Jule Melina Sophie Krohn

Oceanic crust at mid-ocean ridge flanks is believed to harbour diverse microbial communities, supported by circulating seawater and seawater-rock reactions providing nutrients and metabolic energy. My project aims to explore basalt breccias for energy production and its microbial consumption using drill cores recovered at several sites during IODP Exp. 390/393 – South Atlantic Transect.

The breccias are composed of basalt clasts, a matrix of indurated sediment, cemented by carbonate and/or zeolite. They formed as talus deposits of on-axis faults at the southern Mid-Atlantic Ridge, and are thus representative of the widespread phenomenon of talus formation at mid-ocean ridges and seamounts. Despite their frequent occurrence, however, talus breccias have not been target of systematic petrologic and microbial investigation.

We expect the breccias to be an important microbial habitat with conditions conducive for deep life. Their high porosity likely supports continued seawater circulation even far-off axis, causing continued fluid-rock interactions which provides the basis for chemosynthetic life, generating biomass that sustains downstream chemoheterotrophic microorganisms.

I will apply organic and inorganic geochemical and petrological approaches to characterize microbial communities and the habitat of this so-far underexplored microniche. Making use of sensitive lipid biomarker detection techniques, we aim at investigating past and present bacterial and archaeal biomarkers and screening for fungal representatives in the deep biosphere. Analysing rocks of different ages, compositions, and alteration stages, we will link shifts in microbial communities to habitat changes, which will provide insight into relationships between host rock and microbial activity.