Fig 5.

Countergradients of oxygen and sulfide at the sediment-water interface, measured using microelectrodes. Respiration in the sediments depletes oxygen, which in the absence of turbulence exhibits a linear concentration profile from the oxygenated, circulating water above to the anoxic conditions near the interface. The region of transition is the diffusion boundary layer, here ∼500 μm thick. Simultaneously, sulfide diffuses upwards and is respired near the interface, also leading to a linear concentration profile. Shown here is also the location of a mat of the bacteria Beggiatoa, which use gliding motility to adjust their position at the oxygen-sulfide interface. (Reproduced from reference 86 with permission.)