Abstract
Spatio-temporal distribution of temperature beneath the seafloor provides essential information on the thermal and hydrological structure and dynamics. We developed some long-term temperature monitoring systems for observation at seafloor, in a few-m-deep hole, and in deep boreholes. Measurements in a shallow hole were carried out at a hydrothermal field in the southern Mariana Trough and in the western Sagami Bay, and thermistor array system was tested in two onland boreholes in the northeastern Japan for up to 1.5 years. The thermistor elements coated with ‘Teflon’ was proved to be stable and reliable in a temperature range of 0 to 80 °C for more than one year. Shorter time scale and rather aperiodic variations in temperatures were commonly observed in boreholes. These variations would result from convection or any kind of flow within the hole. Such variation can be as large as any signal from the formation, so more careful assessment is necessary for the deep-borehole observatory that is in development at JAMSTEC.
