Fig. 3.

Schematic representation of key processes that occur when ascending high-temperature source fluids mix with seawater (A) under relatively higher temperature (∼149 °C) (B) and lower temperature (<122 °C) conditions (C). At temperatures of ∼149 °C and higher, mixed fluid chemistry is impacted by abiotic reactions involving the aqueous reduction of dissolved species and mineral precipitation, along with thermogenic reactions involving the pyrolysis of living or previously living organic matter. At temperatures at and below 122 °C, microbial metabolic processes may occur in addition to abiotic and thermogenic processes. The metabolic processes could include hydrogenotrophic SO₄²⁻ reduction, anaerobic methanogenesis from CO₂ and H₂, methanotrophy by O₂, sulfide oxidation by O₂, and hydrogen oxidation by O₂.