1114 / 2024-09-20 13:23:45

The ocean’s interior and its role in the carbon cycling

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

Keynote Session

The ocean’s interior is full of life and depends almost exclusively on the organic matter produced in the sunlit surface ocean confined to the top 150 m layer. Hence all the life in the deep ocean depends on the flux of organic matter derived from the surface waters. At the same time, the deep ocean harbors about 670 Pg organic carbon, its vast majority recalcitrant and in the form of dissolved organic carbon (DOC). Consequently, considerable research efforts have been put into quantifying the transport of particulate organic matter (POM) from the surface waters into the ocean’s interior, a mechanism coined “biological carbon pump”. Another mechanism describing the transformation of labile DOM into recalcitrant DOM by sequential uptake and release of DOM by heterotrophic microbes has been described as the “microbial carbon pump” explaining the apparent age of the deep-sea DOM of about 5000 years.

Attempts to balance the organic carbon flux into the ocean’s interior with the organic carbon demand of the deep-sea heterotrophic microorganisms, the main remineralizers in the deep sea, failed, indicating that the presumed demand of organic matter in the deep ocean is higher than its supply. In this presentation, several aspects and enigmas of the biota and biogeochemistry of the ocean’s interior will be discussed covering the presence of non-sinking organic matter, deep-sea autotrophic activity, heterotrophic microbial activity under high hydrostatic pressure and the composition of dissolved organic matter in the deep sea. Taken all these aspects together, a revised view of the deep-sea biogeochemistry and the microbes inhabiting the deep sea emerges with implications for the discussion on impact of human interventions in the deep sea.