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Project Progress

Application of U-tube and fiber-optic distributed temperature sensor to characterize the chemical and physical properties of a deep permafrost and sub-permafrost environment at High Lake, Nunavut, Canada.

During July of 2007 a borehole observatory comprised of a stainless steel U-tube, temperature and pressure sensor, along with heat tracer tape and DTS was deployed in the same borehole that had been drilled and cored in July of 2006. Several samples of water were collected for analyses during July of 2006 before the sample tube froze near the top. During September of 2007, a thermal perturbation experiment was performed where the ambient geothermal gradient was measured two months after the DTS had been installed and the borehole had reached thermal equilibrium. Based on the measured thermal profile the base of the permafrost (defined as the 0°C isotherm) was estimated to be at 458 ± 5 m depth. The heat trace was used to supply ~8000 watts to the borehole for 64 hours to raise the temperature by several degrees and then the heat tracer tapes were turned off. The DTS, which has a 0.1°C resolution, was used to monitor the decline in temperature for the next 58 hours and the thermal relaxation rates were used to calculate the thermal conductivity structure of the 430 meter thick permafrost with a resolution of 1 meter. Using this conductivity profile the ambient geothermal profile was inverted and a 3°C increase in average surface temperature during the last 150 years was detected. These results have been published in Geophysical Research Letters. A plan for remediating the U-tube by insulating the upper 100 meters has been developed, but intense exploration activity at the High Lake mining camp this summer has prevented us from pursuing this option. Stephen Clifford and his colleagues from the Centre d’étude des Environnements Terrestre et Planétaires (CETP); and Institute of Physique du Globe in Paris in France (IPGP) carried out a reconnaissance at High Lake site to determine its suitability for ground truthing space prototype GPR’s.

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