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doi:10.2204/iodp.proc.323.106.2011 Downhole measurementsThe only downhole measurements made at Site U1342 were two deployments of the third-generation advanced piston corer temperature tool (APCT-3) in Hole U1342C. The measured temperature was 4.46°C at 26.2 m DSF and 5.32°C at 35.0 m DSF (Table T17). These two measurements suggest a local geothermal gradient of 97.7°C/km (Fig. F41). A simple estimate of the heat flow can be obtained from the product of the geothermal gradient by the average thermal conductivity (0.991 W/[m·K]; see "Physical properties"), which gives a value of 96.9 mW/m2, significantly higher than existing measurement in the area (the global heat flow database of the International Heat Flow Commission can be found at www.heatflow.und.edu/index.html). Considering the variations in thermal conductivity with depth, a more accurate measure of the heat flow in a conductive regime can be given by a "Bullard plot." The thermal resistance of an interval is calculated by integrating the inverse of thermal conductivity over depth. If the thermal regime is purely conductive, the heat flow will be the slope of the temperature versus thermal resistance profiles (Bullard, 1939). The thermal resistance calculated over the intervals overlying the APCT-3 measurements is shown in Table T17, and the resulting linear fit of the temperature to the thermal resistance gives a heat flow value of 80.9 mW/m2, which is closer to the other measurements in the Bowers Ridge area (Fig. F42). |
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