Seafloor massive sulfide deposits from the Juan de Fuca Ridge: evidence from multiple sulfur isotopes for buried sediment and microbial activity

Abstract

Submarine hydrothermal vent systems hosted at sedimented mid-ocean ridges are often associated with larger seafloor massive sulfide deposits than typical sediment-free mid-ocean ridge systems. The Juan de Fuca spreading ridge contains both sediment-hosted and sediment-free hydrothermal systems (Middle Valley and Axial Volcano, respectively). The ridge also contains the Endeavour vent field, which occurs at the outer extent of turbiditic sediments, where the seafloor is currently sediment-free and consists of basaltic lava flows, but evidence from hydrothermal vent fluid composition suggests the presence of buried sediment. Multiple sulfur isotope ratios of hydrothermal precipitates from these three sites were analyzed to isotopically fingerprint differences in hydrothermal sulfur cycling associated with sedimented and sediment-free substrates. A three-component mixing model in Δ³³S and δ³⁴S space was developed that represents the differing contributions of sulfur derived from seawater, magmatic sources, and both sediment and crustal sulfur sources that have been influenced by microbial activity.