PP43A-2249
Sedimentary Catalysis of Radiolytic H2 Production, and Implications for Subseafloor Life

Thursday, 17 December 2015
Poster Hall (Moscone South)
Justine Sauvage1, Arthur J Spivack1, Ann G Dunlea2, Richard W Murray2, David L Bish3 and Steven D'Hondt4, (1)University of Rhode Island - GSO, Oceanography, Narragansett, RI, United States, (2)Boston University, Boston, MA, United States, (3)Indiana University - Bloomington, Bloomington, IN, United States, (4)University of Rhode Island, Narragansett, RI, United States
Abstract:
Molecular hydrogen (H2) is naturally produced by radiolysis of water in subseafloor sediment due to radiation from decay of sedimentary U, Th, and K. This process has been hypothesized as a significant source of electron donors for the deep biosphere, especially in environments where organic matter is scarce. However, to constrain the importance of radiolytic H2 for subsurface organisms, H2 yields in natural geologic settings must be understood and quantified.

Although H2 production from radiolysis of pure water is well established, the effect of natural materials on H2 yield is previously unknown. Published gamma-radiation experiments show enhanced H2 production from water radiolysis in the presence of various synthetic oxides, clay and zeolite minerals, or certain dissolved anions. Except for single studies of synthetic ZrO2 and TiO2, previous alpha-radiation experiments have been limited to purely aqueous phases.

To overcome this lack of information, we experimentally quantified H2 yields from gamma and alpha radiolysis of pure water, seawater, and slurries (φ = 0.85) of seawater with representative marine sediment types. The H2 yields of our pure water radiation experiments match well-established literature results for both gamma and alpha radiation (0.25 molecules H2/100eV and 1.53 molecules H2/100eV, respectively). In both our gamma and alpha experiments, H2 yields in seawater are statistically indistinguishable from yields in pure water. In contrast, our experiments with South Pacific abyssal clay increased H2 yields from gamma radiation by 3-5-fold and yields from alpha radiation by up to 6-fold, compared to pure water.

These results have significant implications for understanding subseafloor ecosystems. For example, at South Pacific IODP Site U1370, comparison of our experimentally derived hydrogen yields to net oxygen reduction rates shows that radiolytic H2 is the principal electron donor available to microbes at depths greater than a few meters.

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