Collaborative Research: RAPID: Time-sensitive opportunity to access 1.2 billion-year-old brines to quantify microbial hydrogen cycling in the deep subsurface

When water reacts with many rocks deep in Earth’s subsurface, hydrogen can be produced, providing fuel for microorganisms that utilize this deep-rooted geological hydrogen as an energy source. While geological hydrogen has been proposed as a transformative source of energy for human use, the chemical and biological reactions that produce and consume hydrogen in the subsurface are poorly understood, largely due to difficulties in accessing these deep environments. This project will utilize a unique opportunity to sample from one of the deepest gold mines in the world to provide a unique window into deep geological hydrogen processes. This multidisciplinary study of a hydrogen-based ancient brine ecosystem links disciplines from geophysics to biology. This project directly benefits society by providing information relevant to the development of geological hydrogen as an energy source, as well as information on the limits and origin of life on Earth and for the exploration of life here and on other worlds. Deep gold mines in South Africa offer unparalleled access to deep, ancient brine where geological hydrogen is abundant. Production of hydrogen by rock-water interactions in these deep environments could be enhanced by frequent earthquake activity. This project will drill into a deep brine in the Moab Khotsong mine and collect rock and fluids to measure the production of hydrogen from rock-water interactions, and its subsequent consumption by microbes. The hydrogen-cycling microbes will be identified and characterized. Rates of hydrogen consumption will be assessed at multiple scales ranging from individual cells in fractures up to the entire biosphere to determine the extent to which microbes influence hydrogen availability. These data will be used to evaluate whether deep hydrogen is a major contributor to energy captured by microbes, whether subsurface microbial activity increases in response to hydrogen availability, and whether seismic activity triggers pulses of microbial activity by releasing abiotic hydrogen. The project will drill from a mine passage at ~3 km depth to reach a hydrogen-rich brine and recover hard rock and brine fluid for geologic, geochemical, and microbiological analyses. The combined data of seismic activity, chemistry, and continuously sampled microbial community and activity data will be integrated to provide a comprehensive view of hydrogen cycling in the subsurface. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.