The ocean’s interior is full of life depending almost exclusively on the organic matter produced in the sunlit surface ocean confined to the top 150 m layer. Attempts to balance the organic carbon flux into the ocean’s interior with the organic carbon demand of the main remineralizers in the deep sea, the deep-sea heterotrophic microorganisms, failed. This indicates that the apparent demand of organic matter in the deep ocean is higher than its supply. To resolve this discrepancy between the apparent supply and demand of organic matter for the deep-sea microbiota measurements under in situ hydrostatic pressure needs to be performed. In this presentation, several aspects and enigmas of the microbiota of the ocean’s interior will be discussed covering the presence of non-sinking organic matter, deep-sea autotrophic and heterotrophic microbial activity under high hydrostatic pressure. Taken all these aspects together, a revised view of the deep-sea microbial community and their activity emerges with implications for the discussion on the impact of human interventions in the deep sea.

microbes, free-living and marine snow-attached microbes, organic carbon, remineralization