COMPOSITION AND SEDIMENTATION OF HYDROTHERMAL PLUME PARTICLES FROM NORTH CLEFT SEGMENT, JUAN-DE-FUCA RIDGE

In 1990 and 1991, particles from buoyant and neutrally buoyant hydroth ermal plumes above hydrothermal vents at the North Cleft segment of th e Juan de Fuca Ridge were sampled to study their changing composition and fluxes away from the vent field. In the rising buoyant plume, >75% of the P, V, Cr, and As scavenging from seawater by hydrothermal prec ipitates occurs in the first 50 m above the vent. Cu and Zn are most e nriched in buoyant plume particles collected from the first few meters above the vent. However, the degree of enrichment decreases very rapi dly with increased height above die vents due to sedimentation of the more dense Cu- and Zn-rich sulfide phases. Using the plume data, coupl ed with the results of our analysis of sediment trap samples, we estim ated that more than 99% and 99.9%, respectively, of the total hydrothe rmal Fe and Mn produced at the vent field are transported beyond the v ent field and dispersed in the open ocean.