Thermophilic and hyperthermophilic Archaea and Bacteria have been isolated from marine hydrothermal systems, heated sediments, continental solfataras, hot springs, water heaters, and industrial waste. They catalyze a tremendous array of widely varying metabolic processes. As determined in the laboratory, electron donors in thermophilic and hyperthermophilic microbial redox reactions include H2, Fe(2+), H2S, S, S2O3(2-), S4O6(2-), sulfide minerals, CH4, various mono-, di-, and hydroxy-carboxylic acids, alcohols, amino acids, and complex organic substrates; electron acceptors include O2, Fe(3+), CO2, CO, NO3(-), NO2(-), NO, N2O, SO4(2-), SO3(2-), S2O3(2-), and S. Although many assimilatory and dissimilatory metabolic reactions have been identified for these groups of microorganisms, little attention has been paid to the energetics of these reactions. In this review, standard molal Gibbs free energies (DeltaGr(0)) as a function of temperature to 200 degrees C are tabulated for 370 organic and inorganic redox, disproportionation, dissociation, hydrolysis, and solubility reactions directly or indirectly involved in microbial metabolism. To calculate values of DeltaGr(0) for these and countless other reactions, the apparent standard molal Gibbs free energies of formation (DeltaG(0)) at temperatures to 200 degrees C are given for 307 solids, liquids, gases, and aqueous solutes. It is shown that values of DeltaGr(0) for many microbially mediated reactions are highly temperature dependent, and that adopting values determined at 25 degrees C for systems at elevated temperatures introduces significant and unnecessary errors. The metabolic processes considered here involve compounds that belong to the following chemical systems: H-O, H-O-N, H-O-S, H-O-N-S, H-O-C(inorganic), H-O-C, H-O-N-C, H-O-S-C, H-O-N-S-C(amino acids), H-O-S-C-metals/minerals, and H-O-P. For four metabolic reactions of particular interest in thermophily and hyperthermophily (knallgas reaction, anaerobic sulfur and nitrate reduction, and autotrophic methanogenesis), values of the overall Gibbs free energy (DeltaGr) as a function of temperature are calculated for a wide range of chemical compositions likely to be present in near-surface and deep hydrothermal and geothermal systems.

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SummaryThis workshop report describes plans for scientific drilling in the Samail ophiolite in Oman in the context of past, current, and future research. Long-standing plans to study formation and evolution of the Samail crust and upper mantle, involving igneous and metamorphic processes at an oceanic spreading center, have been augmented by recent interest in ongoing, low temperature processes. These include alteration and weathering, and the associated sub-surface biosphere supported by chemical potential energy due to disequilibrium between mantle peridotite and water near the surface. This interest is motivated in part by the possibility of geological carbon capture and storage via engineered, accelerated mineral carbonation in Oman. Our International Continental Drilling Program (ICDP)proposal led to the Workshop on Scientific Drilling in the Samail Ophiolite in Palisades, New York, on 13-17 September 2012. There were seventy-seven attendees from eleven countries, including twenty early career scientists.After keynote presentations on overarching science themes, participants in working groups and plenary sessions outlined a ~U.S.$2 million drilling plan that practically addresses testable hypotheses and areas of frontier discovery in the following areas.• understanding the subsurface biosphere • characterizing the rates and mechanisms of ongoing mineral hydration and carbonation • characterizing chemical and physical processes of mass transfer across a subduction zone • evaluating well-posed hypotheses on hydrothermal circulation, cooling, and emplacement mechanisms of igneous rocks in the lower crust • investigating key problems in the dynamics of mantle flow and melt transport beneath oceanic spreading ridgesThis report places these goals in the context of complementary research via ocean drilling and ongoing studies of active processes at oceanic spreading centers, subduction zones, and peridotite-hosted hydrothermal systems. We end with an outline of the synergy between Oman drilling and the specific drilling proposed in the Integrated Ocean Drilling Program (IODP) proposal "Mohole to Mantle Project (M2M)", IODP Proposal 805-MDP. Workshop Proceedings and ResultsKeynote speakers outlined hypotheses and areas of frontier scientific exploration to be addressed via drilling, including• the nature of mantle upwelling, • the chemical and physical mechanisms of mantle melt transport, • the processes of lower crustal accretion and cooling, • the frequency and magnitude of microseismicity during weathering, • the rate and location of ongoing alteration, and • the composition, density, and spatial distribution of subsurface microbial communities.Additional keynote talks covered state-of-the-art geological logging of drillcore, geophysical logging in boreholes, and data management.Breakout groups considered overarching science themes, then designed idealized projects to address these themes, and finally considered practical constraints. We agreed to focus on studies relevant to global processes. There was a consen...