PHYSICAL CHARACTERISTICS OF THE ENDEAVOR RIDGE HYDROTHERMAL PLUME DURING JULY 1988

We conducted CTD-transmissometer tows from 8 to 26 July, 1988 within 15 km of the central hydrothermal vent site (almost-equal-to 47-degrees 57-degrees N, 129-degrees 06'W) on the Endeavour segment of Juan de Fuca Ridge. Anomalies of temperature, salinity and light attenuation reveal possible new vent sites 4 and 8 km northeast and 6 km south of the central vent site. As a result of widespread plume dispersion, background values of potential temperature, salinity and light attenuation below the 1900 m depth exceeded those for "pristine" ambient waters by 0.05-degrees-C, 0.05 psu and 0.03 m-1, respectively. Maximum plume anomalies relative to the background waters were of the order of 0.10-degrees-C, 0.010 psu and 0.10 m-1 at core depths of 2000-2050 m. Heat and salt anomalies were detectable more than 5 km from the central vent site whereas light attenuation (particle) anomalies were confined to within 2.5 km of the vent site. Based on the background water property anomalies and moored current meter records, the mean (time-averaged) heat fluxes for the survey region were +2.3(+/- 1.5) x 10(8) W in the along-ridge direction (20-degrees-T) and -7.7(+/- 4.7) x 10(8) W in the cross-ridge direction (110-degrees-T). Mean along- and cross-ridge salt fluxes were +7(+/- 5) and -25(+/- 15) kg s-1; mean particle fluxes were +0.09(+/- 0.06) and -0.29(+/- 0.18) kg s-1. Estimates of the instantaneous fluxes derived from coincident current and plume measurements indicate that heat fluxes from the central vent field may have been as high as 1.2(+/- 0.6)x10(10) W and corresponding particulate fluxes as high as 6(+/- 3) kg s-1.