FY 1999

Variability of temperature and currents measured near Pipe Organ hydrothermal vent site

Wetzler, M.A., J.W. Lavelle, G.A. Cannon, and E.T. Baker

Mar. Geophys. Res., 20(6), 505–516, doi: 10.1023/A:1004784405430 (1998)

Temperature and currents were measured ~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 (θ) changes of as much as 0.02°C occurred at all three depths, partly caused by changes in current speed and direction. Spectra of θ showed no prominent spectral peaks, however. An analytic model of heat transport under variable currents was used to help put observed θ temporal variability into context and to point out problems with estimating hydrothermal heat fluxes from mooring data. Model θ 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 θ anomalies as far as several kilometers downstream.