From serpentinization to carbonation : new insights from a CO2 injection experiment

Author Posting. © The Author(s), 2013. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Earth and Planetary Science Letters 379 (2013): 137-145, doi:10.1016/j.epsl.2013.08.017.We injected a CO2-rich hydrous fluid of seawater chlorinity into an ongoing, mildly reducing (H2(aq) ≈ 3 mmol/kg) serpentinization experiment at 230°C and 35 MPa to examine the changes in fluid chemistry and mineralogy during mineral carbonation. The chemistry of 11 fluid samples was measured, speciated, and compared with MgO-SiO2-H2O-CO2 (MSHC) phase equilibria to approximate the reaction pathway from serpentinization to carbonation. Although the overall system was in apparent disequilibrium, the speciated activities of dissolved silica (aSiO2(aq)) and carbon dioxide (aCO2(aq)) evolved roughly along MSHC equilibrium phase boundaries, indicative of 4 distinct mineral assemblages over time: 1) serpentine22 brucite (± magnesite) before the injection, to 2) serpentine-talc-magnesite 2 hours after the injection, to 3) quartz-magnesite (48h after injection), and 4) metastable olivine – magnesite (623h after injection) until the experiment was terminated. Inspection of the solid reaction products revealed the presence of serpentine, magnesite, minor talc, and magnetite, in addition to relict olivine. Although quartz was saturated over a short segment of the experiment, it was not found in the solid reaction products. A marked and rapid change in fluid chemistry suggests that serpentinization ceased and precipitation of magnesite initiated immediately after the injection. A sharp decrease in pH after the injection promoted the dissolution of brucite and olivine, which liberated SiO2(aq) and dissolved Mg. Dissolved Mg was efficiently removed from the solution via magnesite precipitation, whereas the formation of talc was relatively sluggish. This process accounts for an increase in aSiO2(aq) to quartz saturation shortly after the injection of the CO2-rich fluid. Molecular dihydrogen (H2(aq)) was generated during serpentinization of olivine by oxidation of ferrous iron before the injection; however, no additional H2(aq) was generated after the injection. Speciation calculations suggest a strong affinity for the formation of methane (CH4(aq)) at the expense of CO2(aq) and H2(aq) after the injection, but increased CH4(aq) formation was not observed. These findings suggest that kinetically fast mineral carbonation dominates over sluggish CH4(aq) formation in mildly reducing serpentinization systems affected by injection of CO2-rich fluids.This work was supported by an Ocean Ridge Initiative Research Award at WHOI (to FK) and NSF Marine Geology and Geophysics award OCE-0927744 (TMM)

Remote sensing of the Martian surface

Researchers investigated the physical properties of the Martian surface as inferred from a combination of orbiting and earth-based remote sensing observations and in-situ observations. This approach provides the most detailed and self-consistent view of the global and regional nature of the surface. Results focus on the areas of modeling the diurnal variation of the surface temperature of Mars, incorporating the effects of atmospheric radiation, with implications for the interpretation of surface thermal inertia; modeling the thermal emission from particulate surfaces, with application to observations of the surfaces of the Earth, Moon, and Mars; modeling the reflectance spectrum of Mars in an effort to understand the role of particle size in the difference between the bright and dark regions; and determining the slope properties of different terrestrial surfaces and comparing them with planetary slopes derived from radar observations

Carbon isotope composition of organic compounds produced by abiotic synthesis under hydrothermal conditions

Author Posting. © Elsevier B.V., 2006. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Earth and Planetary Science Letters 243 (2006): 74-84, doi:10.1016/j.epsl.2006.01.027.Although it is widely believed that production of organic compounds by Fischer-Tropsch synthesis and related processes occurs in many geologic environments, unambiguous identification of compounds with an abiotic origin in natural samples has been hampered by a lack of means to discriminate between abiotic compounds and organic matter from biological sources. While isotopic compositions might provide a means to discriminate between biologic and non-biologic sources of organic matter, there are few data presently available to constrain the isotopic composition of compounds produced by abiotic processes in geologic systems. Here, we report results of laboratory experiments conducted to evaluate the isotopic composition of organic compounds synthesized abiotically under hydrothermal conditions. We find the organic products are depleted in 13C to a degree typically ascribed to biological processes, indicating that carbon isotopic composition may not be a particularly effective diagnostic means to differentiate between biologic and non-biologic sources. Furthermore, our results suggest that the isotopic compositions of reduced carbon compounds found in many ancient rocks that have heretofore been attributed to biological sources could be consistent with an abiotic origin in a hydrothermal setting.This research supported by the Earth Sciences Directorate of the US National Science Foundation (Grant # OCE-0241579)

Investigation of extractable organic compounds in deep-sea hydrothermal vent fluids along the Mid-Atlantic Ridge

Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 156 (2015): 122-144, doi:10.1016/j.gca.2015.02.022.The possibility that deep-sea hydrothermal vents may contain organic compounds produced by abiotic synthesis or by microbial communities living deep beneath the surface has led to numerous studies of the organic composition of vent fluids. Most of these studies have focused on methane and other light hydrocarbons, while the possible occurrence of more complex organic compounds in the fluids has remained largely unstudied. To address this issue, the presence of higher molecular weight organic compounds in deep-sea hydrothermal fluids was assessed at three sites along the Mid-Atlantic Ridge that span a range of temperatures (51 to >360 °C), fluid compositions, and host-rock lithologies (mafic to ultramafic). Sample were obtained at several sites within the Lucky Strike, Rainbow, and Lost City hydrothermal fields. Three methods were employed to extract organic compounds for analysis, including liquid:liquid extraction, cold trapping on the walls of a coil of titanium tubing, and pumping fluids through cartridges filled with solid phase extraction (SPE) sorbents. The only samples to consistently yield high amounts of extractable organic compounds were the warm (51-91 °C), highly alkaline fluids from Lost City, which contained elevated concentrations of C8, C10, and C12 n-alkanoic acids and, in some cases, trithiolane, hexadecanol, squalene, and cholesterol. Collectively, the C8-C12 acids can account for about 15% of the total dissolved organic carbon in the Lost City fluids. The even-carbon-number predominance of the alkanoic acids indicates a biological origin, but it is unclear whether these compounds are derived from microbial activity occurring within the hydrothermal chimney proximal to the site of fluid discharge or are transported from deeper within the system. Hydrothermal fluids from the Lucky Strike and Rainbow fields were characterized by an overall scarcity of extractable dissolved organic compounds. Trace amounts of aromatic hydrocarbons including phenanthrenes and benzothiophene were the only compounds that could be identified as indigenous components of these fluids. Although hydrocarbons and fatty acids were observed in some samples, those compounds were likely derived from particulate matter or biomass entrained during fluid collection. In addition, extracts of some fluid samples from the Rainbow field were found to contain an unresolved complex mixture (UCM) of organic compounds. This UCM shared some characteristics with organic matter extracted from bottom seawater, suggesting that the organic matter observed in these samples might represent seawater-derived compounds that had persisted, albeit with partial alteration, during circulation through the hydrothermal system. While there is considerable evidence that Rainbow and Lost City vent fluids contain methane and other light hydrocarbons produced through abiotic reduction of inorganic carbon, we found no evidence for more complex organic compounds with an abiotic origin in the same fluids.This research was supported by the NSF Ocean Sciences directorate through grants MGG-OCE 0550800 to T.M.M. and MGG-OCE 0549829 to J.S.S. and C.R.G

One-carbon (bio ?) Geochemistry in Subsurface Waters of the Serpentinizing Coast Range Ophiolite

Serpentinization - the aqueous alteration of ultramafic rocks - typically imparts a highly reducing and alkaline character to the reacting fluids. In turn, these can influence the speciation and potential for metabolism of one-carbon compounds in the system. We examined the aqueous geochemistry and assessed the biological potential of one-carbon compounds in the subsurface of the McLaughlin Natural Reserve (Coast Range Ophiolite, California, USA). Fluids from wells sunk at depths of 25-90 meters have pH values ranging from 9.7 to 11.5 and dissolved inorganic carbon (DIC concentrations) generally below 60 micromolar. Methane is present at concentrations up to 1.3 millimolar (approximately one-atmosphere saturation), and hydrogen concentrations are below 15 nanomolar, suggesting active consumption of H2 and production of CH4. However, methane production from CO2 is thermodynamically unfavorable under these conditions. Additionally, the speciation of DIC predominantly into carbonate at these high pH values creates a problem of carbon availability for any organisms that require CO2 (or bicarbonate) for catabolism or anabolism. A potential alternative is carbon monoxide, which is present in these waters at concentrations 2000-fold higher than equilibrium with atmospheric CO. CO is utilized in a variety of metabolisms, including methanogenesis, and bioavailability is not adversely affected by pH-dependent speciation (as for DIC). Methanogenesis from CO under in situ conditions is thermodynamically favorable and would satisfy biological energy requirements with respect to both Gibbs Energy yield and power

Establishment of the Coast Range ophiolite microbial observatory (CROMO): Drilling objectives and preliminary outcomes

Abstract. This project aimed to establish a subsurface microbial observatory in ultramafic rocks, by drilling into an actively serpentinizing peridotite body, characterizing cored rocks, and outfitting the boreholes for a program of long-term observation and experimentation to resolve the serpentinite-hosted subsurface biosphere. We completed drilling in August 2011, drilling two boreholes with core recovery and possibility for down-hole experimentation, and six smaller-diameter monitoring wells arrayed around the two primary holes, in the Coast Range ophiolite (CRO) locality in the UC-Davis McLaughlin Natural Reserve, Lower Lake, CA. Every effort was made during drilling to keep the cores and wells as free of drilling-induced contamination as possible: clean, purified water was used as drilling fluid, fluorescent microbead tracers were suspended in that water for quantification of drilling fluid penetration into the cores, and high resolution next generation sequencing approaches were used to characterize the microbial populations in the drill fluids and core materials. In December 2011, we completed installation of well pumps (slow flow bladder pumps) in the monitoring wells, and have deployed a set of in situ incubation experiments in the two uncased boreholes. Preliminary findings illustrate natural variability in actively serpentinizing strata, and confirm distinct groundwater flow regimes and microbial ecosystems in (a) shallow, surface-impacted soil water horizons and (b) deeper, ultramafic bedrock-sourced formation fluids

