Award: OCE-2048666

Deep-sea methane seeps are unique ecosystems along continental margins where life is supported by chemical energy rather than sunlight. These habitats support dense, productive communities, which are dependent either directly or indirectly by microorganisms which transform single carbon compounds (methane and carbon dioxide) into bioavailable forms. The extent to which these deep-sea communities are reliant on methane and whether this varies between sites occurring at different water depths, or with distance from an active methane source is currently poorly understood. Anaerobic methane-oxidizing archaea that work together with sulfate-reducing bacteria to oxidize methane using sulfate serve as foundational members of these ecosystems. These archaeal-bacterial partnerships not only transform the local chemical landscape in areas where methane flows to the sediment surface but they also can physically transform the soft, muddy seafloor into a hard ground habitat through the precipitation of carbonate rock. These carbonate structures in turn serve as a unique habitat for animals, especially those requiring hard substrates for colonization. In this project, we contributed new information about the diversity, distribution, and functioning of microbes and microbe-animal symbioses associated with seep carbonates, sediments, and overlying water. Our multi-PI, multi-disciplinary research focused on both the macro- and microbial ecology and biogeochemistry of methane seep ecosystems ranging in depth, methane flux, and water column oxygen concentrations. Using a combination of molecular, geochemical, and fluorescence- and isotope-based imaging, we focused on the interactions and metabolic activities of microbial communities existing within and along the periphery of active methane seeps. We conducted in depth analyses of microorganisms engaged in methane cycling, in order to understand the environmental factors that shape their distribution, activity, and resiliency in these environments. During two oceanographic expeditions using the HOV Alvin aboard the R/V Atlantis, we investigated seep sites ranging in depth from 300 m to ~5000m off Southern California and the Aleutian Islands. Hundreds of environmental samples were collected and analyzed, and geochemical datasets were integrated with microbial community DNA sequencing to examine overall patterns in microbial distribution. These paired analyses revealed a disconnect in some deeper seep habitats between the characteristic porewater geochemical profiles that are diagnostic of active sulfate-coupled methane oxidation, and the prevalence of microorganisms previously associated with methane oxidation (e.g. groups of anaerobic methane-oxidizing archaea, or ANME). Microcosm experiments conducted at sea and in the lab investigated microbial activity under high in situ pressures in specialized chambers and at atmospheric conditions, demonstrating a stimulatory effect of pressure on the anaerobic oxidation of methane. Highlights of our research discoveries include the characterization of previously unknown bacteria on the surfaces of seep carbonates capable of alkane oxidation (e.g. propane and butane), novel animal–microbe symbiotic partnerships dependent on methane, and new evidence that endolithic methane-oxidizing archaea in carbonates from areas of low methane flux (periphery of seeps). The latter are abundant but dormant within carbonate interiors but can be revived and continue to consume methane with sulfate-reducing bacteria when methane once again becomes available. Collectively, our findings have increased our ecological and physiological understanding of deep-sea methane seeps and provide information and data that is relevant for resource management of these remote deep-sea ecosystems.

Last Modified: 08/19/2025
Modified by: Victoria Jeanne Orphan