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| Titel |
New estimates of global CH4 and C2H6 production in the Precambrian crust |
| VerfasserIn |
Chelsea N. Sutcliffe, Georges Lacrampe-Couloume, Chris J. Ballentine, Barbara Sherwood Lollar |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250107588
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| Publikation (Nr.) |
 EGU/EGU2015-7294.pdf |
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| Zusammenfassung |
| Saline fracture fluids found deep within the Precambrian shield possess isotopic and
geochemical signatures consistent with prolonged water rock interaction. Noble gas-derived
residence times of these fluids, on the order of millions to billions of years, highlight their
significance as an ancient deep hydrosphere (Lippmann-Pipke et al., 2011; Holland et al.,
2013). With mM concentrations of dissolved gases such as H2 and hydrocarbons, these
fracture fluids are energy rich and capable of sustaining microbial communities
of H2-utilizing methanogens and sulphate reducers (Lin et al., 2006). Globally,
Precambrian rocks constitute over 70% of the volume of the continental crust (Goodwin,
1996) and represent a substantial under-investigated source of such dissolved gases.
Recent calculations of global H2 production from these Precambrian Shield rocks,
including both hydration reactions and radiolysis, doubles previous estimates to an
increased rate of 0.4-2.3 x 1011 mol/yr (Sherwood Lollar et al., 2014). This has
important consequences for hydrocarbon production, reflected in the high abundance of
CH4 and C2H6 in dissolved fracture gases, up to 80 and 10 vol %, respectively.
Given the long residence times of these fluids, hydrocarbon production could have
persisted on geological timescales. To date, production from this source has not been
incorporated into models of evolution of the early atmosphere. Additionally, the
quantification of abiotic sources of methane and ethane in the analogous terrestrial
Precambrian crust could contribute to our understanding of the origin of the episodic
traces of methane recently detected on Mars (Webster et al., 2014). Investigating
the origin of these gases has important implications for the global carbon cycle,
as well as the distribution of life in the terrestrial deep subsurface and on other
planets.
We examine the isotopic evolution of these fracture fluids in the Canadian Shield and
provide the first attempts to estimate methane and ethane production potential. We base these
calculations on observed dissolved gas abundances in deep fracture fluids within the
Canadian Shield combined with the new H2 production estimates. Together, these previously
unrecognized additions of methane and ethane could have important consequences for
Archean climate models relating to the Faint Young Sun paradox and contribute, in part, to a
missing greenhouse component.
Goodwin, A. M. (1996) Principles of Precambrian Geology.
Holland et al. (2013) Nature 497 (7449): 367-360.
Lin et al. (2006) Science 314, 479-482.
Lippmann-Pipke et al. (2011) Chemical Geology 283, 287-296.
Sherwood Lollar et al. (2014) Nature 516, 379-382
Webster et al. (2014) Science ISSN 0036-8075 |
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