Chemosynthesis

Many microorganisms in dark regions of the oceans also use chemosynthesis to produce biomass from single carbon molecules. Two categories can be distinguished. In the rare sites at which hydrogen molecules (H₂) are available, the energy available from the reaction between CO₂ and H₂ (leading to production of methane, CH₄) can be large enough to drive the production of biomass. Alternatively, in most oceanic environments, energy for chemosynthesis derives from reactions in which substances such as hydrogen sulfide are oxidized. This may occur with or without the presence of oxygen.