GEOPHYSICAL MONOGRAPH SERIES, VOL. 144, PP. 269-289, 2004
Mixing, reaction and microbial activity in the sub-seafloor revealed by temporal and spatial variation in diffuse flow vents at axial volcano
To begin to understand the relationship between microbial communities and the geochemical environment, we have conducted systematic
sampling and in situ analysis of a range of seafloor vents on or near the January 1998 lava flow at the summit of Axial Volcano
on the Juan de Fuca ridge. The systematics of the chemical composition indicate that low-temperature diffuse fluids (3°C–78°C)
at Axial Volcano have a high-temperature (>350°C) reaction-zone component overprinted by lower-temperature reactions. The
low-temperature reactions include production of methane, ammonia and particulate elemental sulfur, oxidation of hydrogen sulfide,
nitrate reduction, stripping of metals from seawater, and reactions that dissolve iron and produce alkalinity. High concentrations
of CO2 from magmatic degassing maintain acidic pH conditions and may be important in promoting low-temperature hydrolysis reactions.
H2S oxidation is the dominant chemical energy source for microbial metabolism at Axial Volcano, and the energy available from
either methanogenesis or iron oxidation is ∼100 times less. Chemical evidence, genetic signatures of thermophilic, non-seawater
organisms, presence of culturable thermophiles, and cell counts elevated above background seawater in low-temperature fluids
indicate microbial activity below the seafloor. Metabolic activity of organisms identified in venting fluids matches the chemical
processes occurring in low-temperature sub-seafloor reservoirs.
Citation: Butterfield, D. A.,