Can dissolving basaltic glass generate enough H2 to sustain a deep biosphere?
|Location||International Geological Congress,oslo 2008|
|Author||Hellevang, Helge; Thorseth, Ingunn; Pedersen, Rolf Birger|
|Holding Date||28 September 2008|
Equilibrium thermodynamic calculations suggest that hydrogen forms when basalt dissolves in seawater releasing ferrous iron which is oxidized causing the dissociation of water into oxygen and hydrogen. This is corroborated by laboratory experimental work. Hydrogen is utilized as an energy source by chemolithoautotrophs and hydrogen-consumers may, by forming organics, represent a basal part of a deep biosphere. The question is whether sufficient hydrogen is produced to sustain a hydrogen-driven deep biosphere over time. At present there is no clear evidence for this.
This study presents batch numerical simulations of basaltic glass dissolution constrained by reaction affinities and reaction rates. The sensitivity of hydrogen formation rate to temperature, initial redox conditions, and reactive surface area per volume aqueous solution is examined. Because local concentrations are dependent on the reaction history as a water package migrates through the basaltic crust, the residence time of water and its implications are discussed. Simulations suggest that variations in these variables in the basaltic seafloor may locally lead to millimolar concentrations of hydrogen, whereas the bulk of the basaltic seafloor may provide hydrogen concentrations which are insufficient to sustain a hydrogen-driven deep biosphere.