The WSTP tool is described in the Leg 141 Initial Reports volume, "Explanatory Notes" chapter (Shipboard Scientific Party, 1992).
The WSTP was inserted and left in place for at least 15 min during each deployment. If taken, fluid samples were not drawn until the probe had been in place for 15 min because the influx of fluids might bias the temperature measurements.
The ADARA tool is described in the Leg 141 Initial Reports volume, "Explanatory Notes" chapter (Shipboard Scientific Party, 1992). During Leg 149, the ADARA tool collected temperature measurements at 5-s intervals over a 15-min period.
The data reduction method for both the WSTP and ADARA temperature probes estimates the steady-state, bottom-hole temperature by forward modeling the recorded transient temperature curve as a function of time. The shape of the transient temperature curve is determined by the response function of the tool and the thermal properties of the bottom-hole sediments (Bullard, 1954; Horai and Von Herzen, 1985). In general, temperature increases following emplacement of the probe are caused by frictional heating of the probe tip during insertion. The temperature peaks after a short period of time and decreases monotonically thereafter, approaching the steady-state temperature of the sediments at a rate inversely proportional to time. Data reduction software developed by Andy Fisher and Moses Sun for WSTP data and provided with the ADARA tool for those data were used during Leg 149 to model interactively the transient temperature curve and to extrapolate for the equilibrium temperature. Variables in the modeling method are the thermal conductivity of the sediments, tool insertion time, delay time between tool insertion and peak temperature, and the length of the portion of the curve to be fit. In practice, relatively few iterations of the modeling procedure were required to obtain reasonable fits to the temperature data that were consistent with the thermal conductivity measurements obtained as part of the routine analysis of physical properties. For all temperature extrapolations, we used 1.3 W/(m·K) for thermal conductivity of the sediment around the probe.
Several potential sources of error contribute to limiting the accuracy of the equilibrium temperature estimated from the WSTP data. First, heating of the probe on insertion is not instantaneous, as the processing software assumes. Because the time of insertion is not known with great precision, some uncertainty is unavoidable in the duration of the transient thermal signal. In practice, this problem was resolved by applying an empirical time shift to the thermal data in such a way as to best fit the theoretical transient response functions of Bullard (1954). Second, the probe was not always completely inserted, may have been inserted into cuttings in the bottom of the borehole, or may have fractured the bottom-hole sediments upon insertion. In these instances, one is usually unable to recover reliable steady-state temperatures. However, one is able to recognize the presence of such problems by the shape of the temperature-time curve, thus avoiding the use of faulty data. The combined effects of these uncertainties can lead to an estimated accuracy of °C in the unreduced temperature measurements.
Temperature differences within a tool run are more precise thanthe absolute temperatures, therefore we shifted temperatures from multiple runs to match the seafloor temperatures. Further, we used the data only to compute temperature gradient and heat flow results.
These do not depend on absolute temperatures.
Temperature gradient was determined at each site to be the slope of a best fitting line to the temperature as a function of depth.
Heat flow is the slope of the best fitting line to temperature as a function of vertically integrated thermal resistivity (VITR). Thermal resistivity is the reciprocal of thermal conductivity. VITR is the integral, from the seafloor to a given depth, of the thermal resistivity. VITR for each site was calculated by a numerical integration of the reciprocal of measured thermal conductivity. In a medium having vertically varying thermal conductivity and only vertical conductive heat transport, temperature is a linear function of VITR.