Abstract
We present noble gas concentrations determined in pore water of deep-sea sediments close to a recently discovered hydrothermal vent site, consisting of a mound structure and several black smokers, located in the northern Guaymas Basin, Gulf of California. Noble gases were used as tracers to identify the origin of fluids within the sediment pore space and to gain insight into transport dynamics of hydrothermal fluids in this region. Our data suggest that Guaymas Basin bottom water is the only source of pore water in the pelagic sediment body close to the hydrothermal vent field. In particular, there is no evidence of any direct (diffusive or advective) transport of hydrothermal fluids through the deep-sea sediments surrounding the black smoker system. This finding implies that at this black smoker site hydrothermal fluids are transported upwards from the fluid source in very narrow pathways below the smokers. Thus, the fluids are only injected into the ocean directly through the chimneys of the black smokers and no additional emission from the surrounding sediment takes place. Helium isotope data show that during a more active phase of the vent field in the past (supposedly representing the early onset of the black smokers 5–6 kyrs ago), bottom water with a different isotopic signature was incorporated into the sediment column.
Highlights
First evidence for hydrothermal venting along ocean ridges and ocean floor spreading centers was found in the 1970s (e.g. Talwani et al, 1971; Corliss et al, 1979)
We present noble gas concentrations determined in pore water of deep-sea sediments close to a recently discovered hydrothermal vent site, consisting of a mound structure and several black smokers, located in the northern Guaymas Basin, Gulf of California
We present noble gas (NG) data from pore fluids of a sediment core taken close to a hydrothermal vent site in the Northern Trough of the Guaymas Basin, Gulf of California, to identify the geochemical origin of hydrothermal fluids in pelagic sediments and identify transport mechanisms
Summary
First evidence for hydrothermal venting along ocean ridges and ocean floor spreading centers was found in the 1970s (e.g. Talwani et al, 1971; Corliss et al, 1979). While minerals precipitate in the pore space of the chimney walls, they become less permeable with time, until fluids are solely ejected at the top (Tivey, 2007) According to this model, black smoker chimneys can be regarded as impermeable barriers against lateral fluid transport. The model only explains what happens directly at the sediment surface at the site of a chimney It does not explain how fluid transport between the hydrothermal source (at several hundred meters depth) and the sediment surface takes place at a vent site, i.e. whether hydrothermal fluids rise up only along narrow vertical pathways through the pelagic sediment body below the chimney structures, or whether there might be a part of the fluids which is transported upwards along more widespread (lateral) pathways from the source to the sediment surface. The active hydrothermal vent field consisting of black smoker chimneys on a mound structure was recently discovered by Berndt et al (2016) during an expedition in the Guaymas Basin (see cruise report RV SO241: Berndt et al, 2015)
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