Dynamic Biogeochemistry of the Particulate Sulfur Pool in a Buoyant Deep-Sea Hydrothermal Plume

In deep-ocean hydrothermal vent systems, oxidation-reduction (redox) reactions involving sulfur are known to fuel primary production via chemosynthesis. The particulate sulfur pool within buoyant hydrothermal plumes available to microorganisms as metabolic substrates remains undescribed. In this study, buoyant hydrothermal plume particles were collected from the Von Damm Vent Field, Mid-Cayman Rise, Caribbean. A novel in situ filtration system and remotely operated vehicle were used to collect samples along vertical profiles above two sites close to the summit of Mount Dent. Particulate sulfur speciation was measured using sulfur is X-ray absorption near edge structure (XANES) spectroscopy. The activity of sulfur-cycling genes in the buoyant plume was measured using metatranscriptomic sequencing. Our results indicate that both solid-state sulfur chemistry and microbial activity within the Von Damm buoyant plume are dynamic and diverse over short temporal and spatial scales. The particulate sulfur species and sulfur-cycling microbial communities generated in the buoyant plume are inputs to the neutrally buoyant plume and thus have potential for distant transport in the deep ocean. The buoyant plume particulate sulfur species include metal sulfides, thiol and organic monosulfide, thiophene, sulfone, sulfonate, ester sulfate, and sulfate. The microbial community carries a suite of active sulfur-cycling proteins (dsrAB, the sox enzyme complex, sqr, psr, dprAB, and SAT). Should these materials be exported to the neutrally buoyant plume, they will have implications for deep-ocean biogeochemistry through sustained biomass production based on sulfur oxidation and reduction.