IODP Expedition 357

Serpentinization is a fundamental process that controls rheology and geophysical properties of the oceanic lithosphere and has major consequences for heat flux, geochemical cycles and microbial activity in a wide variety of environments. However, we currently have no constraints on the nature and distribution of microbial communities in ultramafic subsurface environments, which are characterised by high hydrogen and methane concentrations but little available CO₂. A major goal of the Atlantis Massif Serpentinization and Life expedition is to better understand the role of serpentinization in driving hydrothermal systems, in sustaining microbiological communities, and in the sequestration of carbon in ultramafic rock. The offshore phase of this MSP expedition will use seabed rock drill technology (MeBo and BGS Rockdrill 2) to core a series of shallow (50-80 mbsf) holes along two profiles across the Atlantis Massif, where detachment faulting exposes both mafic and ultramafic lithologies on the seafloor. A spreading-parallel, E-W profile will target the serpentinite basement to explore the extent and activity of the subsurface biosphere and assess how abiotic and biotic processes change with aging of the lithosphere and with variations in rock type. A ridge-parallel, N-S profile into the gabbroic center of the massif will assess the role of differing rheologies in localising detachment faults and will examine how faulting and lithospheric heterogeneities influence hydrothermal alteration and the nature of the deep biosphere.

Expedition 357 Proceedings