Normalized affinities for the oxidation of Fe2+ and H
S in diffuse fluids from the Bio9 area during the period from April 1991 until November 1997. The generally high affinities for iron and hydrogen sulfide oxidation support life catabolizing these reactions. In October of 1994, affinities for both reactions are high, so that tubeworms (H2S-oxidizers) and iron oxidizing microorganism (rusty staining) can grow simultaneously. The demise of the Riftia population in November of 1997 coincides with a sudden drop in the affinity of H2S oxidation.