Prebiotic Organic Microstructures

Micro- and sub-micrometer spheres, tubules and fiber-filament soft structures have been synthesized in our experiments conducted with 3 MeV proton irradiations of a mixture of simple inorganic constituents, CO, N2 and H2O. We analysed the irradiation products, with scanning electron microscopy (SEM) and atomic force microscopy (AFM). These laboratory organic structures produced wide variety of proteinous and non-proteinous amino acids after HCl hydrolysis. The enantiomer analysis for D-, L- alanine confirmed that the amino acids were abiotically synthesized during the laboratory experiment. Considering hydrothermal activity, the presence of CO2 and H2, of a ferromagnesian silicate mineral environment, of an Earth magnetic field which was much less intense during Archean times than nowadays and consequently of a proton excitation source which was much more abundant, we propose that our laboratory organic microstructures might be synthesized during Archean times. We show similarities in morphology and in formation with some terrestrial Archean microstructures and we suggest that some of the observed Archean carbon spherical and filamentous microstructures might be composed of abiogenic organic molecules. We further propose a search for such prebiotic organic signatures on Mars. This article has been posted on Nature precedings on 21 July 2010 [1]. Extinct radionuclides as source of excitation have been replaced by cosmic radiations which were much more intense 3.5 Ga ago because of a much less intense Earth magnetic field. The new version of the article has been presented at the ORIGINS conference in Montpellier in july 2011 [2] and has since been published in Origins of Life and Evolution of Biospheres 42 (4) 307-316, 2012. 
DOI: 10.1007/s11084-012-9290-5 

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Hydrogen generation and iron partitioning during experimental serpentinization of an olivine-pyroxene mixture

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in McCollom, T. M., Klein, F., Moskowitz, B., Berquo, T. S., Bach, W., & Templeton, A. S. Hydrogen generation and iron partitioning during experimental serpentinization of an olivine-pyroxene mixture. Geochimica Et Cosmochimica Acta, 282, (2020): 55-75, doi:10.1016/j.gca.2020.05.016.A series of laboratory experiments was conducted to investigate serpentinization of olivine–pyroxene mixtures at 230 °C, with the objective of evaluating the effect of mixed compositions on Fe partitioning among product minerals, H2 generation, and reaction rates. An initial experiment reacted a mixture of 86 wt.% olivine and 14 wt.% orthopyroxene (Opx) with the same initial grain size for 387 days. The experiment resulted in extensive reaction (∼53% conversion), and solids recovered at termination of the experiment were dominated by Fe-bearing chrysotile and relict olivine along with minor brucite and magnetite. Only limited amounts of H2 were generated during the first ∼100 days of the experiment, but the rate of H2 generation then increased sharply coincident with an increase in pH from mildly alkaline to strongly alkaline conditions. Two shorter term experiments with the same reactants (26 and 113 days) produced a mixture of lizardite and talc that formed a thin coating on relict olivine and Opx grains, with virtually no generation of H2. Comparison of the results with reaction path models indicates that the Opx reacted about two times faster than olivine, which contrasts with some previous studies that suggested olivine should react more rapidly than Opx at the experimental conditions. The models also indicate that the long-term experiment transitioned from producing serpentine ± talc early in the early stages to precipitation of serpentine plus magnetite, with brucite beginning to precipitate only late in the experiment as Opx was depleted. The results indicate that overall reaction of olivine and Opx was initially relatively slow, but reaction rates accelerated substantially when the pH transitioned to strongly alkaline conditions. Serpentine and brucite precipitated from the olivine-Opx mixture had higher Fe contents than observed in olivine-only experiments at mildly alkaline pH, but had comparable Fe contents to reaction of olivine at strongly alkaline pH implying that higher pH may favor greater partitioning of Fe into serpentine and brucite and less into magnetite. Despite the presence of brucite, dissolved silica activities during the long-term olivine-Opx experiment maintained levels well above serpentine-brucite equilibrium. Instead, silica activities converged on levels close to metastable equilibrium between brucite and olivine. It is proposed that silica levels during the experiment may have been regulated by exchange of SiO2 between the fluid and a silica-depleted, brucite-like surface layer on dissolving olivine.This research was supported by the U. S. National Science Foundation Marine Geology and Geophysics program through grant NSF-OCE 0927744 and by the NASA Astrobiology Institute through Cooperative Agreement NNA15BB02A. Additional support to TMM from the Hanse Wissenschaftskolleg (Delmenhorst, Germany) at an early stage of this project is gratefully acknowledged. FK acknowledges support through Grant NSF-OCE 1427274. The IRM is supported by the Instruments and Facilities Program of the NSF Division of Earth Science. This is IRM contribution 1711. We very much appreciate the comments of Fabrice Brunet, Gleb Pokrovski and an anonymous reviewer that helped us refine our interpretations and improve communication of the results