In situ measurement of the thermal conductivity of ocean-floor sediments

Abstract

Twenty-eight in situ measurements of the thermal conductivity of ocean-floor sediments have been made by the transient heating of a small probe attached to a slider on the Scripps Institution of Oceanography temperature gradient probe. For twelve different locations the mean of the difference between the in situ value and the conductivity determination at the same depth on a gravity core was 0.02×10−3 cal/cm sec °C. This indicates that the in situ value is equivalent to a single measurement made at the same depth on a gravity core. A detailed statistical analysis of sixty-six gravity cores gives a 95% confidence limit of 9% for a single conductivity measurement, and hence for a single in situ determination. A detailed investigation of changes of gradient down the temperature gradient probe suggest a possible existence of a 4% increase of conductivity in the second meter. The small value of this increase and the 9% error at the 95% confidence limit gives a combined error associated with the in situ measurement that is smaller by a factor of 2 to 3 than other environmental errors affecting the heat flow measurement. These results suggest that, when the Bullard type probe is used, no core need be taken, thus saving about 30% of ship time. The in situ probe has the additional advantage that it will often return a measurement when the sediment is impenetrable by a piston or gravity core.