Shedding light on the ocean's deep, dark biosphere

The subseafloor environment contains one third of all the microbial biomass on Earth with potential to influence important biogeochemical cycles over geological timescales. Research by microbiologists on subseafloor samples began in the 1950's, but the authenticity of this "deep biosphere" has been debated ever since due to concerns regarding contamination and the in situ activity of the microbes. However, significant progress through technical advances was made in the last decades, and numerous studies have confirmed the presence of an endemic and active subseafloor biosphere. The in situ microbial communities have extremely low activity relative to the surface world, and survive in the absence of sunlight either through chemolithoautotrophic processes or the recycling of ancient organic material. My presentation will introduce the methods used to study these processes, and focus on recent advances in the ecology of this deep biosphere. Specifically, I will discuss metatranscriptomic investigations of the transcriptional activity of subseafloor cells over million-year timescales in anaerobic marine sediment, as well as the combined geochemical and biomarker investigation of fossilized chemolithoautotrophic bacteria and archaea in an ancient serpentinization system. Planned projects and potential target areas for future work will also be discussed.