Radiolytic H₂ in continental crust: Nuclear power for deep subsurface microbial communities

Abstract

[1] H 2 is probably the most important substrate for terrestrial subsurface lithoautotrophic microbial communities. Abiotic H 2 generation is an essential component of subsurface ecosystems truly independent of surface photosynthesis. Here we report that H 2 concentrations in fracture water collected from deep siliclastic and volcanic rock units in the Witwatersrand Basin, South Africa, ranged up to two molar, a value far greater than observed in shallow aquifers or marine sediments. The high H 2 concentrations are consistent with that predicted by radiolytic dissociation of H 2 O during radioactive decay of U, Th, and K in the host rock and the observed He concentrations. None of the other known H 2 -generating mechanisms can account for such high H 2 abundance either because of the positive free energy imposed by the high H 2 concentration or pH or because of the absence of required mineral phases. The radiolytic H 2 is consumed by methanogens and abiotic hydrocarbon synthesis. Our calculations indicate that radiolytic H 2 production is a ubiquitous and virtually limitless source of energy for deep crustal chemolithoautotrophic ecosystems.

Organic nitrogen chemistry during low-grade metamorphism

“…hydrogen and hydroxyl radicals, H 2 , H 2 O 2 , hydrous electrons (e aq -), and H - (Lin et al, 2005). Hydrogen radicals can also be produced by reaction of water with hydrocarbons and nitrogencontaining heterocycles (e.g., Townsend et al, 1988;Moriya and Enomoto, 2001;Yuan et al, 2006) and with fluids (e.g., via gas shift reaction; Sato et al, 2004).…”

Cultivation-Based Characterization of Microbial Communities Associated with Deep Sedimentary Rocks from Taiwan Chelungpu Drilling Project Cores

“…Geochemical and metabolic characteristics are generally consistent with those in sub-seafloor sediments with exceptions that nitrate and ferric iron appear to be more abundant in terrestrial environments and hence nitrate reduction and iron reduction are stimulated at depths above sulfate reduction zones (Lovley and Goodwin 1988). Only a few studies are related to deep consolidated or crystalline rocks (such as granite, basalt and meta-sandstone) (Stevens and McKinley 1995;Pedersen 1997;Haveman and Pedersen 1999;Chapelle et al 2002;Cowen et al 2003;Onstott et al 2003;Lin et al 2005a). The low porosity of consolidated rocks (<1%) renders groundwater confined in fracture networks and potentially isolated from surface recharge during a geological time scale (Torgersen and Clarke 1985;Colwell 2001).…”

“…The porosity and pore throat are independent from depths for the same lithology (Lin et al 2005b). Since the porosity of sandstone is greater than those of siltstone and shale by a factor of 2 to 4, the diffusion flux of substrates in sandstone would be enhanced with the same magnitude ( J = -D C/ z φ ∂ ∂ where J is the diffusive flux, C is the concentration of solutes, D is the diffusion coefficient for a given solute, φ is effective porosity, and z is the distance from a reference point) (Lin et al 2005a). It would be expected that microorganisms residing within sandstone could have access to a greater flux of aqueous substrate than those within siltstone or shale.…”

Characterization of Microbial Communities in Subsurface Nuclear Blast Cavities of the Nevada Test Site

“…The unusual appearance of D. audaxviator and the implication that radiationsupported subsurface ecosystems may exist at DOE sites led the PI to seek input from Dr. Tullis Onstott of Princeton University, the original PI on NSF and NASA-funded research that led to this discovery in U-rich mine ores (9,29,30), for the abovementioned ERSP full proposal. Onstott is a very highly regarded geochemist from Princeton University and was featured as one of Time Magazine's 100 most influential people in the world in 2007.…”

“…8, (9)). As D. audaxviator is reported to utilize radiochemically-produced substrates in the very deep continental subsurface (9,29,30,42), the appearance of a close relative at radioactive, subsurface habitats at the NTS was used in part to justify a full proposal led by the PI Additionally, results from this project and our relationship with Mavrik Zavarin and others from the the UGTA program supported our involvement at the co-I level in a full proposal to the ERSP National Laboratories Science Focus Areas call (DE-PS02-09ER09-07), Geochemical Processes at Femtomolar Concentrations and Nanometer Scales. This was ultimately approved for funding at near its $6,000,000 request and commenced in March of 2010.…”