Characterizing unexplored microbial habitats in oceanic crust along the South Atlantic Transect, IODP Exp. 390/393

• Applicant: Dr. Florence Schubotz
• Subject Area: Geology ; Mineralogy, Petrology and Geochemistry
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 527823540

This proposal seeks funding to work on samples recovered during IODP Exp. 390/393 "South Atlantic Transect" (SAT), during which a transect from ~7 to 61 Ma old basaltic crust was drilled at the western ridge flank of the slow-spreading southern Mid-Atlantic Ridge. The primary goals of SAT were to further our understanding of ridge flank hydrothermal fluid–rock reactions and concomitant distributions and environmental controls of microbial life within the oceanic crust. This project will directly address these topics by using an interdisciplinary approach combining organic geochemical with petrological investigations to examine a previously unexplored crustal microbial habitat within the ocean crust. The proposed work will focus on sedimentary breccias that were recovered at all except the youngest sites with exceptional recovery at 61 Ma old Site U1557. Similar breccias occur worldwide in a variety of oceanic geotectonic settings. We therefore postulate that breccias constitute an important, but so far overlooked component of the crustal deep biosphere. The highly permeable rocks provide ample paths for fluid flow and hence for fluid-rock reactions, which in turn provides biofuels and hence fosters microbial life. In a first step we plan to combine lipid biomarker investigations of the recovered breccias with determining the extent and style of rock alteration. In a second step, the oxidation state of the crustal rocks will allow the estimation of bioavailable energy for microbial biomass production, which we will then relate to the actual distribution of lipid biomass. Detailed structural characterization of lipids will allow the assessment of how the diversity of microbial communities is affected by the increasing substrate age and will identify physiologic adaptations to the respective habitats. Compound specific stable carbon isotopes will be used to determine potential microbial metabolism shifts from chemolithoautotrophic to heterotrophic lifestyles, the latter of which may prevail in older, more oxidized and hence less energy-yielding rocks. Finally, hot spots of microbial life will be visualized and put into spatial relation with the host mineral matrix of the breccias on a micrometer scale by making use of state-of-the-art mass spectrometry imaging combined with micro-XRF. This project thus promises to provide exciting new insights into current knowledge gaps of deep crustal biosphere research and by tapping into the unexplored crustal habitat of brecciated seafloor, will help refine estimates of the deep biosphere and significantly advance our understanding of Earth’s presumed largest microbiome.

• DFG Programme: Infrastructure Priority Programmes
• Subproject of: SPP 527: Bereich Infrastruktur - "International Ocean Discovery Program" (IODP)
• International Connection: USA
• Co-Investigator: Professor Dr. Wolfgang Bach
• Cooperation Partners: Dr. Elmar Albers; Professor Dr. William Leavitt; Dr. Beth Orcutt; Professor Dr. Jason Sylvan