2008 Annual Science Report
University of Hawaii, Manoa Reporting | JUL 2007 – JUN 2008
Chemistry and Biology of Ultramafic-Hosted Alkaline Springs
Ultramafic rock makes up Earth’s mantle and is an abundant material in the inner solar system. When water is added it converts to serpentinite, producing in the process H2 and, when CO2 is present, methane, both of which are ideal fuels for microbial activity. We are studying serpentinite mud volcanoes in the Mariana forearc, where water ascends from the subducting Pacific plate into the overlying mantle, producing large volumes of serpentinite that exhibits unusual fluid chemistry (e.g., pH 12.6) and extremophilic microbial activity, as an analog to extraterrestrial environments such as on Mars and the asteroids.
We have determined that these methane-rich waters, which are the highest pH waters ever found on Earth, support abundant Archaea that anaerobically oxidize methane (AOM) to carbonate while reducing sulfate, all at an in-situ pH of 13.1. Such a high pH cannot be generated by serpentinization alone. In collaboration with Dr. Tom McCollom of the Unversity of Colorado NAI, and with additional funding from NSF, we are modeling the processes that generate this extreme environment, including 1) dehydration and dissolution of subducted organic and inorganic carbon from the subducting oceanic plate with increasing temperature and pressure; 2) ascent of this water and dissolved carbon and its input into the ultramafic rock of the overriding plate; 3) serpentinization of this rock and accompanying generation of H2; 4) reaction of H2 with carbon to make methane that ultimately fuels extremophilic (high pH) microbial communities in the shallow subseafloor. This methane is abiogenic, so this process may be analogous to what may be happening on Mars.