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doi:10.2204/iodp.proc.320321.107.2010

Downhole measurements

Heat flow

Five APCT-3 downhole temperature measurements in Hole U1335B ranged from 1.64°C at 22.3 m to 2.22°C at 98.3 m (Table T30), giving a low geothermal gradient of 7.5°C/km (Fig. F30). The bottom water temperature was 1.469°C, based on the average of the minimum temperature in the five APCT-3 temperature profiles. Thermal conductivity under in situ conditions was estimated from laboratory-determined thermal conductivity using the method of Hyndman et al. (1974) (see "Physical properties" in the "Methods" chapter). The calculated in situ values are up to 2.5% less than the measured laboratory values. Thermal resistance was then calculated by cumulatively adding the inverse of the in situ thermal conductivity values over depth intervals downhole (Fig. F30). A heat flow of 7.0 mW/m² was obtained from the linear fit between temperature and thermal resistance (Fig. F30) (Pribnow et al., 2000), which is a low value compared to nearby sites in the global heat flow database and an order of magnitude lower that the heat flow at Site U1332.

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