TRACKING THE DISPERSAL OF HYDROTHERMAL PLUMES FROM THE JUAN DE FUCA RIDGE USING SUSPENDED MATER COMPOSITION

In 1988 and 1989, particles from on- and off-axis neutrally buoyant plumes over the Juan de Fuca Ridge were sampled to study their changing composition with distance from the ridge crest. Plume depth and particle composition in off-axis hydrothermal plumes were used to identify plume sources and trajectories. Iron and phosphorus concentrations and, in particular, P/Fe molar ratios were found to be sensitive indicators of hydrothermal phases in the suspended matter. Phosphorus, vanadium, and arsenic are scavenged from solution where dissolved iron from hydrothermal vents oxidizes in seawater and forms submicrometer-sized particles of Fe oxyhydroxide. The P/Fe molar ratio (approximately 0.23) is essentially the same for vent fields along Cleft and Endeavour segments, indicating that the scavenging processes are the same for both regions. High P/Fe ratios are observed over the South and North Cleft Segment vent fields and to the west along the Vance Seamount Chain. The seamounts evidently function as a barrier, bathymetrically steering the hydrothermal plumes to the west away from the ridge crest. Since particles from the Endeavour vent field are greatly enriched in copper relative to hydrothermal plumes from other vent fields along the Juan de Fuca Rigde, copper concentrations in the plumes can be used to distinguish plume sources. Based on water column depth and elemental composition, hydrothermal plume particles from specific vent fields on the Juan de Fuca Ridge may be tracked as much as several tens of kilometers from their source using particle compositions.