Noble gases in sediment pore water yield insights into hydrothermal fluid transport in the northern Guaymas Basin

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.