In search of the biosphere underneath the Lost City hydrothermal vent field using in-situ sulphur and multiple sulphur isotope signatures

• Applicant: Professorin Dr. Esther Schwarzenbach
• Subject Area: Palaeontology ; Mineralogy, Petrology and Geochemistry
• Term: from 2016 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 320104891

The proposed project plans to use petrography, in-situ sulphur and bulk rock multiple sulphur isotope signatures as tools to identify microbial activity in ultramafic rocks of the Atlantis Massif and to give further insights into the hydrothermal history of this peridotite-hosted hydrothermal system. The Atlantis Massif is an oceanic core complex made up of ultramafic and mafic lithologies. It hosts the Lost City hydrothermal field, which vents high-pH, H2-rich, low-temperature fluids from carbonate-brucite chimneys. These fluids support a unique microbial community within and in the vicinity of the carbonate chimneys. However, the extent of biological activity within the ultramafic subsurface is not well constrained. The recent IODP Expedition 357 to the Atlantis Massif recovered ultramafic and mafic lithologies from the shallow subsurface of the vicinity of the Lost City hydrothermal field using shallow drilling techniques. These samples provide an exceptional opportunity to study the processes that take place within the ultramafic subsurface. In the proposed study bulk rock multiple sulphur isotopes (32S, 33S, 34S, 36S) and in-situ sulphur isotope signatures of individual sulphide grains will be used to identify processes of past microbial activity, such as microbial sulphate reduction, and to measure various abiogenic processes associated with serpentinization. The sulphur isotope data will be combined with mineralogical observations performed in the proposed study (e.g. sulphide mineral assemblages) as well as data collected from other members of the science party of Exp. 357 that provide insight into the fluid chemistry preserved within carbonate and serpentine veins. This will provide better constraints on the extent of microbial activity within the ultramafic rocks and may provide new insights into the conditions that favour microbial activity in the subsurface biosphere.

• DFG Programme: Infrastructure Priority Programmes
• Subproject of: SPP 527: Bereich Infrastruktur - "International Ocean Discovery Program" (IODP)
• International Connection: USA
• Cooperation Partners: Professor Dr. Timm John; Professor Dr. David Johnston; Privatdozent Dr. Ralf Milke; Dr. Alexander Rocholl; Dr. Uwe Wiechert; Professor Dr. Michael Wiedenbeck