To capture thermal transients associated with temporal variations in BWT, we envisioned a borehole observatory in a new 180 m hole close to Site 642, consisting of a CORK to seal the borehole from the overlying ocean and a thermistor string and data logger to make and record temperature measurements. This configuration allows high-precision temperature measurements as a function of both depth and time. High-precision temperature measurements will be made at two timescales: in quick succession and over longer time intervals. Averaging a quick succession of temperature measurements is an effective way to reduce instrumental and environmental noise. Temperature measurements with an appropriate length of time between them can be used to directly monitor the propagation of transient temperatures (Chapman and Harris, 1992).