Seawater passing through hot oceanic crust initiates a series of reactions that play a significant role in controlling the concentrations and distributions of major ions and trace metals in the ocean. The chemistry of these hydrothermal fluids depends on multiple variables including rock type, temperature, degree of prior rock alteration, convective path length, the effective water/rock ratio, and flow rate (Kadko, 1996;Von Damm et al., 1985). The vast majority of identified marine hydrothermal systems are hosted in mafic rocks (basalt and gabbro), resulting in acidic fluids that are rich in metals. In contrast, fluids that pass through ultramafic rocks (peridotite, including harzburgite and dunite) trigger a water-rock reaction called serpentinization that converts peridotite to serpentinite (a rock composed of one or more serpentine group minerals) and releases free hydrogen (H 2 ) to high pH fluids. High concentrations of H 2 coupled with appropriate catalysts, can lead to the nonbiological synthesis of organic molecules including methane, formate, and short-chain hydrocarbons (