Thorsten Bauersachs

The ocean floor comprises a spatially extensive habitat for microbial life-forms and a highly diverse associated macrofauna. Areas where the ocean floor is covered by sediments have been the subject of investigations of biotic activity but vast regions barren of sedimentary cover, in particular those formed by accretionary structures at Mid-Ocean Ridges (Ridge Flanks, Abyssal Hills, Fracture Zones) where oceanic crust and mantle rocks are exposed, are virtually unexplored. Minerals of oceanic crust and mantle are metastable at seafloor conditions and undergo chemical and lithological alteration (e.g. serpentinization), often mediated by fluids of variable temperature and chemistry circulating through hard-rocks and producing reactants such as reduced gases (H2, CH4) suitable to sustain chemoautotrophy. Aging oceanic crust and exhumed mantle thus serve as probably the largest bioreactor on Earth and as a suitable habitat for microbes. This project aims at a better understanding of microbial community structures, substrate acquisition processes and metabolic reactions in submarine hard-rocks by parallel application of microbiology molecular genetics and molecular lipid geochemistry techniques. The complementary dual applications of these techniques to deep-water hard-rocks are not yet established as routine approaches. Thus, substantial methodical development will be required to artefact-free prepare large volume samples for subsequent sophisticated molecular genetics and lipid analysis. Samples suitable for such method development are difficult to acquire but excellent study material is available to us via large and fresh hard-rock samples dredged during the Sonne cruise (So-237- VEMA Transit) in the vicinity of the Vema transform fault zone (Devey et al., 2015). This region forms the target zone for the planned TRANSREGIO “Maturing oceanic plates: Earth´s hidden reactors” to which this project serves as a feasibility study.