Seafloor eruptions and evolution of hydrothermal fluid chemistry

Abstract

A major challenge confronting geochemists is to relate the chemistry of vented hydrothermal fluids to the local or regional tectonic and volcanic state of mid-ocean ridges. After more than 15 years of sampling submarine hydrothermal fluids, a complex picture of spatial and temporal variability in temperature and composition is emerging. Recent time-series observations and sampling of ridge segments with confirmed recent volcanic eruptions (CoAxial and North Cleft on the Juan de Fuca ridge and 9-10 • N on the East Pacific Rise) have created a first-order understanding of how hydrothermal systems respond to volcanic events on the seafloor. Phase separation and enhanced volatile fluxes are associated with volcanic eruptions, with vapour-dominated fluids predominating in the initial post-eruption period, followed in time by brine-dominated fluids, consistent with temporary storage of brine below the seafloor. Chemical data for CoAxial vents presented here are consistent with this evolution. Rapid changes in output and composition of hydrothermal fluids following volcanic events may have a profound effect on microbiological production, macrofaunal colonization, and hydrothermal heat and mass fluxes. Size and location of the heat source are critical in determining how fast heat is removed and whether subseafloor microbial production will flourish. CoAxial event plumes may be a direct result of dyking and eruption of lavas on the seafloor.

Halomonas neptunia sp. nov., Halomonas sulfidaeris sp. nov., Halomonas axialensis sp. nov. and Halomonas hydrothermalis sp. nov.: halophilic bacteria isolated from deep-sea hydrothermal-vent environments

“…Four strains also reduced nitrate anaerobically. These abilities are hypothesized to be key adaptations for living in warm, heavy-metal-enriched subseafloor habitats associated with hydrothermal vents, where oxygen may become limiting at temperatures as low as~10 u C and nitrate and nitrite may become limiting at~30 u C (Butterfield et al, 1997;Huber et al, 2003;Mehta et al, 2003). The higher phenotypic similarity values amongst the hydrothermal-vent isolates may indeed reflect their common (yet geographically disparate) habitat of origin.…”

“…Low-temperature hydrothermal-vent fluids (<100 u C) are a mixture of sea water and hot hydrothermal or crustal fluid (Butterfield et al, 1997), the salinity of which can vary between one-tenth and twice that of sea water (Von Damm, 1995). Typically, sea water is the dominant component of low-temperature hydrothermal fluids, and its proportion varies inversely with temperature (Butterfield & Massoth, 1994;Cooper et al, 2000;Koschinsky et al, 2002).…”

Microbial Ecology of the Dark Ocean above, at, and below the Seafloor

“…Hence, the biogeochemical and microbiological features of plumes also vary temporally and spatially. For example, following signals of eruptive submarine volcanic events, rapid response sampling campaigns to hydrothermal vent sites have documented significant increases in volatile compounds, such as hydrogen, carbon dioxide, methane, and sulfide gases, within plumes (74,108,282,320,578). When hydrothermal fluids are injected into the water column, they are less dense than the surrounding seawater because of higher temperature, and hence the fluids rise as they mix with the cooler seawater.…”

Mineral–microbe interactions in deep-sea hydrothermal systems: a challenge for Raman spectroscopy

“…There is an established body of research which suggests that hydrothermal flux from a given vent site along any section of mid-ocean ridge should undergo a predictable chemical evolution, linked to the underlying ridge-crest's volcanotectonic cycles (Butterfield et al 1997;Von Damm 2004). The most recent evidence supporting this kind of cyclicity comes from sediment trap samples collected following the latest eruption at the East Pacific Rise (German et al 2008).…”