Normalized affinities for sulfate reduction and methanogenesis in the Tube Worm Pillar area. Affinities are high in the hypothetical fluids calculated from conservative mixing of seawater and hydrothermal fluid. In the measured fluids the affinity is strongly decreased. Notably, affinities drop markedly in the first three years, which reflects the decrease in H2 concentration in that time span (Figure 4). The removal of H2 and the lowering of affinity reflect the exploitation of H2 in fueling catabolic activity. During the last five years of the time series, normalized affinities had plateaued, possibly indicating a steady-state between hydrothermal energy supply and microbial utilization of energy.