Temperature and currents were measured similar to 100 m south of the Pipe Organ vent site on the Juan de Fuca Ridge during a 5-day interval in September 1997 to examine the temporal variability of hydrothermal heat signals close to a source. Temperatures were sampled at three depths every 15 s while current speed and direction were sampled at a single depth hourly. Results show that rapid potential temperature (theta) changes of as much as 0.02 degrees C occurred at all three depths, partly caused by changes in current speed and direction. Spectra of theta showed no prominent spectral peaks, however. An analytic model of heat transport under variable currents was used to help put observed theta temporal variability into context and to point out problems with estimating hydrothermal heat fluxes from mooring data. Model theta distributions, when contoured on a horizontal plane and animated, demonstrate the pooling of effluent over vents at various times, the streaming of effluent as a very narrow plume away from vents at times of large current speed, and the spawning of boluses of heated fluid and their transport away from venting regions when a pooling period is followed by a streaming period. Model results also show that estimated heat flux based on mooring data is strongly dependent on analysis assumptions and suggest that vents are capable of causing measurable theta anomalies as far as several kilometers downstream.