HYDROTHERMAL PLUME PARTICLES AND DISSOLVED PHOSPHATE OVER THE SUPERFAST-SPREADING SOUTHERN EAST PACIFIC RISE

The distribution and elemental composition of hydrothermal plume parti cles were mapped along the superfast spreading southern East Pacific R ise from the Garret Transform Fault to similar to 19 degrees S. Hydrog raphic and optical data were obtained using a series of seven tow-yes and thirty vertical casts employing a rosette sampler with 19-L, PVC b ottles for collecting discrete samples of various dissolved and partic ulate hydrothermal species. The extent of hydrothermal plume coverage over the southern East Pacific Rise between 13 degrees 33' and 18 degr ees 40'S is significantly greater than in other ridgecrest systems. Th e region south of 17 degrees 20'S is characterized by significant enri chments of volatile gases resulting from magmatic input of fresh lava at the seafloor. Between 17 degrees 20' and 18 degrees 40'S, the ratio of S/Fe in the plume particles is highly correlated with the dissolve d gases in the neutrally-buoyant hydrothermal plumes. Plume inventorie s of Fe and S over this portion of the southern East Pacific Rise are 6-150 times higher than what has been observed over other vent fields because the total abundance of plumes is much greater. In addition, si gnificant depletions (>100 nmol/L) of dissolved phosphate over the rid ge axis were observed at the depth of the hydrothermal plumes. These r esults provide clear evidence that this section of the southern East P acific Rise maintains the most extensive complex of hydrothermal plume s observed thus far on the global ridgecrest system.