Chemical mapping of methane in the Northern Guaymas Basin hydrothermal field

The Guaymas Basin is a large marginal rift basin in the Gulf of California with ongoing seafloor spreading and strong hydrothermalism centered around two axial troughs. Extremely high concentrations of methane are discharged from diffuse hydrothermal flow, black smokers, and cold seeps. A thick sediment layer across the basin allows for thermocatalytic production of methane in the hot subsurface, resulting in the discharge of hydrothermal fluids from powerful black smokers with temperatures exceeding 300°C. The cooler surface sediments additionally support methanogenesis, providing a complex interplay between the biogenic and abiogenic systems. The dynamism of the Guaymas Basin means that the flux and distribution of hydrothermal vents in this region can change rapidly, impacting the wider oceanography of the region.

We present here results from a 2024 study of hydrothermalism in the Guaymas basin using a new optical sensor, developed at the Woods Hole Oceanographic Institution. SAGE – the Sensor for Aqueous Gases in the Environment – utilizes laser absorption spectroscopy through a hollow core optic fiber to quantify the partial pressure of dissolved methane extracted from the deep sea. This in situ sensor, deployed during a cruise on the R/V Atlantis allows continuous measurement of methane concentrations with high spatiotemporal resolution, with a sampling rate of 1Hz and a stable response time of 1-5 minutes. This new sensing technique facilitated analysis of the relationships between microbial communities and hydrothermalism and guided dives towards hydrothermal vents based on the real-time methane concentration. It also allowed the comprehensive in situ analysis of a rapidly evolving black smoker vent site in the northern axial trough, allowing the methane export to the water column to be characterized with high spatiotemporal resolution. The low detection limit of SAGE – down to ~10 ppm – allows the analysis of the broader impact of these dynamic methane-based systems into the wider oceanography of the region.