Sulfur mass-independent fractionation in subsurface fracture waters indicates a long-standing sulfur cycle in Precambrian rocks.
The discovery of hydrogen-rich waters preserved below the Earth's surface in Precambrian rocks worldwide expands our understanding of the habitability of the terrestrial subsurface. Many deep microbial ecosystems in these waters survive by coupling hydrogen oxidation to sulfate reduction. Hydrogen originates from water-rock reactions including serpentinization and radiolytic decomposition of water induced by decay of radioactive elements in the host rocks. The origin of dissolved sulfate, however, remains unknown. Here we report, from anoxic saline fracture waters ∼2.4 km below surface in the Canadian Shield, a sulfur mass-independent fractionation signal in dissolved sulfate. We demonstrate that this sulfate most likely originates from oxidation of sulfide minerals in the Archaean host rocks through the action of dissolved oxidants (for example, HO·and H2O2) themselves derived from radiolysis of water, thereby providing a coherent long-term mechanism capable of supplying both an essential electron donor (H2) and a complementary acceptor (sulfate) for the deep biosphere.
Department of Earth Sciences, University of Toronto, Toronto, Ontario, Cananda M5S 3B1.|Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E3.
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L
Li
Department of Earth and Planetary Sciences and GEOTOP, McGill University, Montreal, Quebec, Canada H3A 0E8.
B A
BA
Wing
Department of Earth and Planetary Sciences and GEOTOP, McGill University, Montreal, Quebec, Canada H3A 0E8.
T H
TH
Bui
Department of Earth Sciences, University of Toronto, Toronto, Ontario, Cananda M5S 3B1.
J M
JM
McDermott
School of Geography and Earth Sciences, McMaster University, Hamilton, Ontario, Canada L8S 4K1.
G F
GF
Slater
Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E3.
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S
Wei
Department of Earth Sciences, University of Toronto, Toronto, Ontario, Cananda M5S 3B1.
G
G
Lacrampe-Couloume
Department of Earth Sciences, University of Toronto, Toronto, Ontario, Cananda M5S 3B1.
B Sherwood
BS
Lollar