Chemistry of hot springs along the Eastern Lau Spreading Center

Abstract

The Eastern Lau Spreading Center (ELSC) is the southernmost part of the back-arc spreading axis in the Lau Basin, west of the Tonga trench and the active Tofua volcanic arc.Over its 397-km length it exhibits large and systematic changes in spreading rate, magmatic/tectonic processes, and proximity to the volcanic arc. In 2005 we collected 81 samples of vent water from six hydrothermal fields along the ELSC. The chemistry of these waters varies both within and between vent fields, in response to changes in substrate composition, temperature and pressure, pH, water/rock ratio, and input from magmatic gases and subducted sediment. Hot-spring temperatures range from 229º to 363ºC at the five northernmost fields, with a general decrease to the south that is reversed at the Mariner field. The southernmost field, Vai Lili, emitted water at up to 334C in 1989 but had a maximum venting temperature of only

Metagenomic resolution of microbial functions in deep-sea hydrothermal plumes across the Eastern Lau Spreading Center

“…concentration and bioenergetic potential of sulfur in the water column overprints the geochemical differences in host rocks and end-member hydrothermal fluid chemistry along the ELSC (Mottl et al, 2011), which have been found to influence microbial diversity on the seafloor (Flores et al, 2012;Sylvan et al 2013). These results are consistent with a gene-centric mathematical model of the Abe vent at ELSC, which shows that sulfur metabolisms dominate and that seafloor populations were rapidly diluted out of the rising plume (Reed et al, 2015) and also with more extensive analysis of ELSC plumes, showing that differences in community composition between vent fields are not significant (Sheik et al, 2015).…”

“…Bioenergetic and thermodynamic modeling Equilibrium thermodynamic reaction path modeling was used to predict mineral precipitation, chemical concentrations and activity coefficients resulting from the mixing of sea water with end-member fluid from the hydrothermal vents (Mottl et al, 2011). Supplementary Table S2 lists the end-member fluid concentrations utilized in our model.…”

“…A deep axial valley (~2640 m) with basaltic underlying rock in the north transitions into a shallow axial ridge with andesitic underlying rocks (~1877 m) in the south (Martinez et al, 2006). Six different vent fields have been identified along the ELSC, and the chemistry of hydrothermal fluids exhibits significant inter-field variability, with properties similar to mid-ocean ridges in the north and highly elevated concentrations of H 2 S, Fe and Mn coupled with lower pH towards the south (Ferrini et al, 2008;Mottl et al, 2011). Recently, Flores et al (2012) surveyed seafloor hydrothermal deposits at ELSC and concluded that they host microbial communities similar to mid-ocean ridges except for the Mariner vent field, where the community was heavily influenced by its unique geochemistry.…”

Exploring the Ecology of Deep-Sea Hydrothermal Vents in a Metacommunity Framework

“…At some unusual vent sites in this region, where smoker chimneys are distinctly reddish brown, snails and mussels are notably absent, replaced by low densities of shrimps, crabs, polynoid polychaetes, and limpets. This faunal anomaly may be in response to high metal concentrations (Mottl et al, 2011). On the northern MAR, vent communities along a 3,000 km section between 11 and 38 • N differ markedly in species composition, in patterns that correspond to both depth and fluid chemistry (Desbruyères et al, 2000).…”

“…The availability and nature of reduced compounds will influence the autotrophic base of the food chain while fluid character will affect habitat suitability. Regional community diversity should be affected because of the high within-region variability in fluids and magma supply (e.g., Mottl et al, 2011); however, evidence is accumulating slowly due to limited fieldwork. For example, chronic eruptive activity on NW Rota (Mariana Arc) results in a very limited vent community of a few wide-dispersing species (Embley et al, 2006), while other volcanoes in the arc foster communities that differ from site to site due to dominant fluid and substratum characteristics Stevens et al, 2015).…”