Geothermics and Climate Change: Observatory Mode

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97-06559 Chapman Temperature-depth profiles, measured in boreholes, contain a temporal record of past changes in ground surface temperature (GST) and provide valuable constraints on climatic variations over the last few centuries, a critical time period that extends past the historical meteorological record. Ultimate resolution of the recovered GST depends on the resolution of the subsurface temperature profile and the confidence with which one can partition curvature in the temperature profile between transient causes (i.e. changes in surface temperature with time) and steady-state causes (i.e. topography, terrain and vegetation, heat production and thermal conductivity heterogeneities, groundwater movement, etc.). Because precision monitoring and repeat logging of temperatures in wells will reduce the interpretation ambiguity by isolating the transient component of the temperature field, a program of studying borehole thermal regimes and their changes with time is proposed. This project entails 1) operation of a real-time surface observatory (weather station installed at a borehole site) to monitor meteorological variables and near-surface temperature, 2) repeat logging of boreholes to improve the resolution of the steady-state temperature field, 3) data analysis to calculate the in-situ thermal and physical properties of the boundary, and 4) determining the temporal and spatial resolution of GSTs. The final product and significance of this project is an understanding of ground temperature as a record of climatic change and a calibration for existing and ongoing regional borehole studies. ***