find that the thermal dynamics are well described by one-dimensional linear heat flow with no latent heat effects and resolve a composition- and temperature- dependent thermal diffusivity. Effects normally associated with liquid water in permafrost can be ignored because the temperatures in the ice-cemented ground are always below minus 10 degrees C.

The diffusivity (D) is 2-3 times higher than for freeze-thaw permafrost and has a range of 1-3 x10-6 m2/s. The diffusivity is 18±9% higher in the winter than in the summer, close to that expected from the temperature dependence of the ice-cement thermal conductivity and heat capacity. We estimate the heat capacity (C) of core samples from the installation holes to be 2.0±0.2 MJ/m3 and calculate thermal conductivity profiles with a range of 2-6 W/m°C, that agree with a separate quasi-static analysis. The diffusivity and conductivity profiles correlate very well with the composition and ice content of the recovered cores. Our measurements and analysis provide new precision and accuracy for determining non-constant thermal properties. The graphical analysis is a new approach to the simple extraction of thermal properties from temperature profiles and is more robust than other similar methods.