Low Heat Flow Values Measured on the Hawaiian Ridge

Two days of dives with the ROV Tiburon on the MBARI Hawaiian expedition in May 2001 were devoted to collecting heat flow data on the Hawaiian Ridge near Oahu. Measurements were made with a 60~cm probe developed for the deep submersible Alvin along a 6~km northeast-southwest profile at 32 stations at 200--300~m intervals at about 3400~m water depth northwest of the island of Oahu, near the deep water study area previously sampled by Harris et al. [2000] with a shipboard heat flow probe. Measured thermal gradients were low, from 0--20~mK/meter at the center to around 60~mK/meter near each end of the profile. Two outlying measurements of higher values near the center of this bowl-shaped pattern are found near basement outcrops observed by the ROV. Thermal conductivity measured in situ by the probe and in several push cores was essentially constant at 1.05+/-0.02 W m^-1 K^-1 along the line. Data quality is very good, and we believe that our measurements are reflecting the true thermal gradients in the top 60~cm of the sediments. Although the measured thermal gradients are low, the systematic variation along the profile suggests that the observed bowl-shaped thermal profile has a geologic origin. The amplitude of the basin scale pattern is too large to explain by thermal conductive effects alone. It is consistent with a significant hydrological flow with a recharge zone in the center and discharge at the sides. We are also investigating the relative importance of bottom water temperature variations, sedimentation history and the transient thermal signal of the construction of the island of Oahu on the observed heat flow pattern. kels/heatflow</a>