Dark inorganic carbon (DIC) fixation represents a globally significant yet routinely overlooked component of ocean primary production, capable of increasing total marine PP estimates by up to 22% when accounted for. Beyond its quantitative contribution, dark DIC fixation sustains heterotrophic microbial metabolism in the deep ocean and influences carbon sequestration pathways distinct from the classical biological pump. However, the energy sources that fuel this process in the dark ocean remain poorly understood. In this talk, I will present novel research identifying unexpected electron donors and metabolic strategies that underpin dark DIC fixation across the ocean water column. Using integrated multi-omic and biogeochemical approaches, our findings challenge prevailing paradigms of deep-ocean energy limitation and provide a revised framework for understanding dark DIC fixation as a central pillar of marine carbon cycling.
