text: The degradation of organic matter through respiration in the modern ocean is facilitated by different electron acceptors, their favorability based on Gibbs free energy law, and the laws of thermodynamics.  This redox chemistry is the basis for life in deep sea sediments and determines the obtainability of energy to organisms that live there.  From the water interface moving toward deeper sediments, the order of these acceptors is oxygen, nitrate, manganese, iron, and sulfate.  The zonation of these favored acceptors can be seen in Figure 1.  Moving downwards from the surface through the zonation of these deep ocean sediments, acceptors are used and depleted.  Once depleted the next acceptor of lower favorability takes its place.  Thermodynamically, oxygen represents the most favorable electron accepted but is quickly used up in the water sediment interface and  concentrations extends only millimeters to centimeters down into the sediment in most locations of the deep sea.  This favorability indicates an organism's ability to obtain higher energy from the reaction which helps them compete with other organisms.  In the absence of these acceptors, organic matter can also be degraded through methanogenesis, but the net oxidation of this organic matter is not fully represented by this process. Each pathway and the stoichiometry of its reaction are listed in table 1.
  Due to this quick depletion of  in the surface sediments, a majority of microbes use anaerobic pathways to metabolize other oxides such as manganese, iron, and sulfate.  It is also important to figure in bioturbation and the constant mixing of this material which can change the relative importance of each respiration pathway.  For the microbial perspective please reference the electron transport chain.