Mantle helium in pore fluids of deep-sea sediments around the Azores archipelago

We present noble gas concentrations and helium isotope ratios measured in the pore fluids of two deep-sea sediment cores taken at the Azores Plateau. NeXe concentrations were used to estimate the atmospheric noble gas component within the pore fluids and to then determine the terrigenic helium component. The concentrations of terrigenic 3He indicate the presence of hydrothermal fluids and a mantle He component within the sediment pore space. At both sampling locations, the concentration of terrigenic helium increases with sediment depth. The observed concentration gradients suggest a diffusive transport of He through the sediments. The helium isotope ratio of the source of the terrigenic helium is characterized by a typical mid-ocean ridge basalt (MORB). These results support previous studies suggesting that the pelagic sediments surrounding the Azores host active hydrothermal systems.