Award: OCE-1756419

Actively venting seafloor sulfide-rich metal deposits, first discovered in the late 1970s, are sites of significant biodiversity and primary productivity in the deep ocean. These volcanogenic massive sulfide deposits form at tectonic plate boundaries, along seafloor spreading centers at mid-ocean ridges, volcanic arcs, and in back-arc basins, a result of hydrothermal circulation that occurs during emplacement of new ocean crust. The metal- and sulfide-rich vent deposits form on and below the seafloor as the hot, buoyant, metal- and sulfide- rich hydrothermal fluids rise and exit the seafloor, mixing with cold seawater; the mixing of reduced chemical species in the vent fluid (e.g., Fe2+, H2S) with more oxidized species in seawater (e.g., Fe3+, SO4=) provide energy for life in the deep ocean via chemosynthesis. Since the late 1970s, significant effort has focused on understanding the mineralogy and texture of actively venting hydrothermal sulfide deposits and associated microbiological communities. Relatively little is known, however, about the microbiological communities associated with the deposits once venting has ceased. The deposits are rich in metal sulfide minerals and can persist on the seafloor for tens of thousands of years, with the presence of reduced metal and sulfide offering potential energy sources through oxidation by seawater. This interdisciplinary project (collaborative with Jason Sylvan at Texas A&M and Brandy Toner at University of Minnesota) was designed to investigate the microbiological and mineralogical differences between actively venting versus inactive seafloor hydrothermal vent deposits, and changes that occur during the transition period from actively venting to inactive as the geochemistry of pore fluids within the sulfide deposits change. To meet objectives, samples from both active and inactive deposits were recovered during three cruises, in spring 2019 (cruise AT42-09) and again winter 2019/2020 (cruise AT42-21) using the human occupied vehicle HOV Alvin, and in spring 2021 (cruise RR2102) using the remotely-operated vehicleROV Jason 2. A particularly novel part of the project was the collection of 10 sample suites where actively venting samples were removed from the vent, with one portion of the sample immediately recovered shipboard, and portions of the same sample left on the seafloor in an area where there was no evidence of hydrothermal activity for periods of two weeks (end of first cruise), 9 months (second cruise), and/or 2 years (third cruise) to allow study of microbial community succession and changes in mineralogy and texture as venting "ceased." Analyses of recovered samples provide evidence of primary productivity and presence of microbial biofilms within inactive deposits. Results include: measurements of the incorporation of 14C-bicarbonate during incubation experiments that indicate the presence of microbial communities within inactive deposit samples that fix inorganic carbon; and metagenomic and lipidomic analyses of inactive deposit samples that indicate microbial communities dominated by Alphaproteobacteria and Gammaproteobacteria (Achberger et al., 2024, Inactive hydrothermal vent microbial communities are important contributors to deep ocean primary productivity. Nat Microbiol9, 657-668). Imaging using synchrotron techniques and by scanning electron microprobe were used to document the mineralogical, chemical, and morphological characteristics of microbial biofilms in inactive deposit samples. These findings support that inactive vent deposits are significant, and under-studied, sites of microbial activity and primary production in the deep sea. The collaborative project included training, both at sea and in the laboratory, of several graduate students and postdoctoral researchers. Metadata for collected samples have been submitted to the System for Earth Sample Registration (SESAR), part of the Interdisciplinary Earth Data Alliance, so that anyone can access information. Additionally, representative portions of sample remains are (and will be) housed in the Woods Hole Oceanographic Institution Seafloor Samples Repository, with metadata submitted to the National Oceanic and Atmospheric Administration Index to Marine and Lacustrine Geological Samples (NOAA IMLGS). Last Modified: 03/29/2024 Submitted by: MargaretKTivey