Electrical current generation across a black smoker chimney.

In environments isolated from solar radiation, diverse microbial populations and ecosystems are sustained by the chemical energy supplied from Earth!s interior. The most outstanding example is a deep-sea hydrothermal vent, which discharges enormous amounts of reductive energy in the form of reduced sulfur compounds, H2, CH4, and reduced metals during magma degassing and hydrothermal reactions with hot rocks. 3] Hydrothermal vent chimneys are generated by mineralization in the mixing zone between hot, reduced hydrothermal fluid and cold, oxygenated seawater and provide an ideal habitat for chemolithotrophic microbial communities. As the chimney structures serve as an interface between the Earth!s reductive interior and oxidative exterior, sustained microbial redox metabolism is very feasible. Simultaneously, the energy potential mediated by the chimney structure leads to many hypotheses concerning chemical evolution in the prebiotic ocean and the early evolution of energy metabolisms and cellular functions in the ancient Earth. Black smokers are a type of hydrothermal vent with sulfide-rich emissions that precipitate to form sulfide mineral chimneys consisting mainly of chalcopyrite (CuFeS2) and pyrite (FeS2). The mineralogical and structural characteristics of black smoker chimneys have been extensively studied; however, electrical conduction and electrocatalysis of black smoker chimneys have never been examined. Although bulk crystals of CuFeS2 and FeS2 are typically considered poor conductors, it is predicted that a chimney structure composed of nanoand microsized crystalline particles would have quite a large surface area with the potential of mediating the efficient electron transport. Herein we therefore examine the electrochemical characteristics of the black smoker chimney and seek to estimate the redox potential between the hydrothermal fluid conduit and ambient seawater across the chimney wall. For the analysis, a black smoker sulfide chimney obtained from the Mariner hydrothermal field in the southern Lau Basin was characterized (Figure 1). The observed electrical conduction potential points to a possible new type of energy transport from hydrothermal fluid to seawater by electrical current generation in the sulfide chimney wall.