Biologic agents mediating matter-flow inside the porous igneous oceanic crust, Vesteris Seamount, Greenland Sea

Microorganisms within the lithosphere are biologic agents settling in niches inside the terrestrial and oceanic crust, populating the extreme environments of the deep biosphere. The fossil record of the permeable igneous oceanic crust, constructed out of primitive extrusive rock, opens a window into Earth’s early evolution and serves as an analogue for life in extraterrestrial worlds. In 2019, samples of highly porous basanites of Vesteris Seamount in the Greenland Sea were retrieved during a cruise of the research vessel Maria S Merian. Some of these samples exhibit an endolithic ecosystem relaying on complex interactions between the biosphere and lithosphere. In this study, we present novel x-ray microscopy data that reveal how microorganisms access and migrate through rock interiors. The microorganism-infested samples show dense networks of intergrown filaments and laminated secondary mineralization filling the pore space and following a system of micro fissures through the rock. Rock-dwelling microorganisms like bacteria or fungi are able to mediate ion mobility and therefore contribute to erosion or deposition in such a system. We document the sequence of mineralization and the extraordinary content of body fossils, consisting of a range of mineral phases, including iron oxide, clay and manganese oxide minerals. The minerals reveal growth patterns supporting both biotic and abiotic forces like the ion binding capacity of organic compounds or pH gradients to force precipitation.