Sulfate reduction in the presence of low oxygen levels in the water column of the Cariaco Trench1,2

Precise and closely spaced alkalinity and total inorganic carbon measurements from the water column of the Cariaco Trench indicate an intense zone of sulfate reduction within the oxic waters above the O 2 ‐H 2 S interface. The chemical data suggest that sulfate reduction occurs in the presence of low oxygen levels. The resulting sulfide is subsequently oxidized to S 0 . Although it is not clear whether or how these processes are coupled, the kinetics of redox reactions above the oxic‐anoxic interface modify the chemical distributions expected from the normal constraints of chemical equilibrium.