GEOTHERMAL HEAT-FLUX FROM HYDROTHERMAL PLUMES ON THE JUAN-DE-FUCA RIDGE

Estimates of the heat output of hydrothermal vents, identified along t he Endeavor and Southern segments of the Juan de Fuca Ridge, are used to evaluate the total heat flux associated with hydrothermal circulati on for the ridge segment. A 50-m array carried by DSV Alvin sampled th e temperature and vertical velocity structure of hydrothermal plumes f rom individual vents. These measurements am used to estimate the therm al flux associated with such plumes. The maximum heat flux calculated for a single vent is 50 MW (1 MW = 1 x 10(6) W). The median heat flux per vent is 9 MW and 3 MW, respectively, for the Endeavour Segment (18 vents) and Southern Segment (18 vents). The estimates for any given v ent may vary over an order of magnitude. This uncertainty is due mainl y to the difficulty of locating the centerline of the plume relative t o the point of measurement, although the uncertainties in the constant s for the appropriate equations based on laboratory experiments also c ontribute significantly to the net error. For the Endeavor Segment, th e minimum total geothermal heat flux due to hydrothermal circulation e xceeds 70 MW. The minimum estimate for the Southern Segment is 16 MW. The maximum estimate is probably closer to the total heat flux from hi gh-temperature venting (239 MW and 66 MW respectively). High-temperatu re hydrothermal venting accounts for only a small fraction of the heat available according to steady state predictions of conductive heat fl ux; other hydrothermal phenomena (e.g., diffuse flow) probably account for a greater proportion of the total hydrothermal heat flux.