THE MICROBIAL TURNOVER OF CARBON IN THE DEEP-SEA ENVIRONMENT

The microbial turnover of inorganic and organic carbon in the deep-sea is limited by input of the source of energy, low temperatures and high hydrostatic pressures, in that order of effectiveness. In reference to surface water conditions, these limitations are partly compensated by special adaptations: oligotrophy, psychrophily and barophily. The pool of total organic carbon is largely consisting of unknown recalcitrant compounds, but also contains low molecular substrates readily available to microbial metabolism but below the threshold concentrations for effective uptake. The growth limiting input of photosynthetically produced organic carbon does not apply at certain areas of tectonic spreading activity where the availability of inorganic reduced substrates function as the source of energy for the microbial reduction of inorganic to organic carbon (chemosynthesis) in the presence of free oxygen. Estimated for the deep-sea environment, this chemosynthetic production of of organic carbon compares to 10% of the photosynthetic input.