Based on mass balance calculations, the input of organic carbon into the ocean’s interior isnot sufficient to meet the organic carbon demand of the heterotrophic microbial communityin the deep ocean. The apparent mismatch between the organic carbon supply andconsumption reported for the Atlantic as well as for the Pacific needs to be resolved as itindicates that we have a significant gap in our knowledge of the deep ocean. One major, thusfar largely unrecognized, source of organic carbon in the deep ocean is the presence ofneutrally buoyant marine snow-type particles, which escape quantification using sedimenttraps.
These buoyant marine snow particles are heavily colonized by microbes includingfungi. Another potential source of error is assuming that changes in the hydrostatic pressuredoes not affect microbial activity measurements as almost all metabolic rate measurementson deep-sea microbes are made under surface pressure conditions. In this presentation, I willhighlight recent advances made in understanding microbial carbon production andconsumption in the ocean’s interior with specific emphasis on particle-associated microbialactivity in the deep ocean.