An interdisciplinary approach to sampling hard rock cores of the oceanic crust for microbiological and biogeochemical research

Studying life in the deep, rocky subseafloor involves many layers of technological and methodological challenges, and each drilling project or expedition must make a series of choices to address these challenges. We report on the workflow for sampling hard rock cores for microbiological and biogeochemical research that was developed and optimized during International Ocean Discovery Program (IODP) Expedition 399. All steps of the workflow, including selection of the sample and its shipboard homogenization and subsampling for specific analyses, were designed to maximize the potential for interdisciplinary collaborations and syntheses of results. Furthermore, multiple strategies to minimize and detect potential microbial and organic chemical contamination of the core samples were employed, including the shipboard detection of a fluorescent chemical tracer pumped into the drill fluid. Contamination tracer levels were detectable on the exterior surfaces of the core but absent in the homogenized interiors of most core samples. Based on the experiences and preliminary results of this expedition, recommendations for processing samples on future expeditions are presented.