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Project Progress

Our overarching goals are to understand as much as possible about the geochemistry and microbiology of serpentinizing systems using easily accessible samples from the surface, and to make predictions that will guide subsurface exploration. Progress on this project during 2015 included new thermodynamic calculations of bioavailable energy, new reaction-path calculations that characterize the extent of alteration progress, new models of reactions between organic and inorganic forms of carbon, efforts to link geochemical and sequencing data, and preliminary results on lipids from samples taken from 2014 (i.e., before the RPL project began).

Assessing bioavailable energy from geochemical data is ultimately a search for oxidation-reduction reactions that are far from equilibrium. In serpentinizing systems, these disequilibria mainly involve reduced chemical species such as H₂, CH₄, CO, NH₃, HS^-Serpentinization, Bioenergetics, Thermodynamics, Phylogenetics, Geochemistry, Geobiochemistry, and organic solutes like acetate and formate, and oxidized species such as O₂, SO₄^-2, NO₃^-, NO₂^-, and CO₃^-2. Myriad reactions are out of equilibrium in the hyperalkaline springs of the Samail ophiolite in Oman. In a survey completed by Peter Canovas, the greatest energy supplies at the surface are shown to include hydrogen and methane oxidation, and the most feeble include sulfate reduction and methanogenesis. However, predicted conditions in the subsurface diverge as oxygen disappears and hydrogen production from water-rock reactions enables methanogenesis. Kirt Robinson, who has measured concentrations of acetate and formate in the same springs, has evaluated the energy supplies for reactions involving these organic solutes, together with reactions involving methane, ethane, and propane. These results serve to broaden our view of the complexity of the carbon cycle and energy supplies in the subsurface.

Geochemical data from hyperalkaline springs collected during fieldwork in previous years were used by James Leong to characterize how the water-rock reactions progressed to yield the inorganic composition of the springs. In the process he determined that earlier field measurements of dissolved silica were unreliable and new methods were developed for this important, but dilute, solute. James will compare his results for alteration in Oman with alteration in seafloor systems using samples taken during the recent (Nov 2015-Jan 2016) IODP expedition to the Southwest Indian Ridge. As in Oman, abundant altered gabbros were sampled on the IODP expedition, leading to new insights into the serpentinization of these rocks that are derived from the mantle by igneous processes. James will continue these studies in spring and summer 2016 in Lyon working with Muriel Andriani. Meanwhile, Peter Canovas completed general theoretical models of serpentinization across the olivine-clinopyroxene-othopyroxene ternary space as functions of temperature, depth, and water-rock ratio. These results provide a general thermodynamic framework for alteration that will be encountered during drilling in Oman.

The carbon cycle during serpentinization is an extremely active area of research, and our combined organic and inorganic sampling of hyperalkaline fluids allows novel contributions. Kirt Robinson is focusing on redox reactions that link organic acids and carbonate minerals, and predicting how the relative abundances of organic acids vary with extent of serpentinization reactions. He finds that the various organic acids my be in redox equilibrium with different carbonate minerals (magnesite, dolomite, calcite) depending on the depth of fluid circulation. These theoretical results are providing an additional set of predictions for what will be encountered in the subsurface.

At the same time, progress is being made on combining microbiological and geochemical datasets from hyperalkaline springs. in 2015, Amisha Poret-Peterson and Alta Howells expanded the number and diversity of serpentinized sample locations from which we have sequencing data using samples from our 2014 (pre-RPL) expedition. Grayson Boyer is assisting Alta with the statistical analysis of combined geochemical and molecular data from hyperalkaline ecosystems in Oman, and together they are conducting a comprehensive effort to extract the most influential parameters, which will permit predictions for subsurface microbial communities. Grayson has also extracted lipids from some Oman sediment samples that he will contrast with his library of lipid data from Yellowstone hot springs.