Hydrothermal plume particles and dissolved phosphate over the superfast-spreading southern East Pacific Rise

Abstract

The distribution and elemental composition of hydrothermal plume particles were mapped along the superfast spreading southern East Pacific Rise from the Garret Transform Fault to ∼19°S. Hydrographic and optical data were obtained using a series of seven tow-yos and thirty vertical casts employing a rosette sampler with 19-L PVC bottles for collecting discrete samples of various dissolved and particulate hydrothermal species. The extent of hydrothermal plume coverage over the southern East Pacific Rise between 13°33′ and 18°40′S is significantly greater than in other ridgecrest systems. The region south of 17°20′S is characterized by significant enrichments of volatile gases resulting from magmatic input of fresh lava at the seafloor. Between 17°20′ and 18°40′S, the ratio of $\text{S}\text{Fe}$ in the plume particles is highly correlated with the dissolved gases in the neutrally-buoyant hydrothermal plumes. Plume inventories 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, significant depletions (> 100 nmol/L) of dissolved phosphate over the ridge axis were observed at the depth of the hydrothermal plumes. These results provide clear evidence that this section of the southern East Pacific Rise maintains the most extensive complex of hydrothermal plumes observed thus far on the global ridgecrest system.